I built a 6.5 cm large frame ar. Shoots very well, but i am getting 2 parrallel drag marks on the neck and shoulder. I assume it is from the feed ramps. I tried polishing the sharp corners, but cant seem to get them knocked down. Any suggestions?
Brass neck damage 6.5 build
- Thread starter Forward543
- Start date
Need more information about your build to help you resolve it but its from the sharp corners of your barrel extension upon extraction...
Gas length?
Adjustable Gas Block?
Barrel Make?
If custom barrel what Barrel Extension? BAT?
Buffer?
What ammo or load?
I had this same issue with a custom Bartlein 22" 6.5cm AR barrel on a BAT barrel extension with Rifle gas. That BAT extension has very sharp corners. As suggested by JP I tried polishing the corners of the locking lugs between 12 and 3 oclock with a dremel and the attachment they suggested which looks like a grey eraser head. It helped, the 2 scrapes werent as deep but still there.
After talking to Josh about this at PVA I decided to have a new barrel spun up with a JP QPQ barrel extension which is very nicely machined with no sharp edges/corners as well as +2 gas.
Should have the barrel very soon.
Gas length?
Adjustable Gas Block?
Barrel Make?
If custom barrel what Barrel Extension? BAT?
Buffer?
What ammo or load?
I had this same issue with a custom Bartlein 22" 6.5cm AR barrel on a BAT barrel extension with Rifle gas. That BAT extension has very sharp corners. As suggested by JP I tried polishing the corners of the locking lugs between 12 and 3 oclock with a dremel and the attachment they suggested which looks like a grey eraser head. It helped, the 2 scrapes werent as deep but still there.
After talking to Josh about this at PVA I decided to have a new barrel spun up with a JP QPQ barrel extension which is very nicely machined with no sharp edges/corners as well as +2 gas.
Should have the barrel very soon.
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Thanks, im on it. I never thought about extraction. The barrel is a rifle length christensen. Kak bcg. Non adj gas block. A2 extension with standard .308 buffer.
A 100% fix for this is having +2 gas length, JP or a refined/polished barrel extension and an adjustable gas block. Guys that have switched their rifle gas barrels to this setup have seen the problem non existent anymore.. I did polish my barrel extension and my gas was tuned to just locking back on last round but the problem was still there, just not as deep a scratch.
You can help your issue by polishing those locking lugs and getting yourself an adjustable gas block and tuning it properly...
Most of the vampire bites are from the barrel extension teeth as the ejector forces the spent case towards the ejection port clock position as soon as it starts to clear the chamber during extraction.
As soon as the neck is free from the chamber, it slams into the barrel extension teeth, causing these marks.
As soon as the neck is free from the chamber, it slams into the barrel extension teeth, causing these marks.
Good call to all involved. Polished the lugs. Really cleaned up. I put a resized empty case in the chamber and watched it extract. Its the rear of the lugs that are causing trouble. I also get good 3-4 oclock extraction, so i have not went to adjustable gas. The extended length is a good idea, as is the adjustable, but this one seems to be operating well.
