AR - Failure to lock the bolt back

[88E30M50]

Having an issue with an AR that does not consistently lock the bolt back on the last round. Any ideas on what I should check? It’s only got about 170 rounds through it and was fine for the first 60 but the issue seems to be getting worse, not better. It’s happening with a variety of mags.

Is this a break in issue or is something out of spec?

 

[Cameramonkey]

Factory ammo?

My AR9 wont lock back on light loads.

 

[Sigblitz]

Mag fully seated? Magazine catch issue?

 

[rvb]

you tried different mags, did you try different ammo? and what ammo are you using?

you build it? getting worse is a hint something is changing.
check the carrier key.
check the gas block....
Is the gas block adjustable? back out the adjustment.
Is it clamp on or set-screws? Check that its still lined up.
If it's a fixed front site / pinned, probably not the issue. just make sure the gas tube is pinned in place...

Rings shouldn't go bad that fast, but make sure w/ the bolt pulled fwd in the carrier if you set it on a table on the bolt face, the carrier stays up (doesn't fall under it's own weight. visually inspect the rings.

manually hook a round onto the bolt face and slowly chamber it (w/o a mag). it should chamber smoothly w/ only a little resistance felt as the bolt cams over. or remove extractor and realize there'll be some resistance from the ejector as the bolt enters the barrel extension, but it should still cam over smoothly.

only AR I've had that needed any kind of "break-in" to run was a 9mm (direct blow-back, no gas).

-rvb

 

[Gaffer]

I had one of my builds doing about the same thing. I traded out the bolt catch with one that had a longer "finger" on it. By finger I mean the extension that the empty mag pushes up, which then rotates the bolt catch up enough to capture the bolt. The finger was shorter or something was different with it, and the empty mag didn't get enough bite on it.

Ron

 

[russc2542]

Having an issue with an AR that does not consistently lock the bolt back on the last round. Any ideas on what I should check? It’s only got about 170 rounds through it and was fine for the first 60 but the issue seems to be getting worse, not better. It’s happening with a variety of mags.

Is this a break in issue or is something out of spec?

What caliber and parts used? barrel length, gas length, etc, etc. bought or built?

 

[88E30M50]

This is on a Troy XM177E2 clone and is stock. The ammo it ran fine with was my reloads but that second range trip was with Wolf brass cased ammo. I’ll break out the reloads again to see if maybe it just does not like the Wolf ammo.

I’ll take a look to see how it compares to the other ARs I have to see if I can see a difference in the bolt catch dimensions too.

Thanks guys, lots of good advice offered.

 

[rvb]

This is on a Troy XM177E2 clone and is stock. The ammo it ran fine with was my reloads but that second range trip was with Wolf brass cased ammo. I’ll break out the reloads again to see if maybe it just does not like the Wolf ammo.

I’ll take a look to see how it compares to the other ARs I have to see if I can see a difference in the bolt catch dimensions too.

Thanks guys, lots of good advice offered.

wolf can sometimes be underpowered. that's why first thing I ask is what ammo... and if it worked w/ one ammo and not the other, that's a clue. a lot of ARs are over-gassed and work ok w/ marginal ammo. Maybe try some other good factory ammo to make sure it's not just that your reloads are on the hot side or something...

to be sure it's ammo and not a mag/mag catch issue, load a round, remove the mag, and hold the bottom of the bolt catch w/ your WH thumb. If it still doesn't lock back w/ the wolf (but does w/ other ammo) you know where the issue is....

ps I've not used wolf other than in 7.62. But I know it used to be considered quite inconsistent over the chrono, sometimes no better than PCM 223, sometimes closer to xm193. I knew guys that would practice with it, but not compete because they couldn't trust it to make power factor...

-rvb

 

[Floivanus]

Wolf brass cased ammo is 223 spec, so it could be somewhat underpowered.

I’ve had short stroking issues with wolf and reliable 5.56 guns

 

[88E30M50]

Sounds like the ammo is suspect. I really should know better than to buy crap ammo but sometimes I forget that. This is only the second time I bought Wolf, the first being about 10 years ago when I bought my first AR. That was steel cased and it would not run hardly at all. I’m hoping that I don’t have to relearn this lesson in 10 more years.

 

[ditcherman]

If you are using gen 2 pmags I believe there is an issue with the shape of the mag at the top rear that causes the catch to not work. I used a dremel on a bunch of mags to make them look like gen 3's and they have worked well.

 

[Hop]

The easiest way to tune an AR to run multiple types of ammo is to swap buffers. You don't always go lighter either. Carbines can have very high bolt speeds & can outrun the mag spring &/or bounce forward and miss the catch. I've had to go with a heavier buffer to cure a "won't lock back on last shot" problem.

 

[Floivanus]

Sounds like the ammo is suspect. I really should know better than to buy crap ammo but sometimes I forget that. This is only the second time I bought Wolf, the first being about 10 years ago when I bought my first AR. That was steel cased and it would not run hardly at all. I’m hoping that I don’t have to relearn this lesson in 10 more years.

nope, gun isn’t setup for it, not enough dwell time, buffer too heavy, buffer spring, etc can have that effect.

Every single gun I own reliably runs ALL ammo, if it wouldn’t I would have zero use for it. Steel case blesses my MP5s, SCAR, AR15s, everything.

 

[bwframe]

Anyone got links to a little more detail on determining the best working buffers and spring combos for individual rifles?

 

[1mil-high]

I would bet this problem could be taken care of by using side cutters to cut off one loop of the bolt catch spring. Sometimes the spring can be a little too stiff which can overpower the magazine follower spring. Worst case scenario you are out a spring that is less than $1 to replace.

 

[edwea]

Anyone got links to a little more detail on determining the best working buffers and spring combos for individual rifles?

I've wondered this too. I've built quite a few ar's and generally had good to great results. The spring and pin assembly is easy enough to get right, but I know there is more to the build process for BEST results and build quality. Spring/buffer combos, gas system tuning, etc.

 

[ditcherman]

Anyone got links to a little more detail on determining the best working buffers and spring combos for individual rifles?

I don't have a lot of experience with this subject but don’t believe you can go wrong here -
https://www.jprifles.com/document_pdfs/SCS Selection Guide_758.pdf
but it is money.

 

[MCgrease08]

Here's a pretty thorough overview of different buffers and types of guns they're designed to work with.

[video=youtube_share;DYf-MLMODhA]http://youtu.be/DYf-MLMODhA[/video]

 

[Hop]

Here are the springs I use.
Tactical Springs & Machine Gunners Lube

My stuff runs well with the Spike's ST-T2. Some people bad mouth the Spike's stuff. I'm not sure why. It's filled with powder like a dead blow hammer.
https://www.spikestactical.com/collections/lower-parts/spikes-tactical-tungsten-buffer/

 

[88E30M50]

I kind of punted on this one. Before I could run any decent quality ammo through it, I installed a FA Binary trigger and heavier buffer spring. I had the chance to run it hard this weekend and put about 400 rounds through it using both the Wolf Gold and Federal 55g 5.56 ammo. It ran without a single hiccup.

This is not my go-to rifle and is set up for fun and the binary trigger sure delivers on that. The rifle came with a faux third pin and safe-semi-auto engravings. That third setting now has some meaning to it even if not full auto.