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Posted: 3/18/2012 1:47:27 PM EDT
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I've read thru quite a few of the posts pertaining to the whole short stroking debacle and there's different ideas at to what does/doesn't cause it and with all the help and back and forth it seems to get confusing fairly quickly. So, here's my "beating the dead horse" post...
Equipment: Tactical Innovation lower (post ban) Stag 2H upper with lower pts kit, stock & buffer tube/spring courtesy of Pete in NH 30rd PMags XM193 & M855 Federal Magpul MOE handguard PA 30mm red dot Took her to the indoor range a week ago after the build, and to my aggravation after about 6rds she started to 'short stroke'. Shot a few more rds after pulling the charging handle halfway back and letting it run forward... did this quite a few times and would occassionally shot 2-3 rds before having to repeat the 'manual charge'. This was shooting the M193. EVERY time, the spent casing was extracted and a new rd was loaded... the bolt was fully foward (slapping the forward assist confirmed this)... she just would not fire consistently. So, I figured maybe I didn't clean her well enough before the first session... come home, totally strip down the BCG, soaked, scrubbed, soaked and then wiped clean the components. Coated them w/CLP, reassembled, reinstalled, applied more CLP and then worked the BCG back and forth for a good 1/2hr. Got to fire off a few rds of M855 today after a ham shoot, thinking all of my diligence paid off, and... she's still 'short stroking'. I am in contact with Stag as they are located literally 30mins from my house and they suggested it might be the ammo, but wants an update (which I just sent them). The armorer at the indoor range who's been working with and building AR's for years says it's most likely the gas tube. I'm "iffy" about tearing anything apart to check the gas tube alignment and/or other seeing if Stag replaces/repairs this upper, I don't want them to void the warranty cause I did something out of my pay grade so to speak. So, what do ya'll think? |
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Quoted:
EVERY time, the spent casing was extracted and a new rd was loaded... the bolt was fully foward (slapping the forward assist confirmed this)... she just would not fire consistently. This is NOT typical short stroking. If your rifle is short stroking, it's being remarkably consistent when it malfunctions. Important point: when you say it "would not fire", does that mean the hammer dropped but the gun didn't shoot, or that the hammer wasn't cocked and the trigger was dead? It's quite possible you have a problem with your fire control group in your lower, such that you're getting some hammer follow malfunctions. Most milspec ammo will not fire from a hammer follow. If you had another lower handy, that would be a good test to see if the malfunction happened with another lower. If the hammer IS cocked and new round is loaded and bolt closed, then you probably have an out of spec firing pin or tolerance stacking problem, or again maybe something going on with the FCG. You can occasionally see a situation that looks kinda like short stroking but is actually caused by very high bolt velocity, which gives you bolt bounce at both ends of the BCG travel. Your symptoms don't sound quite like that, but a heavy buffer like an H3, or one of the specialty rate reducing buffers would typically solve that kind of problem. Brand new rifles sometimes fail to close the BCG completely or exhibit other symptoms of short stroking just from a combination of poor gas seal on brand new parts, and rough metal surfaces in the bolt to bolt carrier areas as well as the bolt to barrel extension. Those rifles usually smooth out and function normally in a couple hundred rounds or less, and it sounds like you're already past that point. Something you could try as a test would be shooting a known lower power ammo, say PMC Bronze 55gr FMJ. If you had something like a gas leak going on or some other true short stroking issue, lowering the ammo power should dramatically increase the rate of malfunctions. You should take care shooting until you figure out what is happening though, because if you have a hammer follow, you could at any time get "more than you bargained for" when you pull the trigger, and that's more likely when using ammo that doesn't have the hard military primers. If you try some other ammo, I would limit the number of rounds in the magazine. |
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Currently I only have about' 120-130rds thru her right now... I know, not a lot at all. So the rifle not being 'broken in' is still a possibility.
