Reducing Blowback on an 8" 300BLK

[5RWill]

Doing a pistol build have all the parts on order but i wonder what the blowback will be like? Is it excessive with a 300blk? I was thinking i was going to grab a Raptor SD charging handle but saw mixed results as to whether it really worked or not. So i just got the Raptor LT to save some money. Wondering if i should've went with an AGB or maybe a suppressed BCG to control gas.

Here's the build list as of right now.
CMMG LPK without FCG/Grip
Greyghost precision lower
Aero upper
Aero NIB BCG
Raptor LT charging handle
Ballistic advantage 8.3" premium series
Geissele MK8 7"
Maxim Defense PDW Brace
JP heavy SCS for the maxim

 

[Zebra3]

I prefer adjustable gas blocks to control blowback, but my blk build was before the Bootleg or Gemtech carriers that could be tuned at the ejection port.

If you can wait, I'd look at the new gas block Seekins had at shotshow, its has a two position throw lever that allows you to tune the gas at each position i.e. suppressed and super with a flip of a switch. I'm planning on tuning some rifles when these are released.

 

[5RWill]

There's no rush really everything is ordered but the BA barrel came with a gas block, so i can always just change it out. Wonder if it will fit under the Geissele?

 

[Zebra3]

Most Geissele handguard have a decent amount of space to play with however, I don't want to steer anyone wrong. I'm pretty sure the GB will fit, the lever might run into the handguard. Depending on how it operates you might be able to get away with shaving some of the lever off for clearance.

 

[5RWill]

I might pm Glen to see what thinks. I'm going to run it as is for a little while and see how bad the blowback is first hand i guess.

Do you think a 1in7 twist is too fast if i was primarily to run 110gr VMAX out of it?

 

[padom]

Only AGB I got to clear under a Geissele MK8 was Superlative. SLR and Seekins hits...

 

[5RWill]

Only AGB I got to clear under a Geissele MK8 was Superlative. SLR and Seekins hits...

Yeah i have an MK8 rail on my SPR and it's tight in there, not much space at all.

 

[Zebra3]

Yup, I plead ignorance on the Geissele rails. Haven't held one in a hot minute, I'm running kmrs on mine. I think 1 in 7 will run the vmax fine. I typically run 110 varmageddon or 125 ballistic tips both of which keep very right groups.

Another option you might try is running a lightweight carrier. You would definitely want the agb, but it would use much less gas to run the system. In turn you should have less gas in your face. Depending on how much you want to spend you could get a skeletonized steel carrier (Brownells just dropped a legit one a few weeks ago that runs around $110). Then there are the titanium, and aluminum carriers. I don't have any experience with titanium, but I have used both JP, and whiskey arms aluminum carriers and they run like tops.

 

[5RWill]

Wouldn't it be more beneficial to increase the weight of the carrier rather than decrease without control of the gas? I'll be using that low pro gas block that comes with the barrel at first or a geissele. My train of thought was that the vast majority of blowback was coming from the chamber itself not the gas tube, though maybe that's incorrect. I thought that was the entire premise behind JP's VMOS carrier line for suppressed use. It's to note it's going to be shot suppressed exclusively.

 

[padom]

yea I don't know what he's talking about. You don't want a lighter carrier on an over gased sbr with a non adjustable Gas block. full mass carrier and heavy buffer setup and add an agb tuned to bolt hold open on last round.

 

[Zebra3]

That's correct a lightweight carrier with a non adjustable gas block on an over gassed rifle is no good. But like I said in the post, a lightweight carrier with an agb turned down will work.

Blowback comes from the gas system and chamber, so if you're running a non agb then go with a standard bcg with a heavy buffer and spring to delay the bolt unlocking and reduce blowback. If you go with the lw bcg and agb, then less pressure back through the gas system, also reduces bolt unlocking speed which will reduce blowback. Or you can run the standard bcg with an agb.... Each way works, just depends on what you want to mess around with

 

[padom]

That's correct a lightweight carrier with a non adjustable gas block on an over gassed rifle is no good. But like I said in the post, a lightweight carrier with an agb turned down will work.

