I have a P220 that was made in 1996, the two tone model. Have thought it would be nice to have a red dot option at my age. I notice that some machining companies say you can't mill the P220 and will only put a groove on for a plate, and some say you can direct mill/mount a red dot. Is it the thickness of the slide, and have others had good luck with the milling?

A P220 made in 1996 (assuming it has all of its original parts - i.e. isn't a "FrankenSIG") no doubt has the folded slide (two-piece stamped slide with a removable pinned-in breech block).

A folded slide SIG is definitely not suitable for optics cutting. The most you could do to a folded slide SIG is to mildly "skim" the top of the slide so that you have a perfectly flat surface that would allow you to slightly lower one of these plates that mount in the rear sight dovetail (is this what you mean by "groove for a plate"?). Direct-mounting of any kind is out of the question though. You definitely don't want any mounting screws going into a folded slide (too much hardware underneath the surface that the screws would interfere with or just damage).

If you absolutely insist on an optic on a folded slide, I'd just leave the slide alone entirely and use one of the aforementioned dovetail-mounted plates. The optic will sit high and it's not the most robust mounting solution, but your slide can be brought back to original condition at any time. I hope this helps.

It depends. If it's a newer milled stainless slide it can be cut for an optic but the firing pin safety plunger channel and spring will be exposed.

If it's an older stamped-slide gun (which I'm not 100% but would bet a 1996 vintage gun is), it can't be milled because there's not enough material there. Those older slides are just a relatively thin piece of metal that's folded and stamped into shape, with a separate breech block pinned into them.

Thanks. I'll probably try and outer impact mount that goes in the rear sight groove and see if that is solid enough.

Back in the day when Sig was working on adjustable sights for the P220, they cast a taller front sight and milled a hole in the slide. Then they mounted the sights to the breech block.

I don't think this caught on as there are only a few of these done this way. The red dot would need to have a lot more material removed than a Bo-Mar sight required.

Let us know how the dovetail mounted dot goes, I may be in the market for one as well.

You can usually find a used P220 slide, both milled and stamped types on Ebay for not too expensive. Also if you want brand new, you can just buy a milled slide from Sig's website now, but they aren't cheap.

Just purchase an optics ready current pistol and save that precious P220.

S&W M&P 45? Glock Gen 6? So many options. Literally for 2X the price of a milling job, you can just have a current pistol.

You may also consider the true need of an optic. In a self defense situation, I think muscle memory and sight alignment would work well. Also a good Trijicon HD sight set for $150 could enliven the classic P220. Trijicon will install the sights for you, if you purchase direct from them.

And, you'll need to thoroughly check the optic for clarity with YOUR eyesight. Holosun do NOT work for me. The dot or circle just become starlike fuzzy lights that obscure the target. Trijicon RMR -- nice and clear. Did I mention that the Trijicon is double the price of the Holosun?

Don't forget all your holsters are now obsolete with the optic. Yep, more money. Optics cut leather. So, optics, although truly better, are not a simple decision.

I was able to order a P220 Slide from Sig that was already milled. It was the Legion slide, but I am in california [and cannot purchase any Sig Legion firearms] so they sold it to me anyway. I am happy as I now have the standard length slide [with reddot cut] and the original 4" barreled slide for my P220 Stainless Elite carry .45. I can swap back/forth with no issues, for carry or range.

Maybe contact The Sig Armorer, and see what he thinks. He's also a member here. I used to work for www.vulcanmachinewerks.com a few years ago. I'm pretty sure we did optics cuts on older Sig P220 series pistols from the 80's and 90's. A P226 comes to mind.

Here's the link for The Sig Armorer
https://www.thesigarmorer.com/