entoptics
Well-Known Member
- Joined
- Jan 16, 2018
- Messages
- 878
Was explaining the importance of consistent form to a novice the other day, and it got me thinking about what the actual "numbers" associated with "consistent form" were. Decided to dust off my trigonometry and whip out my slide rule (i.e. google and excel).
...So here's some numbers...
1) Average rifle is about 45" long, so if we do the trig, all it takes to change our take off angle by 1 MOA (0.0166°) is to move the rifle butt a whopping 0.013" (assuming the muzzle end is fixed). Go ahead. Grab your calipers and see what 0.013" looks like...
2) According to QuickLoad, a typical rifle bullet spends about 1.2 milliseconds (0.0012 seconds) traversing the barrel. Typical rifle recoil velocity varies from about 7 ft/s (243 Win, 10 lb gun) to as much as 20 ft/sec (45-70, 7 lb gun). So your rifle is moving on the order of 1/8" (8 lb 243 Win) to 1/4" (8 lb 338 Win Mag) while the bullet is still in the barrel.
Now most of that is rearward obviously, but let's say 1/10th of it translates into angular motion on average (e.g. the rifle butt moves up/down/left/right relative to the muzzle). Per point 1 above, that's about 1MOA on a 243 Win (0.0125"), and 2 MOA on a 338 Win Mag (0.025").
Take home point? If your form isn't consistent enough to have your rifle butt end up in the same place every time the bullet exits the barrel by the THICKNESS OF A FRIGGIN SHEET OF PAPER!!!!!, then that's about a 1/4 MOA added to your group size...
Another fun point along these same lines, is the drastic POI shift one sees when changing loads in handguns.
1) A magnum handgun can generate recoil velocities in the neighborhood of 20 ft/sec also.
2) Dwell time and recoil velocity change dramatically with different loads. Think fire breathing 180 gr 44 at 1600 fps (dwell = 0.52 ms) vs a mild 240 gr at 1100 fps (0.76 ms).
3) Unlike rifles, a whole bunch of the recoil motion is converted into muzzle rise.
For example, a 240 gr magnum load might generate 20% more muzzle flip during bullet traverse than a 180 gr load. That muzzle flip translates to the target, and is why handguns often show the unintuitive behavior of slow/heavy bullets impacting higher than fast/light bullets for a given sight setting.
Hope you enjoy, and let me be clear. All of the above is nearly useless information if your only goal is to be a better marksman. I just thought it was neat how "precise" precision shooting really has to be to make it all work for that
pew......................................................................................................................ting
we all love so much...
...So here's some numbers...
1) Average rifle is about 45" long, so if we do the trig, all it takes to change our take off angle by 1 MOA (0.0166°) is to move the rifle butt a whopping 0.013" (assuming the muzzle end is fixed). Go ahead. Grab your calipers and see what 0.013" looks like...
2) According to QuickLoad, a typical rifle bullet spends about 1.2 milliseconds (0.0012 seconds) traversing the barrel. Typical rifle recoil velocity varies from about 7 ft/s (243 Win, 10 lb gun) to as much as 20 ft/sec (45-70, 7 lb gun). So your rifle is moving on the order of 1/8" (8 lb 243 Win) to 1/4" (8 lb 338 Win Mag) while the bullet is still in the barrel.
Now most of that is rearward obviously, but let's say 1/10th of it translates into angular motion on average (e.g. the rifle butt moves up/down/left/right relative to the muzzle). Per point 1 above, that's about 1MOA on a 243 Win (0.0125"), and 2 MOA on a 338 Win Mag (0.025").
Take home point? If your form isn't consistent enough to have your rifle butt end up in the same place every time the bullet exits the barrel by the THICKNESS OF A FRIGGIN SHEET OF PAPER!!!!!, then that's about a 1/4 MOA added to your group size...
Another fun point along these same lines, is the drastic POI shift one sees when changing loads in handguns.
1) A magnum handgun can generate recoil velocities in the neighborhood of 20 ft/sec also.
2) Dwell time and recoil velocity change dramatically with different loads. Think fire breathing 180 gr 44 at 1600 fps (dwell = 0.52 ms) vs a mild 240 gr at 1100 fps (0.76 ms).
3) Unlike rifles, a whole bunch of the recoil motion is converted into muzzle rise.
For example, a 240 gr magnum load might generate 20% more muzzle flip during bullet traverse than a 180 gr load. That muzzle flip translates to the target, and is why handguns often show the unintuitive behavior of slow/heavy bullets impacting higher than fast/light bullets for a given sight setting.
Hope you enjoy, and let me be clear. All of the above is nearly useless information if your only goal is to be a better marksman. I just thought it was neat how "precise" precision shooting really has to be to make it all work for that
pew......................................................................................................................ting
we all love so much...
