10-02-2017, 08:28 PM
DJL2 Wrote:I'm a new Grendel shooter, but I've built limited data from 25-200m. My observations are thus.
I used a 25m target to get rounds on paper, and centered, before moving to 100m.
@100m, I was about somewhere between .7-1 mrad low (hard to remember, because I had no intent to keep the 25m zero, just adjusted).
@200m, I confirmed that I needed .7 mrad (123 gn ELD-M @ ~2470 fps) of adjustment.
On the flip side, using my 200m zero, I'm only about ~2 inches high @ 100m/150m...
Honestly, under field conditions, that's inside my margin for error as a shooter from anything other than prone supported. As mentioned here, my optic has a zero stop and I am toying with whether to leave that @ 100m or move it to 200m.
Now, all that being said, my greatest experience attempting to shoot multiple distances with one zero is actually using my issue rifle/carbine. I have a healthy appreciation of free-float handguards from the same. Part of the problem is that a 25m zero is poor practice in general, because it can mask errors if you're not shooting dime sized groups. However, if we look at the theoretical PBR 25/300m PBR zero, we note that your best case is being about 5 inches high at your 150 and 200m targets. I admit to not being the best shooter, but I found this not to be an effective PBR zero/trajectory. Just shooting at Ivans w/ either RDS or irons, I needed to make a conscious effort to aim at the base of the target to maximize my hit potential. That's not an ideal hold, either, but I needed/wanted a clear POA reference and "estimate five inches low on this relatively featureless, monochromatic mass" wasn't it.
A 50/200m zero ended up providing me a far more useable trajectory, with far less input required on my part as a shooter. Part of that is because the projectiles is within +/- 3 inches of POA all the way to 250 meters and is no lower (about -5 inches) @ 300m, than a 25/300m zero is high at 150-225m. Accounting for 5 inches of drop between 250-300m is a lot easier for me than accounting for +5 inches in my short-mid range shooting.
These are big targets. An Ivan is, arguably, a much easier target to hit than a deer (for example). I found the +/- 5 inch trajectory tolerance to be far too generous for even this type of shooting, based on my level of skill. It required me to make hold under corrections on the most common targets I was engaging to score hits reliably. I wanted to be able to hold POA centered on my target and make hits - which is what a PBR zero is supposed to support. Moving to a +/- 3 inch 50/200m zero supported that for me. The 300m targets being the least common, it was much less hassle to just hold at the neck/shoulder for that one presentation.
Sorry for the TL/DR...that's how I arrived to my own conclusion on the utility of the PBR zero and what sort of trajectory I'm willing to accept in a PBR zero.
DJ:
Had to read it a couple of times. I doubt your trajectory would be low at 100 given a 25 point of aim / impact. More like about five inches high but won't argue it.
Agree with having to hold low at the 150 and 200 targets with a 300M BSZ. Shouldn't be that way given computer generated data and there are reasons why you had to hold low other than just danger space issues. And high for the 300's. However your experience is more common than not. Which is why I asked how many put paper up from about 25 to the end of their computed danger space and shot a group on each target using a center hold, to actually see what is happening both in terms of trajectory and group size.
Also think your 200 zero would give a higher hit probability given a center hold until you get to 300. Then like you said, a high hold on the 300 targets.
LR55