Rifle Scopes Sight in with 20 MOA tilt Spuhr setup

[Griswald]

Hi to all -

It's my first post on your very informative forum and, in advance, I apologize for what you experienced long range shooters will consider to be very basic, I'm sure. However, my thinking is a little confused at this point and I can sure use your help to clear things up.

I have hunted for many years but mostly short range - maybe out to 400 yards or so. I've always used a standard hunting scope and published ballistics tables to determine approximate holdover and have 'guessed' as to how far to hold my crosshairs up or above the animal's body. I've been very fortunate and have never wounded or lost an animal doing this but it's not my preferred practice. Before too long I'm planning on an elk hunt with my 2 sons and the possible range could be what is quite far for me.

I've recently built up a rifle and it will probably be helpful for me to give you the basic build specs so that you may be better able to help me.
- Mega Arms Maten matched billet upper/lower in .308 Win
- JP Supermatch SS 18" barrel with adjustable gas block and various other components I used to put the upper together.
- JP adjustable fire control
- JP low mass bolt carrier with headspaced bolt
- JP Silent-Captured buffer spring
- Steiner 3-15x50mm police/law enforcement scope with MSR reticle
- Spuhr cantilever mount with 20 MOA tilt

I am at the point where I am ready to go to the range for initial test firing and sight in. Having never used an optics setup this sophisticated I am confused about the following.

When I turn on my laser bore sighter and look at the red dot versus my crosshairs, the crosshairs are very close as regards windage but are very low as regards elevation. In order to get my elevation up to or above my red dot, I have to use quite a lot of my upward elevation adjustment. From my confused thinking at this point, it seems that this is a bad situation as far as the upward adjustment I will have for long range shots after my initial 100 yard sight in.

What am I missing?? There seems to be only one way to properly mount the cantilevered Spuhr setup but I guess I could be wrong about this.

Again, I thank you for your help.

 

[EXTREMEPREJUDICE]

What am I missing??

If I understand your description correctly, the only thing you are missing is how the turrets work. With a 20 MOA base your scope is pointing downward 20 MOA so if your reticle is centered in the tube (half up, half down) your cross hairs should be quite a bit lower (20 MOA, roughly 20 inches at 100 yds) than your point of impact (boresight laser dot.) That allows you to adjust your erector so that the reticle (crosshairs) meets with the point of impact at the bottom of it's travel range. That now gives you quite a bit more travel to raise your POI, of course for longer range as the trajectory of the projectile is dropping due to gravity as it leaves the muzzle. So, by adjusting your turret so that the crosshairs meet the dot you are actually adjusting down, not up. Hope it makes sense..........

 

[Griswald]

If I understand your description correctly, the only thing you are missing is how the turrets work. With a 20 MOA base your scope is pointing downward 20 MOA so if your reticle is centered in the tube (half up, half down) your cross hairs should be quite a bit lower (20 MOA, roughly 20 inches at 100 yds) than your point of impact (boresight laser dot.) That allows you to adjust your erector so that the reticle (crosshairs) meets with the point of impact at the bottom of it's travel range. That now gives you quite a bit more travel to raise your POI, of course for longer range as the trajectory of the projectile is dropping due to gravity as it leaves the muzzle. So, by adjusting your turret so that the crosshairs meet the dot you are actually adjusting down, not up. Hope it makes sense..........

Hello EXTREMEPREJUDICE,

I appreciate your response and I have been traveling so I'm only now able to get back to you. You are correct, my crosshairs are quite a bit lower than my laser dot. When I move the crosshairs up (CCW on my scope) it takes quite a bit of upward adjustment to do so. My scope is mil/mil and, unfortunately, I didn't look at exactly how much I turned the horizontal adjustment before I left town, but it seemed like a lot. Never having done this, conceptually the up is down reality that you point out is very different for me and my understanding is not quite there yet. If I turned my turret CCW in order to move the reticle up to meet the laser dot, doesn't that take away from the remaining elevation adjustment that I have available? If, for instance, if I am sighted in dead zero at 100 yards and I then want to take a 1,000 yard shot, isn't the amount of upward adjustment I have remaining diminished by what I have already taken? Sorry to be so ignorant on this matter but I will learn.

