215 grain cast and 1680 powder

[gunfan2]

I am loading this in the 300 blackout and have dropped the powder charge to 10 grains and I am still getting the sonic crack through my suppressor. This is fired from a 10.5 inch AR. Is is safe to go below the 10 grain amount of powder. I am uncertain, locks back the bolt and ejects about 10 feet away. Any info will be appreciated.

[shell70634]

I shoot a Lee 225 gr pc'd over 11 gr Shooters World Blackout (same as 1680) out of a 10 inch suppressed. It's not supersonic but get first round pop once in a while. I don't remember velocity but think it was about 1015 or so. If I get on the range tomorrow I'll chrono them.

[gunfan2]

Can't quite figure why I'm getting enough velocity out of 10 grain load to go supersonic. Just wonder if dropping the charge will be safe? I'd appreciate the info on your chrno if you go tomorrow.

[P Flados]

1680 has a good track record for not misbehaving with low load density. If you are sonic, going to a charge 0.2 to 0.5 gr below the charge that is just enough to give you the sonic crack should be fine.

I ran Quickload with 10 gr of 1680 and a 225 gr bullet seated 0.567 deep. Predicted velocity from a 10.5" barrel was 950 fps. The can may be adding a little extra and I have had loads that were close to 100 fps over predicted before. However, you may want to double check your load routine (correct powder, correct powder measure setting, etc.).

You should not need to go much lower to get your load sub sonic.

[gunfan2]

1680 has a good track record for not misbehaving with low load density. If you are sonic, going to a charge 0.2 to 0.5 gr below the charge that is just enough to give you the sonic crack should be fine.

I ran Quickload with 10 gr of 1680 and a 225 gr bullet seated 0.567 deep. Predicted velocity from a 10.5" barrel was 950 fps. The can may be adding a little extra and I have had loads that were close to 100 fps over predicted before. However, you may want to double check your load routine (correct powder, correct powder measure setting, etc.).

You should not need to go much lower to get your load sub sonic.

Thanks for the reply, that was my thoughts about lowering the weight much more. I do have an adjustable gas block on this gun, was wondering if adjusting it would have anything to do with the velocity. It is kicking the brass out considerably and locking the bolt back consistently. I know it will never be as quiet as my bolt gun, but the crack has got to go, I shoot in a rural, but have neighbors within a hundred yards, but not of my burm. By the way, I weighed all the charges on this load.

[shell70634]

Just fired 5 rounds 225gr over 11 gr SWBO and got 1044- 1067 fps. Got a first round pop but the rest were quiet. 10 inch AR suppressed