I have an old Model 12 that I'll be sending off to Simmons for the full treatment. Undecided as to whether or not it is worth the extra coin to go with the lengthened forcing cone and backboring. Any opinions on the possible performance increase that will be seen with both or either of these improvements on a dedicated trap gun?

In theory, both treatments will enhance patterns and reduce recoil.

Real life, you'll only know how much if you pattern it first, and again afterwards. Recoil difference will be subjective and hard to measure.

If you're doing a full-on workover, it's probably worth it to get these done. Not sure what the cost is, and only you can decide how much you're willing to spend, but you're not going to make it any worse, and may see some nice gains.

BTW, my dad has an old Model 12 that he had gone over about 30 or more years ago. Same Simmons rib, etc, and custom wood cut to the general dimensions of a Browning Diana grade Superposed that he also had, and measured and finished to fit him. Really nice gun!

He shoots it awesomely, I shoot it like crap. Fits him, not me...

Strech the cone, dont jack with backboring

Thanks for the input, I think I'll go with the cone work and skip the back boring. Seems to be the general consensus when I've asked elsewhere. My next concern is how high to have the comb made. I know I want it higher, just not sure how to determine how high. As far as that goes, I'm not sure exactly how to determine ANY of the stock dimensions.

I would do the forcing cone as well. It will tend to smooth the pattern and make it more even.
Not sure I would do the backbore.

I've been very happy with a .745 bore as far as patterns and recoil go...but whether or not I'd do it to a nice Model 12 is another thought. Gotta Luv a Model 12 trap gun tho...true classic!

Don't get me wrong, I like a backbored barrel but not sure some of the old model 12's have the steel in the barrel. I have seen several that are on the thin side toward the muzzle.
Not real sure how much recoil your going to remove from a model 12 anyway.