Bullet Hardness Affect on Lubricating the Bore

[03lover]

i posted this thread on another forum and got no response so I hope some of the shooters and readers on this forum have some idea of what I am looking for.

I am a believer in the idea that bore lubrication with cast & lubed bullets occurrs best when the pressure of the load in great enough to cause the bullet to obturate in the bore which then forces the lube in the grease grooves under pressure onto the bore.

If this is true it may be the reason some cast bullet loads with hard cast bullets will sometimes cause leading in the bore, especially when the bullets are too hard and the load light.

What I am looking for may not exist. I would like to see a chart that would list cast bullets by hardness and the pressure required to cause the bullet obtruate enough to force the bullet lube out of the grease grooves and onto the bore.

I know Lee has a chart that indicates the pressure levels of many loads but the maximum is a pressure not to be exceeded. The chart doesn't appear to indicate the pressure at which a bullet of a given hardness will begin to obturate. Also those maximum loads are not good for accuracy in fact they are terrible.

My own experience with my cast bullets and purchased cast bullets of varing degrees of hardness has had mixed results when it comes to bore leading. I have had more leading with hard cast than the softer or medium hard bullets when using mild level loads. This suggests the harder boolets are not under enough pressure to obtruate and help with the lubrication.

Most of my handgun loads are lower to midrange velocity, 1100 to 1500 fps. My rifle loads run from around 1200 to 1700 fps. I don't do any long range shooting and don't push my handguns to the limit. I simply enjoy shooting for pleasure and reloading.

I guess the bottom line for my question may be, "Is there a direct link between bullet hardness and the pressure level of the load when bore lead or not is the issue."

[RobsTV]

Taken from:

http://www.lasc.us/CastBulletNotes.htm

"Bullet BHN / "Minimum" Chamber Pressure For Lead Alloys (PSI)

The formula (from the pages of HandLoader Magazine) to determine at what pressure an alloy of given BHN will obturate the base of the bullet and seal the bore. If the bullet is too hard to obturate, gas cutting usually occurs on the base band on the non-driving side of the rifling and barrel leading is likely. Simply multiply the alloy BHN by 1,422.
Example: Alloy BHN of 12 multiplied by 1422 = 17,064. An alloy of 12 BHN should be used with a load that develops a "minimum" of 17,000 psi. Need more info on minimum / maximum alloy BHN? These Glen E. Fryxell articles explain alloy BHN in easy to understand language. "

[375RUGER]

I know this isn't really answering your question, but I cast some that are pretty hard especially when water dropped. I have run them up to 3000fps+ in a 7mmRM and no leading. Also no leading at 1500 fps, same boolits. Same thing with the 44mag, some hard some soft, some slow some fast-no leading. Why? They are the right size and I used a good lube.
The commercial cast you mentioned were probably hard and undersized.
I never got undersized commercial hardcast to not lead no matter how hard I pushed them.

[Larry Gibson]

Another problem is that "hardness" as measured by BHN alone is only half the equation. Malleability of the alloy is the other half. Two alloys of equal BHN can have different malleability's and obturate at different psi's. Additionally the time/pressure curve as governed by the powder's burning rate also can govern the psi at which the bullet will obturate.

You're wanting the quick simple answer that http://www.lasc.us/CastBulletNotes.htm also attempts to answer. However, there really isn't that simple an answer that can be easily answered by the simple formula proffered as it doesn't address malleability of the alloy or the burning rate (time/pressure curve) of the powder.

Larry Gibson

[44man]

In my experience a soft boolit that slumps can destroy the GG's fast, purging lube. I don't profess to know how lube is distributed but feel RPM's might be at work.
There is no need to expand a boolit at all to obturate if it fits. I shoot hard boolits with no leading and get a grease ring on muzzles.
Lube purge is common with the .38 SP using dead soft wad cutters. Lube and lead will exit the gap and the bore will pack with leading.
You got me to look at my 30-30 I have been working with for months, hundreds of shots with hard boolits, testing powders from over 1600 to 2000 fps. Look at the muzzle, hard to see but it is WET with lube. I ran tight triple twill patches on a jag through the bore, TIGHT, had to pound the rod through. Notice there is not a speck of lead. 8391683917

[44man]

03lover, you are in the right place to learn about cast. Some of my big bore revolvers have been shot over two years without a patch through the bores and I use PB, water dropped WW lead.

[detox]

I have been using soft SPG lube in all my guns and have never witness leading in barrel. All of my boolits are sized just slightly over size. I have used alloys from hard linotype to soft 1-20 shot at various velocities 700-1600fps.

