OK, I've been emailing with David Little at Kynamco and am a little confused. Hopefully, you can help me find an answer.
he says...

The 375 Belted 300 gr soft nosed and solid has a maximum service pressure of 19.5 tons/sq in. A nominal velocity of 2500 ft/sec with a muzzle energy of 4070 ft/lb. The lab say that they load the ammunition to the velocity stated and with modern powders the pressures run between 15.5 tons/sq in to 16.5. We try to keep the pressures as low as we can so that in extreme conditions, especially heat, we don't exceed the maximum service pressure.

Now your other comment on powder raised a few eyebrows and some skurrying round the loading rooms to check that all the powder checking gauges etc were working. So there is some concern over your comments. We also test fired some of that batch of ammunition and it is well within spec.
I hope this helps clear up some of your concerns.
Yours sincerely
David

This started with my chronographing some of their factory loads and getting 100fps+ more than their published figures (in two different rifles - both with shorter barrels than Kynamco's test barrel length).

I pulled the bullets on a few of the loads and found a 2.0 grain variation in powder charges between a few of the loads. A little concerning from a QC perspective...

These are 300gr woodleighs, with about 77.0 grains of something in them. (the charge weight indicatest that it's not a "slow" burning powder).

My question is how the hell is he getting these velocities (at these low pressures) - with what appears to be a medium-burn rate powder (again, based on the charge weight), when all of the loading books say that this velocity can't be obtained at these pressures with the slow burn-rate powders, much less the medium burn-rate powders?

What am I missing here?

You're missing the fact that Kynamco may be using a non-canister grade of smokeless powder.

George

OK, so what (in theory) could that be?

There aren't that many powder .mfgs in the world - surely whatever they are using is sold under someone's label somewhere... right?

major ammo manufacturers do not use what is called "cannister powder". THat means they usually do not use what is manufactured and sold in 1# cans as "IMR 4350", "WW 760", or whatever. THey buy large lots of powder that are tested at the end of each production run. The ballistics are measuired and they arrive at the weight needed from this lot of powder to get "X" velocity at "Y" pressure.

If the load is 77 grains with 300 grain bullets it will have a burn rate in the general area of 4350.



If you use a Chrony for your chronograph they often read high and it depends on both light conditions and calibre. In other words on a given day and a given location a chrony might read high on a 375 and be accurate with a 270 etc.



Mike

I agree with your powder guess, but all the load books i've reveiwed suggest a much higher pressure with these loads. I was thinking 4350 or RL-15 or something thereabouts.

the chronograph is an oehler 35p (used with third proof screen) and the same velocities were duplicated two additional times on a total of 3 separate days. I considered that, but have obviously ruled any chronograph error out.

77 grains of Re 15 is way over the top for a 300 grainer in 375. 73 grains is getting to the end of the road and I have just over 2600 with that load in 26 inch barrel.



You said you were getting 100 + on their claimed figures so that puts you at 2600 +



In Model 70s 82 grains of IMR 4350 is good for 2600 + and is very compressed with 300 Hornady Round Nose, so the burn rate is quicker than 4350 since yu are getting 2600 + with 77 grains.



My guess is the powder is a double base powder, like Norma/Reloader or Vitahvouri and with a burn rate between Re 15 and 4350. As others have said it is probably a non canistered powder. In very general terms I have found that when all else is equal the Norma/Reloader powders will give up to 100 f/s more than single base powders and sometimes more. In other words 2600 with the right burn rate of a double base powder might only have the pressure generated by a single base powder giving 2500 f/s



Whatever, it sounds like good ammo



PS I agree with you on the Oehler.



Mike