A few quick questions here. Shotguns so far in life have been something to fire at things on the property that didn't belong. I'm trying to move up the food chain a bit on shotgun knowledge. I'm wondering what is ' back bored' and 'over bored' ? I think I saw what 'back bored ' was , recessed back into end of barrel?? But no no idea why that would be done. Thinking it might be a sort of 'quiet zone' to let shot column calm down before getting out into the air?? Thank you for and advice you may offer and your patience with a newbie.

A few quick questions here. Shotguns so far in life have been something to fire at things on the property that didn't belong. I'm trying to move up the food chain a bit on shotgun knowledge. I'm wondering what is ' back bored' and 'over bored' ? I think I saw what 'back bored ' was , recessed back into end of barrel?? But no no idea why that would be done. Thinking it might be a sort of 'quiet zone' to let shot column calm down before getting out into the air?? Thank you for and advice you may offer and your patience with a newbie.

I'm not 100% sure what back-bored is. An over bored barrel just has a slightly larger than standard inside bore diameter. It's not something I've ever been concerned with, but they are supposed to reduce recoil and have some other advantages.

Back borring involves enlarging a short section of the bore just ahead of the choke.
When the shot charge passes through the back bore it spreads to fill it, then is imediately compressed again in the choke, thereby (enhancing) the choke, a full choke will then act like a slightly tighter full choke.
:cool:
Hope this explains it.

Thanks Cowboy that helps. What I was thinking was back-bored is simply a recessed choke. Good thing they tolerate dummys here. :D

Glad I could help.
BTW, the only dummys here are the ones who don't ask questions.

back boring a barrel creates constriction,a cylinder bore shotgun barrel has no constriction(no choke)12ga. bore dia is .730(for example only)if the barrel outer dia is good say .810,you can open the barrel dia. to .750(depending on barrel type and maker)this gives you a .020 constriction from bore to new choke.if the barrel is 18 inches you go to 16 inches from chamber to mussel,you can also do this with a choke tube,stop 1/2 inch from start of the tube.i do allot of barrel work with back boring and porting and choke tube styles for my law enforcement customers,most police shot guns turn out to be cylinder bore or the new remmington police barrels that wont take a choke tube so i have to back bore to create the choke or make the gun shoot where they want it to shoot,i do some fun 14 inch full bore with breacher tool entry guns that are fun to shoot and at 25 yards with federal 9 pellet hold a patteren about 6 inches,these shoot better with the federal than the sp12 9 pellet remmington.the brecher tool has a choke tube that is mod.and after the back boring and tool fitting has little or no felt recoil.

oh crud,thanks Simmons, my foul there, had my head up my fourth point of contact. The description I (erroniosly) gave was for JUG choke wasn't it?
My appoligies ombesb.

it's just good that the jug choke is remembered,i don't know if they are even still being used,years ago we did them,but with time and the passing of some good gunsmiths,it fell to the choke tube.now if all of thoes model 12's we did would take choke tubes,all i would be doing is tubeing 12's.that would be ok.

I use a winchester super x2 3".
I am trying to find out what is the bore diameter .740 or .742 and what ii the constriction of IMP.CYL, MOD and FULL choke.

Thank you

bore dia differes from gun to gun,a inside micrometer will tell the bore dia.,12 ga. starts at .730 roughly,the tightest constriction is full and the least is cyl.this is something that is easly checked if you have the proper tools to do so.in a pinch,a set of inside calipers will work,if you need a list of constrictions,i will post them tomorow evening.