I keep looking into other issues such as something incorrect with the FCG (spring installed incorrectly, hammer, etc. I even tried charging the rifle, squeezing the trigger and holding it while re-cocking her, and slowly releasing the trigger... I get the 'clunk', but it doesn't seem to happen immediately after the trigger is something If I don't see or figure out something that is blatantly obvious, I'm connection try some .223 Tulammo this week and see if the problem increases. It's funny though, that when I was at the range, the armorer not only dbl checked my rifle and performed a function check, but after I asked him about the 'short stroking' he proceeded to fire 4 rds consecutively... |
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Quoted:
Oh, and to answer your question Gamma, the trigger was dead each time it malfunctioned. If the hammer is down, yet you have good ejection and a live round loaded reliably, you probably have a hammer follow malfunction - ie, something in the fire control group isn't working right and the disconnector is not catching the hammer, so that the hammer just follows the bolt carrier down as it closes. Quoted:
I even tried charging the rifle, squeezing the trigger and holding it while re-cocking her, and slowly releasing the trigger... I get the 'clunk', but it doesn't seem to happen immediately after the trigger is something This statement doesn't make sense to me. I would start looking at a variety of things in the FCG, probably just go ahead and disassemble it. Make sure the hammer and trigger springs are in place and not backwards. Make sure the disconnector spring is actually the disconnector spring and not the bolt catch spring, and that it's in right side up. Make sure the disconnector looks good and that the engagement surface is right, no distortions, knicks, chips, etc. Same with the area on the back of the hammer that the disconnector engages. If you find something wrong, then likely you've found the source of the problem. If not, I would probably reassemble, and put a foam earplug or something in front of the hammer, and do some careful function checks of the fire control group to see if you can identify what is happening. You might have a bad/out of spec part, or just a tolerance stacking issue going on. |
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I keep looking into other issues such as something incorrect with the FCG (spring installed incorrectly, hammer, etc...
Not to beat a dead horse, but are you sure that the hammer spring is configured like the photo. Note that the legs of the hammer spring come from underneath and rest on top of the trigger pin. 
the trigger was dead each time it malfunctioned.
Need specific details. Are you saying that when the hammer is cocked and you press the trigger, the hammer goes forward, strikes the primer but there is no ignition? Does the primer have solid strike hits? Pics of the lower showing the FCG and a pic of the primer hits would sure help. |
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Quoted:
I keep looking into other issues such as something incorrect with the FCG (spring installed incorrectly, hammer, etc...
Not to beat a dead horse, but are you sure that the hammer spring is configured like the photo. Note that the legs of the hammer spring come from underneath and rest on top of the trigger pin. http://img.photobucket.com/albums/v503/AR15forme/IMG_5660.jpg the trigger was dead each time it malfunctioned.
Need specific details. Are you saying that when the hammer is cocked and you press the trigger, the hammer goes forward, strikes the primer but there is no ignition? Does the primer have solid strike hits? Pics of the lower showing the FCG and a pic of the primer hits would sure help. Dead trigger comes from either, In the case of the hammer just following the carrier back forward, not having the disconnector spring installed correctly with the large coil side down into the back trigger slot under the disconnector tail. and/or, the disconnector bind up on either the trigger pin, or trigger slot due to burs. Or, if switching the selector from fire to safe,then back to safe allows the gun to fire again, burs on the disconnector or back hammer sears edges that is not allowing the disconnector to cleanly release the hammer on trigger release/reset. http://www.ar15.com/content/guides/assembly/lower/ |
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Took a quick look just now, and the trigger/hammer springs are in and seated correctly. Grabbed a rd out if a mag, and there IS a very small dimple in the primer. So I'm guessing I was wrong in saying the trigger was totally dead.
I did not even think about checking to see if engaging/disengaging the safety would have any effect. I guess tonight after work I'll tear down the lower and make sure that the disconnecter spring is in properly and look for burrs (which I did not notice upon assembly). |
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Here's what I've found... or didn't find depending on how you wanna look at it.
