Hummer70
Member
It is pretty well understood how you store your ammo and how you make it can affect how it performs but there are other things to be considered.
First a few things need to be understood. The allowable misfire rate on all US made primers I am aware of is one per million. The NATO STANAG requirements concur.
This is a very high misfire rate as last I heard from my contact at Winchester they shot 15 million rounds in house quality assurance testing and had five misfires not attributable to other sources.
"Other sources" now this is where the ship hits the sand or similar terminology we use in the South.
Primers are just like women how you treat them will have a significant effect on what they the do for you and or to you.
Definition of "treat"
Primers that have not been exposed to humidity, heat, oil, mishandling etc need three things to insure basic ignition reliability. They need speed, energy and indent centrality which means the dead center of striker should hit very close to the dead center of the primer .
99.9% of the time a misfire in US centerfire ammo is the fault of the weapon and this is where 99.99% of the shooters don't have the experience or the equipment to determine (1) why it went click and should have went bang, (2) why the SD (standard deviation is what it is) and (3)what effect does extreme spread have on groups?
The above are known as "Copper Holders" in the government and industry which by their name hold "coppers". A copper is pictured on the right. They are cylinders that are machined to very close tolerances. I don't know the current cost now but the gov't paid 2.00 each for them 40 years ago. Most all reloaders sooner or later are exposed to the term CUP (copper units of pressure) used in pressure guns to determine chamber pressures. This has changed over the last 30 years to piezo or transducer technology as it is faster. At any rate the same coppers used in pressure testing are still routinely used in weapons to gage how much striker energy is delivered to a primer.
Most everyone has seen a centerfire headspace gage at some time in their shooting career and as can be seen in the pics a copper holder looks just like a headspace gage except at the rear of the copper holder you will see a hole with a flat bottom in the base and basically looks like a round with a primer in it except it is copper in color.
You need a copper holder for each caliber you want to check and some are interchangeable . For instance the same copper holder can be used for 243,260,7/08/308 and 358 Win.
Pictured are holders for 5.56, 308, 30.06 and I now have one more for medium head belted magnums ( 6.5 Mag to 300 Win Mag).
When the copper is placed in the copper holder it is placed in the weapon and placed in the muzzle down position ( to make sure the holder is supported by the case shoulder) and the trigger is pulled. The striker goes forward, impacts the copper and makes a indent it it. Note: the indent in the copper is very minimal where the indent in primers if much deeper. The depth of a copper indent is significant but the depth of a striker indent in a fired primer has nothing to do with the energy delivered to it. It is very common to hear guys say as they look at primers something like "the firing pin is hitting it hard" which has no correlation with copper. In other words deep primer indents are no indication of how much energy was delivered to set them off but light indents in copper are much more reliable.
The copper is removed and placed in a bench inspection gage with a dial indicator containing a small hemispherical point that will go inside the indent and find the lowest point of the indent. Note in this picture the gage is zeroed with the point on the edge of the copper and the gage is calibrated at zero. Next in the picture below the copper is reoriented to allow the point to go into the indent and the gage is read is thousandths to determine the depth of the indent. This is showing just shy of a .019" indent depth which should give reliable ignition assuming there is no intervention in the striker movement to retard the velocity/energy.
Different ammo requires different indents for reliable ignition For instance utilizing ammunition with small pistol primers copper indents normally have a .009" indent requirement where a 357 magnum handgun specs are generally written to require a .011 indent to insure ignition reliability. A large rifle primer requires .016" indent for SAAMI standards, where others want to see a .020" indent and I have tested rifles that deliver .022"indent and .024"indents. The .022" and .024" specimens were of European military configuration.
My personal preference in my center fire rifles is .020" or deeper. Thus when I order new striker springs I specify the next heaviest energy level when available. Normally springs come in three energy ranges, factory and two more levels which will deliver more energy to the primer.
The M16 spec for the gov't requires a .022" indent as the gov't 5.56 is the second hardest percussion primer in the inventory to ignite, the 50 BMG is the hardest primer we have.
I have tested four new out of the box commercial rifles and experienced .015" indents and one excessive headspace To my shock I had a conversation with a vendor (Chief Engineer and a QA Manager) who makes hundreds of rifles per day and was told they had not checked striker energy in 15 years. They just put them together, shot for group, sent out the door.
That same vendor was at the Charlotte NRA show a couple years back and I cruised in and asked if there was anyone there from engineering and this one guy proudly announces he was from engineering and I asked him what the striker indent requirement was for their weapons and the guy had a blank look as to what I was asking. He directed me to a factory tech and I asked him and he did not know either but he asked me to please explain to him what I was talking about and we talked for about 30 minutes and he said when he got back to the factory he was going to find out because he then realized how important ignition reliability was.
OK you guys are now probably thinking I have had no misfires in years, I am good to go. Well not really. Just because a primer actually ignites the propellant and the bullet goes down range doesn't mean you are going to achieve maximum potential. I call this "the lightbulb theory" meaning if you open a case of 100 watt bulbs and you screw in one and it lights you automatically think the rest of them will light as well. I just experienced this, was at a hotel, bulb was burned out in room, I took it to the desk, guy went and opened a new case of bulbs and handed me one in a box. I got to my room, opened the box and the bulb was broken.
