from the old forum:
I have recently received my latest Mountain Mold order in the mail, 4 moulds, 1 iron and 3 aluminum. I have to say first that I am a hard core iron mould fan. I have collected many different moulds of iron/steel in my 25 years of casting from Lyman, RCBS, H&G, NEI, Saeco, and I now have acquired several iron moulds from Dan. My iron block Mountain Molds are now my favorite bullet moulds. If I had to choose just one material to have a bullet mould made of it would be iron, that said my latest aluminum moulds from Dan have been a real pleasure to cast with. The weight is much lighter than iron so after a long casting session it doesn't feel like as much of a workout. Dan's large aluminum block size with the steel alignment bushings and pins are very durable. The aluminum blocks are in my experience more temperature tolerant. The heat dissipating property of aluminum allows a faster casting rate because it takes less time for the sprue to solidify. My 3 cavity aluminum block mould for a 45 ACP bullet empties my RCBS pot quite fast. When casting a large quantity with the same mould over 2 or more days I don't have to coat an aluminum mould with WD-40 when storing it until my next casting session. At the end of one casting session I made the mistake of leaving one of my Lyman moulds out dry overnight, the next day it already had a coating of rust in the cavities. For smoother operation and to enhance the life of all my moulds, aluminum or iron I coat the under side of the sprue plate and top surface of the mould with moly spray (I use Dow Corning 321). When coating the top surface of the mould I spray it with the blocks closed and bullets in the cavities. I don't want the tolerances of the mould messed up by getting moly spray in the cavities or on the block parting surface. I also spray the mould while it is hot. By spraying a hot mould with Dow Corning 321 the cure time is instant. Now I just need some time to do some loading and shooting with the new bullets.