I'll preface by stating I have little to no interest in .40 cal. Because of that I've been looking into a G20SF Gen3 and just getting a .40 conversion barrel. For those who have done this, how's the reliability?  I don't plan on shooting much .40 but want to have the option as during the last two panics it was all that was available for a while on the shelves. While I could spend $700 on ammo for the .45's and 9mm's...I would rather have another handgun at this point. I already have a G21SF and two G19's in terms of Glocks, and other .45 and 9mm handguns as well. I'm liking the idea of a 10mm for backcountry hiking and range fun now and then, along with the ability to shoot .40 as long as that option proves reliable. Thanks!

Yes, if you get a g20sf and put a 40 cal barrel in it, it should shoot just fine.  The stock recoil spring is 18 lbs and should work good with 40 cal loads.  If you shoot some really hot 10mm (buffalo bore, Underwood)  I would suggest a 22 lb spring.

Gen 4 is the same frame with back straps.

I prefer the 3rd Gen's...and I'm biased as well since my G21 is a Gen 3 SF...

Found a Gen4 blue label gun local for $491. There's also a G20SF at a Sportsmanship Warehouse not too far away I have on a 24 hr hold for about $70 more, but with a mil discount I won't have to pay sales tax. Decisions decisions.

That 40 conversion barrel for the G20 will also work in your G21, so just buy a conversion barrel and a couple g20 mags.

So how do you shrink down the breech face to fit the 40 brass???

Now you could get a 40 Super conversion barrel. That would be a 45 ACP necked down to 10mm.

Since you have a Glock 21 and want a pistol for protection in the backcountry; why don't you get a 460 Rowland conversion for your G21?

It is a stretched out 45 ACP with 44 Mag power level performance. Underwood has 255 gr ammo with 950 '/lbs. of muzzle energy. The 460 Rowland steps all over the 10mm for terminal performance (but then there is ammo availability).

The 460 is not something you will be firing 1,000's of rounds out. So stock up a few boxes now.

Yea I know.... more pistols, more fun. The G20 with 40S&W conversion good train-up to higher power rounds (and ammo availability). But power wise the 45 ACP to 460 Rowland is very noticeable on a steel target or water jugs; people will notice.  Even a hungry bear will decide to go somewhere else (or die) when hit with a couple of 255 grain slugs.

I've considered that as well. I'm enjoying shooting handguns more lately and want to get into some "different" calibers.

I've seen a lot of used police-trade in M&P .40s lately at decent prices.  Although S&W doesn't offer 10mm (yes ) you can get the .40, and a 9mm barrel.  You might also be able to scrounge up a 357 sig barrel if you looked hard enough.

Picked up the Gen 3 G20SF today. Hoping to try it out at the range tomorrow. Bought 50 rnds of FMJ 200gr HSM and 50 rnds of HPR 180gr JHP's. Neither have spectacularly quick advertised velocities but I don't plan on buying too much factory ammo for this thing. Going to buy some brass and get reloading in a few weeks.  Thinking of picking up a 9x25 Dillon barrel for the G20 and a 460 Rowland barrel for the G21. Should make for some good times at the reloading bench.

With the 22lb spring, you won't get entirely reliable cycling of weaker loads on par with .40.

I've left the stock 17lbs spring in it for now. I'll get a few different springs to try and manage the recoil of higher velocity stuff.