Pioneer2
I guess i really do not think you will have any problems shooting the larger longer conicals from your 1/28... They only problem is the selection is kinda limited....
No Excuses makes a slip fit .540 535 grain conicals that will probably shoot great.
Bull Shop is developing some slip 54 cal conicals.
One I really want to try are the Buffalo conical.. 435 and 460... They both have good BC's but I do not know what they are sized at...