Specs for Bore Brushes, Standard, Single-Purpose

<font color="#151B54" SIZE="3">Specifications</font>


Our standard bore brushes are filled with either phosphor bronze or nylon bristles (aka filaments). The phosphor bronze standard bore brushes are constructed of high quality moderate thickness metallic filaments. The thickness diameters range from 0.004" to 0.006" depending on caliber. The nylon brushes are of moderate stiffness at 0.012" to 0.017" diameter, depending on caliber.


For rifle/pistol brushes, the twist rate is 5.7 to 6.8 twists per inch. For shotgun brushes, the twist rate is 4.8 to 5.3 twists per inch. The rate translates into a high density of bristles per inch. Since phosphor bronze filaments are thinner, they are denser on the brush than are the thicker nylon filaments.


Brush connectors are 8-32 threaded males made of sturdy aluminum. Aluminum connectors are not as hard as brass ones which means aluminum parts are safer than brass for the bore. Mohs hardness scales show aluminum at 2 to 2.9 and brass harder at 3 to 4. While hardness further depends on alloy and annealing, you can test it for yourself by scratching connectors with a nail and comparing the depth and width of scratches under a magnifier.


Bristles are twisted between carbon-steel core wires.


Nylon, being a polyamide, creates filaments that have a greater flexural memory (maintain shape) than phosphor bronze filaments. It is because nylon filaments are thicker than phosphor bronze ones, and it is because polyamides have cross-linked polymer chains.


Phosphor bronze filaments brush with more friction than nylon ones because they have less flexural memory (they bend less), and because metal atoms cause more friction than polyamide chains. When compared to stainless steel filaments, phosphor bronze ones have a lower coefficient of friction, assuming similar thickness, and it makes phosphor bronze safer than stainless steel for the bore. However, as phosphor bronze filaments increase in thickness, their coefficient of friction (as it relates scrubbing bores) rises.


When cleaning a bore with ammonia based solvents, in order to remove copper fouling caused by bullet jackets, we recommend our nylon standard bore brushes since nylon is chemically resistant to ammonium ions. However, nylon brushes can become abrasive when their bristles are dirtied by carbon particulates. We recommend vigorously washing nylon brushes after use. They can be cleaned using hot soapy water and vigorous rubbing.

When phosphor bronze brushes are used with ammonia, one can expect clean patches to emerge discolored from a clean bore since ammonium ions reacts with the brush's bristles, being made of metal atoms. If one insists on using phosphor bronze brushes with ammonia cleaners, then, in order to preserve the brush, it should be washed immediately after exposing it to ammonia.

Bore Diameter versus Caliber

For any particular caliber or gauge, inner bore diameter varies. It varies by the barrel maker or the brand-name supplier. Bore ID affects how tightly a bullet squeezes through the bore, whereby a bullet's soft body or its outer covering presses into the bore's rifling. For shotguns, bore ID affects pressure in the bore and spread pattern of shot. When the barrel of a shotgun is overbored, the gun's center of mass is altered.

Caliber Conversion

To convert millimeters to inches, divide by 25.4. Some conversions are listed below:

5.56 mm = 0.219 inch
6 mm = 0.236 inch
6.5 mm = 0.256 inch
7 mm = 0.276 inch
7.62 mm = 0.300 inch
8 mm = 0.315 inch
9 mm = 0.354 inch
9.3 mm = 0.366 inch
10 mm = 0.394 inch
11 mm = 0.433 inch

Gauge Conversion

Below are some examples of conversion of shotgun/smoothbore gauge to inches.

410 cal = 0.41 inch
28 gauge = 0.55 inch
20 gauge = 0.62 inch
16 gauge = 0.66 inch
12 gauge = 0.73 inch
10 gauge = 0.78 inch

Single Purpose

Standard bore brushes are single purpose, and that means they are for the one purpose of brushing. We also supply dual-purpose Jag Brushes TM, which are patent pending worldwide. They perform brushing and wiping at the same time since they have two radial diameters.