In your 30-30, or any bottle-neck case, load the COW directly on top of the powder in suficient quantity to compress the COW when the bullet is seated. The compression keeps the COW from mixing with the powder. Good Luck!
Regards,
Sweetwater
Yes, that will work fine if you work up your loads with the COW. Otherwise it will raise pressures significantly. I've gotten the best results by using a tuft of cotton to finish filling the case to the bottom of the neck. Then fill the neck with COW, and seat the bullet.
FWIW, I've also gotten better and more consistent accuracy if I use no lube or gas check. Sizing is optional, if your chamber will take a bullet as cast. Otherwise shoot them as they drop from the mold. The COW will not only prevent leading, it will do a fine job of scrubbing your bore mirror bright, with no abrasion. The only drawback is that you have to be sure to oil it before putting your gun away, or you can have a rusted bore when you take it back out again.
Molly