Bullet Lube Action Explained

[LiveLife]

From time to time, I read Glen Fryxell's articles on lead bullet related topics.

I used to think the hard lube in the lead bullet's lube ring simply "smeared" on the rifling/bore surface as the bullet traveled down the barrel. I always wondered, how is the bearing surface of the bullet forward of the lube ring being lubricated as the hard lube is only smearing/lubricating behind the lube ring as the bullet travels down the barrel. After reading his article titled "Lubricating Cast Bullets", I realized a lot more was happening with the lube and how the bearing surface forward of the lube ring gets lubed.

Here's his opening question:

OK, I’m going to ask a stupid question. What does bullet lube do?

I’ll bet most of you answered that bullet lube lubricates the passage of the bullet down a rifled bore, to eliminate galling of a soft metal as it traverses a hard metal cutting edge. Well, yeah, I suppose that’s true enough, but that’s not all it does, nor is it necessarily even the most important job that it does. Let’s assume for the moment that lubrication is the sum total of its job -- is the lube on a given bullet lubricating the passage of the bullet that carries it, or the bullet that follows after it?

Part of the problem with this line of reasoning is that it assumes that the lube is delivered to the bore by simple bullet/barrel contact and smearing, and hence the lube can only lube that which is behind the reservoir (lube groove). Looking at things in this manner results in a fairly simplistic, almost static picture (hard surface, soft surface, slippery stuff in between), and the firing of a revolver shot is a very dynamic process. What else does bullet lube do? Or perhaps more accurately, what else is done to the bullet lube?

Let’s just set the record straight, lube is not simply smeared from the lube grooves onto the bore, nor is lubrication the sole function of bullet lube.

He explains in the article that there are several different actions that occur regarding the lube when the primer ignites the powder:

- During the initial powder burn, high pressure gas travels faster than the bullet and turns some of the hard lube into liquid that helps seal the bullet to the bore.

- As the powder continues to burn, bullet base gets compressed from the expanding high pressure gas and squeezes more lube out of the reservoir (lube ring) further increasing the seal between the bullet and the bore.

- As the bullet accelerates, softened/liquefied lube in the reservoir (lube ring) "slams" against the back of the reservoir (lube ring) and further increase the seal between the bullet and the bore.

- As the bullet starts to rotate riding the rifling, softened/liquefied lube gets "flung" outward by spinning centrifugal force which further increase the seal between the bullet and the bore.

- Lube does not just "smear" on the rifling/bore surface as the bullet slides down the barrel but like pressurized oil system in the car engine, liquefies to travel forward of the lube ring to surround the bullet's bearing surface (base of the bullet that engages the rifling) and works to contain the high pressure gas which minimizes gas cutting and leading

He summarizes these actions by stating:

In summary, bullet lube is pumped from the lube groove to the barrel surface by compression, linear acceleration and radial acceleration. In addition, lube is injected forward during the firing process, as the result of high-pressure gas leakage into the lube groove. This injection process forms a floating fluid gasket around the bullet, and serves to limit gas cutting and is a kind of ballistic stop-leak. Hard lubes must first melt before they can be pumped or injected by any of these mechanisms.

And all this time, I thought the hard bullet lube simply "smeared" on the rifling/bore surface. You learn something new everyday.

 

[ranger335v]

"..all this time, I thought the hard bullet lube simple "smeared" on the rifling/bore surface."

I'm not convienced you were wrong.

 

[JASmith]

BDS,

Many thanks -- this is an insightful and informative discussion!

It is also consistent with my understanding of how things work.

 

[ReloaderFred]

Something that was left out is the residual amount of lube left behind after every passing of a bullet. This helps the next bullet "ride the rails" so to speak. That's where the term "fouling shot" came from.

A perfectly clear example of this is the Star Lubrisizer, which pushes an unlubed bullet completely through the sizing die and drops it out the bottom. The bullet is sized and lubed as it passes through the die. A clean die is really, really hard to get a clean lead bullet through, and in some cases the bullet sticks solid. (ask me how I know) You either have to run a lubed bullet through the die first, or lightly oil the first bullet. When the lubing/sizing process becomes difficult due to resistance felt in the handle of the machine, you simply run a lubed bullet through the die again, which imparts a small amount of lube to the walls of the die. This will keep it lubed for about 10 bullets and then you run another lubed bullet through the die, etc.

As noted, there is a lot going with regards to lubrication.

Hope this helps.

Fred

 

[Hondo 60]

Very interesting.
Thanks for posting, so us lazy slobs don't have to go looking.

 

[Walkalong]

It's the same reason gas wax checks or Super Grex under a lead bullet will stop leading, even with an undersized bullet. It seals the bore and stops gas cutting.

 

[MEHavey]

Does anyone else now make something akin to what Super Grex was, and/or a similar plastic shot buffer? That stuff made for a super dependable 50-yard Sharps load under a buffalo slug 25 years ago in the .

(pause.... think, think....trot downstairs....retrieve mold......)

Does anyone know where such a 54 Cal "buffalo slug" mold can be obtained today? I just tried to Google it and nothing came up.



Darn, it's hard getting old....

 

[Walkalong]

PSB may work. I have some, but haven't tried it with lead. It is supposed to though.

http://www.surplusrifle.com/shooting/castfiller/index.asp

Scroll down for a bit on PSB