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| Making a Bullet Trap to Test Terminal Performance
A Better Bullet “Mouse” Trap: I decided I needed to build a bullet trap to test terminal performance as part of my decision making process for hunting bullet selection. I was trying to decide which new .223 bullets might be a capable hunting bullet for small deer, the Barnes 62gr TTSX or the Hornady 70gr GMX (Hunting with the .223). I first studied how to make blocks of ballistic gelatin, the industry standard for testing bullet terminal performance. Ballistic gelatin is a testing medium that scientifically correlates to swine muscle tissue. However, the process of making the gelatin and using it is complicated. Water has to be heated to make the gelatin and then the mixture has to be refrigerated. The gelatin is also supposed to be at a specific temperature for valid test results, 39F or 50F depending on its composition. I needed something a bit easier to work with and one that didn’t make a mess. Since body tissue is made up of mostly water, I rigged up a bullet trap that used a jug of water sitting in front of a box of phone books and magazines as you can see in the first picture.
The water jug sets up the hydraulic shock that makes the bullet open up and mushroom. The paper barrier behind it slows the bullet down and captures it. The depth of the box of phone books and magazines depends on the energy of your bullet, e.g., you would expect a .300 Win Mag is going to penetrate deeper into the paper than a .223 Rem. The set-up shown worked well for a .270 Win. Here is what the bullet trap looks like after the shot.
Not much change. It is easy to separate the phone books or magazines to find the bullet. The bullets I shot from a .223 with a 24-inch barrel were trapped in the 1st or 2nd phone book. The .270 Win bullets went well into the magazine section. You can do multiple shots into the trap. I’ve done up to 3 without issue and, if your shot placement is good enough to reliably vary your impact point, you should be able to do several more. You just need a new jug of water for each shot. For a water container, I reused gallon washer fluid jugs. Reusing containers from antifreeze, milk, or large mouthwash bottles will work also. I found you only need a 2- to 3-inch water column depth to affect bullet expansion. Use the same type of container from test to test if you want to compare different bullets relative performance because I found the reaction of the jug itself provides clues to bullet effectiveness.
So far, I’ve done all my testing at 100 yards. I’m planning a future range session where I will test my .270 hunting load out to 500 yards to see how well they are mushrooming, but I need to collect some more magazines and phone books first. I want to determine the range where I can still obtain a decent sized wound cavity. Below is my experience using this bullet trap configuration. As you will see, I learned more about each bullet’s terminal performance than I expected. I also was able to correlate the .270 130gr GMX bullet performance to results from my elk hunt this past fall. Maybe you will find this process easy enough to use it with your favorite hunting load. You can add your results to the forum topic I set-up to discuss the bullet trap, Making a Bullet Trap to Test Terminal Performance.
Session 1: I did my first terminal tests at 100 yards with the .223 Barnes 62gr TTSX, Hornady 70gr GMX, and the .270 130gr GMX. The 62gr TTSX was first, it went about 1000 pages into the first phone book. Its shock, however, tore the pages into the second phone book, about 700 additional pages. One leaf (4.3 grains) broke off the expanded bullet and was sitting with the core when I extracted the bullet from the trap.
When the 70gr GMX was fired through a fresh gallon jug, it penetrated the first phone book and about 300 pages into the second phone book (600 pages further than the 62gr TTSX). It's shock tore about 500 additional pages.
I was initially impressed but thought I'd hold judgment until I shot the .270 Win. The 130gr GMX obliterated the water jug, drilled through the 3 full-size phone books I had plus 4 additional Guns & Ammo magazines. The shock tore through 4 additional magazines. There was no comparison in energy and penetration between the .223 and .270. I expected the .270 to be more powerful but not this much.
Follow-on analysis: Below is a picture of the three recovered bullets along with their calculated velocities and energy levels at the point of impact. Muzzle velocity was measured with a chronograph. Note, all the bullets retained 100% of their weight (if you include the one pedal which still resided with the 62gr TTSX when I separated it out of the phone book).
