I usually use gas checks when I expect velocities over about 1400 fps. For plinking loads below that speed I don't usually use them, even if the bullet has a gas check base (gas checks are getting to be expensive lately). Generally speaking, you CAN push a gas checked lead bullet just as fast as it's jacketed counterpart, but I have found that my accuracy is not as good (could be the alloy that I'm using - wheel weights). The gas check prevents the base of the bullet from melting when using slower buring rifle powders.
In order for you to use gas checks, of course the bullet must have a gas check base, and you must crimp them on using a die. The die can be the same die that you use in your lubri-sizing machine, one of the Lee push-through type dies, or a special "gas check seating die".
If your bullet does not have a cutout for a gas check, then it would be best not to push the velocities, especially if you're using a softer lead alloy.