Of course, one question leads to another... Is there an easy way (at home) to measure the inside bore of my 12 gauge? I have a vernier caliper but do not have an inside caliper, so I can measure the choke at the muzzle but can't think of a way to measure the inside diameter of the bore. There must be a old trick to do this without buying a caliper.
How to measure inside diameter of shotgun bore?
- Thread starter lord-humungous
- Start date
My father in law just uses a "dime". Turn the dime so your squeezing it with both fingers, try to put it in with the edges touching the side of the choke. He's been shooting for 65 years. This is the old way :
Full choke: dime will not fit.
Modified , just barely fits.
Improved, slides in.
Full choke: dime will not fit.
Modified , just barely fits.
Improved, slides in.
I think that the bore gauge and inside caliper are the same thing. I don't want to buy a tool so I'm trying to devise a quick way to measure the bore without such. Will think about it tonight and post back what I come up with. I'm thinking of something soft that I can "swage" into the barrel part way and then remove and measure (maybe lead). Did I mention that it is a break action? I should be able to access the bore easily.
Shotgun bores often vary greatly within a short distance.
I made this tool...the barrel is held in a vise horizontally.. when it is "hanging" on the bore at the muzzle the gauge is at "0"... as you slide it into the barrel holding the tool with a thumb and finger in the hole in the aluminum block... and keep it centered the gauge reads the thickness of the barrel. Measure each side and measure the outside diameter and you can figure the exact bore dimension at a particular length. Usually with choke alterations you only need to concern yourself with the last 12 inches...
Two 1/2 inch rods, a small barrel bearing, a hunk of aluminum, some Loctite and a dial gauge...
I made this tool...the barrel is held in a vise horizontally.. when it is "hanging" on the bore at the muzzle the gauge is at "0"... as you slide it into the barrel holding the tool with a thumb and finger in the hole in the aluminum block... and keep it centered the gauge reads the thickness of the barrel. Measure each side and measure the outside diameter and you can figure the exact bore dimension at a particular length. Usually with choke alterations you only need to concern yourself with the last 12 inches...
Two 1/2 inch rods, a small barrel bearing, a hunk of aluminum, some Loctite and a dial gauge...
Inside micrometers should work, but the proper tool is a dial bore gauge, lotsa $$. Some barrels are over bored(intentionally) and some are probably under sized(unintentionally), if one is in doubt, it would be worth knowing if it is overbored which would save you from having it done. Choke is also dictated by the diff. between the bore dia. and the choke. The traditional method of using a dime to determine choke is really only useful if you have the std. dia. bore.
Lengthening forcing cones and overboring barrels are usually done on trap guns to improve patterns at long range(handicap) and reduce recoil.
Lengthening forcing cones and overboring barrels are usually done on trap guns to improve patterns at long range(handicap) and reduce recoil.
Are you are just measuring bore diameter 2 or 3 inches from the muzzle and at the choke itself as if calculating choke restriction or suitability for choke installation? In which case you can use a telescopic gauge available at any tool store or Princess Auto. The $20 per set imports work fine. When you have it "set" for the bore measurement obviously it won't pull through past the choke without affecting the adjustment. In which case, with the barrel vertical, just drop it and catch it in your hand at the chamber end. Measure several times just in case of a poor reading.
Yes I see that now.
I'm not that fussy, but I don't shotgun much. I can wingshoot quite well with certain guns though.
I just pattern the gun rather than measure bore, etc.
Bore diameter is important if you want to know the actual measurement of your chokes or some idea of the wall thickness of the barrels although there is a separate tool to more accurately measure wall thickness.
Bores can vary in diameter. While .729 is the standard measurement for a 12 gauge I've seen shotguns that measured as small ast .723 and as open as .735 inches. If you are looking at an older gun knowing the bore diameter can help you determine if at some point the barrels were polished to have pitting removed.
- Location
- Hillbilly shack in the boonies
russian guns have aloth of meat in their barrels, and seem choked right to the numbers , or smaller. take any plastic , or wood that fits nice, then measure that.
I think I'm going to make one.
Lord H:
If you haven't already done something to measure your bore, try this. Make a soft lead slug that is slightly over bore diameter, put some good lube on it then from the breech end drive it into the bore with a mallet and 1/2" or 5/8" rod. Push it all the way to about 4 " short of the muzzle. At that point reverse the process and push the slug back and out the breech end. Measure with your vernier caliper to get the minimum bore diameter. Hopefully the bore will be reasonably consistent in diameter but knowing the diameter immediately behind the choke is most important for your process. Now, replace the slug in the breech end of the barrel and drive it all the way down and out the muzzle. That gives choke diameter.
If you haven't already done something to measure your bore, try this. Make a soft lead slug that is slightly over bore diameter, put some good lube on it then from the breech end drive it into the bore with a mallet and 1/2" or 5/8" rod. Push it all the way to about 4 " short of the muzzle. At that point reverse the process and push the slug back and out the breech end. Measure with your vernier caliper to get the minimum bore diameter. Hopefully the bore will be reasonably consistent in diameter but knowing the diameter immediately behind the choke is most important for your process. Now, replace the slug in the breech end of the barrel and drive it all the way down and out the muzzle. That gives choke diameter.
