In testing Xisico XS25 models - which are very, very similar to the Rugers
- we've found that the synthetic stock guns are typically somewhat less accurate "out of the box" than those with wood stocks.
This is probably because the synthetic stock is much lighter than the wood stocks and so doesn't soak up the recoil so well. If you pop off the buttpad, you'll see that the buttstock is hollow, with just a couple of reinforcing ribs across it. I'm currently experimenting with putting differing amounts of weight inside these buttstock voids to determine the effect on accuracy. Initial results look positive...
I'm sure I can't be the first to try this. Has anyone else been successful with adding weight to these synthetic stocks and achieving an improvement in accuracy?
Another simple idea is to check the quality of the barrel crowning and refinish if necessary. Again, this is for accuracy.
Also check the breech seal in the end of the barrel. Does this give a good seal with the front of the gun's compression chamber? If it doesn't - the breech seal can sometimes sit below the level of the barrel face on these guns - then a shim under the breech seal will raise it into good contact and can give a significant increase in muzzle velocity (we've seen 50fps+ from doing this).
These could be simple, low cost, low tech starting points for your tune.
I hope this helps...
Archer Airguns Inc.
Online stores http://www.archerairguns.com