SW SBR-SOCOM

[phils3]

I am using a cheap caldwell chrono, so I am a little suspicious of these results. Please verify if you get similar results.
217 Gallant cast & coated boat tail, 9.7 gr SBR, R 7.5 prim, coal 2.1” out of an 11” barrel w/ standard buffer & spring gives me about 1050 fps w/ BHO.
125 gr TNT, 22 gr SBR (1 gr over max listed load, max listed 21 gr @ 39970 psi), R 7.5 prim COAL 2.1” out of a 14.5” barrel (pinned) gives me avg of 2365 fps, groups .75” at 50 yds.

[dellet]

I am using a cheap caldwell chrono, so I am a little suspicious of these results. Please verify if you get similar results.
217 Gallant cast & coated boat tail, 9.7 gr SBR, R 7.5 prim, coal 2.1” out of an 11” barrel w/ standard buffer & spring gives me about 1050 fps w/ BHO.
125 gr TNT, 22 gr SBR (1 gr over max listed load, max listed 21 gr @ 39970 psi), R 7.5 prim COAL 2.1” out of a 14.5” barrel (pinned) gives me avg of 2365 fps, groups .75” at 50 yds.

Yes, that sounds high for the charge weight for both loads.

Were you possibly too close to the chronograph, less than 15 feet?

[phils3]

It was roughly 10 feet. My best velocity was 2375. The shooters world load data lists 21 gr max 2184 with a Sierra 125 HP, but the pressure is very low for a super (40k). The Speer 125 TNT seems to do well at a coal of 2.1”, but the seating depth is pretty shallow. I thought it would be fun to try and make use of that little extra space and 14k of pressure. Since the 300 HAMR is just a long 300 blackout, and it lists 2400 fps with 23.3 gr of SOCOM I thought I would end up somewhere around 2300 fps.
At 22 gr the powder is compressed. Maybe the compression is adding a little velocity?
I also didn’t get any signs of high pressure. Just for reference, I do start to get some pressure signs in the same gun when I go over 20-ish grains of H110 and a 110 gr bullet (seated about shoulder depth).

[dellet]

I looked at your numbers, the load data from Shooters World, my notes from testing that powder a few years ago, and honestly they don't add up. Even less when your barrel is 2" shorter.

Basically you are loading more, of a faster powder, getting higher velocity, with less pressure, when compared to Shooters World Blackout or 1680. On face value, I would normally call BS.

I would move the Chronograph out at least 5 feet, 10 is borderline in picking up muzzle blast. Then confirm velocity with bullet drop at distance.

When comparing data with 300 Ham'r, that little bit longer case holds about 20% more case capacity. Basically holds about 5 more grains of powder. Don't let that give you false confidence.

I won't wave the back off flag and say you're in dangerous territory, just that those numbers were not obtainable when I used the powder. So if you change lots of powder, or bullets, I would definitely work it back up.