Primers are a lot like light bulbs, a 100 watt bulb takes approximately 108 to 132 volts to operate correctly and be in spec but 100 volts will light it but not as bright. So will 90 volts, again with less light.
Primers are much the same . For instance primers are identified by the industry and the gov't by terminology known as the ALL NO FIRE DROP HEIGHT and the ALL FIRE DROP HEIGHT. This is determined by a primer test fixture that releases a steel ball to free fall and impact a striker that is touching a primer held in a fixture.
As long as the ball is released from the same height it will arrive at the fixture at the same velocity every time and deliver the same energy to the copper as there is nothing externally that retard the velocity of the ball after release.
This is not true of firearms. Grease in striker channel and retard the velocity of the striker especially in cold weather. Dust in striker channel can have the same effect.
Raising the ball an inch will cause more energy to be delivered to the fixture and a slightly deeper indent will be made into the copper.
Generally the all no fire drop height for large rifle primers will give a .009 impact on copper and a all fire drop height will deliver a .012"indent.
The reason the ALL NO FIRE HEIGHT is established is because primers need to have to be handled for lack of a better term roughly and not go off like ammo being dropped, bulk packed in boxes while transported and in semi auto rifles capable of being chambered with those designs with inertia strikers (M1s, M14s, ARs etc) and not go off when the round is chambered and the "tic" is noted on the primers.
Thusly the coppers and holders can be used to determine how much energy a floating firing pin delivers to the primer. With the delivery of the first M16s it was quickly found that after the rifles were run in and things started moving faster there were "tic offs" when the bolt carrier was released from the full to the rear position. M16s family are required to exhibit a certain cyclic rate new out of the box. M16s subjected to cyclic rate validation later in a test cycle generally exhibit a faster cyclic rate. As well M16s utilizing 20 round mags will exhibit a slower cyclic rate than 30 rd mags. As I recall the difference between cyclic rates of 20s and 30s was about 30 FPS.
The AMU has some problems with "tic offs" on their M14s back in the late 70s when using handloads with commercial primers and loading the rounds in the chamber in slow fire, rocking the mag down, letter the bolt go home . The investigation determined the M14 was being loaded as indicated which was not part of the design as it was designed to start from full to the rear, engage the top round in the mag, getting it moving and remain moving fast enough to chamber the round and the bolt rotate into battery.
For those that have M1As, and are blessed with a FORCE GAGE load one round in mag and easing the bolt forward till the round stops forward bolt movement. After placing the gage on the back of the op rod hand slowly push the round from the rear till it clears the mag lips. Record that reading. Next load mag with ten rounds and try it and finally 20 rounds and try it and you will have a appreciation of how much drive energy the M14 has to have just to strip the rounds from the mag. Removing all resistance increases the velocity of the bolt upon closure. Bolt will arrive in battery much faster than designed increaseing the liklihood of a out of battery ignition politely termed on forums as "kabooms" etc.
The AMU folks were then told to place the tip of the round in the chamber and the base of the round under the mag lip and partially let the bolt go forward before releasing the op rod. Thus the bolt does not deliver the increased velocity explained above.
If memory serves me correctly the "tic" from a dropped bolt should not deliver over .005" indent on a copper or the way you load a single round should be adjusted so that the bolt not achieve it's full velocity potential prior to striking the primer.
Homer Powley of Frankford Arsenal was a high-power competitor who found his groups at long range were vertically stringing but he had no misfires. He checked the striker energy and the copper indents were below the min spec for the weapon but above the "all fire" threshold and he set up a series of tests which confirmed his theory. My section at Aberdeen Proving Ground conducted similar testing at longer ranges (Frankford only had 300 meters, Aberdeen has 2500 yards) of Homer's theory wherein the striker energy delivery for all fire indents at .012" and slightly deeper exhibited another problem.
In depth testing determined the threshold level for all fire ignition actually delivered erratic ignition which were confirmed by chronograph readings which are displayed in SD (standard deviation) and ES (extreme spread). In short the higher the SD and ES the wider velocity a given batch of ammo will produce. Competition shooters by our very nature are always looking for a edge and basic good old boy logic determines things like let's say you have a revolver and everyone knows the double action trigger pull while aiming is much harder to accomplish that the single action and it therefore follows that the lighter the double action trigger pull is reduced the steadier they can hold the weapon while aiming.
Likewise highpower shooters were cutting coils off striker springs making the bolt easier to raise and get moving in rapid fire and basically they did it to themselves by increasing velocity spread in the match ammo they were using.
For instance the Marine Corps Rifle Team wants their standard deviation to be 10 or less. Long range shooters want the SD at 5 or less and industry ammo routines delivers SD at 15 to 20.
What does this mean to us as shooters? Well if all your shots are at say 200 yards or less you won't notice much but at 600 yards vertical shot dispersion shows up and the higher the SD/ES the more the vertical dispersion. As well the longer the test range the more extreme spread.
