Cast it: don't slug it

Guns Magazine, July, 2009 by Holt Bodinson

Determining bore measurements by ramming a lead slug down the tube may be a classic method, but I'll bet there have been quite a few bores damaged by such a routine. Taking a casting of either the bore or chamber is both easier and safer.

Old gunsmithing books often refer to using melted sulfur to make a casting. Sulfur, however, is not an easy element to work with plus it stinks and is corrosive.

Most of the current instruction manuals now recommend Cerrosafe, a readily available casting alloy that melts between 158 and 190 degrees F. I've used it many times, melting it in a Lyman casting ladle with a heat gun. The benefit of Cerrosafe is it shrinks for the first 30 minutes of cooling, aiding its removal, and then returns to exact bore or chamber size at the end of an hour. The only problems I've experienced with Cerrosafe have occurred when taking castings of rough bores and rough chambers. In spite of its initial shrinkage, it can be a bear to get out if the alloy has penetrated a rough surface.

What I use now is good, old, household, paraffin wax. The stuff your granny used to can vegetables and fruit with. It's generally still available in every large supermarket, and one box of it will last you a lifetime.

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Paraffin wax is tough stuff. It's pretty hard when it's removed from a bore or chamber, and it stands up nicely to being miked and measured. What I like about it most is that it's just as easy to work with as Cerrosafe, but it never hangs up like Cerrosafe.

The secret to producing a quality casting with melted wax or Cerrosafe is to pre-heat the barrel or chamber area well before you pour. If you don't warm the metal first, the wax or Cerrosafe will solidify as soon as it contacts the cold metal. The result is a miserable looking, useless casting.

To apply heat, I use a common heat gun (also used to melt the casting material) held in one of Lyman's cast iron casting ladles* I like to heat the metal just enough so it is uncomfortable to the touch. You may have to experiment a bit. Before pouring, you'll need to plug the bore or chamber throat. I use a tight fitting patch or even one of Outers Boreblast foam cleaning wads if the bore is .30-caliber or smaller.

Let the wax set up a few minutes and then just push the completed casting out with a cleaning rod and take your measurements.

Just don't do it in your wife's kitchen. Women really hate to discover paraffin wax splashed all over their kitchen floors. Yes, casting can get messy at times.