? About mounting an scope size

[Shaner72]

Hi.. I was looking at the Bushnell Ellite 6500 2.5-16x50. The dealer at the store suggested I go with the same scope but in a 42 this will get the scope closer to the barrel and would be better than the little bit of extra light the 50 would let in. I will be hunting some varmints and target shooting with it. Looking for some advice on what he told me.

[jhelmuth]

Take two parallel lines (one is the scope axis - the other is the barrel axis), separate them 2" to 2.5" and then find the angle of adjustment necessarry to have those axis cross at an impact point 100yards away. Now move the axis of the scope 4mm higher (less than 3/16"). Now recalculate that angle of adjustment. ...not much change - is it? (~ .150 MOA or 1/2 of one click on a typical 1/4 MOA adjustment)

So does that mean that there is little or no diference. No. But it does beg the question, "What is the big deal? How does this affect my setup and how I shoot?" That depends on how "far" you shoot (the range) and how much adjustment your scope has. Lower is better, but I don't think you're buying much with a 4mm reduction in height (1/2 the distance of the two objectives: 50mm - 42mm = 8mm / 2 = 4mm).

Myself - I would take the best/brightest of the 2 scopes (all else being equal other than the argument for/against the 4mm difference in height).

This would make the assumption that you do not need to change scope ring height significantly (more than 5mm). My guess would be that the scope bore axis will not change significantly and may not be even 4mm diff. in height (depending on how far off the barrel the 42mm would end up).

[pitsnipe]

Take two parallel lines (one is the scope axis - the other is the barrel axis), separate them 2" to 2.5" and then find the angle of adjustment necessarry to have those axis cross at an impact point 100yards away. Now move the axis of the scope 4mm higher (less than 3/16"). Now recalculate that angle of adjustment. ...not much change - is it? (~ .150 MOA or 1/2 of one click on a typical 1/4 MOA adjustment)

So does that mean that there is little or no diference. No. But it does beg the question, "What is the big deal? How does this affect my setup and how I shoot?" That depends on how "far" you shoot (the range) and how much adjustment your scope has. Lower is better, but I don't think you're buying much with a 4mm reduction in height (1/2 the distance of the two objectives: 50mm - 42mm = 8mm / 2 = 4mm).

Myself - I would take the best/brightest of the 2 scopes (all else being equal other than the argument for/against the 4mm difference in height).

This would make the assumption that you do not need to change scope ring height significantly (more than 5mm). My guess would be that the scope bore axis will not change significantly and may not be even 4mm diff. in height (depending on how far off the barrel the 42mm would end up).

This is a very good answer to your question. And I would add/concur that all things being equal (scope bell to barrell height) I would get the 50 mm. That little bit of exit pupil size/light (with the same 16X would be 2.5mm to 3.1mm exit pupil) can come in handy sometimes.

[jhelmuth]

I would add (for clarification) that IF the 2 scopes end up with the same bore axis (IE - no difference between them), then there is absolutely no reason to go with the smaller objective (unless tht scope happens to be betterbrighter (which typically would not be the case unless there is a significant difference in the glass - and thereby the quality/cost)

All the best!

Jim

[Shaner72]

Ya makes sence thank's for the advice guy's.

[fgw_in_fla]

Geez... For a moment I thought I stumbled into Mr. Helmuth's Trig 101 class by accident. Excellent explanation. I always go by what my eyes & shooting abilities will allow.

Do they make a scope with a 10 or 12 inch oblective?

By the way... How goes it there, Mr. jhelmuth? I hope all is well on your end.
Frank in Fla

[jhelmuth]

Thanks for the kudos Frank (I'll take all that as a compliment) ;D.

Things are great. I haven't been able to get out to shoot as much, but I'm hoping to maybe put a few rounds of .223 down the 100 yard range tomorrow morning if I can sneak out for a couple of hours...

Hope you have been well. Love to get a chance to shoot with you sometime...