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View Full Version : 20" ar15 short stroking problems...


SocalShooterX
05-30-2011, 10:35 AM
Hey guys,
so last week I posted about taking my new 20" bcm spr out and having some problems, I cleaned it out and re adjusted the gas block and took it out yesterday and still had trouble.

Basically what's happenning:
rarely it wont eject the shell.
It doesn't lock back.
It will eject the shell but not strip a fresh round.
Occasionally the rounds when I manually strip them get caught on the feedramps which are starting to have marks from the bullets hitting them.
They are m4 feedramps and are aligned correctly.

Last night I took the gas key off and notice a lot of crabon around it and that when I put clp in it it leaked out around it, So I retightened it down as far as possible.
My only guesses on it would be,
Gas block misaligned, heavy buffer and comp reducing recoil too much to recycle, but I did try a standard buffer.
or the gas key was leaking...but I dunno.

I haven't had a chance to take it out since I readjusted the gas key.

Here's the specs,
BCM Ionbond stainless steel 20inch barrel 1/8
YHM folding front sight.
Magpul rifle length hand guard.
BCM upper and bolt.
Magpul ctr stock.
Leupold Mark AR 3x9 with mil dot and burris mount.
spikes tactical heavy buffer.


If anyone has any ideas please let me know!!

dieselpower
05-30-2011, 11:11 AM
several red flags here...
1) "20" bcm spr" & "Last night I took the gas key off" dont mix well...HOW did you remove the gas key? A BCM is Staked. If you removed the gas key at any time before this, then you must replace the gas key and bolts with fresh ones and properly assemble with high temp sealant... did you do all that?

2) heavy buffer = WHY? An SPR only needs a standard buffer.


***********or the gas key was leaking********** bingo!

I'll post the proper way to assemble and seal a Gas key in a minute or two. You NEED (MUST) buy new bolts if the old ones were staked at one time. Its best to ALWAYS replace them after you loosen them up though.

bartt
05-30-2011, 11:14 AM
I had similar problems when first running my AR. Turned out the ports in the gas block and barrel did not line up properly length-wise. I removed the gas block and could see the shadow on the barrel from firing it. The port on the gas block was too far down the length and was cutting barrel port in half, hence decreasing the pressure on the BCG, causing the short stroke.
My cure was to open the port on the inside of the gas block with a diamond burr in my Dremel. Slow and careful did the job. My Ar has never short stroked since.
HTH..

SocalShooterX
05-30-2011, 11:15 AM
several red flags here...
1) "20" bcm spr" & "Last night I took the gas key off" dont mix well...HOW did you remove the gas key? A BCM is Staked. If you removed the gas key at any time before this, then you must replace the gas key and bolts with fresh ones and properly assemble with high temp sealant... did you do all that?

2) heavy buffer = WHY? An SPR only needs a standard buffer.


***********or the gas key was leaking********** bingo!

I'll post the proper way to assemble and seal a Gas key in a minute or two. You NEED (MUST) buy new bolts if the old ones were staked at one time. Its best to ALWAYS replace them after you loosen them up though.

1) what do you mean buy staked? they came off with an allen key and they just unscrewed. But they may not have been sealed right and I'll have to reseal them.

2) i was using a Lower off a carbine and I was using the heavy buffer that was in it allready.

SocalShooterX
05-30-2011, 11:16 AM
I had similar problems when first running my AR. Turned out the ports in the gas block and barrel did not line up properly. I removed the gas block and could see the shadow on the barrel from firing it. The port on the gas block was too far down the length and was cutting barrel port in half, hence decreasing the pressure on the BCG, causing the short stroke.
My cure was to open the port on the inside of the gas block with a diamond burr in my Dremel. Slow and careful did the job. My Ar has never short stroked since.
HTH..


Hmm...I'll take a look at that. I noticed that when I draw lines on the fsb and mark it to line up perfectly the fsb is slanted. I'm %99 sure that the gas hole in the barrel is actually off to the right a little bit. coming from bcm it's unlikely. but it sure does look that way.

dieselpower
05-30-2011, 11:18 AM
Please go here and read this... YM BCGs (http://www.youngmanufacturing.net/stakekeys.php) They are very good BCGs and do not stake them.

