Strange AR15 "Jam"

[dmftoy1]

My buddy and I were out initiating his new 100 yard range yesterday and about 50-60 rounds into our shooting his AR's trigger "locked". It was right after a FTF. The rifle is one of those new bushy varmiteer's. (24-inch fluted barrel, flattop, NM 2-stage trigger).

Anyway, we couldn't figure out what was wrong so we popped the upper off and did a visual inspection and still couldn't see anything at all wrong. One thing I did notice was that even with the hammer cocked the safety couldn't be applied. This Bushy 2-stage trigger has 2 set screws installed into the safety, so I thought maybe one of the screws had moved or ?

Being very careful to count the number of turns I "tightened" the only one that I had an allen wrench for. (the other was so small that even my extensive allen wrench set couldn't fit it . . ??) After 1 complete revolution of the set screw the trigger started to move but was only a "1-stage" (if that makes sense) I told him that I'd probably send it back to bushy as it was under warranty but he was reluctant to do that so we took it back to my workshop. After blasting it with compressed air and putting a very bright light on it we found that a primer was wedged in behind the safety and appeared to blocking the trigger movement. It took about 10 minutes with a dental pick but I finally got it fished out. We went through the empty brass and found one case without a primer. (Federal XM193 - LC04).

So now for a few questions:
How common is something like this? I thought that the reason military ammo used crimped in primers was to avoid this type of thing?

Is a 2 stage NM trigger more susceptible to something like this because of the overtravel adjustment screws or ?

How in the heck do you remove a bushy safety on one of these things? If I could've taken out the one setscrew that sticks way the heck up (say 1/4-3/8's of an inch out of the safety) then it would've come out like a standard safety, but I can't find any allen wrench that would fit this thing. (I've got wrenches down to .050)

Thanks for listening!

Have a good one,
Dave

 

[Bartholomew Roberts]

How common is something like this? I thought that the reason military ammo used crimped in primers was to avoid this type of thing?

It isn't common; but it isn't unheard of easier. Loose spent primers can play hell with the AR15. When one does get loose, the most common failure you will see is the one you described - it wedges itself under the trigger and blocks it. Other failures I've read about or witnessed first hand include, the spent primer being crushed into the gas key rendering the rifle a single shot and the spent primer being smashed into the barrel extension, making it impossible for the bolt to go into battery.

Is a 2 stage NM trigger more susceptible to something like this because of the overtravel adjustment screws or ?

The two-stage triggers, particularly those with set screws, are more susceptible to failure than a stock trigger; but are not any more susceptible to the primer problem usually. Blue loctite can help by keeping the set screws from backing out under use.

In general, your AR may respond poorly to any small metallic debris in the lower.

How in the heck do you remove a bushy safety on one of these things?

The detent that holds the safety selector in is located in the pistol grip. Remove the pistol grip and remove the spring and detent in the lower receiver that is held in by the grip. Once you do this, the safety selector can be removed - though it sometimes helps to remove the hammer and trigger pins as well. At that point you have removed pretty much the entire fire control group and should be able to get at any small debris with ease.

 

[Quintin Likely]

The Bushmaster trigger is a copy of the Compass Lake trigger (or vice versa; I forget), except that the CLE trigger uses a hardened disconnector compared to the Bushmaster. I've got one in my service rifle, and it can be finicky at times. It'll get creepy and gritty if not periodically cleaned, lubed and re-adjusted. The 1/16" allen screw is for adjusting overtravel, and the .035" screw is the lock screw for the overtravel adjustment. http://www.compasslake.com/trigger.htm

The CLE/Bushmaster trigger can be picky at times, just make sure it's kept as clean as possible, and periodically check the set screws to make sure they're tight. You're only supposed to lube it with moly neco slide grease, but I ain't got none of that; I use a high temp moly grease intended for brake calipers, seems to work alright.

 

[dmftoy1]

Thanks!! That's exactly the kind of info I need. Now I have to find some place that sells that small allen wrench for him.

Have a good one,
Dave

 

[taliv]

i agree about the NM style triggers being inherently less reliable. I've experienced a few failures with them that couldn't possibly have occured with a standard trigger.

i love the crisp trigger pull and the two-stage feel, but i have to say i am surprised so many people (e.g. les baer's thunder ranch special) continue to put match triggers on social guns.

 

[Chris Rhines]

The Bushmaster two-stage trigger is, quite frankly, trash. Whoever came up with the idea of using a 3/32" spring-loaded plunger as a second stage - well, I don't know what he was thinking. The best thing you can do with it is remove both screws from the safety and throw them away - you'll end up with a somewhat long but fairly light and crisp single-stage trigger.

Any adjustment screws in a trigger should be cleaned with Acetone and then sealed with Loctite 242 - the red, non-removable stuff. You don't want those screws to move, ever.

A properly set up match trigger in an AR-15 is no less reliable than a standard military one. Problem is, you see a lot fewer properly set up AR triggers than you do thrown-together, slapdash ones. I've never had a trigger group failure on any of the AR triggers I've done, even during rifle classes and high-volume 3-gun matches.

- Chris

 

[desert_scorpion]

Match Trigger alternative

Hi just reading through, thought I would pass on some info. Have you looked at the trigger being offered by McCormick? They have a AR-15 Match Trigger group, it is a drop in, real easy to install. Try taking a look at www.chipmccormickcorp.com

 

[dmftoy1]

Thanks, I'll pass that along to my buddy. I have a RRA NM trigger in a lower I built this spring and I'm really happy with it. I think it would be a straight drop-in also.

Have a good one,
Dave