30” 6.5mm take off barrel. What are you building.

[Mike Matteson]

An old German gunsmith taught me an old world way of dealing with errsion on barrel set backs. If you can find a point where the bore dia matches at the muzzle, that does not wear, with the position of the new throat, you can have great success with the barrel set back.

Again, the muzzle does not wear past the first 1/4-3/8". Using A grizzley rod and reamer pilots that are graduated in .0002 increments, determine the dia at the muzzle. Next, using over size reamer pilots on the Grizzley rod begin measuring wear on the breach end. Put a piece of masking tape on the barrel and mark the distance that each over size reamer pilots penetrates the bore and the location. Find the exact point in the barrel where the "new" throat location will match the muzzle dia. Get ready for a shock at how much has to be cut off.

Set backs with max heavy varmint contour barrels along with heavy Palma can be accomplished resulting in great accuracy results.

It is not uncommon to cut off 9".

I just cut off 9" from a 6BRA of mine, MHV contour. The barrel started showing a shot at 1100 rounds of 105s shot with H4895. Also, I bought a used 6.5/284 fluted barrel with 600 documented rounds. I got the barrel cheap and thought I would take a chance. I determined that the best I could do was to locate the new throat at a place where it was .001 over the muzzle bore dia., bummer....it is going to be a short range hunting barrel in 260 AI. Also to the barrel's detriment, the Muzzle dia and the breach dia are very close but under the fluting, the bore dia opens up to a dimension that I can not measure accurately. The whole project will end up being a lot of work for a fire form barrel, but I got to play. I will buy a lottery ticket if the barrel will shoot 1/2".

Cutting off a barrel, helter skelter without taking to account the bore dia, is a Hail Mary at best depending on your desired accuracy.

Very interesting on your imput. It had been my understanding that the muzzle are being cutting back a couple of inches. I alway kind of wonder about that. I realize that damage to the muzzle causes problems. What I didn't realize is just how much the lands were eroding back into the barrel. I have a better understanding now. Thanks again. At 76 not to old to learn, hard to brake old habits.

 

[VinceMule]

Mike, backwash from powder gasses can sometimes erode the bore 1/4"-1/2" from the muzzle.

Now, having said that, back pressure from using a can is another issue.

Most people never consider a barrel set back.

 

[Mike Matteson]

Mike, backwash from powder gasses can sometimes erode the bore 1/4"-1/2" from the muzzle.

Now, having said that, back pressure from using a can is another issue.

Most people never consider a barrel set back.

I have figure to set back my 6mm/280AI as needed. I do have a 2nd barrel for it too. Figuring that it will be a barrel burner. You are saying "can" as in suppresser? I do have some muzzle brakes on a couple of rifles.
I am getting ready to order out a 2nd longer 25cal barrel. I had a barrel order out over a year ago. People sent ou the wrong barrel and twist rate.
This the 2nd time on re-order on a reamer, and barrel. I know one thing is I will own my reamers going forward.
The other is reload practices have changed over the years. For the better I would say. Sure not back in the days of the C&H presses, sizing & bullet seating dies.

 

[Calvin45]

Mike, backwash from powder gasses can sometimes erode the bore 1/4"-1/2" from the muzzle.

Now, having said that, back pressure from using a can is another issue.

Most people never consider a barrel set back.

What do you mean by “backwash”? I’m trying to understand this phenomenon here. I had wondered if maybe the muzzle end erosion had to do with the very abrupt drop in pressure once the bullet exits completely causing almost like a vacuum cavitation effect on the metal? Cavitation induced by turbulence and especially in the rarefaction following a pressure wave certainly can wreak all kinds of havoc on metals or any other material, it’s interesting to see the pictures of massive ship propellers eroded looking on the sides/edges of the blades that ARENT “cutting” into the water, but are experiencing the suction and turbulence created by the rest of the blade before them having gone through the water and creating that vacuum-ish situation. Cavitation erosion. Is that what’s going on when a rifle barrel erodes more at the muzzle than it does say halfway down the pipe?

 

[VinceMule]

Calviin, you have the idea. It takes a lot of rounds, and not in all calibers. Also, moisture can cause degradation of the steel in the first 1/2" of the barrel on chrome moly barrels.

You can look at the first inch of the barrel back from the muzzle with your bore scope for a start. The gunsmith can use reamer pilots as a gauge to see if the bore gets tighter 1/4"-1/2" in from the muzzle.

 

[dogz]

Q: What are you going to build?

A: None. I would have kept it as-is and used its remaining barrel life until it was due for a re-barrel. It is not worth the time, money, or effort, but that's just me. I understand there are people who have had success in re-chambering, though.

Boom done..............tomato stake