GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: Wolverineshooter on October 27, 2017, 01:00:04 PM
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I read somewhere that you should put the scopes as close to the barrel as you can. That's what I have always tried to do. But on a second thought does it really matter much?
I used the Chairgun and did some calculations. Raising the height by .5 inches may push the zeros further by two to three yards, the pellet drop at 100 yards will be reduced by 2 inches. Which could be a good thing since most hunting or paper Punching are more than 10 yards away anyway.
So I am wondering what are the rationals for keep the scope low? Certainly the torque on the rings will be lower with lower ring height and less shock to the scope. Is this why people want to keep the scopes low?
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Well I found something that makes sense to me.
There are good reasons not to mount a scope as low as possible. The reasons I can see for keeping a scope as low as possible above the bore include minimizing the torque on the rings when the gun is fired, making the scope less likely (maybe) to get caught on brush while being carried, and perhaps to keep the shooters head as low as possible on a battle rifle.
The main concern as to how high a scope should be mountd in my opinion is that the scopes optical axis should be comfortable for the shooter. Either too low or too high will be uncomfortable and won't give a proper "cheek weld" . If "tight to the barrel" is the most comfortable position maybe the rifle's stock needs a higher comb. Obviously the shape of the stock's comb relative to the bore matters. So does the relative shape of the shooter's face, neck, and shoulders, so there's no "right" answer to the exact distance a scope should be mounted from the barrel. On certain classes of firearms a scope needs to be mounted beside the barrel, not above it. An example is a shoulder fired recoilless rifle, or grenade launchers like the M70 and M203.
Reasons for raising the scope include the fact that if a rifle is set up to maximize the "point blank" range such that from zero out to some maximum distance a bullet will fall in a given diameter circle if the sights are aimed at the center of the circle, then the scope height above the bore should be equal to the radius of that circle. That could be rediculous if a very large or very small point blank error diameter is desired but it makes sense for a 5 or six inch diameter circle.
Mounting a scope high also puts the bore lower relative to the shoulder, and assuming the stock is designed for it, reducing the rotational recoil moment when a gun is fired. That helps reduce muzzle flip. The AR-15 is an example of a rifle designed with this and the previous reason in mind. The M14 and M1 were not.
Another reason to keep the scope high is that thermal distortion from warm air rising off a heated barrel is more likely to miss being in the line of sight the higher the scope is mounted if there is any crosswind.
There is a slight increase in sensitivity to canting by mounting a scope higher. On the other hand it's easier to notice that a rifle is canted with the scope mounted higher.
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I like lower more than higher.
Higher messes up your near zero. If all your shooting is at a bait station of known distance, no big deal. But for a more effective point blank zero for general purpose, lower is better.
Muzzle flip? I don’t envision fighting it out at BenGhazi anytime soon. If life came to that, send just enough downrange to get the other sides head down and get out fast.
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I prefer as low as possible, partly because most stocks are too low anyways to provide a proper cheek weld.... Cant is also less of an issue, mechanical strength is better, and we don't have to worry about recoil or mirage.... While a higher mount does move the near and far zeros further out, which can be beneficial in some cases.... it really increases what happens between the near zero and the muzzle to the POI / POA relationship.... Grouse hunting, for example, sometimes gives you surprise shots at very close range, and a high scope requires more hold-over to insure you don't shoot under the target....
Bob
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Yes^
My experience also, even with a center fire rifle, your near zero is messed up far more than your far zero is extended.
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I read somewhere that you should put the scopes as close to the barrel as you can. That's what I have always tried to do. But on a second thought does it really matter much?
I used the Chairgun and did some calculations. Raising the height by .5 inches may push the zeros further by two to three yards, the pellet drop at 100 yards will be reduced by 2 inches. Which could be a good thing since most hunting or paper Punching are more than 10 yards away anyway.
So I am wondering what are the rationals for keep the scope low? Certainly the torque on the rings will be lower with lower ring height and less shock to the scope. Is this why people want to keep the scopes low?
