Bullet Marring in Grendel AR

[DL42]

My grendel is a 22" HBAR Criterion barrel (from Brownells) mated to a Fortis billet receiver set. Ive shot only Hornady Black to this point, and while Ive never had a single hiccup cycling wise in well over 400 rounds, i was rather disappointed in the accuracy- 1.25 to 1.5 moa at 100 yards.

I recently started gathering tools and materials to start reloading. To test chambering of my sized brass and loads, I loaded 5 Hornady HPBT bullets into my once fired brass at 2.260 COAL. I loaded 5 in my magazine and chambered and ejected them all, to simulate auto loading. They all had deep gouges in them. I then grabbed 5 Hornday Black rounds, and performed the same test. They all exhibited the same type of marring. I also loaded 5 rounds into my mag, then slid them out with my thumb. The rounds arent anywhere near the body of the mag as they come out, so the marring isnt from the magazine.

I had never noticed this issue before, but then again, I never really had a reason to. But, that would help explain my less than stellar accuracy results. Did I do something wrong? Should I have the feed ramps polished? Should I contact Criterion?

note: Im working on upoading pics, but the feed ramps line up almost perfectly with the barrel extension.

[A5BLASTER]

It's from the extension. Perfectly normal.

Doubt it added much too the lack of accuracy.

[Red*Lion]

Could you post a pic or two? "Deep gouges" would concern me.

[Lemonaid]

There are some threads here on the forum about this. https://www.65grendel.com/forum/showthre...ass+gouges

[Oryx]

Very common ... the ejector forces the case to the right while the extractors pulls it rearward ... the bullet is hitting on the sharp new lugs of the barrel extension

BTW - I have the 22" Criterion as well and it is definitely capable of better.

[Mike98632]

Search Hellbenders guide to the ultimate AR. I had the same problems with an AR10 it ate bullets and brass. Did shoot rather well though when it ran. The guide will lay out the problems and solutions.I

[DL42]

Very common ... the ejector forces the case to the right while the extractors pulls it rearward ... the bullet is hitting on the sharp new lugs of the barrel extension

BTW - I have the 22" Criterion as well and it is definitely capable of better.

Would you mind sharing what ammo you are using and what results youre getting? Or if you hand load, what is your load of choice? I picked up some 123gr SMK, and some of the Hornady 123 BTHP, none of which Ive shot yet.

The Hornady Black and Federal Gold Medal w/ 130gr Bergers both yielded less than satisfactory results.

[DL42]

Theyre deep enough that my fingernails, short as they are, catch on them. When I built the rifle, I hand cycled several magazines worth of ammo to ensure proper function. I recall scratches on the brass from the magazine, but nothing on the bullets themselves. Im having issues uploading pics because my phones pics are so large that I cant shrink them down enough without cropping out what we need to see.

[Klem]

Dl,

You could put a dot with a marker pen on the case somewhere. Load that into the breech by hand with the dot at 12 O'Clock, then fire it. Then see where the scratches are relative to the dot. This way you also eliminate feeding into the breech as the cause, leaving ejection. Plus you know exactly where the scratches are coming from.

I agree with the others, it's probably caused by being dragged back over the sharp extension lugs, on an angle caused by the ejector spring.

[DL42]

Dl,

You could put a dot with a marker pen on the case somewhere. Load that into the breech by hand with the dot at 12 O'Clock, then fire it. Then see where the scratches are relative to the dot. This way you also eliminate feeding into the breech as the cause, leaving ejection. Plus you know exactly where the scratches are coming from.

I agree with the others, it's probably caused by being dragged back over the sharp extension lugs, on an angle caused by the ejector spring.

I will have to try that. I did also try loading a single round from the magazine, then very slowly extracting it with the charging handle, and the marks were identical.

[Lemonaid]

You could try inserting a round by hand, pushing with a wooden dowel to ensure 100% into the chamber, then using a cleaning rod from the muzzle to push out the round. If it has the scratches its the chamber, no scratches it's the barrel extension (I think about 95% its the extension).
I use this to resize pics for posting, resize to fit 1024 rez. https://picresize.com/results

[Oryx]

Would you mind sharing what ammo you are using and what results youre getting? Or if you hand load, what is your load of choice? I picked up some 123gr SMK, and some of the Hornady 123 BTHP, none of which Ive shot yet.

