How High is too High?

[DadsKrag]

I have ordered a new wood stocked Air Venturi Avenger and Leupold 3-9 x 33 EFR scope. Now I have to decide what Burris rings to order.

Given the looping trajectory, I want the best PBR out to 50yds for squirrel hunting.

With .92 "high" Signature rings I can get + or - 3/8" PBR to 50yds computed with FX Hybrid slugs at 40fpe. I can shrink that to + or - 1/4" with the 1.29" "high rimfire/airgun" rings.

Comb height is not an issue as I can use pads to adjust that, maybe eventually modifying the stock for an adjustable comb. I'm familiar with use of Burris "Posi- align Inserts so that will mitigate any issues with adjusting the scope mounting for the very high mounting.

What other pitfalls might I encounter?

 

[dizzums]

generally the higher you go the 'smaller' your point blank range and it moves it further out and you need a larger killzone to be effective say 1" vs .5 .. so for hunting where ranges are dynamic and usually under 50 yards higher is 'not' better and you'll get more precise shots within reasonable ranges if you get it in tighter .. on most guns the mag and scope bell is what limits how tight you can get it and on some the scope mount rail is already retarded-high ... just do what you can ...

 

[bandg]

generally the higher you go the 'smaller' your point blank range and it moves it further out and you need a larger killzone to be effective say 1" vs .5 .. so for hunting where ranges are dynamic and usually under 50 yards higher is 'not' better and you'll get more precise shots within reasonable ranges if you get it in tighter .. on most guns the mag and scope bell is what limits how tight you can get it and on some the scope mount rail is already retarded-high ... just do what you can ...

Incorrect. Raising scope height increases MPBR, it doesn't lessen it.

 

[Deerstalker]

ChairGun chart for my HW95L/Hawke 4-16 x 44 mm scope. Centerline of this scope is 1.75" above rifle bore.

 

[DadsKrag]

generally the higher you go the 'smaller' your point blank range and it moves it further out and you need a larger killzone to be effective say 1" vs .5 .. so for hunting where ranges are dynamic and usually under 50 yards higher is 'not' better and you'll get more precise shots within reasonable ranges if you get it in tighter .. on most guns the mag and scope bell is what limits how tight you can get it and on some the scope mount rail is already retarded-high ... just do what you can ...

Incorrect. Raising scope height increases MPBR, it doesn't lessen it. 

I have generated some trajectory tables for an FX Hybrid .22 slug at 905fps Mv, approximately 40fpe at the muzzle.

I opted to plot the minimum + or - trajectory out to 50yds with a 45yd zero rather than maximum PBR since 99% of likely shot opportunities at squirrels will be within 50yds. It would be unlikely that I could hold steady enough with an improvise rest on the side of a tree in a woodland setting where I would be hunting for anything longer.

I am also keenly aware of the holdover that various mounting heights will require at 10 yds. Therein lies the problem with higher mounting of the scope.

Therefore, I will list the holdover required at 10yds, the trajectory @ 25yds, the yardage of the apex of the trajectory and the drop below LOS @ 50 yds. 



1st up, 1.6" above the bore axis



1.8 above the bore axis



2.0" above the bore axis



2.2" above the bore axis



And finally, 2.5" above the bore axis



Conclusions to follow in edit:



In the 1st example, 1.6" above the bore axis, the critical values are as follows:

• Holdover required @ 10yds; .46"
• Trajectory @ 25yds; +.43"
• Yardage and apex value of trajectory; 30yds/+.50"
• Trajectory @ 50yds; -.41"

1.8" above bore axis:

• Holdover required @ 10yds; .61"
• Trajectory @ 25yds; +.34
• Yardage and apex value of trajectory; 30yds/ +.44"
• Trajectory @ 50yds; -.39"

2.0" above bore axis:

• Holdover required @ 10yds; .77"
• Trajectory @ 25yds; +.26"
• Yardage and apex of trajectory; 30yds/+.37"
• Trajectory @ 50yds; -.37"

2.2" above bore axis:

• Holdover required @ 10yds; .92"
• Trajectory @ 25yds; +.17"
• Yardage and apex value of trajectory; 35yds+.32"
• Trajectory @ 50yds; -.34"

2.5" above bore axis:

• Holdover required at 10yds; 1.16"
•  Trajectory @ 25yds; +.03"
• Yardage and apex value of trajectory; 35yds +.25"
• Trajectory @ 50yds; -.31"

Conclusions? There is no free lunch. While raising the scope above the bore axis gives less arc in the apparent trajectory between 25 and 50yds, it require more holdover on really close in shots.

