I'm still learning much in the area of ballistics so please pardon me if this is a stupid question.

Let's say I want to know the fragmentiation limits of the 77 gr w/cannelure Nosler.  I put the velo chart below together using a free ballistic calculator and I used the ballistic coefficient of the 77 SMK so I could be a bit off.  It only goes to 300 yards but I think you get the point.

This chart is just an example so obviously we would use a real 77 gr Nosler data and chart for actual testing.

Looking at the chart below we see the velocity starts to drop to the extreme fragmentation range between 225-275 yards.  

Here's my stupid question...  

If you are limited to a 100 yard range, is it possible to simulate the fragmentation effects of longer ranges by downloading the ammo to match the estimated velocity of the distances you want to test?

I.E.  Using the example data below, download a certain number of rounds to reach 2157 fps at 100 yards in order to shoot them into ballistic gel and average the results for fragmentation capability at 250 yards.  

Would this be a valid experiment?  Why or why not?


77 gr with BE .362 @ 2750 fps from a 16" barrel.

Yards/Velocity(FPS)/Energy (ft/lbs)/drop(inches)

25 /2682 /1229 /-.310

50 /2620 /1173 /+.964"

75 /2559 /1119 /+1.945"

100 /2498 /1066 +/2.627

125 /2439 /1017 /+2.963

150 /2380 /969 /+2.944

175 /2322 /922 /+2.535

200 /2264 /877 /+1.700

225 /2209 /834 /+.444

250 /2157 /795 /-1.175

275 /2098 /742 /-3.611

300 /2044 /714 /-6.434



 

Yes it would be valid and you should do it at VERY short range instead of at 100 yards.  Why make it harder than it has to be?

It would be valid. You should do it soon so you can tell me all about it.

Thanks guys, unfortunately my question was only hypothetical in nature because I don't have the equipment to make it happen. [:(]

DevL,

You're right why even mess with 100 yard ranges when you can just do it at 10 feet!

Also, doing the test at short distances may also compensate for the bullet stability issue that Troy mentioned.  Since there will be less time in flight there should be less chance of any adverse effects.

I would also bet just getting ammo downloaded to the needed velocities would be quite a job alone.

Man, this would be a awesome experiment!  I need another job just to support this addiction...[BD]

I disagree.  It would not be a valid test.

Downloading causes a problem.  It gives a round insufficient rotation for a true simulation of a ranged shot.  Because rotation comes down much slower than does velocity you get different ballistic profiles at the same velocity for downloaded rounds vs. rounds that have actually travelled the distance.  We tried downloading at one point and gave it up.  I do not know of anyone who has tested the differences between downloading and actual distance shots to compare but I think it is a rather iffy assumption to make that the performance will be the same.  It might be, but why risk it?  It is easy enough to hit gel sized targets out to 200 unless the round is just not accurate enough to be a good defensive round in the first place.

Just get Mrs. Yojimbo to smile at them - they'll shatter on their own!!

[:D]

You could do it yourself; the info is out there to reload reduced velocity ammo.
The problem is that the rotational speed of the bullet would be a lot lower than a true 600 yard shot; the rotation does not decelerate much at all compared to linear velocity.  The bullet would tumble sooner and more radically than a more-stable 600 yard shot.

I stand corrected. I can certainly see how reduced RPMs would not allow the bullet to fragment as violently and would make it more unstable.  I guess we need to just do some long range testing or get test barrels made in a 1/5 twist to counter act the reduced velocity loads.  If you kept the RPMs the same it would givethe same results.  This would require test barrels with twists that matched the higher veliocity RPMs.

It is not certain that rotation impacts fragmentation dramatically (and there is even evidence to suggest otherwise, though most of it is directed at the lethality of various twist rates.  We found almost no discernable difference between 1:7 and 1:9 at the same range and barrel length, for instance).  It does, however, seem to change the experiment in other ways.  You end up getting mixes of rotation and forward velocity that do not happen under normal circumstances.  We can't be sure that this impacts gel testing but I suspect that it might and in any event why go to the trouble to reproduce and test conditions that will never exist in real life when it is not too hard to put a round into gel at 100-200 meters, unless you aren't careful.  We used to put a heavy steel plate with a cut out in the middle to avoid shots into the edges of the gel, for instance.

It was mentioned to me offline that this has already been tried and it doesn't work.  I guess there's too many factors involved to get decent and reliable results.  It's also probably a lot easier to find a 300 yard range and do the test for real instead of going theough all the headaches...[;)]