Hi Charlie, Around 5 years ago or so there was an arms race to try and get the lowest mounts possible for HFT with Rick Arden’s being the ones as they were made to fit each rifles rail. I had a set for my Steyr and they were soooo low.Originally Posted by Charlie123
If you think about the trajectory of a .177 pellet travelling at approx 775fps and the scope zeroed at 35 yards then usually the primary zero would be 15 yards (pellet strikes target on the crosshair) and the secondary zero (pellet strikes target on the crosshair) would be at 35 yards with the highest point of travel for the pellet being 25 yards. Obviously the main aim in HFT is to get a trajectory that is as flat as possible within the constraints of 12ft/lb.
If you use low mounts then the scope sight line is closer to the barrel which would make for a lower POI at 25 yards, this is a positive if you find that you are having particular problems with 15mm kills in the 20/25 yard area but a negative as your drop at 40 and 45 yards would now be increased (more hold over required) and your POI for sub 15 yards 15mm kills would also increase (more hold under required).
If you use High mounts then the scope sight line is higher and further away from the barrel which would make for a Higher POI at 25 yards, this is a negative if you find that you are having particular problems with 15mm kills in the 20/25 yard area but a positive as your drop at 40 and 45 yards would now be decreased (less hold over required) and your POI for sub 15 yards 15mm kills would also decrease (less hold under required). That’s why medium mounts appear to give a satisfactory middle ground as HFT is all about compromise.
The rules above work for most set ups but it can vary from scope to scope and with the mounts used. For example, I’ve always used a set of quite low mounts but recently dropped a 10x42 Sightron onto medium mounts to see what would happen. I zeroed at 35 yards and added a few extra clicks to give me approx. 37 yard zero, I do this is it means I don’t need to be too accurate with my range finding for 25mm kills at 35 to 40 yards. I then checked my aim points and was surprised to see that it had made a decent set up for HFT.
Normally on low mounts I would find that 16 and 37 were my primary and secondary zero’s with 40 yards being under the ¼ mildot mark and the 45 under the ½ mildot mark. My 13 yard mark would be ½ mildot , 10 yards 1 mildot and 8 yards being 2 mildots.
Now, with the medium mounts my primary and secondary zero’s are 15 and 37 yards (which is surprising) with 40 being ¼ mildot and 45 being ½ mildot. No surprises there that the slightly higher mounts lifted to a longer range POI giving me a flatter long range trajectory. The real shocker was that the 20,25 and 30 yards aim points stayed the same and all the sub 15 yard ranges were exactly the same as they were with low mounts fitted. I did check the power level of the rifle as my findings made me think the power was up….but no and a nice, consistent 775/780 ish fps.
This is a total sod to try and explain textually, a couple of simple line drawings would make it much easier to understand.
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