Need help on daughters science fair project.

[BWE Firearms]

My daughter has decided on a high school science fair project and she asked me for help and I in turn am asking for your help. She came up with the topic "How does bullet diameter effect penetration". Velocity has to stay the same (1050 FPS). I think we should try to keep bullet shape and weight as close to the same as possible. I think we will be shooting into Sem-Test ballistic gel. We will be using our 50 and 338 THUMPERs and a 300 Whisper\Fireball\Blackout. I can get 300 grain round nose bullets for the 338 and 50. Three rounds of each caliber needs to be tested. This also means I will have recast-able ballistic gel for future use if anyone wants any tests done.

Questions:

What distance should I set the gel at?

Whats the heaviest round nose bullet available in .308?

Any other caliber suggestions?

Any other suggestions or comments?

I want my daughter to win this science fair and with your help we can.

P.S. Almost forgot everything will be shot suppressed of course. The school should love that!

[LouBoyd]

With the political climate in most NEA supported schools you're more likely to get your daughter expelled than to help her win her science fair.

If the subject is "How does bullet diameter affect penetration" then you should vary only bullet diameter while keeping other parameters constant. Use three bullets of similar construction (Jacketed lead) or solids of the same weight and shoot them at the same velocity. Perhaps 150 grain RNs. Then graph clearly the depth of penetration vs diameter. You might also plot depth of penetration versus frontal area which is the square of the diameter. I'd expect that to be more linear, but maybe not.

If you vary any other parameter you are not addressing the question directly. You don't want to be asking "how does energy affect penetration" or "How does bullet expansion affect penetration" or "How does bullet nose shape affect penetration" or "How does bullet tumbling affect penetration". It's not easy to vary only diameter, but at least you need to try. You could do a more complex multivariant study with multidimensional computer programs and many assorted bullets, but that's probably too complex for a science fair. Shoot at low enogh velocity so the bullets don't expand in the gel.
I
won two science fairs in high school, and lost two badly. The judges want the science to be explained in straight forward scientific terms and so most people seeing the display will understand the principles being displayed. It should not require tedious reading. The displays must demonstrate the science involved. Spectacle does not win, but neatness and clarity are important. Good science usually does win.

[BWE Firearms]

LouBoyd,

Luckily my daughter is in private school and the school knows I am a gunsmith so they are a little more understanding. As I stated I have the 338 and the 50 that I can get grain RN bullets for and I am trying to think of at least one more cartridge that 300 gr. RN bullets are available for.

Is three different calibers enough or should I have more?

[Alleycat]

I have some 250 gr .308 Hawk bullets sitting around. They will expand a bit. I would say you need to get bullets from the same manufacturer or at least non expanding bullets to get a good test. I have tested expanding bullets from Outlaw State bullets and got almost the same penetration from the 225gr .308s and the 530gr .458s. The ratio of expansion was also close. If you need a few 250 Hawks PM your address and I will send you some.+

[alorton]

I like the idea of doing firearms related science fair projects, I'll keep that in mind when my kids get old enough to do such things.

From a testing standpoint diameter will be much harder to test for than say velocity or mass. It will be hard to hold other variables constant while changing diameter because changing diameter will also change bullet shape. as you get into long bullets it may introduce tumbling which could affect the results significantly.

You will also have to keep the nose of the bullet as consistent in shape as possible as that may also significantly affect the results.

For the media I would fire a test BB into each block similar to what is done with ballistic gel testing for terminal performance and penetration. This will show consistency between gel blocks and validate the data from that standpoint. Obviously a chronograph to record impact velocity will be necessary.

Good luck and let us know how it turns out.

[alorton]

Have you considered a different bullet weight range to test?

A Barnes TSX won't expand at low velocity and if you could live with a +/- 5 grain window you could use the 115gr .257, 120gr 6.5, 110gr 6.8, 120gr 7mm, and 110gr .308. That is 5 different bullets of almost identical construction with varying diameters.

Just a thought.

ETA: Also, the lighter bullets won't require as much test media. I suspect a 300gr non expanding bullet will require alot of gel even at subsonic velocities.