Threaded AR15 SPR barrels, crowns and gunk...accuracy affected?

[RussellC]

Most all AR15 barrels I have used (mostly from Ballistic Advantage) on the threaded end are basically flat around the bore. One Ballistic Advantage Barrel I have is an 18 inch "SPR" barrel, it differs slightly from the other 16 inch M4 type profile barrels I have, the Extension is Nickel Boron coated, and there is a slightly inverted crown, sort or like the crown on a bolt action target barrel's crown.

I was removing the flash hider (basic A2 type) and noticed the "crown" was all lumpy and bumpy looking. Putting a little M-Pro 7 bore cleaner gel on the tip, I let it sit a few minutes and wiped it off. This only removed the black residue from the lumpy surface, but the lumpy material is grey and appears to be lead. Maybe I never noticed this changing barrels and flash hiders before, but I sure don't remember seeing this before.

I know on a Bolt action rifle with a target crown especially, and most crowns in general this is a bad thing accuracy wise. This particular AR is set up like a SPR type gun, so accuracy is important with it more so than my basic carbines.

Is this like a target crown concerning accuracy, and if so how and what is the best method of removal?

Thanks for any and all info here, much appreciated!

Russellc

 

[Allen One1]

I have also noticed a carbon build up on the target crown area under the flash hider. I have a hard time thinking that this doesn't affect accuracy. I'm not convinced that I like the target crown profile on a rifle with a flash hider/brake on it. Would a standard 11 degree crown result in less buildup on the crown?

 

[RussellC]

I'm thinking like you are, the flash hider seems to nix the idea. Looking in the flash hider from the end the barrel goes in, it buts up against the end of the barrel, I just figured the cut it like this for a reason. That said, I;ve always been warned even with a .22 LR not to mess up the crown or accuracy would suffer? I never really thought of it before. Just seeing all that carbon-lead-gunk build up made me wonder.

I have no idea what angle this is, or if it even matters. Just don't like the gunk on there!

Russellc

 

[Skylerbone]

Angle of a crown doesn't much matter, it's there to offer a little protection to the crown (final edge of lands and grooves), it might be that the choice to bevel the crown then butt it against a flash hider is offering a convenient area for debris to gather. Whatever the case it does need to be cleaned like any other rifle or accuracy will suffer.

I'd start with pulling the upper then removing the muzzle device. Use a pierce jag with a small cotton patch soaked in whatever lead remover you typically clean with and let it sit per directions. If you don't have a favorite, Pro Shot or Montana Cowboy Blend work well, Sweets 7.62 for carbon. Then run subsequent tighter patches and remover till it comes out clean. Finish with a lightly oiled patch then a dry one.

 

[RussellC]

The other thing that occurred to me was that if this is lead, is the bullet hitting something like the part of the flash hider that buts against the barrel end and leaving this deposit? Bore gel doesnt make a dent in this mess!

Russellc

 

[Skylerbone]

I was saving these for another thread but here's a mild example of what 50 rounds can do in a factory barrel. Basic 10/22 SS after a regular cleaning. I noticed the fair amount of pressure needed to mop the barrel so I grabbed the lead remover. This one belongs to my significant other, took these about 2 weeks ago.

Basic disassembly for cleaning.


The progression of patches using Cowboy Blend.


A closer shot of some lead slivers and chunks.

 

[RussellC]

Good heavens....I'll get some of that Lead remover!

Russellc

 

[Allen One1]

I pulled mine off to see how bad it has built up since I changed muzzle devises. I have at least 200 rounds through it and it looks more like a light carbon build up. It may get worse if I let it go, but it seems like it is better than when I had the original brake on it. I switched from the original Barrett brake to a Harrell's Tuner. The tuner looks nice and clean with only a carbon layer on it. I found out it is hard to take a good picture of the end of your barrel.

​

 

[Skylerbone]

If you're shooting jacketed rounds though I'd concentrate on a carbon cleaner first and see if that doesn't clean it. Then something for copper. TC Number 13 is a pretty commonly found cleaner that does well with carbon build-up as well, check the muzzleloading section of your local shop.

 

[RussellC]

Yes, that's a pretty light dusting...mine really looks like lead. I have ran my batteries down trying to capture a pic! Just checked after the last application and it is starting to come off... I will get a pic yet!

Russellc

 

[RussellC]

Wow, the more that comes off, the more I think it isnt dished...I am beginning to see the little ledge like your shows, its just so full of crud maybe it just looks dished?!

Russellc

 

[Gtscotty]

It's not an AR, but I have a Tikka CTR in .308 that wore a Silencerco brake for a while. I put somewhere between 800-900 rds through it after I put the brake on and before I took it off. It had a bunch of build up on the crown like you're describing, but still shot well. Cleaning the buildup off didn't seem to make a difference in groups.

 

[HB]

I removed an A2 flash hider from my carbine once (thousands of rounds) and it had severe carbon build up. Enough so that I could cut chunks off with a knife.

My rifle isn't accurate enough to tell but I have to believe it effects accuracy. Although the muzzle is probably free from it the end of the barrel looks like a corroded piece of iron pipe.

 

[Skylerbone]

I've posted this link several times over the years including a few days ago. It may be more than anyone is really looking for but I promise there is insight that's actually backed up and I think it cross-applies well to centerfire as well. Where I thought I was meticulous before in cleaning after every session I am now conscious of what I clean with (including which solvents/oils for the sake of consistency. It's paid off to the point that I feel I am the sole limiting factor when it comes to accuracy.

Bookmark the page and reference it as needed.
http://www.ssvtexel.nl/index.cfm?act=files.download&ui=C5C9D865-2200-0A21-B5F5CF897974784F

 

[FL-NC]

I never noticed an accuracy loss in military sniper rifles with heavy use, often suppressed.

 

[Dr.Rob]

When I first got an AR I'd take off the flash hider every time I cleaned and scrape that stuff off.

A loose flash hider/muzzle device is worse for accuracy than any amount of carbon build up. Tighten it down, forget about it 'til you wear out the barrel.