A 10mm Glock question...

[Hans Gruber]

I tried a couple varieties of Underwoods 10mm ammo in my new G20SF...and the pistol didn't like the heavy hard-cast loads. The G20 factory barrel didn't lead or anything like that..it just wasn't as accurate as the other 10mm factory loads I have shot.

After some experience shooting various bullet weights from my G20 seems to me that my particular G20 shoots best with 180gr or similar weight bullets. These weight bullets shooting perfectly to point of aim on my fixed-sight pistol...

Stevie that's just my point...the factory barrel will not adequately stabilize lead slugs because the lead tends to deform and "slip" rather than "grip" as it does in the lands and groove environment of a traditionally rifled barrel.

But....you've found success with the 180 grain load...which is quite stout on it's own merit and certainly has an edge in reliable chambering under varied conditions.
As good as Underwood's 10mm ammo is from STOCK barrels, push it through a longer aftermarket tube and the chrono results are truly astounding....I've read other posts where people have chrono'd 180 slugs above 900 lb-ft of KE from 6" long barrels and based on my own experience those results are in-line.
I know everyone likes to compare the 10mm to the .44 Magnum...and it's really a valid comparison as long as one is comparing Apples to Apples - whether of the Fuchishima (joke), or Golden Delicious. A 5" 10mm stoked with REAL 10mm ammo (Underwood Buffalo Bore, Corbon) IS the equal of a 4" .44 Magnum power-wise, yet almost 3x "better" due to capacity and FAR EASIER shootability!
On the other hand, take a Ruger Super Blackhawk with 7.5" barrel and a close BC gap around .003" stoked with 300-340 grain hard cast stompers over slow burning powder and the "up-rated" .44 magnum is WAY - WAY above anything the 10mm can possibly achieve!
Having owned both...and USED both to hunt Alligators in south Mississippi, the Glock is the more portable choice albeit not the more "potent" choice!
On the other hand, a 4" S&W .500 stuffed with five, 440 grain Hard-cast sausages delivering 2,000 lb-ft of KE beats the Ruger hands down...though it does tend to vaporize a lot of tissue that damages the skin, and whether you hit the walnut sized brain or not is merely a subject for coffee table conversation, because the huge slugs will shatter the skull and associated structures rendering the gator's jaw function useless! -)
Suffice it to say that when a .500 slug impacts most creatures across a boney structure, functionality beyond that point is impossible.