muzzle erotion

[mark2112]

what size gage pin should fit tight in the muzzle if an m1 barrel was new,what are the go-no-go dimentions on a erotion gage.

[Punch The Clown]

what size gage pin should fit tight in the muzzle if an m1 barrel was new,what are the go-no-go dimensions on a erosion gage.

Technically the bore should measure .300 land to land on a new rifle but .301 or .3015 are probably closer to what you would see. Anyway, .303 seems to be the number where folks claim a noticeable loss in accuracy but who knows. You can have a muzzle that measures .303 but move down the bore .125 and it may measure .301 to .302 which is why re-crowning can freshen up a worn barrel. Tim says he usually improves a barrel by 1 number or better when he re-crowns them. The military only measured throat wear. Stu

[musketjon]

[You can have a muzzle that measures .303 but move down the bore .125 and it may measure .301 to .302 which is why re-crowning can freshen up a worn barrel.]

That's exactly what I had in an original SA 9-42 barrel. I had it counter-bored 3/16" back and now it is effectively a brand-new 60+ year old barrel. A .300 pin will fit but a .301 will not. It went from a 8-9 ring rifle to a 10-ring rifle.
Jon
<a href="http://s660.photobucket.com/albums/uu321/musketjon/?action=view&amp;current=IMG_0024.jpg" target="_blank"><img src="http://i660.photobucket.com/albums/uu321/musketjon/IMG_0024.jpg" border="0" alt="barrel counter-bore"></a>

[paid4c4]

Jon, when you counterbore couldn't you cut the last 3/16" of the barrel off, as it effectively doesn't touch the bullet?
Looks like a great way to save a barrel.
Bill