RCBS Competition vs Lee sizing dies

[Fotheringill]

I have and use the RCBS, Redding, and Lee neck sizing dies. There is remarkably less runout with the Lee collet neck sizer. Seating for all is done with a Redding Competition seater. Go figure.

[Nor Cal Mikie]

If you're going to start loading for a gas gun, full length resize BUT, make sure you don't push the shoulders back too far. .001 to .002 is best. Too much working the brass and you'll end up with case head separation. Sooner or later, you'll run into that. No use rushing it.
I've loaded and fired at least 5000 rounds with RCBS full length dies for my M1A without issues. The RCBS Comp seater works like a charm as well as my Rockchucker press.

[Luckus]

I like Forster fl dies and their mic bullet seater. The seater is easy to read and very accurate. Forster can also custom hone the neck of the sizing die to eliminate the expander ball, or to just kiss the neck. I have two set up this way, a 6 Dasher and a 257AI. The folks at Forster are very accommodating and know what they are doing. It seems that everyone who starts handloading has to go through the neck sizing stage (me included) a few stay with it, but most I think full length size. Imo full length sizing with .002 shoulder set back gives the best results. If you neck size you will eventually have to full length or your cases will chamber too hard or not at all. The Lee collet die works as advertised as I used one on my .308 FTR rig for awhile, but you still have to bump the shoulder after 2 or 3 bangs and start all over. My rifle was just as accurate when I full length sized them, so that's what I did. The most important thing about a sizing die is that it's straight. They all make good ones and sometimes bad ones. Luckus

[RC20]

I think I can add a bit of at least information here, maybe not settle things.

I have two guns I have dialed in, one is a Shilen barrel 30-06. The other is 7.5 Swiss.

The 7.5 Swiss has a RCBS comp sizing and seating die. Its the most accurate (or the one I have found the most accurate load for)

The Shilen is a Forster sizer and bench rest micrometer seater. Its close to the 7.5 but (so far) a tenth or so bigger groups.

The Shilen with the best load is about 1/2 MOA, shade less but no more than 7/16. Even with Lapua Brass.

The 7.5 Lothar Walther is running about .250 (PPU brass() .

My take is there is no difference in good dies, its good equipment, the barrel has to be good, the load has to be good as well as the trigger puller being able to do their end.

A die might show a difference with Tubbs class shooters, but for most of us, max nix.