So lets say you want to shoot in competition at 1000 yards, the ten ring on a 1000 yard target is 20".
Lets say you have 30 cal ammo that gives a extreme velocity spread of 100 FPS (feet per second) and that ammo is fired from a machine rest will give you 40" of elevation at 1000 yards assuming you have a perfect dead center let off every time which is generally not going to occur. It is not uncommon for factory match ammo to have a extreme velocity spread of 60 FPS.
Do the math, your match ammo out of a known heavy hitting test fixture is giving you in the range of 60 feet a second spread and your striker energy is dropping below the .016" indent you are going to induce the ammo to give you closer to the 100 feet spread. Obviously ammo shot from a machine rest that gives 30" of elevation is not going to be able to print inside a 20" TEN RING and even if it did your tired or cut off striker spring is going to increase the 30" vertical spread ammo even more.
The biggest misconception made by handloaders is "I weigh every charge thusly my ammo is very accurate." Not if you have a marginal ignition system as explained above. Kind of like putting a piece of wood under your gas pedal in your race car with a 500 HP engine. You can press the peddle all you want but the speed is not going to be there and a guy in a clunker can blow you off the track because his gas pedal is not restricted.
OK sounds kind of straight forward so far, now is where it gets sticky. Lets say you have a brand new striker spring, you have coppers, holder and fixture and you are getting .020" indent and all you ammo has weighed charges you are thinking, "I am good to go."
Lets just say you loaded all your ammo in the summer time and did all your testing and it is now winter and may be 15°F outside and there is a lubricant inside your bolt that has just thickened up and retards your striker velocity, you are likely to hear a click instead of a bang or find you are getting vertical dispersion.
I have tested weapons to -65° below zero to 160° above at Aberdeen and I have experienced all the way from 100% ignition reliability to absolutely no ignition.
OK that makes sense, what else can shut you down? Dust, mud, corrosion,vibration, carbon, humidity, to name a few.I refer to this as "the mud, the blood and the beer" testing. You would be absolutely amazed at what exposure to salt spray does to a weapon not properly treated. I have seen weapons that could be barely identified as such come out of the salt fog chamber.
The same things that affect a weapon may well likely be disastrous for your ammo as well. I have conducted testing where loaded ammo with primers that were not waterproofed were exposed to a light rain and sustained multiple misfire within 30 minutes.
I have conducted lubricant testings on primers where waterproofed primers started misfiring in a week after ammo was exposed to them. Lots of guys over lube their guns, the lubricant gets inside and tends to cling to the flat surface between the bolt face and case head.
The weakest integrity point on ammo is the primer pockets and the main purpose of waterproofing is to keep the integrity of the propellant and the priming mixture the same. That is why the case mouths are lacquered and primers coated and then packed in cans in a cold room. Ammo in cans that has not been opened has a projected life of 125 years minimum. Ammo that has been removed from cans has a 75 year projected life.
Never heard any projections of "non waterproofing procedure" ammo life. Unfortunately it would take too long to really test it but a chronograph would be the way to do it and a long range machine rest testing for vertical dispersion. I load my match ammo about a week before a big match.
I used to shoot with a guy who had Eley Match ammo he carried in a 50 cal can. He placed a can of Firm Grip in the ammo can and it leaked. The ammo went from shooting a 3/4" group at 100 to a group 36" vertical group. He carried it all the time and towards the end of the day whoever had the best scores he offered a box of it and asked them to shoot the 100 yard stage with it.
Also know a top shooter who flew to Perry from California and packed ammo in cardboard box in luggage. Upon arrival at Perry the ammo had terrible vertical dispersion and it was finally figured out by a pilot/shooter. The cargo holds are not pressurized.
Waterproof integrity of ammo is done by submerging ammo under water for I think 72 hours and observing the area around the primers for bubbles (air trying to escape). I think three bubbles will flunk a lot. Logically if air can get out of a case water/oil can get in.
OK now the good news. Obviously most guys don't have copper holders and coppers so what is a guy to do to determine if their striker springs have become weak. At Aberdeen weapons are completely disassembled and all springs are measured for free lengths and recorded. Springs like AR hammer springs are photographed on a grid and comparisons made for different free orientations.
On a bolt gun I have a supply of new Wolff Springs for my bolt guns. On those guns I have no copper holder for (because last one I bought ten years ago cost me $155.00 to have it made) I disassemble the bolt and install a new striker spring but first I record the free length with a caliper and record it.
During the season I pull bolt down and measure the free length again with a caliper. If the spring gets shorter then you know it is weaker. Also Wolff generally make several spring energies for a given rifle like Mod 70, Mod 700 etc. They make a factory replacement and then a level higher and finally there is a really strong one.
At Aberdeen we had "REFERENCE AMMO" which is a known lot of ammo with known dispersion and known extreme velocity spread and it is used at zero rounds and then periodically at like 1200 round intervals to determine if the SD opens up. Reloaders could do the same thing, especially with the new 1/2 gal vacuum bottles with wide mouths available at Wally World. You could load you best load in cases, shoot them (record the temperature you tested in) , reload with same lot propellant and same primer lot and store them in container. Pack away about 100 rounds. Then periodically remove ten rounds and shoot at the same temperature you shot before and keep records of ES, SD etc along with groups at say 300 yards or more if possible.
