Took my M4 out today and I experienced 3 problems
1.  Light primer hits (failing to discharge, light dimple in primer, but ammo checked out okay in another rifle).
2.  Random 2 round burst firing
3.  Feeding issues

The problem is that I have done a few recent mods to the gun and I don't know which might have caused the problem.  Here are the newest mods on the gun:
- RRA 2 stage trigger- (but it really just feels like a hair trigger- I can't feel the 1st stage at all)
- Gemtech suppressor (I was having accuracy issues with this the other day- could a suppressor cause a gas issue?)
- New bolt carrier- (I upgraded to a chrome one)

Any ideas?

Quoted: Are you sure the light primer strikes are actually strikes?  Do you hear the hammer fall? I ask because just chambering a round will leave that small dimple on the primer because of the floating firing pin. The hammer could be following the carrier and then when the round chambers it can either A) fire a round, or B) do nothing.  This is the simplest answer, solving both problems with one faulty part ( new trigger). If you do hear the hammer fall when you get the no bang...  You might be out of battery, probably caused by the new carrier. Suppressors do cause gas issues, usually causing more gas and carbon to blow back into the reciever than normal.  I suspect they actually lessen the chance of short stroking, but I'm not sure on that one. What kind of feeding issues?

Spent cartridge is partially extracting, next round is jamming into it.

RRA trigger,

The disconnector is binding up in the trigger, and the light primer strikes are actually the hammer following the carrier back down closed.  The same causes the bursts, but the disco is holding the hammer until the bolt slams closed then the hammer is freed.

Pull the trigger and make sure that the disco is moving freely in the trigger, and not binding on the pin. This binding is both the no second stage problem, and the doubling/fail to fire problem.



Dropped case,

The can is causing the rifle to over cycle (read gas port too large with can, and the bolt is opening too fast with the spent case still highly pressure bound to the chamber wall).  Options are either drop in a #60 O ring around the extractor spring to add tension to the extractor to assist it in dealing with the greater surface tension of pulling the more pressure bound case, or install an adjustable gas tube to allow a smaller port setting for when the can is used (read get the action back in tune with the added back pressure when the can is used).

Adjustable gas tubes go for around $60, O-ring goes for a dime.

Quoted: what buffer are you using?

Whichever one comes with the 6 pos collapsible stock.  The short one.

Dano, thanks for the info!

Took my M4 out today and I experienced 3 problems 1.  Light primer hits (failing to discharge, light dimple in primer, but ammo checked out okay in another rifle). 2.  Random 2 round burst firing 3.  Feeding issues

A lot of times hammer springs get put in backwards, causing this.  #2 could be disco spring, disco, trigger or a combo.

Looks like the 2 stage trigger has a bad disconnector.  I had it replaced and it fired fine.  Now I just need to test it with the suppressor.

tweak...what is an H buffer

also what part on the RRA trigger is the disconnector>? Did they replace it you did you have to get a whole new trigger?

wouldnt adding a stronger buffer spring help in this case?

Did you try different magazines?

I forgot all about this thread.  TheRicker hit the nail on the head.  The 2 stage trigger was defective.  Bad disconnector or something.  I put a new 2 stage trigger in and now all is better.

I still have occassional issues on my 10.5" upper when using the suppressor, but I think I need to play with the gas tube or buffer.

Quoted: I still have occassional issues on my 10.5" upper when using the suppressor, but I think I need to play with the gas tube or buffer.

Both!!!!