Monday, May 24, 2021

Bullet Casting 104: Sizing and Lubing

If you’ve been following along in my bullet casting series, you should have a nice pile of cast bullets. However, they’re not ready to load and shoot just yet; before we can get to loading them, we need to go through three steps.

First, we need to make sure that our bullets pass a basic quality check. This means looking for fill-out issues. 
  • Can we see any voids on the bullet? 
  • Are the edges of the bullet bases and grease grooves nice and crisp? 
  • Are the bullet bases clean and square? 
  • Some of the first bullets from any casting session are likely to be wrinkled, and this is caused by a mold that isn’t up to casting temperature. 
  • If the surface of the bullet is grey and appears rough in texture (aka "frosted"), this means the mold temperature was too high.

Any bullets that don’t meet the quality requirements can be tossed back in the pot for your next casting session.

L-R: a frosted bullet, two with poor fill-out, and two good bullets

Some badly wrinkled bullets

Next, the freshly cast bullets need to be lubricated. This does two things: it eases the passage of the bullet down the barrel and, more importantly, acts as a gas seal between the bullet and the barrel. 

No cast bullet will be a perfect fit in the barrel. Any imperfections, especially at the base, will likely cause gas cutting which is where hot combustion gasses from the propellant get in between the bullet and the rifling. This results in increased lead build-up in the bore, reduced accuracy, and more laborious cleanup after shooting.
There are several techniques which can be used for lubricating cast bullets, such as tumble lubing (which works better with specific bullet designs), pan lubing, powder coating, and using a lubrisizer. This last method combines bullet lubing with the third step, bullet sizing.


Tumble (L) vs. traditional lube groove (R) bullets

As they come out of the bullet mold, cast bullets are generally a few thousands of an inch over size and their noses may also not be perfectly round. Both these issues can be resolved by running the cast bullets through a bullet sizer. At heart, any bullet sizer is a very precisely sized and very carefully polished ring of hardened steel that the bullets are pushed through and swaged down to their final size.

Recommended Models
Lee Precision makes a push through sizer that can be used on any single stage press. This is an inexpensive, simple, and effective method of sizing bullets, with lubrication done as a separate step prior to running the bullets through the sizer. 

Among the benefits of this sizing system:
  1. The bullets are pushed through the sizer nose first, which means that you don’t have to buy a selection of punches for your different bullet nose styles.
  2. This system pushes the bullets completely through the sizer, which can increase production speed.

Some bullet casters have even mounted a dedicated single stage press with this sizer attached upside down to speed things up even more.

The Lyman Model 4500 Lube Sizer dedicated bench top lubrisizer is a direct descendent of Ideal’s original Number 1 sizer which dates back over a hundred years (it even takes the same sizing dies and top punches). This type of sizer pushes the bullets in base first, and because of this it requires a top punch of the proper shape so it doesn’t damage the bullet nose. Once the bullet is pressed all the way into the sizing die, bullet lube is applied and the bullet is raised up for removal, then the next bullet is placed on the platform and the process is repeated.

This system takes solid cylinders of lubricant that you can either buy or make yourself. If you live in a colder climate, you might want to add a lubricator heater to your setup.

Finally, there is the Star Lube-sizer by Magma Engineering. This is an almost production level system, combining many of the best features of the sizers I’ve already mentioned. As with the Lee, the Star also pushes the bullets nose first, all the way through the sizing die. When the bullets are pushed through the Star, they drop out the bottom with no additional setup needed, and like the Lyman, the Star takes cylinders of lube and applies it to the bullets as they’re sized. It also has a lube heater. Obviously all these features come with a price, but if you’re going for quantity, it may be a good investment.

In Conclusion
I hope these posts have given you food for thought regarding bullet casting and plenty or resources in case you decide to pursue this hobby.

Remember: take your time, pay attention, treat the process with all due respect, and you’ll have a more harmonious outcome.

Good luck and good casting.

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