Hi Darren
Thanks for this. I will have a look around for some more info on this because I just received my 5 inch 650 mm mirror except when I opened it up they've actually sent a 6 inch ???mm mirror which even if I do some serious cell surgery might fit but my guess is that the focal length is either 750 or 1000 mm which means an even longer, heavier tube than I was planning. I think I may be pushing things considering the mount was too weak even for the original configuration.
I'll look into your suggestion but my first thought was OMG because the I thought the first rule was "Make sure you have no stresses on the primary" and I have to think that pulling the centre out will put pressure on the 4 clamp areas so I think I will end up ordering another correct mirror and sell the (now) 2 useless ones I have.
This astronomy thing is getting toooooo stressful. I am so impressed with the views from my new GS-680 Dob but I am having so many dramas getting a reasonably priced EQ5 (or better) mount and tripod for it (plus the problems with this Powerseeker 127) that I'm feeling very jaded. Are all the ups and downs part of the deal because I'm not sure I like it.
Steve