6.5 Grendel denting brass when chambering

[Wyrd]

Hi,

I have recently acquired my first 6.5 Grendel and I've been loving it so far. The goal was to have a lightweight semi-auto für hunting with a cartridge more potent than .223 but handier than .308 or 6.5CM. The gun uses a 18" Faxon heavy fluted match barrel, aero parts for the upper and a KE Arms KP15 for the lower with a nice trigger as well. I'm always running a suppressor and have an adjustable gas block tuned for that. The gun runs well, never had issues with cycling, ejection, etc. I don't think it's overgassed, it ejects at 4-5 o'clock and reliably locks back after the last round. The gun is shooting 1 MOA with 123grs ELD-M and about 1,5 MOA with PPU or S&B. So far so good.
The thing that irks me though is that the gun is denting the brass cases when chambering a round after a shot. Not every time and seemingly mainly ELD-M though I haven't shot many rounds from other manufacturers. No dents occur when chambering "manually" using the charging handle. Is Hornady using especially soft brass?
I use Amend2 10 round mags. I'm in Germany and we're not allowed to have bigger mags. I've haven't tried a different mag yet but will next time I go to the range.

My theory is that the dent occurs when the cartridge is dragged across the feed ramps and especially the elevated spot in the middle between the two feed ramps. The dent in the brass fits perfectly in there, a main indentation in the middle with lighter scratching to the sides where in contacts the outer edges of the feed ramps. Accuracy hasn't been an issue when firing dented cases but it's still annoying and also a problem if I want to reload cases.

Do you agree with my theory? Do you have any ideas what can be done about it? I'd appreciate your input. I'll add some pics to hopefully make things clear.

[dpete]

That gash is definitely from the feed ramp of the chamber. Have you tried firing several rounds without the suppressor and see if it repeats itself? That would be one other thing to check, along with changing mags, just to eliminate as a possibility.

[LRRPF52]

This is one reason why I de-edge, blend, and polish my feed ramps.

[Wyrd]

Thank you for your comments. So polishing and de-edging the feed ramps would be the way to fix this? Shouldn't be too hard. Do you use a dremel for that or just fine sandpaper wrapped around suitably formed piece of round stock and do it by hand? I'm no gunsmith but have plenty of metal-working experience as a knife maker.

I haven't fired the weapon without the suppressor, will try that as well.

[grayfox]

The Amend2 is a double stack that thins down to a single stack, right? If you can get a 10-round CPD or duramag (I use only the 10-rounders myself), I bet this all would disappear. I have not had any faxon feed-denting issues in any of them that I have shot.

[Wyrd]

The Amend2 is a double stack that thins down to a single stack, right? If you can get a 10-round CPD or duramag (I use only the 10-rounders myself), I bet this all would disappear. I have not had any faxon feed-denting issues in any of them that I have shot.

Yes, the Amend2 is double stack to rightsided single stack. I'll check and see what kind of other mag I can get over here. We do not have your vast amount of choices sadly. They way I'm seeing things right now is that either way polishing the feed ramps can solve my issue, certainly isn't going to do any harm even if another type of magazine won't give me any trouble and if I go nice and slow, it shouldn't be a problem to get the feed ramps nicely polished without screwing anything up.

[Klem]

Wyrd,

You are correct. And this is not an isolated issue with the fatter Grendel case being fed up ramps designed for the thinner 5.56. There is discussion and more photos of this on the Forum going back years via the search function.

52's photo and advice is the way to go. A Dremel and polish will make for a smoother transition from the mag to the chamber, As will having a close look at the feed lips of your mags and maybe even bending them slightly so they are not holding rounds with a death grip. By that I mean holding them firmly horizontally until the tip crashes hard up against the bottom of the ramp. Polymer tipped bullets are particularly susceptable to being deformed at the tip. If you zoom in on your bullet tips I think there is a slight angled dent where it crashed into the receiver and was forced up on an angle by the ramps. This cannot be good for accuracy, especially when shooting long range. At what point the mag releases the round to head up those ramps is the key. The difference between reliable functioning and crashing is a fine line.

Be careful with the Dremel or hand file however as the middle section acts as a pressure-bearing surface, coinciding with a bolt lug when in battery. If you file too much it is no longer sharing 52K lbs of peak pressure with the other lugs. Also if you turn that middle area into a knife edge it then feeds but puts tiny cuts into your cases. These cut marks at the case shoulder/body angle is the lesser of two evils when compared with your current huge dents. Those surface scratch marks are more cosmetic and don't seem to affect case life. Dents however are different and are definitely something to fix.

Be interesting to see how much of those severe dents are fire-formed back out in spent cases.

There also appears to be bullet creep in the photo. The round is now about 60mm long; it won't fit back in an AR-Grendel mag. Looks like the bullets are creeping forward by inertia on being fed into the chamber and coming to a sudden stop. The neck tension holding that Hornady bullet is likely not enough for a semi-auto. Some, if not all the bullets will be flying forward against the lands before firing. This creates an unwanted pressure spike. And if only some of the bullets are touching lands then your groups will have a vertical bias. You can fix this by crimping or tighter necks in hand loads. Unusual if this is factory ammo as bullets are usually held pretty tight. Are these hand loads or factory ammunition?

