I am having a bit of an issue with short stroking on my 7.62X39 AR






I am using a 20" barrel.
Unknown brand spring - 10.5" long
Unknown buffer brand - unknown weight.

Rifle length gas tube
Low profile gas block



I am thinking It has something to do with the buffer/buffer spring.

The rifle will fire and eject. But will mostly short stroke on all metal casing. When shooting brass -Cycles fine (no short strokes) only on certain brand ammo.  






Let me know if there is any other info that is needed.  Willing to experiment to get this rifle to work (although a lot of people are having issues with this platform)


Everyone loves pictures, so here is one
https://dl.dropboxusercontent.com/u/12763400/AR15/AR15.jpg

I don't know if you would want to do this but this is what I would do if it were my rifle and because I have quite a bit of experience with opening gas ports.  That is not the solution for everyone and for all SS issues, so there is a little bit of 'going by feel' as to when to do it and when to look elsewhere.  And, it is NOT the first thing you should do, but rather the last.

I assume you have cleaned your rifle completely and made sure there is no lacquer build up in the chamber.  If you shot lacquered ammo and left a round in the chamber when hot, the lacquer can stick to the chamber and gum up the works right now.  However, that usually results in it no feeding anything, including brass cased ammo.  For kicks and giggles, make sure you chamber is squeaky clean.

First I would check to make sure the rifle is not too fast.  Load one round in the mag and shoot.  Do this 4-5 times.  If the bolt locks back then you are not short stroking but you may have such excessive carrier speed that you are over riding the next cartridge coming up.  That would be an extremely over gassed rifle.  To verify, load the mag with 5 and shoot.  If they shoot OK then load with 10 and shoot.  You may find it shoots fine with 5-10 rounds then starts mis-feeding as you load 15-20...   That may indicate a weak spring in your magazine.  Try other mags with good strong springs to verify.  If is a weak spring, replace.  If it fails to feed and function with any in the mag, then it may be operating too fast and needs to be slowed down.  To do that you could go to a 2HB or 3HB and XP recoil spring, or an adjustable gas block.  Even an XP hammer spring will slow things down some.
If it fails to lock back at all, or locks back when the rifle is clean but then fails to lock by after  few rounds, short stroking is most likely your problem.

Then I would check all gas items.  Make sure the gas block is centered over the port by measuring the location, not just eyeballing or using the dimple, if there was one.  Make sure the gas port in the barrel is clear.  It can clog so double check.  Check the ports in the gas block too.  
Now check the gas tube for obstructions-run a long pipe cleaner or gas tube cleaner through it, then on to the gas key installation.  Make sure there is not excessive leakage around it.  Then the gas rings.  Make sure they are OK.  Don't worry about the slots not being lined up.  It does not hurt anything to stagger the slots but they close up when the bolt is inserted in the carrier anyway but it seems a lot of people cannot get their heads around that.

Next, weigh your buffer.  Weigh it and there is a buffer weight chart around here someplace so you can find what you have.  If it is a 3HB, go lighter.  I would go all the way to standard buffer and spring and see what happens.  If it improves, there you go.  But if you already have standard buffers and spring, I would not go lighter.  Mine runs a 2HB with XP buffer Spring and XP hammer spring.  Runs like a sewing machine with everything I have ever fed it.

Then, after everything else is exhausted and proven to not be the solution, I would move on to opening the gas port.  You need a drill press IMO and a barrel vice.  You CAN do it with a hand drill but the risk of going through too far and hitting the other side of the barrel is high because the amount of metal you are removing you cannot feel.  Use a barrel vice so you can keep the barrel level and the bit perpendicular while drilling.  It is unlikely you can do that by hand but if it is off a little it really won't hurt anything.  Just don't go too far and nick the off side of the bore.
  Use numbered drill bits to find out what size port you have now then go up to the next numbered size unless it is only .001 larger.  Most are .002 and .003 larger, some are as much as ,.004 or .005 larger, so I like to go up .002 min at a time and .004 max at a time.  Enlarge the gas port, use cutting oil and I like to eyeball it down the barrel so I can see the bit come through and stay clear of the other side.  That is why I like a drill press.  Clean the bore, put the gas system together then shoot for function, one shot at a time and do at least 4 shots, I use a minimum of 5 shots.  Sometimes with everything clean the bolt will lock back but by the time you get to shot #5 it short strokes again.  That has bitten me more than once so shoot at least 4 shots.  There is no need to test for feeding.  If the bolt locks back on an empty mag each time then your short stroke issue is solved.
If the bolt does not lock back, take the loads that have not been feeding and load several in the mag.  Now try to shoot.  You may find that they are trying to feed better or may now be feeding OK so you know you are on the right track.  Then open another .002-004 and test again.  Once you get the bolt locking back on each shot, by that time it will be feeding OK too and you can clean things up, put it all back together and have a ball without breaking the bank.

I appreciate the response.

I just got back into town, Ill be testing a couple of these things out and will report back.

Thank you again.