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Posted: 1/3/2012 6:26:21 PM EDT
Hey all. This is my first post to ar15.com so bare with me. I just put together my first ar and I am having a problem with it short stroking every time. It cycled properly for one shot. With only one round in the magazine, once fired the bolt does not go far enough back to catch the bolt catch. My setup is a 20" dpms bull barrel, LMT bolt carrier assembly, daniel defense upper, RRA lower with a collapsable stock with normal carbine buffer. I have cleaned and lubricated the gun several times and it will only eject the shell but never load another in. I have removed the gas tube and gas block and do not see any abnormal wear to the tube. I have tried slightly moving the gas block and still the same thing. I have checked the buffer and spring and made sure the bolt carrier slides into the buffer tube without any problems. The gas keys are in proper position. I have shot about 35 rounds through the gun using mostly 55g PMC ammo and a few 40g fiocchi. At this point I am not sure what is next to try. Please any input would be helpful. Thanks.
Link Posted: 1/3/2012 8:27:37 PM EDT
PMC is likely the weakest ammo you could find. I would try some higher power ammo, after a few boxes it may run on the weaker stuff.

Make sure that your bolt can retract far enough to the rear. It should be able to be retracted about 3/32" to 1/4" behind the bolt catch when pulled all the way to the rear with the charging handle. Make sure the gas key is tight and you don't see any evidence of other gas leaks or gas block misalignment. Might also check the lower to make sure nothing is preventing the hammer from retracting fully, so that it's not dragging excessively on the bottom of the bolt.

If you don't find any other issues, make sure you have lubrication on the inside of the bolt/bolt carrier area (suggestion would be a relatively heavy coat of a lighter weight oil), try some higher power loads, and see if you get function.
Link Posted: 1/4/2012 8:15:19 PM EDT
Short stroke - Rifle gas system generates approximately 13,000 psi, Carbine generates 26,000 PSI you need balance for the system for it to work properly, Carbine spring and buffer are designed to handle the higher pressure. May sound crazy, but Check for gas leak, and reduce buffer weight, or lighter bolt carrier, or adjustable gas block, or lighter spring or a combination of things. Search buffer weights or ejection chart .
Link Posted: 1/5/2012 4:42:13 PM EDT
[Last Edit: 1/5/2012 4:46:22 PM EDT by OverScoped]
you have a rifle length gas system? you need a rifle buffer and spring. I always break in my AR's and sight-in with 5.56 ammo (M193) for the first couple hundred rounds, the after that i switch to whatever i can get cheap.
Link Posted: 1/5/2012 4:57:44 PM EDT
[Last Edit: 1/5/2012 4:57:58 PM EDT by Winn]
Originally Posted By OverScoped:

you have a rifle length gas system? you need a rifle buffer and spring...


That's completely inaccurate.

A 20 rifle is perfectly capable of running with a collapsible stock.

Link Posted: 1/6/2012 3:14:12 AM EDT
[Last Edit: 1/6/2012 3:15:03 AM EDT by Dano523]
Link Posted: 1/6/2012 4:39:51 AM EDT
Thanks for the input. I'm hopefully gonna get together with one of my friends who has an ar and try swapping some parts this weekend to maybe narrow the issue down. Ill try some hotter loads first and see what happens.
Link Posted: 1/6/2012 8:48:06 AM EDT
Link Posted: 1/6/2012 11:12:25 AM EDT

Originally Posted By Dano523:
Originally Posted By Winn:
Originally Posted By OverScoped:

you have a rifle length gas system? you need a rifle buffer and spring...


That's completely inaccurate.

A 20 rifle is perfectly capable of running with a collapsible stock.




Ditto, buffer spring and buffer has all to do with the internal length of the receiver extension tube, and not the upper receiver and it's barrel length.

If you looked at how everything works tacked thread, although different barrel lengths will have different pressures at the gas port, the barrel gas ports are sized accordingly on each length barrels to send the correct amount of pressure dwell back to the carrier to cycle the rifle correctly.


so you are telling me that the gas system length has nothing to do with the buffer spring and buffer weight?
Link Posted: 1/6/2012 2:02:38 PM EDT
[Last Edit: 1/6/2012 2:04:12 PM EDT by Winn]
Originally Posted By OverScoped:

... so you are telling me that the gas system length has nothing to do with the buffer spring and buffer weight?


