Teach me about barrel bulges

[slowr1der]

So I'm curious about barrel bulges. I've never knowingly seen a bulged barrel, but I've read online about them. This has me wondering about them. What do you look for when looking for one? I'm just afraid that if I ever buy a used one, I need to know how to check it as I don't want to buy one with a bulged barrel. Anyway, is it something that is major on the outside? Or is it something that may be very hard to see at times? Should you be able to see it on the inside looking down the bore, or is it normally only visible on the outside? What's the best way to make sure a barrel is not bulged before buying a gun? It also seems that some guns I've seen the barrels are not perfectly 100% smooth on the outside although they are usually very very hard to see a difference, but I've seen some in the light where you can see differences. So how do you know if it's just that or a bulge?

 

[JT-AR-MG42]

Inside look is best.

The bulge will appear to be a circular shadow in the rifling. Not all bulges are the same. Some look like a snake soon after dinner, but I have seen barrels with a bulge so slight I could only feel it on the outside after I had seen it looking down the bore. A slight bulge at the muzzle under the front sight is sometimes the toughest to spot.

A tight fitting patch on a rod can confirm a bulge if you are in doubt. You will feel the loose spot.

As an aside, a buddy had a No.4 Mk1 with a prominent bulge close to midway down the tube. It played havoc with any sort of aimed shooting. We took a long 5/8 drill bit and bored the barrel to the bulge from the muzzle. The gun actually shot reasonable 50 yd. groups after our counterbore efforts. Kinda wished we had chronoed it.

JT

 

[taliv]

Guy who frequents my local gun shop did something very wrong with his new custom rifle. I couldn't really see the bulge on the outside but It was obvious when running your fingers down the outside. Easy to feel.

Every bulge could be different though. I don't know if there is some sort of rule of thumb

 

[Jim Watson]

Agree with JT.
I once got taken on a rifle with a bulged barrel. I wondered why the seller at the gun show had put it out uncleaned. But it was something I liked at a good price and I did not worry about it. I should have, the barrel was not only bulged it was "frosted." Hmm, I didn't know there was any corrosive primed .223 out there; but apparently there is. I had the barrel cut and crowned behind the bulge but it still did not shoot well and I was out $135 for a new barrel.

 

[375shooter]

Does anyone know for sure if it's safe to fire a rifle with a prominent barrel bulge?

 

[LHRGunslinger]

It is not safe!

 

[52grain]

I wouldn't want anything to do with a rifle that had a bulged barrel and I certainly wouldn't shoot it.

 

[wally]

I wouldn't want anything to do with a rifle that had a bulged barrel and I certainly wouldn't shoot it.

I've seen lot of old "farm" .22lr rifles with a ringed barrel that still gave plenty of good service afterwards. I'd agree about centerfire rifles though, or bulges you could clearly see from the outside.

 

[busterbrown]

Why would a bulged barrel be automatically considered unsafe? Apart from accuracy effect a symmetric bulge doesnt seem of much concern

 

[Lee Roder]

Another question, what determines the point where the bulge forms? I can easily see why a barrel might bulge at its breach end, but on another forum where the issue of bulges came up recently, there is a bulged barrel where the bulge is within an inch or so of the muzzle. What would cause the bulge to form at the muzzle? Barrel is not tapered.

 

[desidog]

Why would a bulged barrel be automatically considered unsafe? Apart from accuracy effect a symmetric bulge doesnt seem of much concern

Normally, the round travels down the barrel in contact with the lands and grooves, and at the muzzle cleanly departs, at which point the gases behind the bullet disperse. If the round is stable it will fly true. With a bulged barrel, if it doesn't go terribly wrong, the round will loose the contact at the bulge, and the gases will get past the projectile while still in the barrel, reducing velocity. If it does go terribly wrong, the round will not be stabilized and contact one side of the barrel but not the other, and the bullet could rotate, becoming lodged in the barrel, sideways as it were...then you've got a pipe-bomb going off in your hands. Which part of the gun fails first, be it the barrel or the action will dictate how badly you get injured....so yeah, bad idea.

ETA:

What would cause the bulge to form at the muzzle?

perhaps some dirt or sand, etc, got into the muzzle before firing, and slowed, or checked the bullet at that point. The gases behind the bullet can create bulges; also Germans in the Ardennes.

 

[briansmithwins]

Why would a bulged barrel be automatically considered unsafe?

Every time you fire a rifle the chamber and barrel swell a little bit from the 45k-50k psi gas inside them. Gun makers know that this is going to happen and use steel that's elastic enough to return to its original size. That swelling and return is called elastic deformation and is similar to how a spring works.

When the barrel bulged it exceeded its elastic limit and was permanently deformed. That's called plastic deformation. By definition, you've exceeded the design limits of the barrel. The metal of the bulge is now like a spring that's been pulled on too hard. The metal gets harder but is more brittle. Continued stress will result in a fracture.

Since I like seeing and having working hands I'd replace the barrel if it was me. BSW

http://en.wikipedia.org/wiki/Deformation_(engineering)#Elastic_deformation
http://en.wikipedia.org/wiki/Plasticity_(physics)