Thanks,
Griswald

 

[EXTREMEPREJUDICE]

Actually it's just the opposite. If your crosshairs are moving up, your point of impact is actually going down. Usually, the markings on your turret indicate the movement of your point of impact but when looking through your glass it's the converse............when your reticle moves up your point of impact (in relation to the reticle, as actually the boresighted POI isn't changing) moves down. My guess is that your Seiner is CW (European Standard) and if so, turning it CCW means moving your point of impact (laser dot) down.

 

[Griswald]

Actually it's just the opposite. If your crosshairs are moving up, your point of impact is actually going down. Usually, the markings on your turret indicate the movement of your point of impact but when looking through your glass it's the converse............when your reticle moves up your point of impact (in relation to the reticle, as actually the boresighted POI isn't changing) moves down. My guess is that your Seiner is CW (European Standard) and if so, turning it CCW means moving your point of impact (laser dot) down.

Again, I very much appreciate your response and your trying to explain this further to me. My Steiner 3-15x50 mm has CCW turrets as per the box (I've heard that this is the case with their US stocked product but I don't know this for a fact). So, visually in the scope, I turned the elevation turret CCW in order to have it appear that it was moving up to meet the bore sighter's laser dot. I'm assuming that when I made this adjustment that my POI will go up versus when the crosshair appeared to be very low. If this is correct, and I stress IF since I already have myself confused, then once I have my rig zeroed at, say, 100 yds, and I want to shoot at a longer range, then I won't I have to rotate my elevation turret further CCW in order to compensate for bullet drop? And, if this is correct, then won't the adjustment I've already made decrease the amount of upward adjustment I have left? I'll get it sooner or later - please bear with me. Thanks

 

[NV Ranger]

Think like this. The red laser dot is the bullet impact. If it is hitting above the horizontal portion of the reticle in real life you would turn the elevation turret in the direction corresponding to moving the bullet impact down, in the case of my Steiner 5-25 it is clockwise. The other way to tell is to see that the number markings on the elevation turret are going down, 14 to 13 to 12, etc. I find it confusing thinking in terms of the reticle movement, it's opposite as previously explained. Think in terms of bullet movement and making the bullet move to the center of the fixed reticle, down is down, up is up, left is left, and right is right, as marked on the knobs.

 

[sib1948]

He seems to be really over thinking this. With a 20 MOA base just zero at 100 yards and you'll have plenty of elevation at usual hunting ranges. This issue only becomes more critical when you're planning on shooting out past 1000 yards as long as you scope has plenty on Mil or MOA elevation adjustment, which I expect your Steiner has. Get some sleep. Then get out to the range and you'll see and I'm sure your rifle and scope combination should shine at your max. planned hunting range!

 

[Griswald]

He seems to be really over thinking this. With a 20 MOA base just zero at 100 yards and you'll have plenty of elevation at usual hunting ranges. This issue only becomes more critical when you're planning on shooting out past 1000 yards as long as you scope has plenty on Mil or MOA elevation adjustment, which I expect your Steiner has. Get some sleep. Then get out to the range and you'll see and I'm sure your rifle and scope combination should shine at your max. planned hunting range!

Thanks to all of you for your input. Your explanations have definitely helped me "de-confuse" my mind. I agree, I have been overthinking this but it's my first plunge into optics with these capabilities and there is a learning curve. Nothing will take the place of range time and I can't wait to spend a day seeing how this setup works.

 

[sib1948]

I'm sure you'll find it much easier when you get to range and start shooting! It really isn't rocketscience. I've been shooting LR for 2 years and am still learning small nuisances every time I'm out. Good luck and always be safe. Remember, if a round doesn't discharge, not to open your bolt for at least a minute and if one sounds or feels "different", always check the bore and make sure it's clear before you shoot another round. Accidents can and do happen, if you're not always on guard!