I have used the Lee sizers to size gazillions of pistol boolits with great success but was wondering about rifle boolits at which I am fairly new.
The instructions warn against sizing unlubed boolits so I was wondering if you have to lube the boolit before fitting the gascheck? Surely this would interfere with the grip.
The only way I can see around it is to fit the check to the base of the boolit by hand and then tumble lube em, then size em.
What has been your experience? Am I worrying about nothing?
I have been away from casting for awhile as pistol boolits are so cheap to buy I can't get interested in casting them as I'm a busy guy. I am very interested in getting cast working in my rifles however, especially in the 3006 M17 and 303 No4 which I compete in Military Service Rifle Matches. And there's that Browning BPCR 45/70 which I have a few virgin moulds, just itching to get some lead into orbit and my 30/30 Winchester and 45/70 Marlin which has a lot of game to get into the pot.
Appreciate any help, Mick.

Mick I've sized thousands of bullets with a Lee push thru and don't remember ever lubing one for that trip.

Only caveat with a Lee pusher for checks is making certain their fully bottomed out before running thru the die. Or fully mounted on the shank if that sounds more precise. And that process works best if your also sizing the bullet to some degree.

Worst that's likely to happen running unlubed bullets through a Lee push through is leading the die and having to clean it. I avoid even that possibility by putting a little Lee CASE lube on a pad. Press my fingers on the pad and go to sizing bullets. The trace on my fingers is enough lube, if it is needed at all. Every so often, touch the pad and keep going.