Question about uneven wear on bolt's lug faces

[Klem]

I wouldn't sweat it; those marks are a non-issue. They are on the forward side of the extension so will not be touching or influencing anything when the round goes off. It's just the cheap coating on that new bolt coming off and being left on other surfaces.

Why do you need a GO/NO GO gauge?

[SDW]

I wouldn't sweat it; those marks are a non-issue. They are on the forward side of the extension so will not be touching or influencing anything when the round goes off. It's just the cheap coating on that new bolt coming off and being left on other surfaces.

Why do you need a GO/NO GO gauge?

Yep. I've decided not to worry about it. I'd feel better if it were contacting the extension face evenly all the way around rather than just on the lower half, but it doesn't strike me as a safety issue. I'll do that truing and keep on shooting.

And I only mentioned the headspace gauge in relation to buying a replacement/spare bolt someday. If a brand new bolt shows up in the mail, it'd be comforting to have a way to verify that it's safe to use in whatever barrel I decide to use it with. I have a Field gauge for 5.56 that I've used whenever assembling those uppers. Peace of mind.

[Klem]

I would forgo the gauge and fire the first round from the hip. You can measure spent cases to know the chamber dimensions of each bolt. Save your money and put it towards a better barrel.

[SDW]

Ah, good idea. And I happen to have a set of Hornady headspace comparators arriving in the same box with the Upper lapping tool. They'll come in handy for that. I can use it right away to check my fired brass against my reloaded ammunition; see how badly my Lee FL resizing die screwed them up. LOL

FWIW, I am planning to get a Forster FL sizer and bullet seater before doing any more Grendel reloading.

[SDW]

Regarding the better barrel, we'll see. Tightest group I've shot with his BA barrel is about five shots, about .75" at 100yds. 123 Hornady Black. See group #3 at the upper right (below). FYI, these this target shows my first shots out of the barrel. Worst is about 2.5" or so, but the conditions where terrible. My ammo was cooking in the sun, warm day in the desert. Dumb. I think that messed with the burn rate. Spent cases where flying farther than usual also.

I have several batches of workups to try when shooting season starts again. (For me it's Fall.) Various powers under 123gr ELDs. So that should be a good test.

But if I do feel the need to replace this barrel, I was thinking of one of the PF 750 barrels. 20" also, since I got into Grendel for longer range shooting exclusively. So, same as what I have now but arguably better designed and made.

20badmrSightIn.jpg

[SDW]

Received my lapping tool today. It's the AR-Stoner version, BTW. The In-the-white piece. Won't fit in the receiver. At all. Not even a quarter inch. The way the tool is machined, it has a slight taper on the end, no doubt to help inserting it. But after riding up that a few mm, it gets stuck.

I don't know if it's worth the hassle of sending back. I don't have a lathe though, so turning it down wouldn't be super easy. I might be able to rig something with a drill, and clamp a center punch or something in my vice to go into the pilot hole on the other end, for a "spit roast" effect, and then just go at it with some Emery cloth until it slip into the receiver. One thing I obviously want to avoid is enlarging the bore on the upper receiver.

FWIW, it tried fitting it into my Grendel's upper and a spare Daniel Defense upper I have laying around. No go in either.

[Old Bob]

I have the same Stoner lap tool & it fits in some uppers but not in others. Some uppers have tighter than mil-spec bores. A lapping tool manufactured for mil-spec uppers isn't gonna work. Turning it down is an option I suppose. If mine doesn't fit, I bypass the lapping step.

[SDW]

Understood. I searched online for other people finding this kind of tool too tight. Not hardly any complaints though, which I find strange. Not a single negative product review either saying that it would not fit. Has me thinking, I don't imagine any of these tools working well then in a BCM Upper, with its interference fit on the barrel extension.

That technique I thought of, clamping a spikey pick tool in the vice to use as a pilot, and spinning the lapper with my drill actually works extremely well. It gives me a free hand to apply Emory cloth to the lapper as it spins. I've made a little bit of progress, but it's not quite fitting smoothly yet. And I have to run out to the HW store to buy more Fine and Super-fine/Polishing grade cloth to continue the job.

[SDW]

So... I got that tool turned down to the correct size for a snug fit in the upper receiver, which after some reflection I now recall to be an Aero Precision upper receiver. Overall I think this job was worth the effort. After about 15-30 seconds of spinning it in the drill with 200-grit paste, I inspected the Upper's face and saw that a section of bright metal had appeared, centered at about the 4 oclock position. So more spinning and checking made that bright metal surface grow to half and then finally about 80% of the circumference. I figured that'd do the job. Didn't want to go nuts with it.

I have a couple of other uppers, 5.56s, that I want to hit with this tool at some point.

[Texcl2]