new to shotshells

i was trying to duplicate a load I found in my Lyman manual. It called for winchester AA hulls, winchester 209 primers, WAA12r wads and 38 grains of blue dot powder, 10 O-buck for a velocity of 1375 at 9,500 psi. To start off with the lee-load-all called for a .198 powder bushing (the biggest one it comes with). I dumped ten powder loads in my scale and they averaged 35 to 36 grains. 2 to 3 grains less than what the load called for but i figured that was OK. the buckshot loaded fine but the crimps were horrible. I found if I put a BP overshot card on top of the buckshot it crimped great. My question is: will this overshot card increase the case pressure and if so how much? Will these be safe to shoot?

oops, i was wrong about the overshot card. it is a 12 gauge overshot card from precision reloading. there is no thickness shown on the package.

the overshot card won't increase pressure enough to worry about.
you figure it into your payload weight.
i'd try a few with the card on top and some with it on bottom,it can affect your pattern.
but i doubt 5-6 grs of weight will matter.
with the amount of shells you'll be making, weighing each charge is no big deal.
however you need to be aware that blue dot is temperature sensitive and performance drops off when it gets cold.