calinb
06-11-2017, 03:42 PM
I beagled an RCBS .250-50-RN (57902) mold, which drops .251 in pure lead, for my Lothar Walther airgun barrel. With a single .002 layer of aluminum beagling tape on each side of the mold, I experienced a very fine line in temperature / pressure between good fill-out and finning and air vent fingering. Here's how I completely eliminated the problem. I don't know whether others have done the same, but figured I'd post about it here in the original beagling forum, just to be sure. In fact, the technique worked so well that I'm planning to increase the tape thickness and beagle the mold up even more for my barrel, which slugs .248 / .254. With only two .002 tape layers, I can't currently size the beagled bullets larger than about 252-3/4 thou, without sacrificing roundness.
I removed the mold from the handles and inserted two nicely beagle-cast bullets (no fins or fingers) to mask the cavities. I pressed them firmly into place in their original positions (with their faint seams aligned with the cavity edges). Next I used masking tape to cover the beagling tape, but I made sure I left the bare region around the cavities unmaksed. Finally I sprayed two or three thick and wet coats of Frankford Arsenal Drop Out to the mold faces from the rattle can. (I have finally found a use for Drop Out! :p) I applied enough "paint" to pretty well fill the mold vent lines.
After the Drop Out dried, I carefully plucked the bullets from the cavities and removed the masking tape, being careful to not disturb the underlying beagling tape. Here's where I noticed an unexpected and pleasant surprise. Whereas I only expected to mitigate the fingering at the vent lines, I realized that finning elsewhere around the cavity would likely be reduced (up around the nose of the bullet), because the Drop Out created a small fillet at the edge of the cavity between the mold block faces and the masking bullets. When I removed the bullets, the fillet remained.
Finally, I cleaned up a little Drop Out overspray with denatured alcohol and Q-tips. I was careful to not disturb the small fillets or filled vent lines. I've now cast a few hundred bullets and the result is no finning or fingering at all--even at higher temps and pressure to fill the little 25 cal. mold reliably. I also found the beagled gap between the mold halves to be fully sufficient for venting.
Give it a try sometime and I hope it improves the results of your beagling!
I removed the mold from the handles and inserted two nicely beagle-cast bullets (no fins or fingers) to mask the cavities. I pressed them firmly into place in their original positions (with their faint seams aligned with the cavity edges). Next I used masking tape to cover the beagling tape, but I made sure I left the bare region around the cavities unmaksed. Finally I sprayed two or three thick and wet coats of Frankford Arsenal Drop Out to the mold faces from the rattle can. (I have finally found a use for Drop Out! :p) I applied enough "paint" to pretty well fill the mold vent lines.
After the Drop Out dried, I carefully plucked the bullets from the cavities and removed the masking tape, being careful to not disturb the underlying beagling tape. Here's where I noticed an unexpected and pleasant surprise. Whereas I only expected to mitigate the fingering at the vent lines, I realized that finning elsewhere around the cavity would likely be reduced (up around the nose of the bullet), because the Drop Out created a small fillet at the edge of the cavity between the mold block faces and the masking bullets. When I removed the bullets, the fillet remained.
Finally, I cleaned up a little Drop Out overspray with denatured alcohol and Q-tips. I was careful to not disturb the small fillets or filled vent lines. I've now cast a few hundred bullets and the result is no finning or fingering at all--even at higher temps and pressure to fill the little 25 cal. mold reliably. I also found the beagled gap between the mold halves to be fully sufficient for venting.
Give it a try sometime and I hope it improves the results of your beagling!