sschultz Posted May 2, 2012 Share Posted May 2, 2012 I need some help. Our department is in the process of switching to AR's. We bought 13 guns from DPMS. The guns were cleaned and test fired and sighted in. We then put SureFire supressers on them . They were all test fired again with no problems. These gun have wenr through 2 groups of training with out any issues. Today one of the guns started to not lock back on the last round. I took the suppresser of and it worked fine. I then took the bolt out oiled and tried it again without the suppresser. it would not lock back after the lasr round was fired. I did not get a chance to tear it apart after the class was done. Any of you gurus have any idea what I should be looking for. This is giving me a headache. Schultz Link to comment Share on other sites More sharing options...
steviesterno Posted May 2, 2012 Share Posted May 2, 2012 Sounds like it could be the mag. did you get this malfunction with All mags tried or just one? Link to comment Share on other sites More sharing options...
AlamoShooter Posted May 2, 2012 Share Posted May 2, 2012 I could be even more simple than that. Some of the "new shooting styles has the left hand way back at the lower receiver. Could you have had pressure on the bolt lock with your hand? Link to comment Share on other sites More sharing options...
lee blackman Posted May 2, 2012 Share Posted May 2, 2012 I'm on with stevies on the mag. Maybe changing the magazine spring or follower would fix it. Or maybe a different magazine all together. I know adding a suppressor is like adding more barrel length ahead of the gas port in the barrel. I hear that it can sometimes cause pressure issues that can also cause cycling issue, and some companies like Noveske started offering a switchblock adjustable gas block to solve the issue. Switch for suppressor use, other side for no suppressor. I don't really claim to truely understand but somehow there is a increase in pressure which causes the bolt carrier to start moving earlier than its supposed to which also causes it to not have enough energy to move it all the way back or something like that. So if it doesn't go all the way back it won't clear the back of the follower. But I would assume that also means a failure to eject or something. Link to comment Share on other sites More sharing options...
sschultz Posted May 3, 2012 Author Share Posted May 3, 2012 I am not sure if the mag is the issue the intructers told me that they had tried using other mags before I got there. my first thought was the suppresser also. But why did it wait till after 3 or 4 hundred to start doing this. Schultz Link to comment Share on other sites More sharing options...
gng4life Posted May 3, 2012 Share Posted May 3, 2012 When you get time, clean/check the gas system. How many rounds have been through the rifle? I think Lee is on to something and if they are gas impingement systems, that seems logical. Link to comment Share on other sites More sharing options...
sschultz Posted May 3, 2012 Author Share Posted May 3, 2012 about 3 hundred round or so. But after I oiled the bolt I shot it without the suppresser and it did not lock the bolt back. If nothing else this will help my post count get over 200. Schultz Link to comment Share on other sites More sharing options...
Retread1911 Posted May 3, 2012 Share Posted May 3, 2012 Check the has system first including the bolt carrier key. If it is loose that can cause a problem. also check the gas ring alignment if two are aligned the the reduced pressure of the non suppressor Rounds it could behave that way. What is the barrel length? I have seen more trouble with the 10.5 inch barrels then the 14.5's. Suppressors also increase fouling as well as pressure so a cleaning may also be in order but if it was only 400 rounds that shouldn't be an issue Link to comment Share on other sites More sharing options...
Stlhead Posted May 3, 2012 Share Posted May 3, 2012 After 3 or 4 hundred rounds with a suppressor, that bolt carrier is probably pretty skunky. Clean it and see if the problem persists. Link to comment Share on other sites More sharing options...
sschultz Posted May 3, 2012 Author Share Posted May 3, 2012 Retread its 16 inch barrel. My plan is to srip it down clean it and try it again. Schultz Link to comment Share on other sites More sharing options...
StealthyBlagga Posted May 3, 2012 Share Posted May 3, 2012 If this only happens with the suppressor installed, my guess would be excessive bolt velocity. Empty brass ejecting forwards is another symptom of excessive bolt velocity (all the guns might be doing this). Check the weight of the bolt buffer... a standard CAR buffer will probably be too light. Try an H-buffer or even a 9mm buffer. Link to comment Share on other sites More sharing options...
sschultz Posted May 3, 2012 Author Share Posted May 3, 2012 I took a look today and saw that there is some unusaul wear on the hammer where the bolt carrier rides over it. I called DPMS today and descibed the issue. The guy would not suggest what was wrong with it. So I am dropping three guns off at DPMS tommorow morning. Schultz Link to comment Share on other sites More sharing options...
lee blackman Posted May 3, 2012 Share Posted May 3, 2012 Spike offers a ST-T1 heavy buffer that is filled with tungsten powder, supposed to help with slowing the bolt velocity and aid in bolt bounce, though I've never tried one. AR-Restore makes a hydraulic buffer that is suppose to slow down the cyclic rate of the gun and stop bolt bounce. I've seen one used in a full auto, and for some reason seemed to solve a slew of odd cycling problems the gun was having. I don't claim to know or understand why or even remotely claim that it will help. Just making it known there are bolt buffer options available if you find that it could be an issue. Link to comment Share on other sites More sharing options...
DoubleL Posted May 4, 2012 Share Posted May 4, 2012 My DPMS had the carrier key come loose. At first it was doing what you described, but over a few more rounds without noticing the key it started to malf regularly. Bagged it, got home and field stripped and noticed the key. The staking was weak and allowed the bolts to back out just a hair. Well a hair is all it took to make the rifle a paper weight. Maybe you've got only one loose screw and it's venting just enough gas to screw with the hold open?? After fixing that one issue, I torture tested to 3500 rounds no cleaning. Only oil was a drop of LP in each venthole at the gas rings every 400-500 rounds, and a VERY small amount of quality grease on the carrier contact points. Rifle chugged away like a champ, should have seen the locking lugs at 3500!! Disgusting! It satisfied my needs for dependability, I love that rifle now. Hopefully you will get squared away by the DPMS guy. Post up when you find out what was wrong..... Link to comment Share on other sites More sharing options...
sschultz Posted May 4, 2012 Author Share Posted May 4, 2012 Thanks everybody for the help. I will let DPMS figure it out tommorow. I was less than pleased when the guy at DPMS could not or would not suggest what could be wrong with the gun. Schultz Link to comment Share on other sites More sharing options...
DoubleL Posted May 4, 2012 Share Posted May 4, 2012 I wouldn't place to much importance on the guy on the phone. I've had a few buddies call me and describe malfs with their ARs and I'm always hesitant to tell them what to do without actually looking at the rifle myself. I'd probably be even more hesitant if I was in a paid position for a manufacturer. I feel your pain though, it just plain sucks when a rifle won't run! Link to comment Share on other sites More sharing options...
sschultz Posted May 4, 2012 Author Share Posted May 4, 2012 Update I took the rifles to DPMS and I went with the tech and test fired the gun. It did just exactly what I had told them and would not lock the bolt after the last shot. The tech replaced the bolt and carrier and the gun ran fine. The guy said that there was probbely a gas leak somewhere in the gas system on the carrier. They also fixed two other guns that I brought in while I waited so all is good. schultz Link to comment Share on other sites More sharing options...
DoubleL Posted May 4, 2012 Share Posted May 4, 2012 Sweet!! Nobody likes a paper weight shaped like an AR! Well, that would be cool, just not at the range Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now