The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

dromia wrote:

Alpha1 wrote:What does bullet lube do?

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

Possibly Dave possibly, at the end of the day the performance lube of lube is really dependant on bullet fit and alloy hardness/elasticity. Get good boolit fit and you don't need boolit lube. Whitworth proved this with his hexagonally rifled muzzle loader, but then his forte was being able to measure and work to extremely tight tolerances so boolit fit was well within his capabilities. His contribution to the modern industrial society is vast. Also there are people currently shooting unlubed boolits with mixed success in getting that perfect boolit fit and a properly smoothed barrel.

Lube does what it says on the tin methinks, it leaves a film of lubricant in the barrel which helps reduce friction at the boolit/barrel interface and therefore reduce leading. However with a poorly fitting boolit no amount of lube will compensate for that. Leading in itself is not necessarly a bad thing its the build up of leading that causes problems, see bore conditioning.

Gas cutting, well I'm not sure about that. I've retrieved many shot cast boolits over the years, as have many others, and never seen any gas cutting especially on the base, the temperature spike is there for so short a time that it doesn't seem to melt the lead.

However I suppose that it could have an effect on thin moulding flashings on the base and the lube grooves. With poor boolit fit when the gases over take the boolit then you could get gas cutting of these lead slivers and the type of melted on leading associated with gas cutting. This type of melted on leading could also come from the heat working on lead already left in the barrel from friction.

So in reality with a properly fitting boolit gas cutting/leakage should not be an issue, the whole purpose of seeking good boolit fit is to ensure that the boolit is a perfect as possible when it leaves the barrel so as to make the most of its accuracy potential.

The other role for lube and lube grooves, as I see it, is in helping the boolit maintain its integrity at the moment of firing. The inertia of the boolit means that the base starts moving before front of the boolit causing what is known as "bump up" and this is said to help seal the bore. The Minie boolit is a classic example of this. This bump up can also cause boolit deformation at the nose know as "boolit slump" this is very common in bore riding designs that don't fit the bore.

So what the lube in the lube groove does is act as a sort of shock absorber (haven't got the right word here) that helps the boollit keep its shape and length (BC) as it compresses under the acceleration.

An example of this property comes when sizing boolits down a lot say 0.319" to 0.314". If you do this with an unlubed boolit the lead smears into the lube grooves and can end up a right mess, however if you fill the lube grooves first and then resize the boolit keeps its intergrity albeit with some lengthening depending on the mount of compression needed to push the boolit through the die.

So given proper boolit fit I think the lube performs two functions, it lubricates (fills the pores of the bore, cast boolit barrels need to be seasoned with each lube before you will get top accuracy) the barrel to reduce friction leading and secondly it helps maintain boolit integrity during acceleration in the barrel.

That is in relation to smokeless cartridges, in black powder cartidges it also performs a third function of helping to keep the fouling soft and is often added as grease cookies to supplement the lube in the grooves.

At the end of the day the function of boolit lube is still speculative and one of the reasons for that is it is very difficult for us lay experimeters to get replicable situations for boolit fit, alloy strength, barrel condition, loading, measurement etc etc etc. So as to be able to build up a robust body of empirical data to be able to draw absolute conclusions from.

What I am certain of is if you want to get the the best from your lube then boolit fit is key.

I am also certain that if the want to get the best from any boolit/bullet then boolit/bullet fit is king.

But what would I know.

No doubt there will be questions now about lube types as Sandgroper has alluded to in his reference to Xlox/liquid alox, but b****r that for now as I'm off to shoot cast boolits on a 25yrd range using a Pedersoli Sharps 1874 Quigely rifle chambered in 45-90, could you do that easily and cheaply with you copper condom curios? :lol:

Mike357 wrote:This all makes my head spin and I get a pain behind my eyes!!!
:geek: :geek: :geek:

dromia wrote:I find it a fascinating pastime myself and adds another interesting dimension to hand loading and as such helps us understand our firearms that bit better.

As has been said before, "someone who casts his own boolits is the only hand loader who comes near to making his own ammunition".

Any questions ask away I'll happily share the little I know.

Sandgroper wrote:
Thanks, will do. I've been flicking through a copy of Cartridges of the World and The Handloader Manual of Cartridge Conversions, this Night Shift, and have been thinking about all the old and obscure cartridges I could make and cast for. Joy. :lol:

John25 wrote:Sandgroper says

"Gas cutting, well I'm not sure about that. I've retrieved many shot cast boolits over the years, as have many others, and never seen any gas cutting especially on the base, the temperature spike is there for so short a time that it doesn't seem to melt the lead."

I have a number four spike bayonet frog (I know I should have taken it off!!) coated grey with lead after a hot load - no gas check. - Nothing reached 100x!