Not cycling with subs

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Maflynn06
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Not cycling with subs

Post by Maflynn06 »

This is my first 300 blackout AR pistol, my first suppressor and my first post here so take it easy on me lol.

Here is my setup:
Palmetto State Armory 7.5” AR
Pistol Length Gas system
2.9 ounce Carbine Buffer
Riflespeed adjustable gas block.
Suppressor: Dead Air Wolfman with Micro Brake
Ammo Subsonic: Sellier & Bellot 200gr FMJ
Ammo Supersonic: Sig Sauer 125gr FMJ

On setting 4 on the gas block, the Supersonics were running beautifully. 100 rounds and not one malfunction. Subsonic rounds will not cycle or lock the bolt open no matter what 1-12 setting I was on. Gun sounds very weak and almost no recoil at all. My thought was getting a weaker spring but wanted those with more experience to chime in.

I am here to learn!
BJK
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Re: Not cycling with subs

Post by BJK »

FWIW they won't cycle my AR either. That's why I reload. Yeah, I know not very helpful. I want to get a barrel for my Encore then a whole world of loads opens up.

Maybe someone will have something for your AR.
cdl
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Re: Not cycling with subs

Post by cdl »

My RifleSpeed is the least efficient AGB I’ve ever tried. Great if you’re taming a Lion but a little too much for a mouse. I love it on my 308 and I’ve gotten it to work reliably with A1680 powder on 300 Blk. It’s probable not the best for playing the edges of quiet with custom or light loads. Take that, add a 7.5” barrel with little dwell time, a mellow load and a new gun with tight rings and a stiff new spring and the whole universe is throwing hate at you.

I’d throw on a standard straight through gas block and see if you have a chance. If it does everything you want with that load except lock back, say when it’s dirty, you could tweak the port size few sizes. There is something about knowing where a standard configuration running a standard factory load is at. It’ll serve as a baseline for all the crazy things you can try in the future. If that doesn’t work, it’s probably time to load your own. Crazy comes with the journey.

I have to add, running a carbine buffer, standard spring and stock bolt carrier is like wearing tennis shoes. Everything is snappy and responsive. Almost like that balance was by design. Wearing boots or flip-flops do have their place, but bring disadvantages too.
ReadyAimDuck
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Re: Not cycling with subs

Post by ReadyAimDuck »

I would recommend you find out if your AGB has a narrower diameter opening at its max open setting than the gas port in your barrel before going through the hassle of replacing it with a standard block, especially when others have had issues with that factory load.

The first thing I would do is try a different subsonic load and send us your updates.
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dellet
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Re: Not cycling with subs

Post by dellet »

With that many modifications to a rifle that still does not cycle, I would strip it down and start over.

It’s always possible that it was a bad lot of ammo, but a rifle that won’t cycle a commercial sub load, suppressed, with a buffer that is half the weight it should be sounds like more or a poorly constructed gas system.

Other ammo might solve the symptom, but there rifle will always be suspect.
300 Blackout, not just for sub-sonics.
cdl
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Re: Not cycling with subs

Post by cdl »

Don’t forget the RifleSpeed has a second level of rotation. 13 to 24 per say. It might not positively lock/click without a spacer on the split spring though. Open her way up if you want.

I wasted a lot time. Had that thing on and off half a dozen or more times and I was running suppressed, with an empty buffer, 0.110” gas port, a worn-out recoil spring and I had another inch of barrel. It’s fine with a 220gr bullet and 10.4gr of A1680, I didn’t even need to cheat, but chokes on a 237gr bullet and 9.5gr IMR4227 and all the cheating I could think of. Both loads produce about the same velocity, just over 1000fps, but 9.5gr is quieter than 10.4gr.

I prefer quieter. So I put my Superlative back on and life is good for me again.

One AGB uses a smooth pin that plunges in or out, the other uses a threaded set screw. One has blow-by, one really doesn’t.