[Cherokee]

They way I see it, FIT is more important. If the boolit fits from the get-go, it'll fit all the way and the lube can do what it does. Alloy or hardness has an influnce but second to fit.

[btroj]

Bullet design makes a difference too. Groove shape, size, and placement can alter how a lube is "released" by the bullet.
Like Larry's said, hardness is only a part of the story. Alloy composition is just as important as absolute "hardness".
What hasn't been mentioned is how temperature makes a difference. Lubes that work well at 80 degrees may be horrible at 20 degrees. The opposite is equally true.

In the end it all comes down to balance. Find a lube, bullet, alloy, and load that work well in a range of temps. Stay within a certain window on each and all is well.

Learning how to read the results and determine which variable is the problem is the art of shooting cast. It isn't always obvious and there is rarely a single solution.

[DrCaveman]

To the OP, there seems to be a lot of consensus that boolit obturation isnt what causes lube to flow, but rather what prevents gas cutting around the base and up the sides of the lead boolit. Further that this obturation is often a moot concern when the boolit is sized at or a little above bore diameter

The lube doesnt usually act as a cure-all, in my experience. Nor has hardness, although ive reserved gas checks for everything past about 1500 at this point...except some 357 loads.

I think that enough research has been done around this web sites members to show pretty well that boolit fit is the most important part of shooting accurately and not leading your barrel

[fixerupper]

They way I see it, FIT is more important. If the boolit fits from the get-go, it'll fit all the way and the lube can do what it does. Alloy or hardness has an influnce but second to fit.

This. ^^^

Proper fit is the key to leading. I really dont believe obturation has much to do with dispersing lube in the barrel. Centrifugal force as the bullet spins would have a much greater effect than obturation does, "flinging" out lube on its path down the barrel.

Now.... I DO believe proper hardness has an effect on accuracy..... but not so much on leading.

[btroj]

Fit, however, isn't just making sure the bullet is the right size. Hammer the bullet with chamber pressure and fit changes. Look at a hollow base wad cutter, designed to ensure good seal with the bore at very low pressures. The bullet is designed to change to ensure fit.

A revolver bullet can for the chamber throats, the bore, or both. If it fits the throats but is .004 over bore size does it fit? It will once it hits the forcing cone but what happens as the bullet is deformed?

Hardness, lube, and fit all play roles. Balancing them is important.

[blikseme300]

Bullet design makes a difference too. Groove shape, size, and placement can alter how a lube is "released" by the bullet.
Like Larry's said, hardness is only a part of the story. Alloy composition is just as important as absolute "hardness".
What hasn't been mentioned is how temperature makes a difference. Lubes that work well at 80 degrees may be horrible at 20 degrees. The opposite is equally true.

In the end it all comes down to balance. Find a lube, bullet, alloy, and load that work well in a range of temps. Stay within a certain window on each and all is well.

Learning how to read the results and determine which variable is the problem is the art of shooting cast. It isn't always obvious and there is rarely a single solution.

The "window" is the magical area where everything comes together and the only outside influence is the ability of the shooter.

When I started reloading CB's for rifle I read and re-read all articles and posts but much of what I read did not penetrate my hard-headed skull until I finally got my 30-30 to work the way I wanted. The proverbial light came on and now I have a better understanding of what makes things work. Thanks go out to many of the members here as well as others that have taken the time to share their experience and insights.

[44man]

Boolit design is a big factor, mostly the GG's. Look at a TL and the tiny grooves, if you shoot too much over size they can be wiped off. But they work with regular lube and the proper fit. The Keith has one large groove but I found 2 to 3 grooves is more accurate so it is how I have made my revolver boolits.
I don't think much of a hollow base. They might flare at the gap or at muzzle exit. The Minie' ball has a thin skirt and will turn into a shuttle cock at exit unless light charges are used. As you increase powder, the skirt has to be thicker. I also found the Minie' MUST fit the bore for any accuracy, fit right and you can hit at extreme ranges. I see no reason why gentle black can't be compared to smokeless as far as boolit affects even though smokeless has a faster and more powerful "thump."
Anyway no matter what you shoot, the lube can not go ahead of the boolit, only behind if you have fit. It is what you lay down in the bore that counts so the next shot cleans the bore.
Some call it "seasoning" but infers you are building up a residue and that is what you don't want.
SPG will build residue in a long BP barrel and Alox will have a build up in smokeless. SPG is actually better in smokeless revolvers but the cost is not worth it.
I have been using Felix and CR in my 30-30 and both are working.

