Putting on the rigger guard is my least favorite thing to do.
I was having an uneasy time getting this German Silver trigger guard to bend nicely to fit the pistol grip and was worried about it breaking. I thought that, instead of tapping it into shape against the pistol stock and risk cracking the wood, I would make a shaping form.
I simply cut two blocks of wood to the inside shape of the pistol handle. Then I clamped the front trigger guard tang tightly between the blocks. Next I also clamped the flat down securely. (I had already gut out an area for where the rear tang would go.) Then I tapped the rear extension of the guard against the wood form and it went nicely into shape. I sometimes using a clamp to draw it in also, and I got it close enough that I could lightly tweak it by hand.
It worked pretty well for me.