300 AAC twist rates, barrel length, suppression

[foszoe]

Getting interested in having one of these, well two of these. Internet contradicts itself so I thought I would ask here.
I plan to shoot this pistol/rifle mostly suppressed. About the only time it would be shot unsuppressed is to impress with the suppress.

Powder burn, twist rates, and suppression. or twist rates and suppression.

Myth, fact, or fact but...

1. The powder burn out is at about 9". So I was thinking of a 10.5" upper.
2. The velocity maxes out at 16" barrel. So I was thinking of a 2nd 16" upper.

I have read that the 1/7 twist rate is best for heavier subsonic loads, I have read 1/8 twist rate is best for heavier subsonic loads. 1/7 made sense but i'll let you speak!

Has anyone researched all this before and has some really good bookmarks/links?
Has anyone chrono'd measured bullet drop at 100 yds for various loads?

Does anyone have an opinion to offer?

 

[TacticalFun]

Getting interested in having one of these, well two of these. Internet contradicts itself so I thought I would ask here.
I plan to shoot this pistol/rifle mostly suppressed. About the only time it would be shot unsuppressed is to impress with the suppress.

Powder burn, twist rates, and suppression. or twist rates and suppression.

Myth, fact, or fact but...

1. The powder burn out is at about 9". So I was thinking of a 10.5" upper.
2. The velocity maxes out at 16" barrel. So I was thinking of a 2nd 16" upper.

I have read that the 1/7 twist rate is best for heavier subsonic loads, I have read 1/8 twist rate is best for heavier subsonic loads. 1/7 made sense but i'll let you speak!

Has anyone researched all this before and has some really good bookmarks/links?
Has anyone chrono'd measured bullet drop at 100 yds for various loads?

Does anyone have an opinion to offer?

Neither of those are ideal twist rates for the cartridge. It should be 1:5 for under 11" and 1:6 for 16 to 11.

Sent from my SM-G998U using Tapatalk

 

[turnerdye1]

Neithet of those are ideal twist rates for the cartridge. It should be 1:5 for under 11" and 1:6 for 16 to 11.

Sent from my SM-G998U using Tapatalk

Really? The only gun I've seen use a 1:5 twist is the Sig Rattlers and I think they have 5" barrels. And I've never heard of a 1:6 twist in 300BLK.

OP: Most manufactures used 1:7 twist rates for anything under 16". Some 16" guns have 1:8 twist rates and also work just fine for anything up to 220gr subs.

I've got a 16" 1:7 twist rate and its stabilized 240gr SMK's at 1050fps just fine. So I don't see why anybody would need a 1:5 or 1:6? It doesn't make any sense to me what so ever. Look at guns used in reloading manuals for the test loads. All my manuals show a 1:7 or 1:8 twist rate gun.

If you're into reloading check out Johnny's Reloading Bench on Youtube. He has like 70 videos focused just on 300BLK. Even if you don't reload it'll be good info for you and will show all that 300BLK can do.

As far as drop goes... My 16" gun with 220gr subs at 1050fps drops about 6" at 100 yards. Thats with a 50 yard zero also using a Primary Arms 1-6x calibrated for 300BLK. I haven't done much drop tests yet further out but the scopes calibrated for 250 yards.

EDIT: Just to add I researched barrels from BCM, Wilson Combat, Ballistic Advantage, Faxon, and CMMG. They are all running 1:7 twist rates. And those barrels lengths ranged from 6" to 16". So just get a 1:7 and call it good. And if you are going to run these on an AR style upper make sure to get "PISTOL" gas length. The carbine gas lengths on 16" barrels have been known to cause cycling issues on subsonic loads.

 

[TacticalFun]

Really? The only gun I've seen use a 1:5 twist is the Sig Rattlers and I think they have 5" barrels. And I've never heard of a 1:6 twist in 300BLK.

OP: Most manufactures used 1:7 twist rates for anything under 16". Some 16" guns have 1:8 twist rates and also work just fine for anything up to 220gr subs.

I've got a 16" 1:7 twist rate and its stabilized 240gr SMK's at 1050fps just fine. So I don't see why anybody would need a 1:5 or 1:6? It doesn't make any sense to me what so ever. Look at guns used in reloading manuals for the test loads. All my manuals show a 1:7 or 1:8 twist rate gun.

If you're into reloading check out Johnny's Reloading Bench on Youtube. He has like 70 videos focused just on 300BLK. Even if you don't reload it'll be good info for you and will show all that 300BLK can do.