I used to keep my scopes close to my R9 receivers so there would be minimum pellet rise from my muzzle to the line of sight at my 30 yard zero distance. When shooting hunter class field target matches I do "rangefinding by scope focusing" and since focusing a scope at the closer distances (10-30 yards) is pretty accurate I wanted the flattest trajectory for these targets that aren't affected as much by atmospheric conditions as distances past 30 yards. LOL....when I had an old Japanese 3-12x40 Bushnell Trophy mounted to my .177 R9 I needed to cut a piece out of the bottom of the front lens shade so it could be slipped over the AO of the mounted scope.
When the scope is set higher the "trajectory curve" is benefited at the further distances. Since the field targets set at the longer distances have larger killzones and really aren't a high percentage of the targets set out I personally find it better to favor the low mount for the majority of targets set out.
There are a couple things that play out in the scope height issue. One is the gun used be it piston or PCP since a PCP can be set up to shoot heavy pellets at velocities the piston gun can use with lighter pellets. The higher BC of a heavy 10.5 grain pellet at 880fps allows a flatter trajectory curve than a lighter 7.9 grain pellet at 880fps which may be part of the consideration when choosing scope height. Another issue when shooting "critters" is the fact that unlike the field targets set on a lane.......the kill zone of a squirrel doesn't change with distance. The head if a squirrel will have a killzone about the size of a nickel (IMHO) regardless if it's at 8 yards or 50 yards. It's for this reason that I seldom take shots at tree squirrels past 30 yards and another reason why I use a scope mounted close to the receiver.
I currently can't mount my scope center at the same height as in the beginning because I used to get by using a "low mount" with my 1" tube scopes with 40mm AO, however I currently need a high mount for my 1" (or 30mm) tube scopes with a 50mm AO........
(https://i.imgur.com/TP7YJDHl.jpg)
LOL....I'm currently using this Weaver to dovetail adapter plus a set of Weaver rings......
(https://i.imgur.com/lTtuA7cl.jpg)
(https://i.imgur.com/APC46hUl.jpg)
Makes it easy to swap out scopes without loosening/tightening a bunch of screws and allows the use of a lower scope ring, however this pic shows that the 50mm objective is still pretty close to the receiver so the actual optics and mounts may restrict your actual scope height.
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I prefer low mounting and go for as low as possible especially on guns used at short distances. There are often advantages at long distances with higher scope mounting. External ballistics also plays an important role and has to be considered. Chairgun is very useful for a graphic representation.
(Much of this popped up above while I was making this post)
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For short distances I agree that lower mounts are preferred because the benefits offered by high mounts are not needed, namely, the extended zero range.
But if you have a powerful gun shooting some thing furth out, then a high mount may make sense. Although with drawbacks on recoil.
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I usually mount mine as high as I can and still maintain a comfortable shooting position. MPBR is something I always try to maximize. If one is shooting at very close ranges very often then lower would almost certainly be better but I almost never shoot at a very close target with a scoped rifle. Considering target size is also relevant. The smaller the common target for a specific shooter, the more a lower mounting scheme should benefit them.
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I usually mount mine as high as I can and still maintain a comfortable shooting position. MPBR is something I always try to maximize. If one is shooting at very close ranges very often then lower would almost certainly be better but I almost never shoot at a very close target with a scoped rifle. Considering target size is also relevant. The smaller the common target for a specific shooter, the more a lower mounting scheme should benefit them.
Thanks. Sorry for my ignorance but what MPBR stands for?
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Maximum point blank range, where the apex of the trajectory is out as far as possible. All distances besides that will be holdover, never hold under. Generally in the vicinity of 25 or 30 yards.
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Something that hasn't been clarified here is that as you increase the scope height, although it extends the ranges at which the PBR occurs.... it SHORTENS the difference between the two (known as the Maximum Point Blank Range, or MPBR).... The PBR is where you can hold "dead on" and have your shots fall within the Kill Zone (KZ).... As an example, for my Hatsan AT-44 Long in .25 cal., shooting a 34 gr. pellet (BC 0.050) at 955 fps.... with a 1/2" KZ, using ChairGun....
1.5" Scope height.... Near PBR = 13.5 yds.... Optimum Zero = 38.6 yds.... Far PBR= 42.9 yds.... MPBR Range (difference) = 29.4 yds (68.5% of Far PBR)....
