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View Full Version : AR not locking back after last round.


MKMS
07-05-2012, 6:05 PM
Hey calgunners,

I've taken my first build out to the range twice in the last two weekends and I'm having a problem.
After the last bullet, the BCG does not rack back. It does not happen all the time but occasionally. I've been reading about what causes it, but I am not too sure.

I've tried three different types of ammo:
MFS
Tula
Federal XM193
All had the same problem.

When I ran it wet. The problem went away for a few, but I don't know how much I should put.

I also think it could be my buffer kit. I bought the kit from a gun show in SF. It was a hasty buy and I regret it. I've been reading that that could be the culprit too.

What do you think?

Here is the specs:
PSA 16" LW Mid HF
Delton Lower
RRA LPK
No name Stock kit.

Josh3239
07-05-2012, 6:13 PM
Any markings on the buffer?

ke6guj
07-05-2012, 6:20 PM
try different mags.

how loose is the bolt catch in the receiver? I've seen some where the bolt catch drags in the slot and needs to have the sides polished slightly to loosen it up enough to move freely.

MKMS
07-05-2012, 7:15 PM
What markings do you mean? Sorry I'm new and I don't know what to look for.

I don't think its the Bolt Catch because it does move freely and I was testing that part. I initially thought it was that too.

Josh3239
07-05-2012, 7:17 PM
Ke6guj made a great point, how many mags did you try? Like an markings like an "H".

ke6guj
07-05-2012, 7:20 PM
I don't think its the Bolt Catch because it does move freely and I was testing that part. I initially thought it was that too.

remove the upper from the lower and watch the bolt catch as you insert an emply magazine into the well. As the mag is about ready to lock into place, you should see the mag follower start pushing the bolt catch up. Does it fully push the bolt catch up when the mag is latched?

sharxbyte
07-05-2012, 7:32 PM
any broken lugs on your bolt?
http://i208.photobucket.com/albums/bb197/mugglle/gunz/IMG_20120514_192458.jpg

onegtalon
07-05-2012, 7:37 PM
Do you have a Magpul BAD lever? That can cause the same issue as well.

MKMS
07-05-2012, 7:41 PM
Ive only used P-mags. Yes, I do see the H. What does that mean?

I took out the lower and inserted the mag. It does go all the way up when its inserted in.

No, I have a new BCG so nothing wrong with it yet. (Hopefully never)

MKMS
07-05-2012, 7:44 PM
Do you have a Magpul BAD lever? That can cause the same issue as well.

No, I don't have one. Was thinking about getting one, but I don't know now.. :confused:

chrisf
07-05-2012, 7:46 PM
You and I both brother.

SocomM4
07-05-2012, 7:50 PM
I'd replace the whole receiver extension kit with a name brand one.

xpbprox
07-05-2012, 7:54 PM
Get a name brand buffer spring and buffer then lastly get a named buffer tube.

If you know someone with another ar, mate your upper on to their lower and see how it functions and cycles

Thordo
07-05-2012, 8:45 PM
We've seen this a ton of times with PMAGs. Before you go swapping out perfectly good parts. Test it with a USGI mag. If you are local to SSF and not sure what to do, Bring it in to our shop with your mags.

Thordo

ScottsBad
07-05-2012, 9:08 PM
With the rifle assembled, place an empty magazine in the mag well. Pull the charging handle all the way back and see if the bolt stays back. Try this on all your magazines (empty).

If the BCG does NOT stay back then the problem is in the bolt catch or the magazine. Make sure the bolt catch is engaging the magazine properly. Make sure the bolt catch moves freely.

If the BCG does stay back on all of your magazines then it could be under gassed, or a problem with the buffer tube, buffer spring and/or the buffer.

Usually if the problem is under gassing or a buffer problem you will experience other problems as well such as a failure to feed and maybe a failure to eject.

Most folks don't think the buffer tube/spring/buffer is very important, but it is very important.

Most likely it is your magazines.

Chaos47
07-05-2012, 9:12 PM
Yes, I do see the H. What does that mean?

Means its a "Heavy" Buffer.
Its one step heavier then a regular Carbine buffer.
People like to run H buffers but in a lot of cases its not necessary.
Could this be your issue? I am not sure, I'll leave that to others to guess

MKMS
07-05-2012, 10:09 PM
I was afraid I might have to change the whole kit. That is what I get for getting a no name brand. That wont happen again!