I always get the striker spring that delivers more than factory but less than maximum and so far that seems to be the way to go as I have had no problems. If I was going to be hunting in the winter something that might possibly consider me as his next meal I would have the strongest spring, a well cleaned striker and internal bolt channel and one of two lubricants. LAW (Lubricant Arctic Weapons) or Ed's Red. NOTHING ELSE
Things also thinks to look for in buying a new or new to you rifle. Look at the bolt face and on used rifles you can generally tell if the striker is hitting the primer off center. Obviously this begs the questions 1. how much is too much?, 2. So what it still goes off what's the big deal. 3. What does this indicate?
First off I recommend getting a book entitled "The Guide to Precision Rifle Barrel Fitting by Hinnant. It is primarily a treatise on reworking the 700 Remington actions to achieve maximum performance but the theory works with Mod 70s and others as well.
Ideally on a rifle you strive to assemble for peak accuracy you are looking to achieve an imaginary line running down the exact middle of the bore, through the striker opening and out the back of the bolt through the striker. This alignment also covers the chamber and the round in the chamber being centered on the same line. Basically if this line is bent anywhere in there you can set up a bad vibrations. Think about it, why do nails come nice and straight? Because they drive better. Ever tried to hammer a bent nail?
The biggest problem in maintaining a the straight imaginary line is where the barrel screws into the action. Those of you that have ever tapped a hole for a machine screw know it is extremely easy to have the tap develop a tilt and putting in a long screw shows the tilt. How can you tell how much the line is bent? Look at a fired case and determine how close to dead center the striker has impacted the primer.
The industry recommendation is not more than half the diameter of the striker offset. Most medium bolt face strikers run about .060 to .062" diameter, thusly they basically bless a offset of .031" ! ! ! ! !
Many of you have heard of "blueprinting a action" which basically is a correction of those things that are not properly address in manufacturing that detract from the straight line. On a bolt gun the threads in the action are generally out of square with the imaginary line and need to be straightened. Some gunsmiths take great pains to chuck up actions in catheads and dial them in with a snug mandrel run in the bolt way then recut the threads with a single point tool. Another thing that causes the offset is the front of the action is not square with the center line.
As well it is common for custom barrels to come in and the bore is not centered in the blank. About 30 years ago when I finally got my lathe Cliff Huston taught me how to center a bore before cutting the action threads and chambering it. I have had to turn the outside of a barrel maybe five inches long as the exterior was not trued uniform with the bore. You can't move the bore but you can correct the outside dimensions that will allow centering up the bore in relation to the outside.
As well I have seen several commercial barrels where the bore was not centered in the barrel.
Manson Precision has a action truing kit where the threads are recut with a special tap and fixture that supports the tap being run in straighter.
For Remington actions I have a 1 1/16" X 16 tap altered with a pilot on the end so the pilot rides the bore center line and lets the rails center the tap.
There are two reasons you want center hits, accuracy for one thing and ignition reliability for the other.
Not widely known was there was a off center primer impact study utilizing millions of primers conducted by Frankford Arsenal in the 50s. The primer fixture described above was altered to produce off center hits when the ball impacted the striker. They were tested with .010, .015, .020, .025, .030, etc offsets and a very interesting result occured. Up to .020" offset with the all fire height energy there was no reduction in ignition reliability but they started getting misfires at .025" offset and then they changed the procedure the bottom line being misfires started at .021" offset and became more frequent the more the offset impacts differences were increased.
Too much too late, the M14 was the last arsenal produced weapon and it was already in full production when the test was completed and the design allowed for 1/2 striker offset as did the Garand etc. It is not known whether this information was passed to Al Cole the Chief Engineer of the M14 Program and by the time I got the info on the test study, Al had retired and died or I would have asked him. Al left Springfield Armory and was transferred to Rock Island and he was Chief of the Army Small Cal Lab up until the mission was moved to Picatinny Arsenal in mid 70s. Al wasn't going to have anything to do with Jersey so he called Bill Ruger and asked him if he had a place for himself and he was told the paperwork was be processed when he arrived. Al retired immediately and went to Ruger. When I got to know him (1979 time frame) he was about 70 then.
I do know that Winchester did not have the info and I sent them a copy of the letter report where the findings were presented in a very condensed version.
The only reason it came to light when it did in mid 1980s I was at a major vendors plant witnessing proof firing on a number of weapons we were buying and there were 34 misfires in 1200 rounds. In other words I had same failure I would have experienced if 34 million rounds were fired. I seized the ammo, sent it to Picatinny and had the primer engineers conduct a failure analysis and the report came back that the primers failed due to off center striker indents and a copy of the letter report was included.
Thusly when I look at a used rifle I am about to buy I look at bolt face to see how much offset it has.
In the last 25 years the number of 700s I have seen with dead center hits is like 5 and I own two of those now. There is another one floating around here in 270 I tried to buy and guy would not sell it and it got passed down to a son who will not sell it.
