This article appeared in Fouling Shot #227 Jan/Feb 2014 and was written by CBA member by Bill Duncan Coffman of Cove, AK.
Sprue Plate Wrench
This all started about a year ago when I started casting using a 20-1 lead/tin alloy. The soft alloy was used in an effort to come up with a breech-seat bullet for use in a 30 caliber wildcat. First I lapped three old single cavi-ty Lee molds to get the proper bullet diameter with the 20-1 alloy. The Lee molds are gas-check designs, but the idea was to determine the best as-cast diameter so a custom plain-base mold could be ordered.
It took a number of sessions both casting and lapping before I started getting bullets that would shoot well in the new barrel. When I had the correct diameter, my casting efforts were aimed at producing quality bullets to see what the rifle was capable of with bullets from these modified molds.
The biggest problem was tear-out of the sprue cutoff. I tried tandem casting using two molds, cool-ing the sprue plate with a damp cloth, and waiting for long periods for the sprue to cool. Unless I cooled the sprue puddle excessively or waited a long time, the sprues would not cut cleanly when the sprue plate was whacked with a hardwood mallet. This casting method was, to me, slow and tedious.
I have been casting for a lot of years and have read numerous articles on the subject. All the infor-mation I have come across describes the method for cutting sprues as follows: When the sprue puddle hardens after several seconds, strike the sprue cut-ter sharply. The problem I see with this is unless the sprue puddle is fairly cool, the shear stress applied to the mushy metal is high and tear out occurs. Another draw-back is that one is delivering a sharp blow to a precision tool, not to mention heating it up, then purposely cooling it down.
Sprue Plate Wrench
This all started about a year ago when I started casting using a 20-1 lead/tin alloy. The soft alloy was used in an effort to come up with a breech-seat bullet for use in a 30 caliber wildcat. First I lapped three old single cavi-ty Lee molds to get the proper bullet diameter with the 20-1 alloy. The Lee molds are gas-check designs, but the idea was to determine the best as-cast diameter so a custom plain-base mold could be ordered.
It took a number of sessions both casting and lapping before I started getting bullets that would shoot well in the new barrel. When I had the correct diameter, my casting efforts were aimed at producing quality bullets to see what the rifle was capable of with bullets from these modified molds.
The biggest problem was tear-out of the sprue cutoff. I tried tandem casting using two molds, cool-ing the sprue plate with a damp cloth, and waiting for long periods for the sprue to cool. Unless I cooled the sprue puddle excessively or waited a long time, the sprues would not cut cleanly when the sprue plate was whacked with a hardwood mallet. This casting method was, to me, slow and tedious.
I have been casting for a lot of years and have read numerous articles on the subject. All the infor-mation I have come across describes the method for cutting sprues as follows: When the sprue puddle hardens after several seconds, strike the sprue cut-ter sharply. The problem I see with this is unless the sprue puddle is fairly cool, the shear stress applied to the mushy metal is high and tear out occurs. Another draw-back is that one is delivering a sharp blow to a precision tool, not to mention heating it up, then purposely cooling it down.
Well, with the just described dilemma rattling around in my pea-brain, I retreated to the couch with a cup of tea, a place where an occasional EUREKA moment (and numerous naps) has occurred. My thinking was, if the sprue could be cut slowly, shear forces would be much lower and tear-out would not occur. The problem here is that the extension on the sprue plate is not long enough to get adequate leverage.
Solution, a 6 inch piece of rigid 1/2 inch copper tubing flattened on one end to fit the sprue plate extension, and a 2-1/2 inch hardwood dowel affixed to the opposite end for tapping the hinge pin of the handles to release sticky bullets. The overall length of my sprue wrench is 8 inches. With sprue wrench in hand, I fired up the 20-1 pot and began casting. The wrench worked well but I was still having to wait and/or cool the sprue puddle.
The sprue wrench worked so well on the three 30 caliber molds I was anxious to try it with the other molds I have. A session with a single cavity Lee mold for a 160 grain semi-wadcutter using 30-1 alloy produced tearout. To get this mold to work the pot tem-perature had to be lowered from the 700-750 degree range to 650-700 degrees, the sprue puddle had to be cooled with a brief touch using a damp cloth, and the sprue cut with a quick push.
