I found out something tonight. I was measuring all of my 404 Jeffery loads and found they were all .010" shorter than I loaded them (I measure them after I load each round). And then I use a Lee factory crimp die, but never measured after crimping.

And I measured 2 lots of rounds that I loaded at different dates (months apart) - both were .010" shorter.

Assume the crimping is causing this? I used Northfork bullets. And the crimps are on the gas rings, not in the groove.

Anyway, since it's consistent, and my loads have low SD on the FPS and are accurate, it doesn't matter.

Just curious.

I need to measure my 458 Win (which uses NF) and my 8x57, which uses Nosler ABs and see if I observe the same differences.

It's not really surprising. As you crimp into the groove, the bullet is pulled back just a little.

Got to be careful with the crimp die. It is easy to buckle the shoulder. Not only is it easy to push the shoulder back, it is easy to swage the soft lead inner core of the bullet, and move the center of gravity outside the axis of rotation.



I have chamber reamer cut gages for 223 Rem, 308 Win and 30-06. My 308 reamer cut gage is on the right. The reamer that cut that gage is the same reamer that cut the chamber on a 308 Garand NM barrel. So, when fired cases are dropped in the Wilson gage and the reamer cut gage, I can see the interference fit that happens with an enlarged case.



Now I noticed that 30-06 cases sized in my Bonanza match die, sized and primed, these cases dropped fully into my reamer cut 30-06 gage. However, after a bullet was seated, no crimp, there was resistance to the fully loaded case dropping into the gage. I could push the case flush, with a little force. That tells me that just the force it takes to seat a bullet is buckling the case walls a bit. Adding a crimp will buckle the walls even more.

You answered your own question; crimped on the gas ring, of course it can pull the bullet back .010.