Why did it take me so long to find this, I have had a M21Sf for about a year and use it in IDPA, its the greatest, hands down. I have a 19 but always favored the .45 acp. Slapped on some grip tape a ready to roll. I was asked what overall length do I use, funny, with a 21, if it goes in the mags, it goes through the gun. Thanks for your work here and be safe, shoot straight.