This was posted on another board but makes for good reading.
The biggest enemy (besides some politicians) we face is carbon be it in barrel or cartridge case. I have been doing a goodly amount of testing the last three years and I have now proven to myself that I have wasted some awfully good barrels over the years by my cleaning methods not being effective.
About seven years back (doesn’t seem that long) a friend brought me a 700 Police Sniper with stainless barrel that was almost new. At 600 rounds the barrel was gone. I cut threads and set it back and rechambered with a short throat tight 308 reamer I had made up and he went back to the party. He got 1100 rounds that run before it went. Cut it in half and no rifling ½ in front of chamber.
This guy and another friend are 50/60 vintage and one had a 600 yard range next to his house and these guys got together about six evenings a week year round and fired off 20 to 40 rounds. My friend with the Police Sniper would fire three to five shots and let it cool and another 3 to 5 over a two to three hour period. My other friend had a Chandler Sniper Rifle and he had 10,000 rounds on that barrel at that time and it was still driving them. The difference was the friend with the Chandler was shooting all his while the barrel was warm and immediately cleaning his barrel with bronze brush first and then put it away.
That got me to thinking, our test barrels used for ammo acceptance went 15,000 to 17,000 rounds before they went out of spec. As highpower shooters we think we have done great things with a barrel if we get 5000 rounds. Well think of this way, most chome moly barrels are 4140 and if test barrels and highpower barrels are same steel why then did the high-power barrel fail?
As highpower shooters how many guys do you see cleaning their barrels before they leave each firing line moving back? I know some guys that will clean before 600 but most of us don’t clean until we finish for the day. I believe that is what is killing us, we are allowing the barrels to remain fouled the entire day.
Then it hit me. Only took 35 years but OK I am slow. The difference in the gov’t test barrels is they are only fired a few rounds and cleaned. Ammo tests are conducted as follows:
Three accuracy rigs are taken to range with their log books. Each rifle is placed in a “vice” we called Frankford Arsenal Mounts or hard mounts and one shot is fired at 600 yards. Guy in pits radios back and tells the gunner where he hit and he adjusts the wheels to center the group on a large sheet of blank paper. Ok he generally fires three rounds to get it on and when he is there the pit guy radios back to run the string.
The gunner loads five rounds in mag and has 5 rounds in hand while at the same time the pit man has pulled and pasted the target. The gunner then fires all ten rounds as fast as he can operate the bolt (generally these were 1903 actions) to get all rounds in same wind condition. A good gunner will cycle 10 rounds in 15 seconds since there is no aiming and the mount returns to original condition on firing.
Pit man will pull target and measure the group. If it is in acceptance accuracy he radios the measurement and changes the paper while the gunner removes the rifle from hard mount, records the rounds fired in barrel log and replaces rifle 1 with rifle 2 and repeats the scenario. Same thing for rifle three.
If one of the groups is not acceptable he then has target changed and he fires a group with Reference Ammo which is a special lot known to produce acceptable groups with good barrels. If the group with Reference ammo is not acceptable they deadline the rifle and go get another. If the Reference ammo group is within spec they will retest one time with the lot up for acceptance. If it passes fine, if not the lot is rejected.
I set out to run some experiments to determine the contributing factors based on the above. Three years ago or four (I have CRS) I got a new 700 Remmy 308 for the action and I figure OK I have this thin 22” barrel brand new, lets see if I can extend the life.
First I measured the throat with an erosion gage.
Note: To save lots of writing go to:
http://www.beastwerks.com/Throat_Erosion_Gauge.htm which will explain what these are for and how they are used.
Next I examined the chamber neck/throat area with a bore scope. I have Olympus Series 5 7MM 30 degree and it is marvelous for 7MM and up tubes. I made notes of things I saw such as reamer marks in forcing cone etc.
I have a goodly number of 173 pulls so that was to be my test bullet with 4895 mainly.
I started shooting it and cleaning every 12 rounds or so and I had 50 dedicated IMI cases that were recycled through this rifle time and again. First loading was IMI factory with 180 grain Sierra BT hunting bullets.
I fired the 50, cleaned the barrel and immediately reloaded the ammo and a very strange event happened. The primer pocket residue was quite soft and fell out almost as a powder. First I thought the IMI boys had a different primer mix but read on, as it turns out they did not. Next I borescoped the barrel again and took erosion readings every so often.
At 8 rounds erosion gage showed 8 ½ rings, at 100 rounds 10 ½ rings, at 150 rounds top of 11th ring and then it stopped. The reason for the rapid advancement is the raised metal on rifling left over and from the reamer marks being blown away.
OK I had 11 rings at 150 rounds, 11 rings at 250 rounds, 11 rings at 350 rounds, bottom of 11th ring at 529 rounds, 754 rings bottom of 11th ring. Note the 11th ring is about .015 wide and the other rings are centered every .100”. (Note: testing at APG many years ago determined the wear rate on 30 cal rifle barrels normally advanced at .100 per 1000 rounds. This is the reason the Garand/M14 gages have .100” separations between rings.
Otto Haenel was Test Director on that test and he told me he took 10 new M1s and a 2 ½ Ton GI truck full of ammo and after initial measurements fired 1000 rounds on each rifle and then took the barrels to metrology for measurement. The testing was stopped when the barrels reached rejection criteria which is about 8 to 9 inches at 100 yards depending on whether it was M1 or M14.
Borescoping during this series was amazing in that when I got my bore scope I looked at every bolt gun I have and made notes of throat condition as compared to the number of rounds. I already knew that on most of my tubes on my target guns (308/30.06) the reamer marks are generally gone at end of the first HP match or two which with zeros is about 200 rounds of course.