3.0" Scope height.... Near PBR = 23.4 yds.... Optimum Zero = 47.8 yds.... Far PBR = 51.9 yds.... MPBR Range (difference) = 28.5 yds (54.9% of Far PBR)....
Just something else to consider....
Bob
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Good Stuff! I only recently started using Chair Gun and if it is only reasonably accurate, it is great. Really gives the ability to quickly analyze many variables (in this topic scope height) and get starting point(s) for actually shooting.
On Window 10 a bit of computer learning was needed to get the installation to run.
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Good Stuff! I only recently started using Chair Gun and if it is only reasonably accurate, it is great. Really gives the ability to quickly analyze many variables (in this topic scope height) and get starting point(s) for actually shooting.
On Window 10 a bit of computer learning was needed to get the installation to run.
Same here.
I do use ChairGun to get a vague idea of the trajectory differences before testing different tune levels, however "actual trajectory plotting" at my 53 yard back yard lane is a necessity. For me CG data isn't accurate enough to use "as is" with my recoiling springer but the output is "reasonably accurate" for "rough trajectory calcs".
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On Window 10 a bit of computer learning was needed to get the installation to run.
What did you do to install on Win 10? I was not able to do it.
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Ever since I started shooting FT, I like my scopes kind of high off the bore. I've centered my Sightron a good 3" above the center line of the bore.
I shoot unlimited class, because my crappy eyesight needs at least 30 power to be half way competitive. The 3" height has it's drawbacks for shooting inside 15 yds.
I use hold overs and don't click, so I have to hold over 7 stadia or 14 MOA on the cross hairs at 10yds.
Here's my holdover chart for 3" above the bore shooting 13.4 gr JSB Monsters at 818 FPS with a 28 yd zero
yds stadia
10 7
11 6
12 5
13 4.2
14 3.5
15 3.0
16 2.5
17 2.0
18 1.5
19 1.2
20 1.0
21 .7
22 .5
23 .3
24 .1
pretty much flat out to 37.5 yds
40 .2
42.5 .5
45 1.0
47.5 1.2
50 2.0
55 I still use 2.0 stadia
Now here's the kicker. Since AAFTA rules state the kill zone must be 1.5" beyond 45 yds I'm using the high scope mount to help me with this. You see, I've found out that I can use a 2 stadia hold over at anything between 50 and 55 yds and still make it inside that 1.5" KZ most of the time.
I hold 2 stadia at fifty and it shoots a little high into the kz. I hold 2 at fifty five and it shoots a little low into the kz. Nine times out of ten this works for me, so I'm sticking with it. I've barely eeked into the 50 club the last several matches by doing this. Now if I could just make myself practice off hand shooting ;-)
I have a really hard time range finding correctly beyond the 47 yd mark is the reason I do it like this.
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On Window 10 a bit of computer learning was needed to get the installation to run.
What did you do to install on Win 10? I was not able to do it.
The CG install went perfectly well and a desktop icon was created, but when clicking it a small box popped up with an error about no Java home (or something similar) and to install either JDK or JRE - meaning to me :o ??? :-[
So in my unorganized, undocumented way, I to www.java.com (http://www.java.com) and downloaded the "Recommended Version 8 Update". After that the same error occurred so I searched the web for information on java home and environment variables. But various references did not provide the answer as the "Control Panel" has no submenu that the references stated. I used the Windows 10 "Search" button next to the "Windows" button and entered "environment". That returned "Edit the system environment variables" which when selected brings up a request to enter the admin password and then a window comes up with "Environment Variables" in the lower right corner. Select that and the system variables are displayed. At this point I did not know where the Java installation was placed, but I finally located that in "C:\Program Files (x86)\Java". SO - select "New..." which brings up another window and enter Variable name "EXE4J" and Variable valve "C\Program Files (x86)\Java" (no quotes), and select OK in this window and the previous window. Now selecting the Chair Gun desktop icon should start Chair Gun.
Note: I discovered that any images created from Chair Gun are placed in C:\ProgramData\ChairGun4\Images.
Hope this helps. The vagaries of Windows paths still confuse me a bit.
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On Window 10 a bit of computer learning was needed to get the installation to run.
