ENERGY IS ONLY PART OF THE STORY

Many years ago I had a .22RF Martini action rifle converted to centrefire and rebarreled to .32-20 (more on this to come in another post).  In short, the reason for the build was to create a small game rifle shooting subsonic ammo through a suppressor that would still have generous knock down power on the very large European hares we have in NZ.  My load was a Lyman 311008 plain base, flat nose bullet of a nominal 115gr over 4.3gr of Unique for 1030fps producing 271 ft/lb of muzzle energy or twice that of a 37gr HVHP .22RF round.   Twice as much may sound impressive but 271 ft/lb is pretty tame when you consider a .22WMRF produces 324 ft/lb and a 7.62X39 1527 ft/lb.  Energy however is not always a true indication of how well a hunting load will perform.  Projectile nose profile, expansion or lack of said and momentum (velocity x mass) also play a significant role and those who shoot round balls from muzzleloading firearms will confirm this.  A large, blunt, lumbering projectile will drop an animal as convincingly as a super light screamer. 

A good, practical demonstration of this comes from an experiment I conducted a few years back.  Sourcing some discarded 25lb blocks of bakery margarine/shortening as a test medium I decided to compare the ‘wound’ channels created by .22RF hunting ammo and my .32-20 subsonic small game load.  The blocks were placed end on at 50 yards one round of each load was shot length ways into the shortening.  A thin mixture of plaster was then poured into each cavity and allowed to set prior to the blocks being cut open to reveal the end result.  these are as follows.  The top cast is the .32-20 and it should be noted the very end of the plaster broke off so the cast does not reflect the full 15 inches of penetration. 

plaster018_zpsdff7f0fb

It is easy to see that the non expanding .32-20 115gr bullet impacting at a slower velocity generated a much larger wound channel in all dimensions.  Though the beginning of the channel is not significantly wider the blunt, flat nose bullet maintains the channel for longer and further than the rapidly expanding and decelerating .22RF bullet. 

Seen below the .22RF bullet expanded in text book fashion to a diameter greater than the .32-20 bullet however in doing so it slowed up and stopped in approximately 6 inches whilst the .32-20 bullet ploughed all the way through the block. 

dscn4871

Three factors are at play here in making my .32-20 small game load the superb performer it is on hares.

  • An expanding bullet sheds velocity very rapidly as frontal area increases in size and resistance.  The result is a short wound channel.
  • Momentum; mass X velocity.  The .32-20 subsonic load has twice the energy but three times the momentum.  Energy relies on squaring the velocity.  Momentum does not.
  • Nose profile.  The work is being done by the transfer of energy from the flat nose bullet.  A round nose bullet would not have created such an impressive channel.  Indeed I have used RN bullets in the Martini with very poor results on small game.

A rather sobering revelation came from this experiment also in regards to over penetration.  Upon firing the subsonic and supressed .32-20 round I heard a distinct “TWACK” of lead striking wood.  A quick evaluation of the path of the bullet caused me to walk 100 yards beyond the test medium to discover the FN bullet lodged about 1 inch into a pine fence post.  To recap, the bullet departed my company at 1030fps, travelled 50 yards, went end to end through 15 inches of shortening, travelled an additional 100 yards and embedded itself a good inch into a pine post.  And that my friends is why we make sure there is a good back stop behind our targets!!

Another good example of what a soft lead bullet moving sedately can do is an experiment using my .310 Cadet rifle and wet phone books placed at 100m (110 yards).  The 120gr round nose, 40-1 alloy bullet left the muzzle at 1370fps, traversed 110 yards and penetrated a full 13 inches of wet telephone book. 

dscn2682

Something to think about.

Keep your powder dry. 

Jeff

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About JeffinNZ

Dedicated cast bullet shooter, runner, fisherman and father for two beautiful girls.
This entry was posted in Ballistics, Handloading. Bookmark the permalink.

2 Responses to ENERGY IS ONLY PART OF THE STORY

  1. Chaz Forsyth says:

    Great Jeff,

    I’ve never poured plaster of Paris into a cavity, what a great trick!

    CF

    Chaz Forsyth (previous email address forsyths@clear.net.nz)

  2. Ric l Carter says:

    Good article, Jeff!

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