The intriguing part about the +2.5" scope mount is that the virtual zero range is 25yds. Even though it would require over an inch of holdover at 10yds, this could easily be accomplished by holding just a little below a gray squirrels head to make a solid head shot.

I'm leaning towards the highest practical mount with Burris .129" height rings.

 

[bandg]

Certainly true-no free lunch. Higher mounted scopes can create some issues and solve others. I prefer higher mounted scopes in most cases, both because I can get a more comfortable and repeatable head position (maybe I resemble a bobblehead) with a higher mounted scope (in most cases) as well as because they can extend MPBR just a bit. It isn't a lot physically speaking but just a bit can be noticeable at longer air gun ranges. To me it is an advantage to be able to hold dead on a bit further out. Others might not view that as an advantage. Everyone will have different preferences but higher mounted scopes can create slightly longer MPBR's if one allows the pellet to rise above LOS just a bit-the "2 zero" method of sighting. If one prefers to use "single zero point" sighting then lower mounted scopes can have advantages if comfortable.

 

[DadsKrag]

MPBR's if one allows the pellet to rise above LOS just a bit-the "2 zero" method of sighting. If one prefers to use "single zero point" sighting then lower mounted scopes can have advantages if comfortable.

Just for "fits and giggles", I plugged in 25yd zero. It gives 2 zeros, one at 25yds and another at 45yds. @ 10yds it is just under 1.16" low, @ 50yds it is .38" low .82 low @ 55yds. @ either extreme one could hold off just a bit and assure a solid hit with a hold in a vertical line with the ears. (I prefer neck shots as a center of vitals hold) Hold just above the top of the ears @ 10yds, right on the top of the ears for 55yds. From 20-50yds hold vertical center of the neck under the ears.

 

[Scouty]

I prefer higher mounted scopes in most cases, both because I can get a more comfortable and repeatable head position (maybe I resemble a bobblehead) with a higher mounted scope (in most cases) as well as because they can extend MPBR just a bit.

Are you saying a higher scope over bore position extends the range of the MPBR or that it extends the position of the MPBR further out from the gun? Or both?

When I play around with the basic desktop version of Chairgun a higher scope position seems to shorten the range of the MPBR slightly but puts it further out.

But I'm relatively new to all this so I may be doing something wrong.

 

[bandg]

DadsKrag-

That is how I set my air rifles up but I focus on the intermediate maximum height point since I don't use a program. With the majority of my air rifles, if I set it about 1/2" to 5/8" high at 35 yards then I can hold dead on from just inside 20 yards to around 50 yards and hit squirrel head size targets. Other methods certainly exist and can work just as well but this works for me. My Pulsar HP shooting 13 gr. Monsters allows dead on hold out to at least 65 yards (my common maximum air gun shooting range) when zeroed this way but I'm not sure at what distance it would "fall off" since I haven't checked that yet. But I bet it would be 70 or just beyond as set up. I do use tall mounts and a lower mounted scope on the same gun might move that maximum dead on point to 65, 60, or maybe 55 yards. Not a major difference, just a bit more range to hold dead on and I find the taller mounted scope infinitely more comfortable to shoot. When shooting NSA 12.5's in my Condor with a very high mounted scope, I noticed what seems to be an even flatter trajectory in the 50 yard range out to my 65 yard maximum and wouldn't be surprised if that gun shooting those slugs could reach 80 or beyond for a similar dead on hold. Different strokes for different folks.

 

[bandg]

I prefer higher mounted scopes in most cases, both because I can get a more comfortable and repeatable head position (maybe I resemble a bobblehead) with a higher mounted scope (in most cases) as well as because they can extend MPBR just a bit.

Are you saying a higher scope over bore position extends the range of the MPBR or that it extends the position of the MPBR further out from the gun? Or both?