First a few things need to be understood. The allowable misfire rate on all US made primers I am aware of is one per million. The NATO STANAG requirements concur.
This is a very high misfire rate as last I heard from my contact at Winchester they shot 15 million rounds in house quality assurance testing and had five misfires not attributable to other sources.
"Other sources" now this is where the ship hits the sand or similar terminology we use in the South.
Primers are just like women how you treat them will have a significant effect on what they the do for you and or to you.
Definition of "treat"
Primers that have not been exposed to humidity, heat, oil, mishandling etc need three things to insure basic ignition reliability. They need speed, energy and indent centrality which means the dead center of striker should hit very close to the dead center of the primer .
99.9% of the time a misfire in US centerfire ammo is the fault of the weapon and this is where 99.99% of the shooters don't have the experience or the equipment to determine (1) why it went click and should have went bang, (2) why the SD (standard deviation is what it is) and (3)what effect does extreme spread have on groups?
The above are known as "Copper Holders" in the government and industry which by their name hold "coppers". A copper is pictured on the right. They are cylinders that are machined to very close tolerances. I don't know the current cost now but the gov't paid 2.00 each for them 40 years ago. Most all reloaders sooner or later are exposed to the term CUP (copper units of pressure) used in pressure guns to determine chamber pressures. This has changed over the last 30 years to piezo or transducer technology as it is faster. At any rate the same coppers used in pressure testing are still routinely used in weapons to gage how much striker energy is delivered to a primer.
Most everyone has seen a centerfire headspace gage at some time in their shooting career and as can be seen in the pics a copper holder looks just like a headspace gage except at the rear of the copper holder you will see a hole with a flat bottom in the base and basically looks like a round with a primer in it except it is copper in color.
You need a copper holder for each caliber you want to check and some are interchangeable . For instance the same copper holder can be used for 243,260,7/08/308 and 358 Win.
Pictured are holders for 5.56, 308, 30.06 and I now have one more for medium head belted magnums ( 6.5 Mag to 300 Win Mag).
When the copper is placed in the copper holder it is placed in the weapon and placed in the muzzle down position ( to make sure the holder is supported by the case shoulder) and the trigger is pulled. The striker goes forward, impacts the copper and makes a indent it it. Note: the indent in the copper is very minimal where the indent in primers if much deeper. The depth of a copper indent is significant but the depth of a striker indent in a fired primer has nothing to do with the energy delivered to it. It is very common to hear guys say as they look at primers something like "the firing pin is hitting it hard" which has no correlation with copper. In other words deep primer indents are no indication of how much energy was delivered to set them off but light indents in copper are much more reliable.
The copper is removed and placed in a bench inspection gage with a dial indicator containing a small hemispherical point that will go inside the indent and find the lowest point of the indent. Note in this picture the gage is zeroed with the point on the edge of the copper and the gage is calibrated at zero. Next in the picture below the copper is reoriented to allow the point to go into the indent and the gage is read is thousandths to determine the depth of the indent. This is showing just shy of a .019" indent depth which should give reliable ignition assuming there is no intervention in the striker movement to retard the velocity/energy.
Different ammo requires different indents for reliable ignition For instance utilizing ammunition with small pistol primers copper indents normally have a .009" indent requirement where a 357 magnum handgun specs are generally written to require a .011 indent to insure ignition reliability. A large rifle primer requires .016" indent for SAAMI standards, where others want to see a .020" indent and I have tested rifles that deliver .022"indent and .024"indents. The .022" and .024" specimens were of European military configuration.
My personal preference in my center fire rifles is .020" or deeper. Thus when I order new striker springs I specify the next heaviest energy level when available. Normally springs come in three energy ranges, factory and two more levels which will deliver more energy to the primer.
The M16 spec for the gov't requires a .022" indent as the gov't 5.56 is the second hardest percussion primer in the inventory to ignite, the 50 BMG is the hardest primer we have.
I have tested four new out of the box commercial rifles and experienced .015" indents and one excessive headspace To my shock I had a conversation with a vendor (Chief Engineer and a QA Manager) who makes hundreds of rifles per day and was told they had not checked striker energy in 15 years. They just put them together, shot for group, sent out the door.
That same vendor was at the Charlotte NRA show a couple years back and I cruised in and asked if there was anyone there from engineering and this one guy proudly announces he was from engineering and I asked him what the striker indent requirement was for their weapons and the guy had a blank look as to what I was asking. He directed me to a factory tech and I asked him and he did not know either but he asked me to please explain to him what I was talking about and we talked for about 30 minutes and he said when he got back to the factory he was going to find out because he then realized how important ignition reliability was.
OK you guys are now probably thinking I have had no misfires in years, I am good to go. Well not really. Just because a primer actually ignites the propellant and the bullet goes down range doesn't mean you are going to achieve maximum potential. I call this "the lightbulb theory" meaning if you open a case of 100 watt bulbs and you screw in one and it lights you automatically think the rest of them will light as well. I just experienced this, was at a hotel, bulb was burned out in room, I took it to the desk, guy went and opened a new case of bulbs and handed me one in a box. I got to my room, opened the box and the bulb was broken.
