**FIXED**2nd opinion on bolt catch problem

[dlxcupid]

I might know the answer to this but I just wanted a 2nd opinion from you guys.

I just finished my AR15 build, I went to shoot it yesterday and the bolt doesn't catch after the last round is fired. But when I manually cycle the bolt back on an empty mag, it functions normally and holds the bolt back.

Here are the specs:

POF Gen 3 lower
JP lpk
Wilson Combat TTU trigger
Larue Stealth 16" upper
Magpul furniture: UBR, MIAD
Slash 6.5oz Heavy buffer with Wolff power spring
PMAGs

Now I got 5 different PMAGs to try and they all do the same thing. I'm thinking the heavy buffer is the culprit. The bolt catch finger is protruding out to the follower and nothing's sticking. I doubt it's a gas issues with a Larue upper but who knows. What do you guys think?

edit:
Ammo used
xm193, xm855, Prvi 69gr, Black Hills 75gr


<span style="text-decoration: underline"><span style="font-weight: bold">**UPDATE**</span></span>

<span style="color: #FF0000">Ultimately a regular standard buffer spring fixed it. At first I just replaced the buffer spring and kept the 6.5oz buffer on, probably 1 out of 10 mags, it wouldn't catch after the last round. I then used a Daniel Defense T2 4.3oz buffer and I shot about another 7 mags and it was functioning properly so far. I ran out of ammo so I can't say. The buffer spring definitely fixed the problem.</span>

 

[pawprint]

Re: 2nd opinion on bolt catch problem

I agree, however; before I made any changes I'd check ammo. A heavier bullet/slower powder may make the "problem" GO AWAY. What's your load? I'd suggest your best 69SMK/Varget load-good luck! Please post back the "cure".

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

I don't reload YET, I edited the post and added the ammo I shot it with. Before anyone goes crazy and asks why I chose the heavy buffer before even trying a regular buffer, I talked to Clint over at heavybuffers.com about my build and it's what he recommended. I didn't think twice about it.

 

[Sebben]

Re: 2nd opinion on bolt catch problem

Sometime when I cycle my weapon manually with an empty mag the follower of my P-mag will tilt forward causing the bolt catch finger to rest behind the follower. Like this.

 

[bm11]

Re: 2nd opinion on bolt catch problem

I had the same issue in a Larue OBR after switching to a carbine length stock.

What ended up being the case is that the longer AR-10 length buffer I had couldn't travel far enough into the AR-15 spec carbine tube (my parts supplier shipped me the WRONG item.) So it wouldn't hold back on the last round. It would hold back on an empty mag when cycled manually, BUT it turns out it was the follower catching the bolt and not the catch.

I would look into the length of your buffer.

 

[ORD]

Re: 2nd opinion on bolt catch problem

That combination of the HSS buffer/Wolff XP spring works very well on suppressed rifles/carbines and on the "larger" AR-15 based calibers, but I don't know about it for "regular" shooting with factory .223 ammo. If Clint says it should work...it SHOULD work.

If you have an extra normal power spring sitting around, you might give it a try and see if that gives you the little extra "boost" you need to achieve 100% reliability on LRBHO.

 

[TonyAngel]

Re: 2nd opinion on bolt catch problem

I'm not a Larue fanboy, but I have to acknowledge that they build good stuff. I doubt it's the upper.

To be honest, I don't know and have never dealt with Clint or heavybuffers.com, but when you call a place called heavybuffers.com and ask if you need a heavy buffer, I can take at wild guess at what they're going to tell you.

Personally, I don't just go with a heavy buffer right from the get go and I never use a buffer spring heavier than milspec. I can see the wisdom of using a heavier than standard buffer to smooth things out a bit, but have never seen any benefits from going with a heavier spring.

I really don't remember the specs on the upper that you are using, but isn't it a 16" rig with a mid length gas system? Mid length gas systems have a pretty short dwell time and operate at pressures a good bit lower than a carbine length system. The really heavy buffers are more suited to carbine gas systems and just aren't needed with a mid length gas system. I wouldn't go heavier than the equivalent of an H2 buffer (around 4.5 oz., I think).

I think that your rifle is just way over sprung with about two oz too much buffer weight.

What is your ejection pattern like? Is it throwing the brass behind you at around the 4:00 or 5:00 position?

 

[sinister]

Re: 2nd opinion on bolt catch problem

Drop the Wolff and use the standard spring.

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

Sebben - no, the finger always rests on top of the follower.

bm11 - I've got a LR308 with PRS setup and the buffer on my AR15 is definitely shorter so I'm pretty sure it's the right one.