When I play around with the basic desktop version of Chairgun a higher scope position seems to shorten the range of the MPBR slightly but puts it further out.

But I'm relatively new to all this so I may be doing something wrong.

Both, as long as one allows the maximum acceptable rise above line of sight for the intended target size. If one uses the single zero method it would be a bit different but I never set anything up that way. You might experiment with such using the single zero method and post on what you find.

 

[Scouty]

I prefer higher mounted scopes in most cases, both because I can get a more comfortable and repeatable head position (maybe I resemble a bobblehead) with a higher mounted scope (in most cases) as well as because they can extend MPBR just a bit.

Are you saying a higher scope over bore position extends the range of the MPBR or that it extends the position of the MPBR further out from the gun? Or both?

When I play around with the basic desktop version of Chairgun a higher scope position seems to shorten the range of the MPBR slightly but puts it further out.

But I'm relatively new to all this so I may be doing something wrong.

Both, as long as one allows the maximum acceptable rise above line of sight for the intended target size. If one uses the single zero method it would be a bit different but I never set anything up that way. You might experiment with such using the single zero method and post on what you find.

I'll try to take some screen grabs later this week if I get a chance. I'm not shooting much nowadays due to an inner ear issue so real world results will have to wait.

I'm surprised by what you mention above but it's certainly possible I'm wrong. Probably likely I'm wrong.

I never use single zero either. I stumbled across PBR quite by accident and it worked well for me before I had a chronograph or downloaded Chairgun.

I'd like to know if I'm doing something wrong. Would like to get my guns tuned and set up close to how I expect to use them when I get to feeling better.

 

[bandg]

It's possible you are absolutely correct and I've lost my mind. The above is my view on how it functions and follows from a course in ballistics that I took in the 70's. One very useful method used to illustrate this relationship was taught in that course. Get yourself a piece of white paper and draw a straight line across the length of the page. That represents LOS which is always straight. Then get a transparent sheet and draw a representative "ballistic arc" on it with a marker. It will be relatively flatter near the "muzzle" and gradually curve progressively downward as it moves across. That arc is variable from projectile to projectile based on velocity and weight but is remarkably similar when scaled. Such an arc will relate to your projectile when shooting LEVEL but will vary in shape when shooting noticeably inclined or declined. Then you can lay the transparency with the arc representation over the sheet of paper with the LOS representation and play around with different angles (scope heights) as well as single vs. double zero method, and see how they interact. This might be something that would be helpful. I haven't done such in many decades and maybe I need to refresh myself on it.

 

[Scouty]

I found myself with an extra ten minutes. I put Crow Magnum pellets into Chairgun since I have some and think they'd be a great close range rabbit pellet. Given their low BC relative to weight they likely amplify the effect as I'm visualizing it.

I used the extremes of scope height in DadsKrags posts.

With a 1.6" scope over bore height and a kill zone of 1/2" the PBR is 8.0 to 23.9 yards, or a total of 15.9 yards.

With a 2.5" scope over bore height and a kill zone of 1/2" the PBR is 11.4 to 26.7 yards, or a total of 15.3 yards.

So the scope height increase caused a 3.8% decrease in PBR range.

But the same increase also caused the far, 1/4" low "zero" to be 11.7% further out.

Using your example of overlaying the LOS onto the ballistic arc, I see it conceptually as that PBR slice being taken further out where projectile drop is more significant.

I included screen grabs from Chairgun. Did this quick. Would like to know if I'm doing anything wrong.

 

[bandg]

All I can note is that there doesn't appear to be much (if any) rise over LOS in your stuff. I don't use that platform at all so I'm not familiar with it. If I recall correctly, the more rise over LOS that is allowed, the greater the advantage to the higher mounted sight. I don't disagree that any such changes will move the effect closer or further away in range. But I stand by my view that a higher sight can allow a longer MPBR.

