Really not benchrest but I have a rifle which i slugged the bore due to accuracy problems that are driving me nutz! The bore is .0001 (one thousanth) oversize. How much should this affect accuracy?

Doug,
That isn't your problem.
Butch

Butch the rifle is a 375 jdj that I built useing a shilen #5 CM barrel. When i shoot cast bullets that are .001 to .002 over bore size the guns shoots well but it won't shoot jacketed bullets as their diameter is .375 & the bore is .376, no gas seal with jacketed bullets ? Groups are about 2 1/2" at best with all kind of different loads. A friend who shoots nothing but cast suggested slugging the bore & thats when we found the oversize issue.
I am going to really hate being restricted to shooting cast bullets.

Doug,
The bore size of a 375 Shilen or other brands are .366 approx. The groove size is 375. You said .0001 oversize. What is .0001 oversize?
Butch

When I slugged the bore with a hard cast .377 dia bullet it comes out .376 groove to groove. When I tapped a jacketed .375 Hornady into the muzzle only the lands mark the bullet. The groove to groove diameter is .376 & the diameter land to land is .369.

Have you called Shilen? That is what I would do.
Butch

I might do that. Thanks Butch. I guess I should have slugged the bore before I started this project. I'm just glade the rifle is for me and not a customer.

Their seems to be a problem with their website. Do you have their phone number Butch?

Doug,
They are fighting an internet problem as we speak. Try 1-972-875-5318.
Butch

If you are using a hard thick jacketed bullet using something thinner such as the bullets made for the .375 Win.
You might not believe this but the large majority of barrels on the planet are oversize and shoot well. Many of the European military rifles were designed with .002 to .003 clearance and the lands were expected to displace enough metal to bump the bullet up to fit the grooves.

Oh yeah my Marlin .375 Win has a groove diameter that is .3775 opening to .3778 at the muzzle.

Interesting. Thanks I'll have to try that.

Have you tried the 260gr. Accubonds? They seem to outshoot every load I have had as my go to loads for .375s, including 2 375jdj's...

Bob I do have some 260 ABs but havn't tried them yet. Based on your experiences I'll give them a try. What powder & load do you use with the 260s?

I always use a pure lead slug for slugging a bore. Easier to push through.
I think they will give a better reading than a hard cast slug.
The harder the slug the more it will spring back to a larger diameter.
Leo

That is one reason I do not use Shilen barrels; I have had problems with them walking shots.
What action is it built on; maybe it is bedding.
I only use Douglas barrels. They work.

quote:

Originally posted by dpcd:
That is one reason I do not use Shilen barrels; I have had problems with them walking shots.
What action is it built on; maybe it is bedding.
I only use Douglas barrels. They work.

One of my 375/404 rifles has a Shilen barrel - the other has a Lilja barrel.

They both shoot extrembly we’ll - they still shoot touching 3 shots at 100 yards.

I have experimented with different size bullets in these 375/404.

As we make our own lathe turned bullets, we can control the diameter to any size we wish.

I cannot remember finding any appreciable difference - 100 yards - in bullets diameter that varied up to plus or minus 0.003.

Nor could we notice any excessive pressure signs in the loads we use for hunting.

I actually make my own hunting bullets for these two rifles slightly undersized.

We had a Blaser R93 in 375H&H that had a very small bore size!

Was blowing primers on starting loads with our Walterhog bullets.

It started shooting well with bullets - I think - which were down to 0.372.

I tried 0.277 bullets in a 7x64 rifle, and they shot reasonably well - as accurate as some factory ammo in 7x64???!!

That is a difference of 0.007”.

0.0001 inches is one ten thousands of and inch.

In my experience, shooting 3 different rifles in 308 Winchester, plus or minus 0.002 in bullet diameter had no effect on accuracy.

The bullets I made myself on our CNC lathe.

I was told once that the Ruger New Model Single Six Convertible barrel was bored for the 22 WMR, and that was the reason why 22 RF was less than accurate. I dunno.

HOLD ON!!! .0001 is NOT one thousandth. .0001 is the tolerance for match grade barrels; they can't vary more than that for the length the bore.
Whatever your problem is, that ain't it. I don't use those barrels any more but not for that reason.
Anyway, uniformity is far more important than exact size.
I must not have read the OP before. I often answer questions without reading them first.

Sheesh! His post was from 2011.