Barrel Machining

C

cris

Guest
The rimfire crowd believes that you cannot do anything to the exterior of a barrel, fluting, threading, contouring, without affecting the bore dimensions.

I was privileged to witness a graduate level experiment with barrels, lead slugs, an air gauge and a master gunsmith. Without sharing anything yet, both the professor and the gunsmith agreed that every barrel is different.

I would not ask this question on the rimfire forum since I can imagine the fight that would ensue, so what do you think?
 
Sorry, I shoot rimfire and ag. Here is what I discovered. I bought one of the Anschutz 'Match' bbls from Numrich. They are a 1.25" straight cylinder. I turned one down to app .850 but left a near full dia section at the chamber end to allow for a shoulder diameter usable on a Remington 40X. When pushing a lead slug up the bbl you could feel the constriction at the shoulder. These bbls have a straight bore with a constriction at the muzzle end aka choke. When I say you could feel the constriction I mean that the slug got very tight at that part of the bbl. Once past the shoulder the slug then had very little resistence until you got to the choke section of the bbl.

One other thing you will learn with these bbls. The crown must be at the tightest part of the choke. These bbls require shortening app 3/8".
 
CRB go to rimfire accuracy forums, read the thread on rotary forged barrels, you will have your answer.
 
If every barrel is different, how eggzakly does this differ from what the rimfire guys say? Obviously, if true, one should risk such alterations to a great barrel only with the knowledge that it could affect things, right?
 
I would also like to add that imo there is no more horrible of a task than turning the OD of a bbl. I don't know how you would turn a typical air rifle bbl with the small OD that is normally used. Even getting down to .825 is a female dog and the longer the bbl the worse it gets. I have one more of the Annie 1.25" blanks that I will probably use for an AR15 dedicated 22lr upper and hopefully that will be the last time I ever turn the OD of a blank. A 1.25" blank is ideal for the AR as you can turn the tenon to fit the upper rec without any adaptor. I will probably turn it to .900 with about 2" at the muzzle a bit larger OD to increase the choke effect.
 
You are correct. I don't have a really sophisticated setup for my lathe, and being a chep foriegn import with geared head, the lathe itelf isnt that good anyhow. I had to turn a 16mm Lothar Walther barrel from 16mm down to .500" for its full length the other day, and it took around three hours to do it! I use a steady rest, at first running ahead on the stock diameter, then following on the just turned dia. of the barrel, which is chucked on one end and running on a live center on the other. I didnt have lot of trouble with concentricity, but it was just a pain on full slow feed with cuts of around .005" to keep things going smooth enough. Sadly, the barrel didn't shoot any better than the factory Crosman barrel (which WAS a pretty decent shooter btw.), so I used a day and a hunnert bucks to end up almost where I started.
 
The only way I could get a decent cut on the short stiff Annie blanks is to reduce the OD .030" per cut with a pretty fast feed. Generates a lot of heat but no chatter. Makes a hell of a mess. You will be burned.

Fortunately I have had great success with these bbls I have turned. The best group I have ever fired was with one of these bbls. .059" 5 shot at 50 yds. Almost makes it worth the effort.
 
Ray, Haven't turned an Annie blank down, but have done a lot of turn downs over the years - it is a pain... Best method I have found is to use a very sharp high rake bit with a very deep chip breaker and take a large (.100" ) cut with slow feed (maybe .001" per rev.). This peels the metal off without overheating the barrel and it takes fewer passes. The forces are against the headstock and you will get less flexing of the barrel. An automatic shut down on the lathe power feed lets you go and do other things.... A follower rest can be used as the barrel gets whippy on the last few passes.

Scott
 
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