Primers are a lot like light bulbs, a 100 watt bulb takes approximately 108 to 132 volts to operate correctly and be in spec but 100 volts will light it but not as bright. So will 90 volts, again with less light.
Primers are much the same . For instance primers are identified by the industry and the gov't by terminology known as the ALL NO FIRE DROP HEIGHT and the ALL FIRE DROP HEIGHT. This is determined by a primer test fixture that releases a steel ball to free fall and impact a striker that is touching a primer held in a fixture.
As long as the ball is released from the same height it will arrive at the fixture at the same velocity every time and deliver the same energy to the copper as there is nothing externally that retard the velocity of the ball after release.
This is not true of firearms. Grease in striker channel and retard the velocity of the striker especially in cold weather. Dust in striker channel can have the same effect.
Raising the ball an inch will cause more energy to be delivered to the fixture and a slightly deeper indent will be made into the copper.
Generally the all no fire drop height for large rifle primers will give a .009 impact on copper and a all fire drop height will deliver a .012"indent.
The reason the ALL NO FIRE HEIGHT is established is because primers need to have to be handled for lack of a better term roughly and not go off like ammo being dropped, bulk packed in boxes while transported and in semi auto rifles capable of being chambered with those designs with inertia strikers (M1s, M14s, ARs etc) and not go off when the round is chambered and the "tic" is noted on the primers.
Thusly the coppers and holders can be used to determine how much energy a floating firing pin delivers to the primer. With the delivery of the first M16s it was quickly found that after the rifles were run in and things started moving faster there were "tic offs" when the bolt carrier was released from the full to the rear position. M16s family are required to exhibit a certain cyclic rate new out of the box. M16s subjected to cyclic rate validation later in a test cycle generally exhibit a faster cyclic rate. As well M16s utilizing 20 round mags will exhibit a slower cyclic rate than 30 rd mags. As I recall the difference between cyclic rates of 20s and 30s was about 30 FPS.
The AMU has some problems with "tic offs" on their M14s back in the late 70s when using handloads with commercial primers and loading the rounds in the chamber in slow fire, rocking the mag down, letter the bolt go home . The investigation determined the M14 was being loaded as indicated which was not part of the design as it was designed to start from full to the rear, engage the top round in the mag, getting it moving and remain moving fast enough to chamber the round and the bolt rotate into battery.
For those that have M1As, and are blessed with a FORCE GAGE load one round in mag and easing the bolt forward till the round stops forward bolt movement. After placing the gage on the back of the op rod hand slowly push the round from the rear till it clears the mag lips. Record that reading. Next load mag with ten rounds and try it and finally 20 rounds and try it and you will have a appreciation of how much drive energy the M14 has to have just to strip the rounds from the mag. Removing all resistance increases the velocity of the bolt upon closure. Bolt will arrive in battery much faster than designed increaseing the liklihood of a out of battery ignition politely termed on forums as "kabooms" etc.
The AMU folks were then told to place the tip of the round in the chamber and the base of the round under the mag lip and partially let the bolt go forward before releasing the op rod. Thus the bolt does not deliver the increased velocity explained above.
If memory serves me correctly the "tic" from a dropped bolt should not deliver over .005" indent on a copper or the way you load a single round should be adjusted so that the bolt not achieve it's full velocity potential prior to striking the primer.
Homer Powley of Frankford Arsenal was a high-power competitor who found his groups at long range were vertically stringing but he had no misfires. He checked the striker energy and the copper indents were below the min spec for the weapon but above the "all fire" threshold and he set up a series of tests which confirmed his theory. My section at Aberdeen Proving Ground conducted similar testing at longer ranges (Frankford only had 300 meters, Aberdeen has 2500 yards) of Homer's theory wherein the striker energy delivery for all fire indents at .012" and slightly deeper exhibited another problem.
In depth testing determined the threshold level for all fire ignition actually delivered erratic ignition which were confirmed by chronograph readings which are displayed in SD (standard deviation) and ES (extreme spread). In short the higher the SD and ES the wider velocity a given batch of ammo will produce. Competition shooters by our very nature are always looking for a edge and basic good old boy logic determines things like let's say you have a revolver and everyone knows the double action trigger pull while aiming is much harder to accomplish that the single action and it therefore follows that the lighter the double action trigger pull is reduced the steadier they can hold the weapon while aiming.
Likewise highpower shooters were cutting coils off striker springs making the bolt easier to raise and get moving in rapid fire and basically they did it to themselves by increasing velocity spread in the match ammo they were using.
For instance the Marine Corps Rifle Team wants their standard deviation to be 10 or less. Long range shooters want the SD at 5 or less and industry ammo routines delivers SD at 15 to 20.
What does this mean to us as shooters? Well if all your shots are at say 200 yards or less you won't notice much but at 600 yards vertical shot dispersion shows up and the higher the SD/ES the more the vertical dispersion. As well the longer the test range the more extreme spread.
So lets say you want to shoot in competition at 1000 yards, the ten ring on a 1000 yard target is 20".
