A friend has restored an old Belgian .52cal rifle with septagonal rifling.
We have ordered a mold for round balls,now I just need to get an idea of where to start with loads. I can only get FFF powder here.
Thanks.

Assuming it's been reproofed, or at least inspected by a gunsmith qualified to judge it in good shooting order, the place to start would be around 50 grains of powder under a snug combination of ball and patch - such as may need a short starter but can be seated without pounding. I wonder a little bit about the twist of the septagonal rifling. If it's quicker than one turn in five to six feet it might be intended for conicals. Is this a caplock or firelock? Military or sporter? Please keep us posted.

It restored by one of the more competent smiths in the country, so I'm not too worried about it being safe to shoot, all the same I wouldn't want to push it either.

It's a caplock, I think from the late 1800's Quite a nice rifle, most likely a hunting rifle from the beginning, not a military. I will check the twist rate next time I see it, and take some pics too.

Anyone know who will make custom minié molds?

The first check is to measure the nipple hole . .033 is max opening inside nipple Mick some paper clips and get the no go which would be .034 and check your opening , the rule is 2 grains times the caliber as max load, your gun man should have told you this information ! 3F I only use 80 grains of Hodgdons triple 7 3F in my 50's and 60 in my 58's they blow up a 1 gallon milk bottle full of ice at 50 yards & clean threw a 2x4 at 100 yds 80 grains for your rifle will stop snything you are hunting if shot placement is made in kill zone .