TM9-1005-319-23, Chapt 3, para 3-5 is the US Military troubleshooting guide on gas key failures. Figure 3-9, page 3-25 starts the repair porcedures.
Do not disassemble the key and bolt carrier assembly unless the bolt carrier key is defective as
determined by inspection procedures described in section III, preceding.
1. Using socket wrench handle and tight fitting 1/8 inch socket head screw socket wrench attachment, remove
two carrier and key screws (1).
NOTE
The heads and part of the bolt carrier key may be ground off in order to remove bolt carrier key from
bolt carrier if carrier and key screws cannot otherwise be removed.
2. Remove bolt carrier key (2) from bolt carrier (3).
b. REPAIR
NOTE
Do not retorque carrier and key screws if staking marks do not indicate loosening screws.
Repair by replacing, torquing, and restaking carrier and key screws. Refer to the following reassembly procedures.
3-26 Change 5
ARMY TM 9-1005-319-23&P
AIR FORCE TO 11W3-5-5-42
c. REASSEMBLY
NOTE
Do not reuse old carrier and key screws
New carrier and key screws must be
used at assembly.
1. If disassembled, place bolt carrier (1) In vise
using vise law caps Install and position bolt
carrier key (2) on bolt carrier ( 1).
2. Install two carrier and key screws (3). Always use
new screws.
3. Use a tight-fitting 1 8 inch socket head screw
wrench attachment and an Inch-pound torque
wrench to torque the carrier and key screws (3) to
35 to 40 Inch-pounds (3 95 to 4 52 N m)
3-27
ARMY TM 9-1005-319-23&P
AIR FORCE TO 11W3-5- 42
3-9.KEY AND BOLT CARRIER ASSEMBLY (CONT.).
c. REASSEMBLY (CONT.)
NOTE
Field staking method will be used by field
units.
4. Use solid center punch and hand hammer to
stake the two carrier and key screws (3) In three
places.
FIELD REPLACEMENT STAKING
5. Reassemble rifle, refer to page 3-77
CAUTION
If blanks are used, blank firing attachment (BFA) must be attached
NOTE
If the bolt carrier key is replaced, three to eight rounds of blank or ball ammunition must be fired to
ensure a seal is created. Manual operation of the rifle may be required. If blank ammunition is
utilized, M16A2 Blank Firing Attachment must be adapted
3-28

I would also use the sealant that YM uses and NOT stake. Its your call on what you do.

Hope this helps.

dieselpower
05-30-2011, 11:25 AM
1) what do you mean buy staked? they came off with an allen key and they just unscrewed. But they may not have been sealed right and I'll have to reseal them.

2) i was using a Lower off a carbine and I was using the heavy buffer that was in it allready.

please read up on staking. The gas key screws were loose. either someone screwed with it or the factory didnt assemble it proper.

you see there are many people who hate the fact some manufactures do not use a hammer and chisel to crush the bolt heads making it nearly impossible for them to move. Some of those people actually loosen the gas key bolts before shipping to you...as a way to get others to hear about your troubles and scare them into buying a higher priced one..or another brand. I am not saying that is what happened to you...could be the guy at the factory didn't torque down the bolts. You just need to understand this is the pro-life vs pro-abortion debate in the AR15 community...staked or not staked. Its a freaking ugly debate.

go to my link or search TM9-1005-319-23. go to chapter 3 and page 3-25 and start reading. It has good pictures too.

notme92069
05-30-2011, 11:34 AM
I would really look at changing the buffer. I had to go to a Spikes buffer but I have a carbine shooting 124gr 7.62 x 39. You shouldn't need it with a rifle shooting 55 gr .223

dieselpower
05-30-2011, 11:41 AM
I would really look at changing the buffer. I had to go to a Spikes buffer but I have a carbine shooting 124gr 7.62 x 39. You shouldn't need it with a rifle shooting 55 gr .223

Id do both. fix the gas key and lighten up the buffer a bit.

bwiese
05-30-2011, 12:20 PM
What worries me is the individual started taking crap apart before reading the USGI TM.

He may well have screwed up more things than he could fix.

I see a new gun + a non-chrome-lined barrel (chamber).

I also see a 'heavy buffer' - gawd knows why, did the OP order it because it felt good?

For a 20" A2 rifle, the regular buffer Works Just Fine. Don't fix what's not broken.

Milspec AR bolt carriers have staked gas keys. You shouldn't have been able to remove the key without grief/force.
If your gas key is not staked, it should be.

[Benchrest match guys run under a different set of rules, and Young's Mfg carriers are not for everyday use.]

If you want a 100% operational AR as long as you can, you need a staked gas key..

Also 80+% of consumer AR failures are tied to poor lubrication and lousy magazines (apart from using wrong springs in wrong places).

Go lube the damned gun using CLP *FIRST*, before you start diddling with it. Make it 'wet', wipe down a bit after.
Also, use the Chamber Brush vigorously to clean the chamber. There could be old crud from test firing or it could be a tad rough (+ machine debris) in there.

