How to test bullet expansion?

[Reelamin]

rpm slows as soon as it leaves the barrel along with speed. I learned that over 50 years ago playing with spinning tops

Hmmm I have a totally different recollection of why tops spun longer or faster 50 years ago. None of it had to do with barrel twist rate. It only had to do with how fast you got it spinning by the length of cord and the weight of the top. I have some shooting to do, but I will research the heck out of this. Could you hook another old brother up and search the internet for some mathmatical/scientific data to support an item will spin faster or slower because it is pushed down a set spin rate faster or slower. I have only seen videos where they used gel and used two different twist rate barrels.....and proved the claim wrong and can accept that is only one test of a theory.

 

[DoneNOut]

This was intended for @cohunt. Watch the Independent tests and even guys testing it in gel videos. They pretty much call BS on the spinning claim. Some even run totally different twist barrels and really call BS on the claim.

I watched one video and it did make a difference, as I expected, so I didn't search further on the topic. LOL
I'm no physimachist, but I would think the initial spin imparted on the bullet is faster fired at full power than slows down range. Shooting a reduced load at a slower initial spin would result in a lower RPM.

 

[Plinker147]

There is ytube videos of people shooting into ballistic jell of about every bullet you can find. Why re-event the wheel, watch videos and pick your bullet. Bourbon creek has a bunch of good tests

 

[DoneNOut]

It's also important to remember that gelatin is not to mimic 100% the effects on biological targets. It just creates the standard for constant variable, one element of the "Scientific Method" as well as other criteria, repeatability and data gathering.

I've found I can expect 1.5-2X further penetration in animals than in gelatin. Gelatin imparts constant resistance to the bullet, where in biological targets there are spaces between organs, with varying tissue and bone densities.

 

[cohunt]

rpm slows as soon as it leaves the barrel along with speed. I learned that over 50 years ago playing with spinning tops

I was under the assumption that Rpm does not slow down as fast as velocity does, rpm keeps its speed up much better than muzzle velocity. So when you download a bullet, the rpms will be slower on impact than if you shot it at distance. I'd bet someone here actually knows the equations needed to calculate these numbers.

This was intended for @cohunt. Watch the Independent tests and even guys testing it in gel videos. They pretty much call BS on the spinning claim. Some even run totally different twist barrels and really call BS on the claim.

I know a guy that tested the rpm vs mv in ballistic gel and his findings were pretty conclusive--- compared side to side, a full mv shot at distance always showed better bullet expansion than a downloaded bullet at close range.

 

[Zen Archery]

How about live game?
Nathan Foster (NZ) has probably done the most infield research I've come across. His books are a tad costly but worth it if you're really interested.

Extensive Field-Tested Rifle & Cartridge Research - BallisticStudies.com

Expert rifle & cartridge research, carefully compiled through extensive field-testing & freely offered to the firearms community.

www.ballisticstudies.com

If you're into Pod Casts here's a 2 hour long discussion that mostly stays on point but very humble and informative.

 

[cohunt]

How about live game?

That's why I suggested a hog-- they work alive or dead for expansion testing.
I know a few guys in TX that have used hog carcass for expansion testing.

You could probably hook every member up with 1 or 2 and still have plenty to shoot

 

[Tank308]

I'm trying to rap my head around this. If your data says the impact velocity at 500 yds is 2000 fps. Then you load down to where your impact velocity at 100 yds is 2000 fps. Just for bullet expansion test. How is the impact rpm different. I understand rpm formula. Higher muzzle velocity equals higher rpm. Less time of flight I believe. But the OP is trying to duplicate impact velocity. I'm trying. But my hamster wheel is a little rusty.

 

[Jclark225]

I'm trying to rap my head around this. If your data says the impact velocity at 500 yds is 2000 fps. Then you load down to where your impact velocity at 100 yds is 2000 fps. Just for bullet expansion test. How is the impact rpm different. I understand rpm formula. Higher muzzle velocity equals higher rpm. Less time of flight I believe. But the OP is trying to duplicate impact velocity. I'm trying. But my hamster wheel is a little rusty.

Haha you're not alone there, I had the same question.
I've owned the hunting rifle I use most often now for a while and have recovered enough bullets out of animals to have a good "feel" for where I should and shouldn't be shooting. That said (if I can find a good deal) I'll possibly be switching calibers for a little better range and lighter weight for a bucket-list hunt next year. I just want to be confident whatever bullets I go with will do what they're supposed to. It'd be nice to test on hogs as some have mentioned but the places I've looked up ware too pricey so I've got to come up with decent simulation.

 

[Radman]

Milk jugs full of water lined up. Be sure to use at least 6 and hit them straight. This will be your cheapest and easiest test. I know it's not real world (actual game) performance but will expand bullets efficiently This is 280Rem 100yds water jugs approx vel 3000fps

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That's what I've done many times. I have been surprised many times! Deer slugs & heavy .45-70 rounds are so impressive. Seldom do mine pass through more than 2 jugs but their expansion is killer.

 

[Radman]

Hello, new to this forum and have a question. For those who've tried, how did you test bullet expansion at distance?

I've packed newspaper into a tub then soaked with water to try to simulate an animal's body cavity and it worked okay but only for one or two shots before the tub is useless.

However I was able to put it out on the range and "catch" my bullets to see how they perform at varying velocities to determine where my max range should be. Sure I can group well at 700 but if the bullets don't expand, it's like hitting them with a field point arrow. (Looking at you Mr. 28 Nosler shooting that elk 6 times from 900)

Anyway just wondering what people have tried and what worked. Thanks!

I applaud your thinking!

 

[LongBomber]

I'm trying to rap my head around this. If your data says the impact velocity at 500 yds is 2000 fps. Then you load down to where your impact velocity at 100 yds is 2000 fps. Just for bullet expansion test. How is the impact rpm different. I understand rpm formula. Higher muzzle velocity equals higher rpm. Less time of flight I believe. But the OP is trying to duplicate impact velocity. I'm trying. But my hamster wheel is a little rusty.

The bullet rpm does not slow as fast as the velocity. to put it in simple terms with a 1:8 twist barrel has the bullet leaving the barrel making one rotation every 8". At 500 yards with the velocity slowed significantly and the rotation slowed slightly the bullet maybe doing one rotation every 5".
It is easy to duplicate the lower velocity, keeping the rpm (or twist rate if you think of it that way) while dropping the velocity is tougher.

 

[Reelamin]

Here you all go. I learned some things in regards to RPM and velocity in pure numbers. My simple brain is still trying to put it in reality and compare what I understand, believe, with what I'm seeing on ballistic get tests. I will say I'm not changing a darn thing because of bullet RPM at target impact. Yes, I can be a slow learner.

Bullet RPM Calculator

Bullet RPM Calculator; Calculate Spin of a Bullet in RPM

findnchoose.net

 

[AaronSkipDavidson]

Rotational speed=twist rate*muzzle velocity*unit conversion factor

Rotations/minute=(rotations/inch)*(feet/second)*(12 inches/1 foot)*(60 seconds/1 minute)

So as MV increases, so does rotational speed.