Modifying scope mounts

[Segata]

Apologies if I have asked this before, I did search my Username and nothing came up.

Last summer I was give a Webley Falcon and a pile of scope mounts to try and get working as time went one I found out that it used an older type of mount so nothing off the shelf in the modern day is going to fit, since then it's been amongst the pondering of can I file out a set to match as I've likely not the funds or luck to get a genuine set up.
What I want to know is how precise do I need to be to matching measurements?
I'll be using mostly hand tools so I don't have the luxuries of fine adjustment that say a mill has and I also don't want to waste what could be otherwise of use to someone so I want to make sure before I start.
I am a complete novice when it comes to scopes as I generally shoot Irons although the further into my 30s I get the more it seems optical assistance is required.

[angrybear]

What is it that you think you need exactly ? From the pic's I can find, the Falcon seems to have a normal dovetail rail.

They need to be a perfect match & completely parallel

[Segata]

It looks normal until you try to mount a conventional one on it, it's 11mm wide but has a deeper curve which there are vintage mounts that match but funds what they are and rarity I'm better making one fit if I can.
What I need to know is measureent wise how close do I need to be, I'm pretty much going to be going by trial and error by hand so theres a chance there maybe a maginal difference in the mounts sizing, I need to know if this will cause problems i.e both mounts need to match with 1/1000th etc or is roughly right ok?

[ashf9999]

Yeah you are correct re the rail being not quite suitable for modern mounts. The scopes from the period mostly were low powered affairs with integral mounts, and the mounts resembled a pair claw pincers more than the modern profiles.

Now if budget doesn’t stretch to a period Webley or BSA scope, I hate to say it, the cheaper fixed power tubes from the likes of Richter Optic, so for example the 4x20 Crystal, are in a strange sort of way suitable. Spec-wise very much the type of thing you’d have got in the day and lightweight too. Obviously not a great field of view and being a sub-tenner scope don’t expect the world. I’ve got 4 of them on small vintage Webley rifles, and for plinking they do the job as scopes fine.

If you want to take a file to modern mounts, all I can say is try your best and see. Most mounts are made from precision drawn aluminium profile, which won’t be too tight a tolerance. You’ll know it’s right assuming 1) you don’t crimp the tube and 2) the pellet doesn’t cross from one side of POA to the other at different distances.

[Born Again]

If you're thinking of filing some metal away to give more clearance for the compression tube then the alignment shouldn't be affected. If you are filing the mounts to make them fit a wider rail then I'd suggest you only file the movable sides, that way you'll always have two factory made fixed edges for alignment.

[angrybear]

So If I understand correctly; the convex profile of the actual dovetail is too tall, as modern mounts have a flat profile between the clamps so you need a more concave profile ?

I've got a pair of single strap 25mm with a slight concave profile you can have, not a great pic due to the shadow but can be seen compared to the flat of the 30mm,

[Shed tuner]

Assuming the scenario is as per AB's hypothesis.... I had this with a sharp ace... I just filed a concave section in the centre of their underbelly... and it's defo not a critical dimension, just needs to clear...