American Airguns Blog
Wednesday, May 13, 2009
Field Targets and Splits
I have been working on a new gravity fall field target design over the past few months. The design is a combination of a couple other target designs with my own improvments added in. I had always thought that gravity targets were split resistant in that any split would not take down the target.
That had always been a problem with spring loaded targets, with the trip point set down to 2-3 ft. lbs. a moderate split would take down the target. The main reason for this is that the target mechanism is "prelocked" by the spring pulling (or pushing) the face back into the sear mechanism. The gravity fall target don't have this problem, or so I thought.
After testing a couple of my new targets I realized that minimal split would still take the target down. This confounded me. I did more testing and found that if the nose of the pellet hit on the inside of the kill zone, the paddle swung back and the face fell. Since my target was based partly on a couple other designs, I decided to see how those targets handled a split. As it turns out those targets also reacted the same way, if the nose of the pellet made it inside the kill zone the target went down. I have a version of just about every target type every made and so I tried them all and to a target, every one of them reacted the same way.
It makes sense too. The face has a much bigger mass than the pellet and with the nose of the pellet hitting on the inside of kill zone only a small amount of energy is transfered to the face while the rest of the pellet continues to travel forward and hitting the paddle. The face moves back very slowly due to the small amount of energy applied to the it while the paddle gets hit with most of the pellets energy, which drives it back faster and harder. So, the face won't lock up the mechanism fast enough or hard enough to prevent the the face from falling.
If the pellet nose hits on or outside the killzone edge, everything locks up and the face won't fall. I didn't have a target with the kill zone paddle that is smaller than the kill zone but I would think that the split would work in reverse on that type. The bottom line is that I don't think, or at least I haven't seen, any target design is totally split proof.
That had always been a problem with spring loaded targets, with the trip point set down to 2-3 ft. lbs. a moderate split would take down the target. The main reason for this is that the target mechanism is "prelocked" by the spring pulling (or pushing) the face back into the sear mechanism. The gravity fall target don't have this problem, or so I thought.
After testing a couple of my new targets I realized that minimal split would still take the target down. This confounded me. I did more testing and found that if the nose of the pellet hit on the inside of the kill zone, the paddle swung back and the face fell. Since my target was based partly on a couple other designs, I decided to see how those targets handled a split. As it turns out those targets also reacted the same way, if the nose of the pellet made it inside the kill zone the target went down. I have a version of just about every target type every made and so I tried them all and to a target, every one of them reacted the same way.
It makes sense too. The face has a much bigger mass than the pellet and with the nose of the pellet hitting on the inside of kill zone only a small amount of energy is transfered to the face while the rest of the pellet continues to travel forward and hitting the paddle. The face moves back very slowly due to the small amount of energy applied to the it while the paddle gets hit with most of the pellets energy, which drives it back faster and harder. So, the face won't lock up the mechanism fast enough or hard enough to prevent the the face from falling.
If the pellet nose hits on or outside the killzone edge, everything locks up and the face won't fall. I didn't have a target with the kill zone paddle that is smaller than the kill zone but I would think that the split would work in reverse on that type. The bottom line is that I don't think, or at least I haven't seen, any target design is totally split proof.
Wednesday, March 04, 2009
Scope Click Values
I have been using ballistics program for many years to estimate the trajectory of my airguns. I even wrote my own program for Windows with a very simple interface. However, none of the programs ever seemed to be very accurate at closer ranges like 10 or 11 yards. I just figured it was an estimation error in the programs calculation.
I remember many moons ago Rodney Boyce teaching me a really easy way to measure the actual click value of a scope. I don't remember the formula anymore but I figured out a pretty simple way to measure it and calculate the click value. It is pretty simple, just pick a close distance to shoot, say 15 or 20 yards, and record the distance. Measure out the distance to be accurate. Put out a target and shoot 5 or 10 shots into the target. Then click the scope up (or down) a number of clicks to get the groups apart and record the number of click of change. I used what I thought would be about 1 inch of clicks. Then shoot the same number of shots at the new setting. Then measure the distance between the groups and record it.
With these three values, the click can be calculated using the following formula:
D = distance to the target
c = number of click adjusted between groups
d = distance between the groups
click value = ((100 / D) * d) / c
Years ago I had tested my Baush & Lomb 6-24x scope and found it to be .125" per click just as specified. The Burris Signature 8-32x was specified at 8 click per MOA but they measured 6 clicks per MOA. Since measuring the click values way back then I just always used .125" per click for the Elite series scopes. Well I decided to check one of my current Elite 6-24x scopes tonight and found that it measures around .133" per click. That surprised me and make more sense that my numbers up close would be so far off. I didn't have time to plug in these values into trajectory program and then shoot test them. So, that gives me something to try in the next few days.
I remember many moons ago Rodney Boyce teaching me a really easy way to measure the actual click value of a scope. I don't remember the formula anymore but I figured out a pretty simple way to measure it and calculate the click value. It is pretty simple, just pick a close distance to shoot, say 15 or 20 yards, and record the distance. Measure out the distance to be accurate. Put out a target and shoot 5 or 10 shots into the target. Then click the scope up (or down) a number of clicks to get the groups apart and record the number of click of change. I used what I thought would be about 1 inch of clicks. Then shoot the same number of shots at the new setting. Then measure the distance between the groups and record it.
With these three values, the click can be calculated using the following formula:
D = distance to the target
c = number of click adjusted between groups
d = distance between the groups
click value = ((100 / D) * d) / c
Years ago I had tested my Baush & Lomb 6-24x scope and found it to be .125" per click just as specified. The Burris Signature 8-32x was specified at 8 click per MOA but they measured 6 clicks per MOA. Since measuring the click values way back then I just always used .125" per click for the Elite series scopes. Well I decided to check one of my current Elite 6-24x scopes tonight and found that it measures around .133" per click. That surprised me and make more sense that my numbers up close would be so far off. I didn't have time to plug in these values into trajectory program and then shoot test them. So, that gives me something to try in the next few days.
S
