So after second time out with the new (first) AR build a couple of times my bolt did not hold open..   and actually what was worse was it would close after staying open on an empty mag inadvertently.  I only had one mag with me so I could not identify if it was strictly the magazine or not.

 

The BCG on that build was a POS, so I just got a replacement one and oiled it up and dropped in and spent the last 15 mins function testing with snap caps just over and over again was discharging the rounds and running the charging handle and just did various runs of mag in, mag out, check the feeding etc..

 

I know that me pulling back on the CH with my hand cannot 100% simulate the force and speed of live round cranking it back but way more times than I'm comfortable with the bolt would not stay open on an empty mag.   that's #1.   #2 what really concerns me is one time when it held open, and then I rested the rifle down on the desk by the butt, on contact the bolt released.   So I tried it again, pulled bolt locked back.   then with some force I smacked the butt on the desk and BAMMO, the bolt closed.

 

so my question is, how solid is your bolt catch?  Can someone go grab their rifle and lock the bolt back and then give it a nice tap on the ground or a desk vertical to give it a POP..  does the force of the pop release the bolt catch?   Is that normal?   If someone told me that the hard force of the thump on the stock is enough vibration to knock the bolt of the catch I would believe it, but I'm so new to the platform I don't know what acceptable or not.   That's why I'm doing all these function drills.

 

 

Totally normal.

It should work. Either its spring its weak or it is dragging too much from being new and it will break in. It may require some effort to drop, but it should always lock back.

The bolt not locking back on an empty mag while firing is typically a symptom of a gas issue.

 

Inertia will allow the bolt catch to release the bolt. That's normal.

Did you build this ar or was it off the shelf?  What gas system and what buffer are you using?

I wont say it's a gas issue yet because all of the above I'm doing dry firing with snap caps. 1 out of 8 times as I was testing functioning on an empty mag the bolt would not hold back. (but perhaps my hand was just not yanking it back enough). So then when it did hold back and i would drop the mag and as I'm going to push a new one up BAMM it would release withou me pushing the release. It's almost as if the catch was very very weak. An inadvertent release concerns me. It's not good if i have an open bolt and i reach for new mag and the bolt drops I then have to drop the mag to pull the bolt back again. That can't be normal. So that's why I'm asking how "sensitive" your rifle is to bumping it will the catch release if you smack your rifle.

I've seen some lousy bolt catches.  One that comes to mind was a Stag factory build.  The catch actually had the tip that contacts the follower too short (not there).

 

Do a few things, make sure the catch is free for it's full range of motion and not dragging and preventing it from coming all the way up.   #2 is the spring strong enough?  Is it the correct spring? #3 is the back of the catch where it contacts the bolt "square"?

 

In bolt lock back the bolt should not fall when the stock is impacted.

? I am sorry I am not following a few points....

 

I though you said this concern started because it happened whilst shooting....

 

You are concerned over the bolt not locking firmly on an empty mag when dry firing? Go shoot it. If it doesn't work then, we can help. There are too many variables doing what you are doing to diagnose anything.

 

What LPK did you use?

 

Why would you have to "drop a mag to pull the bolt back again" if the bolt goes forward before you are ready? That happens sometimes especially during a transition where the bolt release can get hit by your sling/great/body. Just insert the mag on a closed bolt - same as if you were conducting a Tac-load or a reload with retention - then run the charging handle.

 

In bolt lock back the bolt should not fall when the stock is impacted.

Incorrect. If the bolt is locked to the rear either with a loaded/partially loaded mag or with out a mag in the gun at all and you bump - even gently - the stock straight down (grab it by the muzzle, keeping the barrel perpindicular to the deck) on the ground the bolt will absolutely release.

 

Go try it. I just did it ten times in a row each on a Colt, and 2 BCM uppers/SLR15 lower rifles with Colt LPK installed to make sure I wasn't losing my mind...

 

Inertia makes the bolt carrier group and buffer compress the action spring, removing tension on the bolt catch. Even the slightest compression of the action spring will allow the spring that keeps the bolt catch out of the way until it is engaged, either manually or by the mag follower, to do its job and return the bolt catch to its natural passive position, thereby disengaging the bolt catch and allowing the BCG to go into battery.

 

This can not happen if an empty mag (assuming the mag is good) is in the gun as the magazine follower will physically keep the mag catch engaged with the tension of the mag spring behind it, overcoming the tension of the bolt catch spring.

