how to smooth sharp edges on barrel extension lugs

dan158

New member
This is not on the ramp but above and on the back side of the lugs.. My brass are getting nice scars and think this is why getting split necks.. Or should I call the barrel manufacturer and see if they will fix it?? This is my first year I fired it since I built, not sure if they will take care of it because its been 2 years since I purchased barrel... Thanks . Dan
 
ypu have gotten some good info in your other thread. My suggestion is to go back and re-read the replys = lower your powder charge and anneal you brass.
 
Originally Posted By: midwestpredatorypu have gotten some good info in your other thread. My suggestion is to go back and re-read the replys = lower your powder charge and anneal you brass.

Lowering powder charge is not going to remove the markings on my brass.. I can duplicate them just from chambering a dummy round and ejecting.. So my charge has nothing to do with the markings and deep scratches I am getting..
 
Try a dremel with a polishing wheel. I've got a small pointed polisher that works well for that and the feed ramps.
 
Originally Posted By: 204 ARTry a dremel with a polishing wheel. I've got a small pointed polisher that works well for that and the feed ramps.

Its actually on the extraction of the case. So wouldn't I have to get to the back of the lugs to smooth those ones?? And to get that angle I would have to take the barrel off the receiver I would think.. Thank you. Dan
 
Originally Posted By: dan158Originally Posted By: 204 ARTry a dremel with a polishing wheel. I've got a small pointed polisher that works well for that and the feed ramps.

Its actually on the extraction of the case. So wouldn't I have to get to the back of the lugs to smooth those ones?? And to get that angle I would have to take the barrel off the receiver I would think.. Thank you. Dan

No. You need to get to the edge of the lugs. It doesn't take much. A small file like RK said would work too. Don't get carried away.
 
And for the record, I don't usually worry about it, and after a few hundred rounds it smooths itself it seems. It's not causing the split necks on your 204, hard brass is. I've split my fair share of 204 necks, now they all get annealed before the 2nd loading. No more split necks.
 
Originally Posted By: 204 AROriginally Posted By: dan158Originally Posted By: 204 ARTry a dremel with a polishing wheel. I've got a small pointed polisher that works well for that and the feed ramps.

Its actually on the extraction of the case. So wouldn't I have to get to the back of the lugs to smooth those ones?? And to get that angle I would have to take the barrel off the receiver I would think.. Thank you. Dan

No. You need to get to the edge of the lugs. It doesn't take much. A small file like RK said would work too. Don't get carried away.

Oh ok got it.. Thank you all and will not over do it. Just hit couple times with a rat file and try then.. Again, Thank you all.. Dan
 
Small diamond file, then a Popsicle stick wrapped in paper, then a Popsicle stick rubbed with lapping compound. Then lap the bolt lugs using compound rubbed on the back of the lugs. Get over generous with that and it'll round the corners.

Clean up the bottom two lugs on your bolt too, while you're at it, so you avoid the scratches on the cases from the bolt riding over top as they strip the round above it.

As others mentioned, scratches/gouges aren't causing split case necks. It doesn't happen that way.
 
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Originally Posted By: Varminterror

As others mentioned, scratches/gouges aren't causing split case necks. It doesn't happen that way.

The ones that split was 4-5th reloads and the gouges didn't help on the next reload.. These gouges in my opinion are pretty deep.. Thank. Dan
 
I crossed over my 200th ground up build this winter, worked on hundreds of other AR's over the years, and the last time I checked my batch-tracking sheet, I was over half a million reloaded rounds to feed them (vast majority = 27.3grn Varget under 50grn V-max or 55grn HPBT). They tend to beat the he11 out of brass, especially the way the factory AR industry has gone with a pattern of severely over-gassing their actions to ensure reliability.

To steal the term from Kimber; doing the "melt job" on the barrel extension lugs takes elbow grease and time. It's easier before you install the extension, but most folks aren't equipped to remove or install one on their own. I have a few sets of mini-files just for this purpose, including some with the handle/spindle cut off so I can PULL the file from the head end, to let me work the backside edge of the extension lugs from both directions. The Popsicle sticks, paper, and compound work well to polish up once the major cut is made - and again, the same melt job should be done on the bolt locking lugs as well. Mapping the bolt to the extension once the rest is done ties it all together and helps reduce the risk of broken locking lugs (and potentially improve accuracy).

It's not rocket science. The AR-15 was designed to be serviced by grunts with an enlistment IQ requirement of 80 (benchmark average person is 100). They aren't magic. Just spend the time to fix the laziness built into your rifle by factory producers. Gouges on your NECKS which are that deep can also be driven by an over zealous ejector spring or an over-gassed action (way too much force going on at that part of the stroke). Smoothing it up will help, but might just leave you with dented necks instead of gouges.

Any CHS or rim damage? How much is your shoulder moving forward upon firing? Any idea what your throat dia is? What's your loaded round neck dia vs. your fired cases? Drop the tip of your caliper into the gouge - how deep is it really?
 
Originally Posted By: Varminterror



Just spend the time to fix the laziness built into your rifle by factory producers.

Its not factory barrel... Its A JP super match barrel and it upset me that I paid a lot for that barrel from them back in 2014.. This is my first year to fire it..
 
Originally Posted By: dan158Originally Posted By: Varminterror



Just spend the time to fix the laziness built into your rifle by factory producers.

Its not factory barrel... Its A JP super match barrel and it upset me that I paid a lot for that barrel from them back in 2014.. This is my first year to fire it..

Really doesn't matter who built it, commercial suppliers don't fit and tune their parts, as you're finding out.

But it sounds like you have it all figured out. The advice you asked for is looking you in the face above this post, if you don't want to take it, then be happy living with a typical brass-eating AR.
 
Black Hole uses BAT extensions. They will often scratch brass. It takes me about three minutes to go in with a Cratex polisher and break teh sharp edges on the extensions if the problem pops up. Sometimes machining quality is almost too crisp and precise in today's world.

I'm sure that JP would fix them for you but of course you're looking at $10.00 postage and the inconvenience of a tear down.

Greg
 
Originally Posted By: GLShooterBlack Hole uses BAT extensions. They will often scratch brass. It takes me about three minutes to go in with a Cratex polisher and break teh sharp edges on the extensions if the problem pops up. Sometimes machining quality is almost too crisp and precise in today's world.

I'm sure that JP would fix them for you but of course you're looking at $10.00 postage and the inconvenience of a tear down.

Greg

I took it to my local gunsmith to clean them up and he just called tonight and said it was done.. I didn't want to get into that after thinking about it..
 
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