Coming back to the Grendel...

[daved20319]

Been gone awhile, traded in my Grendel on a Creedmoor. But have finally come to the realization that I'll probably never get to stretch it out to 1000 yards, so why have a 1K yard rifle? So to take its place, I came back to Grendel, only in the AR platform this time, my previous rifle was a Howa 1500.

So this is a budget build, BCA side charger upper and Aero Precision lower. Yesterday was my first chance to shoot it, and I was only able to put about 35 rounds through it. Fairly well behaved for a new build, but I did have some hiccups, most notable was several failures to extract, which also resulted in some double feeds. Also had issues with the slide not locking back on an empty mag. I blame some of it on ammo, I was shooting some reloads left over from my previous Grendel, and some on just everything being new and tight. That said, a few issues I have questions on.

So I have 1 factory cartridge, something Federal with what looks like a Speer TNT bullet. I get 1.86" with my case comparator, fired brass was coming in at 1.96+". Is it just me, or does that seem high?

Because of the extraction failures I pulled the extractor and looked it over pretty carefully. Couple of things got my attention. First, not the extractor but the ejector, the spring seems REALLY stiff. It's been awhile since I played with an AR, is that normal? On the extractor, there was a little rubberish nub inside the extractor spring, doesn't really seem to have a purpose, other than possibly acting as a bumper. Do I need it? Also, the lower bolt face edge of the extractor is slightly higher than the bolt face, shouldn't it be flush?

Fit and finish on the upper is actually better than I expected, although there are some rough spots, most notably the feed ramps. I'll be pulling the barrel so I can polish those, and I'll be checking headspace at the same time. Any other suggestions for things to look at? Any other suggestions in general? Thanks.

Dave

[fmyellowj]

I don't think the cartridge headspace is off. I measured some PPU 110 gr FMJ before/after firing in my Faxon 18" Gunner barrel, measured using the B350 Hornady comparator the pre-fired cases measured an average of 1.210" out of a sample size of 16, while the fired brass measured an average of 1.222", 0.012" of difference. Granted, I've abused this barrel greatly with (what was formerly) cheap Wolf steel cased ammunition, but I can't imagine the seven hundred or so rounds fired would have damaged the chamber in any way permitting too excess of headspace.
I cannot speak on any of your other questions, but I believe your measurements are normal.

[Klem]

Dave,

Brass headspace cannot stretch 0.1" without coming apart.

SAAMI permits 0.0171" of stretch in the blueprints between max chamber reaming (1.2301") and min ammunition dimensions (1.213"). No doubt there will be some extra stretch built in for safety but your 0.1" will come apart for sure.

What are you measuring to get 1.96"/1.86"? Can you describe what you are doing please.

[daved20319]

Brain fart, Klem, that should have been 1.196/1.186", so .010" stretch, not .1 . Thanks for the stretch info, though.

Dave

[Klem]

Dave,

Not a problem - perfectly within spec.

Not unusual that factory ammo will stretch 0.01" or more on first firing. Mine is even more.

[daved20319]

Thanks, Klem. So any ideas on the extractor, specifically that it's not flush with the bolt face? I can think of a scenario where that could cause an issue, either with the extractor loosing its grip on the case rim, or causing damage to the rim. Time to load some mid-range rounds for testing, factory ammo is still pretty much unobtamium in my neck of the woods. Later, and thanks again.

Dave

[Klem]

Dave,

Failure to extract is not down to one problem with a simple solution. It could be one of a few possibilities.

Yes, the ejector should be stiff to compress. If your ejection pattern is 4 O'Clock and the case necks are un-dinged from the deflector then it is fine. Some guys (including me) cut a couple of coils off the ejector to stop the necks getting dinged, but that does not sound like your problem.

It could be that the case is still obdurated against the walls of the chamber and under pressure while the carrier is wanting to pull the case out. That is a common fault with failure to extract.

The case should be able to seat flat against the bolt face. If the extractor is then being pushed out by the rim the extractor will not be able to properly hook the case. Is this what you mean?

Yes, leave the little plastic nib in the middle of the extractor spring where it is. But, if there is a D-Fender rubber O-ring around the outside of the spring, get rid of it - you don't need it and it will increase the chance of the extractor breaking.