The Hornady Black and Federal Gold Medal w/ 130gr Bergers both yielded less than satisfactory results.

Right now shooting 107 SMK's and 123 Lapua Scenars with Tac. The 107's are probably my favorite load pushed by 29.9 gr

[DL42]

[ATTACH=CONFIG]17675[/ATTACH][ATTACH=CONFIG]17676[/ATTACH][ATTACH=CONFIG]17677[/ATTACH]

Here are some pics of the bullets and the feed ramps and barrel extension. If you look closely, you can see that the scratches are both parallel and perpendicular to the bullet. I'm 95% sure that when this barrel was installed that the bullets were not getting scratched this badly. The brass had some marks from the magazine, but I really don't care about that. I'm just trying to figure out why the bullets seem to be getting marred all of the sudden.

[Lemonaid]

My take on it from the pics. : Possible bullet striking at where there is supposed to be a small smooth radius at the chamber entrance.
Possible bullet hitting on magazine front lip and perhaps bullet hitting on a sharp corner at the feed ramp.
The marks look different from other barrel extension gouges that I've seen. As it's near the tip, unlikely it's something inside the actual chamber.
DL42, what magazines are you using and is there evidence at the front inside lip of foul play?
The radial marks at the base appear to be where the bullet is engraving on the lands?

[Oryx]

From what I can see in the first picture - there are 2 distinct marks. One is a faint radial mark around the tip that is caused by your seating die. You should see this on all your rounds.
The second definitely looks like scratches from either feeding into the chamber or extracting. Given the jagged nature of the marks it looks like it's happening at a slow rate like when you are pulling the charging handle to extract the round from the chamber. If it was feeding and from an open bolt it would likely happen rapidly and be more uniform... Just my thoughts.

If you want to test it takes a little work but fairly easy. You need to remove the ejector plunger and spring out of your bolt. This will allow you to chamber and then remove without the ejector forcing it sideways toward the port when extracting from the chamber. You should then be able to narrow it down to going in ... or coming out. I would put my money on extraction.

I don't think it's into the lands that hard at mag length. If it was hitting that hard into the lands it might start to set back the bullet into the car and you can also check that by an OAL measurement.

[A5BLASTER]

Ok I see the problem.

You need to polish and blend your feed ramps. Your right side feed ramp is out of line with the extention feed ramp and causing your issue.

Like I stated before, perrty typical and not really adding to the lack of accuracy. But the feed ramp is what is causing the issue at hand.

[Red*Lion]

Ok I see the problem.

You need to polish and blend your feed ramps. Your right side feed ramp is out of line with the extention feed ramp and causing your issue.

Like I stated before, perrty typical and not really adding to the lack of accuracy. But the feed ramp is what is causing the issue at hand.

You have a better eye than I do. With that said, it really never hurts to polish and blend feed ramps. I had to do a pretty aggressive job on my 11" 7.62x39 pistol, but it ended up helping a lot.

[DL42]

You have a better eye than I do. With that said, it really never hurts to polish and blend feed ramps. I had to do a pretty aggressive job on my 11" 7.62x39 pistol, but it ended up helping a lot.

I believe this is exactly what is causing my issue, I just find it odd that it the issue hasn't existed the whole time this upper has been together. When I torqued the barrel nut, I torqued it around 60 lbs/ft, and I also used Indian head to create a tight seal, so I would be shocked if the barrel has actually rotated some over the course of shooting it. At this point, I am going to send it out to a gunsmith to have the feed ramps polished and matched to the barrel extension.

[DL42]

I just loaded two more dummy rounds as a test. No gouges whatsoever. That is another reason I tested factory ammo along with my test loads. I do believe that the marks are occurring while the round is being chambered. I also tried resting the load on top of an empty chamber and chambering it that way, with the same results. I just find it so odd that the rounds did not come out like this when I built the upper.

[A5BLASTER]

I believe this is exactly what is causing my issue, I just find it odd that it the issue hasn't existed the whole time this upper has been together. When I torqued the barrel nut, I torqued it around 60 lbs/ft, and I also used Indian head to create a tight seal, so I would be shocked if the barrel has actually rotated some over the course of shooting it. At this point, I am going to send it out to a gunsmith to have the feed ramps polished and matched to the barrel extension.

Break it lose and retorque it to 40lbs and see what it does.