Question on Counterboring

[english kanigit]

I realise that it sometimes has to be done due to damage but what is the overal effect on the rifle when the barrel is counterbored? Does it effect accuracy?


ek

 

[jonnyc]

I asked a similar question on another forum when I was considering a counter-bored M38. The majority belief was that it did no harm, and actually increased accuracy.

 

[Mauserguy]

Counterboring pushes the crown back to good rifling. Assuming that it is done properly, it can only improve accuracy.
Mauserguy

 

[rockstar.esq]

Mauserguy got it right. My tag on is that is sometimes allows a rifle's accuracy to be improved by shortening the bore while maintaining a minimum barrel length as might be needed to pass muster with the ATF.

 

[Dr. Dickie]

Right, my understanding of the reason that it improves the accuracy of the weapon (better it improves the precision) is that the final bit of rifling the bullet interacts with is going to have the most impact on where it goes--the last thing to touch it before it goes ballastic. Once the rifling around the crown is eaten away, the actual rifing that interacts with the bullet may push the bullet off or cause a funny exit. Cutting it back to good rifling should give the bullet an even rifling on exit and improve its repeatability.

 

[KINGMAX]

M38 and counter boring

I once heard the the counter boring adds to the barrel harmonics, thus more accurate.

YES-I do own a M-38
YES-it is counter bored
YES-it is very accurate
YES-it does have a streak of fire when shot
YES-it still kicks like a mule
YES-it is one of my favorites

 

[dfaugh]

once heard the the counter boring adds to the barrel harmonics, thus more accurate.

Say what?

Anyway, many of the milsurps you find will have significant muzzle wear from using steels cleaning rods. If the muzzle is worn (bullet not getting an even engagement of the rifling, when it exits the barrel), accuracy WILL suffer (sometimes horribly).

To correct it you have 2 options: shorten and recrown the barrel, or counterbore it. If you want to maintain it in its original configuration, counterboring is the only option. If "sporterizing" (which I've also done) shorten and re-crown.

Re-crowning is easier (with the proper tools), because to counterbore you have to make sure that the counterbored area is ABSOLUTELY perpendicular to the bore. I'm about to try this on an SMLE that I want to restore...I have a 5/16 (.312) reamer, now I just have to figure out how to make it go "straight".

P.S. In my experience, the worn area is usually at least an inch long...so just recrowning, without shoutening usually won't cut it. You need to get back an inch or so, to get back to "good" rifling.