View Full Version : how to bore a rifle

January 11, 2010, 02:26 AM
i have a 300 win mag and i want to bore it out to a 338 win mag. the cartridge seems very similar in length.does anyone have any tips or info on what i have to do?

January 11, 2010, 02:33 AM
Gunsmith or machineist that really likes guns. You could always just buy a new barrel.

Bud Helms
January 11, 2010, 04:26 AM
That would be a rechambering and reboring. I don't believe you will get away with a rebore and not a rechamber.

That's why they make replacement barrels.

January 11, 2010, 08:55 AM
CNC Lathe - $14,000
Drill, groove cutter, reamer, gauges - $500
Having made your own .338 blunderbuss - priceless

I'd go with Bud's advise, a rebarrel with correct head space can be had for around $350.

January 11, 2010, 09:21 AM
You need to be set up like a rebore shop, with the beans to rebore the barrel larger (deep hole drilling), and a rifling machine/fixture.

The base cartridges are the same, so a simple rebore/rerifle should dothe trick - although I haven't checked the cartridge specs against each other to see whether or not the barrel needs a rechambering, or a setback, or nothing else due to cartridge/shoulder length.

Unless your already setup & good to go, the $245 a rebore shop like Jes Ompaugh (sp?) in OR charges is a waaaay easier, less costly, way to go.


LongRifles, Inc.
January 11, 2010, 09:54 AM
First, it's quite, quite rare for someone to do this when a premium match grade barrel can be bought and installed for around $600 bucks.

Also, It's not as simple as a CNC lathe. I own two slantbed turning centers and I wouldn't be able to do this on either of my machines. A deep hole gun drill probably a more appropriate machine. In this case you'd skip the drilling portion and ream the bore to the larger caliber. Then either recut the rifling, rebutton, or broach it.

Either way it's a task that 90% of gunsmiths out there would avoid as it's just much simpler and less brain damage for everyone to just hang a new stake on the receiver.

Hope this helped.


January 11, 2010, 01:36 PM
Rifling is harder than just boring to size.

A new barrel would probably be cheaper.

January 11, 2010, 02:00 PM
Definately re-barrel. I wouldn't have even thought of re-boring. I've used barrels from ER Shaw several times, and I've had sub moa accuracy from all of them. ER Shaw will ship a barrel in the white to your door for around 200 bucks. I can headspace, attach, and parkerize myself, so I can get out cheap. You could probably find a smith to blue or park and mount the barrel for around 250. Don't get stiffed on the blue job. There won't be a tremendous amount of prep work going into a shaw barrel if bluing. With park, normal prep and blasting will be in order.

Jim Watson
January 11, 2010, 02:37 PM
The REAL problem, even for a pro gunsmith, is that it cannot be done except by setting the barrel back, rethreading and rechambering after the rebore. The .300 W.M. is .156" LONGER from head to shoulder than the .338 W.M.

James K
January 15, 2010, 02:39 PM
"How to bore a rifle."

My first thought was, "Sit it down and tell it stories about your hunting trips."


January 15, 2010, 03:41 PM
Go to www.cutrifle.com the do reboring/rifling.

January 19, 2010, 09:40 AM
The only case I'd go for reboring is if the existing bore is totally shot out and there is something of value on the outside of the barrel, such as special sights or you need to preserve the exterior look of a classic rifle. In most cases, it would be more cost effective to re-barrel. If your bore is good, I'd stick with 300wm as it should handle anything that the 338 can handle, especially if you reload.

Bart B.
January 25, 2010, 07:17 PM
Note that reboring and rerifling a barrel will usually end up with one that's not too accurate. The reason is the first inch or so of the new bore and groove dimensions at each end are not the same as the dimensions between these two points. New barrel blanks have their muzzle's cut off an inch or so and the chambering reamer takes out the bad part at the back end. Some custom after market barrels were marked with a line at each end denoting that the dimensions between these front and back marks were the best part of the barrel.

If one wants to preserve a barrel's outside finish, marks and dimensions, it's best to have it gun drilled to an oversize dimension then have a liner made to fit it. Assuming one can make a liner a "shrink fit" by having it a few ten thousandths larger than the gun drilled barrel, then freezing the liner and heating the barrel, the liner could be pressed in. The result may be as strong and save as the original barrel. But this will cost a very thick billfolds dollar supply.

January 25, 2010, 09:58 PM
Bart- Are there smiths out there that would line a centerfire barrel? I'm probably just way out of the loop on this topic, but I was under the impression that only rimfires could be safely lined. Enlighten me if you could.

guns and more
January 25, 2010, 10:27 PM
how to bore a rifle
Make it watch Barbara Streisand movies.

mega twin
January 26, 2010, 07:05 AM
guns and more,I think they outlawed that at Gitmo:o

James K
January 26, 2010, 11:37 PM
You can't line a barrel for a high pressure cartridge using the normal liners, they are too thin. The problem is that no liner can be made to fit perfectly with full support at all points, so the liner has to be thick enough to stand the pressure by itself. The usual liners (as sold by Brownells and others) are made for .22 and older low pressure black powder cartridges like .44-40.

I think Bart is talking about the situation where high pressure is involved, but it is important to retain the original markings, as in a collectors item. As he says, you would have to have a liner specially made (by turning down a standard barrel blank) with sufficient thickness to contain the pressure, and ream out the original barrel to a thin shell. That requires a fair amount of skill, well beyond the usual simple lining job.


February 4, 2010, 04:09 PM
How to bore a rifle, tell its stories.. God that is classic!