I'm in the process of barrelling a low wall .22 BPCR for my wife.  Threaded and chambered the blank, and was arbitrarily going to cut/finish the muzzle to 32 inches.

I'm a believer (not necessarily a practitioner, however) of the let the barrel tell you how long it wants to be method.

That method, applicable to cast bullets, and particularly .22 rimfires, is to slug the barrel, and map tight, loose, and choke spots.  The theory is that the muzzle should end on a choke spot for best accuracy, on a tight spot as long as not too abrupt if no choke spot is available, and never on a loose spot.

This barrel has a great choke spot near the muzzle, about 1 1/2 inches long.  Followed by a pretty uniform spot (not loose) and then by a tight spot, with the last 1/2 inch or so a loose spot.  

The choke spot is from about 28 1/2 to 29 3/4 inches from the breech.  The tight spot is about 32 1/2 inches from the breech.

The theory would have me cutting the barrel at 29 1/2" or slightly more.  To match another rifle, I prefer 32".  The tight spot would say 32 5/8".

Since I have the option to easily change the muzzle by doing the work myself, I'm going to make the barrel about 32 3/8".  My rationale is that's the beginning of a tightening area after a uniform area.  Plus how long I want the barrel.

If it doesn't shoot accurately, I'm going to cut it off and refinish it at 29-1/2", to see if the choke improves it.

(You need to Login or Register to view media files and links)
(You need to Login or Register to view media files and links)   

Exactly what I do Dave.  I lapped a few and they shot ok but not great, even with the tightest spot being the last inch.  I've had much better luck without lapping. 

I recently barreled a Peregrine with a Lilja blank, slugged it several times, from each end, before and after cutting the octagon, determined the tightest spot.  I wanted it to finish at 30 -30.5" but the tight spot ended up making it 29-1/4.  No regrets, it has about 1200 rnds down it now and it's been been proving itself shooting caps, and 100 & 200 yard paper. 

What chamber are you cutting?

Greg

I don't mind lapping but there's some Knowhow to it that you really need to play with.  Just for fun I cast 2 Laps.  One with the Barrel just warm to the touch and the other to where Water would almost sizzle off.  A measurable size difference between them.
The last barrel I did took about 80 passes to blend it the way I want.  Most of my strokes were in specific areas and maybe only a dozen full strokes.  David

Many years ago someone tested the accuracy of .22 barrels by continuously shortening them.

The conclusion was you need at least a 22 inch long barrel to obtain accuracy to fully burn up the propellant and get maximum gas expansion.

Too long ago for me to remember who did the research back in the late 1980s or early 1990s.

Picture of my 22 inch long choked gain twist RKS barrel on a BSA Martini International MKII used with a scope but has a bloop tube extension to improve the minute of angle for iron sight competitions.

Anything longer just improves your minute of angle if you are required to use iron sights.

BR50 accuracy of rifle shown.

You NEVER lap a RKS barrel.
It has a continuous precision cut sloped choke decreasing by .0004" from the breech to the muzzle.

Niedner did research too almost 100 years ago. I read an article in an old Journal about it. He would put the barrel in one overcoat pocket and the action and butt in the other. I think it was about Michael Petrov getting an ATF exemption because the barrel was under legal length. I wonder who has that rifle now.