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.