What did you do to install on Win 10? I was not able to do it.
The CG install went perfectly well and a desktop icon was created, but when clicking it a small box popped up with an error about no Java home (or something similar) and to install either JDK or JRE - meaning to me :o ??? :-[
So in my unorganized, undocumented way, I to www.java.com (http://www.java.com) and downloaded the "Recommended Version 8 Update". After that the same error occurred so I searched the web for information on java home and environment variables. But various references did not provide the answer as the "Control Panel" has no submenu that the references stated. I used the Windows 10 "Search" button next to the "Windows" button and entered "environment". That returned "Edit the system environment variables" which when selected brings up a request to enter the admin password and then a window comes up with "Environment Variables" in the lower right corner. Select that and the system variables are displayed. At this point I did not know where the Java installation was placed, but I finally located that in "C:\Program Files (x86)\Java". SO - select "New..." which brings up another window and enter Variable name "EXE4J" and Variable valve "C\Program Files (x86)\Java" (no quotes), and select OK in this window and the previous window. Now selecting the Chair Gun desktop icon should start Chair Gun.
Note: I discovered that any images created from Chair Gun are placed in C:\ProgramData\ChairGun4\Images.
Hope this helps. The vagaries of Windows paths still confuse me a bit.
Craig, that is genius, it worked!
I do not know how you figured this out but without your help I will have no clue. Thanks!
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There is an easier method. Uninstall Chairgun, install Java, then reinstall CG.
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I'm sure there was. But not known here. Thanks! :D
Greg,
You're welcome!!! ;D
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Point Blank Range is a specific distance from the shooter where your projectile will hit exactly on point of aim. There can be either ONE or TWO PBR's for a given rifle/pistol depending on how one chooses to zero that gun and this is related to height of the sight above the bore. If you choose to zero your gun so that the projectile NEVER rises above line of sight then you will have ONE PBR-the zero distance.
If you zero your gun so that the projectile DOES go above line of sight and then falls back across the line of sight at some further distance then you will have TWO PBR's. The projectile crosses line of sight at the near PBR, arcs above line of sight for some distance, then gravity pulls it down and it crosses line of sight again at the far PBR and continues dropping below LOS.
MPBR is a span of distance usually stated from shooter out to a maximum yardage where the projectile remains an "acceptable" distance ABOVE or BELOW line of sight. It is related to sight height above bore, performance of the projectile, AND TARGET SIZE. MPBR and distant PBR may be related but are not necessarily the same thing.
For an extreme example, think of zeroing your super ultra magnum rifle at 20 yards. 20 yards would be the near PBR but the projectile would rise so far above LOS that it would not be practical. At some extreme range (assume 1000 yards for this example) the projectile would fall to cross the LOS again at the distant PBR. The distant PBR would be a really long range out but the SPAN OF DISTANCE from the 20 yard near PBR in this example to the distant PBR would really be unusable in terms of aiming and hitting any normal sized target. You would have 2 PBR's (points where the projectile hits exactly where aimed) but really an unusable rifle at any distance other than those two specific distances. Calling the distant PBR point the MPBR is wrong in this case
Consider a 10" diameter as your common target. You can zero your gun to rise up to 5" above LOS where you will hit the top edge of the target if aiming at its center. The projectile then arcs (gravity) moving back down to center on the target and continues to fall until it hits the bottom edge of the target. That distance from where the projectile hits the bottom of the target back to the shooter is the MPBR for that specific setup and is determined by projectile performance, sight height above bore, and specific target size. Within that MPBR you can aim at the middle of the target and expect to hit it. Now assume that you need to hit a 4" target with the exact same gun and sight while still aiming at the center. You would have to change your zero distance so that the projectile would not rise more than 2" above the LOS in order to aim at center and be sure of hitting on the top edge. This would move the near PBR out some distance but it would also lessen the overall MPBR since you have less projectile "arc" to utilize.