I think a buddy of mine has a USGI mag so I'm going to have to wait until we hit the range again. Thank you for the offer, Im not close to the area but if I get some free time, Ill see if I can roll on through!

Ya, when I rack back, the bolt catches when an empty P-Mag is inserted.

Sorry, let me clarify. I actually dont have an H. I thought you meant like an H when it racks back and some grease forms. It formed an H when I did that. (Bone headed mistake)

vintagearms
07-05-2012, 10:23 PM
My guess would be mags or buffer. The ammo could cause this but you said you tried Federal XM193 so im my mind that would be ruled out. Im going to suggest a good quality usgi mag with a green or magpul gray follower.

mif_slim
07-05-2012, 11:04 PM
Check your gas block before doing anything else. If its not aligned you'll get shortstrokes too.

Yerman
07-06-2012, 12:03 AM
It's the PMAG's...Guaranteed... http://www.youtube.com/watch?v=PUpqHeb_8vI&feature=plcp

Replace them with a bunch of these...http://www.riflegear.com/p-345-stag-arms-10-round-30-magazine-223556mm.aspx

04_e46
07-06-2012, 12:13 AM
had a friend with the same problem, he replaced his buffer tube, and buffer spring and it works properly now.

MKMS
07-06-2012, 6:15 AM
Im not so sure its the mag. I tried what the guy did in the video and mine went up the whole time.

How would I check the gas blocks if you don't mine me asking.

I believe it really is my buffer kit. I think I am just going to have replace them. I got it at a gun show from a person who looked like he got no business throughout the day. DAMN my impulse buy!! I got to over zealous about my 1st build.

Mail Clerk
07-06-2012, 7:16 AM
MKMS,

What might be happening is during recoil the follower in the mag might be wobbleing past your bolt lock lever. I'd reinsert the mag and on the tab look for scratch marks that might indicate this is happening.

I too am guessing that your spring/buffer is too heavy and during recoil your bolt is moving way too fast therefore not causing the follower not to trip. In my mind it's basically a timing issue. It's simular to issues happening to many 45 auto pistol gurus.

Mail Clerk

killathrilla
07-06-2012, 7:26 AM
...

ScottsBad
07-06-2012, 7:40 AM
MKMS,

What might be happening is during recoil the follower in the mag might be wobbleing past your bolt lock lever. I'd reinsert the mag and on the tab look for scratch marks that might indicate this is happening.

I too am guessing that your spring/buffer is too heavy and during recoil your bolt is moving way too fast therefore not causing the follower not to trip. In my mind it's basically a timing issue. It's simular to issues happening to many 45 auto pistol gurus.

Mail Clerk

I'm not sure I agree with this. A heavy buffer/stiff spring will slow cycling. The heavy buffer will keep the bolt locked a little longer and with a mid-length gas system the entire system should cycle more slowly. If the spring is too weak the system could cycle too quickly and bounce the bolt, over gassing could be a problem too. If the spring is too heavy and/or the buffer is too heavy OR if the system is under gassed you might get short cycling, but that would also show up as failure to feed.

Anyway, If you think it is the buffer...

JUST GET THIS.
http://www.laruetactical.com/mil-spec-receiver-extension-kit


But I would try it with a good USGI magazine first.

mif_slim
07-06-2012, 8:24 AM
To check the gas block, you look if its aligned with the gas port. To do that it depends on your gas block design, but its their hex, slip on or Philip type. Loosen those and slip the gas block off. Before doing this mark the BG and a point of the barrel so you can align it up again. If the gas block is not aligned correctly you will get short strokes like your describing.

Check this first before buying any mags to test or all the other trouble. At least this ones free.

sseric75
07-06-2012, 9:32 AM
Your Buffer is too heavy. The bolt carrier is not going back far enough to lock the bolt. I bet you your issue will be fixed if you use a carbine buffer.

Josh3239
07-06-2012, 7:39 PM
Your Buffer is too heavy. The bolt carrier is not going back far enough to lock the bolt. I bet you your issue will be fixed if you use a carbine buffer.

