how should i mount my bipod ?

Wow, that's pretty...sure you want to drill into that wood? How about a small back pack and/or a sandbag? I can't speak for a Diana, but I can say that my NPs shoot a little loose if I rest them on anything harder than my palm or a soft-ish bag. I imagine a bipod would have a similar effect (on my guns, anyway). Just something to consider if you're zeroing on the 'pod, but won't always be shooting from it. Is your gun's balance point near the trigger guard (common with break barrels, I think)? If so, I'd think you would would want to mount a bipod near there anyway (for recoil/consistency sake?). I may be waaay off base with this, but it may be worth researching/considering.
 
Perhaps, do NOT "mount" it?
Shooting stix keep getting lower in cost yet higher in quality. Recent ruling in Field Target made "attached" bi-pod's illegal then I saw the some people changed to a bi-pod with a sort of half pipe ( maybe pvc heat shaped very close to your rifle's profile, lined with mouse pad + sticky something? ) attached to a bi-pod. Very stable. You would think it WAS attached vey well. If you could afford a nice pan, tilt, adjustable I think "nit and just lay your rifle in in you would be happy. And it drops right off for easy woods/other carry. On a lower budget I think (?) bog-pod - walmart/dick's/- plastic standard stix work very well., angain super easy transport and very light weight.
If you must "unclemikes" does make barrel mount clamp mounts in the 15-16mm range.


bog-pod "stix"





Depending on your shooting style/needs consider a mono-pod with a spike, they are very steady in the 11" range if belly shooting.

John

 
"Barrel mounted" will likely effect accuracy by altering the barrel resonance. Some experiment with different weights, and placing them in different spots along the barrel. I suspect going from "weight of gun resting on barrel" when rested on the pod to "weight of bipod and mount weighing on barrel" when shooting off hand might have a negative effect on you POA/POI/zero etc. I have used a Primo's Trigger Stick with some success, though the short one (for shooting seated) seems to be no longer available. While a bit pricey, I have tried an "economy" monopod...might be ok for a camera, but wouldn't bear the weight my springer.