[03lover]

My thanks to all of you for your many suggestions and varied experiences.

The bullet that tends to start leading first is a 165 grain Hunter Supply plain base bullet. I haven't checked the hardness yet, and the diameter is .311". According my slugging of the bore, the bullet is at least .001" over groove diameter. I have no idea what lube Hunter used.

The other four bullets I have been working with that are my own cast bullets and are gas checked. My lube is just above soft and requires some heat on the luber/sizer when sizing and lubing bullets.

I have been checking the bore after every fifty rounds and the leading is at the breech end and extends a few inches forward of the bore throat. It is light and usually the first ten to twenty strokes with a bronze bore brush will produce a patch with a number of lead specks. The second brushing can have a few specks, the third may or may not have any.

One bullet, a 155 grain Lyman with six grease grooves doesn't lead. The other gas check bullets produce less lead than the Hunter bullets and two have two grease grooves and one has only one. These bullets have all been sized .310" and I use them in many other .30 cal. rifles without leading. This could be suggesting a fit problem or perhaps a bore problem, even though this Winchester Model 94 was unfired when I purchased it.

Given the chance my bore slugging that indicated a groove diameter of .310" wasn't the best measure of the bore, I will be trying fifty rounds of each bullet sized at .309" and maybe even .308" depending on what results I get with the .309" diameter bullets. I know bigger than .310" doesn' work because the Hunter Supply bullets come sized .311" and produces the most lead. I also have a Saeco 182 grain gas check bullet with three grease grooves and at .310" diameter I do get minor leading after fifty rounds. This is with 8.2 grains of Unique powder, a pretty light load. The Saeco bullet drops at .312" diameter but I don't think there is any reason to try it larger than the .310" I have been using.

My late fall outdoor projects are starting to get in the way of my load testing and with the deer season starting in early November that shuts down my shooting until the end of November. Needless to say, here in Minnesota that means snow and cold weather. I can heat my fifty yard shooting bench as long as the outside temperature doesn't go much below 20 to 25 degrees and the snow isn't so deep that I have trouble getting to my shooting range with the tractor. Those factors usually mean I shoot less often after Thanks Giving and I have a mild case of Stir Crazy until the snow melts and the ground firms up enough.

Thanks again. I will keep you posted with results of any additional testing.

[JeffinNZ]

The Lee formula is flawed at best. Do the numbers on .22RF ammo and you will see. It shouldn't shoot.

[03lover]

I have tested the Hunter Supply cast bullet and found it to be 27.2 on the BHN scale. One of my wheel weight cast bullets checks out at 14.3.

The Hunter Supply bullet is plenty hard enough according to some that it shouldn't be the reason it leads more than some others although the leading is minimal enough after (50) rounds that it isn't affecting accuracy yet. I am thinking the .311" diameter could be the problem.

I am hopeful the additional testing with smaller diameters will prove this to be true.

[btroj]

Plain base bullets tend to go awry at 1500 fps or so in many rifles. Powder choice becomes critical. While a max load of Unique may give 1500 fps it is much harder on a bullet than a larger charge of 4895. Pressure curve matters, more so when the bullet is on the ragged edge anyway. A plain base bullet being pushed hard needs a gentle start and this means a slower burning powder.

Peak pressure isn't everything, pressure/time curve counts more than peak pressure.

[44man]

Plain base bullets tend to go awry at 1500 fps or so in many rifles. Powder choice becomes critical. While a max load of Unique may give 1500 fps it is much harder on a bullet than a larger charge of 4895. Pressure curve matters, more so when the bullet is on the ragged edge anyway. A plain base bullet being pushed hard needs a gentle start and this means a slower burning powder.

Peak pressure isn't everything, pressure/time curve counts more than peak pressure.
Exactly right!

[03lover]

btroj,

Considering what you have stated, that is probably why the Hunter Supply bullet performs better with my surplus WC820 powder. Maybe I have to go slower yet. I still get minor leading with the WC 820.

[btroj]

I never saw what cartridge you are loading. Is it a 30-30? If so the there are many powders that will work.

What cartridge, gun, and powders re you using now? Detail could help us decipher the root cause.

[03lover]

btroj,

The cartridge is 30-30 Winchester. The rifle is a pre 64 Winchester Model 94.

I have been working with Unique and WC 820 at this point. I prefer not to get into using too many different powders if I can. Unique has always worked well for me and I usually can find a powder charge that shoot accurately without much trouble in a mess of rifles. It is a little position sensitive and my best accuracy using Remington #9-1/2 primers is always with the powder laying in the bottom of the chambered round. Not to the rear which is not as good and not to the front which is the worst.

