A Little Food For Thought On Slug Expansion

.22 NSA 17.5 @ 32fpe / 920fps recovered out of a squirrel this morning. Neck shot as moved after I shot, but completely blew ping pong ball size cavity in neck, including spine, DRT slug final resting spot was opposite side of entry behind shoulder under the skin.

Kral bullpup 

It has been shown in high speed photography that bullets expand rapidly immediately upon impact within 1” of penetration . I am referring to tests with jacketed bullets out of powder burners but I would believe the same would be with lead bullets and hollow point slugs in Airguns

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NOTE: The numbers I calculated here are based upon a radius of about 3mm which is close enough to give us a very good approximation.

No, it does not follow that lead at AG velocities would do the same. This is because the rotational velocity of pellets is so much lower than that of bullets from PBs. Lets consider a 55 gr bullet from a 5.56. Muzzle velocity is about 3200 fps. Stabilization is obtained with a 1:12 twist. At the muzzle the bullet is rotating at 3200 revolutions per second. This equates to 192000 RPM (~11000 G). Now consider the pellet being launched at about 1000 fps and stabilized with a 1:18 (or less, sometimes considerably less). That pellet is rotating at about 666 revolutions per second or 40000 RPM (~530 G). This rotational velocity is retained far longer than forward velocity but that is a topic for another discussion (about key holeing and spiraling). The bullet's rotational velocity is more than four times that of the pellet/slug from the AG. This centrifugal energy contributes immensely to the expansion of the bullet from the PB. I would venture to suggest it is the PRIMARY mechanism whereby expansion happens in any frangible projectile designed to be launched from a powder burner. That slug being suddenly slowed from transitions from air to a liquid medium literally destroys the projectile. During penetration the bullet deforms from the impact and that further reduces the rotational velocity. The two work together so well that I have seen 45 gr bullets from my .22 K-Hornet fail to penetrate completely through a ground hog at less than a hundred yards.

Is that to say that someone can not design a pellet capable of the same sort of rapid expansion? No, not at all. They build such bullets for PB pistols all the time. Such a pellet will look a lot like this and like this it will cost about a buck a pop... =)

oldspook - Nice detailed write-up. 

As you said someone could make rapid expansion airgun slugs. Like my friends design in this photo. A slug that will excel at rapid expansion for small 1 1/2"- 2" thick pests. 



Velocity and design can make airgun HP's surprisingly effective. 

oldspook - Nice detailed write-up. 

As you said someone could make rapid expansion airgun slugs. Like my friends design in this photo. A slug that will excel at rapid expansion for small 1 1/2"- 2" thick pests. 

Velocity and design can make airgun HP's surprisingly effective. 

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That looks like the idea. I was giving it some thought today and came to the conclusion that three petals would probably easiest to implement. What was the impact velocity of those slugs?

  What was the impact velocity of those slugs? 

38gr. @ 940 FPS at the muzzle. Shot some over the chrony at 100 yards recently and it was down to 800 FPS. So I'm sure it's well under 650 FPS at POI. Not to bad of performance for that slow. I'm just glad to see air gunners and the airgun industry acknowledging HP's for modern PCP guns. Pellets or slugs.......many new offerings coming out. 

The other question is what was the medium those slugs were shot into to get those results. I have been seeing recent testing done into full buckets of water, full size ballistic gel blocks and heavy dense clay blocks. I know this exaggerates the expansion we get on the usual small pests and small game we shoot often weighing a few ounces to a couple of pounds. Don't get me wrong I am very happy we are getting slugs, hybrid slugs and new pellet designs like the JSB Hades to shoot. The increase b.c. and longer retain energy alone makes for increased shooting ranges as long as you can get the accuracy.

Just the other day I did some more tests into ballistic gel with the .22 cal. Hades. The gel blocks weighed the same as squirrels, starlings and pigeons and were shot at 50 yards. The expansion was very minimal with the petals barely opening. You might say big deal as far as the results but I know in the field they were dropping pigeons at 80 yards one day along with some other pest birds. Before I was shooting the JSB 18.13's and more than half the time the pigeons when hit would fly off but crash within a hundred yards. What is the difference with the Hades only having minimal expansion. I believe as usual dome pellets just pencil on through small game while the Hades head design slows down its penetration and creates a better wound channel and dumps more of its energy. 

As far as slugs go I hope to do more testing on my ballistic gel different weight blocks. I still believe a lot of the devastation on smaller pests has a lot to do with higher fpe and kinetic energy. Bill 

PS I do have the .25 cal Hades on the way and the FX Hybrid Slugs in .22 cal on order too for testing.

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A lot of good points. My test medium was a 2.5" thick column of water in an aluminum can, with a pass through into plastic shopping bags that prevents further expansion. Not an industry standard gelatin for sure. But, having shot many cadavers. I've found that an adult Squirrel hit broad side heart/lung shot (minimal bone) to be very close. 

I like your doing the gel blocks weighed the same as squirrels, starlings and pigeon. That 's how I've always gone about testing for closer to the right scale of mass. 

I've shot the Barracuda Hunter pellets with minimal expansion on cadavers. But experienced the same results you experienced with the Hades in the field. More FPE does seem to make a significant difference, especially if the velocity is high enough at POI. Some HP designs can makeup for lack of velocity or FPE, as can be seen in the split slugs.

Be interesting to hear what the Hybrid slugs do to the "sized" gel blocks. 

Interesting results there Bill. 

Well, I did my own bit of terminal ballistic testing with NSAs in .22 and .25, and VK's in .22.

I decided to use limes... yes limes... about 1.5 inch thick, filled with water and fibrous bands, all covered in a peel (skin if you will)... seemed as good of any for simulation. I lined up 6 in a cardboard tube and fired end on. 

Results were pretty amazing. 

Very top, Fx .22 hybrid slug (arrived yesterday, testing pending, plus I ran out of limes and my basement range is gooey as heck.. least it smells nice)

2nd down, .22 VK HP-DB 22gr fired at 930 fps from an Edgun R5M. Penetrated 2 limes, lodged in 3rd. Great expansion to .29 cal. (These are designed very similar to the hybrids)

3rd down, .22 NSA HP-DB 20.2gr fired at 960 fps from R5M. Penetrated 2 limes, dented 3rd, was found in between. Great expansion to .30 cal. 

Bottom, .25 NSA HP-DB 29gr fired at 930 fps from Taipan Veteran Long. Penetrated 2 limes, dented 3rd, was found in between. GREAT expansion to .38 cal. 

33gr JSB King heavy fired at 904 fps cruised through all 6, to my amazement, and I could not retrieve pellet. 



So thats that... just information is all... but after shooting small game with pellets, then slugs, I am fairly convinced they expand to some degree. The damage done to the limes was pretty catastrophic. I'll run the hybrids through as well as hades and polymags to asses their performance on hapless innocent fruit, when I get another few bags and have some time off. 

I probably spend more time testing HP's than I do shooting paper and such.

I have video of cadavers, (Starlings and Ground Squirrels) that literally fly up 6+" into the air and fly back 12 - 18+" hit by the right slug, and just roll over with the wrong one.

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Tom,

I'd love to see some of your test results — both in ballistic gel and in cadavers!

I'd like to answer the question:

How much does slug/pellet X expand at impact velocity Y?



I found one test of the H&N Baracuda Hunter Extreme that is exemplary of what I'd like to see (cf. pic).



Matthias