The 7.62 cartridge was initially developed during WW2 with IMR 4895. I have found references to IMR 3031 in early cases, but IMR 4895 was shorter than the lincoln logs of period IMR 3031. IMR 3031 is currently a short cut powder, a little faster than IMR 4895, and it is a great 308 Win powder.
There are three 4895's, that is IMR4895/H4895/AA2495. These are so close in charge versus velocity to be indistinguishable over a chronograph. Accurate Arms told me their AA2495 followed the same pressure curve as IMR 4895. Hodgdon 4895 when it was initially brought out, was a copy of IMR 4895, but over time they have tweaked it, supposedly it is an extreme powder, but I can't see what they are advertising over a chronograph and if there is too much powder in the case, primers get blown, just like regular 4895.
Incidentally, AA2520 is a ball powder and Accurate Arms told me they blended it to the IMR 4895 pressure curve. When it was the soup du jour, it became very popular with the NRA across the course service rifle crowd. Back then, that meant the M1a/M14. Of course it shot well, was dirtier than the stick powders. The gas system was always filthy after a match with AA2520. The primary selling point was better metering. This is one of those things that fits the world view of shooters. That is, they believe that if it throws better, it must be more accurate. This is not necessarily true, IMR 4895 throws for me, plus or minus a half grain. IMR 4350 throws plus or minus one and a half grains. I will weight out 4350 charges, but I have shot lots of cleans with thrown 4895, or AA2495, as shown in these targets:
Humans see patterns all the time that don't exist. I have chronographed a couple of ball powders, rifle and pistol, and just because they throw better, does not result in tighter extreme spreads and standard deviations over the chronograph. An example of this human bias, there are those who measure rim thickness in 22lr and claim miraculous accuracy improvements. Eley, at the Smallbore National Championships, said this was all bunkum, and put up a chart showing over 100 measurements they make and control on match 22lr. The equipment seller picks one, one easy thing to measure, sells the equipment, hypes up their snake oil through articles and shills. It is all nonsense and the Texas Sharpshooter fallacy. The rim thickness guys are not shooting enough ammunition to make their case, though they make a good sales pitch. Snake Oil salesman sell hope, and something that fits the world view of their buyers. None of the National Champions I know or asked, measure rim thickness. They decide what is good ammunition based on the groups they shoot.
Not a single one of these rounds was checked with a rim gage.
In so far as IMR 4895, it has a wide sweet spot. I used the 39 grains load standing and sitting rapid fire at 200 yards. It shot well, those are 20 round groups I posted. Those were thrown groups. I threw ten charges and when the average was close to 39 grains, I was ready to dump the charges and seat the bullets on my Dillion 550B. I only weighed long range ammunition because I was worried about blowing primers. IMR 4895 was the powder used in the National Match ammunition. Top target is a 30-06, the lower, 7.62mm, and the propellant for both was IMR 4895. The bullet was the limiting factor, in my opinion. The old 174 FMJBT is accurate, but not as accurate as the 168 SMK's which replaced it. The propellant stayed IMR 4895 after the bullet change in National Match ammunition. Neither of these loads are magnums, the 7.62 load could have been bumped up, but the most accurate groups in AMU testing at 600 yards were at 2550 fps. Also, for the Garand and the M14, the gas system has to be taken into account.
Varget is an excellent 308 powder. The primary reason Varget has displaced IMR 4895/IMR 4064 in F Class shooting is that shooters can get higher velocities before blowing primers. These guys are pushing 185 grain Bergers and 200 gr Bergers so fast they are eating 308 barrels up in a couple of thousand rounds. I used to be able to take a 308 barrel 4000+ rounds, but half my shots were with 39 grains load, one quarter were with 40.5 to 41.5 grains IMR 4895, and only my 600 yard loads were pushing it. I still think IMR 4895 is the "standard" in the 308 Win, and what you can do is say, X powder throws better than IMR 4895, Y powder is a bit faster, maybe in time Varget will be the new standard, don't know. It is an excellent powder in the 308 Win over all bullet weights.
When it comes to powders, and what is the best powder, just what are the differences between powders?. Outside of the obvious physical differences, ball/stick, short cut/long cut, just what do you know about the burn rate characteristics?
What you know is some burn rate chart, which is about as useful as measuring to the ten thousandth's with a yard stick. The ranking is quite mysterious, but given within a class, lets say something I am familiar with IMR 4895. Or 4350. Specifically what are the differences in the pressure curve between IMR 4895/H4895/AA2495/AA2520? Or IMR4350/H4350/AA4350/short cut 4350? What is the difference between Titegroup and Bullseye? What do you know outside of what industry tells you? What if the pressures curves (on average) were within 5%, or 3%,or 1%, or 1/2%, if all the different brands within a class have pressure curve differences less than 3% different from each other, is that difference significant. Significant enough for all the hoopa about that powder? Or proof that one powder is vastly better than another with a 3% pressure curve difference? I think there are well over 100 powders in the burn rate chart, and I am getting to believe the greatest difference (in classes, whatever that might be) is mostly advertising. Blaring labels and in print articles with three shot groups and a lot of hype. We really don't have the information to allow us to make good judgements. We have advertising in the print media, anecdotal information and our own limited experiences. Most of which is inconsistent, confounding, and contradictory. And that is as industry wants. It is as Noam Chomsky says"
the purpose of advertising is to create ill informed consumers who make irrational choices.
The standard load for a M1a was a 168 SMK with 40.5 to 41.5 grains IMR 4895, LC case, and CCI #34 primer. Actually the 34 primer came after the M1a was displaced by the AR15, but the #34 primer is the military, less sensitivity primer. And it shoots very well in gas guns. The powder charge more or less depended on the the tightness of the throat and barrel. As the throat moved, you bumped up your charges. These were not meant to be magnum loads. The rifle would malfunction is over gassed. Shooters wanted accurate, perfectly reliable ammunition. Today, the mantra is more means more, so more velocity means more. Actually, if your wind call is off, more velocity will not move the bullet into the middle of the X ring. Going to a higher ballistic bullet is far better than adding more powder to the case at reducing wind drift at distance.
