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Blowback In Your Face

Posted: Thu Aug 08, 2019 5:23 pm
by BulletFactory
I built a nice 300 BLK 9" tax stamped. It has an ACOG with an RMR on it. When you shoot using the RMR, you get an unpleasant puff of smoke in your eye upon every shot. Especially with supersonics.

Is there anything that I can do to correct this problem?

Re: Blowback In Your Face

Posted: Thu Aug 08, 2019 5:50 pm
by BulletFactory
The RMR is atop the ACOG, and both are offset about 25 degrees. Looks cooler and holds easier.

Re: Blowback In Your Face

Posted: Thu Aug 08, 2019 8:28 pm
by Boolit_Head
You can:

Don't shoot supers
or
Use a adjustable gas block to turn the gas down
or
Use a gas buster or similar charging handle

Or any combination of the above with differing results. :lol:

Re: Blowback In Your Face

Posted: Thu Aug 08, 2019 9:13 pm
by dellet
Boolit_Head wrote:
Thu Aug 08, 2019 8:28 pm
You can:

Don't shoot supers
or
Use a adjustable gas block to turn the gas down
or
Use a gas buster or similar charging handle

Or any combination of the above with differing results. :lol:
Change powders.

Don’t know why any of it would change when using an RMR, or not, but I’ve never used one.

Re: Blowback In Your Face

Posted: Thu Aug 08, 2019 9:22 pm
by blaster
my 9" AR pistol also used to blow back in my face when shooting. I have no idea why but it quit doing it all by itself!? :roll:

Re: Blowback In Your Face

Posted: Fri Aug 09, 2019 12:07 pm
by BulletFactory
You have to hold your head up higher when using the rmr because it sits so high above the bore. This happens to be where the gas is blowing around. I went through several powders this year looking for an accurate load. One for supers and one for subs. CFE BLK, H-4227, LilGun H-110, H-4198, and a couple others I dont remember off hand. I have dies to make the bullets, so I was able to mess around with a lot of weights, jackets and bases. I ended up with a 115 grain bullet for supers made from once fired 5.7 with 22.4 grains of CFE BLK. 1800fps. The subsonic was a copper jacketed round made from 5/16" soft copper tubing. It uses a boat tail, comes in at 205 grains, and is propelled by H-4227 at 1025fps. I finally got the rifle to function by opening up the barrel gas port to .110". Seekins Prescision gas block is wide open. Has to in order to cycle with both rounds, but the gun does work. Theres a JP captive spring, with one tungsten and one steel weight.

Only problem, is Im getting blasted with it. What charging handles were you talking about? Boolit Head?

Re: Blowback In Your Face

Posted: Fri Aug 09, 2019 12:29 pm
by mbogo300
Install a Superlative ARMS Adjustable Gas Block with Bleed Off.

It worked for me when shooting supersonic rounds suppressed.

Re: Blowback In Your Face

Posted: Fri Aug 09, 2019 1:00 pm
by plant.one
have you considered something like this to vent the gas elsewhere?

https://www.rainierarms.com/ar-gas-vent/

Re: Blowback In Your Face

Posted: Fri Aug 09, 2019 1:03 pm
by dellet
BulletFactory wrote:
Fri Aug 09, 2019 12:07 pm
You have to hold your head up higher when using the rmr because it sits so high above the bore. This happens to be where the gas is blowing around. I went through several powders this year looking for an accurate load. One for supers and one for subs. CFE BLK, H-4227, LilGun H-110, H-4198, and a couple others I dont remember off hand. I have dies to make the bullets, so I was able to mess around with a lot of weights, jackets and bases. I ended up with a 115 grain bullet for supers made from once fired 5.7 with 22.4 grains of CFE BLK. 1800fps. The subsonic was a copper jacketed round made from 5/16" soft copper tubing. It uses a boat tail, comes in at 205 grains, and is propelled by H-4227 at 1025fps. I finally got the rifle to function by opening up the barrel gas port to .110". Seekins Prescision gas block is wide open. Has to in order to cycle with both rounds, but the gun does work. Theres a JP captive spring, with one tungsten and one steel weight.

Only problem, is Im getting blasted with it. What charging handles were you talking about? Boolit Head?
You have a problem with the rifle and how it's set up, combined with powders that produce way more gas than needed to cycle the action. Possibly poor bullet design or a loose bore.

9" pistol gas with an H2 weight buffer should not need a port larger than about .085" with a suppressor. You are under buffered and over ported.

I would slug the bore and or capture a bullet. I am guessing a captured bullet would be black with carbon in front of the base. Neither of those powders in the loads you are shooting them have enough pressure to properly obturate the bullet. You might try sizing to .309". I think it's possible you are losing too much pressure past the bullet to cycle the action.

You may also have a gas leak somewhere else.

If the only time the gas is an issue is holding your head high, it's probably coming out the ejection port. Again poor powder choices and or low pressure causing a poor burn rate and lots of left over gas.

Re: Blowback In Your Face

Posted: Fri Aug 09, 2019 4:02 pm
by BulletFactory
Ok. I will look into it pretty soon. Lots going on. What a great post sir, thank you.

I'm going to try to get the forward assist.