HELP request - 45acp pistol caliber carbine jamming "nose up"

[Phazer]

I recently assisted another shooter build a 45ACP pistol caliber carbine. We'd done 9mm builds together and had no issues. Well, it appears that our luck ran out.

The lower build is based on this lower:
C-45 Stripped Billet Lower Receiver -- RAW -- Glock Style Mags


Assembly seemed to go smoothly. Trigger group works perfectly.
The upper went together without a hitch (LRBHO stripped upper, Kaw Valley Precision 16" barrel, New Frontier Armory 45ACP BCG, heavy recoil spring, and 7.5 oz heavy buffer). Barrel: Kaw Valley Precision AR-15 16'' .45ACP 4150 QPQ AR-15 Barrel

After initial assembly, three dummy rounds seemed to manually cycle and eject alright. But...once we got the range we noticed that nearly every round that we tried to chamber (from various magazines loaded with 1, 5, or 10 rounds) jammed "nose up" in the barrel.

We tried several batches of reloads (which all "plunk tested" perfectly into the barrel) and factory ammo. We kept getting the same nose-up results. When some rounds did chamber, I could feel the round hesitate as it hit the top of the chamber and managed to finally seat.









Here's what the configuration looks like before chambering:
(note: all dings in the dummy rounds are from prior jamming)











This has been very frustrating because when we did manage to sight in the carbine with rounds that did chamber, it was very accurate at 25 yards.

If anybody has any recommendations as to how we can resolve this problem, please share your knowledge. I want to learn and I'll pass on the information the guy who now has a non-functional new build.

Thanks.

 

[kev74]

The only thing that comes to mind is to maybe alter the bullet length. Longer or shorter might help them load easier.

 

[Phazer]

The only thing that comes to mind is to maybe alter the bullet length. Longer or shorter might help them load easier.

Thanks for the input.

We tried OAL from 1.25" to 1.27".
We tried mostly 230gr round nose bullets.
Some 230gr Federal hollow point hi-shok SD rounds were also tried...same nose-up jam problem.

 

[kev74]

Thanks for the input.

We tried OAL from 1.25" to 1.27".
We tried mostly 230gr round nose bullets.
Some 230gr Federal hollow point hi-shok SD rounds were also tried...same nose-up jam problem.

Maybe try some at minimum overall length and some as long as will fit in the magazine.

Are the magazines you used all the same brand? A different brand might work better.

 

[GUNSICK]

Magazines might be the issue.

 

[turbobike]

Had the same problem with mine, I took a page from the 1911 guys. I created more of a feed-ramp on the bottom side of the barrel chamber and blended the upper part of the chamber were the bullet catches withing the chamber. The basic "fluff-n-Buff" with a dremmel polishing wheel and red rouge polish. Cured the feeding issues.
Also I polished my bolt face to let the round slide up the face of the bolt better. You can see your problem manifesting from the pictures, the sharp edge is cutting into the nose of your bullet, leaving a gouge in the lead.
Also these Glock carbines like ALLOT of mag spring pressure, try a Wolf + pressure mag spring or double up the stock mag springs

 

[dsdmmat]

Try looking at the extractor, pull it out and see if there are any burrs on it that would prevent the shell from sliding up onto the bolt face. Also what brass was the dummy's made with? Was it the same brass that failed to feed? Look at the rim thickness on the ones that feed vs the ones that don't. You may have to file a little off the back side of the extractor to get the proper clearance.

 

[Phazer]

Magazines might be the issue.

All were 10-round OEM Glock 21 magazines. When the owner got the rifle home outside of NY, they texted me that 13-round OEM Glock 21 magazines caused the same nose-up jams.

 

[Phazer]

You may have to file a little off the back side of the extractor to get the proper clearance.

Good thought. I tried manually seating rounds on the bolt face. Seemed to work smoothly.

 

[dsdmmat]

Good thought. I tried manually seating rounds on the bolt face. Seemed to work smoothly.

Massaging the extractor cures a lot of similar feeding issues in 1911s.

 

[Phazer]

Massaging the extractor cures a lot of similar feeding issues in 1911s.

I don't have access to the carbine at this point. But when I looked at that BCG, I couldn't see just how to remove the extractor (though, I think I saw a pin on the underside). I'll have to get the owner to request a diagram from the manufacturer.

 

[Eddie Gunks]

1.25-1.27 is. Ot a very big OAL separation.

Make some REAL short and REAL long.

Try HP and SWC as well.

What buffer are you using? I think the bilt maybe over/under running the mag spring. .

 

[Phazer]

1.25-1.27 is. Ot a very big OAL separation.

Make some REAL short and REAL long.

Try HP and SWC as well.

What buffer are you using? I think the bilt maybe over/under running the mag spring. .

I meant to say we tried rounds with OALs of 1.25", 1.26", and 1.27" (different batches).

HP SD rounds jammed the same way.

