Article #6: Cast bullet lubrication


Notorious member
The Basement Articles #6: Cast bullet lubrication

After more than four years of non-stop testing by my myself and a few other dedicated accuracy enthusiasts, and an ongoing, 2400-some post thread on another site documenting the endeavor, I'm going to attempt to condense the essential information we've gathered about cast bullet lubrication into a single post.

I think I might even be able to do it in a single sentence: An effective cast bullet lubricant provides a fluid film barrier between the bullet and barrel during the firing event, leaves the surface of the bore the same condition shot-to-shot, and completely departs the bullet at the muzzle to prevent balance disturbances farther downrange.

Sounds simple, doesn't it?

I thought for many years that the most important qualities a bullet lube could possess were the correct "lubricity", or slickness, and the correct overall viscosity for the pressure and velocity of the load. I also thought that lube acted somewhat as a "ballistic stop leak", to put it in Glen Fryxell's terminology.

While I maintain that lube does actually help a teeny, tiny bit to obturate the bullet, I think it's on a much smaller scale than I once did. As for lubricity and viscosity, I have a different way of looking at that now, too. If a lube is too slippery, it can behave unpredictably in the bore, causing the bullet to stutter and skip, or even hydroplane as a car can on a wet, uneven road. Viscosity, defined as resistance to flow, is less important than shear stability and what Runfiverun and Eutectic have recently brought up with the subject of "wipe pressure".

Eutectic's concept of Consistency Of Residuals Encountered, or CORE, is the solid gold key to achieving an accurate-shooting bullet lubricant. Building a lube formula that leaves the bore in a stable, repeatable condition shot after shot, in any weather, any temperature, five seconds after the last shot from a hot barrel or the first shot from a cold barrel five days later does more for accuracy than just about any other single factor I can think of. Observing the residue around the first bullet hole in a target fired from a cold barrel previously fouled with the same lube tells a tale, as does where that first shot lands compared to the following shots in the group. Observing what's left in the bore by a given lube also gives us clues, and testing dozens upon dozens of formulas, compiling data, and studying the effects of many different lube ingredients begins to paint a picture of what substances work and which ones don't.

The last factor I mentioned in the first post has proven to be very important, too. I started devising "jettison tests" a few years ago where I shoot through clean cardboard at a distance of just a few inches to observe the pattern and and size of the lube droplets, and also observe how dirty they are, and the relative state of the lube as it flew off, or failed to fly off of the bullet. I look for a dirty, atomized mist. Chunks of clean lube show that at least the bulk of it wasn't reaching the liquid state under pressure, and therefore not doing any good. Making it out of the gun and flying out of the grooves in chunks can slightly destabilize the bullet and open up groups. Making it halfway or more to the target before losing all of the lube, or making it to the target with a few bits still in the grooves is even worse. It may not sound like much, but a speck of lube hanging in the edge of a groove at 150,000 rpm or more can play hoc with accuracy. A lube that goes liquid in the barrel is likely to purge more consistently each shot, not hurt things if a blob is blown ahead of the bullet and "run over" later down the tube, and wipe more completely away each shot leaving less behind to affect the next shot. Leaving a minimum behind is the easiest way to control the effects of WHAT is left behind.

Waxes have been our nemesis from the start. The current evolution of Thick 'n' Thin, or TnT lube, which is essentially an ester-based, NLGI #6+ sodium brick grease, leaves very little behind, is soft, jettisons well, flows well in the cold yet won't melt even at take-your-skin-right-off temperatures, has very little bleed, doesn't build up in the barrel, doesn't leave enough oil behind to cause cyclic purging, and works at low and fairly high velocities. Another formula, which has proven over the past couple of years to be up to all of the aforementioned tasks and has done even better at high velocity is another soap lube, experiment #68, or "SL-68". Member JonB has been making and testing this formula along with myself and Brad, and some other advantages we have observed with this formula is how "dry" it shoots, meaning that it leaves little to no oily residue on the outside of revolvers, in the gas systems of self-loading guns, or in the action/magazines of self-loading pistols. It has a melt point of nearly 300 degrees F, quite the advantage in hot summer weather, yet in below-freezing cold, the lube remains pliable. In tests from 105F to minus 7F it has held its own. While the "Quest" for a truly universal, all weather, all temperature, all load level lube that can tolerate a variety of bore finishes and lube groove designs well may never be fulfilled, we have a few things that fill the bill pretty well so far.


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