Hummer70
Member
I guess this could be subtitled : OK you have an AR, here is just a small bit of the bad news you may likely sustain in the life of the system. You may also apply these "symptoms" to other rifles.
The military specification of the M16 family requires them to be capable of delivering a 4.5" group at 100 yards out of the box but this is with a lot of ammo that will group slightly smaller and is known as the control lot. It does not mean all the ammo you get will behave as below. Some will be much better and I suspect some much worse and the wrong ammo will take out a new AR barrel in about the same time it takes you to drive to the range and back.
For instance normal acceptance for GI ball ammo is a 2" mean radius at 200 yards which in shooters terminology means a much larger extreme spread. These are shot at the arsenal that loaded the ammo from three test fixtures which if they have not been replaced still consists of a accuracy barrel on a Remington 700 actions that has a stock cut off about 1/2" forward of the action and the butt end cut just leaving the pistol grip area placed in a Frankford Arsenal Mount which clamps the heavy barrel in a rest secured in about 15 tons of cement.
Different lot numbers will deliver tighter group sizes but the kicker is (on gov't ammo) all three test fixtures must deliver the 2" mean radius. Precise records are maintained on each rifle to include firing pin energy testing, the number of rounds on the barrel, etc etc. Should one fail, there is a refire with reference ammo (known to be very high quality so stamped on the boxes) and if that passes the candidate lot is refired in the same rifle. If it meets it passes, if it fails the entire lot is rejected.
Ammo can be failed for a variety of other reasons beyond dispersion. Failure to fire, fail the water immersion testing, failing to achieve the required Standard Deviation, and about a dozen more things.
Those with chronographs, get hold of yourself. They will accept ammo that delivers a SD of 40 fps. Match shooters want their ammo to deliver a max of 10 fps SD and some can get theirs down to 5 SD. The higher the SD the more vertical group stringing you will see at longer ranges.
If you have a ballistic program calculate a given bullet loaded to your desired velocity and fired with a 100 yard POA/POI and have it list the impact points at 200-600 yards. OK lets say you put in 3100 FPS. Put it in again and 3060 and note the vertical point of impact changes. Lets say it is 15" lower which pretty will tells you that the best you are going to get vertically is a 15 group at 600 yards.
Obviously what we buy off the shelf may or may not meet the Gov't/NATO requirements and there is something you need to know. If a lot of ammo is failed for any reason the manufacturer may sell it on the commercial market to recoup manufacturing expenses.
Action shooters will in all likelihood never be able to determine what their ammo does as we normally don't buy ammo in 20,000 round lots. Thus begging the question what is one to do that one can afford to determine how well their rifle groups as the brass piles up.
The easiest thing to do is load your own control lot. Normally this is not done with ball propellant as the vast majority of ball propellant lots are known to be very erosive on rifle barrels. Then every 1000 rounds or so take it out and shoot it for group. You could load up say 300 rounds of a known good propellant/bullet combo, store it in a 50 cal ammo can and shoot say (5 rounds off the target to condition it) a 10 round on the target every 500 rounds to see what is happening in your barrel.
How much difference in barrel life you may expect to see on a 5.56 barrel and what defines the term "shot out". As indicated above a new barrel acceptance is 4.5" extreme spread at 100 yards. The rejection is 7.2" and no conventional match shooters wants to go to competition with a weapon/ammo combination that prints 10 shots over an inch in diameter. It is one thing to be beat in competition but when the winner is shooting a 1" rifle/ammo combo and you are shooting 4" ammo, the chances of you not winning is.............
5.56 ammo loaded with ball propellant is not likely to give an acceptable barrel life much beyond 2400 rounds. CIP in the M16A1E1 (adopted as m16A2) testing the groups shot at 1200 and 2400 rounds were just a tad larger than at 0 rounds. At 3600 rounds groups had opened up considerably. At 4800 rounds groups were right at rejection (7.0" average) and at 6000 rounds we could not keep groups on a 8X12 ft. target at 800 or700 meters and covered the entire board at 600 meters so I stopped the test as the barrels were gone.
