Slugs --- Testing How Much They Expand and How Far They Penetrate
Slugs for airguns won’t ever replace pellets.
But they aren’t just a fashion, either.
Slugs easily cut wind drift by more than half.
And at longer ranges they hit quarry with twice the energy.
Those are reasons enough that I want slugs (not the slimy ones, though if they are cured with lemon and served with yam and hot chili peppers, they are quite good!).
The Benefits of Hollow Points
But almost all commercially available slugs come as hollow points – and for a reason. The hollow point is supposed to expand upon impact and make a larger permanent wound cavity. This is good if your quarry’s kill zone is rather soft and fleshy, as a bigger wound produces a higher rate of DRT’s (over the F&D’s and R&D’s*). (However, if your quarry’s kill zone is a big head protected by tough bones, penetration is probably more important than expansion.)
*[F&D = fly & die | R&D = run * die]
If the hollow point projectile (slug or pellet) increases in diameter, so does the impact area, and so does the volume of crushed tissue as the projectile bullies its way through the quarry – leaving the permanent wound cavity.
For example: A .22cal projectile (slug or pellet) that expands to .295 increases its impact area by 66%.
And at that increase, even a 1½"-short wound cavity therefore increases by 85%! 85% more tissue crushed!
[Metric: A 5.5mm projectile expands to 7.5mm. Even a 4cm-short wound cavity is thereby increased by 85% – resulting in 85% more crushed tissue.]
Also worth considering is the Meplat = the flat part of a wadcutter or the flat part of a hollow point including the open HP cup.
▪Most slugs have very narrow hollow point cups, giving the slug the general shape of a spitzer bullet. A spitzer will tend to slice through flesh rather than crush the flesh — and crush we want — to increase the damage, i.e., the permanent wound cavity!
▪A domed pellet will also crush flesh much less than a blunt flat projectile, i.e., one with a large meplat, a flat surface like a WC or HP.
➔ Some tests show how hollow point slugs with very small HP cups have not much expanded their overall diameter, HOWEVER they have opened up the HP cup and therefore have now a large meplat to crush tissue.
In some sense, they fly with the BC of a slug, and crush tissue like a wadcutter = the best of both worlds...!
What Helps the Hollow Point to Expand
After seeing the often poor performance of hollow point pellets – I wanted to know what expansion I could expect from hollow point slugs.
Bob Sterne (HardAir Magazine and GTA) published some very insightful articles and posts about the subject (cf. links).
https://hardairmagazine.com/ham-columns/bob-sterne-discusses-hollowpoint-slug-design/
https://www.gatewaytoairguns.org/GTA/index.php?topic=174584.msg155979642#msg155979642
Just to summarize Bob’s excellent discussion:
Some of the attributes that support expansion of a slug are as follows:
• larger HP opening
• thinner walls of the HP cup
• softer lead
• deeper HP cup
• slits (predetermines tearing points) open the HP in petals and can aid in fragmenting the slug
• harder impact material (animal flesh is softer than play-dough is softer than clay)
• higher impact velocity! (as the tests will show, depending on the impact velocity the HP will “work” – or not expand)
• a HP cup that is very deep can aid in fragmenting the slug
HP Projectile Tests
Data on HP slug expansion is still scarce, but in the following posts I’ll share the Projectile Expansion and Penetration Tests .22cal that I’ve found so far.
Take the test results with a grain of salt (or a 22-grainer of lead if you like). As more test data becomes available some test results might prove to be too optimistic, or pessimistic.
Some Benefits of the Test Results for the Shooter
• You will note in the tests that depending on the impact velocity the HP will “work” – or not expand. Knowing the muzzle velocity of a slug that your gun likes, you can do some simple ballistics to figure out at what maximum range you still can expect reasonable expansion in the quarry.
• If you have the choice of several slugs that your gun likes, based on the test results you could choose one that has better expansion, or choose a lighter (=faster) slug.
• If you wanted expansion at farther ranges, you could increase the power of your gun based on your ballistic calculations.
I thank all the airgunners who have run these sometimes very time-consuming tests, and for putting them out there for us so we could learn from them. THANK YOU!!
Matthias
An Overview and Some Background of the Projectile Tests in this Thread
When sifting through the projectile tests (PT) I decided to leave out play-dough, clay, and water as ballistic mediums as they exaggerate HP expansion. Reading what terminal ballistician have written, I considered ballistic gel, ClearBallistics.com gel, glycerin soap, wet newsprint, and of course... – real quarry (dead or alive)!
The testers often do not give specific details of their test protocol (which kind of ballistic gel they are using), nor do they give exact data (impact velocity) or measurements (expanded size of the slug). I had to do some ballistic calculations and often measure the proportions of the expanded slugs in the images in order to arrive at the data as presented below.
All the tests include the following:
• a test designator, PTXXX (where XXX is a counter; PT = projectile test)
• the ballistic medium
• impact velocity, and impact energy
• meplat (expanded flat portion of the nose, if applicable)
• expansion (total diameter)
• impactand/or penetration
• source (and notes)
Measurements in imperial and metric.
