Workbook

LESSON 204: CUTTING AND THREADING THE BARRELS

(Revised 09-22-00)

The purpose of this lesson is not to lecture on what is or is not legal under the various Gun Control

Acts. It is your responsibility to comply with all applicable rules created by the tax collectors at

ATF. The text of relevant laws is in a different section. It is unlawful to have a "barrel threaded to

accept a flash suppressor" on a post 1994 rifle, and is illegal to have a barrel shorter than 16" without

ATF registration and approval ($200 tax).

CUTTING A BARREL

The easiest way to cut a barrel is with a chop saw. This method takes about ten seconds. A hacksaw

takes longer, but is less expensive. Then you can hand file the end of the barrel flat, or you can rotate

it against a belt-sander to get a smooth surface. Finish with 600 grit, if desired. If you are installing

a muzzle control device or a (gasp!) flash hider, there is no reason to crown it. If you are going to

leave it exposed, it is a good idea to protect the rifling. Take an RCBS case neck reamer and use it to

deburr the inside. It leaves about a 45 degree crown. You can put this in a three-jaw chuck in a

power drill and cut a deep crown. Brownells also sells a set of piloted cutters for hand-crowning.

You may cut a barrel that is attached to a receiver to 16". Measure barrel length from the end of the

barrel, through the bore, to the bolt face with the action closed. A permanently attached muzzle

control device / flash hider is included in the overall length Therefore, If you are permanently

attaching such a device, you may cut the barrel shorter than 16" so long as the permanently attached

muzzle device brings your overall length to > 16". You may not, however, cut the barrel to < 16"

when the barrel is attached to the receiver, because you would then have, even for a short time, an

unregistered short-barreled rifle.

THREADING A METRIC BARREL

Take your barrel and wrap a piece of masking tape ½" from the end of the barrel. Take your bench

grinder. Insure the edge is 90 degrees. If not, true the wheel in as with your owner's manual. Take

the shelf that is in front of the wheel and slide it in as far as it will go toward the wheel, without

touching. Having too large a gap between the wheel and your shelf can allow the wheel to grab the

barrel and hold it while merrily grinding away.

You need to reduce this shank to 9/16” (.551") so scribe a .551" circle on the front of your barrel so

you will know how much metal to remove. There are two ways to do it on your "poor-man's lathe".

First is by cutting flats. Mark eight equally spaced spots around the barrel. Cut each one flat on the

grinder, making an octagon barrel. Once again, keep it quenched. It should never change color or

become too hot to touch. Quench after every cut. Then cut eight more flats on each of the eight

points on the octagon. Repeat as necessary to get your diameter down to almost .551" Finish by

rounding your 16 points with a hand file, using the sharp edge of your file to cut the shoulder to a

sharp 90 degrees. The second way is quicker, but involves a bit more coordination. Lightly hold

your barrel against the grinding wheel while turning it rapidly until you have reduced the outer

diameter to .551". Finish with a hand file as with the first method.

You must now turn the outer diameter of your barrel to 15mm (15.08mm / .594" to be exact) Check it

first, if its an StG, it probably is there already. You can do it by having a step from 15.31mm to

15.08mm, or in the case of short barreled guns, it's easier to start at the front sight and do the whole

barrel forward of the front sight. Mark the barrel with tape 66mm from the end of the muzzle and

turn if against the belt sander (with hard backing) and a very fine grit belt. You are not removing

much material. Finish by "shoe-shining" with emery paper. Slide your muzzle device over and see

if it sleeve fits tightly. A slight air gap won't hurt, but looks tacky.