That is what I was leading to. Have experienced that problem before.

Dhena81
07-06-2012, 8:08 PM
20 round Pmags have been known to have issues though I can't comment with 100% faith since I don't own any. The Pmag 30's are the best mags money can buy better than NHGMT mags w/ magpul followers IMO. The BAD lever doesn't mess with locking back in any of my AR's and I have one with around 8k rounds through the same AR with one installed since it was NIB.

I think it's either the buffer spring combo, your gas port diameter is to small, your gas block/barrel seal, carrier gas key leakage, or gas rings on your bolt. Your most likely short stroking so your either over sprung or you have issues with your gas system.

Prc329
07-06-2012, 8:44 PM
20 round pmags are know to have that issue. They use a different follower then the 30 rounders. It's not the same anti-tilt design. I have 6 10/20 pmags and 1 has this issue.

tradecraft
07-06-2012, 8:46 PM
Sent you a PM if you want to try a lighter buffer.

Rattlesnake6.8
07-06-2012, 9:42 PM
I had the same problem on my first build. I thought it was the buffer, spring or pmag. Switch the parts and same problem.. Lube the bolt catch and bcg very good. Viola! Problem solved. The littlest thing can be on top of your nose, dont over look.

sigstroker
07-06-2012, 10:57 PM
He has no functioning or feeding problems. Doubt if the gas system or buffer or spring are causing it. GI mags are the easiest to try.

Mail Clerk
07-07-2012, 5:02 AM
Like Rattlesnake6.8 said...try what he did and perhaps things will smooth out for you.

Mail Clerk

MKMS
07-07-2012, 7:37 AM
Thank you guys for all the suggestions. I'm going to make a check list and try to see what is really causing it. I just need to find some range time in my schedule.

Rattlesnake6.8, looks like you might have a point. When I did lube up the ar, at the range, it did go away and was even taking Tula without a problem. My question is how much do you have to put?

Thank you guys all again!

B W E
07-07-2012, 7:29 PM
The buffer spring is too long..... Cut it down an inch or get the shorter one.

Lexustech48
07-07-2012, 7:54 PM
@MKMS Here is a link to a maintenance thread over @ ar15.com:

http://www.ar15.com/forums/t_3_7/548967_AR15_LUBE_POINTS.html

too lazy to hyperlink it. =)

gemini1
07-07-2012, 9:24 PM
Buffer spring too long? are there different sizes of carbine length buffer spring?
Cut it down an inch, and you risk the buffer slamming hard at the rear end of the tube.
OP just as you said, the problem disappears when its oiled, then just oil it. It does not need to be dripping wet, a couple of drops is more than enough. If you're shooting a thousand rounds on a range trip, might as well bring the gun oil along, and apply as needed.

B W E
07-08-2012, 12:03 PM
Buffer spring too long? are there different sizes of carbine length buffer spring?
Cut it down an inch, and you risk the buffer slamming hard at the rear end of the tube.
OP just as you said, the problem disappears when its oiled, then just oil it. It does not need to be dripping wet, a couple of drops is more than enough. If you're shooting a thousand rounds on a range trip, might as well bring the gun oil along, and apply as needed.

Well, there are certainly different lengths of buffer springs, correct? He did say he bought it on a whim at a gun show. Perhaps he has a retractable stock ( we dont know) with a standard buttstock buffer spring.

This is the identical problem my buddy had a couple weeks ago. Using PMags, his bolt would nt lock to the rear. He tried my standard mags, same problem. Just for the heck of it, when we were leaving we lowered the tailgate and laid our guns out. Both all stag, both MagPull MOE stocks. We removed our buffer springs, and mine was an inch or so shorter. We put my buffer spring in his gun, and everything worked fine. Put his in mine, bolt would not lock back.

ScottsBad
07-09-2012, 4:49 PM
Your Buffer is too heavy. The bolt carrier is not going back far enough to lock the bolt. I bet you your issue will be fixed if you use a carbine buffer.

If it is an H buffer and a standard spring (assuming the spring is good) the rifle should cycle reliably on a mid-length (if maintained properly) unless it is under gassed, then it might short cycle, BUT then you would get other problems like FTF.

