When a barrel is set back because of erosion of the lands from many rounds, how far back do you usually need to set the barrel back?

Is this a recommended procedure?

Thanks, Fred

I have had them turned back about 1 thread,then ream out the chamber to specs.

Thanks plainsman. I had heard the erosion does not go down very far so it must be true. I figured a couple threads at least.

Thanks again.

I've set my NRA match bolt gun's barrel back three(3) times now,.....It's a GREAT 1 in 8" .223 that shows .0001" (per shot!) of throat loss, when running "across the course",rapid fire, etc.
Sierra told me that the long "Flying Snake" 80 Gr, SMKs would be a bear,...and they were right. So,.....every 1000 rounds or so, I've payed for the play.

the first 2 setbacks were .100" ( one turn on a 1 in 16 pitch), third was .200. The barrel's got one of those Clamp on Front Sight/ Globe mounts, so indexing is no real chore

I just wish I'd had a longer cylindrical O.D.,I'd do it again,..... But,...it's time to spool up the new one.

Gotta' say, the thing was always a great rifle, and seemed to just get better with each setback.

If you're only gonna' do it once,....go 2 threads, but than and again,..... a Hundred thou is a LOT of new material to dig into.

You're right, .....just freshening the throat up will probably be enough.

Old axiom,......"The Barrel's the cheapest part of the rifle"

Let us know how it plays out.

GTC

I toggled this post because it wasn't in the Campfire forum and I have a question, did you set the barrel back 1 turn which with a 1 in 16 pitch would be .0625" or did you set it back .100 which would indicate a 1 in 10 pitch if you went 1 turn?

To the OP, barrels are usually set back an even 1 or 2 turns so any printing or sight holes are properly indexed.

Until the bad area is gone. To regain lost accuracy through barrel setback, you will need to put it back like it was. Back to fresh metal. Erosion can affect a fairly large part of the bore. I would scope the bore to see if it will clean up within a reasonable distance, but the cost to cut a new tenon, new threads, chamber, throat and install can be half the cost, or better, of a re-barrel. I would have a real heart to heart with the customer before doing it. After I scoped it.

The gun in question, is a Sako 223 with a Douglas barrel. I have no idea how many rounds have been shot thru it, as I bought it used. It was such an accurate gun, shooting in the .200's. Now the accuracy has gone to over 1/2-3/4". So I am assuming the barrel has some erosion. I will get it bore scoped as I don't want to do the work until I know what is causeing the problem.

The problem has to lie in the barrel as I have refreshed the bedding.

I appreciate your assistance.

Fred

If there was no change after the bedding, then you could have a barrel problem. Don't overlook the crown. The crown is one of the most critical yet one of the most overlooked areas when trying to locate causes of accuracy problems. Crowns need to be recut from time to time to maintain it's edge.

I was probably cross referencing to Sharps rifles (10TPI)

So sorry.

GTC

Malm

In your opinion and experiences, does shooting have any eroding factor on the crown or is it damage caused from mishandling? I once bought a new Remington 700 that had a bad crown, but it was not noticable using a glass. It was simply a process of elimination in finding the problem.

No, the least amount of wear on the barrel is at the muzzle. Crowns sustain damage through neglect and careless cleaning.

Setting back a barrel is tricky, easy when you know how to measure wear.

Your gunsmith should have a set of pilots for each caliber graduated in 0.0002 increments. He needs to determine which is the tightest pilot that will go in the muzzle.

As the area in the throat errodes, it becomes larger. At some point it will be the same dia as the muzzle. You gunsmith can determine this with his set of pilots.

We used this system when we were shooting many tens of thousands of rounds of p. dogs. A typical days shoot was 650 rounds of centerfire with some days going 1000-1200 rounds. We had our own reamers made and would set back the chambers on our 243 AI's in about the 1800 mark. How much we set them back was between .750 to 2" to get into fresh lands. There was usually fire cracking, but that did not seem to matter much. What did matter was having good rifling to get the bullet started straight in the barrel.

We touched up our crowns with a cut off push rod out of an engine with valve grinding compound.

Later on we started trying to measure our barrel wear and telling the gun smith how much to cut off. We had Dan Green make us the end of a chambering reamer that held a pilot only. We had this piece brazed on a welding rod. We ordered a set of pilots in 22 and 243 caliber. We first determine what pilot fit the muzzle tightly, then we would put a .0008 over dia pilot on the end of the reamer fixture. The welding rod was inserted into the breach end of the barrel and "pulled" into the barrel tightly. We marked the spot on the outside where the +.0008 pilot stopped. Next, we did the same procedure with a .0006 pilot, then a .0004, then a .0002 pilot. From there you coud pretty well guess how much you needed to cut off to get into fresh rifling.

This trick of measuring leade growth was taught to me by a master gunsmtith that is long gone...hope someone may get some use out of it.

Accuracy of .375 and below was the only thing acceptable for our dog rifles.

I bought a Krieger 6mmBRX take off barrel with shot out throat.
I cut new barrel threads and a new 6mmBR chamber.
I have pin gauges in sub thou increments.
I cut the 25.5" barrel down until a .2365" pin gauge fit the bore tight as tight as at the muzzle.

That was until the barrel was 22" long.

I had to cut off 3.5" of barrel to get the right bore in front of the chamber.

Before Varmint Hunter magazine came out, p. dog shooting was 650-1200 rounds a day of centerfire.

We started off with 29"-30" unturned blanks or Max heavy varmint countours with 6" of straight cylinder infront of the action.

We would rechamber twice in the 243 AI, then go to 6 BR at the 24" length...accuracy was bug holes.

We found that powder type made a big difference in throat errosion with ball powder giving the least amount of throat wear.
Stick powder eat throats in high volume shooting.

Interesting.

GB