Workbook

LESSON 202:

CONVERTING AN ISRAELI BARREL TO STANDARD THREAD PITCH

(Revised 09-22-00)

Lock barrel in vise jaws (not holding by gas block). Leading with the tapered side, a 1" x 16 tpi die

should spin 50-60% of the way on without tension. Continue tightening, using cutting fluid

(Tapmatic, Du-Rite, etc) or lubricating oil. Goal is to keep work cool and keep chips clear. Go slow,

backing die out often to clear chips. Die should never become too hot to hold in your hand. On a

side note, you can use valve lapping compound and a lot of working back and forth to lap the barrel

and receiver together, but consider this mating as permanent, because both barrel and receiver are

now halfway between Metric/Inch and Israel.

*Note. The Term "Inch Pattern" refers to the L1A1. That is Australian, British, Canadian,

and Indian (although Indian parts vary slightly). The term "Inch Pattern" however is a bit

misleading when compared to metric, because both Inch and Metric guns are built to the

English thread pitch and are mostly interchangeable with metric. It is more a general term

for the system of the country of origin, and perhaps "Commonwealth Pattern" and "Belgium

Pattern" would be more accurate. Israeli is different only in the barrel thread, and front

sight thread. Some Argentine guns also use the non-standard Israeli front-sight thread pitch.

After the die is all the way up to the shoulder, unscrew and repeat, leading with the flat side of the

die. This should cut the last few threads a bit more and will take the recut threads all the way to the

shoulder. Some dies are tapered on both sides. If this is the case, you will have to use more strength

to tighten the last few turns when barreling. Lathe turn the barrel and skim any high points from the

torque shoulder, being careful not to reduce the shoulder. Brake the 90 degree edge. If not using a

lathe, lightly file and sand any burs from the edge of the shoulder, being careful to keep it squared.

Then, by rotating the barrel 45 degrees against a sanding block, (fine - 180 grit or less) Break the

sharp 90 degree edge just to the point where it won't cut you.

The barrel is now ready to install on your receiver - sometimes. Some barrels (mostly Israeli) have a

peculiarity. Screw it all the way into the receiver and it stops - not on the shoulder against the

receiver face, but on the breech face against the rails/feedramp. Lathe turn with a steady rest or flat

file the breech face, continually changing direction of cut by rotating barrel to keep it perpendicular.

It's okay to have a tiny gap between the breech face and the rails/feedramp. One source even

suggests that a .020" gap is beneficial to accuracy, although I have been unable to verify this. If

your file starts squeaking and squealing, the metal is too hard and you are wasting your time with a

file. You'll have to use a sanding block and 120 grit emery paper. You can also rotate the barrel

against the hard backing of a belt sander if you are careful to keep the part cool and square. You

should rotate at least a 1/4 turn each time. Just touch it lightly to the belt - go slow. Check fit

several times until it is the shoulder, not the breech face that stops on the receiver. Then polish

throat down to 600 grit. Finish with felt polishing wheel and white compound, if desired.

Another point of consideration with rethreading an Israeli barrel is that the new threads need to seat

themselves to the threads on the receiver - they are a bit thinner and sharper now than they were

originally. You want to make sure any "seating" is done before final torquing of barrel. So before

adjusting the barrel shoulder, tighten the barrel on hard, then unscrew. Repeat this two or three more

times. Now any irregularities in the new threads have been seated to the receiver threads. You may

now adjust the shoulder and do your final torquing to top dead center.