Barrel Crown Defects on New Barrel? Picture & Questions

[Ellery Holt]

Barrel Crown Defect?

Here is a picture of the barrel face on my new Bushmaster ‘pre-ban’ configured A2 profile barrel. I have concerns that the denting and ripples on the flat end of the face of the barrel will affect accuracy. Also I am curious as to what causes this particular pattern of impressions on the barrel face.

Here’s the picture and a description of what I can see up close.

Just outside the upper left corner of the picture I’m holding a flashlight and shining it parallel across the face of the barrel to bring out contrast in the denting of the barrel face.

This is a distinct pattern that looks like the face of the barrel was hammered by something with a large circumference. The face is very slightly higher at the upper left in the picture – not as higher as it looks, that’s just the light bringing out the contrast.

The 45 degree chamfer is pristine and is in excellent condition (this barrel hasn’t ever been fired). The edge that last touches the bullet as it exits looks perfect. The edge that is the beginning of the face of the barrel looks perfect too except that it extends just a little bit more outward in the upper left area of the picture since the barrel face is a little bit higher there. Here's an exaggerated picture of what I mean about the champher extending further into the higher area.

When I screw on a Phantom flash suppressor without the peel washer it contacts the upper left of the face first as shown by the transfer of oil. The peel washer I have stops the inside face of the Phantom flash suppressor from touching the barrel face by one half a turn of the FS.

I had another Bushmaster barrel, a post-ban, that had these same large-circumference dents only they were very very slight, and again the chamfered crown area and surface was perfect.

So, my two questions:

1) Will the denting and ripples on the flat end of the face of the barrel will affect accuracy?

2) What causes this particular pattern of impressions on the barrel face?

Thanks so much.

Edited to add: By the way, of all these different surfaces and angles and such, what is the 'crown' exactly?

Thanks again.

 

[dakotasin]

the crown is that part immediately surrounding the bore, w/ the chamfer. the rest of the area is just the muzzle.

looking at your pictures, it doesn't appear that these scratches or whatever interfere w/ the crown, so there should be no effect on accuracy. however, look at your crown to be sure the scratching does not extend into it.

if i was in your situation, i would take the gun to a 'smith, and have him cut a quarter or half inch off the barrel to get everything true, and re-crown. cost of a cut and crown should be around $40. check to find out about the threading for your f.s., but i suspect you'll want to cut and crown (and thread) to get the mating surfaces square.

i have no idea what could be scratching your muzzles, but if it is consistent from one bushie to the next, it may be from the saw when they cut your barrel.

 

[Jaywalker]

I'll jump in with a reasoned, erudite opinion, some of which may even be right.

First, the chamfered area is the crown. If it is as you describe it, pristine, then probably the unsightly areas will not affect accuracy. The crown's purpose is to ensure that the barrel "lets go" of the bullet all around the diameter of the muzzle hole at exactly the same time - letting go at one side and not the other would affect accuracy. The point of the chamfer is to protect the edges of this critical hole. If you were to promise never to bang it into anything, you wouldn't need the chamfer as a perfect 90 degree barrel cut would suffice.

Second, from what I can see, the scars appear to be from the saw that cut the original barrel length down to what you now have on the finished rifle - barrel blanks are longer during the drilling, (possibly) lapping, and rifling stages. Crowning is done after that.

Third, if you own a Pre-Ban upper, I hope you also own a legal Pre-Ban receiver, or are otherwise entitled to own such an upper. If you do not, or are not, you are possibly in violation of federal law.

Fourth, as these are cosmetic issues, but do indeed look worse than I expect to see from Bushamster, you might try contacting their customer service. Perhaps they can suggest an approach to repair or exchange it.

Jaywalker

 

[Amish_Bill]

Bushmaster has traditionally been good about replacing unfired components that don't meet your requirements. This is an obvious factory mar, so they should be nice about exchanging it for you.

That is under the finish, right? It looks almost like it's to bare metal. If it is to bare metal, call them and tell them that your barrel arrived scratched.

Note about taking an AR part to any old gunsmith.... I've seen one come back from a "fine smith".... to bad this "fine smith" was only setup to do traditional blued guns. Can you imagine the result of someone using a blueing tank to touch up a parkerized barrel? It was UGLY!

 

[Ellery Holt]

Another Picture

Okay... saw cerf marks... I can see that. It sure makes more sense than the idea I had that the muzzle had been hammered on.

And thanks for the definition help too.

In that first picture it sure does look like deep cuts, but they're actually 'steps' and I took another picture to try and capture that better. I took this picture using a magnifying glass in conjunction with the camera, and I like the results.

You can see that the crown is indeed very nice. The saw marks show as 'steps' and maybe you can even see that the chamfer has a little more area where the muzzle is a tiny bit higher.

The park treatement goes halfway into the muzzle I see now too -- does that matter?

With this new view guys, how sure are you that the issue won't affect accuracy?

You see, the cosmetic issue doesn't bother me... it'll be under the flash suppressor anyway. I don't want to exchange it if it's sure that it won't affect accuracy.

Thanks again

 

[Amish_Bill]

Judging by that last picture, the marks are purely cosmetic. They don't extend into the bevel leading to the rifling.

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