Issue with new AR bolt stopping short

[Clay]

As some/most/all of you know Im not much of an AR guy. Ive had them in the past but have been AR-less for a couple of years. I had most all of the support items for one, including a stripped lower. So, I built the lower, and it sat around for a while. Then I bought a PSA middy CHF upper less the BCG.

It took a while to get the upper, but once it arrived I pulled the BCG out of my S&W 5.45x39 AR, put in a 556 bolt, and put it in the rifle along with a BCM medium gunfighter charging handle. The bolt did seem kind of tight in the rifle, but everything was new for the most part, so I didnt worry about it.

First trip out it was basically a single shot. It wouldn't eject, OR if it did eject it would short stroke and not pick up the next round. I didn't lube anything when I put the BCG/charging handle in, other than what was already on the BCG. I was shooting tula and silver bear 223. The silver bear seemed to be a bit better, but it still didnt cycle well.

I took it home and lubed it up and it seemed to smooth out the action of the BCG a bit. Today I finally got back to the range and this time I could run a 20 round mag through it and only have one or two issues. Still using tula and silver bear ammo. The typical problem was the rifle would fire, eject the spent round, and then when heading back to battery it would stop about 1/2 way there. Looking in the ejection port, there was the bolt. The round that was stuck had marked on it like it was getting stuck going into the chamber, in between the two feed ramps in the barrel, like it was going in the very middle.

Mags were 20 round Pmags, a 30 round Pmag, and 1 USGI 30 rounder. All of them had the same failure. The bolt still seems to be stiff, not as stiff as before but now it is lubed. There is some wear on the charging handle as well. I almost wonder if the charging handle is too tight in the upper from the wear.

anyway, thats a lot to go through. Does anyone have any thoughts?

thanks,
clay

 

[mvician]

lube the bolt, shoot some better ammo

what buffer weight and spring are you running?

 

[TAT7]

Do you have M4 feed ramps?

Ramps line up with barrel extension?

Was the wear on the inside of the charging handle? Like wear the gas key rides? If so check alignment of gas key to bolt and make sure it is still staked properly. Also check gas tube alignment on upper. Maybe it's hitting the BCG gas key.

From all the different issues you have had....short stroke, wear on charging handle, and won't fully go into battery, I would think its something along the lines of a gas issue/gas parts issue....if something was wrong with hard parts, then you should have the same issue over and over, not different issues....or is could just need broke in badly....I've seen rifles fail horribly for the first 100 rounds, then take off like a raped ape...let us know...

 

[Clay]

lube the bolt, shoot some better ammo

what buffer weight and spring are you running?

the buffer and spring were from a lower parts kit I bought a couple of years ago, so I have no idea what they are and they dont have any markings.

and I will lube the bolt and try some milspec ammo.

Do you have M4 feed ramps?

Yup. In fact I think the marks on the ammo that jamed was from it hitting the feed ramp, but I think the bolt might have been sitting on top of the ammo from the looks of the failure.

Ramps line up with barrel extension?

yup

Was the wear on the inside of the charging handle? Like wear the gas key rides? If so check alignment of gas key to bolt and make sure it is still staked properly. Also check gas tube alignment on upper. Maybe it's hitting the BCG gas key.

No the wear was on the top and sides. One one side it was on the top, on the other side it was on the bottom. almost like there is a torque or twist n it.

From all the different issues you have had....short stroke, wear on charging handle, and won't fully go into battery, I would think its something along the lines of a gas issue/gas parts issue....if something was wrong with hard parts, then you should have the same issue over and over, not different issues....or is could just need broke in badly....I've seen rifles fail horribly for the first 100 rounds, then take off like a raped ape...let us know...

Im thinking it may be ammo related to a degree and I just need some full power ammo, OR a different buffer/spring.

 

[03A3]

You might remove some lube and then hand cycle it a couple of hundred times. Seriously. While you're doing that think about how the AK works every time.
An unmarked buffer is likely a CAR buffer, and should when all it is right, be correct for the ammo you were using.
Be sure to lube the gas rings thru the holes in the side of the bolt carrier, but I'm sure you knew that already.
And you could do the "short stroke" test. Load one round in all of your mags and see if the bolt locks back when the round is fired. Note that a number of people have reported that some of their 20 round Pmags won't consistantly lock the bolt open after the last round. Mine do but I only have 3 of them.

 

[Clay]

If I had to guess its a CAR buffer since it was a CAR stock w/ the kit.

Ill give that a go and see what happens. and Ill lube the gas rings like you said.

 

[chubbs]

Try some brass cased ammo. The steel runs fine in some but hangs up in others. Also I would clean my bore real good.

 

[Ljungman]

If the carrier is new to the rifle, as it didnt come with it, the specs may be .001 to close. May need to lube it up and keep chucking rounds out of it until things "wear in". I did the same thing with several of my Black Rain builds. They are tight for the first 100 rounds then they run just fine.
1. Take a charcoal marker/or black marker amd color your bolt carrier. Place carrier in rifle and cycle by hand once or twice. Close your eyes and "Feel" for grinds, or anything not smooth feeling.
2. Pull carrier out. See where the marker is rubbed off. The rails are supposed to be rubbed off. See if other areas like the sides or top of carrier are rubbed off and then look in inside the upper to note where the marker rubbed onto. Clean and repeat again. If the marker is on the same spot, take a small patch of small grit sandpaper and LIGHTLY rub the markered area. Then rinse and repeat. usually very little needs to be removed. could be an area that was mis-milled or cast, or the coating is thicker there.
Some may also say to check the gas block alignment as a slightly off block can prevent all the pressure from exerting on the bolt making it short cycle. Ive seen some pretty canted gas blocks on an AR and it did little to slow them. My bet is the carrier is in an upper with tighter specs. I would run full power military ammo through it and try the above marker/sand. Good luck, and hope it works out.

 

[U.S. Patriot]

1. Lube the bolt and carrier, then cycle the bolt 100 times or so.
2. Make sure your gas key screws are tight and staked.

I would try those two things first, then go from there.

 

[Clay]

Well I lubed/cleaned, cycled it, cleaned and lubed again, and went to the range.

I ran 100 rounds through it today.

40 rounds of M193 ball.
20 round of Norinco brass cased
40 rounds of PMC brass cased


It ate it all, no stoppages, and the bolt locked back each time. I wish I had brought some steel cased ammo with me to try after this, but it did seem to run a bit smoother by hand. Ill try some steel cased stuff at a later date.

thanks everyone!

 

[Martin Draco]

Do you have headspace gauges? I have a similar problem with a S&W 5.45x39 carrier that I put a 5.56 bolt in. I checked it with a GO-gauge and it didn't close. Do you know anybody you can borrow a BCG from and try it?

 

[Clay]

well quick update on this one.

I bought a new Rock River chromed BCG when primary arms was running a sale. I put it in and it seemed to run much smoother. I also noticed when I put my 5.45 bolt back in the carrier, and it fit much better than the 5.56 bolt I had in it, so that could have been part of the issue.

Today I ran to the range for a quick 15 minutes (all the time I had).

I put 130 rounds through it with zero issues. Hopefully this will be the solution to the problem. Ill put more through it when I have time.