- Tore the lower apart and don't see/feel any burrs anywhere. - Verified that the trigger and hammer were installed correctly. - Safety selector seems to operate normally and is not loose. - The disconnector spring came installed from Stag... I gave it a fairly good pull, and it didn't budge. Other than looking a little 'skewed'... Here are some pics as show & tell (and to verify against posted instructions) as I tore the lower down: http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-16-33_577.jpg http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-16-50_281.jpg http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-17-01_825.jpg http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-21-30_462.jpg http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-22-36_429.jpg http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-25-42_324.jpg I'm not 100% sure how much 'play' there should be between the disconnector and the trigger and it's not the greatest pic, but: http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-34-12_351.jpg I did notice something quite odd with one of the three (3) rds that did not fire... kinda scary to be honest with ya: http://img.photobucket.com/albums/v660/No_Boost/2012-03-19_16-16-10_299.jpg Notice something a little strange?! I'm not reassembling anything and haven't heard back from Stag yet. Not like I'm going to the range tonight anyways. 
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Carrier without bolt, drop it into the upper and make sure that the carrier key and gas tube are correctly aligned to make sure that this is not keeping the bolt from fully locking up.
Bolt and firing pin alone, shove the FP into the back of the bolt all the way forward and spin the FP. If it binds out the spin, something is out of spec. Next shove the FP all the way in, and check the protrusion of the FP tip out the bolt face. In spec will be .032 to .036 protrusion. If needed and find a ridge bur on the back of the bolt where the FP stop collar seats out against, remove the bur so the FP can fully protrude correctly. And the dents that you see on the FP, looks like FP free floating normal tags on loading/hammer follow through, than the FP actually reaching the primer when the hammer came down on FP strike with the bolt locked home (as if the bolt was not fully locked up, with the back of the carrier blocking the FP from reaching full protrusion. |
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Quoted:
Carrier without bolt, drop it into the upper and make sure that the carrier key and gas tube are correctly aligned to make sure that this is not keeping the bolt from fully locking up. Floats in and floats out, no binding. Quoted:Bolt and firing pin alone, shove the FP into the back of the bolt all the way forward and spin the FP. If it binds out the spin, something is out of spec. Next shove the FP all the way in, and check the protrusion of the FP tip out the bolt face. In spec will be .032 to .036 protrusion. If needed and find a ridge bur on the back of the bolt where the FP stop collar seats out against, remove the bur so the FP can fully protrude correctly.
FP spins free. Protrudes out the BF .030" (calipers and depth mic), no burrs. |
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I did notice something quite odd with one of the three (3) rds that did not fire... kinda scary to be honest with ya: If you're looking at the light marks on the primers, normal, don't sweat it. The firing pin is free floating, so when the BCG slams into battery the firing pin contacts the primer, but not enough to light it off. Some do this more than others. Nice pics. Nothing sceams out as being off. An odd side note; I have noticed that the Stag disconector springs in the couple kits I have here, are as long as the springs you show. Current Colt springs (black) are shorter. 
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Quoted:
Other than the FP not protruding as far as spec, I don't see anything. That can be enough to give you failure to fires. The tiny indentations are normal for chambered rounds in an AR, but not ones attempted to be fired. Again though, if the hammer does not fall when you pull the trigger because it's already down on a chambered round, you have a serious malfunction that needs to get corrected, which is likely in the lower parts or lower. |
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Gamma, I did perform all the function checks listed in the how-to guides. A few times even... right after initial assembly and after both times I had issues (with different ammo).
I looked at the lower itself, and if there's something 'wrong', it's not blatantly obvious.
Guess I wait an see what Stag says. |
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Had a similar problem with one of my builds. A 16" Beaver Creek barrel. After trying different ammo, mags, re aligning the gas block, changing buffer and tube. I trued up the gas hole to .063 and now it works flawlessly. I placed on old aluminum cleaning rod in the barrel and when I felt it touching I stopped drilling. Just a thought. Good luck.
Q. |
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21 days to the day I was notified they received the upper and no word yet... 2 full weeks with no contact... just sent them an email asking the status and/or if my rifle is in queue for work this weekend...
Is this "industry standard" for current customers who are not happy with their product or am I over-reacting?! 
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I still haven't seen a definitive answer to the initial question about the "dead" trigger.