Also - I assume you're using a BulletButton maglock - a bad mag that sits a little high can cause 'carrier drag' on both its rearward and forward motion and not extract well nor feed well, leading to the incorrectly-named 'double feed' (i.e, extracted round and new round trapped in upper).

And don't mess around with fancy PMag crap when you're trying to get a new gun to work - get the 10rd clone of a USGI mag and work from there.

notme92069
05-30-2011, 12:27 PM
I see a non-chrome-lined barrel (chamber) and a new gun.

What worries me is the individual started taking crap apart before reading the USGI TM.

He may well have screwed up more things than he could fix.

80+% of consumer AR failures are tied to poor lubrication and lousy magazines.

Go lube the damned gun using CLP *FIRST* before you start diddling with it. Also, use the Chamber Brush vigorously to clean the chamber.

I would agree with polishing the chamber. I did this also as I had extraction problems with the new AR

SocalShooterX
06-01-2011, 7:54 PM
Hey guys! thanks for all your input,

Here's the update,
re-installed the gas key with new screws and the bcg is fine but the guns not working.

Still had short stroke issues, this time it would eject every round but wouldn't lock back or catch the next round, I forgot I had taken the stock buffer out when i went to the range so i didnt get to test it with the light buffer.

If you guys have any other ideas and/or a way to check if the fsb is lined up perfectly with the barrel I would greatly appreciate it.

Thanks in advance!
to address some earlier comments.

The reason I have a heavy buffer in it is that it's the lower off my carbine, it's not running a A2 style stock and buffer. I completed the upper and took it off the carbine.
not the best idea but it worksish.


Additional notes.
The rifle would cycle fine when shooting the hornady 75gr trainning ammo with steel casings.
I dont know if that gives you any clues to what the problem is but thought i'd throw it out there. Anything lighter than that it jams.

Thanks again.

Hoop
06-01-2011, 8:46 PM
What is the other brand ammo you are using (the stuff that doesn't work?)

SocalShooterX
06-01-2011, 9:00 PM
What is the other brand ammo you are using (the stuff that doesn't work?)

The ammo I just used was winchester 5.56 55 gr ammo.

What else didn't work-
Hornady tap 62 gr.
Federal premium super match 69 gr.
box of 62 gr reloads.
Federal 5.56 55gr.

Hoop
06-01-2011, 9:20 PM
Wrong buffer + spring or gas leak/gas port too small are the only ideas I have.

SocalShooterX
06-02-2011, 9:09 AM
Could it have something to do with the bolts gas rings?

I don't have much experience with gas system bcgs. Since my
Other ar is a piston system so I couldn't tell.

dieselpower
06-02-2011, 12:09 PM
I think this is another BCM gas port issue. Third time we have seen this. Its a SS 1:8 20" that is having issues with lighter (shorter) rounds. the gas port might be too small. This was researched by others who had this issue, then reported back to us what they had found. From what I remember its normally only seen with under 55gr and cheap ammo.

From what you are now telling us, the only thing you can do is go with a semi-auto BCG or C-type BCG and a light buffer. see if that doesn't shave off enough mass to get the BCG to move back far enough to pass the bolt catch.

check the gas tube for a slight bulge in it where the gas key locks up. that slight bulge helps seal the gas key and tube. I have seen were a mis-alignment and worn bulge caused issues. check the end of the gas tube for excess carbon build up...maybe the FSB is off and bypassing slightly.

if all of this checks out... I would suspect the gas port is too small and not proper for a SS 1:8 20" gas system..

stevie
06-02-2011, 12:23 PM
Are you sure the gas block is aligned properly? Sounds like you built this yourself.

AR-15 Rep
06-02-2011, 1:08 PM
I would just do some checks on the bcg, make sure it rides smooth on the gas tube. You can pull the bolt out and see how it feels ( remember the bcg only travels flush with the upper across the back ). You could check the other things members have suggested but I wouldn't get too far into it. I am sure BCM is aware of issues and should take care of them.

SocalShooterX
06-02-2011, 8:39 PM
Hey guys! thanks for input!
Especially dieselpower.

I realigned the fsb and checked it with a pipe cleaner and took it out to the range today.

With the lighter buffer I could get the ammo to cycle correctly. With my magpul 10/30 mags the gun wouldn't lock back, with my c mag 10 rnd stubby it would lock back.
I switched to hornady tap 62 grain and both mags would lock all the way back.

sometimes the 55 gr with the magpul pmag would lock back on the bolt carrier but not the bolt itself. Still seems like slight short stroking.