A retest was conducted with three different rifles with same ammo, (XM855E1), SS109, M193 and other combos and we went through 10,000 rounds a day for 14 straight days shooting 12-14 hours a day. The exact same results with the XM855E1 were sustained however the SS109 ammo fed rifles were still in spec at 12,000 rounds. I had the same 100 yard groups at 4800 rounds with XM855E1 that I got with the SS109 at 12,000 rounds. Don't know what it was but the Belgian Gov't loaded their ammo with but it was obvious their propellant that was not as erosive as our WC846 propellant.
When the M16A1E1 Test was conducted at Aberdeen Proving Ground in early 80s all the rifles delivered for testing averaged between 3" and 4" at 100 yards. After targeting all rifles (I believe it was 12) I selected the best one, the worst one and one in the middle so endurance was started with the best and the worst delivered and median.
We shot 120 round segments, two mags 3 shot bursts, two mags semi auto which is basically known as a "median schedule". A hot schedule would have been fired at a faster rate and a cold schedule a slower rate. Barrels were cooled with forced air directed up their muzzles with bolts open placed on a specially designed rack that was plumbed to have a brass tube direct the air into the muzzle. By the time the last barrel was fired the first barrel was cool and the whole series started over again.
We cleaned them every 600 rounds or at the end of the day's firing whichever occurred first. During endurance firing the gunners knew to cease fire immediately and I would tell them to go take a break and I had to sit down and study everything closely to determine what exactly caused the stoppage and to what to charge the stoppage to. It could be ammo, magazine, rifle, or operator error.
Some failures are simple, some quite time consuming and there is a whole page of codes such as:
FBR failure of bolt to remain to the rear after last round in magazine fired.
OK lets say a FFR (failure to fire) is sustained. Some of the questions that needed answers were: 1. was the bolt all the way in battery? 2. You need to record such things as weapon number. 3. what round number it occurred at in the magazine. 4. Magazines are all numbered and the same magazines rotated through all rifles. So the mag is removed and examined for signs of failure, the rounds are removed and counted to determine the round number. Initially the stoppage may be charged to the weapon if no other evidence is noted. 5. What round number in the whole test series. 6. If the same problem occurs again with that magazine in a different weapon you have to write a new report and ultimately may remove the charge from the weapon and charge it to the magazine. 7. That round is saved, tagged and disassembled later to determine if the pellet was in place and pellet properly formed etc. Note: the majority of stoppages in the M16 family is known to occur on the 1st, 2nd or third round fired as the ammo stack is under much higher tension in the first three rounds. That is why I recommend a HD weapon have their magazines loaded with 26 rounds and stored on a empty chamber as I know that in a hurry the odds of my getting a stoppage before I get going good is much higher when the charging handle is released.
As well storing a rifle with hammer/striker under full compression should not (per spring engineers) lose energy but they also say you don't know if you have a properly made spring until you compress it for a number of months and test it with coppers to determine if the spring has taken a "set" and now delivers less than desirable energy.
Then storing a round in chamber muzzle down with too much lubricant on the bolt carrier is likely to migrate to the primer, kill it and when you need it you get a "click" which I would not like listed as my cause of death.
OK back to the report taken at time of stoppage. Detailed notes are taken and most of a Stoppage Report is down before firing is resumed. You cannot remember the exact details of exactly what you saw at 0830 hours when you get back to the office about 3:30. The report is written up, then secretary types it and it is reviewed at three levels locally and submitted through channels to Test and Evaluation Command HQ to the Liaison Officer who makes a copy for the file and he forwards it to the agency that is paying for the testing.
Failures to fire are supposed to be extremely rare if the weapon is known to exhibit the required striker energy which is checked at zero rounds and every 1200 rounds through 12,000 rounds. The allowable misfire rate on US ammo is one per million and I had five FFRs occur in only 244,000 rounds and that caused considerate concern.
One last interesting test you can accomplish is shoot a 5 round group at 1000 inches, then at each 500 rounds. Keep and mark all the cards as to the round point it was fired. When the barrel starts to go you should see the holes becoming elongated and the more you shoot it the more the holes will become elongated.
