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All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: YEMX on August 26, 2014, 05:57:01 AM
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A lot of you may or may not know what Maximum Point Blank Range (MPBR) is, and if you do you may not use it, or agree with the idea of it. This post is for those of you that do/have used it. More specifically, those of you that may have used an online calculator somewhere on the web to figure out what your MPBR is. I've been using the shooterscalculator.com MPBR calculator, and once I plug in all the factors, I'm getting:
Near zero: 12 yards
Far zero: 22 yards
Minimum PBR: 10 yards
Maximum PBR: 23 yards
I'm not going to worry about the 100 yard zero, because it's ridiculous. -81.something inches low or some such. If I'm reading the results correctly (which I'm probably not) I can zero my airgun in at 12 yards- double checking my zero at 22 yards? The minimum I can shoot is 10 yards, and the maximum I can shoot is 23 yards? Am I reading this chart right? I know it's a noob question, but I just want to throw a simple 4x32 scope on my yard gun (for rats and other small pests), and zero it quickly, and be able to shoot targets at varying distances. I built it to be a little over 12 fpe, and to be honest, it's mostly for plinking, and if the opportunity presents itself, I'll take out an english starling or a rat. I've got other rifles that will take care of anything larger! I set the target size to .25, so technically as long as I do my part, and have sighted it in well, it shouldn't shoot higher or lower than a 1/8" at the given yardage. Again, technically, is this correct? I kinda want this carbine to be a set it and forget it kind of rifle... Well, I'll double check it occasionally of course, but for the most part, set it and forget it. Thoughts?
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You can shoot and hit your target between 10 and 23 yards without a hold over.
Same numbers as my Mac1 1322.
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Go to American Airguns trajectory calculator. Type in your data, then hit calculat. .. Great tool... Set your starting range at 10yds, zero range at 22 yds. You'll need to know your MV and ballistic coefficient. They do the rest. As a general rule, a 10.5gr dome has a BC of 0.025. Have fun !
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It's not so much that you can't shoot close, but that you'll be shooting below your point of aim at close distances. Whatever the scope is above the barrel at really close. If you plan on shooting mostly close I would tighten up the MPBR a bit. It's designed for maximum, but you can tweak it. It's easy to do so in Chairgun which is free. The idea of MPBR is to provide you with a range of distances that you can just aim by the cross-hairs. It's a range of distances through which the projectile doesn't deviate very much through a vertical window; in reality it comes up into the window, goes to the top of the window and then descends down to the bottom again. A typical airgun window is 1", which at the top is going to be shooting half an inch high and at the short distance and long distance will be a half an inch low.
With firearms it works the same way, but the distances are much greater, so the zeros might be 150yd and 350yd and you know that at less than 150yd your going to hit a bit low (up to scope height at real close). But then you may not want to take shots farther than 200yd (accuracy drops off, less chance of a clean kill), in which case you could adjust your PBR to less than maximum and get a tighter vertical window that is more more on closer (perhaps dropping that 150yd to 50yd). Then you'd be effectively flat shooting from 50-200yds. If you then wanted to make a long shot at 400yds, you could always take your time and figure in the drop. Chairgun lets you know the drops at any distance you want.
It all depends on where you want to shoot. My point is that if a 23 yard shot is unlikely or feels risky, you can always tighten up the MPBR to PBR and have a flatter close in vertical spread. Perhaps be right on from 5 to 15 yards.
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The concept of PBR is tied into the "Kill Zone" (KZ), which is a circle in which you want your pellets to stay.... It is built into ChairGun and I use 1/2", which means the trajectory will stay within 1/4" below (closer than the near zero), 1/4" above (between the two zeros) and 1/4" below (past the far zero) in calculating the PBR.... If you use a larger KZ, like you would with a PB on Deer (eg. 4") the trajectory will be further above and below the zero POA line.... With a 1/2" KZ, your pellets should stay within 1/4" above or below your line of sight between the minimum PBR and the maximum PBR, the distances in between would then be your "point blank range"....
If you chose a KZ larger than twice the height of your scope (common on PBs) then there is no minimum PBR, it is at the muzzle, which is why PB calculators only talk about the maximum PBR, which they term the MPBR....
Bob
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Don't forget kill-zone size. A 1/2" KZ will result in a much shorter MPBR than a 1" KZ. In Chairgun, (using the Optimum Zero function) I use a KZ of 1" for a PBR of 12 yds. to 46 yds. Change to 2" and it goes from 6.5 to 56 yds. At 1/2" it goes from 16 to 41 yds. All with the same pellet and MV.
Was typing this as Bob was posting his. Sorry for the redundancy, but it is that important.
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try Chairgun...
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Thank you all! I've just downloaded Chairgun, I'll be fiddling around with it as soon as I can get some real free time!!
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Chairgun is a long standing program, that you'll be impressed with. Well worth your time.