Bolt Lock Back Issues... Not Sure Why?

[jsbhike]

Actually yes. About 38 today. About 25 degrees less than a month ago when I last shot it...






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Not quite the level of high/low difference I was thinking, but could be one part of the issue.

If things were on the ragged edge of locking back before then the temperature drop could be lowering the pressure just enough to be the difference in Day A vs. Day B. Not a cause, just a variable that is showing an underlying issue.

[georgeib]

Whenever I read "Wolf" I think of melted steel case resin sticking on things.

Internet myth. The lacquer doesn't melt and doesn't get sticky, or even soft. You should see people take a blowtorch to it in an attempt to get it to run ir soften.

The issue with steel cased ammo is that the steel doesn't expand and seal the chamber during firing like brass does. Thus allows some blow by and can accumulate carbon in the chamber.

[mark5pt56]

Other than the stuff listed, try pulling the bolt catch and checking for anything inside or a weak spring. I had an odd one the other day, the detent got stuck in the depressed position. Also check for correct lock up with the pmags. Put pressure on them, mainly to the rear, possible the followers may be worn at the contact point and not engaging the BC. I've found some of them to have a slightly shorter follower, coupled with that and if the catch area is worn, it may cause issues.

[arptsprt]

Interesting. Take it it wasn’t very obvious? I assume the pin started to shear due to the non-concentric force being applied?

I’ll check on this. From visual inspection the pin and rotation of the catch around the pin seems nominal.

Were you able to fix the hole? Not sure how you could? That would sure suck to have an issue like this on a registered lower.

I started having problems with lock back on one of my lowers. The pivot hole for the bolt release wallowed out and the roll pin started to shear.

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[arptsprt]

Thanks. Will do. Odd though that the initial PMags used were brand new M3. Followers wouldn’t be worn yet. All other PMags including a few 20 rounders failed too.

Seems to me this is pointing to a catch issue and tolerance stacking with the geometry of the PMags.

Other than the stuff listed, try pulling the bolt catch and checking for anything inside or a weak spring. I had an odd one the other day, the detent got stuck in the depressed position. Also check for correct lock up with the pmags. Put pressure on them, mainly to the rear, possible the followers may be worn at the contact point and not engaging the BC. I've found some of them to have a slightly shorter follower, coupled with that and if the catch area is worn, it may cause issues.

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[MistWolf]

Interesting. Take it it wasn’t very obvious? I assume the pin started to shear due to the non-concentric force being applied?

I’ll check on this. From visual inspection the pin and rotation of the catch around the pin seems nominal.

Were you able to fix the hole? Not sure how you could? That would sure suck to have an issue like this on a registered lower.

The damage was to the bolt release. I think the steel was soft. I fixed the problem by replacing the release & roll pin.

[joeg26er]

The damage was to the bolt release. I think the steel was soft. I fixed the problem by replacing the release & roll pin.

Brand of bolt catch?

[Dr. Bullseye]

The way I read this, you tested each variable separately. This is the way to trouble shoot any problem. The only problem resulted in the use of Pmags, either generation. On the other hand USGI did work. Shouldn't you be looking a those pmags more closely?

[gaijin]

The fact your GI mags functioned/lock back and Pmags didn’t pointed to bolt release.

[arptsprt]

Fair enough. And yes.

I keep probably 15-20 mags in the range rotation. USGI NHMTG and Okay and PMags Three of the mags that would not work were nearly brand new Pmag M3 windowed mags. Then tried several more seasoned M3 and M2 with no luck.

Again, all have worked before.

I took the catch out last night. Haven’t put it back together yet. Nothing looked out of whack but I’ll pop in a new spring and maybe a new catch when I reassemble.

However....
—————————
I’m not a patient individual so I was able to sneak up to the range real quick this morning with the two uppers and another SBR lower from my factory Daniel Defense Mk18. Also an H3 buffer.

Same batch of PMags and USGI mags.

Zero issues. Uppers functioned flawlessly and bolt locked back every time.

It’s a lower issue for certain. Again probably something with the catch.

Thanks again for all the input and suggestions.

The way I read this, you tested each variable separately. This is the way to trouble shoot any problem. The only problem resulted in the use of Pmags, either generation. On the other hand USGI did work. Shouldn't you be looking a those pmags more closely?

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