I'm working on a 500 yard target load for my 308.
I have a factory Remington 700 LTR with a factory chamber. I have a candidate with 175g SMK's that provided mostly sub-minute groups, clusters under half minute, at 500 with a 6x scope. I want to tweak this load a bit and wondered what folks with factory chambers do for the best accuracy, fireform or full resize. I have standard RCBS dies and a RockChucker. All the cases so far have been necksized, trimed to length and chamfered. I have not been tumbling cases just cleaing any excess carbon from the exterior and case neck.

Do you neck-size with a neck-sizing die or partial neck-size with a full-length sizing die?

The partial neck size leaves a thick portion of neck to help centering, in my mind it's actually better than true neck-sizing with a neck-sizing die.

However, in my opinion there is still chance for deformation caused by friction---The neck is pushed into a smaller hole and squeezed into correct size, nothing guarantees the resized neck will be in-line with the chamber neck. A Lee collet die does not resize neck by pushing it through a smaller hole, it squeezes it against a mandrel so it will be straight. Also, if my visualization is correct, the case body is not stressed when neck-sizing with a Lee collet---the shellholder provides pressure by butting against the collet. The case body is free to float except neck I think.

My preference is Lee collet > partial neck-size > full neck-size > full-length-size

Hope this helps

Here's my technique. I'll work my through the process of finding what powder charge with the specific bullet/primer/case works best. Then I uniform the primer pocket and try that against an equal number of un-uniformed to see which is best. Then I uniform the flash hole, using the same proceedure. All the while I'll make sure the case length is the same from begining to end of the testing. Then I'll uniform the case neck for thickness and test that against the same number that has not been uniformed for thickness.
Then I'll move the full length sizing die up one half to three quarters of a turn and compare that to the full length sized cases.
Then I'll test the finished load, assuming that each step of the above is an improvement, against the final load.
Sometimes I'm surprised with no difference and other times there's a considerable change.
Jim

My experience has shown that how much you need to size the case depends on the chamber. All of the above comments seem very applicable. I have an oversized chamber in a 223 that gives its best acuracy if I partial neck size using a full length sizing die. My 22/250 likes to be full length sized with a shoulder setback of .001. My .270 likes the die turned about an 1/8 turn off the shell holder. It also depends on the construction of the die being used as some are bigger inside and some are a low base die which seems to squeeze the case back to near original dimensions. Note that not all shellholders are equal so you must stay with the same holder for consistency. They are supposed to be .125 thick (case head to top.) Some are .128 which means you may be undersizing the case in certain situations.

A friend who is a High Master always full length sizes. His chamber is fairly tight and does not work the brass much. His rationale is this. By full length sizing every time you bring the case back to a standard dimension consistently. If you neck size, especially with hot loads, you will have to eventually full length size to get the case in the chamber. At that time you now have a different case dimension and the gun will shoot differently for the full lenght sized rounds versus the previous neck-sized rounds. He has a point. He also shoots at 600 and 1000 yds with a peep sight and wins matches.

If the Lee die won't give good results, then I use a full length die set above the press ram by a certain distance using a thin washer. Sometimes the best accuracy is achieved with a .050 setback washer. Some do best with a few thousands setback.

Pyrotec's responses seems to capture the best progression of sizing. Least brass work is best if possible.
Ron

I asked Bart Bobbitt why he full length sizes all his cases with a FL die with the neck lapped out and no sizer ball, when the Redding FL bushing dies would do the same thing. He said that was because he already had the lapped dies.

My 223 and 257 RIA both like cases 2/3 neck sized with a FL die with no sizer ball.

MCL:
Usually neck sizing produces better accuracy.
BUT. There is always a but.
But sometimes it dosen't. You just have to find out what YOUR rifle likes. Then don't argue with it, just feed it what it likes.
Not rocket science but another excuse to go shooting.
muck