Overbore/Backbore = Same Thing?

[Patriot_1776]

I just wanted to have some clarification on these two features I read about.  The Mossberg 835 is overbored to .775" they say, aside from their standard 12ga dia. bbls which is .732".  Then the Weatherby SAS shotguns they say they are backbored to .735".  And Browning says their's are also backbored (don't have bore measurements.).  What I'd also like to know, is what is the standard 12ga. bore dia.?  I know that overbore definitely means larger than standard; but does backbore mean smaller than standard?  That is where I get confused.  I've also read that too much shot constriction can decrease pattern integrity due to deformed shot (most likley with lead shot...).  So my final summary of all this if backbore means what I think, what would be better overall: An overbored bbl, or a backbored bbl?  Thanks ahead of time.   Patriot

[savageT]

I just wanted to have some clarification on these two features I read about.  The Mossberg 835 is overbored to .775" they say, aside from their standard 12ga dia. bbls which is .732".  Then the Weatherby SAS shotguns they say they are backbored to .735".  And Browning says their's are also backbored (don't have bore measurements.).  What I'd also like to know, is what is the standard 12ga. bore dia.?  I know that overbore definitely means larger than standard; but does backbore mean smaller than standard?  That is where I get confused.  I've also read that too much shot constriction can decrease pattern integrity due to deformed shot (most likley with lead shot...).  So my final summary of all this if backbore means what I think, what would be better overall: An overbored bbl, or a backbored bbl?  Thanks ahead of time.   Patriot

http://website.lineone.net/~dave.cushman/shotshellloads.html
Standard 12 gauge bore ID is 0.729".

Jim

[TPhunter]

Back bored and over bored are the same thing

[Patriot_1776]

Thanks very much guys for straightening all that out for me.   Patriot

[Busta]

Back bored and over bored are the same thing

Not on all firearms. The Mossberg 835 overbored is the same inner diameter from the end of the chamber/forcing cone all the way to the choke tube. Back-boring can start as a standard bore at the chamber/forcing cone and slowly open up to the backbored dimension about 8-12 inches from the choke.

I have an extreme example of a back-bored barrel in my Knight TK-2000 12ga Muzzleloader. About 10-12 inches from the "JUG CHOKE" (screw ON choke), the barrel is at least a 10ga bore. The remainder of the barrel from the breechplug to the back-bored area is nominal 12ga bore.