ORD - I was forewarned about this situation but never took it into consideration since Clint has a fairly good reputation on the web at least. I don't have any spare parts lying around since this my first build and my other AR is a LR308 with rifle length gear.

TonyAngel - Can't really comment on ejection pattern, it's raining it's ass off here so my only options was a local indoor range with a 3ft wide lane. If I had to guess, yes I think it's the 3:00 - 4:00 position since I'm lefty shooting a right handed AR.

Just placed an order with Palmetto for some ammo, picked up a regular carbine buffer with carbine spring and a DD 4.3oz buffer while I was at it. Will update if problem is fixed. In the meantime.....GUN PORN!!

How it all began:
http://www.snipershide.com/forum/ubbthre...156#Post2462156

 

[TonyAngel]

Re: 2nd opinion on bolt catch problem

Don't you just love that UBR? It's heavier than most, but goes a long way to balancing things out. I think it actually makes the rifle FEEL lighter when carrying it.

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

yea I absolutely love it! it is heavier on paper but it really balances out the rifle as a whole. This thing is a pig sorta, 10.5 lbs with optics and around 11 lbs with a full mag, but it's really balanced and shoots like a dream. 200 flawless rounds so far. Haven't really shot it out to 100 but at the indoor range, I was shooting really tight groups with xm193 @ 25yds shoulder fired and being drugged up on cold meds.

 

[KTDLS7]

Re: 2nd opinion on bolt catch problem

If the buffer/spring replacement does not fix the lock-back, ensure the correct bolt catch spring was installed. Too strong spring may function manually, but not function when firing.

Kevin

 

[thinwater]

Re: 2nd opinion on bolt catch problem

If the bolt catch misses the follower when you have the upper off, then no amount of changing springs, buffers etc... will fix this. There are two things to check. One, make sure the mag well is centered in the lower. If it was Milled/EDM/Broached off center the mag will be off center and the follower will miss the bolt catch.

If the mag well is centered then the hole in the side of the receiver that the roll pin goes through that holds the bolt catch in is drilled to far to the "Left" or outside of the receiver. If it is to far to the left, the bolt catch will be to the left also and miss your follower.

I had to really work on this issue when I started making billet .308 receivers so I have learned this the hard way.

You may be able to use the receiver by using an AR 10 bolt catch, assuming that you can get to the roll pin in that receiver and get it out. Some billet receivers use a blind hole and the roll pin cant be removed. The AR 10 blot catch has the little tit that the shell follower hits more to the right of the bolt catch due to the thicker AR 10 receiver. It is only a couple of bucks and would be worth trying if nothing else works.

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

Thinwater - if you're talking about the finger on the catch, yes it does sit on top of the follower like I had said few posts ago.

 

[thinwater]

Re: 2nd opinion on bolt catch problem

It looks off to the left to me but looks like it should still work. I would make sure it works freely and that the spring is not to tight (Could be caused by the hole not drilled deep enough if he spring is correct).

Here is one I just took a pic of with an orange follower.

Follower picture

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

it moves freely with not too much effort, less effort than pressing the mag release button.

 

[50-140]

Re: 2nd opinion on bolt catch problem


Magpul recommends an H,H2 or H3 carbine buffers for the UBR stock, the heaviest of the three is the H buffer which is 3.8 oz. That's a petty large difference from the 6.5 oz you're using.

If your bolt won't lock back on the last round to an empty mag, it's short stroking. In addition to a buffer issue, you have to consider a gas problem.
Being a complete laRue upper, it would be unlikely to think it was at fault, but it could be. How is your gas key staking, is it properly staked and tight? Are you seeing any blow by in the gas block area?

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

Gas key looks properly staked, I don't see any blowby or excessive carbon buildup by the gas block area. I figured it'd be a buffer issue like I said on the original post. I got couple of buffers and a regular carbine spring coming from Palmetto to try it. Will post if problem is solved, which I'm thinking a lighter buffer will do.

 

[Sebben]

Re: 2nd opinion on bolt catch problem

Question somewhat relating to this subject. Is it acceptable to have any gas residue near the gas block?

 

[dlxcupid]

Re: 2nd opinion on bolt catch problem

updated on fix!

 

[Captain Moroni]

Re: 2nd opinion on bolt catch problem

Heavy buffers can help at times but they can also be hard on your bolt and BCG. Think of it as using a sledge hammer to close the bolt each time.

 

[ORD]

Re: 2nd opinion on bolt catch problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dlxcupid</div><div class="ubbcode-body">updated on fix! </div></div>

Good deal! Glad you got it squared away!