300 whisper ssk 14" contender

[Kirb]

I have had my ssk barrel for a couple years just getting ready to shoot I want to shoot cast bullets. at about 200 GR. When I get the bullet seated the gas check is well below the neck of the case. I dont like to shoot them like that. I have tried 200 gr RCBS and a NEI mould 190 gr and a lyman mould I think it was a 311296 173 gr. and the only one to work so far is the the RCBS SIL. 165 Gr that drops 173 Gr ww gas check bullet best overall cartiage length I can get is 2.105. I dont know How many people on this forum shoot the contender. I see contender21 shoots cast bullets am I doing something wrong do I have a short throat or do you want the bullet to take up case capacity with sub sonic loads.

Thanks
Kirb