Belt Fed said:
Are these things designed to be near spot on once a distance has been set?
Example:
I have it set to 1 for 100 yards. If i successfully sight in at this distance, when I rotate the drum to 200, will the POI be near center?
...once zeroed with the "correct" ammunition the range marking will be perserved to be "near" spot on...that particular diopter "appears" to be a Swiss rear diopter for the 55x series of rifles...
...there are several ways you can zero her...
...first off...when using a diopter sighting system...you need to " ensure that the periphery of the foresight tunnel and the diopter aperture are concentric."...the front sight post should be roughly in the center of the foresight tunnel in order to get the proper sight picture...likewise...as with most diopter systems...you shoot POA=POI with the front sight post's top "center over target"...all elevation adjustments to zero the weapon are made with the rear sight only...the 100 meter setting is your CQB setting...
...if i remember correctly...these particular diopters are calibrated for the GP 90 cartrage...and will work "relatively" well with ammunition with a muzzle velosity of "roughly" 3000 fps and that have a ballistic coefficient of about .330...the greater the deviation from these perameters...the larger your striike error will become in elevation...especially as you increase the range...
...one way to zero them would be to initially use your "near zero" to establish a rough "far zero"...and then "always" confirm your far zero at the appropiate range...ie at crossover...
...it is preferable to zero the weapon at 300 meters...POA=POI...using the 300 meter aperature...to start...set up your target at ~ 33 meters and fire POA=POI...then move your target out to 300 meters and confirm...adjust as necessary... you will have to adjust your elevation and most probably your windage...but less on the windage...after you zero at 300 meters...leave it there...
...you can also shoot POA=POI @ 50 "yards" using the 200 meter apperature...same as before...confirm at 200 "meters"...you "may" be a little off at 300 meters using this method...but will "probably" shoot more accurately at closer ranges "depending" on the ammunition you will be using...and it's velosity and BC...at short ranges the velosity and ballistic coefficient won't be so much an issue as it will at longer ranges...
...to "half ass" perserve the range markings on your rear diopter...i recomend...to start with...using a FMJ lead projectile of between 60 and 64 grains developing a muzzle velosity of roughly 3000 fps...this would mean that the barrel length will need to be at least 16 inches or longer in most cases to get the best results...
...to give you more flexability in the choice of your ammunition...i would zero @ 50 "yards" POA=POI as before...adjust and confirm @ 200 "meters"....with the ammunition you will be using..and hold over/under as needed @ 300/400 yards...using the 200 meter aperature...you never know though...the 300/400 meter aperature may bring you close...doesn't hurt to try them...
...i hope some of this makes sense...