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SFP mil dot calibration


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#1 Miseryguts

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Posted 14 June 2017 - 07:14 AM

Hi, I have a nice old weaver scope on a 22 rifle. The reticule is mil dot at x24.
Now the trajectory of the 22 means that I often need to hold over/under by fractions of a mil, so I know that if I turn my mag down to x12, I have a 1/2 mil dot reticule, but how accurate is that?? (I know I could make a barber pole and set it up at 50 or 100 yards and check it, but it is easier and quicker just to ask!!)

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#2 terryh

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Posted 14 June 2017 - 12:04 PM

MG,

 

Have you got that the right way up??

 

SFP the ret stays the same and the target gets bigger/smaller with zoom, so halving the zoom and the ret will cover more of the target - or am I thinking this out wrong (would have to go away and draw it perhaps?)

 

 

T



#3 gbal

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Posted 14 June 2017 - 02:54 PM

All to easy to muddle/express none too clearly.
Check your SFP old scope is SFP (very likely in old Weavr-as per Terry's advice)
Check that the 'mildots' are indeed one mil dot apart-and at what magnification-it won't be at all....
The space between two 'mil dots' should be I mil/3.6 inches at 100y (military dots rather than mils dot might help)-remember the dots were not designed to be exact ballistic drops or for 22 rf-though later there were dedicated BDC reticules for 22rf-one size nearly fitting all...(the dots/hash marks did correspond to fixed distances-often marked on the reticule....fixed mag keeps it easier- but:
Changing magnification -esp with a SFP scope and a large mag range-is a recipe for errors in field shooting,unless the shooter is uber familiar with drops etc and that rig/ammo and the scope's calibration.

Fortuitously,most 22rf ammo sighted in at 100 zero will close to 3.6 inches high at 50yards (Eg Eley 40g@1058fps is 3.6";Eley subs @1065 is 3.9".That might be made useable.....BUT....an SFP scope is only calibrated correct at one magnification-hopefully you know which on your old Weaver-the barbers pole will tell you-if it's at top mag,you may want to redo for maybe half that X-if top mag is too much-your choice,but you have to remember it-put a tipex dot on the mag ring...

There is NO SUBSTITUTE for actual live fire shooting with your 'barbers pole' and targets,to check just what YOUR (old) scope does and at different magnifications.... Your ammo should be close to 2.2 high at 25y;3.9 at 50y,3.2 at 75y with zero at 100y-that's Eley subs data,but almost all normal 22rf data is very close to that. If you want a sensible 50y zero,then you'll have to check your drops etc-or get some 50y zero data.
It's not actually that difficult-and the drops are small for 22rf /100y ...well under 4 inches max (a bit variable with zero distance)but it neeeds careful set up...based on a decent sample live fired -your bullet dispersion at 100y will be maybe 2+inches,so you need quite a few shots to get some idea of average drop group centre...do it once,properly-it's not expensive ammo,compared to missing.

Worth googling 'SFP mil dot use in a 22rf'-you'll see that opinions vary-as does understanding....and so do scopes....esp older ones,which may well have good glass....you just need to know your beast...

gbal

#4 Miseryguts

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Posted 14 June 2017 - 03:15 PM

OK, I thought it might be wishful thinking< the Barber's pole it is then!

ATB MG



#5 Miseryguts

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Posted 14 June 2017 - 03:18 PM

Should have also said, yes it is SFP, and yes Weaver have confirmed it is mil dot at x24 as I said in the OP



#6 gbal

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Posted 14 June 2017 - 04:34 PM

IT helps to have that info from Weaver.
The snag here is really it's unlikely anyone will have drop data/mil dot adjusts for a mag as high as 24,for rabbit shooting.
I has to be possible to use the mil dots-but it will have to be checked out by sooting-and if you have Hyper vel ammo (why?) It changes a tad...range dependent. t will be tricky to change mag,whatever s the dot calibration will only be 'on' for one mag..
cf a true mildot su tends 3.6'at 100y-just what is needed,in one sense...but at what mag in a SFP scope....for that scope 12x would be 7.2 inches....but then you see the I other issue....we only need 3.6 inches....which is rather small for most hi mag scopes....and especially over the top if the calibration is at top mag....
Thee will be a mag/dot-or part dot that fits-but it will really have to be fire tested....as must any such fine tuning-rifles/amo/slopes and shooters just differ!...add in Field of View,if that matters,and well ..you see how it gets a lot of bother for a small click/hold over solution.
I read once of. a (us) shooter who claimed to have 50y zero,one mil dot up for 75,two for 100,and three for 125....but he didn't give the scope detai;s-critically at what mag....so the net etc can help but doubtful for high mag....
I tried differnt rilfes/scopes-up to 24x,some with dual stadia lines,to avoid dot blotting out too much of the bunny! "Better" cartridges -etc etc...the golf clubs solution-have a good caddy,or take the rifle that is set for the modal distance on that ground, more expense of course,then eventually a cf-flattens enough out t0 250 y-again ,at a price,though then the higher mags have some utility....
Maybe someone will do the math,if given all the details,or have the experience...if not,there are more boring things than shooting/sighting in one's favourite rifle/scope combo.....and ethically reaping the benefits thereafter :-)

gbal




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