How Accurate are Range Calibrated Turret Knobs?

Discussion in 'Long Range Hunting & Shooting' started by Ingwe, Jul 20, 2018.

  1. Ingwe

    Ingwe Well-Known Member

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    For example the knobs made by Kenton Industries and Swarovski, which are made with range in yards inscribed on the knob.

    Assuming that the data you provide them such as velocity, BC, scope height above bore, temperature, elevation above sea level is 100% correct, how accurate are the turrets?

    I do understand that the only way to be 100% sure is to see where your bullets land but generally, how accurate are the calibrations?

    Thanks Fellas!
     
  2. dok7mm

    dok7mm Well-Known Member

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    I think they are, but only at one set of conditions and one load. I never wanted to handicap myself like that.

    You could could set up a generic elevation, temp and humidity to try to cover a wider range OR set up multiple turrets for different locations & conditions. That said, dope cards are more accurate and cheaper or use a ballistic app.
     
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  3. Ingwe

    Ingwe Well-Known Member

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    Thanks for the response:)

    I should have added that I do only use one load and will use the gun in the same conditions.

    Thanks for mentioning that.
     
  4. codyadams

    codyadams Well-Known Member

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    If you keep your ranges within reason, and hunt with the same load around the same time of year, it should be close enough. Keep in mind though, I would not stretch it much farther than 600 yards. Beyond that, say 800, simply the difference in weather and therfore air pressure from one day to another can make enough of a difference to miss or be dar enough off your mark to possibly wound the animal.

    Best solution, get the kenton knobs with the etched range, as well as the MOA markings at the bottom of the turret. Use the yardage for quick shots 500 and closer, and a ballistics app and dial your MOA for farther shots. Plus if you do happen to change your load, you aren't stuck with a useless turret.
     
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  5. Ingwe

    Ingwe Well-Known Member

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    Thanks Brother.

    So you are saying that past 800 it might be off enough to miss/wound a deer-sized animal? I thought that it would be a matter of an inch or two.
     
  6. BallisticsGuy

    BallisticsGuy Well-Known Member

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    Like the man above said, keep your ranges limited to half a kilometer and under and you're golden for the most part. Going past 500m with a BDC after game or steel (unless the BDC is properly calibrated to the conditions of course) is IMHO just asking for a bad time.

    BDC's are "correct" for one atmospheric condition only but you'd be surprised how broad that one condition can actually be. As you stray from that conditions set in temperature or air pressure they (BDC's) get less and less accurate and as ranges increase they also get less accurate. Those two growing inaccuracy curves add to each other.

    Now for the numbers. Given a solid zero, even with a 130F temperature change (which is equal to a few thousand feet of elevation gain) you're looking at:

    .25MOA delta from a super fast and high BC screamer like a 105-115gn 6mm at >3K fps.

    With a .30 cal with 175gn JHP's at 2750 it's about 1.5MOA (around 7-8 inches).

    With something that's comparative ballistic garbage like a .223 77gn SMK load at 2850fps you're looking at about 2MOA (.6Mils or ~10") of POI change going from 0F to 130F.

    So if you were to base your BDC on a 60F temp and a particular barometric pressure, then you're pretty much within .3Mil (1MOA or about 5.4") at 500yrds in any temperature you might consider shooting in provided that the barometric pressure is the same. You increase that error with elevation change but you can go 1000' up or down and still be within a click or 2.

    If you'd like to get into racing some paper for simulation purposes I'm happy to help. PM me and we can chitter chatter about specific conditions, distances and ballistics.

    500m is where I call the line on shooting at stuff that bleeds with a BDC. My personal limit. After that I'll calculate a dial + hold firing solution specific to the conditions.
     
  7. codyadams

    codyadams Well-Known Member

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    I'll show you pictures of a ballistic calculator for example. It will be same elevation, but different temps and pressure for say a snowy, 15° day and a warmish, 65° sunny day. These are changes you will encounter. Very easy swing here in Wyoming during elk season.... Screenshot_20180721-085722.png Screenshot_20180721-085732.png These two are with pressure, temp, and humidity from a 15° cold day, snowy or foggy, and low pressure. Screenshot_20180721-085934.png Screenshot_20180721-090023.png And these are the same location, same ranges, same gun and load, but a pleasant 65°, sunny, high pressure low humidity day. At 500, there is a difference of .5 MOA in impacts in the two days, or 2.62". So, still close enough for hunting purposes. However, at 850 yards, the difference is still .5 MOA, but impacts differ by 4.45", and this is with a highly efficient load (147 eld-m @3040 fps) if you are shooting something less efficient, the differemce will be more.

