Thinking Out Loud
My Mind Wanders On the Subject of Cast Bullets

by Jim Taylor

Reading articles and questions on shooting cast bullets gets my mind wandering around the universe.  Sometimes I wonder if we have ever really learned anything or are we doomed to repeat the mistakes, tests, and  findings of those who have shot before us?   For instance: What is the "correct" diameter of bullet to shoot in my sixgun?"  Should it be 1. Bore Diameter?  2. Chamber throat diameter? 3. Slightly larger?  4. Slightly smaller?  Does it matter?

My Second Generation Colt SAA .45 had a .451" barrel.  But...the chamber throats were .457"!!  If I shot bullets that fit the chamber throats they were way oversize for the barrel.  And if I shot bullets sized to bore diameter they obviously would rattle down the chamber throats. What was there to do to make it shoot decently (besides get a proper cylinder)?  Was there any way to make this gun shoot accurately in the shape it was in? 

The answer is yes, sort of.  If you accept the limitations of the loads.   The first accurate load I found was a .460" diameter round ball. Lubed and pushed into the chamber until it hit the "step" - the area where the chamber goes from cartridge diameter to (roughly) bore diameter - and with a slightly shortened case containing 5 gr. of Unique, this loose gun would shoot into an inch at 25 yards if I did my part.  The oversize ball acted as a crimp, holding the powder charge back and allowing it to burn. (Otherwise the load will "poop").  By the time the ball moved 1/4" it was sized to chamber throat diameter.  By the time it made it's journey through the forcing cone it was sized to bore diameter. It exited the barrel as an elongated bullet which was rounded on both ends.  And shot pretty well.

The other load was more "normal".  I used the Lyman mold #454424 - the Keith 260 gr. semi-wadcutter.  These were cast soft (1 part tin to 10 parts lead), sized .454" and loaded over 9 gr. Unique.  The shot OK - not great.    I could count on them to shoot around 2" - 2 1/4" at 25 yards consistently. Somewhat undersized for the chambers and oversized for the bore, they worked OK as long as I used good lube on the bullets.  (I don't consider 2" at 25 yards to be great accuracy, but it was better than 3" and larger.)

Internal Ballistics

Dr. E.B. Mann in his book, "The Bullet's Flight From Muzzle To Target"  said (around the turn of the century) that we should consider the bullet to be basically elastic. It gets squeezed, pushed, pulled, stretched and hammered on it's trip from the cartridge to the muzzle. When the primer lights the powder, the base of the bullet moves first.  With a soft bullet and high-pressure loads the base "runs up" toward the nose of the bullet before the nose moves.  Since the lead has to go someplace the nose gets wider and shorter before it begins to move.  As an example, anyone who used the old "half-jacket" bullets of years ago in the .44 Magnum could tell you,  using full-power loads you could lead the barrel.  Under the   acceleration of hot loads the nose would squash out past the half-jacket and lead the bore. 

When the primer lights the powder in a cratridge, the first thing to expand is the cartridge case.  Gas blows around the bullet shoving lube, smoke, and sometimes lead particles ahead of the bullet.  Then the bullet base slugs up if everything is working correctly, fills the chamber, seals it and the building pressure moves the bullet.  During this time the bullet gets shorter and fatter. ( The closer the tolerances in the chamber the less distortion on the bullet)  When it exits the chamber (in a revolver) it has to jump across the gap between the front of the cylinder and the rear of the barrel.  The tighter this gap the less pressure is lost and the less the velocity declines.  (Heavy bullets are long for their caliber, thus bridging the gap better.  With some the nose of the bullet is almost into the rifling while the base is still in the chamber throat.)

The bullet then enters the forcing cone and is expanded somewhat, then it is forced to shrink again to fit the bore - if the bore is tighter than the chamber and throat.  If not, and if there is enough pressure, the bullet slugs up to fit the bore as it continues it's trip toward the muzzle.  Leading is often caused in this part of the trip by the bullet not sealing the bore and allowing the expanding gases behind it to leak past.  If the base of the bullet is not true, or if it does not seal, you will get leading. Especially in the breech end of your barrel.  

Gas Pressure (we've all been there!)

If you screw the barrel out of a revolver and fire lead bullets from the gun with no barrel, the soft lead bullets will slug up and expand, sometimes all the way to the thread size in the frame.  It is caused by gas pressure on the base of the bullet.    While not near as noticeable, gas pressure on jacketed bullets can distort them also - but that is another story.

