AR10 projectile scaring

[Bob Mckenzie]

Hi folks,

Just completed my ar10 6.5 creedmoor build and have put 30 rounds down range.

I noted today at the range, when I decided to not fire and pulled the live round from the chamber it had some scaring on the projectile...

This will obviously effect flight characteristics, but how much?

I noted a horizontal line at the ogive-ish which seems to be lans engagement... and a few longtitunal nicks and scratches (m4 feed ramps maybe?

I also noted a slight firing pin dent on the primer most likely from slamming into battery... is this a concern?
Does anyone have experience with this issue?
How to fix?

These are the first rounds through as mentioned

Shooting 140gr. And 147gr. Hornady ELD match

Using Rainier Ultramatch and JP LMOS BCG

Thanks!

 

[newguy2k3v2]

I haven't seen an ar yet that doesn't scar up rounds a little bit. They still shoot fine. Just don't make a habit of chambering the same round over and over.

 

[7mmFanBoy]

No. barrel extension scratches round only don't fire it ejector pushes round against barrel extension. Common ar firing pin shouldn't be an issue

 

[Hellbender]

An old post of mine shows how to fix this...

http://www.snipershide.com/shooting/threads/3-how-to-ultimate-ar-barrel-extension-clean-up.46567/

I've got a whole series (10 or so) of these old "Ultimate AR" posts if you want to search my name.

 

[Coyote Kev]

An old post of mine shows how to fix this...

http://www.snipershide.com/shooting/threads/3-how-to-ultimate-ar-barrel-extension-clean-up.46567/

I've got a whole series (10 or so) of these old "Ultimate AR" posts if you want to search my name.

Followed that link. Looks like good info but could use more detail. What did you use to smooth those feed ramps and lugs? What do we need to be careful of? Can you easily screw it up and cause more problems than you fixed?

 

[Bob Mckenzie]

Followed that link. Looks like good info but could use more detail. What did you use to smooth those feed ramps and lugs? What do we need to be careful of? Can you easily screw it up and cause more problems than you fixed?

Agreed, for me I have a Rainier ultramatch with a TiN barrel extension so it’s already pretty polished...
The lugs on the right are pretty sharp and do scratch the brass

 

[Hellbender]

Get a small dowel of some kind ( 3/16-1/4" diameter) and wrap some 400 grit wet/dry (black) sandpaper around it and go to work on the sharp edges.
Anyplace the brass can hit. You cannot remove enough material with this to do any damage.
Then you can buff it with a Dremel and felt buffing pad with compound when you are done to a high polish.

The Creedmore (6 or 6.5) shoulder location and angle are not ideal for an AR platform, as the case shoulder does not lift the nose of the cartridge at the right time to properly guide it into the chamber. The tip of the round usually hits right below the chamber and dings up the tip.

A correct shoulder angle (like a .308) raises the tip to the proper angle and guides the round properly into the chamber.

You can help by slightly spreading the front of the mag feed lips (metal mags).

 

[Coyote Kev]

Get a small dowel of some kind ( 3/16-1/4" diameter) and wrap some 400 grit wet/dry (black) sandpaper around it and go to work on the sharp edges.
Anyplace the brass can hit. You cannot remove enough material with this to do any damage.
Then you can buff it with a Dremel and felt buffing pad with compound when you are done to a high polish.

The Creedmore (6 or 6.5) shoulder location and angle are not ideal for an AR platform, as the case shoulder does not lift the nose of the cartridge at the right time to properly guide it into the chamber. The tip of the round usually hits right below the chamber and dings up the tip.

A correct shoulder angle (like a .308) raises the tip to the proper angle and guides the round properly into the chamber.

You can help by slightly spreading the front of the mag feed lips (metal mags).

So if we know that the Creedmoor isn’t really built for the AR 10 platform, why don’t companies that make AR creedmoor barrels change the geometry of the feed ramps and barrel extension to accommodate the different shoulder angle and length?

 

[Hellbender]

So if we know that the Creedmoor isn’t really built for the AR 10 platform, why don’t companies that make AR creedmoor barrels change the geometry of the feed ramps and barrel extension to accommodate the different shoulder angle and length?

Not a simple fix with just a bbl ext/feedramp mod.
The distance from the face of the chamber to the front of the mag is wrong, a lot easier just to make it a .260 Rem or .243, which works perfectly.
But I know it's not the "Cool, new thing"....LOL!

And 99.9% of the people will never know the difference anyway, because they're not a good enough shooter to see or know the difference.

And the Creedmore's can still be made to shoot very well, the bullet nose deformation will only affect things way out there (past 400 yards) when the slight BC drop will start being apparent.