PDA

View Full Version : Short stroking on new upper help please...


AlliedArmory
03-01-2010, 10:21 PM
I went to ASR to try out my new upper/optic etc. It's a CMMG 14.5". Standard Carbine buffer and spring. I cleaned/lubed it very well when I first got it. Keep in mind I'm using the same lower half than before and never had any kind of issue with it other than some short stroking with Wolf ammo (but this was with my old upper).

Out of 8 mags, it had a FTF 4 times. Of course the brass was all dented. Also on a few occasions, the bolt wouldn't lock back on the 10th round.

Only thing I can think of is the ammo. But this is Federal XM193 5.56. I didn't have any other 5.56 ammo on me, so I couldn't test it further. Any other possibilities?

aplinker
03-01-2010, 10:31 PM
More info would be helpful...

In total you had 4 FTF out of 80 rounds with a brand new upper?

Where was the brass ejection (angle & distance)?

What mags?

Did you do the obvious - check for gas leaks and carrier staking?

FMJBT
03-01-2010, 10:34 PM
Check for gas tight integrity, look for carbon fouling around the gas block which would indicate a leak. Check the carrier key to make sure it's torqued down tight and properly staked too. If the gas block is mounted at a slight angle, it might also be choking off the flow of gas if the port in the block doesn't line up with the port on the barrel. If all that checks out, check to make sure the gas rings on the bolt don't have all their split ends lined up, allowing gas to bypass the seal on that end.

Josh3239
03-01-2010, 10:40 PM
Shoot it more, break in that gas port. Make sure you use 5.56mm.

If all that checks out, check to make sure the gas rings on the bolt don't have all their split ends lined up, allowing gas to bypass the seal on that end.

Myth. The AR runs fine with only 1 gas ring. Besides during all that shooting the gas rings rotate themselves anyway. Lining up the gas rings is a waste of time.

AlliedArmory
03-01-2010, 11:18 PM
to answer a few questions.

10/20 pmags build myself
not sure about the brass ejection angle.

carrier seems fine

i think there may be a gas leak at the gas block. check these pics below

i see some fouling around the gas tube and on the barrel.

http://farm3.static.flickr.com/2678/4400174523_afe50b008d_b.jpg
http://farm3.static.flickr.com/2792/4400939612_e8e178e8f7_b.jpg
http://farm5.static.flickr.com/4023/4400939036_051e024c6b_b.jpg

AlliedArmory
03-01-2010, 11:22 PM
gonna take off the rail right now to see further in

AlliedArmory
03-01-2010, 11:31 PM
ok got the rail off now. seems to definitely be a gas leak. os this normal fouling or excessive for only having 80 rds shot through it?

is this something I can fix myself? or must i take it to a smith?

http://farm5.static.flickr.com/4068/4400196887_b45ff8ed22_b.jpg

aplinker
03-01-2010, 11:55 PM
I don't see enough fouling there to say it's a leak.

I'm not a fan of the follower in 20rd PMAGs - they're not anti-tilt. I wonder if that's your issue.

You never answered: you had 4 failures total out of 80rds?

Honestly, 80rds isn't enough to say it's an issue. You need to run the rifle more.

Always check your brass (both where it's going and how it looks). You can learn a lot about how your rifle is functioning.

AlliedArmory
03-02-2010, 12:06 AM
I don't see enough fouling there to say it's a leak.

I'm not a fan of the follower in 20rd PMAGs - they're not anti-tilt. I wonder if that's your issue.

You never answered: you had 4 failures total out of 80rds?

Honestly, 80rds isn't enough to say it's an issue. You need to run the rifle more.

Always check your brass (both where it's going and how it looks). You can learn a lot about how your rifle is functioning.

yea. 4 failures out of 80 rds.

i'll clean it up and take it out again with different mags and see whats going on. ill try and put 200-300 rds though it

freonr22
03-02-2010, 12:10 AM
Is the scraping on the carrier above the tube normal? it almost looks like something is digging in
http://farm5.static.flickr.com/4023/4400939036_051e024c6b_b.jpg

aplinker
03-02-2010, 12:11 AM
That's what I would do. Definitely on the mags, too.

Watch for the indicators listed above, and try to describe each of the individual FTFs as well as you can.

Try shooting single rounds and counting % of lockbacks.

aplinker
03-02-2010, 12:12 AM
I don't think that's scraping - I think it's the carbon build-up from when the carrier separates from the gas tube.

Is the scraping on the carrier above the tube normal? it almost looks like something is digging in
http://farm5.static.flickr.com/4023/4400939036_051e024c6b_b.jpg

freonr22
03-02-2010, 12:16 AM
thank you. I didnt know they would get that build up so quick

pacrimguru
03-02-2010, 12:22 AM
there's a good chance it's the mags. try using different mags next time too.

AlliedArmory
03-02-2010, 12:24 AM
thanks guys. i guess i need to take a day off and hit up ASR :)

aplinker
03-02-2010, 12:31 AM
thanks guys. i guess i need to take a day off and hit up ASR :)

Yes, it's very important. You can't have a rifle that will not be reliable should a 9.2 earthquake hit LA this weekend and/or someone finally makes those zombies.

AlliedArmory
03-02-2010, 12:50 AM
Yes, it's very important. You can't have a rifle that will not be reliable should a 9.2 earthquake hit LA this weekend and/or someone finally makes those zombies.

very true. But I do have my 590A1 as a nice backup :)

I played enough Resident Evil to know you need to shoot them in the head