Rifling in AR-15 Barrels

Hand-Lapped Barrel versus Budget Barrel

The first bore-scope view pictured below shows the rifling on a new Ballistic Advantage "Modern Series" AR-15 barrel.  Note the distinct tool marks forming “ridges” on the rifling running perpendicular to the direction of bullet travel.









The next bore-scope view shows the rifling of a hand-lapped Krieger AR-15 barrel.  Note the absence of perpendicular tool marks on the rifling.  This particular barrel does have approximately 100 rounds fired through it, but this is what the rifling looks like when you receive your new barrel from Krieger.







The next bore-scope view shows the throat of an unfired Krieger barrel.  You can see that the rifling proper (indicated with the red arrow)  just ahead of the leade, shows no perpendicular tool marks.









Hand-lapping is a time consuming, labor intensive process.  This is another example of what you’re paying for when buying a top-tier barrel.



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No way!.  My bla bla what ever $79 barrel shots nats ass all day!   Just kidding,  nice example pics OP.

Well that's not to say the barrel with the tool marks won't shoot nicely - it may also have dodgy fouling characteristics or other negatives, though.


I have a hammer forged barrel from a very reputable maker that looks like that top picture.   I'm assuming the tool marks were in the blank before forging.

All other things being equal I'd much rather pay for the nicely finished bore, obviously.

An issue with hammer forged barrels is that most of their chambers are still cut with reamers.  Tool marks remain in the throat.  The bullet , or most of it, passes through those rough edges before entering the bore.  

Hand lapping a single point cut or button rifled barrel also does not address the throat.  

This is why many custom barrel makers recommend a break in procedure to bullet polish the throat while simultaneously get copper out of both the throat and the rifling grooves before it builds up.

You end up with a lapped bore and throat.

Tubb's Final Finish bore polishing bullets, but only use half of the kit. There is no need to shoot the entire set of bullets IMO.

I'd like to see an before and after of a barrel that has been swabbed/lapped with JB Bore paste and kroil.

I'd love to see a comparison of the "budget" barrels (Criterion, BHW, Faxon, etc)

Would a "break-in" routine work better to smooth out the tools marks versus just plain firing X amounts of ammo then clean? Or at least to reduce copper fouling?

Someone here did a report on another forum.

If I recall correctly, group potential was the same, but the broke-in barrel went longer before accuracy fell off and was much easier to clean than the control barrel.

I'd be interested to see what higher quality production barrels look like i.e. Larue, Rainier etc.

I’ll see if I can scope both this weekend. Both have some rounds on them, but less than 250 on each. Also have some BA and bartlein’s with low round count.

I do know I had a 700p with a less than stellar looking bore, but it hammered! Could get 300+ rds on it before accuracy would fall off, which worked for my application. Sometimes the scope will only tell half the story.

Oh, I love that kit.

Bore dimensions play a larger role in the accuracy of a barrel than the interior finish.

Guessing you mean consistent bore ID from one end to the other?

Beyond that would a rougher bore that gathers copper in spots not be expected to be worse than one with a smoother finish?

Last question.  I get that one would not want to fire lap (Final Finish) a new Lilja but would it do as Tubbs claims and give a barrel that's getting shot out some bonus life beyond trying to save some sewer pipe of a bore that's junk (or is that all FF is really good for)?

Here are a couple pictures from a LaRue in-house "Rearden Steel" tAR barrel. The bore scope is not a nice as Molon's,  but you get the idea. This barrel has 1000-1500 rounds fired.

Throat:


Port:


Muzzle/Crown:


I've posted before, the LT in-house barrels are a bit of a mystery to me. Look good on the scope, shoot well, and seem to wear quite well. I have a douglas SPR barrel that shows a lot more wear at 1000 rounds than this LT barrel does, but I do not think it is a fair comparison as the douglas has fired almost all MK262 pressure ammunition while the LT shot mostly 55gr .223.

I've also scoped a 7.62 tOBR barrel from LT. Also very polished, sharp rifling. Their older LW50 barrels are hard to see much with a less expensive scope due to the odd rounded rifling.