Now I have a barrel at 754 rounds that has been cleaned very frequently and I still have reamer marks ! ! ! Now it is a given that the 22” sporter barrels were shall we say did not have a high life expectancy from the accuracy standpoint but here I have one that is going strong.
Quick side note: At this same time frame I found a Sears Mod 53 (Mod 670 Winchester basically in 30.06) and I did the same procedures and had it up to 500 rounds and the throat condition was the same. Basically I had similar conditions in 308 and 30.06 with frequent cleanings.
Back to the Remmy 308 saga. I decided to see what a hot schedule would produce. I had upped the number of shots to 22 round strings between cleanings and taken barrel temps. Depending on ambient temp the barrel temp taken 3” from muzzle gave 122 to 126F shooting 22 rounds in about 12 minutes to 14 minutes which is what is normally takes me at 600. I upped the firings schedule to about a 8 min minute string and barrel temp went to 165F. Bore scope and erosion gage showed no change. Next I shot a string in maybe four minutes and barrel temp went to 190F at the muzzle!
This time I recorded movement on the erosion gage. I had noted a little heat checking around 650 that took a 30X borescope to see and it was progressing slowly. At 900 rounds I was just below 11th ring. At 1009 rounds the last trace of the reamer marks were gone, I was still just below 11th ring and pulled the barrel off and rechambed with 7/08 heavy barrel I know call the Confederate Swamp Gun. It is a swamp cut Pacnor barrel about 23 ½ inches that was originally chambered in 280 Remington and had about 3500 rounds on it. A friend pulled it off and gave it to me.
OK lets go back a bit, during my initial borescope sessions with my bolt guns I saw a horrible condition. Gouges about ¾” long in the throat area. Only thing I could figure was dirty ammo and if I drop ammo I take great pains to clean it off and I really could not fathom what was happening and why then the little Remmy 700 gave me the answer.
After one firing session at the 250 round point I did something different, I did not reload the ammo immediately but put it on bench and loaded it a week later and the primer residue was nice and hard as I was used to finding. Next I borescoped the barrel and I have a identical gouge I saw on my other bolt guns.
This ammo had gone from the loading tray to CaseGard box to gun and back in box and back to loading tray and the cases didn’t even touch the bench. It didn’t take long to figure out it was the primer residue dropping through the flash hole when I cleaned cases and it stuck to the carbon on inside of case. On firing it got up into throat and was laying there waiting for the next round to embed it in bullet jacket and start engraving the barrel.
I then read where Mitch Maxberry had concluded primer residue was doing the same to his guns.
Next I had a nice conversation with a PhD. Chemical Engineer and asked him about the formation of carbon and what happens. He confirmed it does get hard when it cools down but had never seen a study to determine hardness against time.
Now everyone that reloads has noticed on some ammo when the expander ball is pulled back through the neck the amount of force goes up tremendously and on cases that have not had the necks scrubbed the force is enough to almost lift the loading table. Obviously this is not helping the neck and stretching follows.
Pull you FL dies down, wipe off the expander button and see if you have any scoring on your expander ball. Bet you do. Now think of this, what caused it? What is put in steel to harden it? Carbon. A brass case is not hard enough to score hardened steel expander ball but embedded carbon inside the case mouth sure is.
I now thoroughly clean my case necks, size them without expander ball and then on a separate operation I run a expander mandrel in from the top and expand it to where I have .001 to .0015 grip on my long range ammo.
A lot of folks judge the quality of their ammo by the amount of seating force. Uniformity of velocity is directly related to BULLET PULL forces and not bullet seating forces. MIL SPEC on M118 Long range has a minimum bullet pull of 10 lbs. Ball ammo has a min pull of 45 pounds. THERE IS NO MAXIMUM BULLET PULL SPECED ! ! ! !
Want a shocker, pull down a box of M118 Match and measure the amount of force required to unseat bullets with a Force Gage. It is not uncommon per ammo engineers to see a bullet pull of 300 POUNDS. Anybody want to bet a variation of 10 lbs to 300 lbs won’t cause trouble in River City?
I measured the amount of force my Hollywood loading tool produced in an effort to check bullet pull. I used two force gages. I sent one up to measure the amount of down force in pounds and the other to measure the amount of force applied to the handle. If I remember correctly the pull force was about 6 ½ times higher than the handle force so 10 pounds of handle force is 65 pounds of pull and I have had M118 want to lift my loading table off the floor and with what is on it is several hundred pounds.
It wouldn’t hurt to invest in a force gage. They are on ebay for a fraction of what they sell for new. I would get no less than a 50 lb gage and better yet a hundred pound. The electronic gages will measure and record the highest force delivered during a cycle and are very nifty.
Carbon in the case neck will grip the bullet by differing degrees, clean out that carbon and you will find you have a much more uniform bullet pull.
Food for thought. Check Sierra ballistic tables for 30 cal match bullets at 1000 yards. Say 2700 fps and then check 2600 feet per second and 2800 feet per second and see what the difference is in bullet drop. OK if your extreme velocity spread is 50 feet per second and you know the bullet will drop 40 inches with 100 feet velocity change then you know you are looking at 20 inches of vertical dispersion before you add in sight error, heart beat, mirage, wind, etc.
You want long range ammo to have an extreme spread of 25 fps or less if you expect to stay anywhere near the X ring. Otherwise you have done it to yourself to show up with a combination that won’t do it.
Oh by the way I have chronographed M118 and 60 feet per second variance between rounds is about average. I have seen it at like 80 feet per second. Anyone want to go to 1000 yards with ammo shooting 36” of elevation?
Bottom line guys, clean your barrels often, clean your brass every time, clean your primer pockets making sure no carbon goes though flash hole as CARBON IS THE ENEMY right behind anti gun politicians.
