Good evening,hope you can help me here,I recently stripped my 48 and replaced the seals and spring but noticed there was no spacer/top hat at the breech end,as the old spring was bent I wondered if the lack of this centralising washer which slides inside the piston was the cause, does anyone have the dimensions for this so as i can get one made, Thanks.

You can install one, some aftermarket places do not recommend it. Hector Medina made one for a recent tune on a 48 he did:

http://www.network54.com/Forum/79537/message/1142908947/

I chose to just polish the spring end and go without as the spring is constrained to a great degree by the ID at the top of the piston:

http://home.comcast.net/~scot_for_sale/guns/RWS48_tune/index.html

As the stroke is long in these guns and the springs have significant pre-load, their ability to deflect radially during cocking is greater than shorter stroked guns. I went with a max length Delrin rear guide on my gun thinking that the piston will constrain the radial deflection of the forward portion of the spring. I'm happy with the result of the tune, I don't know how much the spring is bent as I haven't had it apart after the tune.

Another solution is a piston liner. I did an R7 and installed a Delrin liner that is a .005" or so bigger ID than the measured OD of a fully compressed spring. This gun is very, very smooth (but part of that is the low power) and I'm planning to do another in the near future. With a nicely centered piston rod, buttoned piston, tight rear guide and close piston sleve, the spring doesn't have much choice other than to compress in a straight line!

-Scot

Thanks for that. I've bookmarked the site, cheers, Steve.