Thanks for the plug, Ronin.
IM, synthetic stocks are a PITA,they tell me, to alter. Don't start on it,yet.
Sounds to me like either your stock doesn't fit well,your form needs a little honing, or both.
That 1100 with 10 shots aboard must gross over 9 1/2 lbs. It doesn't kick much with a full load, but as it diminishes in weight,it kicks harder, right?
First,get a standard,utility grade lumber stock to work on. Old beater 870 stocks may work. I think they need a larger hole for the action spring housing, but I'm no gunsmith. Stick on a good pad like a Decellerator or KickEez, and fire with an empty mag to see how it does. If your thumb bumps your nose, it's too short. If there's more than three fingers' width between thumb and nose, it's too long.
We're not done yet with fit. Once the length is more/less correct, check the drop. Mount the weapon and see if you see any rib. A little's OK, but more than a little may mean a high strike. If you have trouble seeing the bead at all, there's too much drop. Correct by shimming between the rear of the receiver and the stock. I use Aluminum foil, pieces of old hulls and toothpicks are also used.
This is a good place to run some pattern tests, to see if POA and POI are the same.
Next, mount it a few times and have someone push it gently back into your cup,that's the area where your arm and torso join that receives the butt. See if it pressing harder at the top or bottom. If it's pressing equally, you're almost done.If not, use shims between the stock and pad to correct the pitch.
Finally,try rounding off the toe of the pad if it seems to press in a little too hard,or if that's where it's most ouchy after a range session. You may also want to relieve the inside edge of the pad to conform to your body better. Go light and slow with this, easier to take some off than put it back on.
Next, let's deal with that "Pig on snow shovel" feeling of extreme muzzle tonnage that 10 round mag and contents give you. Add some weight in the stock, I use a few old hulls filled with shot and crimped hard.Then they're secured in the bolt hole in a fashion that precludes shifting. This will return the balance point closer to the middle and also the extra weight will cut the kick a bit.
At this point, try it out. If you can handle more weight,add a Side Saddle,since the weight's close to the balance point, it shouldn't be a prob.
If it's still causing you pain and trauma,then you can get into the expensive gunsmithing like backboring and porting.
Of course, you may also shift to R/R ammo.
For form, I recommend the thread on Proper Mounting Techniques.
HTH....