The military specification of the M16 family requires them to be capable of delivering a 4.5" group at 100 yards out of the box but this is with a lot of ammo that will group slightly smaller and is known as the control lot. It does not mean all the ammo you get will behave as below. Some will be much better and I suspect some much worse and the wrong ammo will take out a new AR barrel in about the same time it takes you to drive to the range and back.
For instance normal acceptance for GI ball ammo is a 2" mean radius at 200 yards which in shooters terminology means a much larger extreme spread. These are shot at the arsenal that loaded the ammo from three test fixtures which if they have not been replaced still consists of a accuracy barrel on a Remington 700 actions that has a stock cut off about 1/2" forward of the action and the butt end cut just leaving the pistol grip area placed in a Frankford Arsenal Mount which clamps the heavy barrel in a rest secured in about 15 tons of cement.
Different lot numbers will deliver tighter group sizes but the kicker is (on gov't ammo) all three test fixtures must deliver the 2" mean radius. Precise records are maintained on each rifle to include firing pin energy testing, the number of rounds on the barrel, etc etc. Should one fail, there is a refire with reference ammo (known to be very high quality so stamped on the boxes) and if that passes the candidate lot is refired in the same rifle. If it meets it passes, if it fails the entire lot is rejected.
Ammo can be failed for a variety of other reasons beyond dispersion. Failure to fire, fail the water immersion testing, failing to achieve the required Standard Deviation, and about a dozen more things.
Those with chronographs, get hold of yourself. They will accept ammo that delivers a SD of 40 fps. Match shooters want their ammo to deliver a max of 10 fps SD and some can get theirs down to 5 SD. The higher the SD the more vertical group stringing you will see at longer ranges.
If you have a ballistic program calculate a given bullet loaded to your desired velocity and fired with a 100 yard POA/POI and have it list the impact points at 200-600 yards. OK lets say you put in 3100 FPS. Put it in again and 3060 and note the vertical point of impact changes. Lets say it is 15" lower which pretty will tells you that the best you are going to get vertically is a 15 group at 600 yards.
Obviously what we buy off the shelf may or may not meet the Gov't/NATO requirements and there is something you need to know. If a lot of ammo is failed for any reason the manufacturer may sell it on the commercial market to recoup manufacturing expenses.
Action shooters will in all likelihood never be able to determine what their ammo does as we normally don't buy ammo in 20,000 round lots. Thus begging the question what is one to do that one can afford to determine how well their rifle groups as the brass piles up.
The easiest thing to do is load your own control lot. Normally this is not done with ball propellant as the vast majority of ball propellant lots are known to be very erosive on rifle barrels. Then every 1000 rounds or so take it out and shoot it for group. You could load up say 300 rounds of a known good propellant/bullet combo, store it in a 50 cal ammo can and shoot say (5 rounds off the target to condition it) a 10 round on the target every 500 rounds to see what is happening in your barrel.
How much difference in barrel life you may expect to see on a 5.56 barrel and what defines the term "shot out". As indicated above a new barrel acceptance is 4.5" extreme spread at 100 yards. The rejection is 7.2" and no conventional match shooters wants to go to competition with a weapon/ammo combination that prints 10 shots over an inch in diameter. It is one thing to be beat in competition but when the winner is shooting a 1" rifle/ammo combo and you are shooting 4" ammo, the chances of you not winning is.............
5.56 ammo loaded with ball propellant is not likely to give an acceptable barrel life much beyond 2400 rounds. CIP in the M16A1E1 (adopted as m16A2) testing the groups shot at 1200 and 2400 rounds were just a tad larger than at 0 rounds. At 3600 rounds groups had opened up considerably. At 4800 rounds groups were right at rejection (7.0" average) and at 6000 rounds we could not keep groups on a 8X12 ft. target at 800 or700 meters and covered the entire board at 600 meters so I stopped the test as the barrels were gone.
