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DH2
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Posted: 7/23/2012 9:24:59 PM
Hello all, I'm trying to troubleshoot the rifle I built. It very reliably (as in, every single time) short strokes. Now, when I had the chance I swapped the upper to a different lower and it worked flawlessly. I am betting it is because my lower is using a rifle buffer, spring, and tube whereas the other lower was using a carbine buffer, spring, and tube. Those are the only parts (other than hand guards and barrel nuts) that are different between our rifles. I am thinking that either a heavier buffer or a stiffer buffer spring will fix this problem. Does anyone have any suggestions as to spring/buffer weight or any other potential sources of this problem?

Note: The piston system is aligned correctly and doesn't bind.


Specs:
6.8 spc
16" bison armory stainless bbl (midlength)
Osprey defense fail zero piston and carrier
Mega upper/lower
Fulton A1 stock kit
PSA lower parts kit
MOE handguard
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007Kevin
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Posted: 7/23/2012 9:37:26 PM
If the gun is short stroking a stiffer buffer spring is just going to make it worse. You would want a weaker spring because the force pushing the bcg back isn't strong enough to clear the casing. You should be able to swap your upper from a carbine stock to a rifle stock without issues regardless of gas system.

Can you give a little more information on what is happening that you think it is short stroking?
DH2
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Posted: 7/23/2012 9:56:16 PM
Well, the bolt does not go rearward enough to eject the round or strip off a new one. I know the bolt is in motion because I can feel it doing so.
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strat81
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Posted: 7/23/2012 10:47:42 PM
Are you sure you have the proper length/type buffer and spring for your particular receiver extension?

Disassemble the stock and look inside the receiver extension with a flash light. Does it look like the bolt carrier is making contact with the tube? A bent or misaligned receiver extension can cause those problems.
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Gamma762
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Posted: 7/24/2012 2:06:46 AM
[Last Edit: 7/24/2012 2:08:33 AM by Gamma762]
Originally Posted By DH2:
Well, the bolt does not go rearward enough to eject the round or strip off a new one. I know the bolt is in motion because I can feel it doing so.

Do you mean when fired, or when cycled by hand?

If it's when fired, you may have some kind of partial gas blockage what is restricting gas flow. What kind of gas block is installed? Is it straight, and installed in correct alignment with the gas port, taking into account a missing handguard ring if applicable?
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007Kevin
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Posted: 7/24/2012 11:01:08 AM
Originally Posted By Gamma762:
Originally Posted By DH2:
Well, the bolt does not go rearward enough to eject the round or strip off a new one. I know the bolt is in motion because I can feel it doing so.

Do you mean when fired, or when cycled by hand?

If it's when fired, you may have some kind of partial gas blockage what is restricting gas flow. What kind of gas block is installed? Is it straight, and installed in correct alignment with the gas port, taking into account a missing handguard ring if applicable?


OP said he tried the upper on another lower.
countrygunner
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Posted: 7/24/2012 11:45:26 AM
Does your gas piston system have an adjustment? Some of them have like 3 stages and maybe the stage you have it on won't cycle with a rifle length gas system. I'm sure the gas piston system is the issue if your sure the gas hole is lined up.
jaqufrost
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Posted: 7/24/2012 12:39:59 PM
Sounds like it needs a little more gas. Alternatively you could put a spacer in the back of your rifle extension and put a carbine spring and buffer in.


One other thought, is the hammer binding on the back of the carrier while the trigger is pulled? You can test this by clearing the rifle, pulling the trigger, and while keeping the trigger pulled charge the rifle. It should move freely to the rear without binding.
thornejc
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Posted: 7/24/2012 12:49:17 PM
[Last Edit: 7/24/2012 2:06:16 PM by thornejc]
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Posted: 7/24/2012 1:41:41 PM
What ammo are you using?
You should contact Osprey and you should do a web search for any Osprey problems.
I would also look for leaks.
Gamma762
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Posted: 7/24/2012 1:55:32 PM
Originally Posted By 007Kevin:
Originally Posted By Gamma762:
Originally Posted By DH2:
Well, the bolt does not go rearward enough to eject the round or strip off a new one. I know the bolt is in motion because I can feel it doing so.