So, it doesn't add up very well. In any case, I learned these lessons the hard way. You gotta buy good parts if you want your rifle to be reliable. There is no way around it.

You don't have to buy gold plated stuff, just good quality stuff.

You can buy a good quality spring from Wolff for $10-15 bucks.

vliberatore
07-09-2012, 5:12 PM
It's the PMAG's...Guaranteed... http://www.youtube.com/watch?v=PUpqHeb_8vI&feature=plcp

Replace them with a bunch of these...http://www.riflegear.com/p-345-stag-arms-10-round-30-magazine-223556mm.aspx

^This.

My 30rd Pmag works fine. When I use my 20 rd Pmag it won't lock back.

MKMS
07-24-2012, 5:39 PM
I finally got to the hit the range today and it shot flawless. I guess it was really simple. I just had to run it wet before I started my session. I'm glad I didn't have to buy any new parts. Thanks everyone for the help and suggestions.

Besides that, I also got to try out my eotech xps2. I think I got it sighted in, but iono if its right. I was hitting around the bullseye at 50 yard while occasionally hitting dead center. Sitting down, is it always suppose to hit dead center?

DR1VEN
07-24-2012, 7:52 PM
I had the same problem on my first build. I thought it was the buffer, spring or pmag. Switch the parts and same problem.. Lube the bolt catch and bcg very good. Viola! Problem solved. The littlest thing can be on top of your nose, dont over look.

Was going to say this^^^ was dead on...always fall back on K.I.S.S.

No need to go running around spending money on parts before checking basics.

I ran into this same issue a week ago. Assuming your AR is a DI system keeping it wet is imperitive. All that carbon can gum up the works with as little as 200-300 rounds from a fresh cleaning. The H-Buffer without more than 2000 rounds thru(break in point) can still eject brass and strip the next round without other problems occuring when not fully being broken in. That little bit of carbon build up it just enough for the full tension in the newer H-Buffer to reverse to strip right before lock.

dirty and underpowered loads will excellerate the problem sometimes.(I was running .223 factory reloads)

if it happens again, a quick spray in the quick lube holes of the Bolt Carrier Group and running the charging handle 10-15 times should do the trick without even field stripping it. (wipe away excess)




I finally got to the hit the range today and it shot flawless. I guess it was really simple. I just had to run it wet before I started my session. I'm glad I didn't have to buy any new parts. Thanks everyone for the help and suggestions.

Besides that, I also got to try out my eotech xps2. I think I got it sighted in, but iono if its right. I was hitting around the bullseye at 50 yard while occasionally hitting dead center. Sitting down, is it always suppose to hit dead center?

I sight in at 25 yards with .223. Run a 5 round group to really see where your shooting accounting for any of your own inconsistency to hold zero on target.(3 rounds not enough to get a read including our own variables)

sight zero at 25yards = zero again at 100yards depending on load and bullet.

small aiming adjustments from there will end up zero at different yardage.

the EO tech holds zero very well....scratch that....EXTREEMLY well.(love my XPS)

Take a class if you havent already.... immensely invaluable.

I recommend the guys at Falcon Ops if in southern CA....one of the best investments I have made to date.......HUGE amount of BANG for the buck(pun intended:D)

Happy Shooting...:gunsmilie:..... and KEEP IT WET

Yerman
07-24-2012, 11:59 PM
sight zero at 25yards = zero again at 100yards depending on load and bullet.



Sure about that? That seems like a pretty heavy bullet.

http://www.calguns.net/calgunforum/showthread.php?t=484096

SuperSet
07-25-2012, 8:49 AM
I'm hoping that he means he starts at 25Y to get an approximate zero and then zeroes again at 100Y. Some guys like the 100Y zero (like DeFoor and Howe) since you're always low. I prefer the 50Y zero since it shoots flatter.
The 25Y zero is a definite no-go from my experience. You're going to be shooting high a lot.

DR1VEN
07-28-2012, 4:45 PM
Sure about that? That seems like a pretty heavy bullet.

http://www.calguns.net/calgunforum/showthread.php?t=484096

lol...sorry...ment 50 and 200(just about anyways.more like 212)...good catch. my bad.

good thing about CG...some one will always catch it.:D

teach me to post advice after being up 17 hours...lol