30.06 counterbore

I have a Brazilian Mauser looks like the last 2-3 inches of the muzzles rifling is worn to nearly nothing. Not sure on this depth as currently only got a broken wrist and trying to work out how much of the muzzles rifling is worn.
Questions, can I counterbore upto this depth, what dia should I counterbore being such a deep counterbore and what is the prefered method to carry out this proceedure.

Myles

---------- Post added at 07:03 PM ---------- Previous post was at 07:01 PM ----------

What is the best way to work out how deep the wear is.

Myles

You could try slugging the barrel from the chamber end, or use a tight patch on a cleaning rod and push through until you feel the pressure release, measure the distance traveled against total barrel length, add a few mils for a fudge factor and work on that.
Or you could inspect the barrel with a bore scope to ascertain the extent of wear and damage, my scope has measurements on the probe, which makes my life easier, but is'nt helping you. It may be more productive to replace or reline the barrel.

I am assuming your rifle is 7mm, and if so a No. 1 buckshot pellet (.30) would be the proper size for slugging your bore. Oil the bore and seat the pellet in the end of the bore. Start pushing it through the bore and notice where it tightens up. Bump it back out from the chamber end and note if it has a full set of lands engraved on it. Since you will have to open a shell for the pellets, you will have more than enough pellets to try this several times. The counterboring itself is best done on a lathe.

I must not have read your post very good. The title says .30-06, and in this case you would need to use "0" buckshot. You can also push it down to where the bore tightens up, then push it out from the breech and note the position of the rod when it starts to loosen up.

If it were mine I'd shoot it first, it may just surprise you. Counterboring it 2-3'' or more, in my opinion, would hurt more than it would help. I'm not as knowledgeable on internal ballistics as Patrick Chadwick and some others are so I may well be wrong on this but I'm reasonably sure the gases escaping past the bullet before it leaves the muzzle would have some kind of negative effects causing it to be hopelessly inaccurate at anything other than close range. I have a Mosin Nagant thats been counterbored 1 1/4'' and it does'nt shoot well at all past 50 yds and I'm convinced the reason why won't is that it's been bored too deep.

Counter boreing was an accepted practice with people for years, such as the Germans. If done correctly it CAN produce accurate results. Vintage Hunter, your M.N. may have other issues that aren't apparent. When I counter bored, I used a lathe with the muzzle as close to the headstock as was safe. Use the drill chuck in the tailstock and I used an appropriate sized four flute end cut milling cutter. I just went as far as to bring the rifling back to prominence. Less that 1/2" I think. Problem solved. Also good to remove ring at muzzle too.

But as Vintage Hunter says, shoot it first. If you're using jackets it may shoot passably.

Re: counterboring

My name probably popped up because I am sceptical about counterboring. It may well make a rifle shootable that would otherwise be useless. Counterbores I have seen (mostly on Eastern bloc rifles) were of the order of 2 cm, maybe an inch. I think 3 inches is probably not going to work satisfactorily - or if it does, the setup is likely to be extraordinarily load-sensitive. The reason for this pessimism is that when the bullet is travelling through the counterbored section, it is in free flight. But the barrel is also moving sideways - it jumps and vibrates.

Even if the bullet does not actually touch the sides of the counterbore (in which case it will exit the muzzle at some totally unpredictable angle, and you will be lucky if it hits the target at all) the sideways displacement of the counterbored section relative to the bullet (meaning that the bullet is way off center in the air channel) will have a similar effect to a very uneven crown - there will be a sideways force that will push the bullet way off line.

The best you can do is probably to use a bullet that is as close to the groove diameter as you can get. If the diameter in those last 3 inches is greater than that (i.e. the bullet loses contact with the barrel at some point) then I think the case is hopeless. Note that I said losing contact. Merely having fading rifling is not as bad as that! So (as usual!) clean-shoot, clean-shoot... until you are really sure that the barrel is spotless - then make your judgement.

Patrick
:wave:

Patrick

It sounds like the rifle is not a collectors piece. If counter boring doesn't work or is too costly you might consider shortening the barrel and reinstalling the front sight and hardware. You will need to do some shortening to the stock also.
john

You can counterbore with an 11 degree shoulder, then vent 3 rows at 1/3rd placements around the first inch or more with no ill effects to accuracy and less recoil to boot. The counterbore must be done perfectly symmetrical as with the holes, HTH-Steve (gunsmith since 1984)

Quote:

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Originally Posted by jamie5070

It sounds like the rifle is not a collectors piece

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Jamie,
Other than the last 3 inches of the barrel. The rifle is in great condition. Specially now I removed the 2mm of varnish that has protected the metal and woodwork for 30 odd years. Looks like it is a hopeless case saving this barrel, so I am not going to mess with it unless I can source another barrel.

Myles

Their is absolutely nothing wrong with counterboring as long as it:thup::thup: was done correctly by a old world craftsman who took pride in his craft as most all of them did and not some drunkin shoemaker saying pass me the next rifle.I have a honey of a VZ24 that is counterboard and shoots just fine

if your going to use a lathe...and its a hunting rifle already anyway...why not cut and recrown the barrel? i offer several crowns...target, and hunting...fix it right....