I don't know what a boolit is, but if you are speaking about bullets I can give an accurate answer.
I hope that statement isn't offensive, but the web site name being used for bullets is something that bugs me every time I see it! No one will ever see me write it, and I like to keep it off my forum. Thanks everyone for respecting me on this tiny issue.
Checks that are loose after sizing, and especially when going down to nominal size like you are, indicates a check shank that is too small. However, since they stay on, but can be removed with your finger nails, they do have a grip, and all my molds use straight check shanks. As these bullets enter the rifling they will get crimped in another .008 inch, or whatever rifling depth is, and be as tight as any check can be while doing their job.
If the check shank were tapered as most mold makers make them, you'd suffer accuracy loss.
Some lots of gas checks have harder than normal metal, which springs away from the bullet after sizing, and if that is the problem, they will spring away after leaving the bore, leaving a rattle at the bullet base which will hurt precision accuracy. Most handgun shooters will never know if this is a problem as it is slight, but annealing the checks will cure the problem.
For the above reason, gas checks can often be turned with the fingers after installation, even though the check shank is perfect, and the checks are crimped in deep enough that they cannot be removed with the fingers.
Should anyone have a high velocity rifle mold with checks that are this loose, and feel it is causing accuracy problems, or if anyone has one of any caliber and they are quite certain loose checks are hurting accuracy, I will repair the mold free. I'm speaking here ONLY of LBT molds of coarse, and if you'll read this paragraph carefully you'll notice I didn't but a time limitation on it, nor does one have to be the original purchaser.
