The reason I changed my recoil spring set up on my Glock G20SF. Not sure if the same holds true for your S&W autos.
From Buffalo Bore's website:
"Full power 10mm ammo has always generated enough recoil and pressure to require a pretty stiff recoil spring in your handgun - this of course depends on several variables such as your slide weight, etc. When the cartridge fires, it generates enough pressure/recoil to prematurely open your breech face in some guns. When this happens, the opening breech face has an effect on the burn rate of the powder. This can result in some fairly high extreme spreads in velocity. If you are experiencing extreme velocity spreads of more than 50 fps, simply install a stiffer recoil spring. For example, I have an original Colt Delta Elite. This gun with the factory spring runs extreme spreads of about 35fps with both of these 10mm loads. I am happy with 35 fps, so I leave the Delta Elite as is. I also have a custom built Para Ordinance with a Nowlin barrel. It runs extreme spreads of about 70 fps with its original recoil spring. When I install a spring that is 4 lbs stiffer, the extreme spread drops to about 35 fps.
The new Glock model 20 comes with a recoil spring that allows the breech face to open too soon and my new Glock model 20 will get extreme spreads of about 100fps with the factory spring installed. When I go to a stiffer recoil spring, the extreme spreads drop to about 50 fps in my new Glock model 20. Of course none of this will be an issue in a revolver. None of this will be an issue in real life either, as these high extreme spreads don't hurt accuracy or function. However, I mention this because if you are like me and want things to be as correct as possible, I have outlined the problem and the solution. The industry fixed all these problems initially, by watering down the 10mm ammo over the last several years. The watered down 10mm ammo does not generate the pressure/recoil to open the breech face early. If you want the full powered 10mm ammo we make, you simply need to tweak your pistol. Or just realize that you are getting some fairly high extreme spreads and ignore it or live with it."
I learned some things.
1) I swapped out the standard recoil spring for a non-captive Wolff guide rod and #22 lb spring...it ran flawlessly with all ammo.
2) I like 10mm....a lot! Water filled milk jugs, water soaked telephone books, very thick polyethylene pads.....all had incredible and violent damaged inflicted on them. Bigger boom/snap than 9mm but very controllable.
3) I was shooting Georgia Arms new "Canned Heat" 180 gr FMJ (1100 fps) range ammo, Hornady 155 gr HP using an XTP bullet (1265 fps), and Buffalo Bore's 180 gr JHP (1350 fp). The GA stuff was excellent range ammo....accurate and pretty powerful. The Hornady was excellent though I wanted some of the 180 gr stuff....but the 155 gr would be excellent for SD. The biggest disappointment was the Buffalo Bore. The stuff was explosive....it damn near vaporized the water jugs. The issue? They stopped using Speer Gold Dots bullets for whatever reason and it shows. Every bullet that I recovered had complete core and jacket separation. Sometimes the separation started before it made it thru a single jug of water.
This was my 1st shot....just shooting at a single water soaked telephone book with thick pads behind it.
The entrance...lower right:
The exit:
Then I moved to shooting thru a milk jug filled with water....backed by the soaked phone book....then backed by 12" thick poly pads.
That is when the disappointment started. I was digging fragments out of the milk jug, the phone book and the pads. The bullet started to come apart almost immediately.
This was typical of what I found:
Fun day of shooting. I am sold on 10mm....I will be testing some Double Tap stuff next.