Lets say you have 30 cal ammo that gives a extreme velocity spread of 100 FPS (feet per second) and that ammo is fired from a machine rest will give you 40" of elevation at 1000 yards assuming you have a perfect dead center let off every time which is generally not going to occur. It is not uncommon for factory match ammo to have a extreme velocity spread of 60 FPS.
Do the math, your match ammo out of a known heavy hitting test fixture is giving you in the range of 60 feet a second spread and your striker energy is dropping below the .016" indent you are going to induce the ammo to give you closer to the 100 feet spread. Obviously ammo shot from a machine rest that gives 30" of elevation is not going to be able to print inside a 20" TEN RING and even if it did your tired or cut off striker spring is going to increase the 30" vertical spread ammo even more.
The biggest misconception made by handloaders is "I weigh every charge thusly my ammo is very accurate." Not if you have a marginal ignition system as explained above. Kind of like putting a piece of wood under your gas pedal in your race car with a 500 HP engine. You can press the peddle all you want but the speed is not going to be there and a guy in a clunker can blow you off the track because his gas pedal is not restricted.
OK sounds kind of straight forward so far, now is where it gets sticky. Lets say you have a brand new striker spring, you have coppers, holder and fixture and you are getting .020" indent and all you ammo has weighed charges you are thinking, "I am good to go."
Lets just say you loaded all your ammo in the summer time and did all your testing and it is now winter and may be 15°F outside and there is a lubricant inside your bolt that has just thickened up and retards your striker velocity, you are likely to hear a click instead of a bang or find you are getting vertical dispersion.
I have tested weapons to -65° below zero to 160° above at Aberdeen and I have experienced all the way from 100% ignition reliability to absolutely no ignition.
OK that makes sense, what else can shut you down? Dust, mud, corrosion,vibration, carbon, humidity, to name a few.I refer to this as "the mud, the blood and the beer" testing. You would be absolutely amazed at what exposure to salt spray does to a weapon not properly treated. I have seen weapons that could be barely identified as such come out of the salt fog chamber.
The same things that affect a weapon may well likely be disastrous for your ammo as well. I have conducted testing where loaded ammo with primers that were not waterproofed were exposed to a light rain and sustained multiple misfire within 30 minutes.
I have conducted lubricant testings on primers where waterproofed primers started misfiring in a week after ammo was exposed to them. Lots of guys over lube their guns, the lubricant gets inside and tends to cling to the flat surface between the bolt face and case head.
The weakest integrity point on ammo is the primer pockets and the main purpose of waterproofing is to keep the integrity of the propellant and the priming mixture the same. That is why the case mouths are lacquered and primers coated and then packed in cans in a cold room. Ammo in cans that has not been opened has a projected life of 125 years minimum. Ammo that has been removed from cans has a 75 year projected life.
Never heard any projections of "non waterproofing procedure" ammo life. Unfortunately it would take too long to really test it but a chronograph would be the way to do it and a long range machine rest testing for vertical dispersion. I load my match ammo about a week before a big match.
I used to shoot with a guy who had Eley Match ammo he carried in a 50 cal can. He placed a can of Firm Grip in the ammo can and it leaked. The ammo went from shooting a 3/4" group at 100 to a group 36" vertical group. He carried it all the time and towards the end of the day whoever had the best scores he offered a box of it and asked them to shoot the 100 yard stage with it.
Also know a top shooter who flew to Perry from California and packed ammo in cardboard box in luggage. Upon arrival at Perry the ammo had terrible vertical dispersion and it was finally figured out by a pilot/shooter. The cargo holds are not pressurized.
Waterproof integrity of ammo is done by submerging ammo under water for I think 72 hours and observing the area around the primers for bubbles (air trying to escape). I think three bubbles will flunk a lot. Logically if air can get out of a case water/oil can get in.
OK now the good news. Obviously most guys don't have copper holders and coppers so what is a guy to do to determine if their striker springs have become weak. At Aberdeen weapons are completely disassembled and all springs are measured for free lengths and recorded. Springs like AR hammer springs are photographed on a grid and comparisons made for different free orientations.
On a bolt gun I have a supply of new Wolff Springs for my bolt guns. On those guns I have no copper holder for (because last one I bought ten years ago cost me $155.00 to have it made) I disassemble the bolt and install a new striker spring but first I record the free length with a caliper and record it.
During the season I pull bolt down and measure the free length again with a caliper. If the spring gets shorter then you know it is weaker. Also Wolff generally make several spring energies for a given rifle like Mod 70, Mod 700 etc. They make a factory replacement and then a level higher and finally there is a really strong one.
At Aberdeen we had "REFERENCE AMMO" which is a known lot of ammo with known dispersion and known extreme velocity spread and it is used at zero rounds and then periodically at like 1200 round intervals to determine if the SD opens up. Reloaders could do the same thing, especially with the new 1/2 gal vacuum bottles with wide mouths available at Wally World. You could load you best load in cases, shoot them (record the temperature you tested in) , reload with same lot propellant and same primer lot and store them in container. Pack away about 100 rounds. Then periodically remove ten rounds and shoot at the same temperature you shot before and keep records of ES, SD etc along with groups at say 300 yards or more if possible.
