Suppressor causing my AR to fire bursts and fail to reset

[okie]

This is a relatively new Colt Mk18 upper on an LE6920 lower. Everything is stock except the trigger, which I replaced with a Geissele Super Dynamic. I think it probably has about a thousand rounds through it total.

I had put several hundred rounds through it without any issues and then all of the sudden now it's firing two and three round bursts and failing to reset. I tried a good thorough cleaning first of all, and that didn't help. I took out the trigger and thoroughly cleaned and inspected everything and don't see any problems there. Passes dry fire function checks with no problem.

I've also tried different buffers and ammo to no avail. This includes an H3, so I don't think the bolt is going too fast. It's having no problems picking up rounds or locking back on empties.

What I discovered today is that with a suppressor on it, seemingly any suppressor, that's what appears to be causing the issue. No suppressor, no issue.

Prior to this thing developing out of the blue though, it never gave me any issues no matter what. I had used different buffers, steel ammo, suppressed, unsuppressed, rapid fire...no issues anywhere.

Sitting here scratching my head how this could just develop out of the blue on a relatively new gun, and why the suppressor would aggravate the issue. I say aggravate and not cause because it ran for many rounds just fine with suppressors on it, so I don't think that's the root of the issue.

[MistWolf]

I think it's a spring in the FCG. Without the suppressor, carrier speed is low enough to not cause an issue. But add the suppressor the carrier speed is increased enough to overcome the action of the marginal spring. Probably the semi-auto sear spring.

[Pappabear]

I have no idea, but I would ask Geissele if they have any thoughts. I also would put another trigger in it and see if it persist. Maybe narrow down the issue if its the trigger.

PB

[okie]

I think it's a spring in the FCG. Without the suppressor, carrier speed is low enough to not cause an issue. But add the suppressor the carrier speed is increased enough to overcome the action of the marginal spring. Probably the semi-auto sear spring.

That's what I was thinking, too. Sucks though since it's a brand new trigger (practically speaking). What's more, it's a coaxial type pass through silencer with almost no back pressure, and I tried slowing the bolt down with an H3 buffer to see if excessive bolt velocity is the culprit. I don't think it's too excessive since it's not ejecting too bad.

[MistWolf]

That's what I was thinking, too. Sucks though since it's a brand new trigger (practically speaking). What's more, it's a coaxial type pass through silencer with almost no back pressure, and I tried slowing the bolt down with an H3 buffer to see if excessive bolt velocity is the culprit. I don't think it's too excessive since it's not ejecting too bad.

Ignore ejection angle. It has nothing to do with your problem.

It's possible the semi-auto sear spring was damaged during installation.

Even with a coaxial suppressor, gas drive needs to be correct. I don't know what your upper is, but it could be overgassed without the suppressor.

[Todd.K]

This is not uncommon, and the first thing I was going to ask if you didn’t specify in your post would be what trigger you installed.

You are bump firing with the lighter trigger and increased recoil of the suppressor.

[okie]

This is not uncommon, and the first thing I was going to ask if you didn’t specify in your post would be what trigger you installed.

You are bump firing with the lighter trigger and increased recoil of the suppressor.

The silencer actually reduces recoil by a lot. Probably half or more. I thought I was bump firing too at first, but then after deliberately holding down the trigger I realized that's not what was happening.

Also, the trigger is now failing to reset, which is new. First it was just firing bursts, and now every like fifth round maybe it's failing to reset.

And there's also the fact that I fired hundreds of rounds through it, suppressed, with zero issues, with this same trigger.

[Disciple]

Reminds me of this earlier thread.

https://www.m4carbine.net/showthread.php?232126

[1168]

There was a thread like this on reddit earlier this week. It sounded as if the dude was having hammer follow causing a burst, with the failure to reset issue being caused by a light strike due to the hammer follow catching it not quite in battery. He also had a G trigger, I think.

Bump firing would be plausible, but it sounds like you ruled that out.

I have no idea why your suppressor would be causing it.

[okie]

There was a thread like this on reddit earlier this week. It sounded as if the dude was having hammer follow causing a burst, with the failure to reset issue being caused by a light strike due to the hammer follow catching it not quite in battery. He also had a G trigger, I think.

Bump firing would be plausible, but it sounds like you ruled that out.

I have no idea why your suppressor would be causing it.

Yea I've been doing some googling and it seems like lots of people with Geissele triggers are having this issue. Seems like hammer follow is the issue. Seriously thinking about just ditching the Geissele trigger and going back to the milspec one. This is just ridiculous.

One possible issue might be the 22 conversion kit I've been using. I can't really verify, but apparently people are saying that those break Geissele hammers. My hammer doesn't show any visible damage, but who knows.