Pull a .22 Long Rifle bullet from it's case and notice how the base of the bullet is 'way undersize to the rest of it.  Recover a fired .22 bullet and notice how the base has blown out and slugged up to fit the bore.  The same principle is at work. Expanding gas pressure causes the soft lead bullet to "upset" or "slug up" or "expand" - however you want to term it, and fill the bore of the barrel.

Leading can be caused by a bullet being too hard to "slug up" and fit the bore at the pressures you are firing it at.  It can be caused because the bullet does not fit the bore at any normal pressure. Gas blows past and the bullet will lead.  Leading can be caused by poor lubrication or not enough lubrication - usually indicated by white leading near the muzzle. It  can also be caused by driving too soft a bullet too fast. Mostly, leading is not caused by heat.  Yes the friction co-efficient is very high.  But the bullet is not in the cylinder/barrel long enough to melt lead.  Most leading is caused because the "gasket" (in this case, the bullet) did not seal the barrel properly.

Heat

You can test the "heat" theory yourself.  Pure lead melts at 621° F. Take some bullets and  cover the bases with wax that melts at considerably less temperature.  We used low-temperature wax that melted around 400° F.  Load the waxed bullets in your cases and fire them into something from which you can recover them.  The wax on the bases will not be melted.   This was in .44 Magnum and .357 Magnum handguns.  I have not tried it in rifles.  It is possible you could run into a whole different set of circumstances there.

Gas checks on the bases of cast bullets are one way to get the bore sealed. The are what their name implies: "Gas Checks". If made properly and fitted correctly - and soft enough to work right - they provide a gasket to keep blow-by to a minimum or not at all.  Often, to make them work best, gaschecks need to be annealed.    That is another story also.  If the  gaschecks are soft enough they seal the bore quite effectively and allow higher pressures and velocities without leading.  

Some years ago J.D. Jones of SSK Industries came out with his very fine 320 gr. 44 Magnum bullet. He sent me (as well as others) his early mold for testing.    After running a bunch of them I found they leaded quite badly due to lack of lubrication. But by putting a gascheck on the plain-base bullet it stopped the leading and they were quite accurate.  I sent him my report and sometime later he sent me the re-designed mold with a larger lube groove.  This bullet could be run at 1400 + fps in the .44 Magnum with no leading problems without having to resort to a gascheck. It is a very fine bullet. Accurate and hard-hitting. Larry Kelly used this design to take 7 elephants with the .44 Magnum revolver.

Gascheck - Freechec

Those of you reading carefully noted that in the paragraph above I mentioned putting a gascheck on a "plainbase" bullet.  A bullet not designed for gaschecks.  This was accomplished with a tool called the "FREECHEC TOOL".  This handy little gadget allowed you to make gaschecks out of aluminum cans.  You punched them out yourself and formed them yourself.  I have Freechec Tools for .357, .44 and .45 calibers in my shop.  For both plainbase and gascheck bullets.

By putting a gascheck on a plainbase bullet you could run a marginal bullet (one that was prone to lead) to decent velocities without the leading problem. You could take a good bullet and often make it better.  The Freechec Tool was developed years ago by Paco Kelly and Ed Wosika.  It has been out of production for a long time.  I hear rumors that HANNED PRECISION may be starting into producing them soon.  If so I believe there is a market out there among bullet-casters.

The Freechec also increased accuracy.  I fired 29 5-shot groups with the Freechec and 29 5-shot groups without in the .45 Linebaugh Ruger. All the groups were fired from the bench at 25 yards using 6 different bullets from 255 gr. to 340 gr. weight. Velocities were from mild to fierce.

The Freechec groups average 1.5" for all shots.

The non-Freechec groups averaged 1.9" for all shots.

Does Bullet Diameter Matter?

I also shot different bullet sizes in this gun to see what effect the different diameters would have on accuracy. I do not know how they will work in your gun but this is what happened in mine.

.450" diameter averaged 2.3" @ 25 yards for all shots

.452" diameter averaged 1.8" @ 25 yards for all shots

.454" diameter averaged 2.08" @ 25 yards for all shots

Velocities on the loads ran from 962 fps to 1346 fps with bullet weights from 255 gr. to 340 gr. in all the sizes.  Apparently with this gun the bullet diameter does not matter all that much.  Of course it has the Taylor Throat which I am sure does help. Your gun may not be quite as forgiving.

I am sure a professional Ballistician will recoil in horror at my inept description of interior ballistics.  I apologize. I may have inadvertantly left something out of the equation, or incorrectly described something that goes on when a cartridge is fired. My intention is to get us to examine what we are doing  and not to mislead anyone.  I like experimenting.  But safely. Stay safe and have fun.   That is the main idea.