Blowback comes from the gas system and chamber, so if you're running a non agb then go with a standard bcg with a heavy buffer and spring to delay the bolt unlocking and reduce blowback. If you go with the lw bcg and agb, then less pressure back through the gas system, also reduces bolt unlocking speed which will reduce blowback. Or you can run the standard bcg with an agb.... Each way works, just depends on what you want to mess around with

yea no. the carrier weight has jack shit to do with the amount of gas/pressure coming through the gas tube. that is controlled by the gas port, gas block, and gas tube length. I've built 100's of AR's and never once used or heard of someone using a lightweight BCG in a SBR build. full mass is the only way to go here.

 

[BLDTYLRY]

I'm running a 8" 300 Blackout SBR with a Sandman S suppressor, SLR AGB, and JP Ultra LMOS (Aluminum) Carrier with no issues. The AGB mitigates overgassing and being the carrier is so lightweight it doesn't require as much gas to cycle reliably. I shoot subs out of this system so I set the AGB once and I'm done.

 

[5RWill]

Damn think i should just get an AGB?

 

[BLDTYLRY]

An AGB is a better choice over an adjustable carrier if you are concerned with gas blowback. You didn't mention if you are running a suppressor or not. If you are not running suppressed then run a non-AGB with a H2 or H3 buffer and standard weight BCG and spring; you shouldn't have much blowback unsuppressed.

 

[5RWill]

I already mentioned it was going to be shot suppressed exclusively in post #9, just not the OP. Going to see how it goes and probably order a SA.

 

[strikeeagle1]

I see the OP is going to run a pistol, so I guess the blowback issue depends in part how the operator holds it with a "brace".
I almost always am shooting with safety glasses so they really help mitigate some of the blowback; I use PRI "gas buster" charging handles; this is one of my .300 BO SBR builds that fits nicely in a small Blue Force Gear Jedburgh pack. Since the armadillo's never hear the muzzle report, just for fairness I warn them with a Allahu Akbar just before breaking the shot; you can see one of their now vacant domiciles at the base of the tripod.

Upper
PWS Mark 109, 9.75” 1:8 twist
LaRue LT872 QD RMR mount
Trijicon RMR 3.25 MOA
Surefire X300 Ultra
Aimpoint T-1 , LaRue LT660HK QD
Surefire 762 SOCOM2 suppressor
Surefire WarComp QD muzzle device

Lower
GPI Legacy Arkansas Ranger M4A1
Magpul MAID grip
Leitner Wise Buffer retainer
Magpul aluminum trigger guard
Geissele SSA trigger
Battle Arms short throw ambidextrous safety
Wilson Combat match grade small parts
Wilson Combat buffer tube
Trident Tactical buffer spring
Law Tactical Gen3-M folding stock adapter
Rogers Super-Stok & cheek pad
Rogers single point harness adapter / sling QD
Phase 5 bolt assist lever
Rogers Mag-Grip
Tactical Innovations Teflon tension screw
Precision Reflex Gas Buster charging handle
Fabricated stock-ELS-spare magazine carrier system
Rogers Magazine Grip

 

[Yondering]

yea no. the carrier weight has jack shit to do with the amount of gas/pressure coming through the gas tube. that is controlled by the gas port, gas block, and gas tube length. I've built 100's of AR's and never once used or heard of someone using a lightweight BCG in a SBR build. full mass is the only way to go here.

Everything zebra3 said is correct. Sometimes you gotta slow down a little and think about what was said. He did not claim that changing carrier weight causes a different amount/pressure of gas through the tube. Read it again.

 

[supercorndogs]

yea no. the carrier weight has jack shit to do with the amount of gas/pressure coming through the gas tube. that is controlled by the gas port, gas block, and gas tube length. I've built 100's of AR's and never once used or heard of someone using a lightweight BCG in a SBR build. full mass is the only way to go here.

I am pretty sure he is saying you can turn the gas down more with a lighter carrier, thus less gas for your face.

 

[Badfinger]

Side charging is how you keep gas out of your face! The rear of the receiver is closed so nothing comes back at you.

 

[5RWill]

Finished it last night. Well shoot it this weekend with the Omega and see how it goes.

 

[bigdaddydmd]

How was it? Did you go with an AGB or feel that you have too if you didn't? I've got a similar 300Blk build + Omega going on right now.

 

[5RWill]

I've not noticed any at all honestly. Got a good group with 19.5gr of H110 with the 110gr Vmax at 2050fps. Will probably do an AGB for the 11.5 5.56 though. 8.3" 300blk doesn't seem to need it.

 

[bigdaddydmd]

Thanks for the range report. Glad its not as bad as you expected. Gives me hope since I didn't get an adjustable gas block.