Home Forums Reloading Big Game Rifles Seeking your opinion on .375 H&H data

Today I was working up the load for my Sako M85 .375 H&H, armed with a chrono.

I was using:

250 gn Barnes TTSX
IMR 4350 ranging from 74 gn to 76.5 gn by 1/2 gn increment
Norma brass
Federal Premium Match Large Magnum Rifle primers
COL 3.555"

I was able to get sub 1" MOA w/ 74.5 gn and 75.5 gn loads. However my chrono readings were only ranging from 2075~2157 whereas the factory load data shows expected velocity between 2422~2604 using 71 gn to 79 gn. Another odd thing was that at 76 and 76.5 gn the velocity readings actually dropped to 1700~1885 which seemed illogical.

Perhaps it's time to get a new chrono but could there be any other explanation?

Regards,

Sounds like the chrono. Are the batteries good? More powder equals more pressure it cant go slower.

Good point 23lx. I will replace the battery to make sure before I go back out to the range again. I will be working up a load using 270 gn Barnes TSX next to see whether I can get a better group.

How far was the chrony set from the muzzle?

Sunny,cloudy, sky screens installed?

Did you shoot any other ammo over the chrony that day?

I would agree with the other comments regarding chrono problems, low battery, too close to the muzzle, etc.
However, I would not be surprised if the 2100fps or so speeds are correct. In my experience with loading the 375 H&H, IMR 4350 is on the slow side for lighter bullets and even though the burn rate might be ok for 300gr bullets, it takes a lot of compressing to get a full load in the case. I would recommend something in the Reloder15 or Varget range if you have access to them.
Good luck,
Steve

Good post Steve. I'd also suggest RL 15 instead of IMR 4350 for lighter bullets in the 375. This is coming from a big time 4350 user for other cartridges.. Good luck with it.

Thank you so much for the replies everyone. To answer Steve4102 it was an overcast day and I had sky screens installed.

I will order some RL 15 and check it out when I work up a load using 270 gn TSX. Also I will make sure to replace the battery before heading out to the range.

Regards,

I would not chalk it up to a Chronograph problem.

How long is your barrel?

If you have a short barrel you give up velocity. In addition, if you are using a slow for caliber powder, you can hit a point of diminishing returns where more powder results in less velocity.

I can hit that point in a .270 Winchester with a 130gr bullet and a 22" barrel, but not with a 26" barrel. This is one of those hidden areas where barrel length makes a difference.

In addition, a half gain just isn't that much of a change when you are dealing with such a large powder charge. So when dealing with a small change and a small sample size, random chance can result in invalid results. The smaller the sample and the larger the standard deviations the less likely your results are statistically valid.

There have been times when I've been just shooting one of each increment to work up and find pressure, before loading full strings, and sometimes I'll go up a three increments before the velocity will raise. I don't worry about it, because I know these results are not statistically valid, and I'll get better results when I shoot my longer strings.

Personally, I'd switch to a faster powder and try again.

Thanks for the input antelope_sniper. I did not know about the "point of diminishing returns" though it sort of makes sense. Additionally the bbl length is 21 1/4" on my Sako which may contributed to the issue at hand.

I just ordered a 1 lb bottle of RL 15 so when I get it in I will be loading up w/ 270 gn TSX w/ it to see how it performs. Thanks again.

Regards,

+1 on the faster powder...lots of choices work in the .375

One other thought. TSX and TTSX bullets have less bearing surface, which means less pressure, which in some cases equates to less velocity. The composition of the copper differs from gilding metal on many jacketed bullets, also possibly adding to a loss od pressure and velocity.
In my experience with other cartridges, switching to a faster powder, and a tad heavier bullet, with more bearing surface actually increased velocity.