As I said previously, it's perfectly normal.

Just for verification purposes, I pulled 4 rifles out of the safe and tested all of them. All 4 (Colts) bolts dropped when the stock was impacted.

High Exposure has the mechanics correct , the inertia of the impact takes the tension off the bolt catch, and the bolt rides forward.

Okay so all great replies. So check this out. One reply above asked if it was a Stag LPK? It is!! That's remarkable info about the size of the catch. Next, I'm okay with the bolt releasing on a smacked it makes sense if you let off the tension it would do that, duh I should have known that.

 

I will take a picture of the catch up against the bolt an you guys can tell me if it's holding good enough. Thanks!

? I am sorry I am not following a few points....

 

I though you said this concern started because it happened whilst shooting....

 

You are concerned over the bolt not locking firmly on an empty mag when dry firing? Go shoot it. If it doesn't work then, we can help. There are too many variables doing what you are doing to diagnose anything.

 

What LPK did you use?

 

Why would you have to "drop a mag to pull the bolt back again" if the bolt goes forward before you are ready? That happens sometimes especially during a transition where the bolt release can get hit by your sling/great/body. Just insert the mag on a closed bolt - same as if you were conducting a Tac-load or a reload with retention - then run the charging handle.

 

Incorrect. If the bolt is locked to the rear either with a loaded/partially loaded mag or with out a mag in the gun at all and you bump - even gently - the stock straight down (grab it by the muzzle, keeping the barrel perpindicular to the deck) on the ground the bolt will absolutely release.

 

Go try it. I just did it ten times in a row each on a Colt, and 2 BCM uppers/SLR15 lower rifles with Colt LPK installed to make sure I wasn't losing my mind...

 

Inertia makes the bolt carrier group and buffer compress the action spring, removing tension on the bolt catch. Even the slightest compression of the action spring will allow the spring that keeps the bolt catch out of the way until it is engaged, either manually or by the mag follower, to do its job and return the bolt catch to its natural passive position, thereby disengaging the bolt catch and allowing the BCG to go into battery.

 

This can not happen if an empty mag (assuming the mag is good) is in the gun as the magazine follower will physically keep the mag catch engaged with the tension of the mag spring behind it, overcoming the tension of the bolt catch spring.

 

 

Sorry this is what I meant to say!

Totally normal.

Never happened to me in my life.

 

BTW, in before the "everything is as good as a Colt."

 

Oops! Too late.

Never happened to me in my life.

 

BTW, in before the "everything is as good as a Colt."

 

Oops! Too late.

That's because you are abnormal.

 

Try it, then after it happens you won't be able to say that anymore.

Never happened to me in my life.

 

BTW, in before the "everything is as good as a Colt."

 

Oops! Too late.

 

 

Try it, then it will happen to you, even on a colt. If it doesn't there is something wrong with the rifle. 

 

EMPTY mag in and EMPTY gun, lock bolt back, whack butt on the ground with the muzzle up and butt down, everything should stay locked because of the magazine spring pushing up on the follower and the follower pushing on the bolt catch. 

 

NO magazine in an EMPTY gun, lock the bolt back, whack butt on the ground with the muzzle up and butt down, bolt should close because the BCG moved rearward and removed friction form the bolt catch and the spring in the bolt catch does what it does and moved it back to it's resting state which won't stop the BCG from moving. 

 

No, butterfly farts shouldn't make the bolt drop, but without the mag in, it is far from bomb proof. 

So update on me. Did about 100 rounds in batches of 5 rounds per mag this weekend. So that's like 20 mag changes. Zero failures and zero inadvertent drops on no mag in.

 

Felt great. Think I got my 50 yard irons zeroed. Next up first time with the RDS. Really wish i could borrow a scope. I'm curious to see if my rifle could put them in the same hole on purpose, not luck.

So update on me. Did about 100 rounds in batches of 5 rounds per mag this weekend. So that's like 20 mag changes. Zero failures and zero inadvertent drops on no mag in.

 

Felt great. Think I got my 50 yard irons zeroed. Next up first time with the RDS. Really wish i could borrow a scope. I'm curious to see if my rifle could put them in the same hole on purpose, not luck.

Just drop the dot in top of the irons while looking through the sights and viola! Youre co-witnessed. (I'd still verify it though)