Smoothing Barrel Extension Lugs

[Ronin22]

Got a Wilson Combat AR barrel and it scores/scratches the brass on the neck and bit on the shoulder of the fired case upon extraction/ejection. I can chamber and eject lives rounds and it doesn't happen. It's only on fired cases, so it's happening on the way out.

I think the barrel extension lugs are sharp at the 12 oclock. Thinking just using a piece of sand paper with my finger to smooth the back sides of the lugs a bit.

Possibly a better way? Thoughts?

 

[supercorndogs]

It's more the 1-3 o'clock lugs. The backside isn't what you want to smooth down, it's the machined edges that need deburred. Sand paper or a jewlers file will deburr then OK. I like to deburr that area and the feed ramps as well as polish the feed ramps before I install a barrel.

 

[John?]

@Ronin22

I use a manual deburring tool to lightly break the edges of rough parts. The tools come in all shapes and sizes so pick what you think will fit best. My most used deburring tool is a simple triangular tool, like a triangle file with no serrations. They are cheap and you can’t do a lot of damage with one.

 

[Bobby Ball]

For what it's worth, I do it on every build. Right or wrong idk, but my thought process is that it helps keep my brass and bullets from getting beat up and affecting accuracy on the bullet as well. Also (in my head) it helps to stay cleaner, or makes it easier to clean from fouling.

 

[msgriff]

Something to keep in mind is mil-spec barrel extensions are case hardened. The thickness spec is 0.010"-0.015" before grind, 0.005" minimum after grind. Not a big deal in low wear areas, but completely removing the hardened depth near the bearing surface or high wear areas of the barrel extension might not be a good idea.

 

[flogxal]

Don't know if diamond stones come in small enough/thin enough sizes but they work really well on deburring and even de-gouging (shallower gouges) of alpine ski edges. I use them for other debur jobs when I can fit them in the space, the ones I have are about 3/4" wide and 2" long and made by DMT just for ski tuning.

 

[Bobby Ball]

I generally do most of it by hand with sand paper or a fine diamond file. Depending on the quality of the part that shows up I'll usually start with 300 wet followed by 600 and 1200. Sometimes I'll wrap it on a fine file to help. And when that's all done I usually use green rouge on a polishing wheel on my Dremel.

 

[padom]

Ive been doing this for a long time. For large frame gassers I only buy the JP QPQ honed and deburred barrel extensions and give to my smiths when spinning me up a barrel.

For sharp barrel extensions this Dremel bit was recommend to me by JP many many years ago. Isn't going to eat material.away and deburs beautifully.

You really only.want to hit the backside edge/side of the lugs in that 1-3 o'clock position where the brass neck/shoulder slams into and drags across upon extraction.

And you can hit the edges of the lugs just above the feed ramps...

With this bit, you can hit these areas with the extension on the barrel. Need to pull it from the upper.

https://a.co/d/a5NSABT

 

[Ronin22]

Ive been doing this for a long time. For large frame gassers I only buy the JP QPQ honed and deburred barrel extensions and give to my smiths when spinning me up a barrel.

For sharp barrel extensions this Dremel bit was recommend to me by JP many many years ago. Isn't going to eat material.away and deburs beautifully.

You really only.want to hit the backside edge/side of the lugs in that 1-3 o'clock position where the brass neck/shoulder slams into and drags across upon extraction.

And you can hit the edges of the lugs just above the feed ramps...

With this bit, you can hit these areas with the extension on the barrel. Need to pull it from the upper.

https://a.co/d/a5NSABT

Just use that bit alone, or as a last polish after some sandpaper?

 

[LRRPF52]

Some shops used to tumble polish their extensions.

The case hardening/heat treat really is critical at the lug roots, which I don’t mess with.

The vampire neck effect is from the leading edges of 2 lugs in the extractor clock position during the extraction and pivoting force caused by the ejector, countering the purchase of the extractor lip on the other side of the bolt.

As the spent case withdraws from the chamber and the neck clears the breech, the ejector forces it into the lead edges of the barrel extension, causing those gouges.

You can deal with it in several ways:

De-edge the corners of the lugs in that clock position.

Reduce ejector spring pressure by shortening the ejector spring or using a lower power ejector spring.

Reduce cyclic rate with adjustable gas and action spring weight.

The main concern for reloaders is obviously split necks from continued gouging and re-sizing/firing.

 

[padom]

Just use that bit alone, or as a last polish after some sandpaper?

Just that bit alone..nothing else required

 

[Desert_Racer]

Small felt wheel on the dremel and Mother’s wheel polish is what I use. If there’s a burr, a small jeweler’s file nice and easy or a piece of emery cloth wrapped around my finger is what I use. Not saying is the “right” way, but it’s worked for me across countless barrels. This is on my 308 LMT barrel.

You can feel the difference when chambering a round. Before polishing, if riding the charging handle while chambering a round, the projectile will hang up on the feed ramps and stop. Copper marks are left on the feed ramps. Burrs gouge cases and in some instances leave little pieces of brass shavings in the barrel extension. After polishing, you can ride the charging handle forward while chambering a round and it won’t get hung up anymore. Feels like it’s riding on glass. No more marks to cases.

 

[Ronin22]

Some shops used to tumble polish their extensions.

The case hardening/heat treat really is critical at the lug roots, which I don’t mess with.

The vampire neck effect is from the leading edges of 2 lugs in the extractor clock position during the extraction and pivoting force caused by the ejector, countering the purchase of the extractor lip on the other side of the bolt.

As the spent case withdraws from the chamber and the neck clears the breech, the ejector forces it into the lead edges of the barrel extension, causing those gouges.

You can deal with it in several ways:

De-edge the corners of the lugs in that clock position.

Reduce ejector spring pressure by shortening the ejector spring or using a lower power ejector spring.

Reduce cyclic rate with adjustable gas and action spring weight.

The main concern for reloaders is obviously split necks from continued gouging and re-sizing/firing.

That's exactly what they look like.