We're using a heavy buffer spring (for .308) with a 7.5oz buffer:
Kaw Valley Precision AR-15 Solid Stainless Steel Blowback Buffer - 7.5oz

 

[Eddie Gunks]

Carbine buffer?

Run ar15 carbine spring with heavier buffer.

Make the rounds REAL short and REAL LONG.

1.25-1.27 is “regular”

Try SWC and HP

 

[Acer-m14]

Gas system ? short stroking like the issue with 300BO ...

 

[Phazer]

Gas system ? short stroking like the issue with 300BO ...

No gas system. Pistol caliber carbine is just blowback.

 

[Eddie Gunks]

i just had a similar problem with a 9mm build. i tried everything. turned out to be a bad barrel .

 

[Phazer]

i just had a similar problem with a 9mm build. i tried everything. turned out to be a bad barrel .

I'm thinking that the feed cone may need some mild reprofiling to smooth out the somewhat sharp leading edge.

 

[Robin]

Had the same problem with mine, I took a page from the 1911 guys. I created more of a feed-ramp on the bottom side of the barrel chamber and blended the upper part of the chamber were the bullet catches withing the chamber. The basic "fluff-n-Buff" with a dremmel polishing wheel and red rouge polish. Cured the feeding issues.
Also I polished my bolt face to let the round slide up the face of the bolt better. You can see your problem manifesting from the pictures, the sharp edge is cutting into the nose of your bullet, leaving a gouge in the lead.
Also these Glock carbines like ALLOT of mag spring pressure, try a Wolf + pressure mag spring or double up the stock mag springs

This would be my assessment as well.
Robin

 

[Eddie Gunks]

I'm thinking that the feed cone may need some mild reprofiling to smooth out the somewhat sharp leading edge.

Don’t fuck with it. Return the barrel.

 

[Phazer]

Don’t fuck with it. Return the barrel.

I certainly wouldn't do it. I'd have a gunsmith look at it.

That said, the carbine was taken home to another state by the owner. So, they're monitoring this thread for suggestions. If they get anything done that resolves the issue, I'll post the solution.

I believe that they are planning to take it to a professional gunsmith for an evaluation.

 

[Fj40klr]

It’s the New Frontier Armory BCG. Load a brand new cartridge and let the gun jam. Remove the cartridge and feel the back of the case around the primer. You will find deep scratch marks caused by the bolt face. I had the exact same issue and I filed off the sharp edges of the bolt face.

 

[Phazer]

It’s the New Frontier Armory BCG. Load a brand new cartridge and let the gun jam. Remove the cartridge and feel the back of the case around the primer. You will find deep scratch marks caused by the bolt face. I had the exact same issue and I filed off the sharp edges of the bolt face.

Interesting.

I'd try checking that out, but the rifle is not mine and is not in New York. I'll pass on the information.

 

[thegatman]

The only thing that comes to mind is to maybe alter the bullet length. Longer or shorter might help them load easier.

I agree but i always thought that the chamber breech should be beveled. I know the pistols are like that.

 

[kev74]

I agree but i always thought that the chamber breech should be beveled. I know the pistols are like that.

I've screwed up enough stuff to have learned to start with making changes to the stuff I can undo first. Once you start grinding on the barrel, you're committed.

 

[Deplorable Me]

I don't see much of a feed ramp. Could that have anything to do with it?

 

[tony]

Not a 1911 guy or a smith but just my thoughts on what I see. Digs in the bullet look to be made by a very sharp edge. Hard to tell from the pics if there is any kind of chamfer or radius on the breech face. Angle of cartridge coming out of the mag might be a little excessive. No ramp or chamfer at bottom would most likely force the cartridge up on its way into the chamber causing a dig from striking the top edge of breech face. Keep us posted on the fix.

 

[Phazer]

Keep us posted on the fix.

By what I've learned, the owner took the carbine to a gunsmith. The gunsmith believed that the feed angle from the mag was too steep. He put in some kind of set screw to change the angle of the magazine a small amount (by what I'm told) and have rounds feed flatter. Apparently, it worked a few times, but it is still inconsistent. By report, the gunsmith thinks that the lower is out-of-spec with regards to the mag well.

Note: I have not seen any of the attempted repairs since the carbine is in another state since it was assembled.

 

[Fj40klr]

I built the same kind of gun. New Frontier Armory AR45 upper, lower, BCG, and a Kaw Valley 8 1/2” barrel. The BCG is milled out for the ejector on one side but the face of the bolt on the other side has a sharp edge at the 7-8 o’clock position. Once that edge is removed the gun will cycle properly. Here is a photo of how my gun was jamming.

 

[Eddie Gunks]

B By report, the gunsmith thinks that the lower is out-of-spec with regards to the mag well.

.

Ha ha ha. Get a new smith. If bet $ to donuts the lower is not out of spec......

Talk about a stretch.

Facepalm.