Post*tune Seating Depth Change

A

abintx

Guest
Once a proper tune has been established for your barrel [powder charge, neck tension, and seating depth] with bullets going through the same hole:

When do you make an adjustment to compensate for barrel/land wear?

After 100, 200, or 300 rounds etc.?

When, and if you do, how many thousands farther out do you seat the bullet?

Anyone exercise a rule of thumb?

Or, do you resort to the initial tune procedure?

Thanks for your reply. Art
 
If you've set up for seating depth as a function of jam plus .010" or jam less .007", etc. then it becomes a straight forward exercise of checking jam and adjusting accordingly
 
Rule Of Thumb

Art,

To compensate for barrel wear Jackie sets his barrels back every 400rds and Gene b chambers up a new barrel every 750rds....

Hope this helps...

V
 
Barrel set back. That's the explanation I was looking for. I knew jackie did something to compensate for wear. I just couldn't remember what it was. Thanks, Vic
 
Vic
I think that there sometimes is more than one seating depth, or rather you dont have to be at any given seating depth by the nats a--. What i mean is that i have found that most of my cut rifled barrels will shoot within say .007 seating depth range. I can seat a bullet as 2.525 " with my tool" and shoot that depth with good results and then shoot the same load set at 2.530 and also get excellent results. When i find this in a barrel, i tend to stay on the long side of the jam so i dont have to worry about moving the bullet out if the throat wears a little. Now maybe not all barrels are like this, but i have found this to be true in more than one barrel.
Also when i have a barrel that i dont see much change with while looking for the seating depth, i shoot that barrel at 200 yards, and not 100 yards. 200 yards will really show those little changes that you wont see at 100 yards. I once heard a smarter man than myself say to always tune at 200 yards. I now know first hand why that man made that comment.
There will be a lot of times at 100 yards, that i just dont see much change by moving the bullet in or out a few thou. Take that load to 200 and it becomes very clear. I will also say, when you think you have the right seating depth found while shooting 100 yards, shoot that that load at 200 yards, because you may be surprised in what you see. What you think might be correct, could be way wrong!! Just my experience. Lee
 
Art, when I asked Tony Boyer this same question, he told me that he did not change the seating depth to accomadate for throat wear. Although he doesn't fire more than 1000 rounds through a barrel that he uses in major matches, it is amazing to me that the original seating depth will remain the same. Good shooting....James
 
Seating depth ain't likely to matter much to a barrel Tony shoots at a "major match".
 
Lawrence.
Good video. Do you think that you could have gotten to the same place with a powder charge adjustment, leaving the seating depth where it was? I should add that I have seen exactly the same thing that you showed on your video, more than once, at about the same amount of change. I think that this can happen when the load is on the ragged edge in the first place, and a little wear takes place, and conditions change a bit.
Boyd
 
Hello Boyd.

I had been chasing the powder load all day on Saturday and for the Sunday morning match. This was the Sunday afternoon 100 yard agg and I was still stuck with the vertical that you saw on the first target. The groups tightened up only when I changed my seating depth. When I got home I measured my lands with the Stoney Point gauge and found that the lands had moved in to the barrel about .002. So my field adjustment had basically chased the lands as they had worn. As a point of interest, this was a small match so I had one of my favorite old barrels on the rail. At the end of that shoot, that barrel had 3,226 rounds through it. It is an old Krieger with a .237 ID and it just loves to shoot.
 
Lawrence,
Thanks for the additional information. Let me ask you one more question. Although most short range benchrest shooters use bronze brushes and pull them back into the muzzle, brushing on both the in and out part of the rod stroke, there has been some discussion on the internet about some supposed problems caused by this, at the crown, and the use of brushes in general. How have you cleaned this barrel? Have you had it recrowned, or set back?
Boyd
 
Boyd,

About 10 years ago, after hearing that high pitched screech of the brush going through a barrel, I decided to not use a brush at all. My first patch is Butch's bore shine. Second patch is short stroked with Butch's and some Sweet's copper remover. Third patch is Butch's and Sweet's slowly pushed through. I then let everything sit until its time to clean patch it for the next match. About every 100 rounds, I short stroke some JB's bore compound. None of my barrels have seen a brush in the past ten years.
 
I usually retire a barrel at somewhere between 1,400 and 1,800 rounds. A couple of years back, after being amazed at how well that rail gun barrel kept shooting, I grabbed one of my retired HV barrels, JBed it, turned some new brass and found that the throat had moved out about .003. Loaded up its favorite load of N133, sat Bart's double ogive at the new seating depth and that thing started shooting as if it only had 300 rounds through it. Since that time I have "unretired" a couple of LV barrels with the same results.
 
So....what is your mixing ratio for Sweets to BBS, or do you just put them on the patch sequentially? With 133 I have short stroked BBS for several patches, until the last patch only showed the color of the solvent. Beyond being more aggressive on copper, is there any other reason for the Sweets? Although I have not given up on brushing, I do a lot less, particularly if I can get a good looking patch by the fourth, short stroked. I only reach for the brush is I can't "get there" with a reasonable number of patches, or if there are a lot of rounds down the barrel since the last cleaning.
 
Couple of drops of Butch's then a couple of drops of Sweet's. I figure the Butch's goes after the carbon and Sweet's takes care of the copper.
 
Something to think about guys, a few years ago Jim Borden did a study and wrote an article about ammonia cleaners and barrel life.

Think about this, you come off the line and the barrel is really hot and you wet it down with BBS MX, Sweets, etc and let it set. Knowing what I know about chemistry and nitric compounds and heat this is not good. Working in a very large chemical plant for 40 years and seeing what acids do to 304,316, 319, stainlesses and Inconel/Hastalloys etc. steels, etc. makes me really wonder if we know what we need to use?

If the barrel is not coppering do we even need ammonia cleaners? I started a couple of new barrels out recently only using Hoppes. We'll see.

Sorry for the hyjacking...do we need a new thread?
 
So ... to summarize the answer to my original question, it sounds like there are two methods:

1. move the bullet out/seat it longer in the case as the throat wears

or

2. set the barrel back.

Thanks, gentlemen.
 
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