What was the point of counter boring?

[Guamsst]

Anyone know why the Russians counter bored so many Mosin Nagants and what was the benefit?

[p246]

To re-establish a good crown in a damaged rifle barrel. This allows gases to escape evenly as the bullet leaves the rifling thus improving accuracy. Done during armory refurbs generally.

[kcw]

I don't specifically know why the Soviets did it, but typically, counter boring was done to eliminate cleaning rod wear on the rifling near the muzzle;, with the idea being to improve accuracy. I have a Korean War M44 "bring back" in which the 1st 1/2" of barrel interior was horribly pitted (even though the remainder of the barrel was beautiful). "As is" it would throw a 3' group @ 100yds. After my "free hand" counter bore job back to good rifling (approx. 5/8"), it tightened down to about 4".

[p246]

I can only assume the Russians had a lot of damaged crowns or maybe there was an issue with the original crown making process. I.ve also heard as kcw said metal cleaning rod damage at the crown was a large reason for counter boring. I counter bored a couple old rifles years ago with some improvement in accuracy but both rifles were pretty rough.

[Art]

It's a heck of a lot easier fix for an otherwise good barrel with a damaged crown or excessive muzzle wear by counterboring than putting on a new barrel. The Soviets used some techniques during arsenal refurbs that we wouldn't but they worked just fine.

[Tuna]

We did the same thing with the 30 carbine. In fact it is in the TM's to use a counter bore to improve the accuracy of the weapon. This was because many were damaged by the steel cleaning rods used on them. Not a lot of them were done this way as it was time consuming so many of the armories just skipped it and put on a different barrel but they are out there if one was to look for them.

[Guamsst]

Cool, thanks guys. I thought I was right about refurbishing the crown and it does make sense that America would just rebarrel in most cases while soviets would counter bore.

[Hefights]

The Finns placing a high value on accuracy were known for re-crowning the M39s and finding them this way is common.

[dave]

In Scoot Duff's book on the M1 there is a pic of GI's marching, in the rain. One has the cleaning rod sticking out of the barrel of his MI. Probably needs counter boring if still around to-day! hehehe.

[Guamsst]

don't forget the Israeli Mausers stored outdoors uncovered with used motor oil poured over them. I ad a buddy who owned an Israeli mauser that needed to be counterbored about 15 inches. It shot OK but there was a large ring rusted out of the rifling pretty close to the chamber.

[therewolf]

The issue with counter-boring relates directly to the cleaning

rod attached to the rifle. You can clean the barrel from the

muzzle, but the rod is too short to clean the bore from the

breech.

Obviously, drop the bolt and clean the bore from the chamber,

whenever possible. Cleaning from the muzzle extends wear

prematurely upon the crown.