In hunting terms, consider setting up a rifle for a deer size kill zone where you want to aim at the center of the zone with no holdover or scope "clicks" and be confident in a clean hit. You would have an MPBR for that specific setup of rifle/scope/bullet, a range out to which you can aim dead center and not worry about rise or drop. That MPBR would extend from bore to the range at which the bullet fell below the kill zone. Now take the same rifle out to shoot squirrels in the head (not practical but informative). In that case, your MPBR would be a very short span of distance centered around the near PBR due to the smaller target size. A short part of the distance from bore to squirrel head might not allow center aim since the projectile must approach LOS from below (scope height) into the acceptable size range of the smaller target and just beyond that near PBR the bullet would miss high for that smaller target and would continue to impact high until the shooting distance approached the distant PBR. If you knew the squirrel was at the distant PBR distance you could hit it but you've lost the MPBR concept of knowing that your aim will hit a specific size target from bore to a given distance.
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There is an easier method. Uninstall Chairgun, install Java, then reinstall CG.
Good to know. Will do that for the next computer. Thanks
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You certainly don't want it too low.
Too high, just to provide some trajectory compensation would also be a mistake as your chin will float around on your stock.
Another consideration is: are you setting up a high power PCP, or an under 12 fpe springer with a loopy trajectory? I'd go "lower" with a PCP.
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Something that hasn't been clarified here is that as you increase the scope height, although it extends the ranges at which the PBR occurs.... it SHORTENS the difference between the two (known as the Maximum Point Blank Range, or MPBR).... The PBR is where you can hold "dead on" and have your shots fall within the Kill Zone (KZ).... As an example, for my Hatsan AT-44 Long in .25 cal., shooting a 34 gr. pellet (BC 0.050) at 955 fps.... with a 1/2" KZ, using ChairGun....
1.5" Scope height.... Near PBR = 13.5 yds.... Optimum Zero = 38.6 yds.... Far PBR= 42.9 yds.... MPBR Range (difference) = 29.4 yds (68.5% of Far PBR)....
3.0" Scope height.... Near PBR = 23.4 yds.... Optimum Zero = 47.8 yds.... Far PBR = 51.9 yds.... MPBR Range (difference) = 28.5 yds (54.9% of Far PBR)....
Just something else to consider....
Bob
Thanks Bob, good points.
For the airguns, the "high" and "low" in my mind are more like 1.75 vs 1.25, so I will use my Hatsan AT44S10 as an example. I use H&N Baracuda, 31gr, BC=0.042, speed 720fs. Killzone=0.5, This is un-tuned factory setting.
with scope height 1.25, optimal far zero at 28.3, PBR" 8.8 to 31.7 yards (diff=22.9)
with scope height 1.75, optimal far zero at 31.3, PBR" 11.9 to 34.6 yards (diff=22.7)
If I tune the gun to have more power, speed=850fs, then
with scope height 1.25, optimal far zero at 32.9, PBR" 10.2 to 36.8 yards (diff=26.6)
with scope height 1.75, optimal far zero at 36.3, PBR" 13.8 to 40.1 yards (diff=26.3)
Indeed the higher mount will have a shorter distance between the PBRs, but only slightly. I tend to think you may encounter something a bit far than a bit close so I would give the far end more weight, therefore I may prefer 1.75 over 1.25 where I may struggle for the mount sometimes.
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You certainly don't want it too low.
Too high, just to provide some trajectory compensation would also be a mistake as your chin will float around on your stock.
Another consideration is: are you setting up a high power PCP, or an under 12 fpe springer with a loopy trajectory? I'd go "lower" with a PCP.
That is another reason I am thinking to make the mount higher. I struggled with some guns in getting clear pictures. So after all the calculations I think I do not lose much if I stop struggling to always have the lowest mount. I think the thing to look for is the comfortableness when shooting and not worried about the mount being half inch higher.
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Interesting points raised here. To add to what Bob has already stated. I have always gone as low as I can, most of the air rifles I have used have either no comb or very low ones. I often have to pad the stock to get enough cheek height other wise I find myself raising my head to get a clear site window. I don't shoot long distances, for me most shots are inside 35 yards. Most hunting shots are between 12 and 25 yards. I zero with a .5 kill zone which works great for my needs. Outside of that I use the mil-dots.
The various scenarios for using low or high mounts is something i'm go keep in mind going forward. Really great information and I admit is challenging my steadfast belief in always going low.
Dave