by Keith Wood - Friday, April 20, 2012
The Background: Ever since I read Ross Seyfried’s piece on “Firelapping” in an old issue of Guns & Ammo, I’ve been intrigued by the process. These days, Beartooth Bullets sells a complete firelapping kit which helps unlock the mystery for first-time firelappers.
The Questions: Does firelapping work? Does the Beartooth Firelapping Kit work as-advertised? Can it be handled by any competent handloader?
The Concept: Most factory barrels are blemished by toolmarks and other tiny imperfections that can have a negative effect on accuracy. Furthermore, a bullet should be constricted as it moves from the chamber to the muzzle so that it constantly “bites” the rifling. Ideally, the muzzle end of a barrel should be fractionally smaller than the breech end. Revolvers represent an entirely different problem as each chamber has its own dimensions. Basically, if any chamber in a revolver’s cylinder is smaller than any portion of the barrel, the bullet will be forced into a diameter smaller than the bore. This is bad. “Thread choke” is another problem with the same net effect: many revolvers have a constriction in the bore where the barrel threads are “crushed” into the frame, this “choke” swages the bullet down at the beginning of it’s path and prevents it from full-contact with the rest of the rifling. If everything is dimensionally “correct”, a funnel effect is created as the bullet is constricted by the chamber, forcing cone, and then the bore with a good bite on the rifling until it exits on its path to the target.
In theory, firelapping uses projectiles impregnated with a mild abrasive to smooth out imperfections in the bore. The process “wears down” high spots in the barrel steel from the breech end forward, which helps create the dimensional constriction that we’re looking for.
For complete instructions on firelapping, I highly recommend the Beartooth Bullets Technical Guide.
The Test: I chose two revolvers, a Ruger Blackhawk in .45 Colt, and a Ruger Bisley Blackhawk in .44 S&W Special for our test. I cleaned each revolver thoroughly and fired multiple 5-shot groups at 25 yards for accuracy with each of 3 different loads.
Following the instructions, I slugged the bores of each revolver to measure their dimensions. The .44 had significant thread choke while the .45 had thread choke plus undersize cylinder throats. To save myself some time & headaches, I sent the .45’s cylinder off to www.cylindersmith.com to be reamed to spec while I went to work on the .44.
After completing the messy process of loading 50 rounds of lapping loads over a light powder charge, I headed to the range and let them do their work. With no sign of a reduction in the thread choke, I moved to a more aggressive abrasive than what is contained in the Beartooth kit (Loctite/Clover Brand 280 grit) and fired 12 rounds. 24 standard lapping rounds later I re-slugged the bore to check my work.
Significant thread choke remained so I backed-up to the 280 grit and fired 20 more rounds followed by an additional 30 rounds with the standard 320 grit compound. Finally, the lead sinker pushed through the bore with no sign of resistance and measured .430”. Following Beartooth’s advice to the letter, I polished the bore with 100 strokes of 320 grit compound on a tight patch which created a brilliant shine.
Would this shiny bore shoot? Let’s head to the range and see.
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