 

[tracker1955]

The new wood-stocked Avenger looks to use the same but re-machined stock as the Nova Liberty, with the normal high rings required to clear the magazine, the cheek rest needs to come up 3/8 to 1/2 inch. I put a Goda Grip cheek pad on my Nova Liberty and really like the comfort of the soft rubber pad. Well worth the $20 cost.https://godagrip.com/cheek-pads-2/

 

[bandg]

I'm going to offer an apology to dizzums. He was correct about MPBR as the term is strictly defined. That being from the nearest point you can hit a given target with direct hold on to the longest distance you can do the same. Coming from a background of firearm shooting, extremely short distances are often overlooked and the focus is on performance at the longer usable ranges. I personally view my airgun shooting similarly and rarely shoot at extremely close ranges with anything scoped but I realize that many will not view it this way and they are correct in that view.

That said, a higher mounted sight will, in almost every case, allow a longer maximum range (distance, not span) shot for a direct hold hit given the same gun, projectile, and target size than will a lower mounted sight. The span (nearest to furthest) of such MPBR is often shorter for the higher sight because a lot of the nearest distance (10 to maybe 15 yards) is discounted in the calculation since you hit LOW at those very near distances. But this is an airgun forum and such extremely close range shooting is important to many and should not be discounted.

If one regularly shoots inside 15 yards, having a sight mounted as low as possible can be an advantage. Ability to get the eye comfortably behind the sight is pretty important for such. But as noted, if one never shoots at extremely close distances with their scoped gun then the higher sight will, in almost every case one can check, provide a few extra yards of "dead on" range given the same gun/projectile/target.

 

[DadsKrag]

I found myself with an extra ten minutes. I put Crow Magnum pellets into Chairgun since I have some and think they'd be a great close range rabbit pellet. Given their low BC relative to weight they likely amplify the effect as I'm visualizing it.

I used the extremes of scope height in DadsKrags posts.

With a 1.6" scope over bore height and a kill zone of 1/2" the PBR is 8.0 to 23.9 yards, or a total of 15.9 yards.

With a 2.5" scope over bore height and a kill zone of 1/2" the PBR is 11.4 to 26.7 yards, or a total of 15.3 yards.

So the scope height increase caused a 3.8% decrease in PBR range.

But the same increase also caused the far, 1/4" low "zero" to be 11.7% further out.

Using your example of overlaying the LOS onto the ballistic arc, I see it conceptually as that PBR slice being taken further out where projectile drop is more significant.

I included screen grabs from Chairgun. Did this quick. Would like to know if I'm doing anything wrong.

You didn't do anything wrong. You used an 18.21gr pellet with a BC of .012 @ 550fps while I am using a 22gr slug with a BC of .08 @ 905fps. Your combo is tailored to rabbits which will favor the short range ballistics while I am setting up for squirrels which will require an edge at the far extremes of PBR.

While it is true that the higher sight mount does reduce the distance of + or - PBR slightly, the higher sight mount favors the longer distance shots at the expense of the short range holdover needed.



I would be interested in seeing what your program comes up with for a + or - PBR of .38" with the projectile weight, BC and MV data I used

 

[DadsKrag]

OK, I found a MPBR calculator. It only shows a table, no graph, but it has the pertinent data.

Target size .75" (+ or - .38")



1.6" scope mounting height;

Minimum PBR = 11yds

Maximum PBR = 46yds

2.5" scope mounting height;

Minimum PBR = 17yds

Maximum PBR = 52yds

It appears that both mount heights share the same 35yd min/max PBR distance. The higher mount just moves that distance out 6yds.

 

[DadsKrag]

The new wood-stocked Avenger looks to use the same but re-machined stock as the Nova Liberty, with the normal high rings required to clear the magazine, the cheek rest needs to come up 3/8 to 1/2 inch. I put a Goda Grip cheek pad on my Nova Liberty and really like the comfort of the soft rubber pad. Well worth the $20 cost.https://godagrip.com/cheek-pads-2/

Since the "tactical" rings I am using are about 3/8" higher than regular high rings, I'll probably need about a 3/4" comb pad.

Thinking about this until I can do some stock work.



E-BAY LINK

 

[tracker1955]

That should work if you're ok with the appearance, I'm just not a big fan of the whole sock on the back look, that's why I prefer the self-adhesive pad. If it's comfortable to your face and your eye aligns properly for a good sight picture, those are the most important things, appearance is secondary. I think the Avenger has the potential to be a great entry-level gun but they gotta get the air leaks straightened out, and they still need to address the crummy poppet design.