Question on 'neck sizing only'.

[Mr Dean]

In an effort to trouble-shoot an ill performing gun (see my other posts under Newbie hunter...) I am hoping to find detailed info on neck sizing only.

I use RCBS equipment. Someone told me that to neck size w/ the full length dies, all I need to do is back off the die one and a half turns after touching the ram in the upright position (clearance of a nickel).

Is this sound advice or do I need to buy the special dies for this?
Should be mentioned that the cartridge is the 300 Winmag.

Thanks in advance,
Dean.

 

[LoneStar]

That advice may be just asking for trouble. With many cases/dies, the case body is touched by the die before the neck is fully sized. What this does is push the shoulder forward while the neck is reduced, effecting headspace and adding another variable you probably didn't want. To neck size correctly you should use special neck sizing dies - an added cost. While much is made of benncrest shooters neck-sizing their brass, what you seldom hear is that they also use special shoulder-bumping dies to push the shoulder back slighty, giving better case/chamber fit after several firings.

Neck sizing is not the perfect method we've heard about for years. No factory chamber is perfectly concentric, so if the case is not inserted back into the chamber in exactly the same orientation, any accuracy advantage of neck sizing is lost. Cases seldom have the same wall thickness all the way around either, and when fired the case assumes a "banana" shape which won't fit any chamber perfectly after neck sizing. This fact is one reason that short cases hold most all the accuracy records.

A better method, if you still want to use your existing dies, is to full length size them, but carefully. Loosen the expander plug screw slightly so it doesn't pull the neck off-center as the case is withdrawn from the die. Don't set the FL die to bottom on the shellholder; instead, back it off half a turn and try it in the rifle. If it chambers hard, turn the die in 1/16th turn and try it again until there is just a slight resistance at the choulder (smoke it to make sure). The top long range competition shooters FL size all their ammo and they get the best accuracy using that method.

 

[RiverOtter]

A .300 win also has a relatively short neck. By the time you run the case into the FL die enough to size enough of the neck to properly hold the bullet, the shoulder has already been bumped back a fair bit. When I set up a FL die for partial sizing, I back the die off a couple turns and run a case in and see how far down the neck that black powder belt goes. I keep adjusting down until the black belt is about 1/2 of the caliber.

If you have access to a concentricity gauge, compare a fired case to a FL sized case. If your chamber is more concentric than your dies, I would neck size. If the opposite is true, then I would favour FL sizing.

RO

 

[Casey]

Everything that LoneStar and RiverOtter said. And... go here to a good article on PFLR (Partial Full Length Resizing).

http://www.24hourcampfire.com/reloading.html

Casey

 

[Mr Dean]

Lonestar: As per your post, this is how things are being done. Admittedly not knowing why, though. The one thing different is that I don't back of the expander for the down stroke. Next session of reloads, I'll adopt this practice into my routine - Thanks.

RiverOtter: Your point of the short neck is exactly where my head was at. Don't have that gauge you refer to, but will ask around.

Casey: Just picked up the reading material off of my printer (7 pgs). Will look it over tonight. At a glace, it seems very interesting!

Once again guy's, Thanks!
Dean.

 

[longwinters]

Whoever gave you advice about turning out the full length die was not giving you bad advice. It has been many reloaders practice for years and is also recommended in some reloading books. It is not a hill I would choose to die on, but I have been resizing this way every since I started reloading several years ago. Granted I have not reloaded all my life but I have shot several thousand rounds without problems doing it this way out of a number of rifles. And I have achieved sub MOA accuracy on a pretty consistent basis, as have others that I have reloaded for.

In fact, I have read that many bench shooters only neck size for best accuracy, although I don't doubt they use a competition die to do it.

The great thing about these sites is you will find a host of ideas to think about. The bad thing about these sites is you will find a host of ideas to think about :lol: .

Long

 

[Mr Dean]

Casey: Thanks for that link. Some good reading material there. Checked out some more stuff on that web site...AAALL GOOD!

longwinters : "The great thing about these sites is you will find a host of ideas to think about. The bad thing about these sites is you will find a host of ideas to think about".

Ya got that right :!: