My first attempt with reloading yielded poor results at the range. The accuracy of the load (.450 Marlin, 57 grains H322, 300 gr Partition, Winchester LR primer) was fine. What I shot was around a 2" group except for one flyer.

The problem is only 8 of 20 rounds fired successfully. My first thought is perhaps I didn't get the primers seated properly. I don't think the primer is bad. Is there anything else I need to consider that might cause this?

Any help would be appreciated. Thanks!