Very few folks have seen it but gov’t has reference lots of ammunition. This is a controlled lot used to qualify accuracy barrels and to confirm instrumentation for P&V barrels.
Not to be confused with Proof Rounds, or Acceptance Test Lots, this ammo is made up special and is certified to be in the velocity window (max/min velocity) and to print in a given accuracy at a given range. 200 yards for 5.56 and 600 yards for 7.62.
Ammo is certified through a dispersion acceptance procedure and for instance on the 7.62 ball it is shot from three different accuracy barrels at 600 yards from three different rifles. It must meet dispersion in all three barrels.
The ammo to be accepted is fired a 10 round group at 600. Target is pulled and measured.
If the dispersion is outside acceptance they may shoot again or they may pull the Reference Ammo out and run it which is known to be accurate.
If they run the Reference ammo and it prints within acceptance, they will rerun the ammo up for acceptance. If it still fails the ammo lot is rejected.
Loss of velocity comes from large number of rounds on barrel. Well let me rephrase that a bit. The throat becomes longer and the pressure does not build as high, thus losing velocity. So if you keep the throat from wearing you will retain velocity longer and hopefully barrel life. Velocity rejection for gov’t is when the reference ammo loses 200 feet per second below the original tested velocity for that lot in a given barrel. As long as the barrel is shooting well loss of velocity is not that critical to a match shooter. For military applications with Ordnance Tables it must stay within a given performance envelope so that sight graduations are still useful. You will note AR sights are graduated in even numbers. So at 6 you want the ammo to hit pretty well on at 6 etc. If barrel is getting along in life you may hit low at 6 setting from what you are used to.
HOW DO I GET REFERENCE AMMO? Actually you don’t need gov’t reference ammo, can’t get it either but you can make your own much easier and with better quality. OK how does a average guy do his own reference ammo?
Best way when you have a new barrel and develop your “GO” load that shoots good. Load up 200 rounds with same propellant lot number, same lot of bullets, same lot of primers and if possible same lot of brass. Weigh everything and assemble all rounds the same.
Go out and shoot a couple warm up shots and then shoot 3 TEN SHOT groups at a given range. If you have 200 yards do it there.
Record the time of day you shoot, the temperature, sight settings etc. You can pick a given day like a week into next season etc. Then at say 2000 round intervals reconduct the same test at the same time of day (light direction on post sights will change things) and most importantly at the same temperature give or take a couple degrees. Light and temp is the most critical. If you have the ability to mount a good scope then light is not that important. In warm climates you need to shoot in morning or evening so mirage won’t be a factor. For instance on a 600 yard bench rest range I use I can go out and set up a rifle with 15X or 20X scope and set it on a 3” dot at 600 yards (painted on a steel plate).
I can set the rifle so it has a natural point of aim. During mid day in summer I cannot keep dot under the cross hairs as mirage will move the dot to all four quadrants of the scope. In short the cross hairs remain still and the target appears to move. The all time best conditions is to shoot on a cool overcast day. The chronograph screens seem to love it too.
If possible chronograph all shots and put everything into a file at as close to zero rounds as you can get. At 2000, 4000, 6000 etc reconduct same test and see what the dispersion differences are, then what the average velocity reading is and perhaps your sight settings if you have a target sight. You may have changed loads along the way, that is fine but unless you shoot with the same lot every time you won’t know what the actual changes are for that barrel.
I would cut and save all groups with the chrono records. I paste my groups on back of the chrono record.
Actually starting about 6000 you might speed up the testing to every 1000 rounds. That should take you to 8000 rounds. The more reference ammo you store away the longer you can do your testing and more good data you get. All things being considered you might consider 300 rounds of reference ammo. This should take you to 10,000 rounds and if you clean often you should have enough ammo to last you a year or two for reference purposes.
Store your ammo in GI ammo cans in a cool dry environment away from massive heat changes.
If you have a basement, great. Don’t store it in outside shed where it goes from hot to cold. If nowhere else under your bed or in closet.
Assuming you use a erosion gage to record throat wear when you get through with the first barrel you will have a wealth of historical information you can pass on to friends or keep for your files.
I take erosion gage readings at every 500 rounds you can as well to compare gage readings to velocity changes at the 2000, 4000, 6000 mark in the life of the barrel.
This all may change if you are a match shooter. You may want to consider doing the sequence every 1000 rounds as those heavy bullets tend to be harder on barrels. I know guys that shoot heavy bullets and they tell me their tubes are gone at 2000 to 3000 rounds.
One very strange event I noticed when using GI M855 ammo, I knew the barrels were about to go when unexplainably I would get a wild shot at 9:00 at 100 yards off the bench in the increment testing. It may be one in 30 rounds but there was one. The next increment testing I would get one maybe two a little further towards 9:00.
Now I cannot explain this phenomena but that is what I saw for what it is worth.
For that matter if an AR owner could lay in several thousand SS109 rounds and I mean genuine.
Loaded by FN, that would be as good a reference ammo as you could buy arsenal loaded. You can handload your own reference ammo more accurately but if you are not a handloader, SS109 would be my choice.
If you want to go really first class get a case of FED MATCH 69gr. and pack it away and can be assured of top accuracy potential.
I believe it comes in 500 round cases so you would be set up for maybe two barrels. The main thing is same lot number and buying by the case is the best way to achieve repeatability.
I also understand Black Hills loads some excellent ammo in 69 gr. Sierra. If anyone else makes it I am not aware so someone else might be able to expand that data base.