    Now, you can help yourself out by finding the median temperature, elevation, station pressure, humidity, ect., and use that to calibrate your turret, and you will be close. Still though, wind direction can effect this in a significant mannor, cross vs. Head vs. Tail, and it all adds up. Plus left or right wind with spin drift added to your left to right but subtracted from your right to left.....if your shooting past 500 or so, just use a calculator and input an exact number to your turrets to ensure a good hit. This 500 number can increase or decrease based on a few things, are conditions close to your calculated turret, is there very little wind, ect.

    You will have to use your best judgement, but generally, if you are 500 or farther from a critter, you will have the extra 30 seconds to 1 minute to use your phone app to get an exact dope. We strive for good first round impacts, give yourself every chance you can.
     
  8. Ingwe

    Ingwe Well-Known Member

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    Incredibly informative responses fellas, thank you SO MUCH!

    I think that I will limit my shooting to 500yds;)
     
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  9. Patrick Traynor

    Patrick Traynor New Member

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    Lots of eye opening reply’s, thanks to all.
     
  10. Buzzsaw

    Buzzsaw Well-Known Member

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    Cody is correct on these turrets. I had Swarovski create one for my Z6, 5-25. It's on my Barrett Fieldcraft 6.5 Creedmoor. So far I have dialed it to 300 and center hit steel. The turret goes to 600, as this is a hunting rifle. I will take it to 600 soon to see if it stays accurate.

    IF I were to want a 1000 set up then I would go to dialing dope.
     
  11. Allen Kitts

    Allen Kitts Member

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    I think it depends on the rest of your setup. I have a Nightforce NXS 5.5-22-50 with a range dial made for my ballistics and am using a G-7 Ballistic rangefinder which has a built in weather station which makes all the calculations for you. Just dial and shoot. I can tell you out to 1400 yards I would not want anyone shooting at me with this set-up. As with any set up though you should always shoot your rifle and take down your ballistics findings and always check them against a ballistics program. This particular system has worked for me for the last ten years or so with no flaws whatsoever. As long as you can get a good wind speed reading and direction the range finder even give you the moa hold off for that. Don't get me wrong, its the day in and day out practice that makes you a better shooter but having the right equipment sure does help!
     
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  12. lyotehunter

    lyotehunter Well-Known Member

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    If you take your time to get detailed info. They work perfect.i have some that are a stick on label that work but i shoot to 1000yds.record velocity,temp ,altitude,humidy,all info about the bullet etc. Then you must go shoot and do some final adjustments the more you shoot the better it gets.then shoot before the hunt etc. And make sure everything still s correct.
     
    Last edited: Jul 26, 2018
  13. hhonker74

    hhonker74 Member

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    My CDS was accurate to 500yds on my .243 win VX-3i. I haven't shot farther as its my hunting rifle.
     
  14. Bman940

    Bman940 Well-Known Member

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    Excellent answers! That is why LRH is one of my favorite sites to visit for information. I use 3 custom turrets for my Nikon XR scopes. As stated above knowing the limitations and uses is very important if you want real world accuracy in the Fall compared to dialing the scopes in in May. I talk to a lot of folks about custom turrets and like the ballistic's screenshot above, knowing the conditions you will use your rifle in makes a huge difference. Entering that data you will encounter at 7000 feet or in my case, frigid Kansas is a key factor. A big question I get asked a lot is can I use the MV stated on the box. Um, no. Chrono your load, as we all know, with any program the more accurate the data entered the more accurate our results will be. I also have a .243 that I have 2 custom turrets for, one for deer hunting and one for 55 gr . predator hunting. If you lie the idea of dialing in your shot to a ranged distance, a custom turret is a great way to go. Great thread!