I had about the same results using a two cavity Ohaus iron mold casting 38 caliber wadcutters with a 30-1 alloy. Guess this is why Al Miller wrote the article Casting Techniques to Fit the Mould in The Art of Bullet Casting.
When casting 38 caliber bullets I found I could get smooth bases with minimal sprues if the sprue plate was not closed completely, the sprue plate hole overlapping the edge of the bullet cavity, a technique touted by Wayne Blackwell and Jim Carmichel. This leads me to believe that a 38 caliber bullet, being larger in diameter, retains more heat in the center of its mass; the edge of the just poured bullet losing heat more quickly into the mold.
As a final test before submitting this article, I broke out the Lee 180-R mold and after a short casting session ended up with 70 bullets of which 81% were within 0.3 grain. Formerly the results of a casting session produced a batch of bullets that when weighted gave a bell shaped distribution with the majority of keepers in the mid weight range with heaver and lighter bullets tapering off on either side. In this last session, the 0.3 grain keepers were the heaviest, the vast majority of rejects being lighter, and three bullets 0.1 grain heavier. This suggests that by not having to interrupt the casting rhythm with the cooling cycle, the mold remained at a higher more consistent temperature and the mold was filling out more completely.
I am a dipper guy and one of the weaknesses in my technique is consistent filling of the dipper to get equal pressure on the column of molten lead. I think that by paying attention to this detail, and lapping the ladle spout so there is no leakage, I can do even better. During this last session I also tried using a sharp whack, which usu-ally produced some tear out.
With the above being said, I cannot imagine that some bullet caster out there has not tried or is using a sprue wrench type device. An example may be the Lee 6-cavity molds, which have a long handle on the sprue plate to provide enough leverage to cut 6 sprues. It looks like they were designed to be pulled, not whacked. My guess is the sprue wrench-slow cut procedure may be best suited to smaller diameter bullets, using molds that lose heat quickly. The only one way to find out is give it a try.
The sprue wrench worked so well on the three 30 caliber molds I was anxious to try it with the other molds I have. A session with a single cavity Lee mold for a 160 grain semi-wadcutter using 30-1 alloy produced tearout. To get this mold to work the pot tem-perature had to be lowered from the 700-750 degree range to 650-700 degrees, the sprue puddle had to be cooled with a brief touch using a damp cloth, and the sprue cut with a quick push.
I had about the same results using a two cavity Ohaus iron mold casting 38 caliber wadcutters with a 30-1 alloy. Guess this is why Al Miller wrote the article Casting Techniques to Fit the Mould in The Art of Bullet Casting.
When casting 38 caliber bullets I found I could get smooth bases with minimal sprues if the sprue plate was not closed completely, the sprue plate hole overlapping the edge of the bullet cavity, a technique touted by Wayne Blackwell and Jim Carmichel. This leads me to believe that a 38 caliber bullet, being larger in diameter, retains more heat in the center of its mass; the edge of the just poured bullet losing heat more quickly into the mold.
As a final test before submitting this article, I broke out the Lee 180-R mold and after a short casting session ended up with 70 bullets of which 81% were within 0.3 grain. Formerly the results of a casting session produced a batch of bullets that when weighted gave a bell shaped distribution with the majority of keepers in the mid weight range with heaver and lighter bullets tapering off on either side. In this last session, the 0.3 grain keepers were the heaviest, the vast majority of rejects being lighter, and three bullets 0.1 grain heavier. This suggests that by not having to interrupt the casting rhythm with the cooling cycle, the mold remained at a higher more consistent temperature and the mold was filling out more completely.
I am a dipper guy and one of the weaknesses in my technique is consistent filling of the dipper to get equal pressure on the column of molten lead. I think that by paying attention to this detail, and lapping the ladle spout so there is no leakage, I can do even better. During this last session I also tried using a sharp whack, which usu-ally produced some tear out.
With the above being said, I cannot imagine that some bullet caster out there has not tried or is using a sprue wrench type device. An example may be the Lee 6-cavity molds, which have a long handle on the sprue plate to provide enough leverage to cut 6 sprues. It looks like they were designed to be pulled, not whacked. My guess is the sprue wrench-slow cut procedure may be best suited to smaller diameter bullets, using molds that lose heat quickly. The only one way to find out is give it a try.