Hornady modified cases for OAL...should they be re-sized?

[Wannashootit]

Like many, been using these for years to determine OAL with the comparator.

Getting ready to do it again for a new .260, and I got to thinking...

The LNL case is (presumably) a SAAMI spec case. Fireformed cases are going to be close, but depending on the chamber, the datum line of the fireformed cartridge is going to be different.

So, since we've all gotta start somewhere, it's done with the LNL case (although I've read of guys modifying their own fireformed cases from the get-go, skipping this extra step?).

But after the first range trip (with any new rifle) I measure headspace of the fireformed case with headspace comparator gauge, then adjust the FL sizing die for about .002 bump.

So to the question:

Should I run the modified case, through the sizing die (and re-take OAL measurements after) after it has been set for correct shoulder bump? Or is the difference too small to be significant enough to mess with?

 

[1lnbrdg]

No

 

[GrantA]

It would make no difference in the OAL of the cartridge. The only reason you might have to is if you have a very tight chamber and the brass just won't fit.

 

[smschulz]

If you resize you won't be able to put your projectile in for measurement.

 

[mattmcg]

Absolutely unequivocally yes. In fact, I just ran into a scenario where my Hornady modified case was out of round, and hung up in the chamber giving me an artificially long OAL result. Threw my smith and reamer maker for a loop until I identified the problem.

From now on, I will resize using a body die and make sure to not bump the shoulder unless the cartridge is out of spec. If your tools aren't accurate, your results will never be either.