300 Blackout with 175 gr. bullets

[clowdis]

I have tried the 220 grain bullets including factory and handloads and they all tumble even at 50 yds. The barrel is a 9 twist in an AR so this shouldn't be happening but it does. I'd like to drop down to 175 grain bullets and try some subsonic loads with them but I don't see any loading info for those bullets. Anybody have any input?

 

[savagedasher]

I don’t think you can keep the bullet subsonic is probably the reason you can’t find a load

 

[Lefty Trigger]

Reloader #7 at 11.2gr or IMR 4198 at 11.3gr will be around 1050fps,.... Sierra data for their 175gr bullets. Check their site as they have sub-sonic loads all the way down to their 110gr bullets.

 

[clowdis]

Thanks Lefty!

 

[RDA72927]

Having a load that run's subsonic is EASY. Having a load that runs subsonic and cycles the AR correctly is another. Getting enough pressure to cycle everything and the bullet stay subsonic is the challenge.

 

[dellet]

First thing is to verify the twist

Part of it depends on the bullet shape, sometimes even powder choice depending on bullet construction. Cast and monolithic act completely different than jacketed.

Below is a 208 ELD at 200 yards in an AR with a 1/10 at 1040fps




Here is a solid copper same distance and powder at 1030 fps. The bullet length was the basically the same, but this was a round nose, flatbase.


The solid copper started looking better for stability when I switched to a higher pressure powder. I am pretty sure the base was getting gas cut based on what the captured bullets looked like. Once I got enough pressure to obturate the base they straightened out more in flight, but still had a slight wobble at 200 or so.

I will also add that you want to check your loads without the suppressor, you be having a slight strike.

 

[Lefty Trigger]

Having a load that run's subsonic is EASY. Having a load that runs subsonic and cycles the AR correctly is another. Getting enough pressure to cycle everything and the bullet stay subsonic is the challenge.

This is true, I missed that in the OP's first thread and my 300BLK is a bolt rifle that will make a huge difference in what will function.

 

[dellet]

This is true, I missed that in the OP's first thread and my 300BLK is a bolt rifle that will make a huge difference in what will function.

It really just depends on how the rifle is set up, and knowing that would be helpful.

The hardest would be carbine gas and no suppressor, he would be limited to a few powders. Pistol gas and suppressed there's at least a dozen powders to choose from depending on barrel length.

Easiest combination would probably be Shooters World Blackout or 1680 with a 175 SMK. Then he could run the same bullet/powder combo anywhere from 1-2000 fps in a 16" barrel and have full function even without a suppressor.

 

[clowdis]

The rifle has a pistol gas setup and a 16" barrel. The bullets tumble with or without the suppressor so I don't think baffle strikes are the problem. I'd like to keep the bullet subsonic if I can but I think that the next trip to the range will have subsonic as well as supersonic ammo to try. There doesn't seem to be any problem at all with cycling, the rifle cycles fine, just doesn't shoot......at all.

 

[1lnbrdg]

Not sure how it would work in a 300 BO AR but I used to load 30.06 "gallery loads", 147gr FMJBT "ball". Those bullets wouldn't shoot worth a flip normally but on suggestions from a cast-bullet shooter, I loaded them backwards in the case (pointy end inside the case) and had several groups sub-1" at 100 yds. Used Unique powder but been long ago, not sure what the amount was. Pulled powder data from the Lyman cast lead handbook.

Squirrel hunted with them some, lot of drop though.

 

[dellet]

What's the load, bullet and velocity?

What bullets have you used successfully as a sub?

 

[Lefty Trigger]

Bullets that tumble are a stability issue vs twist rate. The 9 twist may be a factor in your bullet selection and getting them to stabilize. My 300blk is a bolt rifle but it has a fast twist at 7.5 and in the greater scheme of things that's really fast for such a huge bullet but the speed is the reason behind it, if its slow you need to spin it fast to make it stabilize. With your 9 you may have to "speed them up" or keep dropping down in bullet length/weight till they stabilize. Once you find a bullet that it likes work with it on your sub-sonic loads.

 

[Dave in WI]

First thing is to verify the twist

This. Most 300 BLK utilize 7 or 8 twist to successfully stabilize heavy/slow bullets.