Gas gun problem

[Raptor77]

trying to put together a SHTF/truck gun. AR15 in 223 Wylde 10.5" barrel with adjustable gas block. Have tried two different buffers, a standard buffer and an H3. Both buffers will cycle fine if I adjust the gas for each of them. The problem is that I can't get the BCG to lock open after the last round with either of them. Asked my local gun store and they said that I should try heavier bullets (I didn't remember at the time what I was running.) Turns out I'm putting 75g bullets through it, so that can't be it. Also said that I should try a pistol buffer in a rifle buffer tube and spring. BCG locks open by hand as it should, but not when firing. What else should I try? How much more should the gas block be opened past the point where it starts cycling?

Thanks for any help.

 

[iktomi]

The typical answer is to tune an adjustable to bolt locking open... and add a click or three for 'reliability'.

 

[Raptor77]

So what do I do about the BCG not locking open after the last round?

 

[doubloon]

So what do I do about the BCG not locking open after the last round?

Don't know if you saw what @iktomi said so maybe wasting breath [electrons].

Give it more gas or get a lighter/shorter spring or fix/clean the spring in the bolt catch or all of the above.

When you said it locks back as it should by hand is that relying on the empty mag to engage the bolt catch or is the bolt catch being manipulated by hand?

It's possible the bolt is out running the catch but that seems odd if it's cycling and picking up new rounds. So maybe it's going just far enough to pick up a round and not quite far enough back for the bolt catch or maybe the bolt catch is sticky/slow.

What size buffer? pistol? rifle? carbine?

What size spring rifle? carbine? pistol?

What weight spring? standard? extra heavy? light?

​

 

[6.5SH]

Does the BCG lock back when cycled by hand? ETA: missed you said it did.
Where is the brass ejecting with each change?
Have you tried a different magazine? A weak magazine spring can cause exactly what you are experiencing.

 

[Raptor77]

BCG locks back by the mag when using the charging handle. Brand new P-mags. Carbine buffers. Carbine gas tube I think. Carbine spring I think.

 

[msgriff]

Short stroke test to confirm being under-gassed:

1) Pull back charging handle and manually engage the bolt catch
2) Load one cartridge in mag
3) Inset mag, release bolt to chamber cartridge
4) Firmly push and hold the bottom portion of the bolt release lever and fire

If the bolt catch doesn't engage, it's usually a gas system issue. This can include things like the carrier key and gas rings.
If the catch does engage, there is another procedure to follow.

 

[Raptor77]

I don’t know where the brass is ejecting. I was using a brass catcher

 

[doubloon]

I'll give you $50 for the complete lower plus $20 for shipping.

 

[Raptor77]

I'll give you $50 for the complete lower plus $20 for shipping.

Trying to fix, not sell.??

 

[doubloon]

$40 for the lower, $10 for shipping

 

[Raptor77]

$40 for the lower, $10 for shipping

I’m not a keyboard warrior, looking for actual help. Don’t have many gas guns. I do bolt action. Buy elsewhere

 

[mettee]

Can you list your exact parts? Bcg, barrel, receiver extension, spring? I see the two buffer weights you are trying and they should both function as far as lock open but they would change the unlock time slightly.

Also important to confirm gas port size as close as you can measure. Possibly the port is smaller than usual.

 

[Bobby Ball]

Just to clarify if it wasn't apparent in the other posts, you can have enough gas to cycle the bolt and chamber rounds but still not have enough gas to lock the bolt back. I just finished tuning my 10, my approach (right or wrong) was to adjust the gas until it would catch and hold the bolt open. (I did find a point during the adjustment where the empty mag would hold it back, but as soon as I dropped the mag it would send itself home). And I would verify that with checking my ejection pattern which was about 3:30-4 o'clock. After that, I started focusing on adjusting the buffer. In my case it was still bottoming out under recoil, so I added weight. It made a large difference, but after several magazines it seemed like the total cycle was a touch too prolonged, so I reduced the weight a little, and now it cycles great. I shoot fairly heavy loads (I think), so you might find the opposite works, but the procedure seemed to be very effective. I think I had 90% of the adjustment done in about 20 rounds.
Hope that helps you out.

 

[Jgault]

I didn’t see mention of what gas block you are using, is it a click or screw adjust? How close is the block to fully open when it cycles correctly? When you do lock the bolt open is the bolt face just behind the lip of the ejection port?. If your gas block is the screw and set screw variety you could be fully open and it simply doesn’t have enough gas, which would mean the gas block isn’t aligned to the gas port. If it’s the screw type block it’s easy to open the port and think because you turned the screw again it’s getting more gas, but it’s already opened fully

 

[LRRPF52]

What’s your gas port diameter?

Was the gas block slip-fit and can you see leakage around the gas block and gas tube?

Does your bolt carrier have the correct tri-bore inner diameters or is it loose? (requires armorer gauges to determine)