As far as drop goes... My 16" gun with 220gr subs at 1050fps drops about 6" at 100 yards. Thats with a 50 yard zero also using a Primary Arms 1-6x calibrated for 300BLK. I haven't done much drop tests yet further out but the scopes calibrated for 250 yards.

Yes. The round was designed with 1:5 twist at acc and currently Q.

Sent from my SM-G998U using Tapatalk

 

[turnerdye1]

Yes. The round was designed with 1:5 twist at acc and currently Q.

Sent from my SM-G998U using Tapatalk

I see that Q's Honey badger is running a 1:5 twist rate with a 7" barrel. But AAC's current factory rifles builds from 9" to 16" are using 1:7 twist rates now. In general I think 1:7 is the best option for function and stability on most barrels. 1:5 seems to be for super short sub 5" barrels

OP: Also I located this article and read through it. Seems to be pretty informative and has ballistics, drop info, and more on it. https://americanarmamentco.com/300-blackout/

 

[Hookeye]

I might do one for hypersonic (deer hunting for my kid).
That or a 6.5 Grendel.

 

[laf]

The interesting part to hear on Q's podcast is their theory about rotational velocity making up for lost horizontal velocity. Send the projectile out subsonically but have it spinning faster to make up for lost forward energy. Kevin isn't a dumb guy and he's doing real world testing on the fast twist barrel rates for other cartridges too. I have a 1:7 8.5" that I use with supers and subs out to 100 yards and it's fine. Most shots I make with that cartridge are under 120 yards and I'm confident with the supersonic pill's performance at those ranges.

 

[foszoe]

Going back and forth between a Saint Victor 9" 1/7

OR A PSA 9.5" 1/7 upper only

 

[turnerdye1]

The Saint's are pretty nice! If you have the money I'd say go for it. If money's tight an upper is never a bad idea. You can always build out a lower later

 

[jeffsqartan]

I've had 4 different 300blk barrels.
16" (don't remember the twist)
8.5" - 1/7
8.5" - either a 1/7 or 1/8, honestly can't remember
5" - 1/7

The 5" barrel just got here this week. After handling it in my gun for a few days, I very much enjoy the shorter barrel. It doesn't seem like much of a difference, but it's nice.

My favorite, and the one that I've had the most seat time with, is the 8.5" with 1/7 twist. It's a Ballistic Advantage barrel. I have shot 110gr Vmax all the way up to 245gr lead subsonics. I typically handload all of my ammo. I've shot the supers out to 400 yards and the subs out to 300. The drop at 300 is hilarious. I also rock a Primary Arms 1-6x scope that's got BDC data for 300blk and it's been quite accurate.
At this time, I believe 8.5" is the ideal barrel length for 300blk when suppressed and 1/7 twist is totally fine for this barrel length. I don't have stability issues with well made bullets.

 

[foszoe]

eyeballing these . Not as an either or but a both ;0
https://palmettostatearmory.com/psa...10-5-lightweight-m-lok-upper-with-bcg-ch.html

https://palmettostatearmory.com/psa...eight-m-lok-upper-with-bcg-ch-5165448932.html

 

[BigRed3588]

Going back and forth between a Saint Victor 9" 1/7

OR A PSA 9.5" 1/7 upper only

I assembled mine with the BCM 9” 1/7 and was pleasantly surprised by the accuracy out to 100 yards (both subs and supers). I primarily shoot mine suppressed and wouldn’t suggest going much shorter than 9”, especially if you plan to shoot from a bench rest. I use a bleed-off gas block and a BCG designed to redirect the gas and still have trouble firing more than 5 rounds in succession if I’m hunkered down over the rifle. Standing isn’t an issue though.

One word of caution: It’s a fun round and has a tendency to get really expensive, really fast.

 

[sloppyjoe]

I've had good luck with 1:7 twist. I had one PSA 7" barrel with 1:8 rifling and it shot fine unsuppressed, but when you put the can on, the rounds started keyholing. Luckily no baffle strikes, but seems like the subsonic rounds were just barely stable without the can. Switched to a ballistic advantage 8.3" with 1:7 twist and no issues suppressed or unsuppressed.

 

[turnerdye1]

This thread finally made me pull the trigger on an AR upper in 300. I’ve had a lot of fun tinkering with my 300 bolt gun.

Found BFKings firearms last night. Seems like a good place for budget builders. They have 9” 1:7 nitride 300 blackout barrels for 90 bucks and blem uppers for 40 bucks. I went ahead and threw an upper together for 220 bucks.

We’ll see how it goes. They seem to have good reviews for the price