Mail Clerk
06-03-2011, 6:56 AM
Hey guys! thanks for input!
Especially dieselpower.

I realigned the fsb and checked it with a pipe cleaner and took it out to the range today.

With the lighter buffer I could get the ammo to cycle correctly. With my magpul 10/30 mags the gun wouldn't lock back, with my c mag 10 rnd stubby it would lock back.
I switched to hornady tap 62 grain and both mags would lock all the way back.

sometimes the 55 gr with the magpul pmag would lock back on the bolt carrier but not the bolt itself. Still seems like slight short stroking.

Check your magazine spring and see if it may be too weak. Your issue could be jut a timing issue

Mail Clerk

SocalShooterX
06-04-2011, 9:22 AM
Check your magazine spring and see if it may be too weak. Your issue could be jut a timing issue

Mail Clerk

How I would check to see if it's a week spring?

EvolutionGSR
06-04-2011, 6:06 PM
Could it be the ammo? I just took a new upper out today. I have the same issues of an occasional bolt not locking back on the last round, and an occasional not picking up the next round out of the mag. It was happening on 10/20 pmags and my old 10/20 bushmasters did it once. When I shot AE 62 grain out of it, it never happend. It happed very few times with Prvi 62 grain, and mostly on Fiocchi 62 grain. Someone also tried Federal .223 walmart value packs and xm193 out of it and it ran fine. I'm thinking my gun likes federal, or the fiocchi.stuff might be underpowered? Im trying to figure my problem out too. Im hoping the cheap fiocchi was the problem and am going to get some more cheap ae and federal and have a range session.

dieselpower
06-04-2011, 7:14 PM
How I would check to see if it's a week spring?

open the rifle up and look at the bolt catch make sure it moves freely.
insert an empty magazine and watch the bolt catch make sure the magazine follower pushes up on the bolt catch.

r6raff
06-04-2011, 8:45 PM
Occam's razor Bro. You were checking the gas key and stuff when, before doing anything you should have realized you were using a heavy carbine buffer with a 20" rifle length gas system... that should have been the first thing you checked before potential screwing up other things. That and mags. I troubleshoot things for a living and 99% of the time it is the stupid, most basic issue that causes the trouble... when I hear hoof beats I think Horse, not Zebra.

Good you got it figured out though, atleast you didn't replace every part of the rifle chasing a buffer/magazine issue, I knew a guy who did that, bought a new BCG, GasBlock etc, and ended up being a bad Magazine lol. When I ask ed him why he didn't check the mag first he said "The issue seemed to be worse than what a simple magazine could mess up." I laughed and wished him luck in life... hes gonna need it :43: I was kidding him of course. I told him, that on the bright side he practically has another AR in parts in his safe lol

PEBKAC
06-04-2011, 10:40 PM
20" bcm spr

F =

spikes tactical heavy buffer.

m *

short stroking problems...

a

Sounds like that m needs to be reduced to increase that a. ;)

SocalShooterX
06-04-2011, 11:10 PM
Occam's razor Bro. You were checking the gas key and stuff when, before doing anything you should have realized you were using a heavy carbine buffer with a 20" rifle length gas system... that should have been the first thing you checked before potential screwing up other things. That and mags. I troubleshoot things for a living and 99% of the time it is the stupid, most basic issue that causes the trouble... when I hear hoof beats I think Horse, not Zebra.

Good you got it figured out though, atleast you didn't replace every part of the rifle chasing a buffer/magazine issue, I knew a guy who did that, bought a new BCG, GasBlock etc, and ended up being a bad Magazine lol. When I ask ed him why he didn't check the mag first he said "The issue seemed to be worse than what a simple magazine could mess up." I laughed and wished him luck in life... hes gonna need it :43: I was kidding him of course. I told him, that on the bright side he practically has another AR in parts in his safe lol


Yeah I tink from now on, i'm just gonna check with the experts on here before I do anything stupid, definitly learned my lesson. and I'm definitly someone who would have replaced everything, I was allready looking at getting a new carrier group. haha. But i suppose with time and the all the crap I get from the guys online i'll learn to get by without Effing to much stuff up. :D

Thanks again for all your help.

jumbopanda
06-05-2011, 3:04 AM
Use either a standard carbine buffer, or better yet switch to a standard rifle stock and buffer assembly and report back. I've also heard good things about the Vltor A5 stock, but that might be a bit expensive.

qaz5109
06-05-2011, 10:27 AM
i would try the upper on a diffrent lower to determine if the upper is the problem or if its the lower start there.My buddy ran into this same [problem turned ot to be a spring in the trigger assembly.