Accuracy is not the issue with this rifle and loads, it is the minor leading with a couple of bullets and the Hunter Supply leads the most while still being minor in nature.

I will be testing a number of the bullets I am working with as soon as possible, at diameters smaller than I have been shooting, just to rule out a bullet size problem if that is the cause.

Bullet lube could be part of the problem. My Lyman 311291 and Lyman 311466 do not lead at 7.4 grains and 8.2 grains of Unique respectively. I believe I sized and lubed these bullets with LBT lube. The Saeco bullet #305 F5J does start to lead after (50) rounds and it appears to have LBT lube also. The Hunter Supply Bullet lube is anybodies guess.

Because the leading starts in the throat of the bore and progresses to a couple of inches forward I am guessing part of the problem can be the shape of the bullet noses and the pressure curve as some have suggested. It could be these bullet noses are slamming into the throat of the bore too fast, too hard, whatever and leave some lead in the bore before any of the bullet lube can do its work. The rest of the bore is free of any lead.

This suggests I should try an even slower powder with the Hunter Supply bullet to see if that fixes the problem. I will do that after I fire all the loads using smaller diameter bullets. One thing at a time. RIGHT. When best bullet fit is determined, I can go onto powder choice.

[btroj]

I really, really like 2400 in my 30-30. 16 gr, no filler, gives 1600 fps or so, good accuracy, and no leading. I use a GC bullet. Lube doesn't seem to matter much in my rifle until temps get below 40 degrees.

Powder burn rate makes a figure difference in many cases. I like to think of powders as fitting a velocity window in a particular case. Unique may work for 12 to 1300 fps in 30-30 but it fails when you want 1500. 2400 is awesome up to around 1700 but RE7 is better at 2K. Want max velocity? Try 4898, 748, RE15 or something like that.

[03lover]

btroj,

My WC 820 acts a lot like 2400. That is why I tried it. I will have to try 2400 to see if I can find any difference.

[runfiveslittlegirl]

i think the 820 is an AA#9 replacement which is pretty close to 2400 a bit faster but close.

[Iron Mike Golf]

...I am a believer in the idea that bore lubrication with cast & lubed bullets occurrs best when the pressure of the load in great enough to cause the bullet to obturate in the bore which then forces the lube in the grease grooves under pressure onto the bore....

This is all thought experiment, so take it with a dose of salt:

I suspect that what forces the lube against the bore is the displacement of the lube by the lands. If you've attained obturation, there's nowhere for the lube to go and it's an incompressible fluid (I think).

[DrCaveman]

You want a nice slow bump in the 30-30, try h414 powder. I seriously thought it would be too slow, but about 32.5 gr behind an rcbs 30-180-fn gives about 1950 fps from a marlin 336

Fine hunting accuracy. Prob 4-6 moa at 100 yds which is beyond my iron sight allowable range anyway. Stone cold killa at 75 yds and under, and mellow to shoot

Proper fit for these results is important. Proper hardness is less important, i think. Proper pressure curve (like btroj and others mentioned) seems to play a huge part in boolit performance, to the point that it can supercede hardness and lube choice.

It is all a dance, a balance, anyhow. Didnt you know that we are all actually ballerina yogis, earth(lead)-loving alchemists, recycling(reloading) reusing (lead recovery), environmentally and socially responsible folks? Not bs, i think the woods is the best place to be. Bless hunting season.

[BAGTIC]

I don't believe rpm's have anything to do with it. If it (centrifugal force) were enough to force the lube into the grooves I would not retrieve from target range berms so many cast bullets with grooves still full of lube.

I agree that if one starts with a large enough bullet in the first place there is no need for it to expand to fill the grooves.

[Old Dawg]

I suspect 'The Formula' is not an indicator of lubricity but instead an indicator of how much pressure is needed to expand an undersize bullet up to bore size. If one starts with a bullet large enough to fill the grooves in the first place it should not be of much concern.

BTW, the word is 'effect', not 'affect'.

[Bret4207]

Several years back we had a very lengthy thread on the hows and whys we think lube works. IIRC a lot of common sense theory was discussed. Things like the incompressibility of a fluid, the fact that there is no "pump and reservoir" pushing fresh lube out to the exterior of the boolit as it travels up the barrel, that rotation doesn't do it either, that basically we don't really have a clue how lube really works, only that we can observe when it works or fails. If you could find that thread it might shed more light on things.