Rifle Scopes Scope-mounting conundrum

[twadsw01]

I purchased a Bushnell Elite 6500 4.5-30x50mm and a Leupold 1-piece picatinny rail mount to go on top of my Rem 700 5r. The Elite supposedly has 50moa of elevation/windage adjustment range, so with the 20moa rail, I was expecting to have around 45 moa of adjustment to get the projectile to near 1000 yds (playing it close, I know) -> 50moa/2 (where optical zero exists; the point at which the line of site and bore are parallel) - 20moa (rail slant) = 5moa of additional upwards adjustment remaining, and 45moa in the down direction. If I use 2 or 3 moa of adjustment to get the 100yd zero, then I'd expect to have more like 7 or 8moa at the top end remaining.

After zeroing the rifle at 100 yds, I found a few things that were surprising: 1) the scope actually has 52 moa of elevatoin range (not *that* surprising), 2) There is almost 16moa of upwards adjustment remaining instead of 7-8moa, like I would have expected. The rail is a Leupold Mark 4 picatinny (model 59235), and I can't find solid information online about how much cant this rail has to it; I've seen both 1/4degreee (15moa) and 20moa in different places. The package the rail came in says nothing about the cant.

Am I mis-calculating, is the rail really not 20moa, or do these sorts of errors lie within the realm of normal manufacturing variances?

 

[BobinNC]

Re: Scope-mounting conundrum

I love conundrums. OK

1) Your doing it wrong. If your scope has 52 MOA of adjustment, that 26 up and 26 down. Add a 20 MOA base, and you should have 46 up, and 6 down.

2) I have no idea what Leupold does with their bases. Call them and ask. In fact call them three times and average their answers. Only way to be sure with Leupold Customer Service. Some of the folks that answer the phone do not know squat about their products.

3) And yes, manufacturing tolerances between your rifle, bases, rings and scope, and how you mount it all, will have an influence on the answer you really get.

 

[twadsw01]

Re: Scope-mounting conundrum

Alright, thanks alot. I sent a note to their customer service to see if I could get some answers. I suppose some measuring with a micrometer and a little simple geometry might also help me obtain the slope of the rail.

If that rail ends up actually being 15 or so, I reckon I could go with a 25moa base, or maybe even a 30, and still have a few spare moa of upwards adjustment. Even if I used a base with such a cant to it as to not be able to obtain a 100yd zero, I could zero it at a longer range (200, 250yds?) and use the appropriate hold-"under", as it were, for hitting targets at ranges closer than my zero. Right?

Are lots of 1000yd shooters shaking their heads at this post and saying that I should just get a scope with more adjustment range (because I'm using this one pretty close to it's extremes)?

 

[twadsw01]

Re: Scope-mounting conundrum

Okay, I've been told that the rail is 20moa. I guess then, that this problem I'm describing (having more top-end adjustment than I expect once mounting the scope) could occur if what I call the "optical zero" - the elevation setting for which the line of sight is exactly parallel to the bore - is actually not in the center of the scope's elevation adjustment range.

For example, if the "optical zero" on a 52moa scope is actually at 36moa from the maximum "down" elevation adjustment rather than 26moa as it ideally should be, then, once paired with a 20moa rail, I'd have 16moa of adjustment in the "down" direction and 36moa in the "up" direction, rather than only 6moa down and 46moa up. Correct?

Is it even possible for an actual "optical zero" to be that far from the ideal?

 

[twadsw01]

Re: Scope-mounting conundrum

I've been doing a little research and have discovered that, yes, it is possible for what I call the "optical zero" to be that far off from the ideal, b/c of variation in the holes drilled on the receiver, barrel alignment to action, etc. It's not necessary that something be 'off' inside the scope in order to have such a discrepancy between optical (or "mechanical", as I've read a few places in the past few hours) zero and the actual zero.

It seems that what I'm doing then by adding a 30moa base instead of the 20moa base which originally was expected to give me enough range, is compensating for whatever factors have caused the mechanical zero of the scope to be so far off from the expected value. I used a 20moa mount, had 10 moa more down adjustment than expected, so I'm changing to a 30moa mount in order to compensate and reclaim 10moa of upwards elevation adjustment from the "down" end to the "up" end.

 

[gugubica]

Re: Scope-mounting conundrum

Wow, thats cutting it really close.

When you crank the turrets all the way until they stop, are you making sure the reticle is still moving all the way? Sometimes the turrets will still turn, but the reticle quits moving.

I would verify that you actually have 10 MOA of RETICLE travel, not just knob travel.

 

[twadsw01]

Re: Scope-mounting conundrum

I've not verified that there's 50moa of actual reticle travel, but would be sorely disappointed if someone makes a product and advertises that it's got 50moa of adjustment, but it in fact does not.

 

[Urimaginaryfrnd]

Re: Scope-mounting conundrum

When the manufacturer tells you the scope has 50 moa of internal adjustment it is obvious that they made it to only shoot under 600 yds which is the first clue that it is the wrong optic to select for long ranger. Even though you can get to your 100 yd zero and your thousand yard correction you are still working at the extreme limits of what the scope is able to do and that is not really good for the scope long term. You are likely to have problems with the scope over time is it is used close to its limits a lot.

 

[gugubica]

Re: Scope-mounting conundrum

The problem is that if you have to have your reticle at the top of the tube to be zeroed, then you don't have any windage adjustment left. Don't forget, you are dealing with a cylinder, not a box. So, if your reticle is cranked all the way up against the tube, it can not go side to side at all.

 

[gugubica]

Re: Scope-mounting conundrum

On those same lines, you will NOT have the max amount of elevation travel if you have any windage dialed in at all.

 

[twadsw01]

Re: Scope-mounting conundrum

Hmmm, yeah, that makes sense. I'll just have to see where my max range is then with this setup.

It's funny how wide the variation in recommended minimum scope magnification range is for 1k yd. shooting when reading articles and forums. I've read that 10x is "more than enough" in one place, then the very next article or forum entry I check, someone will be talking about "never going below 25x". It's tough to get good information on this, and most normal working folks don't have the dough to blow trying 20 different scopes to see what "works for them".