I am new to the subsonic world.

I have a custom Bolt gun in 300BO: Rem 722, Bartlein 5R, 1:8, 16.5". This builder has built many custom extremely accurate rifles for me. I do not question the rifle. I have tried many bullets all in the 200g or heavier weights. Lots of powders. Best load so far is RL7 11.5 grains, .75" groups with a SD of 4. 0.027" off lands. 208g ELD-M at 973 FPS. American Eagle brass, annealed and using Fed GM205M

Should my expectations for these subsonic loads be the same as my other custom rifle / loads? My other rifles are all < .5" moa

Thanks for your input.

I think you are getting better accuracy than it should get. I don't consider the 300 bo a match level design.

Actually the .300 BO is a very good match cartridge design. My similar .300 Whisper 10” Contender barrel from SSK will agg in the 0.7s with supersonic loads.

The OP’s load is likey a bit too slow, Speer recommends a starting load of 12.1 grains of RL-7 under a 200-grain bullet. That’s ‘way under the speed of sound and a pretty long bullet to run that slow.

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I have tested up to 11.9g RL7. I have 12.0,12.1,12.2 ready to test. Speed of sound at 25F using online calculator is 1079fps. I can easily get to -10 where I live, which is 1040 fps. Not that I would be out shooting when it is that darn cold!!

I have been up to 1130"s fps with other powders shooting in the summer, but get some super sonic in that range. I want a load that will remain subsonic for all seasons in my area. Other powders had most groups around 1.5"- 3" range.

Thanks again for the input.

quote:

.75" groups

Wow that is just horrible.

200+ grs is on the verge in a 1-8 barrel, especially at lower velocity's.
just for fun try some 180's.

the AAC guns run a 1-7 for the 200-240gr slow motion heavy bullet range.

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Originally posted by p dog shooter:

quote:

75" groups

Wow that is just horrible.

I read .75" group.
roger

Is your rifle suppressed? If not, there is no point in using extra heavy bullets at subsonic velocities. I like a 130 grain Hornady at about 2150 fps in my custom .300 Blackout. Zero 1.5" high at 100 yards and you're good to a little past 150 yards without elevation compensation. And the faster bullet drifts much less in the wind. If I had not had a supply of the Hornady 130's already on hand I would have gone to the Nosler 125 Ballistic Tip.

quote:

I read .75" group.

Did not get the period copied fixed it.