Do you mean when fired, or when cycled by hand?
If it's when fired, you may have some kind of partial gas blockage what is restricting gas flow. What kind of gas block is installed? Is it straight, and installed in correct alignment with the gas port, taking into account a missing handguard ring if applicable?

OP said he tried the upper on another lower.

Yes, another lower with a much lighter buffer. Could just mean he's not getting enough energy to cycle the heavier buffer setup.

Originally Posted By thornejc:
I don't know if it is possible for you right now but the LMT Enhanced BCG fixes short stroking issues on a very consistent basis. It is designed to run in suppressed rifles but it takes care will take care of short stroking issues as well.

AFAIK, LMT does not recommend the "enhanced" BCG for anything other than a carbine gas 14.5 or 16" barrel when using full power ammo. It's specifically designed to help correct the excessive dwell of those configurations by delaying the unlocking sequence, which also helps with suppressor use and other overgassed rifle configurations. I can't fathom how it would do anything good for a rifle that is short stroking.
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thornejc
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Posted: 7/24/2012 2:15:01 PM
Originally Posted By Gamma762:
Originally Posted By 007Kevin:
Originally Posted By Gamma762:
Originally Posted By DH2:
Well, the bolt does not go rearward enough to eject the round or strip off a new one. I know the bolt is in motion because I can feel it doing so.

Do you mean when fired, or when cycled by hand?
If it's when fired, you may have some kind of partial gas blockage what is restricting gas flow. What kind of gas block is installed? Is it straight, and installed in correct alignment with the gas port, taking into account a missing handguard ring if applicable?

OP said he tried the upper on another lower.

Yes, another lower with a much lighter buffer. Could just mean he's not getting enough energy to cycle the heavier buffer setup.

Originally Posted By thornejc:
I don't know if it is possible for you right now but the LMT Enhanced BCG fixes short stroking issues on a very consistent basis. It is designed to run in suppressed rifles but it takes care will take care of short stroking issues as well.

AFAIK, LMT does not recommend the "enhanced" BCG for anything other than a carbine gas 14.5 or 16" barrel when using full power ammo. It's specifically designed to help correct the excessive dwell of those configurations by delaying the unlocking sequence, which also helps with suppressor use and other overgassed rifle configurations. I can't fathom how it would do anything good for a rifle that is short stroking.


Yea... I did some more research and I think you are right. I had a friend that had a rifle that was short stroking and couldn't figure it out and threw another friend's LMT enhanced in and it fixed the problem so he bought his own and it worked flawlessly. I also was reading on another forum (M4Carbine) and a guy was talking about how it fixed his too. Probably should have taken a larger sample size because I looked into it some more and saw where some people's rifles were still SSing with the LMT enhanced. Thanks Gamma and good luck OP.
EdgecrusherXES_45
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Posted: 7/24/2012 2:26:27 PM
First off we need more info.

What kind of lube are you using are you using enough also?
What ammo are you using Tula or XM193?
Could be a combination of the two not enough lube and weak ammo. These are the two simplest things to check and remedy before you go onto other causes. Usually the simplest answer is the right one.
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007Kevin
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Posted: 7/24/2012 5:12:17 PM
Originally Posted By Gamma762:
Originally Posted By 007Kevin:
Originally Posted By Gamma762:
Originally Posted By DH2:
Well, the bolt does not go rearward enough to eject the round or strip off a new one. I know the bolt is in motion because I can feel it doing so.

Do you mean when fired, or when cycled by hand?
If it's when fired, you may have some kind of partial gas blockage what is restricting gas flow. What kind of gas block is installed? Is it straight, and installed in correct alignment with the gas port, taking into account a missing handguard ring if applicable?

OP said he tried the upper on another lower.

Yes, another lower with a much lighter buffer. Could just mean he's not getting enough energy to cycle the heavier buffer setup.

