Gas Check Question

I mainly do swaged boolits but have recently got into casting and have a question. If I gas check the boolits made , do they need to be lubed also?

Yes, gas checks are not a substitute for lube.

Ok, how about half jackets. Lube those also?

Yep. Gas checks do 2-3 things, but lubrication to help prevent leading isn't one of them.

They need to be lubed, Paced or Aloxed. I PC larger diameter and Alox smaller diameter.

Gas checks work in conjunction with the correct bullet lube to prevent gas cutting which causes leading. Actually, I theorize that in a way, the gas check does nothing but create a high pressure ring of lube that the gas cannot escape around. As the bullet travels down the barrel, there is a film of lube left behind by the previous round fired. The gas check is a kind of scraper and the lube piles up in front of it. This creates a high pressure ring of lube and to a point, the dynamic truth of the matter is that the harder the propellent gasses push, the more this ring of lube resists the gas pressing against it.
There comes a point where the lube itself starts deforming the bullet and it emerges looking like an hourglass (slightly). When you approach 2900 FPS, the bullet begins to lose it's grip on the rifling, base first. This is why (in my opinion) it is darn near impossible to go faster than 3200 FPS because typical bullet alloys cannot resist the compression. There are things that can be done to mitigate this with bullet design.....ish......sorta. but none of them I have played with deliver reliable results and fliers become commonplace.
Given this is the purpose and function of the gas check, half jackets, etc, (ie, none of these things take the burden of barrel contact and traction on it from the lead) then lube must be present. Only until the copper cup assumes full responsibility for contact and traction on and in the barrel can the problem of lube be dispensed with.