What's the story with possessing semi-auto ARs in Germany? Is this on a Waffenschein? Expensive?

Klem

[lazyengineer]

E-Lander makes a 10 round magazine. Try that.

Personally, I have a doubt the Amend2 dimensions can work right. Plastic has to be thicker walls than steel. Grendel leaves no room for that, hence the odd single-stack behavior inside the mag-well necessary for the plastic-wall magazine - because double stacked Grendel won't fit.. Which means that even though it's fed on the right side of the magazine, is it really as far off to the right as it's supposed to be, since the wall thickness still has to be thicker? i.e., is the round still a bit too centered, and going to hit that center lug between the two feed ramps? From this thread, it would appear the answer to that, is yes.

Try a steel wall magazine, like the E-Lander 10, and I suspect this will go away.

As to Dremel'ling lugs on your rifle . man I'd do some hard research on that. That's the "hold's 50,000 PSI of power" part. Maybe it's OK, donno.

[Wyrd]

Thanks for your comments. These are factory loads, Hornady Black. I just measured the dented cartridge with a caliper, it is still exactly the same length as a "fresh one", 5,7cm overall including bullet and still fits the mag fine. So thankfully at least that is not an issue.
The only steel magazine I can get over here is C-Products. Haven't read much good about them but those 25 bucks don't hurt me much if it sucks.

The dents are completely formed out after firing however some cuts and scratches in the case material remain.

ARs are no problem to get here in Germany, neither with a hunting license nor as a sport shooter. For the time being anyway, some idiot politicians keep trying to impose a ban of "assault weapons". So we'll see how that goes in the next few years. We are however already not allowed to get any mags bigger than 10 rounds for center fire semi automatic firearms. Pistols and rimfire are no problem.
Everything concerning guns is more expensive here, my Grendel upper with Faxon Match barrel, Aero parts and Hera Arms bolts assembly cost me 2300 Euros.

As for taking a dremel to the feed ramps, one can go very slowly and gently, basically just smoothing out and taking off edges with polishing compound, not removing much material, not getting anything hot and not changing the geometry.

[LRRPF52]

Thank you for your comments. So polishing and de-edging the feed ramps would be the way to fix this? Shouldn't be too hard. Do you use a dremel for that or just fine sandpaper wrapped around suitably formed piece of round stock and do it by hand? I'm no gunsmith but have plenty of metal-working experience as a knife maker.

I haven't fired the weapon without the suppressor, will try that as well.

I use a bullet-shaped Cratex bit with my "advanced degree in Dremology" (LOL), and carefully de-edge those sharp corners and blend them so they match up well with the extended feed ramps in the upper.



Before doing that, I place a round piece of foam inside the lug recess to occlude the chamber from any abrasive materials getting in there.

I mount the barrel in a vice as-seen with insulators, then de-edge the sharp corners with the Cratex bullet-shaped bit.

Then I use the cotton polishing wheel with Jeweler’s rouge to polish up the job so the coefficient of friction for bullet meplats is really low. You spin the wheel in the rouge ( I use white rouge.) to get enough of it on the wheel, then polish the surfaces. I do my pistol feed ramps the same way.



It’s funny you bring this up because as I was test-fitting my 10.5” Criterion build (which I did not de-edge or polish yet), I got dents on my case shoulder.

On all my other Grendels, I don’t get the dented shoulder from the feed ramp corners because they’re all de-edged, blended, and polished.

From a production standpoint, manufacturers can do this with tumble-polishing of the barrel extensions or running the ramps over an Aluminum Oxide wheel carefully.

[dammitman]

"advanced degree in Dremology",,,,,, thats awesome,,,,,i always thought i should have been recognized as well,,,,,

[TedBrewer5]

I chased this same problem though not as severe as yours. Polished the feed ramps and slightly reworked front middle area. Helped some. Reworked my mags and that pretty much solved the problem. Fire formed brass popped the dent out but you could see where it had been. It had my concerned as to how many reloads I could get from the damaged brass

[Wyrd]

I de-edged and slightly rounded the corners by hand with 1000 grit sandpaper and then polished the feed ramps with a dremel using a soft cotton head and red polishing compound. We'll see if that helped any. Sure looks nice. I did shoot a doe this morning with the gun and the cartridge that was chambered after the shot looks a lot better though it still has some minor denting. I'll hit the range tomorrow, that will tell. TedBrewer5 what mags did you use and what rework did you do to them?

[Wyrd]

Quick update: Shot about 30 rounds today and though I didn't check every round chambered after a previous shot, all fired brass was perfectly intact so no cuts or severe denting that wasn't formed out after the shot. Possibly the problem was indeed solved by polishing the feed ramps. I'll keep looking out for dents, we shall see.

[Okie_Poke]

This has been an informative post. Thanks to all.