Originally Posted By thornejc:
I don't know if it is possible for you right now but the LMT Enhanced BCG fixes short stroking issues on a very consistent basis. It is designed to run in suppressed rifles but it takes care will take care of short stroking issues as well.

AFAIK, LMT does not recommend the "enhanced" BCG for anything other than a carbine gas 14.5 or 16" barrel when using full power ammo. It's specifically designed to help correct the excessive dwell of those configurations by delaying the unlocking sequence, which also helps with suppressor use and other overgassed rifle configurations. I can't fathom how it would do anything good for a rifle that is short stroking.


I forgot about the weight difference. So, he needs a lighter spring or buffer, or increase the gas.
DH2
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Posted: 7/24/2012 7:48:58 PM
[Last Edit: 7/24/2012 7:52:06 PM by DH2]
Originally Posted By strat81:
Are you sure you have the proper length/type buffer and spring for your particular receiver extension?

Disassemble the stock and look inside the receiver extension with a flash light. Does it look like the bolt carrier is making contact with the tube? A bent or misaligned receiver extension can cause those problems.



Buffer tube, spring, and buffer were all part of an A1 stock kit from Fulton armory. It is a rifle length spring and rifle weight buffer. I noticed no damage to the buffer tube after ~75 rounds of use. I'll be double checking all of those when able.


Originally Posted By countrygunner:
Does your gas piston system have an adjustment? Some of them have like 3 stages and maybe the stage you have it on won't cycle with a rifle length gas system. I'm sure the gas piston system is the issue if your sure the gas hole is lined up.



The Osprey piston is a non adjustable system. Checking the gas block is very high on my list of culprits, but because the upper still cycled on a different lower, I believe there is a separate primary issue.


Originally Posted By EdgecrusherXES_45:
First off we need more info.

What kind of lube are you using are you using enough also?
What ammo are you using Tula or XM193?
Could be a combination of the two not enough lube and weak ammo. These are the two simplest things to check and remedy before you go onto other causes. Usually the simplest answer is the right one.


Bolt carrier and piston are both fail zero coated. Presumably this means they do not require lubrication to function correctly. I'm not saying that the fail zero is some kind of panacea, but product as advertised does not require lube. Ammo was 115gr Silver state Armory 6.8 SPC.


Originally Posted By jaqufrost:
Sounds like it needs a little more gas. Alternatively you could put a spacer in the back of your rifle extension and put a carbine spring and buffer in.


One other thought, is the hammer binding on the back of the carrier while the trigger is pulled? You can test this by clearing the rifle, pulling the trigger, and while keeping the trigger pulled charge the rifle. It should move freely to the rear without binding.


I shall test the hammer for binding and if worst comes to worst I'll try the spacer.
Thank you delemorte for the membership!

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countrygunner
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Posted: 7/24/2012 9:01:32 PM
ammo should be hot enough coming from silver state. If the piston system isn't adjustable than it should cycle on both lowers. I would check for binding anywhere in the system and proper gas hole alignment. That's all it could be considering you put it on another lower and it cycled fine with a carine buffer and spring which is lighter than a rifle length.

So check the buffer tube, buffer, and spring to see it there is binding, check the bolt carrier and inside the upper for rubbing, and for god's sake oil that thing. I have had fail zero bolt carriers and NIB coated Glocks and while they are "slicker" that still need lube especially in a dirty gas system like an ar 15.
countrygunner
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Posted: 7/24/2012 9:04:13 PM
ammo should be hot enough coming from silver state. If the piston system isn't adjustable than it should cycle on both lowers. I would check for binding anywhere in the system and proper gas hole alignment. That's all it could be considering you put it on another lower and it cycled fine with a carine buffer and spring which is lighter than a rifle length.

So check the buffer tube, buffer, and spring to see it there is binding, check the bolt carrier and inside the upper for rubbing, and for god's sake oil that thing. I have had fail zero bolt carriers and NIB coated Glocks and while they are "slicker" that still need lube especially in a dirty gas system like an ar 15.