high standard 40
05-04-2017, 12:35 PM
I've been a member here for quite a while and this forum has taught me volumes of valuable information. I thought I would share what I have learned, in particularly as it applies to casting alloy melt temperature and mold temperature.
First a little relevant history. 90% of all my casting is done to feed my IHMSA silhouette guns, primarily 3 different 7MMs. One common mold works for all three, that being an RCBS 7mm 145 SIL. I do need to size these differently for each of my three 7mm handguns. From the start with this mold, I had problems getting a bullet that was of sufficient diameter to fill the generous chamber on my XP100 7TCU. Erick at Hollow Point Molds fixed that issue for me but that is an issue apart from this discussion. I have focused my efforts in the last few years to make the absolute best bullets possible and have tried endless different techniques to improve my consistency. Some will say that a silhouette target is rather large and benchrest accuracy is not needed to shoot perfect scores. I agree as far as normal matches go, but if you are fortunate enough to make it to the shootoffs where targets can become very small and at distances many would believe impossible, then extreme accuracy becomes a must. With this in mind, I will share what I have learned in regards to casting temperatures as they relate to optimum mold fillout.
When I do everything just right, my RCBS 7mm 145SIL mold will give me a bullet with drive bands that measure .287" and a bore ride nose that measures .279". I'm then able to size the nose to .277" which fits all my 7mm guns. I have heard it said many times here and elsewhere that casting temperatures for best mold fillout are at a level that will produce a bullet that falls from the mold with a lightly frosted surface. Factors to consider here are the temperature of the melted alloy, the mold operating temperature, and casting cadence. But I have discovered, at least as it applies to my mold and alloy, that a lightly frosted bullet will actually be undersized and lighter in weight than a bullet with a shiny surface. As an example, with my mold, if any of the bullet nose is frosted, the .277" die will not touch the frosted areas of the nose when sizing, indicating incomplete mold fillout. I get a full .279" nose when I run my alloy at 710 degrees controlled by a PID. This gives me a bullet with a uniformly shiny surface. I also closely time my cadence to keep mold temperature as constant as possible. For the record I use only foundry certified 92-6-2 alloy.
So I guess what I'm saying is that while there are many techniques that can be considered standard and "gospel" so to speak, there are also no absolutes. What works for one person may not work for everyone. If what is considered to be "tried and true principles" don't work for you, don't be afraid to think outside the box. For me, I have found that hotter is not better, at least with this one mold.
First a little relevant history. 90% of all my casting is done to feed my IHMSA silhouette guns, primarily 3 different 7MMs. One common mold works for all three, that being an RCBS 7mm 145 SIL. I do need to size these differently for each of my three 7mm handguns. From the start with this mold, I had problems getting a bullet that was of sufficient diameter to fill the generous chamber on my XP100 7TCU. Erick at Hollow Point Molds fixed that issue for me but that is an issue apart from this discussion. I have focused my efforts in the last few years to make the absolute best bullets possible and have tried endless different techniques to improve my consistency. Some will say that a silhouette target is rather large and benchrest accuracy is not needed to shoot perfect scores. I agree as far as normal matches go, but if you are fortunate enough to make it to the shootoffs where targets can become very small and at distances many would believe impossible, then extreme accuracy becomes a must. With this in mind, I will share what I have learned in regards to casting temperatures as they relate to optimum mold fillout.
When I do everything just right, my RCBS 7mm 145SIL mold will give me a bullet with drive bands that measure .287" and a bore ride nose that measures .279". I'm then able to size the nose to .277" which fits all my 7mm guns. I have heard it said many times here and elsewhere that casting temperatures for best mold fillout are at a level that will produce a bullet that falls from the mold with a lightly frosted surface. Factors to consider here are the temperature of the melted alloy, the mold operating temperature, and casting cadence. But I have discovered, at least as it applies to my mold and alloy, that a lightly frosted bullet will actually be undersized and lighter in weight than a bullet with a shiny surface. As an example, with my mold, if any of the bullet nose is frosted, the .277" die will not touch the frosted areas of the nose when sizing, indicating incomplete mold fillout. I get a full .279" nose when I run my alloy at 710 degrees controlled by a PID. This gives me a bullet with a uniformly shiny surface. I also closely time my cadence to keep mold temperature as constant as possible. For the record I use only foundry certified 92-6-2 alloy.
So I guess what I'm saying is that while there are many techniques that can be considered standard and "gospel" so to speak, there are also no absolutes. What works for one person may not work for everyone. If what is considered to be "tried and true principles" don't work for you, don't be afraid to think outside the box. For me, I have found that hotter is not better, at least with this one mold.