Needing to use charging handle to chamber round - small frame ar

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penguinofsleep

Sergeant of the Hide
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Nov 26, 2020
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Somewhere USA
#1
Have a small frame where I have to chamber a round by pulling back on the charging handle. When the bolt is locked back (via the bolt release), it doesn't sit back far enough to chamber a round when after inserting a mag by dropping the bcg using the bolt release. Will catch a round 100% of the time so far when pulling on the charging handle. Everything else has run 100% from day 1 except for this minor issue. No abnormal wear marks, nicks, etc. anywhere in the rifle or parts that would indicate any kind obvious misalignment of parts that could cause this.

I suspect one of the below is sitting in the rifle is causing the problem - anyone have any ideas to help me speed this investigation up?

Standard forged upper and lower with a standard bolt catch - no ambi or extra "non standard" parts.
6.5grendel with duramag 10rd grendel mags. Last round hold open works 100% of the time with all mags.
JP Enhanced bolt + JP lightweight bcg + JP captured spring in a carbine length buffer.
 
#2
Is the round crashing into the feed ramps on the barrel extension? Is your extension clocked in the upper receiver? Have you tried different magazines to eliminate the mag from being the culprit?
 
#5
So when you're locking the bolt back, it's locking on the front of the carrier, as opposed to the bolt face where it should be. (I assume)

First simple question, since you say it's feeding okay.... are you just not pulling it back far enough?

(I had some non standard setup that would cause me to do this, as that last little bit was fairly hard)
 
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#8
Have a small frame where I have to chamber a round by pulling back on the charging handle. When the bolt is locked back (via the bolt release), it doesn't sit back far enough to chamber a round when after inserting a mag by dropping the bcg using the bolt release.
Click to expand...

Unless the bolt isn’t locked back normally, it has plenty of space behind the cartridge in-presentation to strip the cartridge from the magazine. What happens when you hit the bolt release?

I personally de-edge, blend, and polish all my barrel extensions so there is no real ability for the cartridge not to feed into the chamber.

I also chamfer the ejector so right side presentation doesn’t bind against the side of the ejector.

Troubleshoot your BCG and JP SCS to see where your bolt is actually locking up as well.

There are bolt travel specs for the AR-15 to ensure the BCG retracts rearward enough.
 
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#9
Redlion said:
It seems like it would be a buffer/buffer tube issue if you can not capture a round with the bolt locked back. The BCG seems to be stationed too far forward if I am following? What buffer tube are you running?
Click to expand...
Yes, the BCG is sitting too far forward when locked back by the carrier. Everything else works fine.

Won't be able to post pics for a few days but will do so if it's not solved by then.
 
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#12
penguinofsleep said:
Yes, the BCG is sitting too far forward when locked back by the carrier. Everything else works fine.

Won't be able to post pics for a few days but will do so if it's not solved by then.
Click to expand...
Your SCS spring might be too much spring weight.

Can you physically retract the BCG all the way to the rear to achieve bolt hold open on the bolt lugs?

If not, your RET might be turned-in one too many rotations as well or out of spec.
 
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#13
My large frame 308 would do that when I first built it. The catch would engage with the carrier and not the bolt face.

It would happen mostly because that last inch or so would require a good bit more effort to overcome. And the gun didn’t cycle very smoothly.

You know what fixed it? Shooting the gun. Everything just needed to break in a bit. The rough edges needed to be worn down.

Everything fit together nice and snug, which is an ideal starting point, but required breaking in. The gun ran like a scalded dog the whole time though.

I also added a JP high pressure bolt with the one piece gas rings. Talk about a HUGE (that’s what she said) difference in how easily the gun cycled!

Like a lot of people, I thought something was wrong with it because of the way the gas rings work. But nope, still running like a scalded dog.

Now I’m working on getting it to slow down a bit because it cycles so easily. 🙄😂
 
#14
cas6969 said:
So when you're locking the bolt back, it's locking on the front of the carrier, as opposed to the bolt face where it should be. (I assume)

First simple question, since you say it's feeding okay.... are you just not pulling it back far enough?

(I had some non standard setup that would cause me to do this, as that last little bit was fairly hard)
Click to expand...
This is what I'm guessing is the issue. I know if I manually induce that problem.

Is this happening when your shooting and the bolt is locked back on an empty mag? Or are you manually locking the bolt back and loading that way?
 
#15
If the bolt catch is catching on the carrier rather than the bolt it is PROBABLY because the bolt is going back far enough to cycle the rifle, but not far back enough for the catch to hook on the bolt. My guess would be too much spring.