I was surprised that the 70gr GMX penetrated significantly farther that the 62gr TTSX. Then I started noticing the little things. The 70gr GMX did not have enough velocity on impact to fully mushroom (notice the hollow-point cavity still is present). I expect the GMX needs about 2000 fps of velocity to begin opening up, which is typical of monolithic bullets. Looks like it needs significantly more than 2500 fps to fully open. The GMX is a 95% copper / 5% zinc bullet which is harder than Barnes’ 100% copper bullets. (Note, the new copper/zinc MonoFlex bullets from Hornady, their new lever-action tipped bullets, are supposed to only need 1600 fps to begin to open up due to the softer flexi-tip.) I also noticed that the water jug the 70gr GMX penetrated only had one vertical rip in the plastic on the rear side. The water jug the 62gr penetrated had 3 vertical rips, front, rear, and side plus the jug lost its top. It appeared to me that the 62gr TTSX had more initial shock because it opened faster and expanded more than the 70gr GMX leaving the 70gr GMX with more energy remaining to penetrate with a slightly smaller diameter. Based on this, I think the 62gr TTSX would be better for deer and the 70gr GMX on the hogs where I am likely to need more penetration.
Because the .270 Win showed significant more performance, I plotted out their respective energy profiles for comparison. The bullet capture test left an impression on me as to just how much more powerful the .270 Win was than the .223 Rem. Not only did it penetrate deeper, it left a gapping hole in the phone books and paper dust everywhere. The .223 bullets just tore their way through. I graphed the energy levels of all three bullets out to 500 yards. Yes, if the conditions were right, I would use my .270 Win to harvest a deer at 500 yards. My .270 with the GMX bullet (0.453 BC) still had more energy at 500 yards than either .223 bullet did at the muzzle. The .270 had the same energy at 700 yards as the .223 bullets did at 100 yards.
Session 2: At the next trip to the range, I used the bullet trap to capture a Barnes 110gr TTSX and a Berger 150gr VLD. I wanted to see what the terminal performance difference was going to be between a bullet that was designed for expansion with 100% weight retention (TTSX) and a bullet designed to penetrate a couple of inches then fragment (VLD). From the picture below, you can see the surprise that awaited me. The TTSX performed as expected. It mushroomed to twice its size and bored through 3 phone books and 7 magazines, similar to the 130gr GMX shown from the 1st session (note the 110gr TTSX at 100 yards has more energy due to its still higher velocity). The VLD, however, piled up as a flatted slug 15 magazines deep. Nice penetration but no fragmentation and in a strange state with the hollow-point tip still intact as you can see from the picture below.
Follow-on analysis: Investigation of the water container and the first phone box, revealed clues that the VLD bullet did not expand on impact but yawed and was turned 90 degrees passing through the first phone book. The jug showed the bullet impacted on center-line and penetrated through the full diameter of the water jug. Thus, it wasn’t as an off-center hit that could have caused the bullet to yaw and not expand. BTW, I believe there is an advantage when using a rectangular jug as the depth of water penetration is consistent if you impact is slightly off center. The exit had an elongated tear as shown in the picture below. You can also see the elongated penetration through the first phone book compared to the round TTSX bullet penetration. The VLD bullet actually went through the remaining phone books and magazines backwards until the copper jacket crumbled and the bullet expanded to a stop. I was not able to find the 6 grains of missing VLD bullet weight as a fragment.
The reaction of the water jug also indicated that the 62gr TTSX shot during the first session had more impact shock than the 150gr VLD in the second session. The 62gr TTSX had more tears in the jug plus blew the plastic cap off the top. It is possible that using plain water as the initial entry medium in the bullet trap is not appropriate for a legacy lead-core bullet, however, I don’t believe that to be the case. If I wasn’t a fan of monolithic bullets before (which I was), I certainly am now.
The terminal performance of monolithic .270 Hornady 130gr GMX in the bullet trap also matched my hunting experience with elk this fall. I shot three 130gr GMX bullets through the chest cavities two cow elk at 225 yards up the side of a mountain. In the picture below, you can see that the entry wound into the chest cavity was the same diameter as the exit wound indicating rapid GMX expansion (both elk had similar terminal affects). The reason I shot at two elk is my hunting partner dropped my first elk with a neck shot using a 110gr TTSX as it stepped out from behind a tree a couple of seconds after I had shot. The pine tree blocked both of us from seeing the elk at the time of each other’s shot. The full story is covered in this post, New Mexico Elk Hunt.
I’ll add more to the forum topic as I develop the bullet trap further. Have fun exploring the performance of you hunting bullets!
Posted by slimjim on Friday, June 01, 2012 (04:41:31) (8012 reads) [ Administration ]
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