Science Fair project

[CMV]

I loaded all the rounds for it so I guess it's reloading related....

Anyway, for this year's (7th grade) science fair I helped as usual. We did "does a bullet go faster from a shorter or longer barrel?"

Not at all PC and we'll probably get a letter sent home or something to that effect for just sending pictures of firearms to school, but he probably had the most fun out of all the kids doing his project. And he did learn something - his hypothesis was that it would go faster from the shorter barrel because there is less friction traveling a shorter distance in the barrel.

We tested 9mm out of 3.25", 4.9", & 16.6" barrels and .223 out of 16" & 20" barrels. I was a little surprised to see that a 9mm went about 150 fps faster out of the 16" Beretta CX4 vs the 5" Beretta 92FS - I didn't think there would be all that much difference past 5" for a pistol round - but it was about 13% more.

Loads were 4.8gr W231 + 115 gr Hornady FMJ & 24.2gr H335 + 55gr Hornady FMJBT. Avg vel for 10 shot strings (Chrony worked wonderfully on this overcast day with 0 errors for this & a bunch of other testing):

9mm
3.25" 1090 fps
4.9" 1144 fps
16.6" 1290 fps

.223
16" 2777 fps
20" 3031 fps

 

[Kernel]

I would of said "longer & shorter" instead of "larger & smaller". But that's a small point. Cool science project.

 

[J_McLeod]

Interesting. I would have thought you'd get a lot more of a velocity increase between the 4" and 16" barrel with the 9mm. I wonder if a slower powder would get more.

 

[CMV]

Not much of a difference between them. Looking at the extreme spreads, from the slowest out of the 4.9" & the fastest out of the 16.6" the difference is 250 fps. 1112 to 1362.

Looking at the same extreme differences - the slowest out of the 3.25" & the fastest out of the 4.9" the difference is 97 fps 1073 to 1170. That's the one I thought the length would really show a big difference.

Overall from the slowest out of the 3.25" to the fastest out of the 16.6" the difference was 289 fps.

Would be interesting to see what other burn rates would do. Maybe next year

 

[Grumulkin]

There is some barrel length at which any bullet will start slowing down. The length would depend on the volume of powder burned, friction between the bullet and bore, etc. In fact, if a barrel were long enough, the bullet would stop completely.

 

[Kernel]

It's said that somewhere around 16" will give the best velocity in the .22 LR. A barrel that's shorter, or longer, will be slower.

But there are a lot of variables, besides length, that effect velocity. Number of lands & grooves, type of rifleing, chamber & bore dimensions, freebore & leade, surface roughness, type of barrel steel, and probably a dozen other things. So any comparison that uses different firearms will be apples-to-oranges.

To minimize these unknowns, you could start with one gun and one barrel, then cut it down and recrown. Do that over and over, an inch at a time, till the barrel is only one inch long. I kinda remember seeing a website a while back that did just that. It was called "Velocity by the inch" or something like that.

 

[MEHavey]

"Not at all PC and we'll probably get a letter sent home or something
to that effect for just sending pictures of firearms...."

We would love to hear the outcome (even the teachers' lounge screaming
& yelling) that comes out of this project. Please, keep up posted !

 

[Walkalong]

I would have thought you'd get a lot more of a velocity increase between the 4" and 16" barrel with the 9mm

It depends on the powder. I have tested on load that gave almost no gain in the 16" barrel over a 5" barrel, but most gain significant velocity. I have shot several 9MM loads through a 3", 4 1/2" or 5", and 16" barrels.

 

[MrCountyCop]

No one asked so i will. What grade did he get? Looks like an "A+" project.

 

[DickM]

To minimize these unknowns, you could start with one gun and one barrel, then cut it down and recrown. Do that over and over, an inch at a time, till the barrel is only one inch long. I kinda remember seeing a website a while back that did just that. It was called "Velocity by the inch" or something like that.

Yes! Great project and they have a ton of information in this issue. It's actually "Ballistics by the Inch" and you can find it here.

 

[CMV]

No grade yet - turned in today. I don't know when they judge/grade them but its typically not for a few weeks until they find out what they got. Last year he didn't even get a grade - they just got credit for turning it in. The kids who just slapped together some crap at the last minute got the same credit as the kids who spent a lot of time and effort doing good projects. I was kind of upset by that one because we built a working catapult from scratch and then tested the distance and height it could launch various projectiles. We didn't cure cancer or anything but spent a lot of time on it. I learned from that experience and all the prior ones to just do something simple and enjoyable for both of us because as long as we check all the boxes for required sections and layout it will get an A or 'credit' regardless of how good it is.

 

[jmorris]

From a science stand point, it's flawed. I get a range of velocities out of simply different firearms, same barrel length, load , conditions, etc.

Buying a long barrel and chopping it down and inch and recrowing/chronographing each time would be much more accurate.

 

[Greg Mercurio]

jmorris: lighten up. It's a 7th grade science project, not a NASA evaluation of the effects barrel length on initial velocity correlated to causal effects of ....

I hope the principal has a bloody discharge from his nose after the science teacher craps his pants. PC is too loften considered over learning.

Hats off to you dad!

 

[bad375]

I'm a middle school technology teacher (in Texas) lots of my students hunt and shoot. We do talk guns and ballistics. I love this project, good job!!!!!!! It would have been an automatic A from me.

 

[Elkins45]

I was a middle school science teacher for a good part of my professional life. My experience has been that science teachers are the least PC in the education business, and that more than a few appreciate the technology and craftsmanship of firearms. A lot depends on where you live.

And jmorris is right. I wouldn't have given it an A in my class because he didn't control all the variables. Who's to say the velocity differences aren't due to tighter/looser bores, different rifling designs, etc? 7th graders are plenty smart enough to understand what a controlled experiment is. But I would have given him a big thumbs up for having the balls to actually investigate something interesting rather than doing some kind of PC crap like "investigating the attitudes of LBGT students toward Glee vs football".

 

[MEHavey]

I was a middle school science teacher for a good part of my professional life

Hear hear !! Both congrats & condolances. Middle School is THE worst in terms trying to keep hormonal cats in line. (Been there, done that )

My experience has been that science teachers are the least PC in the education business,

Aaaaggghhh.... But there's always Miss Brown, the "Art" teacher down the hall who graduated from Antioch Yellow Springs in the late `60s :banghead:

I wouldn't have given it an A in my class because he didn't control all the variables.

Which is why God invented the 8th grade ... so next year's science project on guns do exactly that !

 

[tschlich]

Great Job!

I wanted to do a similar project testing Bullet weight and powder variables to determine fastest velocity but my son's school has a rule about explosives being used in the experiments. Oh well. Actually was looking for an excuse to buy a chrony and slip it by the wife!!

Tim

 

[mahansm]

I wind up judging a fair number of science fair projects. For 7th grade this is excellent work. I would expect a high school student to account for the fact that he has not controlled for different barrels (surface roughness, exact diameter, etc..) and chambers (exact size).

One thing that is in the rubric is ideas for continuation; investigating effects of different bullet designs, powder charges, powder types, seating depths, etc...

Let us know how it was scored.