If you fire, and then the hammer does not drop with the next pull of the trigger (ie, trigger is "dead"), you have a hammer follow malfunction. If you can't tell, try going to "safe" after you fire a shot - if it can't go to safe, then the hammer is down. On rare occasion IIRC you can have a hammer follow malfunction that shows up in live fire that doesn't show up in the manual function test. |
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It sounds to me as a fail to fire, not a short stroke. Every time the fail to fire occurs, is this happening when just random firing the gun, or are you pushing the forward assist after each round is cycled into the chamber to make sure the bolt carrier assembly is fully seated and the bolt is fully locked into the barrel lugs (barrel extension)? If it occurs during just random firing and not pushing the forward assist before each round is fired, then it sounds like bolt bounce. If it is possibly bolt bounce, then have you tried a heavier buffer assembly, as the heavier counterweight of the buffer should help reduce bolt bounce?
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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Quoted:
I still haven't seen a definitive answer to the initial question about the "dead" trigger. If you fire, and then the hammer does not drop with the next pull of the trigger (ie, trigger is "dead"), you have a hammer follow malfunction. If you can't tell, try going to "safe" after you fire a shot - if it can't go to safe, then the hammer is down. I honestly don't remember now if the hammer dropped with the next squeeze of the trigger or not... One of the things that I checked before sending the upper back to Stag. I could not change the selector to 'safe' unless the hammer was down. Now, granted, I didn't try this after firing, just during the malfuction test. I contacted Tactical Innovations in ID, and asked for info... they said: We'd be happy to measure the receiver and ensure that its in spec if you wanted to send it in but for the symptoms you describe, it most likely is an issue with the lower receiver fire control parts, since the receiver does not do anything for function other than hold the hammer and trigger and disconnector etc in position.
And Stag said: I can take back your lower for inspection if it is a stag. As far as I know the upper has tested on a stock lower receiver.
On a good note, they are sending my upper back with a new lower parts kit. I have another lower and parts kit that I just acquired today so I'll be able to check things on two different platforms if need be. So... I guess another update will be in order. |
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It sounds to me as a fail to fire, not a short stroke. Every time the fail to fire occurs, is this happening when just random firing the gun, or are you pushing the forward assist after each round is cycled into the chamber to make sure the bolt carrier assembly is fully seated and the bolt is fully locked into the barrel lugs (barrel extension)? If it occurs during just random firing and not pushing the forward assist before each round is fired, then it sounds like bolt bounce. If it is possibly bolt bounce, then have you tried a heavier buffer assembly, as the heavier counterweight of the buffer should help reduce bolt bounce? CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 IIRC I never hit the FA. It was random "short stroking/FTF" but more often than not didn't fire. Fire... eject... load... click... nothing. Pull the CH back half way, let it go, fire... eject... load... click... nothing. |
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You need to pin down the trigger situation when it "didn't fire". OP, make it easy on yourself and google the instructions to fully function test your FCG. You can do this in the comfort of your house even. Got a link? Google is pointing me at links/posts ppl have made regarding failures of the function test. I did the function test listed in the 'DIY' section... maybe something a little more 'in depth' is what you're referring to? |
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She's back. Brand new lower parts kit installed, function check complete. Hopefully no issues when I hit the range this Friday. Have another complete lower on standby though, just in case.
http://img.photobucket.com/albums/v660/No_Boost/2012-04-24_18-32-11_116.jpg |
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She's all set! Received a new FCG from Stag, installed it this afternoon and 6 mags later she's officially 100% functional! I have a feeling it was the disconnector spring, cause the one I received with the replacement lower pts group looked an felt different.
Aside from a little aggrevation with the return and 'no issues found', I'm a happy customer. Thanks Daniel @ Stag customer service and thanks to everyone here for the input! Much appreciated! Now, onto project #2! 
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Quoted:
She's all set! Received a new FCG from Stag, installed it this afternoon and 6 mags later she's officially 100% functional! I have a feeling it was the disconnector spring, cause the one I received with the replacement lower pts group looked an felt different. Aside from a little aggrevation with the return and 'no issues found', I'm a happy customer. Thanks Daniel @ Stag customer service and thanks to everyone here for the input! Much appreciated! Now, onto project #2! Excellent. I have a suspicion that you had a bolt catch spring installed with the disconnector, that will usually cause malfunctions. |
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