How much buffer mass are you running with that bolt carrier group? Although my first guess would be too much spring, it could be too much buffer weight as well or rather than. Assuming that your rig is properly gassed to run a lightweight bolt carrier group, I'd probably try reducing buffer mass to get a full stroke during the action cycling. Too light on the spring and youre gonna have feeding issues.
 
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#16
penguinofsleep said:
Have a small frame where I have to chamber a round by pulling back on the charging handle. When the bolt is locked back (via the bolt release), it doesn't sit back far enough to chamber a round when after inserting a mag by dropping the bcg using the bolt release. Will catch a round 100% of the time so far when pulling on the charging handle. Everything else has run 100% from day 1 except for this minor issue. No abnormal wear marks, nicks, etc. anywhere in the rifle or parts that would indicate any kind obvious misalignment of parts that could cause this.

I suspect one of the below is sitting in the rifle is causing the problem - anyone have any ideas to help me speed this investigation up?

Standard forged upper and lower with a standard bolt catch - no ambi or extra "non standard" parts.
6.5grendel with duramag 10rd grendel mags. Last round hold open works 100% of the time with all mags.
JP Enhanced bolt + JP lightweight bcg + JP captured spring in a carbine length buffer.
Click to expand...

First ensure your bolt catch is in fact grabbing the front bolt and not the underside of the carrier group .
IF the above problem is happening ,then as Sargent Angle said it's generally a buffer spring or short housing butt-stock . Preventing full travel of the BCG thus negating bolt latch engaging on bolt face .
 
#18
Will try to post pics tomorrow but to answer questions about springs + buffer weights:

JP light steel carrier (not one of the ultra light aluminum competition carriers) + 2 tungsten + 1 steel weight (equivalent of H2 I think?) + 2nd lightest spring in the SCS package (come with 4 springs).

Also, I'm about 500 rounds in on all of the parts so I suspect it's not a "break it in" issue at this point. I suspected this at first as well.
 
#19
penguinofsleep said:
Will try to post pics tomorrow but to answer questions about springs + buffer weights:

JP light steel carrier (not one of the ultra light aluminum competition carriers) + 2 tungsten + 1 steel weight (equivalent of H2 I think?) + 2nd lightest spring in the SCS package (come with 4 springs).

Also, I'm about 500 rounds in on all of the parts so I suspect it's not a "break it in" issue at this point. I suspected this at first as well.
Click to expand...
Ok, just get back to basics. First fire a round with one round in the magazine. Does it lock back? If so, is it locking on the bolt carrier or the front of the bolt? If it locks back on the front of the bolt, rather than the bolt carrier, you're getting full travel. How many mags do you have? Try a different mag.

If it locks back on the bolt carrier or doesn't lock back at all, my first guess would be that the rifle is undergassed for the amount of mass/spring weight you're running. Again, assuming that you're barrel is appropriately gassed, I would lighten buffer mass. Try two steel weights and 1 tungsten or 3 steel weights. Which spring is considered "standard?" Which ever one it is, use that one.

Spring rate is used to control bolt velocity and has little (or at least less) effect on closed bolt lock time. Buffer mass is the chief control of closed bolt lock time. It sounds like you have too much closed bolt lock time. Less mass will reduce lock time.
 
#20
So... going to have some egg on face with this post - but I tried to reproduce yesterday and this morning with some identical dummy rounds. Could not reproduce the issue anymore... so I guess I won't know the root cause, but it went away. Still need to live fire but I could reproduce this with dummy rounds in the past. Makes me wonder if it really was just the parts needed to break-in and it took longer than I expected.

As of now, on all mags, dummy rounds or manual manipulation, when the bolt locks, it's always the bolt face against the bolt stop. I cannot get the bolt to lock on anything else. The last inch or so of travel is not any harder to overcome at this point. The magazines were not tuned and mag springs + followers were not replaced either. I did not add or remove the washer behind the SCS (some buffer tubes / builds need this for spacing, as mentioned in the JP manual + variation in thread timing would dictate).

I also just remembered - initially, when I first encountered this issue, every time I would manually drop the bolt with the charging handle on a new mag, I still felt the little "click" of the bolt stop falling so to say immediately, so it most likely was locking properly against the bolt face even at the beginning. Have some more thoughts on what may have happened given the above, but much of it seems unlikely to me based on other factors so I'm excluding since this post is long enough already.
 
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