Slugs for airguns won’t ever replace pellets.
But they aren’t just a fashion, either.
Slugs easily cut wind drift by more than half.
And at longer ranges they hit quarry with twice the energy.
Those are reasons enough that I want slugs (not the slimy ones, though if they are cured with lemon and served with yam and hot chili peppers, they are quite good!).
The Benefits of Hollow Points But almost all commercially available slugs come as hollow points – and for a reason. The hollow point is supposed to expand upon impact and make a larger permanent wound cavity. This is good if your quarry’s kill zone is rather soft and fleshy, as a bigger wound produces a higher rate of DRT’s (over the F&D’s and R&D’s*). (However, if your quarry’s kill zone is a big head protected by tough bones, penetration is probably more important than expansion.)
*[F&D = fly & die | R&D = run * die]
If the hollow point projectile (slug or pellet) increases in diameter, so does the impact area, and so does the volume of crushed tissue as the projectile bullies its way through the quarry – leaving the permanent wound cavity.
For example: A .22cal projectile (slug or pellet) that expands to .295 increases its impact area by 66%.
And at that increase, even a 1½"-short wound cavity therefore increases by 85%! 85% more tissue crushed!
[Metric: A 5.5mm projectile expands to 7.5mm. Even a 4cm-short wound cavity is thereby increased by 85% – resulting in 85% more crushed tissue.]
Also worth considering is the Meplat = the flat part of a wadcutter or the flat part of a hollow point including the open HP cup.▪Most slugs have very narrow hollow point cups, giving the slug the general shape of a spitzer bullet. A spitzer will tend to slice through flesh rather than crush the flesh — and crush we want — to increase the damage, i.e., the permanent wound cavity!
▪A domed pellet will also crush flesh much less than a blunt flat projectile, i.e., one with a large meplat, a flat surface like a WC or HP.
➔ Some tests show how hollow point slugs with very small HP cups have not much expanded their overall diameter, HOWEVER they have opened up the HP cup and therefore have now a large meplat to crush tissue.
In some sense, they fly with the BC of a slug, and crush tissue like a wadcutter = the best of both worlds...!
What Helps the Hollow Point to Expand After seeing the often poor performance of hollow point pellets – I wanted to know what expansion I could expect from hollow point slugs.
Bob Sterne (HardAir Magazine and GTA) published some very insightful articles and posts about the subject (cf. links).
https://hardairmagazine.com/ham-columns/bob-sterne-discusses-hollowpoint-slug-design/
https://www.gatewaytoairguns.org/GTA/index.php?topic=174584.msg155979642#msg155979642
Just to summarize Bob’s excellent discussion:
Some of the attributes that support expansion of a slug are as follows:
• larger HP opening
• thinner walls of the HP cup
• softer lead
• deeper HP cup
• slits (predetermines tearing points) open the HP in petals and can aid in fragmenting the slug
• harder impact material (animal flesh is softer than play-dough is softer than clay)
• higher impact velocity! (as the tests will show, depending on the impact velocity the HP will “work” – or not expand)
• a HP cup that is very deep can aid in fragmenting the slug
HP Projectile Tests Data on HP slug expansion is still scarce, but in the following posts I’ll share the Projectile Expansion and Penetration Tests .22cal that I’ve found so far.
Take the test results with a grain of salt (or a 22-grainer of lead if you like). As more test data becomes available some test results might prove to be too optimistic, or pessimistic.
Some Benefits of the Test Results for the Shooter
• You will note in the tests that depending on the impact velocity the HP will “work” – or not expand. Knowing the muzzle velocity of a slug that your gun likes, you can do some simple ballistics to figure out at what maximum range you still can expect reasonable expansion in the quarry.
• If you have the choice of several slugs that your gun likes, based on the test results you could choose one that has better expansion, or choose a lighter (=faster) slug.
• If you wanted expansion at farther ranges, you could increase the power of your gun based on your ballistic calculations.
I thank all the airgunners who have run these sometimes very time-consuming tests, and for putting them out there for us so we could learn from them. THANK YOU!!
Matthias
An Overview and Some Background of the Projectile Tests in this Thread When sifting through the projectile tests (PT) I decided to leave out play-dough, clay, and water as ballistic mediums as they exaggerate HP expansion. Reading what terminal ballistician have written, I considered ballistic gel, ClearBallistics.com gel, glycerin soap, wet newsprint, and of course... – real quarry (dead or alive)!
The testers often do not give specific details of their test protocol (which kind of ballistic gel they are using), nor do they give exact data (impact velocity) or measurements (expanded size of the slug). I had to do some ballistic calculations and often measure the proportions of the expanded slugs in the images in order to arrive at the data as presented below.
All the tests include the following:
• a test designator, PTXXX (where XXX is a counter; PT = projectile test)
• the ballistic medium
• impact velocity, and impact energy
• meplat (expanded flat portion of the nose, if applicable)
• expansion (total diameter)
• impactand/or penetration
• source (and notes)
Measurements in imperial and metric.
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