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The only time you really need to crimp is for tube fed guns or heavy recoiling cartridges.

yes the neck sizing determines the tension...

the dies wont need adjusted in that department unless you get into technical stuff and buy special bushings to adjust the tension...but for most rigs you'll never notice what you gain from that..a true benchrest rig and you might...

i never actually measured my necks but they are a bit smaller than bullet diameter...when the bullet is seated, it expands the neck enough for the bullet to fit very snug...

:biggrin:If you want to crimp, your bullets have to have a cannelure which is an indentation around the bullet. Any decent reloading manual will tell you exactly how to do this. You said that you reload 38 special, any wadcutter lead bullet will have a cannelure so you probably already know about this. In most bolt action and magazine fed rifles this is not necessary, semi autos or tube fed rifles or hard kicking rifles usualy will require a crimp.:biggrin:

No need to crimp the 7mm08...

I have loaded cartridges as heavy as the .338 WM and 9.3 x 62 and never needed to crimp...

Just another thing about crimping you may want to know. Lee sells a factory crimp die. I works by squeezing the case into the side of the bullet. Thus no cannelure is needed for crimping, you can crimp any bullet.

I see this as a tool to easily deal with inconsistent neck tension. The kind you get with lee collet dies. Anyhoo, I have them but haven't used them much.