When all things are not equal.....
                                                Pressure vs. Velocity
by Paco Kelly

One of the things I find fascinating because it goes against logic is pressure and it's relationship to velocity in guns.  One would think that as the pressure goes up, there would be a parallel increase in velocity.....no matter which powder is used.  Ain't SO!

Where one powder may give 40,000 psi and 1500 fps, with the same bullet, cartridge, primer, gun, everything but a different powder - one still giving 40,000 psi - there can be vastly different velocities.

For example:  With 296 powder, 12.4 grains under a 200 gr. lead bullet in .357 magnum cases gives 1335 fps.....with the same gun 4.3 grains of IMR 700X gives only 795 fps.  Yet they both generate 35,000 psi!  That is not an absolute anomaly either.  IMR 4227, SR4756, SR7625, IMR PB and number of others generate 35,000 plus psi and still don't even break 1000 fps.

Many would say it is the quickness or slowness of the burning rate.  And SOMETIMES that is right.  But in the above list IMR 4227 gives only 966 fps at a cost of 35,500 lbs. of pressure.  And 4227 is considered a slow pistol powder.  Still, today with cast bullets in some rifle rounds it is superb.

Some believe that no matter the powder, the revolver burns 99% of it before the bullet gets out of the forcing cone.    Recent tests have shown with some slow powders like 2400, the powder is not consumed until well into the first inch of the barrel.  One way the normal shooter that doesn't have a lot of scientific pressure measuring equipment can prove this to himself is to load a one-inch snub nose .38 ( like the S&W Chief's Special) with 10 gr. of 2400 under a cast 158 gr. lead bullet and fire it inside a large plastic garbage bag.  The bullet will exit but the unburned powder can be collected, if careful to get it all, from inside the bag.  I've collected as much as 4 gr. of unburned powder doing this test.  (I fire 5 rounds and divide the total amount collected by 5)

With 2 inchers and above it's all burned...even slow powders.  So actually with 2 and 3 inch barrels slow powders can be used somewhat satisfactorily.  That's where some of the handgun pressure testing is faulty.  If the inducer or sensor is placed in the barrel and peak pressure is gained before the bullet passes the sensor, the less pressure existing when it does pass will be read instead of the peak pressure.

Obviously the same amount of powder but in a different size cartridge case will give different pressures.  When 10 gr. of 2400 is fired in a .38 Special case it is no doubt a PlusP load.  But in the .357 magnum case it is a medium load and in the .41 magnum case it is a mild load.    One of the things that Remington did a number of years ago is to find the reason for for guns being damaged with target ammo was to place the bullet deeper and deeper into the case.  With a .38 Special case and 3.6 gr. Bullseye....15,500 psi was the result of normal loading positions with wadcutters of 147 grains.  Push the wadcutter just 1/8 of an inch into the case and the pressure raised to 19,800 psi.   With a quarter inch depth to the wadcutter the pressure was above 25,000 psi....and when it was pushed to bottom out the pressure was near 100,000 pounds!  ( That is damn near an explosion more than a pressure rate. No wonder there were so many blown handguns with target loads...)

Number of years ago a good friend was playing with ball loads in his Cattleman .45 Colt single action revolver.    He was using small amounts of fast pistol powder.....really target-type loads.   He noticed in one of his loads, the ball was pushed down, way past the halfway point, in the case.  He fired it anyway, not knowing of the pressure problems inherent with that kind of loading. It bulged his cylinder at that chamber.  Luckily he was able to get another cylinder, and the frame wasn't stretched.  This is also why handloaders  must be careful in loading long heavy bullets.  Since most cylinders only allow so much length of bullet to the mouth of the chambers....the rest of the the length must be pushed into the case, constricting the amount of powder room.

With today's hunting trends towards very heavy bullets for the caliber, that means the length of the these bullets is much longer than what the normal loads were just a few years ago.  Careful reloading is essential.  To give an example of this, the .44  magnum loaded with    250 gr. cast Keith semi-wadcutters vs. the 310 gr. semi-wadcutters in the same case......it is not all weight addition, but also the restriction in the powder space with the 310 gr. bullet that can cause the problems.  With 9 gr. of Bullseye under the Keith 250 I get 40,000+ psi.  But the in the case with the 310 gr. bullet the same amount of Bullseye give just under 54,000 psi.   This is not a load that should be fired in a Ruger Super Blackhawk much less something less strong like a S&W N-frame .44 mag.

One of the loads I use in my strong Ruger .45 Long Colt-chambered SA revolver is a 200 gr. cast round-nose bullet over 30 gr. of H4227.  At a cost of 29,000 psi plus and 1600 fps velocity, the muzzle energy is 1137 ft. lbs.   Which is in the 40 caliber magnums range.  A 200 gr. .45 bullet is fairly short in a .45 Colt case, but 29,000 lbs. is a heavy load.    My Ruger hasn't complained yet, and I have been shooting it for years......but, and it a big "but"...someone else's Ruger Blackhawk may not be able to stand the pressure, especially over successive firings.   Remember steel can become fatigued over many firing and finally let go.  And when a revolver lets go....you don't want to be holding it, or even own it.  You have suddenly turned a number of hundreds of dollars worth of machinery into scrap metal, along with a few fingers maybe.   Ruger's Redhawk is a safer gun in this chambering.  Mine also takes the 30/H4227/200CB without a hitch.....and gives outstanding accuracy.

I used this load on a feral pig, a pen-raised pig gone wild.....not a Russian-type Boar.   At close to three hundred pounds this was still a mini-tank.  The 200 gr. roundnose (really, blunt nosed, like a fist) at about  20 yards went through the right shoulder and exited the off side after breaking the left leg just below the shoulder.  Piggy went down in front but squealed quite loudly and earned another round in the skull for his performance.  The short-barreled .45 Colt/Rugers are the poor man's magnum....and reloaded right will do just about everything a commercial .44 magnum load will do.    Ruger by the  just began this year (1998) to offer its outstanding Super Redhawk in the .454 chambering.  Firing commercial loads of .45 Colt in this Ruger feels like firing .38 wadcutters in an L-frame .357.

Like I said in the beginning....pressure in handguns with differing powders is not something you can corral, throw a saddle on and anticipate it's movements while riding.   The non-careful reloader is going to get thrown and hard.  It's just a matter of time.

The best reloading books that I have that give pressure readings are Richard Lee's book MODERN RELOADING and METALLIC CARTRIDGE RELOADING by M.L. McPherson.  Both of these authors have taken the time and the money to bring us us pressure readings for both rifle and handgun reloads with powders that are available to the reloader today.

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