I always get the striker spring that delivers more than factory but less than maximum and so far that seems to be the way to go as I have had no problems. If I was going to be hunting in the winter something that might possibly consider me as his next meal I would have the strongest spring, a well cleaned striker and internal bolt channel and one of two lubricants. LAW (Lubricant Arctic Weapons) or Ed's Red. NOTHING ELSE
Things also thinks to look for in buying a new or new to you rifle. Look at the bolt face and on used rifles you can generally tell if the striker is hitting the primer off center. Obviously this begs the questions 1. how much is too much?, 2. So what it still goes off what's the big deal. 3. What does this indicate?
First off I recommend getting a book entitled "The Guide to Precision Rifle Barrel Fitting by Hinnant. It is primarily a treatise on reworking the 700 Remington actions to achieve maximum performance but the theory works with Mod 70s and others as well.
Ideally on a rifle you strive to assemble for peak accuracy you are looking to achieve an imaginary line running down the exact middle of the bore, through the striker opening and out the back of the bolt through the striker. This alignment also covers the chamber and the round in the chamber being centered on the same line. Basically if this line is bent anywhere in there you can set up a bad vibrations. Think about it, why do nails come nice and straight? Because they drive better. Ever tried to hammer a bent nail?
The biggest problem in maintaining a the straight imaginary line is where the barrel screws into the action. Those of you that have ever tapped a hole for a machine screw know it is extremely easy to have the tap develop a tilt and putting in a long screw shows the tilt. How can you tell how much the line is bent? Look at a fired case and determine how close to dead center the striker has impacted the primer.
The industry recommendation is not more than half the diameter of the striker offset. Most medium bolt face strikers run about .060 to .062" diameter, thusly they basically bless a offset of .031" ! ! ! ! !
Many of you have heard of "blueprinting a action" which basically is a correction of those things that are not properly address in manufacturing that detract from the straight line. On a bolt gun the threads in the action are generally out of square with the imaginary line and need to be straightened. Some gunsmiths take great pains to chuck up actions in catheads and dial them in with a snug mandrel run in the bolt way then recut the threads with a single point tool. Another thing that causes the offset is the front of the action is not square with the center line.
As well it is common for custom barrels to come in and the bore is not centered in the blank. About 30 years ago when I finally got my lathe Cliff Huston taught me how to center a bore before cutting the action threads and chambering it. I have had to turn the outside of a barrel maybe five inches long as the exterior was not trued uniform with the bore. You can't move the bore but you can correct the outside dimensions that will allow centering up the bore in relation to the outside.
As well I have seen several commercial barrels where the bore was not centered in the barrel.
Manson Precision has a action truing kit where the threads are recut with a special tap and fixture that supports the tap being run in straighter.
For Remington actions I have a 1 1/16" X 16 tap altered with a pilot on the end so the pilot rides the bore center line and lets the rails center the tap.
There are two reasons you want center hits, accuracy for one thing and ignition reliability for the other.
Not widely known was there was a off center primer impact study utilizing millions of primers conducted by Frankford Arsenal in the 50s. The primer fixture described above was altered to produce off center hits when the ball impacted the striker. They were tested with .010, .015, .020, .025, .030, etc offsets and a very interesting result occured. Up to .020" offset with the all fire height energy there was no reduction in ignition reliability but they started getting misfires at .025" offset and then they changed the procedure the bottom line being misfires started at .021" offset and became more frequent the more the offset impacts differences were increased.
Too much too late, the M14 was the last arsenal produced weapon and it was already in full production when the test was completed and the design allowed for 1/2 striker offset as did the Garand etc. It is not known whether this information was passed to Al Cole the Chief Engineer of the M14 Program and by the time I got the info on the test study, Al had retired and died or I would have asked him. Al left Springfield Armory and was transferred to Rock Island and he was Chief of the Army Small Cal Lab up until the mission was moved to Picatinny Arsenal in mid 70s. Al wasn't going to have anything to do with Jersey so he called Bill Ruger and asked him if he had a place for himself and he was told the paperwork was be processed when he arrived. Al retired immediately and went to Ruger. When I got to know him (1979 time frame) he was about 70 then.
I do know that Winchester did not have the info and I sent them a copy of the letter report where the findings were presented in a very condensed version.
The only reason it came to light when it did in mid 1980s I was at a major vendors plant witnessing proof firing on a number of weapons we were buying and there were 34 misfires in 1200 rounds. In other words I had same failure I would have experienced if 34 million rounds were fired. I seized the ammo, sent it to Picatinny and had the primer engineers conduct a failure analysis and the report came back that the primers failed due to off center striker indents and a copy of the letter report was included.
Thusly when I look at a used rifle I am about to buy I look at bolt face to see how much offset it has.
In the last 25 years the number of 700s I have seen with dead center hits is like 5 and I own two of those now. There is another one floating around here in 270 I tried to buy and guy would not sell it and it got passed down to a son who will not sell it.
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