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Leupold TMR reticle?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/28/2009 at 14:31
Kray View Drop Down
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OK.  So I kind of gave up on the idea of mounting a scope on my carry handle and decided to re-build with a flattop receiver.  I was looking at the Leupold MR/T with the TMR reticle and noticedit had holdover marks for a 5.56 77 grn SPR round.
 
My problem is I can't seem to make the ballistics work.  When I try to cross reference the data, it seems to be off by quite a bit.  I was using a ballistics calculator and assuming a 77 grn BTHP bullet with a B/C of .372 running out at 2750 fps.
 
I wonder why the TMR holdover doesn't compute with my calcs?  Am I using the wrong specs for the round?    What is the assumed zero range for the TMR to come up with the holdovers marked?   
 
Anybody else utilize this TMR with 77 gr rounds and find the hold overs correct? 
 
Could I possibly ask more questions?
 
Kevin Loco
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/02/2009 at 18:42
Urimaginaryfrnd View Drop Down
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Now you've opened a can of worms.  Different barrel length change the velocity. Different ammo changes the velocity and trajectory.  For BDC knobs to be accurate you have to calculate them for the ammo you will be using as well as elevation and temperature.  http://www.kentonindustries.com/
Kenton Ind will engrave knobs to your specs.      Jump and Spinproblem solved.
 
As far as the reticle goes if you are using the marks for holdover go to the range shoot three shots at the same target at 200, 300, 400, 500, 600 all holding the center cross hair on the center of the target.  Take a can of spray paint and mark where the holes are on the paper then go  back to those distances and write down which line on the TMR corresponds to what distance at each range.  Note like all BDC it only works if the power of the scope remains constant usually done at the highest power.  But you can have a table for the highest power and a table for the lowest power made up very rapidly.


Edited by Urimaginaryfrnd - March/02/2009 at 18:48
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/02/2009 at 19:59
supertool73 View Drop Down
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That reticle is just a mil based reticle.  It is not calibrated for a single load.  You need to create a load and then figure out what your drops are and then u can use the mil marks to shoot for distance.  http://www2.leupold.com/products/reticles_SPR.htm  That is why you cannot get your data to fit it.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/02/2009 at 21:48
Dale Clifford View Drop Down
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the mk 262 spr load will need about a mil at 200m but its velocities are closer to 2650, around 2mil at 300 and 3 mil at 400 m. which makes it a load calibrated to a reticle. (mildot).  the set up works well and here is drop chart showing  the drop in mils.

 

Trajectory
Input Data
Ballistic Coefficient: 0.350 G1 Caliber: 0.224 in
Bullet Weight: 77.0 gr
Muzzle Velocity: 2650.0 ft/s Distance to Chronograph: 10.0 ft
Sight Height: 1.50 in Sight Offset: 0.00 in
Zero Height: 0.00 in Zero Offset: 0.00 in
Windage: 0.000 MOA Elevation: 0.000 MOA
Line Of Sight Angle: 0.0 deg Cant Angle: 0.0 deg
Wind Speed: 10.0 mph Wind Angle: 90.0 deg
Target Speed: 10.0 mph Target Angle: 90.0 deg
Temperature: 59.0 °F Pressure: 29.92 in Hg
Humidity: 0.0 % Altitude: 0.0 ft
Vital Zone Radius: 5.0 in
Std. Atmosphere at Altitude: No Pressure is Corrected: Yes
Zero at Max. Point Blank Range: No Target Relative Drops: Yes
Mark Sound Barrier Crossing: No Include Extra Rows: No
Output Data
Elevation: 1.185 mil Windage: 0.000 mil
Atmospheric Density: 0.07647 lb/ft³ Speed of Sound: 1116.5 ft/s
Maximum PBR: 284 m Maximum PBR Zero: 242 m
Range of Maximum Height: 135 m Energy at Maximum PBR: 627.8 ft•lbs
Sectional Density: 0.219 lb/in²
Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(m) (mil) (mil) (mil) (mil) (ft/s) (none) (ft•lbs) (s) (mil) (mil)
0
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/04/2009 at 21:28
Kray View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: January/08/2006
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Thanks guys.

I appreciate the input.  Looking at Dale's, data my ballistic calcs. were quite a ways off.
I was working off estimates, not actual 262 data.
 
 
 
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