And yeah, regular 45 acp wouldn't be no good for thick skinned fare, but 45 Super out of that long slide G21 of yours would be a mini hand cannon, definitely do the job for anything in our area and maybe bigger (a few Alaskans tout it).
Actually, I've found that it's not as impressive as I'd hoped. In fact, the 45 Super was a disappointment without adding a fair sized muzzle brake to my pistol.
You see, I've shot 45 Super out of my G21L as well but with disappointing results for me. The problem is that without a muzzle brake, a 200grn Speer Gold Dot bullet at 1,307fps is about as far as I can push the 45 Super in my pistol because the recoil is significantly higher than the 10mm's. I've also tried 230grn bullets but the recoil is even more severe. So heavy that I'm concerned about battering the frame and slide and destroying my pistol. In fact, I was so concerned that, while I loaded up 100rds of 45 Super, I've only ever shot 15 of them.
I was very surprised at that situation because shooting either a 165 or 180grn 'nuclear' level load 10mm load out of my G20L (which if you remember, is the same gun with just a different barrel and mags) produces a surprisingly soft recoil even with my hottest 10mm loads. So soft that a few who've I let shoot it with my 'nuclear' loads are almost disappointed because they expected a 'fire breathing monster' type recoil when they see the chrono results before they shoot it.
A neighbor I shoot with who owns both a G20 and G29 has also shot my 'nuclear' 165grn loads in his pistols and agrees they are a handful in either his G20 or 29 but when he shoots them in my G20L with it's 4.75oz heavier slide and barrel, he can't believe how soft the recoil is and how comfortable they are to shoot. He also agrees the balance of the pistol is better as well.
However, when I let him shoot a few .45 Super loads in my G21L, he agreed that the recoil is significantly higher than the 165grn 10mm (the higher of the 165 and 180). In fact, he was quite surprised as the 45 Super loads aren't anywhere near 'nuclear' level as my 10mm loads are. We both agree that the 10mm loads are both a strong push while the 45 Super load is more of a strong jolt.
Yes, a muzzle brake with the 45 Super loads would allow for a hotter load and the use of heavier bullets, but I don't see the practicality of a muzzle brake on a pistol just to shoot 45 Super as it isn't necessary with my 10mm. Besides, to produce more muzzle energy than my 165grn 10mm loads we'd be talking a 230grn 45 Super at 1,375fps and that would produce a significant increase in recoil over the 200grn loads with even more battering potential.
And the worst part of the difference isn't the recoil. It's that the .45 Super loads produce less muzzle energy. I'm using the same platform and the same powder, Power Pistol, and nearly the same bullet weights but the muzzle energy the 45 Super produced was a disappointment to me.
The chrono data I generated at my range which is located at 6,100ft above sea level on an 84°, sunny day shows that the 10mm produces significantly higher muzzle energy (ME) than the 45 Super because of it's much higher velocities.
10mm:
165grn Gold Dots:
1,589fps producing
925ft/lbs ME
180grn Gold Dots:
1,479fps producing
874ft/lbs ME
45 Super:
200grn Gold Dots:
1,307fps producing
759ft/lbs ME
That's 166ft/lbs more ME for the 165grn 10mm and 115ft/lbs more ME for the 180grn 10mm than the 45 Super.
Finally, with both calibers sighted in at 100yds, the 165grn 10mm is a flatter shooting load as one would expect, with a drop of 8" less at 200yds than the 200grn 45 Super. And yes, I shoot my 10mm pistol with iron sights at steel plates at 200yds routinely.
It's quite fun to step up to the line after someone with a scoped AK stops shooting at the steel plate and missing a few shots, and raise my pistol up with it's iron sights and fire at the same plate and ring it over and over again. (All I need do is aim at the top of the plate and the bullet will strike the plate a bit below center. It's actually quite simple.)