No, that's not what's been said.

Link Posted: 1/6/2012 4:00:39 PM EDT

Originally Posted By Winn:
Originally Posted By OverScoped:

... so you are telling me that the gas system length has nothing to do with the buffer spring and buffer weight?


No, that's not what's been said.

OK, because in my original statement I clearly asked if he had a rifle length gas system. Then i said something about a rifle spring and buffer and somehow that got turned into a me getting TOLD I was wrong. Now that I clarifed, I'm still wrong? That is what has been said.

Link Posted: 1/6/2012 4:04:58 PM EDT
[Last Edit: 1/6/2012 4:12:25 PM EDT by Winn]
Originally Posted By OverScoped:
Originally Posted By Winn:
Originally Posted By OverScoped:

... so you are telling me that the gas system length has nothing to do with the buffer spring and buffer weight?


No, that's not what's been said.


OK, because in my original statement I clearly asked if he had a rifle length gas system. Then i said something about a rifle spring and buffer and somehow that got turned into a me getting TOLD I was wrong. Now that I clarifed, I'm still wrong? That is what has been said.


At this point, you've made it clear that you don't have a basic understanding of the topic.


ETA: Please don't take that as an insult. Do you understand the differences between a rifle/A2 buffer system and a carbine buffer system?

Link Posted: 1/6/2012 4:13:10 PM EDT

Originally Posted By Winn:
Originally Posted By OverScoped:
Originally Posted By Winn:
Originally Posted By OverScoped:

... so you are telling me that the gas system length has nothing to do with the buffer spring and buffer weight?


No, that's not what's been said.


OK, because in my original statement I clearly asked if he had a rifle length gas system. Then i said something about a rifle spring and buffer and somehow that got turned into a me getting TOLD I was wrong. Now that I clarifed, I'm still wrong? That is what has been said.


At this point, you've made it clear that you don't have a basic understanding of the topic.



Thanks for the education.
Link Posted: 1/6/2012 4:14:06 PM EDT

See my ETA comment above.

Link Posted: 1/6/2012 4:31:22 PM EDT

Originally Posted By Winn:

See my ETA comment above.



YES I understand. I am trying to help here and it feel like you two are all over me. I think you are missunderstanding what i am trying to say. I asked what gas system he had. he never said. To my understanding, a carbine spring and buffer will cause short stroking if used in the longer gas systems. We still dont know what gas system he has, all we know is he has a collapsable stock and a carbine buffer and I'm fully aware that the stock choice has nothing to do with barrel length.
Link Posted: 1/6/2012 8:09:22 PM EDT
Link Posted: 1/6/2012 9:30:21 PM EDT
[Last Edit: 1/6/2012 9:32:48 PM EDT by Winn]
Originally Posted By OverScoped:
Originally Posted By Winn:

See my ETA comment above.



YES I understand. I am trying to help here and it feel like you two are all over me.

Honestly, no one is "all over you".


I think you are missunderstanding what i am trying to say.

That's possible ... my apologies if so.


I asked what gas system he had. he never said.

True, but he did state that he's using a 20" bull bbl, and it's a pretty safe bet that it's got a rifle length gas system.


To my understanding, a carbine spring and buffer will cause short stroking if used in the longer gas systems.

This is really the crux of the matter ... if using a collapsible stock, then there are several variables in terms of different buffer weights and springs - but - to make a blanket statement that a carbine buffer system won't work well, and what's necessary for longer gas systems is a rifle buffer system, simply isn't accurate.


We still dont know what gas system he has, all we know is he has a collapsable stock and a carbine buffer and I'm fully aware that the stock choice has nothing to do with barrel length.

Correct, the stock itself is not really a factor.



Link Posted: 1/7/2012 4:47:57 AM EDT
Thanks for the explanation. Hopefully we all learned something.
Link Posted: 1/7/2012 5:27:11 AM EDT
It has a rifle length gas system, just so everyone is on the same page.
Link Posted: 1/7/2012 8:12:23 AM EDT
Originally Posted By OverScoped:

Thanks for the explanation. Hopefully we all learned something.


At this point I'll defer to Dano and Gamma762. They both know a lot more than I do.



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