Friday, February 03, 2006


Field Target Knockdown Energy

I got a Crosman 1377 a while back to simplify testing my targets in the garage. I had been using a old Benjamin rifle but it was just a bit too cumbersome and didn't have as much range of power as the 1377. It got me to thinking about a subject that I have mulled over many times before, target knockdown energy. I have heard talk over the years about how easy some targets will trip without a face hit taking it down. I sat down and really thought about it and had a realization.

My realization is this, having all targets fall at the same power level may not be the best way to setup targets. A 3/8" target doesn't need to trip at 2-3 ft lbs when it is being hit with 8-16 ft lbs of energy at the maximum of 20 yards. It is even worse as the target is moved in from the maximum distance, at 10 yards it will see 9.5-18 ft lbs. At those power levels, most targets will trip easily with a split.

I ran some numbers and here is what I came up with. A rifle shooting at the 20 ft lbs maximum would shoot at around 18 ft. lbs. at 10 yards so all targets would have to potentially withstand a faceplate hit at 18 ft lbs without falling since some larger kill zone targets are used for closer off hand shots. I calculated the energy for a 10.5 ft. lbs. rifle to get the minimum energy at different distances. I picked 10.5 ft lbs since there are some sub 12 ft lbs rifles out there and it gives a bit of a buffer. The chart below shows the max and min energies at the max and min distances for the two power extremes.

Pellet Muzzle Muzzle 10 yard 55 yard
Weight Velocity Energy Energy Energy
7.9 775 10.54 9.43 5.68
10.5 930 20.17 17.90 11.10

Using the 10.5 ft lbs rifle above and the AAFTA recommended maximum distances, I calculated what the minimum knockdown power required for each kill zone size at the max distance. Note, I filled in some other standard kill zone sizes that weren't included in the AAFTA recommendations.

Kill Max Min ft lbs Min Velocity
Zone Yards Knockover Knockover
3/8 20 8.43 693
1/2 30 7.53 655
5/8 35 7.12 637
3/4 40 6.72 619
7/8 45 6.36 602
1 50 6.00 585
1 1/4 55 5.68 569
1 1/2 55 5.68 569

I have seen several target designs that fall over with a split and I have seen some that will fall over for a high power rifle but not a lower power rifle. I was shooting a 4bar type target (Knockover, Gamo, Stoutenberg type) in my garage with my FWB300 and it went down easily with a split on the face. My FWB only shoots around 550 fps at the muzzle so this particular target was falling much too easily.

Adjusting each target based on the target kill zone would make it more difficult to knock over with a split while ensuring that it would still be able to be knocked down with a clean hit. It would make target adjustments a bit harder for the match director but it could potentially make it fairer to all shooters within a division.

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