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PostPosted: Thu Jul 17, 2014 7:20 am 
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Location: North of Kenora
I thought this was about chairgun results? The two guns sighted in at 10 yards will have two completely different points of impact at various ranges. The OP was wondering why he was hitting low at 20 when sighted in for 10.
I have no augment with you in regards to the amount of drop versus bore line. This will not change significantly if the bore is tipped down or level.
What does change though is the resulting lower impact point with a "drooped" barrel versus a parallel one.
Chairgun has no way of knowing the angle barrel vs.scope in your gun and thereby assumes your barrel and scope are in line.
Even if you change the distance and make the bore line closer (as in your example) the program has no idea the barrel is pointing down relative to the centerline of the scope.
The ultimate result of this is the shooter will run out of "up" adjustment on his scope at longer ranges and wonder why his gun is shooting too low.
This sounds a lot like what the OP is describing (though he hasn't run out of adjustment yet), and changing the scope boreline figures in chairgun are not going to make his gun shoot any higher at longer range or match chairguns results at different distance when sighted in for a closer range.
I was originally merely offering a suggestion(barrel "droop") as to why the gun was shooting low at range in comparison to chairguns projected figures, not attempting to get into a terminology argument.
I still think though, a compensating mount will go a long way to alleviate the OP's chairgun /sighting woes.
I think I have written enough for now(right or wrong)
My apologies for the thread hijack to the OP.

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PostPosted: Thu Jul 17, 2014 7:20 am 
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Deleted....Double post

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PostPosted: Thu Jul 17, 2014 8:24 am 
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I don't see how droop can factor into it in any way other than complicating the measurement of scope-bore offset. There are simply two lines that intersect at a point. Barrel droop only impacts the physical difficulties of achieving the intersection, but once the intersection is achieved must surely be of no further consequence?

If the initial trajectory of the pellet is above the horizontal then the curving pellet path intersects the POA at two distances. I've not used chairgun, I guess it has some way of determining if the calibration distance is at the first or second intersect? Or is it assumed that the pellet is always on a descending trajectory? Not trying to start an argument, I'm just interested in the concepts as someone new to scopes.


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PostPosted: Thu Jul 17, 2014 1:00 pm 
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Location: Coalmont BC
Quote:
The two guns sighted in at 10 yards will have two completely different points of impact at various ranges

Really?.... please explain, because I thought my example just proved otherwise....
Quote:
Chairgun has no way of knowing the angle barrel vs.scope in your gun and thereby assumes your barrel and scope are in line.

The scope (line from reticle to target) and the barrel are NEVER in line (ie parallel), or it wouldn't be possible to sight in the gun at any range....

You got it exactly right, EverHopeful.... Once the gun is sighted it, Chairgun works as intended, whether or not the barrel has droop.... It also doesn't matter if you achieve sighting the gun it by adjusting the reticle or by using a drooper mount, or by shimming the scope in the rings.... Once it's sighted in, Chairgun works, and it doesn't matter how you get there.... That was all I was trying to say.... I'm not arguing about the usefulness or not of a drooper mount or shimming the scope to achieve that.... If you run out of internal adjustment, you have no other choice, but I didn't read that as being the case in the original post....

Bob

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PostPosted: Thu Jul 17, 2014 3:44 pm 
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Location: Nova Scotia, near Halifax
so there is no way in chair gun to input your own poi's??
because i could input some already!!! :mrgreen:

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PostPosted: Thu Jul 17, 2014 5:07 pm 
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Yes, you can use the BC Calculator to input your POIs at two ranges, and when used in conjunction with your muzzle velocity it will calculate your BC, and then use that to draw the graph for the remaining POIs....

Bob

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Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Jul 18, 2014 11:13 pm 
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Location: Surrey, BC
Hello there, I have tried the chair gun program before but unless you have input the correct values for each variable, the result will varies.

I simply gave up and just map out my POI shooting at various ranges to know exactly where my shots will land and I write theses numbers corresponding to each mil dot on my scope. Simply and effective.

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PostPosted: Sat Jul 19, 2014 9:56 am 
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I would agree there is nothing that beats hands on testing.... The BC values in ChairGun are an average and vary with velocity and even barrel to barrel.... The only sure way to get the POI for your gun is to measure and plot it at various distances.... Chairgun is, however, a very useful tool to get close.... PROVIDING you input the proper data.... GIGO (garbage in, garbage out)....

Bob

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Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Jul 19, 2014 5:04 pm 
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Location: Nova Scotia, near Halifax
i know, but it's so pretty!!!!

i am going to do it the old fashion way. just need to devote some time.

thanks for the info guys. i will fool with chair gun maybe later to fill in the spaces.

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sub 500 .177 Crosman TR77 NPS 4-16x40 UTG
sub 500 .177 Hatsan mod 33 with Quattro trigger open sites


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PostPosted: Fri Oct 10, 2014 9:23 am 
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What magnification is your scope mil dots accurate at? Second focal plane scopes only have one mag where they are accurate. First focal plane scopes are accurate at all mags. If you have the scope at 4x and the mildots are accurate at 12 then you get 3x the observed mil dots, or 3 when it should be 1. Barrel droop doesn't matter, only scope height, zero distance, pellet BC and velocity.


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