Federal GMM 168 gr gets stuck in tight chamber

[wielywilly-g]

I have a fairly new Rock River Arms LAR-8 308 in 26" bull varmint and have been shooting FGMM 175 gr fine. I purchased 200 rnds of FGMM 168 gr recently and while they shoot fine, if I try to cycle them out of the chamber with the charging handle (with 2 hands and lots of sweat) the bullet gets stuck in the chamber and the brass ejects and powder goes everywhere.
It has happened 4 times. I inspected the stuck bullets after pounding them out and there seems to be no burrs, just 1/8" wide band of what looks like a pressed in mark in the copper.

Does this sound like I have a bad sized chamber or a bad batch of ammo or maybe lead build up in the chamber? I’ve tried solvent and a chamber brush with no affect. I have about 140 rnds through it of various other types and 40 rnds of the FGMM 175. This thing is under ½ MOA at 100m so I don’t really want to send it back to RRA.
I have never heard of this before and can’t find any help in the search so any help would be greatly appreciated.

 

[Force_Multiplier]

Re: Federal GMM 168 gr gets stuck in tight chamber

sounds like the bullets aren't seated deep enough, if everything else worked fine... and if they were seated properly you'd have a hard time pulling the out w/ the charging handle

 

[DP425]

Re: Federal GMM 168 gr gets stuck in tight chamber

are there any marks from the rifling? Got pictures of the bullets? Could help out quiet a bit.

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

Here is a picture of the bullet showing the marks I was talking about. I don't see any rifling marks.

 

[9H_Cracka]

Re: Federal GMM 168 gr gets stuck in tight chamber

Those marks are from the straight section ID not being large enough. This happens when chambering with a worn reamer.

I would send it back to RRA for a re-barrel, or you could have a competent smith run a reamer in it by hand to clean it up. An M852 reamer would for sure open up the straight section as this is the standard "match" reamer used for making NM M-14s, back in the day, when they used to run a lot of M80 ball through them at 200 and 300 yards for matches as well as practice.

With the reamer mounted on a T handle along with cutting fluid and a magnifying goggle, you can track the progress of the reamer and where it is removing metal, stopping when the oil wipes off the shoulder part of the reamer, without affecting headspace.

In the pic below, I was cleaning up a chamber that had been cut with a worn reamer. This took over an hour, being very careful as I went so that I did not egg the body section. You can see material coming out of the throat and body. It needed to go in about another .150" to finish the job.

Chips are blown off and the reamer re-lubed every time it comes out to be checked for progress.

This was a pre-Camp Perry emergency fix for a friend. I took it to the range afterwards and fired a 100-7X rapid prone with it at 100 yards. He took it to Camp Perry and in the squadded practice shot 5 straight Xs with it at 600. Yea, it still shot OK.

Good luck getting it squared away. The only other possible explanation is the 168s somehow left Sierra oversized on their OD. You might throw a micrometer on their straight section and see what the come out to. .3080" should be the number you come up with.

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

Thanks a bunch! They mic out at .3084.

 

[9H_Cracka]

Re: Federal GMM 168 gr gets stuck in tight chamber

HUMMMMMM....

Hold the phone - Just hung up with Paul Box at Sierra. The 2168 bullet should have a straight section OD of .3080" as I posted above.

.3084 = either they came from Sierra that way OR Federal somehow damaged them in the seating process.

It is virtually impossible for them to have come from Sierra that way, but your first call should be to Federal.

Call them with the lot #, purchased from vendor, etc. ASAP and they will take care of you.

Post back how they respond please. Thanks.

 

[acidone]

Re: Federal GMM 168 gr gets stuck in tight chamber

i'm not so sure that they could have been damaged during the seating process at federal. The only real way that could have happened was if you were pressing the bullets between two metal planes and actually forced the bullet to "bulge" in the middle. Since there isn't anything below the base of the bullet, besides powder that would crush before the bullet expanded, I'd be more likely to point the finger at sierra. Theres also a chance that you're measuring burrs created after chambering the round. Have you tried pulling a new bullet that hasn't be cycled thru the rifle? Just a thought, hope it helped!

 

[9H_Cracka]

Re: Federal GMM 168 gr gets stuck in tight chamber

The straight section protrudes in front of the case mouth - try measuring it there as well in the other rounds you have in the case.

Found out via email the OP bought the ammo from a discount distributor that has disappeared... kinda makes me think somehow the guy got hold of some reject FGMM.

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

I went out at noon to a local gun shop who had them in stock and purchased a box GM308M. There is a number stamped on back 2 21N325. These new ones measure .3081 to .3082.

I will measure some straight out of the box tonight and post back. I am starting to think the reamer might be what I need.

 

[9H_Cracka]

Re: Federal GMM 168 gr gets stuck in tight chamber

Sierra's tolerance is +/- .0002", so those you just picked up are in spec.

 

[dieselten]

Re: Federal GMM 168 gr gets stuck in tight chamber

also be aware of what you are using to measure the bullets. If you are using a digital caliper (even a Mitutoyo or better) just because it reads to the fourth decimal place does not mean it is accurate that far. Read the owners manual for actual tolerance of the caliper.

 

[9H_Cracka]

Re: Federal GMM 168 gr gets stuck in tight chamber

He works somewhere that has a machine shop and machinists. I trust his findings.

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

The measurements were done with a micrometer from the guy in the machine shop that drilled and tapped 4 blind holes in the cast receiver of my Ruger M77 MarkII for a Ken Farrell 20MOA base. He does not use digital. He is very good. Plus we are under ISO9001:2008 so we get everything including micrometers calibrated or verified every year.

There are some in production that use those digital calipers, but I personally don't trust them. I am in engineering and use a standard caliper. I have a real nice Starrett mic at home and I will get it out tonight and do some more investigation. I have learned a lot on here and it will help in the debug process. Thanks!

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

With my micrometer:
The 175 gr measered avg .3076
The old 168 gr measured avg .3082
The new 168 gr measured avg .3080
Everything over .3080 had a press fit into the chamber so it looks like I need a reamer if I want to open the chamber for the 168 match stuff.

All my other non-match 308 ammo measured .3071 to .3077

Thanks for all the help!

 

[9H_Cracka]

Re: Federal GMM 168 gr gets stuck in tight chamber

Back to the worn reamer theory it seems. .3082" is within Sierra's spec.

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

Update: Just got it back from Rock River Arms and they opened up the chamber a bit to allow those Fed GMM 168 to manually cycle smoothly. I went there in person and talked to BJ and showed him the bullets that had stuck. They were quite concerned and very propt to fix it. They did it in less than 1.5 hr. This is the best company I know of for customer service/support.

 

[wielywilly-g]

Re: Federal GMM 168 gr gets stuck in tight chamber

Still shots good after the work.

109 yards

410 yards