Bird
02-17-2016, 04:43 AM
Thought I would relax and cast up some bullets for a couple of hours.
Loaded the pot with clip on wheel weight alloy and prepared to cast some RCBS 45-300 fn bullets. This mold has always cast beautiful, consistant bullets since I bought it.
After the first 5 or 6 casts, I started dropping them in water for added hardness. I measured the rear driving bands, and they gave me a reading of 0.4583, which is normal and good as I run through a 0.4585 sizer.
I stopped casting to have a cup of tea and decided to take a closer look at the bullets and measure a few more. The smallest rear driving bands were 0.4579, which points to an uneven casting practice. I then measured the front driving band, which were at 0.4568, no good. Every bullet had a forward driving band of approx 1 thou smaller than the rear band.
I took the mold apart and scrubbed it out, reassembled it and cast some more. Same problem again. I checked previous bullets I had cast some months ago, and both driving bands were exactly the same at a little over 0.458 each. What was going on?
The coin dropped. The good bullets were air cooled, but the bad bullets were water dropped. I cast more bullets and air cooled them, and everything returned to normal. No more reduced forward driving bands.
From my experience with this, it appears The greatest shrinkage occurs at the hottest part of the bullet when water dropped, which is the middle of the bullet which cools the slowest in the mold. Quite logical really.
I thought it worth while to post this observation, as the undersized forward band would not engage the rifling sufficiently, and may cause problems.
I searched the forum, and found no specific mention of this. If this bullet cast sufficiently oversize, then this would not be a problem when resized to fit the bore. No more water dropping for me with this mold, if I need larger or harder bullets I will have to add lino.
I hope this will be of use to others.
Loaded the pot with clip on wheel weight alloy and prepared to cast some RCBS 45-300 fn bullets. This mold has always cast beautiful, consistant bullets since I bought it.
After the first 5 or 6 casts, I started dropping them in water for added hardness. I measured the rear driving bands, and they gave me a reading of 0.4583, which is normal and good as I run through a 0.4585 sizer.
I stopped casting to have a cup of tea and decided to take a closer look at the bullets and measure a few more. The smallest rear driving bands were 0.4579, which points to an uneven casting practice. I then measured the front driving band, which were at 0.4568, no good. Every bullet had a forward driving band of approx 1 thou smaller than the rear band.
I took the mold apart and scrubbed it out, reassembled it and cast some more. Same problem again. I checked previous bullets I had cast some months ago, and both driving bands were exactly the same at a little over 0.458 each. What was going on?
The coin dropped. The good bullets were air cooled, but the bad bullets were water dropped. I cast more bullets and air cooled them, and everything returned to normal. No more reduced forward driving bands.
From my experience with this, it appears The greatest shrinkage occurs at the hottest part of the bullet when water dropped, which is the middle of the bullet which cools the slowest in the mold. Quite logical really.
I thought it worth while to post this observation, as the undersized forward band would not engage the rifling sufficiently, and may cause problems.
I searched the forum, and found no specific mention of this. If this bullet cast sufficiently oversize, then this would not be a problem when resized to fit the bore. No more water dropping for me with this mold, if I need larger or harder bullets I will have to add lino.
I hope this will be of use to others.