Blackout subsonics not cycling

[brmfan]

Trying to get Rem 220 subs to cycle. Ejects but won't pick up next round and closes on empty chamber.

Using a 16" new ER Shaw barrel with carbine length system on a Bushmaster upper and lower, A2 front sight base, and BCM M16 carrier with standard buffer spring. Tried both carbine and H2 buffers.

Standard buffer was a no-go but got it to cycle 2 rounds only a couple times with the H2. Still won't hold open on last shot using new Pmags. Running the BCG pretty wet and using a YHM 7.62 Phantom on brake QD mount. Cycles just fine with supersonics.

I'm leaning toward enlarging the gas ports (until I can get an SBR stamp) but any other suggestions??

 

[UtopiaTexasG19]

If you re-load you need to try some different loads to see what works best in your rifle. A lot of folks use adjustable gas blocks on the 300 Blackout in able to shoot both sonic and sub sonic rounds. I am fortunate in that my 16" shoots both sonic and subsonic with a fixed gas block but apparently there is a huge variation in makes. If all else fails try 300blktalk.com where the constant 300 users hide out. Have you tried any sonic loads yet?

 

[brmfan]

UT: Already been all over that sight. Yes, super sonics work just fine, both the 115 and 147's. As I said, I almost got it to cycle with the 220's using the H2 buffer, but I'm thinking it's simply undergassed. Wanted a second opinion before going the gas port widening route.

 

[UtopiaTexasG19]

Occassionally you hear of a gas block not being seated correctly over the barrel where the gas flow is slightly blocked. Is your gas block pinned or clamped to the barrel?

 

[CCCLVII]

you havent been shooting cast bullets have you? I did that to a Desert Eagle and at first it would only cycle hot ammo then it cycled nothing. It was not a cheep fix

 

[brmfan]

Nope. Just factory.

UT: It's a pinned A2 front sight base.

 

[ShamrockArmory]

Cast bullets in anything with a gas operating system is a big no go.

 

[eodinert]

You can get away with cast lead in a 300 with subsonics because the velocity is so low.

It sounds like a gas port/gas flow issue to me, were I you I'd pull the front sight post and measure the port.

Also, if you SBR that barrel, depending on how short you go, it may not work with carbine gas. Short .300's really want pistol gas.

 

[1911rocks]

Gas Tube length

Carbine or Mid-Length?

 

[Willie Lowman]

You say it cycled a couple times with a H2 buffer. Have you tried going to a buffer lighter than that? Using a lighter bolt carrier?

 

[tmorone]

Since this is in the NFA section, is it safe to assume you're running a suppressor?

300BLK barrels are usually advertised that they won't properly cycle with subsonic ammo without a can. I've got 9" and 16" uppers in that caliber and run both with an H2 buffer. Supers cycle 100% but the subs really only work 100% when running suppressed.

The beauty of that round is that when you suppress the subsonic round using the same gas system you get very little back in your face due to over-gassing. If they won't cycle WITH a can, that's a totally different beast.

 

[Willie Lowman]

In the first post he says

using a YHM 7.62 Phantom on brake QD mount

So, I'd say he is using a suppressor.

 

[tmorone]

Good eye Willie, bad job me.

 

[eodinert]

300 will run unsuppressed subsonics if its set up right.

 

[brmfan]

Eodinert: I'm just trying to get subsonics to run period! I checked the port and it measured just at 0.120" so being undergassed doesn't seem to be the issue. I also ordered a reduced power buffer spring, so hopefully with the H2 buffer that will solve the problem.

Otherwise, I'll just have to find a 16" barrel with a pistol length gas system. However, given that everything is currently out of stock with no backorders in sight it may be quite a while before I find one.

 

[Willie Lowman]

The H2 buffer isn't the lightest buffer out there. Also, there are lighter bolt carriers available. I'd try reducing mass behind the bolt before I reduced the spring strength to keep feeding reliable. JP makes some light bolt carriers. BravoCo. has standard and H weight buffers.

 

[brmfan]

Willie: I have lighter buffers and BCGs but I figured with the lower pressure the added weight of the H2 would increase the dwell time and give the carrier a bit more shove. I'll try different combinations but I'm thinking I'll just shelve the subs until I can get a barrel with a pistol length system.

 

[tmorone]

brmfan,

Finding the correct carrier, spring, and buffer can be a pretty path of trial and error.

I had a rifle that wouldn't run with an AUTO carrier and any weight of buffer or spring. Even the wolff xp spring and an XH buffer from heavy buffers.com. And that buffer is all stainless with tungsten inserts (as heavy as they come).

The solution was to run the XH buffer, wolff spring, and a SEMI carrier. What sounded like something that couldn't work, did. Good luck man, it's a good feeling when everything starts to work right.