doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Small bulge 5" from standing breech - any ideas?

I have a 12ga Fox cromox steel barrel with slight bulge about 5" ahead of the back end. In other words 2 inches ahead of front of the chamber and forcingcone. Bulge measures .017 inch more than the bore diameter in that area. Ribs still look tight and barrel rings. Looking in the bore , bulge (dark spot) is only on the side of barrel farthest from center rib. Bore is perfect on side closest to center rib. In other words the bulge is not all around the circumference. The barrel outside surface can be filed to contour and reblue but what options do I have to open the bore in that area so bulge can't be seen? My Skeets shows the bulge is .017 above bore diameter but that's only on one side. Bore probably has to be opened at least twice that to clean up the ring bulge.? Ideas please. Thanking you.

That is good sized bulge in a scary spot......there is no cleaning that up. Those barrels are toast!

Check with Mike Orlen, he will have some thoughts. When I was was young and dumber I shot a short chambered LCS 16 with a worse bulge in a high pressure area and still have all fingers.
Dumb luck?

Bill

The metal has stretched beyond its elastic limit which completely changes its properties. My eyes and fingers I value......

When you look down the bore is that area like a black hole? The guys are right. Time to call in a pro. That barrel is most likely ruined.

SKB is a professional in all sense of the word and there is none better. Look no further Joe, if he said the barrels are done then the barrels are done.

Check with Kirk Merington he is the good barrel man.

Just my swag. If I were to just assume that the bulge is all the way around and about .017 per side or .034 diameter in an area of the barrel that was .728 bore and .928 O.D., that amount of stretching of the metal comes to about 3% "elongation" in a circumferential direction. If the O.D. is smaller, then the elongation is slightly less greater.

Just using 4140 normalized as a baseline here, it has around a 18% elongation at failure. Of course, as the elongation gets greater, the material thins, at these higher elongation numbers.

The chart below shows the red line, starting on the left, going nearly vertical but slightly leaned, in a straight line. That is the elastic region where any stretch will return to original shape. When it takes that corner and starts to arc to the right, that corner is the beginning of the plastic (yield point) region. That dot represents the ultimate strength, and the x to the far right is the failure point at 18% elongation.

If you draw a line straight up from the mid point between 0.02 and 0.04 on the bottom (3% elongation), you see that it intersects the red line at about 105,000 psi. To yield it further, it will take 105,000 psi instead of the 95,000 psi it took to yield the not previously yielded normalized steel. The steel becomes slightly stronger from the cold forming at lower yields like yours and up to about 8%.

Chuck, 4140 is very good steel and I don't know for sure on how many barrels were ever made of this. I think most were in the high 10 series and would think the elasticity is different, and so would the tensile strength.

Regardless, thanks for looking into this, and 5" from breech is still way to close for comfort. It could have been an imperfection in the steel to cause this and an x-ray might help to determine this.

David,
While I don't have definitive evidence, the Chromox Fox barrels are likely not a 10xx series but rather I believe they are a 4xxx series or something close. Tensile will vary, but the elongation is going to be 'in the neck of the woods' and this bulged barrel is way down in the elongation 'woods'. In the example above, there's about a 10% increase in yield strength from the elongation of 3%.

Things you and millions of others rely on daily for your safety are made from cold formed steels. Most people don't realize this.

While an Xray may reveal inclusions and some flaws, it's really difficult to see much. If there was a flaw like an inclusion, it wouldn't have bulged in a ring.