More 224 Valkyrie - troubleshooting

[Ray P]

When doing a chamber check on an AR, with sized case and a stripped bolt, how hard should the bolt be to turn into position?

Tried to diagnose a feeding problem with my new 224 Valk. Using factory Hornady ELD-M cartridges, about one in four rounds won't let the bolt close. Since a go-gauge is at least a week out, I did some prelim checks. First, I stripped two factory rounds, reseated a 88gr ELD-M to 2.245" COAL, and seated a SE 77 gr match king to recommended 2.160" COAL.

Put some dykem on the points, and dropped each into the (removed) barrel in front of a stripped bolt. I had to use a 1/8" brass rod to help rotate the bolt home on each. The ELD-M showed a definite ring on the ogive. None such on the MK.

So:
Is slightly more than finger tight too tight for the bolt to turn into position?
If too tight, can the bolt be lapped into barrel lugs?

 

[Varminterror]

Is slightly more than finger tight too tight for the bolt to turn into position?

Yeah, pretty much. If the cases are sized properly for the chamber, the bolt should close. Your notes sound like the bullets are seated too long for your throat, but I’m not sure your test was designed properly to let you see whether it was the case or the bullet causing the interference.

If too tight, can the bolt be lapped into barrel lugs?

Yes, lugs can be lapped in an AR, but they should not be lapped to correct incorrect seating depth or insufficient headspace, or tight chamber.

This method works. A heavy rubber band driving a cleaning rod through the barrel against the bolt head also works.

 

[Ray P]

Yeah, pretty much. If the cases are sized properly for the chamber, the bolt should close. Your notes sound like the bullets are seated too long for your throat, but I’m not sure your test was designed properly to let you see whether it was the case or the bullet causing the interference.
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Thank you, that is very helpful info!

To clarify, I stripped two factory rounds (pulled bullet, removed powder & primer) to ensure I was starting with a to-spec case. First I tried chambering the empty cartridge just to check chamber fit. It was tight, but with the brass rod for leverage the bolt would close. Also helps if I turn it the right way. (Some of the difficulty may have been my total lack of experience with checking the chamber on a gas gun.)

The next thing I did was load a pulled ELD bullet back into one of the empty cases, set to the same COAL as the rest of the box. That round was a bit harder to get the bolt closed, and a ring on the ogive was present after removal.

The last thing was to load the other empty case with a shorter bullet. I used a Sierra 77 gr Match King to Sierra's recommended COAL of 2.160, chambered it with a slight bit more than finger pressure, and there was no ring on that bullet.

So at best, I believe I have a tight chamber, and a throat that's just a bit too short for 88 gr ELD-Ms at factory COAL.

So lapping may not be the best answer. Okay, got it.
It's irritating that this is so close to being functional with the long bullets. I think I will next load up some of the once-fired cases with the Match kings (and a random mid range CFE 223 load) to see if a shorter bullet eliminates the feed problem. Like I said, only one in four wouldn't completely chamber at first attempt.

 

[Ray P]

Since the stripped cases are slightly more than minimum dimension, and only causing slightly more than finger tight resistance for bolt closing, there's a good chance the barrel & bolt will pass a go gauge check when it gets here. No guarantee, but a good chance.

 

[Lenny62]

I would suggest you procure one of these.
HORNADY LENGTH GAUGE | Brownells It would be very useful in troubleshooting this little challenge.

 

[Ray P]

I would suggest you procure one of these.
HORNADY LENGTH GAUGE | Brownells It would be very useful in troubleshooting this little challenge.

Definitely.

 

[Ray P]

Go-gauge showed up today. Bolt will only close 50% of the way on a Carson go-gauge using finger pressure.

I'm going to put this barrel and bolt aside while I ponder options. Along with the prepped brass.

But on the bright side I have a shiney new MosTek barrel and fitted bolt in 6.5 Grendel due in the next two weeks. So I will repurpose the 224 upper to 6.5 for the short term.

 

[Ray P]

Yeah, pretty much. If the cases are sized properly for the chamber, the bolt should close. Your notes sound like the bullets are seated too long for your throat, but I’m not sure your test was designed properly to let you see whether it was the case or the bullet causing the interference.

I still don't know if it is tolerance stacking, a short chamber, or both. The go gauge is starting to convince me a short chamber & throat are a big part of the problem. I've reached out to TacticalKinetics for some insight.

I know for bolt action guns, target barrels are sometimes deliberately sold with a short chamber for the gunsmith to final-ream. Not visualizing a way to do that on an AR barrel without some fixture to keep pressure on the bolt and reamer from the breach end. In other words, not a typical home hobbyist setup.

Anyway, I have a plan to salvage the rifle with a new barrel and matching bolt in 6.5 Grendel. And investigating options to salvage the 224V barrel down the road.

 

[citizenconn]

Good luck. Have you pulled the barrel yet? If so, just reconfirm that a round hand fed into the chamber won't drop in or go in with a gentle push. If not, you definitely need to send it back for a replacement.

 

[Ray P]

Good luck. Have you pulled the barrel yet? If so, just reconfirm that a round hand fed into the chamber won't drop in or go in with a gentle push. If not, you definitely need to send it back for a replacement.

Definitely. I pulled the barrel and stripped the bolt before running the chamber checks.