Seems kind of silly to waste $200 on a setup that’ll probably not run that ammo with a $30 block either.

I think the Riflespeed is a really cool AGB. On the right gun. I own two of them.
dpete
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Location: Northern WI

Re: Not cycling with subs

Post by dpete »

What size is the gas port in the barrel? I'm guessing its too small. If the gas port is too small, no amount of opening on an adjustable gas block is going to help with cycling. Drilling a port up in size is an easy operation even with a hand drill. You already have a perfect guide hole, and you just need to go slow, use some cutting oil, and let the bit eat its way through. If you are worried about popping through and hitting the opposite side of the bore you can insert a wooden dowel into the barrel. My pistol gas 8" barrel had to be drilled out to .108" before it would cycle subs, and with an adjustable gas block you can dial the gas down when using supers.
knj300blk
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Re: Not cycling with subs

Post by knj300blk »

I have an A15 300blk and had a similar issue. My goal was to be able to shoot any 300blk ammo suppressor or unsuppressed.

As normal, 300 supersonics are going to cycle right out of the box flawlessly. In my case, i bought a brand new Aero Precision full upper and full lower, nickle boron Aero bcg, Aero breach charger handle. The upper has a 16" barrel, but pistol length gas system. The buffer assembly in the lower is whatever Aero puts in their by default.

As mentioned, by many 300blk subsonics unsupressed will not cycle. Well after very minor mods my gun does cycle them. Those subsonics produce less gass pressure, so you are undergassed. The bolt does not go far enough to load the next bullet from the mag. In my case, the shell would actually eject, but a fail to feed next.

Here is what i tried and what worked and what didnt. And what i plan to do to refine things further.

1) Reduced power Spring with SpringCo Yellow - (insert buzzer sound) did not work.
2) Kynshot Hydraulic Buffer RB5000L for 300blk - did not work with original spring or springco yellow spring. Failed to feed.
3) Drilled out gas port from factory .075" to .082" (or 2.10mm bit)and added Aero Precision gas block. - Worked, but not with all sub ammo. For example, 220 grs Ammo inc. worked 100%, while Sellier and Bellot (S&B) 200grs failed to feed. The adjustable gas block port was all the way open.

Next Steps:
1) Drilled out to .085" (or 2.15mm drill bit) to let more gas in. My last setting had the gas port all the way open and was still under gassed by observation that "some" subs did not work. The bigger drill out will give me more gas to work with during gas block adjustments.

Note about the drilling: I am making very small "barrel gas port size" changes then restesting to see impact. I used a high speed drill and just went very slow letting the bit do the work. I am careful to not drill into the other side, and i run a 300blk brass snake through the barrel afterwards. I looked in the barrel and it looks perfect.

2) Purchased Light weight, 8oz bcg from Brownells. The thought is less gass needed to move back a light bcg.

I have these two changes above done, but not tested as of 07/01/2023.

other:
1)I got a flaming pig for a different reason (shooters perceived sound management), but I have read they can produce small, incremental amounts of backpressure that can be noticed in my particular situation where subsonics are not consistently cycling all sub ammo. If assertions on backbressure bear out i may no feed issues with the 200grs S&B ammo.

2)Also, planning to to grab an Omega 300 supressor but have not gotten around to purchasing yet.
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dellet
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Re: Not cycling with subs

Post by dellet »

knj300blk wrote: Sat Jul 01, 2023 5:57 pm I have an A15 300blk and had a similar issue. My goal was to be able to shoot any 300blk ammo suppressor or unsuppressed.

As normal, 300 supersonics are going to cycle right out of the box flawlessly. In my case, i bought a brand new Aero Precision full upper and full lower, nickle boron Aero bcg, Aero breach charger handle. The upper has a 16" barrel, but pistol length gas system. The buffer assembly in the lower is whatever Aero puts in their by default.

