Here's food for thought on RL15.

I was working on some reduced loads for a 577/450 Martini Sporter rifle. (*** See Administrators note below ***) Shooting 500 gr. bullets with 75 grs. of RL15 at 2000 fps at an estimated 35,000 CUP in a 6 1/2 pound Martini felt neither fun nor safe. I was getting hang fires and misfires at 45 to 50 grs. No bullets stuck but lots of clumps of unburned powder and neck blow by at the lower end load range. After shooting a shot we would see these clumps of powder laying on the ground down range smoldering and then suddenly flare up. I solved this problem with an over powder wad of kapok. I am leery of any wad especially in a bottle neck case. When it warms up I am going to try puffalon for over powder wad.

Could it be that the large charges are partially igniting and the powder column is being blown down the barrel and then igniting? Or perhaps continuous ignition as it goes down the barrel.

I don't know if my experience with RL15 contributes any ideas to cause of this double blow up, but I would hate keep it to my self and it was important

Edited by NitroX to add the following from a post later in this thread. I want to remove any ambiguity in the above post for safety reasons.