Shooting the breeze BASC - The British Association for Shooting and Conservation  
Go Back   Shooting the breeze > The Chat > General Airgun Chat

General Airgun Chat Chat and banter that doesn't fit anywhere else...

Thread Tools Display Modes
Old 31st December 2013, 03:51 PM
SDplinker's Avatar
SDplinker SDplinker is offline
Pellet testing...yawn
Join Date: Apr 2011
Member of: CASA - California Airgun Shooters Association
Location: Atascadero, CA, USA
Posts: 363
Default Scope rail droop and optical zero

Sorry, I'm hopeless at the math ..... hoping someone can help or get me in the right direction.

I'm going to mount a big Nikko mk1 on my Steyr LG100. I have my eye on a 2nd hand Welman rail which is a Weaver rail with 16MOA of droop built in. Trying to calculate the following - if I optically center the turrets and mount the scope:

1. At what height would the scope need to be to have the gun zero'd at 35 yards?

I'm not sure of the height of the Welman rail but since I'm after overall scope height I'm not overly concerned. If someone can help with the math then I should be able to figure out the height the rings need to be.

I know this involves trigonometry but those skills have evaporated since college. Want to save myself buying multiple rings to get it right. Plan is to go with some Leupold QRW.

Reply With Quote
Connect With Facebook to "Like" This Thread

Old 31st December 2013, 04:03 PM
RobF's Avatar
RobF RobF is offline
My Empire of Dirt
Join Date: Mar 2010
Member of: Southampton Buccaneers, Parkstone, South Dorset
Location: Poole, Dorset
Posts: 10,167

Ignore the scope for the moment...

If you imagine Line of Sight and Bore to be exactly horizontal, then you need to know the drop from the bore line to your point of impact at 35yds... depends on power. But chairgun will give you that. From that you can work out the angle in MOA. But unless your drop (including the unknown scope height) is 16 MOA, you'll have to dial it in anyway.

Better to keep optical centre, put the scope where your head wants it to be, and use adjustable mounts. Saves bashing on a calculator, then finding out your scope won't either keep optical zero where you want it (which is 55, not 35yds) and then finding mounts/rail combo that fits.

Well, that's my opinion anyway.

When dealing with MOA's you're talking fractions of a mm at the scope end in terms of angle to shift them. I cant remember what the numbers were, but a friend asked me to work out what he'd need in order to shift the scope by 20MOA or something similar and it worked out we were looking at an adjustment of fractions of a mm to keep it optically centred. Although you're looking for a larger amount, it's likely 16 MOA won't cross the pellet flight where you want to and any adjustment will be tiny... so hence the suggestion of sticking the scope where your head and body wants it to be, and adjusting it to that.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep
Reply With Quote
Old 31st December 2013, 04:18 PM
SDplinker's Avatar
SDplinker SDplinker is offline
Pellet testing...yawn
Join Date: Apr 2011
Member of: CASA - California Airgun Shooters Association
Location: Atascadero, CA, USA
Posts: 363

Makes sense Rob. Now to figure out a way to get that Steyr cheekpiece up higher and keep the gun lower.... I presume someone makes longer posts?

I'm going to keep exploring options. My attraction to the QRW was the ease of taking the scope off and on to fit in a much smaller gun case. One of my best friends drives a Mini - tough fitting 52" rifle cases in his car for matches :-)

Also trying out one of the Mac1 adjust hamster mechanisms. It would be really useful for up and down shots but adds one more thing to adjust. Perhaps better to spend money on a high custom mount and just use the Steyr hamster at factor height (on the LG100 it's about level with the bottom of the trigger guard).

Thanks for the advice!

Reply With Quote
Old 31st December 2013, 07:51 PM
greyskullnz greyskullnz is offline
Account Deleted
Join Date: Aug 2009
Location: Wanganui NZ
Posts: 268
Default optical zero for Steyrs

Been down this road.

If you are not going down the adjustable rail road, or the adjustable rings road, you will have to go down the shimming road. Not so bad if you end up epoxy bedding the rings after you find your optimum height and tilt.

zero'ing at 55 yards means zeroing at a fraction over 16 yards so that saves needing 55 yards to set up in.

Raising the front of the scope means the back comes back more into line with your eye at the rear and the cheek height prolem is eased a little. Changing adjustable butt for a better hyead position can help this too. Remember the head takes a different position for each position we use.

I used a cheap set of Leapers high weavers on the standard Steyr rail to discover the tilt required at first. cheap disposable mounts. I then discovered the amount of tilt required by clamping the rifle and firing at 16 yards, finding the number of clicks it needed to converge on POI and voila you have the number of MOA you need to either shim up the front. After shimming bedding set mounts is important so the tube is not bent or crimped. Adjustables are the way to go for international competition as environment/altitude can change what tilt you may need between locations and quick adjust as well as quick release makes sense. Whatever you end up using make sure its robust.

About 3 in is about right for the Steyrs, and the original Steyr rail can be used quite happily to achieve that. I also still use the Steyr handrail, although on occasion wish it was about 10mm deeper, but not a drawback at all when shifting to the forced positions.

Just my opinion, but with limited revolution adjustment available, mechanical centre is probably more important than optical centre so you have a good range to work within, rather than optical centre and running close to the end of adjustment.......causing mechanism problems on really close shots etc etc.


Last edited by greyskullnz; 31st December 2013 at 07:55 PM.
Reply With Quote
Old 31st December 2013, 09:51 PM
Jon Jon is offline
Senior Member
Join Date: Nov 2008
Location: Nr Wolvo
Posts: 769

Casey its not necessarily a standardised droop, as said time and time again it depends upon the actual scope used.
By that all scopes have a massively different optical centre none worse than the BSA/Niko from one to the next. Some Niko been known to have optical zero at 71MOA whilst others 26MOA who knows.

Its the same across the manufacturers, theres no set standard though Falcon and S&B tie in repeatedly with same amount which is a lot more than 16MOA, in turn closer to March optical zero but way too much for most Leup models.
I know the exact optical zero for most well made scopes.

Check those QRW fit picatinny MOD Spec 1913. Burris are good so are Third Eye and Kelblys.
Cant beat a properly cut dovetail offering more grab.
Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
optical centre robsue20 General Airgun Chat 10 16th November 2012 12:11 AM
Scope mounts with built in "droop"? Cooperman General Airgun Chat 7 3rd August 2009 02:01 PM

All times are GMT. The time now is 01:38 AM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd. Skin design and concept by Attitude