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Velocity vs. Barrel Length
August 2005
Bennet Martinez

My school was having a science fair and as a requirement for my Science grade, I had to do a project. I now wanted to do something a little more unusual so my project would stick out in everyone’s memories. I wasn’t quite sure what I was going to do it on. There seemed to be limitless choices, and there were few restrictions. So with that in mind, I decided I could probably do a project on ballistics, it was related to the physics and energy category after all. I knew there must be someway to incorporate ballistics into my assignment, but I was having difficulties either thinking up one I could do, or getting the resources to do a project (some required multiple firearms). But then my father pointed out that we have three different .260’s of different barrel lengths and we could chronograph them.

I started by creating a question and hypothesis. My question would be “How does barrel length affect velocity?” I then hypothesized that a longer barrel would have a slightly higher velocity. Then I would need some sort of way to present my data, like with a chart or graph, and to finally come up with a conclusion. I was then ready to test my hypothesis.

A few weeks later an opportunity came when we were going for a visit to my grandparent’s house in Chino Valley. So when we went up there we would be able to find a remote location to conduct the experiment. We packed up the rifles and chronograph and were ready to begin testing. We had a general idea of where to go, but not quite. The area was mostly flat, with little or no backstop.

After much searching my father and I found a small abandoned rock quarry in which to set up in. There we began our testing. It took a while, but I had fun shooting.

In the experiment I followed some procedures I set up. For the experiment I was using 3 different .260’s each with a different barrel length. The .260’s I used were a 14 inch single shot Lone Eagle handgun, a 20 inch bolt-action Browning Micro Hunter rifle, and a 22 inch bolt-action Browning Stainless Stalker.

Average Velocities
Barrel Length Load 1 Load 2
14 2265 2314
20 2500 2523
22 2565 2636

We would only be testing two different loads in the three guns. For Load 1 I used a Sierra 85 grain hollow point with 27.0 grains of XMP 5744 powder and an overall length of 2.664 inches. For Load 2 I used a Hornady 100 grain soft point with 35.0 grains of IMR 4064 powder and an overall length of 2.780 inches.

I would fire 10 rounds of each load in each of the .260’s. Then I would record the velocity of each round fired and find the average. I also recorded standard deviation, minimum and maximum velocities, and extreme spread, which I ended up not using though.

It just took a while to fire each shot and record every single velocity. I even forgot to record one of the velocities, but was able to figure it out with the average (which the chronograph gives you automatically).

Well I did get uniform results from my experiment, and basically it all matched up to my hypothesis, which was “The longer the barrel, the higher the velocity”.

The longest .260 had the highest velocity with both loads. This is probably because the powder can burn longer in the barrel and push the bullet farther while still in the barrel, of course to a certain extent, where the powder is all burnt up.

I also calculated the averages, then graphed them on an Excel chart. Excel can then use the data to estimate a trend line from which a formula could be drawn (see chart on next page). Using the formulas it is then reasonable to say that there is about a 40 foot per second increase for each increase of one inch of barrel length within the range of about 12-24 inches.

Velocity is important for two main reasons: to have a straighter projectile path and to better penetrate game. Velocity affects straightness; because the faster the object is shot the straighter it goes. This is good to remember because when you sight in your rifle you would want to keep in mind how far the bullet drops at various distances. When shooting game you also want to make sure the bullet has enough energy to penetrate it. You can use the formula k=1/2mv² to calculate kinetic energy (energy of a moving object), which is one measure of how hard the bullet will hit the animal. Velocity is one of the variables (the one being squared) so the higher the velocity, the higher the kinetic energy.

Now I had my data and was ready to present it. The procedures were pretty simple. To display it I had a green presentation board on which I glued everything. I had to include a question, a hypothesis, procedures, a list of my materials, data, a conclusion, and some visual aids such as pictures. I also had included some miscellaneous info, like info on a chronograph, which most people at my school probably never heard of, along with more minor information.

I was running a little behind on the morning the projects were due, so I skipped my morning class to make sure I was able to finish putting my pictures on the presentation. I just needed to see what the school thought about it.

During science class I was able to help set up the projects. Then while I was walking back to pick up some more projects, the principal came up to me. She said that I’m not in trouble but she needed to talk to me anyways. It turned out that my pictures were “inappropriate” for the younger children. I shouldn’t have put pictures of guns on my presentation. Well, I had to take them down after all the trouble I went through to put them up. At least I get to show some of them in this article.

When I got my project back, I still got full points though. My teacher graded it before the pictures were removed so everything ended up well.

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