Power vs Caliber vs Pentration

[Blackpaw]

Okay....this is a bored one night two months back for something to do on a Sunday evening. And this is not a comment on overall effectiveness, just my “observation.”

Before I went to the USA I had my Leshiy 2 in .177 cal power adjusted to 16ish ft/lbs using 10.34 grain JSB heavies. I thought it might be interesting to see what differences in penetration would be at 16 ft/lbs at 10 yards (all I have indoors) between a .177 and 25 cal JSB pellet. For the 25 cal I used my Taipan Vet Compact using 25.34 grain King Heavies.

Using metal plate (cookie sheet) and I wanted to see if at the same energy level which pellet caliber would penetrate further. (Sorry never took photos and now both guns still in USA, so can’t repeat test and don’t get me started why the Leshiy 2 is still there). Plain and simple the .177 penetrated the cookie sheet and the .25 did not.

Though I am not a ballistics expert I feel the reason the .177 penetrated further than the .25 was “the focal point” of impact energy vs mass. Basically a thin knife with the same force cuts deeper than a thick knife. The energy dispersion of the .25 cal pellet was less focused than the .177 cal pellet thus, its “pin point energy” transfer was less for the .25 cal pellet. YES, this is only 10 yards, and I know down range momentum would flip the results, but this what I observed.

Based off my observation in low energy close quarters shooting a 25 cal MIGHT be less likely to penetrate the backstop than a .177.

 

[Raider03]

You have the right idea. Both pellets had the about the same energy at impact. The impact force is more difficult to estimate, but, if the impact force is about the same for both pellets, then the impact pressure (force/area) will be much higher on the 177 cal because it has a much small cross sectional area. The target material can only withstand a maximum stress (lbs/square inch - PSI) and the impact pressure (also PSI) of the 177 cal exceeded that limit, so it was able to penetrate. From what i have read here and in other forum it is common for small calibers to penetrate more then larger calibers at similar energy levels. The 25 cal at low energy is more likely to ricochet off the backstop. A knife's edge is an extreme example of this, the edge has a very small contact area. So even a small force will then generate very high contact pressures.

 

[vmaxpro]

At the same fpe it makes sense. At the same velocity no way. A 8gr .177 at 1000fps vs a 50gr .30 at a 1000 isnt even close. Its prob safe to assume given the same fpe the .177 would penetrate more however Id be curious to see that test in something softer. 

 

[Guest]

To calculate the pressure on the cross section of a pellet at the point of impact:

Calculate cross section (Radius X Radius X PI) your answer will be in square inches.

Take that number and divide it into One (it will be less than one) to get the number of pellet cross sections in a square inch.

Then multiply that by the energy of the projectile at the point of impact ( or in this case at the muzzle).

For a rifle shooting at 16 fpe you get the following values.

0.177 = 162 foot pounds per square inch equivalent.

0.20 = 127 foot pounds per square inch equivalent.

0.22 = 105 foot pounds per square inch equivalent.

0.25 = 81 foot pounds per square inch equivalent.

So you can see a .177 will get deeper penetration any time it lands with more than half as much energy as the .25 lands with or said another way, the .25 caliber will need to land with 32 foot pounds of energy to penetrate to the same depth in the same medium as a .177 that lands with 16 foot pounds of energy.