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Gas checking cast lead bullets.

August 17, 2014

If you’re now getting into reloading your ammunition and casting your own lead bullets, here’s some useful information on taking your home made bullets up to the next level of velocity, approaching the speeds of full metal jacketed ‘factory bullets’.

The problem one faces when trying to push lead bullets faster and faster out your weapon barrel is that the greater velocity is achieved by larger powder loads (and different powders as well) placed into your cartridge as the reloading process is accomplished. The greater the pressure of the burning gases generated as the firing of the round happens pushes the bullet faster, but the typical lead bullet will begin to melt around the edges as this massive gas burst shoves the bullet out the barrel, with the flame of gas pushing by the bullet in the grooves of the barrel. This melted lead is left in the barrel, accumulating with every bullet fired in that same situation. Soon, the accuracy is compromised and the leading problem accelerates.

Some clever shooter in the past came up with an idea of swaging a thin cap of harder metal than lead onto the bottom of the bullet to ‘take the heat’ so that the bullet could be successfully pushed faster without the melting problem leaving lead streaks inside the barrel. These ‘caps’ are called gas checks. The metal, around .010″ thick, is shaped into a disc as it’s punched out of the thin sheet of copper or aluminum.

Aluminum gas checks

Aluminum gas checks

The closeup picture above shows some of my .357 magnum bullet gas checks. These can be purchased for about 3 or 4 cents each from online reloading suppliers, or if you wish maximum independence you can use a ‘Freechex‘ punch and die and make your own from aluminum or copper flashing material from Home Depot. 

Lee precision standard lube groove

The bullet above, from Lee precision, is a .357 lead, semi-wadcutter, specifically designed as you see, to have a gas check disc added to it’s base, with a nice little recessed base that the gas check cup fits into nicely as the bullet is sized, passing through the sizing die, giving us consistent diameter bullets.


However as you see in the next picture above, the base of this hollow point lead bullet, also that started out as a Lee precision lead bullet mold, has a beveled base that is NOT intended to have a gas check added to it in the normal processing of the cartridge assembly. So, what to do? We need sufficient velocity for a hollow point bullet to do it’s thing, expanding as intended for maximum effect. We do ‘bullet modification’!

The gas check is the correct diameter to work with any .357 cast bullet, but the trick is in the base design of the bullet. That means we’ll need to adapt the gas check to a bullet that was never really intended to have one.


So, we place the hollow point bullet base into a gas check cup, and gently tap it into place, the idea being to seat it nice and squarely on the base of the bullet. I’m not too worried about damaging my bullet, because I quench my cast bullets in water as they come out of my molds. This makes them hard as possible….and I’m not pounding on them, just gentle little taps.


Then I lubricate the bullet very well using my case lubing pad and generous amounts of that lubricant. I wear a latex  glove on my left hand while handling bullets and lube to avoid the lead and the case lube is rather sticky and nasty after a while.


Then I place the bullet, base up, on the ram of my Lee sizing die, and push it up through the die.


This changes the gas check from this:  SANYO DIGITAL CAMERAWhere you can plainly see the gas check just sitting on the base of the bullet, to as we see in the next picture, an almost invisible, very well swaged on aluminum base on this bullet, successfully going onto the next step of lubrication later on. 


This now allows this bullet, after the next steps of lubrication (by the ‘pan’ method) and loading, to be fired much faster, going from around 800 feet per second with no leading to around 1,200 feet per second, or better, still without leading up the barrel.






One Comment
  1. d reading this, very good stuff, thanks.

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