New DPMS issue...won't fully cycle.
Hey guys, I've been a lurker for a while but now I have a problem so here's my first post :-) I've searched through the forums and haven't found the same problem I'm having, so hopefully I'm not repeating something that was posted yesterday or something...
My friends and I are all in the process of building our own AR's, and one of theirs is finally assembled but is having trouble. Here is the gun specs and the problem:
All 5.56 DPMS parts except the BCG (Bushmaster), barrel (Daniel Defense 1/7) and gas tube (Stag).
After fully assembled, we fired the weapon and the bolt ejected the empty casing, went forward and "click". It failed to load the next round. We proceeded to try again through several ammo types (all 55 grain) and several magazines with the same results. One time I got it to fire four straight rounds, another time two rounds before it gave us the click. Every single other time it would only fire the chambered round. Each time that it failed it either skipped the next round completely, or tried to load it but didn't catch the cartridge right - getting it stuck somewhere halfway between the magazine and battery.
We tried firing one round in the magazine to see if the bolt would catch, out of 10 or so tries it didn't catch once.
From my fairly limited knowledge, I'm wondering if it is the buffer. Everything appears perfect in the gas tube alignment, it's straight, tight and seems to be the correct length. The BCG seems to slide over the gas tube fine as well. I've got a Spike's buffer on mine that I will trade into it for testing tomorrow. I also have a Spikes gas tube with Yankee Hill gas block to try out if I need to go that direction......but want to check your guys thoughts to see if I'm at least in the right ballpark before I waste a bunch of time.
Hopefully that's not too long...trying to be as descriptive as possible.
Thanks for any help in advance!
definately sounds like shortstroking
try blowing through the gas tube with a piece of tubing to make sure it's in there right.
check to be sure the carrier key is tight and well staked and check the gas rings
Make sure your gas block is on correctly. If you have a free float tube you should have a small gap where the handguard cap usually sits. It is small but it might make a difference
Already checked the stakes/key & rings...they were all fine. The gas tube idea sounds like a good way to check it :-)
Espos1111 - I already know that it's flush against where that plate would be, I totally wasn't thinking and pushed it all the way. That will be my first thing to check, although I don't know that it will make a difference...I'll check back with you guys tomorrow/Sunday when I find out what happens. Thanks for the quick help!
Verify the gas system completely as mentioned above.
Don't use crap ammo like Tula for the troubleshoot.
Use some Lake City XM193 and get it running on full power ammo.
Then if you want to shoot bargain ammo you can tune the gun for it if necessary, like going to a lighter buffer.
Sooo I tested out with all the stuff checked, used PMC Bronze 55 grain, and still had the same failure to cycle. I changed out his stock buffer for a Spike's buffer as well with no change. I'll change out his BCG with another one tomorrow and see what happens. No idea where to go from there...
Would help to know what stock is in play.
If an A-1 length, could have the longer A-2 butt stock screw installed, which will be protruding into the back of the tube and preventing the bolt from coming back far enough to strip a round out of the mag.
If a telescoping stock, then make sure that it has the shorter carbine buffer in play, and that the spring is only around 10.5" long. If he has a standard spring in play (11.75" long), it will coil bind out before the bolt can come back the needed distant to strip a round out of the mag.
Also, double check alignment of the barrel extension to the front take down block (center of feed ramps should be center of the front block) and gas tube to key alignment (carrier without bolt in the upper to confirm such).
Hey guys, thanks for all the help. We took the gas tube off and looked at it early in this process, running clp down it to make sure it was open with no trouble whatsoever - looked perfect and was installed perfectly. With that in mind we changed out the buffer system, didn't work. Checked (perfect) and changed out the BCG, didn't work. Changed the gas block...nooo joy. Finally, we just changed that perfect looking tube fore a Spike's tube and the thing works beautifully. 100 rounds of different types and grains with no malfunction. I have no idea what could be wrong with this tube...maybe some manufactured obstruction or something - but the new one is working so we're set. Again, thanks for the knowledge assist. I'll keep all your input in mind if I ever run into these issues again.
Originally Posted By Dilhack:
Hey guys, thanks for all the help. We took the gas tube off and looked at it early in this process, running clp down it to make sure it was open with no trouble whatsoever - looked perfect and was installed perfectly. With that in mind we changed out the buffer system, didn't work. Checked (perfect) and changed out the BCG, didn't work. Changed the gas block...nooo joy. Finally, we just changed that perfect looking tube fore a Spike's tube and the thing works beautifully. 100 rounds of different types and grains with no malfunction. I have no idea what could be wrong with this tube...maybe some manufactured obstruction or something - but the new one is working so we're set. Again, thanks for the knowledge assist. I'll keep all your input in mind if I ever run into these issues again.
Glad you got it running !
This is a good example of why this practice of pouring CLP into a suspect gas system is not a good check.
You apparently had a partially blocked tube and the CLP was able to work around it.
The inside diameter of the gas tube may have been a bit smaller (thicker wall) therefore there is less VOLUME of gas moving through the tube.
It is the volume of gas that moves through the tube, not the amount of pressure, that pushes the BCG backward.
