20 GAUGE
BORE IS .619
FULL CHOKE .590 AC. .029
MODIFIED CHOKE .604 AC. .015
IMPROVE CYLD. .613 AC. .007
SHOTGUN REAMERS
12 GAUGE Pilot Body Choke
Rough reamer .656 .694 -
Finish reamer .694 .730 .694
16 GAUGE
Rough reamer .562 .640 -
Finish reamer .640 .673 .640
20 GAUGE
Rough reamer .531 .590 -
Finish reamer .590 .619 .590
The dimensions I have given here are the ones that I have used with good results. These are more or
less a happy medium on chokes and bores. For example a full choke browning has a bore diameter of
.730, and a full choke, which is .699. Winchester is .730-bore diameter, and the full choke is .699. Who
is to say which one is best. If you do much work on shotgun barrels you will soon find there are no two
alike, and I have found that will vary as much as .042 from maximum to minimum. The old German
shotguns are usually tighter yet. What this means if you haven't figured it out yet is that you will probably
have to make special tools for each different barrel.
The old types of barrel reamers that were used in the past are usually used in the finishing of the choke. I
have found that these give a good job, but took quit a bit longer and did not give the results that I wanted
on the bore. With the reamers described, you will usually not have to hone or polish any part of the
barrel, except the choke section. I will show you how the reamers are made and the oil tube clamp for