Chair gun and..

[Anothermiss]

The "scope height" parameter. How is this measured? Is it from centre of bore to the centre of the scope or centre bore to bottom of objective lens?

I've never actually known which it is.

[Shed tuner]

centre to centre.
You plotting your .20 trajectory ahead of a new purchase ?

[NickG]

I put a straight edge on top of the scope so I can calculate center to centre at the end of the barrel.

[Shed tuner]

I put a straight edge on top of the scope so I can calculate center to centre at the end of the barrel.

and presumably you factor in the eccentricity of the bore

[Anothermiss]

centre to centre.
You plotting your .20 trajectory ahead of a new purchase ?

Funny you mention that. I'm trying to replicate the figures quoted by gsxman on that thread. I'm off out shooting the 177 on targets this morning in prep for some ratting tonight.

If it ever stops raining...

[NickG]

and presumably you factor in the eccentricity of the bore

Just try to get it as close as possible, some put foil over the scope with a small hole in ( like a pin hole camera) and shoot a shot at a sheet of paper held against the barrel, didn't work for me 🙄

[angrybear]

Funny you mention that. I'm trying to replicate the figures quoted by gsxman on that thread. I'm off out shooting the 177 on targets this morning in prep for some ratting tonight.

If it ever stops raining...

It's supposed to be C to C at the muzzle, but I measure C to C at the breach & take off 1-2 mm,
you will never get more than "ballpark" accuracy because your velocity is going to be, at best, the average from your testing, but I find Chairgun is usually within "human error" level of accurate.

p.s I couldn't plot anything close to the .66" drop at 45yds that he claimed, but good luck trying
you need; scope height, pellet weight, velocity, zero range, pellet profile, bc.

[eyebull]

Within a few mm is fine and within the tolerances of your velocity figures (and claimed pellet weight!) as Angrybear says.
You need to confirm and fine tune zero with testing anyway. Chairgun etc. best used as a starting point to give you an idea of your trajectory, not as a cast iron thing.

[Anothermiss]

It's supposed to be C to C at the muzzle, but I measure C to C at the breach & take off 1-2 mm,
you will never get more than "ballpark" accuracy because your velocity is going to be, at best, the average from your testing, but I find Chairgun is usually within "human error" level of accurate.

p.s I couldn't plot anything close to the .66" drop at 45yds that he claimed, but good luck trying
you need; scope height, pellet weight, velocity, zero range, pellet profile, bc.

I've struggled to plot it too, unless ME exceeds 12ftlb.

[Anothermiss]

I've managed to get the curve closest to gsxman's figures by applying a 38 yd zero at 900fps with the jsb express (I think that what he uses) but this is 14.2ftlb?

Can he clarify his settings? I'd be well happy with his curve but I'm struggling to find the numbers in sub 12.

Interestingly, if you enter figures to create 14.2 ftlb with . 20 cal ftt trophy, the difference between. 20 ftt and 177 cal express in terms of impact is 1/3 of an inch at 50 yards but retains 1.2ftb more energy.

Perhaps gsxman is running hot and doesn't realise it? At sub 12, I can't get anywhere near the stats he's given.

[Anothermiss]

Gsxman - any help with this one, pal?

[gsxrman]

I've managed to get the curve closest to gsxman's figures by applying a 38 yd zero at 900fps with the jsb express (I think that what he uses) but this is 14.2ftlb?

Can he clarify his settings? I'd be well happy with his curve but I'm struggling to find the numbers in sub 12.

Interestingly, if you enter figures to create 14.2 ftlb with . 20 cal ftt trophy, the difference between. 20 ftt and 177 cal express in terms of impact is 1/3 of an inch at 50 yards but retains 1.2ftb more energy.

Perhaps gsxman is running hot and doesn't realise it? At sub 12, I can't get anywhere near the stats he's given.

I thought I could "screen print" the graph but obviously I cant.
How do i get the graph directly onto a reply.

Any how I use Crossman Premier 7.9, 2" scope height and FPS of 816 with a 39 yard zero!

[Shed tuner]

use "snipping tool" within MS windows to capture it, then save it to you hosting site.

With a near 40 yard zero, you have an apogee way above your zero range in the midrange, which is pretty horrible.

See my graph for how to zero with a decent PBR, based on a 1" KZ:

[gsxrman]

use "snipping tool" within MS windows to capture it, then save it to you hosting site.

With a near 40 yard zero, you have an apogee way above your zero range in the midrange, which is pretty horrible.

See my graph for how to zero with a decent PBR, based on a 1" KZ:

Peak of my arc is .48 above zero at 28 yards. Half an inch. Which is less than the size of a 15mm kill. For me it is the longer range targets that are troublesome on HFT and FT. Like I was saying, 3 yards out at 40-55 yard range makes a massive difference on your graph and to other calibres. That's where comps are won and lost.

[gsxrman]

https://www.dropbox.com/scl/fi/9p2ci...fn995ap4g&dl=0

See if this works