Garrett 310 gr Hardcast Hammerheads will not fit in the rotary magazine of a 77/44. They will chamber and fire as a single shot but the 310 gr bullet is either too long, or is seated shallow to make room for more powder. If you reload, you'll want to stay within the SAAMI length specs. for the .44 mag if you plan on using the 77/44 rotary magazine. Garrett's are loaded hot but within SAAMI pressure specs. and the 77/44 chamber handled them just fine. I hope this helps but if you have questions it'll have to wait until I get back from the north woods. Leaving today to look for bambi.