Geometric puzzlement

[Adam77K]

It strikes me that these days with more and more people using bigger (longer) scopes it's about time that airgun manufacturers started making their scope rails with a built-in incline. I know that you can get inclined rails for Steyrs etc but why is this not more common on mid-range guns?

I'm not including the budget end of the market here of course. With a cheaper springer where the rails are cut into the compression cylinder it would unnecessarily add to the costs.

Scopes do perform so much better when they are near optically centred. What I'd like therefore is a precision engineered one-piece scope riser, which clamps to standard dovetails on most rifles but has another dovetail on the top surface, is machined with an incline.

If someone manufactured something like this I'm sure it would sell well. I envisage one aimed at FT, with an angle optimised for typical 12 fpe trajectory drop at 50m range and high line of scope above bore. It's at 50m (55 yds) you need the scope to be performing at its best. Also there could be one optimised for hunting/HFT with a lower sight line optimised for maybe 30m.

[Goes off to play with Chairgun and scientific calculator]

[Adam77K]

According to my calculations an incline of between 20 and 25moa would be ideal.
This is based on chairgun's drop predictions for .177 Exacts launched at 11.5fpe at a range of 55 yds and sight line 2" above bore line.

[Baldie]

According to my calculations an incline of between 20 and 25moa would be ideal.
This is based on chairgun's drop predictions for .177 Exacts launched at 11.5fpe at a range of 55 yds and sight line 2" above bore line.

Looking more and more like airgunners should have Picatinny rail used for 1000 yard target work. Will wonder off for a mo and take piccy of my CF.

[Baldie]

I use 30mm scopes, with Sportmatch R/F mounts.

Rimfire/airgun with 4-16x56 SWF.

With this exception.

Centrefire with 4-16x56 Custom jobbie.





Didn't take long .....

[xbow]

I checked with "The font of all (engineering) knowledge", (Tim!) at work and he offered the following: "you won't get far trying to lap aluminium with a steel bar, the grinding paste sticks to the softer material and laps the harder one"! I assume then that the benchrest guys are using steel mounts?!

The other thing I don't like about many types of rings are the "this will fit X+X+X size dovetails" Really, and how far off the boreline is you scope going to be then? These: http://www.deltainc-usa.com/jdkstuff...ext15apr02.htm or these: http://www.bkltech.com/ are a better idea I reckon.

[sarf]

"you won't get far trying to lap aluminium with a steel bar, the grinding paste sticks to the softer material and laps the harder one"!

He's got a point. I've only used abrasive paper so far. I'd like steel mounts but haven't been able to find any for airgun 'scope rails.

These: http://www.deltainc-usa.com/jdkstuff...ext15apr02.htm or these: http://www.bkltech.com/ are a better idea I reckon.

Agreed. Does anyone import BKL? I see they offer drop-compensated mounts:

Available Bullet Drop Compensation::
.004" per inch-typical for Rimfire applications
.007" per inch-typical for Airguns applications - and 7/1000 is about what we've discussed as a suitable slope!

[Baldie]

Agreed. Does anyone import BKL?

They do, but you wouldn't buy them if you had a choice. BKL won't export direct though. The UK distributor has to make a profit, but the price difference between US and UK prices, must mean they are hand couriered.

Can't respond to the .308 at 600 yards vs airgun at 55 yards.

















But I may know a man who can.

Will PM "The Cavalry".

[Adam77K]

Nice find - that is exactly what I want - 0.007" per inch is spot on with my calcs too.

Only 50 bucks too, but it's probably nearer 100 quid by the time it reaches these shores

[I'd prefer another inch in length, but wouldn't we all ]

[sarf]

I checked with "The font of all (engineering) knowledge", (Tim!) at work and he offered the following: "you won't get far trying to lap aluminium with a steel bar, the grinding paste sticks to the softer material and laps the harder one"!

Slightly off-topic . . I'm familiar with the effect that Tim is describing. However, I've always presumed that the cause is the fact that all aluminium will have a very thin surface coat (once exposed to air) of aluminium oxide, which is of course extremely hard and often used as abrasive. Unless this surface layer is broken through, the aluminium oxide will resist the grinding paste better than the steel. Well that's my theory anyway.