Rebarrel CZ 550 Varmint
Hi guys, I would like to ask you for some advices. I want to rebarrel this rifle with custom built chamber, but it's not clear some details.Especially it is free bore, what is the best length of it? I shoot always with bullet in lands and I want to shoot from magazine. Is there any minimum size or Can i have whatever I want ?
Second thing is : Neck diameter, I want to have tight neck to get the best accuracy.I shoot .337" loaded cartridges. Could it be exact the same diameter of neck ? I mean safety.
You didn't specify a caliber, but I'm guessing that since you say a 0.337" loaded neck OD it's a .308 Win.
If you want to be able to feed from the magazine, make up a dummy round with the bullet of your choice that's short of the absolute maximum the magazine will feed, then seat the bullet a bit (technical term) deeper. That will allow you to chase the rifling as the throat erodes. Using a comparator that will allow measuring from the head of the case to the ogive on the bullet (where the bullet will contact the rifling ±), take a measurement, and add 0.005" to it.
That's just a best estimate, but if the freebore is short the only thing you'll lose will be a few ft/second of velocity. If the freebore is too long you could end up with less than expected accuracy, and not being able to chase the rifling for as long as you could with less freebore.
I hope that makes sense.
If you're going to have the work done by someone else, try to find someone who has a good reputation for building match rifles. Their advise is good to follow. I've found in dealing with several gunsmiths that they know what works and what doesn't. BUT just because a guy has a lathe and can chamber barrels doesn't mean he'd be someone to (re)barrel a match rifle. Doing the job right may cost a bit more, but not enough more to make you sorry you paid that bit extra.
Originally Posted by dan12
You need some neck clearance. So, if your loaded rounds are .337 and your reamer is .337 your tolerance for neck runout and dia would be +.0000"!! Not good!
Post what purpose of the rifle, cartridge, twist rate, bullet and brass you plan to use and people may be able to give you some specific advice about necks.
Sorry guys I forgot, It's 308w. I use this rifle for sniper competitions. In this factory rifle is 1:12 twist, I shoot 155,167gr Lapua Scenar,168 MK Sierra, 175 VLD Berger, generally is from 155gr up to 175gr bullets. Brass is Lapua and Sellier Bellot. These both have the same diameter of the neck of loaded cartridge.(0.337"). My factory neck is 0.344" what seeems to me quite generous,Am I right ?
Relating to magazine length:
For example 168MK Sierra is in lands in 2.906"(OAL) and max magazine length is 2.835".
No turn neck!? It would be a bummer to pull the bullet out in the middle of one of those comps..
Originally Posted by dan12
PTG Reamer 308 Winchester MatchProduct #: 889590
Is what I have to build the rifle below. 155,168 and 175 all below max coal. No turn neck...but shoots really well. You can get a print from PTG. I looked for it but could not find it.
Last edited by Bnhpr; 12-23-2009 at 02:58 AM.
Do you have any targets of this rifle?
What about the neck tolerance? If it is tight how much is it ?
There is a 5 shot test target only beside it.... a single hole, but it is not a proper evaluation of the rifle. I will say it is very accurate for a no-turn neck. Or skim neck. Like I said, I cannot find the reamer print and I'm not home to get a hard copy. You can email PTG and they will send you a print. I seem to remember .003 clearance no turn Lapua brass. So if you skim .002, you have .005 clearance. I have shot this rifle no-turn and with skimmed necks and the skimming does make a difference with less fliers. I would think for your type of competition, you would not want to run too light neck tension and risk leaving a bullet in the throat and powder in the bolt way. This sucks, and has happened to me. Good luck
Last edited by Bnhpr; 12-24-2009 at 07:30 PM.
Dan, you might want to try..............
a 1 in 10" twist for your rifle. I know, ALL the factories cut a 12, but you might want to try a 10.....