A retest was conducted with three different rifles with same ammo, (XM855E1), SS109, M193 and other combos and we went through 10,000 rounds a day for 14 straight days shooting 12-14 hours a day. The exact same results with the XM855E1 were sustained however the SS109 ammo fed rifles were still in spec at 12,000 rounds. I had the same 100 yard groups at 4800 rounds with XM855E1 that I got with the SS109 at 12,000 rounds. Don't know what it was but the Belgian Gov't loaded their ammo with but it was obvious their propellant that was not as erosive as our WC846 propellant.
When the M16A1E1 Test was conducted at Aberdeen Proving Ground in early 80s all the rifles delivered for testing averaged between 3" and 4" at 100 yards. After targeting all rifles (I believe it was 12) I selected the best one, the worst one and one in the middle so endurance was started with the best and the worst delivered and median.
We shot 120 round segments, two mags 3 shot bursts, two mags semi auto which is basically known as a "median schedule". A hot schedule would have been fired at a faster rate and a cold schedule a slower rate. Barrels were cooled with forced air directed up their muzzles with bolts open placed on a specially designed rack that was plumbed to have a brass tube direct the air into the muzzle. By the time the last barrel was fired the first barrel was cool and the whole series started over again.
We cleaned them every 600 rounds or at the end of the day's firing whichever occurred first. During endurance firing the gunners knew to cease fire immediately and I would tell them to go take a break and I had to sit down and study everything closely to determine what exactly caused the stoppage and to what to charge the stoppage to. It could be ammo, magazine, rifle, or operator error.
Some failures are simple, some quite time consuming and there is a whole page of codes such as:
FBR failure of bolt to remain to the rear after last round in magazine fired.
OK lets say a FFR (failure to fire) is sustained. Some of the questions that needed answers were: 1. was the bolt all the way in battery? 2. You need to record such things as weapon number. 3. what round number it occurred at in the magazine. 4. Magazines are all numbered and the same magazines rotated through all rifles. So the mag is removed and examined for signs of failure, the rounds are removed and counted to determine the round number. Initially the stoppage may be charged to the weapon if no other evidence is noted. 5. What round number in the whole test series. 6. If the same problem occurs again with that magazine in a different weapon you have to write a new report and ultimately may remove the charge from the weapon and charge it to the magazine. 7. That round is saved, tagged and disassembled later to determine if the pellet was in place and pellet properly formed etc. Note: the majority of stoppages in the M16 family is known to occur on the 1st, 2nd or third round fired as the ammo stack is under much higher tension in the first three rounds. That is why I recommend a HD weapon have their magazines loaded with 26 rounds and stored on a empty chamber as I know that in a hurry the odds of my getting a stoppage before I get going good is much higher when the charging handle is released.
As well storing a rifle with hammer/striker under full compression should not (per spring engineers) lose energy but they also say you don't know if you have a properly made spring until you compress it for a number of months and test it with coppers to determine if the spring has taken a "set" and now delivers less than desirable energy.
Then storing a round in chamber muzzle down with too much lubricant on the bolt carrier is likely to migrate to the primer, kill it and when you need it you get a "click" which I would not like listed as my cause of death.
OK back to the report taken at time of stoppage. Detailed notes are taken and most of a Stoppage Report is down before firing is resumed. You cannot remember the exact details of exactly what you saw at 0830 hours when you get back to the office about 3:30. The report is written up, then secretary types it and it is reviewed at three levels locally and submitted through channels to Test and Evaluation Command HQ to the Liaison Officer who makes a copy for the file and he forwards it to the agency that is paying for the testing.
Failures to fire are supposed to be extremely rare if the weapon is known to exhibit the required striker energy which is checked at zero rounds and every 1200 rounds through 12,000 rounds. The allowable misfire rate on US ammo is one per million and I had five FFRs occur in only 244,000 rounds and that caused considerate concern.
One last interesting test you can accomplish is shoot a 5 round group at 1000 inches, then at each 500 rounds. Keep and mark all the cards as to the round point it was fired. When the barrel starts to go you should see the holes becoming elongated and the more you shoot it the more the holes will become elongated.