As mentioned, by many 300blk subsonics unsupressed will not cycle. Well after very minor mods my gun does cycle them. Those subsonics produce less gass pressure, so you are undergassed. The bolt does not go far enough to load the next bullet from the mag. In my case, the shell would actually eject, but a fail to feed next.

Here is what i tried and what worked and what didnt. And what i plan to do to refine things further.

1) Reduced power Spring with SpringCo Yellow - (insert buzzer sound) did not work.
2) Kynshot Hydraulic Buffer RB5000L for 300blk - did not work with original spring or springco yellow spring. Failed to feed.
3) Drilled out gas port from factory .075" to .082" (or 2.10mm bit)and added Aero Precision gas block. - Worked, but not with all sub ammo. For example, 220 grs Ammo inc. worked 100%, while Sellier and Bellot (S&B) 200grs failed to feed. The adjustable gas block port was all the way open.

Next Steps:
1) Drilled out to .085" (or 2.15mm drill bit) to let more gas in. My last setting had the gas port all the way open and was still under gassed by observation that "some" subs did not work. The bigger drill out will give me more gas to work with during gas block adjustments.

Note about the drilling: I am making very small "barrel gas port size" changes then restesting to see impact. I used a high speed drill and just went very slow letting the bit do the work. I am careful to not drill into the other side, and i run a 300blk brass snake through the barrel afterwards. I looked in the barrel and it looks perfect.

2) Purchased Light weight, 8oz bcg from Brownells. The thought is less gass needed to move back a light bcg.

I have these two changes above done, but not tested as of 07/01/2023.

other:
1)I got a flaming pig for a different reason (shooters perceived sound management), but I have read they can produce small, incremental amounts of backpressure that can be noticed in my particular situation where subsonics are not consistently cycling all sub ammo. If assertions on backbressure bear out i may no feed issues with the 200grs S&B ammo.

2)Also, planning to to grab an Omega 300 supressor but have not gotten around to purchasing yet.
Seems like lately Aero precision is coming up a lot in “won’t cycle threads”.

A 16” pistol gas barrel on a correctly set up upper and lower has no reason to be under gassed. To the point where either the the rifle or the ammo is basically crap. Just my opinion.

It’s really hard to tell what might e the problem, and unfortunately, you need something that is a “known good” component. Ammo, upper, lower combination of those.

I would check for leaks in the gas system, buy known good ammo, Remington or Hornady and go from there. I’m a bit surprised the S&B has problems, that’s why I would be looking hard at the rifle.

The trigger might be dragging on the carrier, gas tube may be plugged, pull the bolt out of the carrier, clean and lube it well and make sure all passages are clear.

Get a couple hundred rounds through it, strip it down again and go back to subs.

If you find any trace of copper on the back side of the bolt, it’s a huge flag that port has a burr and is peeling the jacket off the bullet. This will clog the system very quickly.

Clean and well lubed are your friend with subs and a new rifle
300 Blackout, not just for sub-sonics.
knj300blk
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Re: Not cycling with subs

Post by knj300blk »

Based upon what I read AR makers are porting 300blk assuming you will be suppressing subsonics. That is a fair assumption. That said, a any barrel with a .075" gas port is not going to cycle subs unsuppressed. Suppressed it would've.

However, I am one one those weirdos that wants to shoot subs unsuppressed. Bases upon what i have read it doesnt happen consistently with a gas port less than .090". At .085" where i drilled out to, I am very close. As mentioned, ive gotten one brand of subs to cycle 100%.

The Aero precision adjustable gas block might be leaking. I took it apart and there is evidence this may be the case. I have superlative arms coming to try so i can rule that out before drill out. If the gas blocks ends up not being the issue, I am drilling out to .090" or .093" as a next step. I have kak, 3pc light buffer kit coming as well with 1.7,2.2 and 2.6 oz buffers to try as well.

I will get it to work, mark my words. I'll report back here with the final configuration.
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