Here's a recent article about a 10mm Glock G20 having a "catastrophic disassembly" (as I call it) from an over pressure round. Modified G20 with match barrel (i.e. tight chamber), long barrel, and +P ammo add up to a bad combo. But there are multiple perfect storm events here that I think shooters need to know about.
Here's the story: http://www.thetruthaboutguns.com/2017/01/jeremy-s/rip-glock-20-kaboom/
There are multiple things happening all at once to create a very high pressure round in this case. First, the standard Glock 20 chamber of the barrel is a standard chamber. It is much more open and is not as tight as a "match" barrel is. With a more open chamber, there is more room. More room means less pressure on a given round. In this case, the shooter installed a Lone Wolf after market match barrel. The match barrel has a much tighter chamber. Tighter chamber means less internal room, which means more pressure. If you take a standard 10mm round loaded to normal max pressure, and fire it in the standard factory Glock barrel, all is good. When you fire that same round in a match barrel with a tighter chamber, that same normal max pressure round, has less room in the chamber, therefore your pressures go up. Simple physics, right.
Now, take the Underwood ammo used in this case. They show this 140 grain LeHigh Penetrator round going 1500 fps. Data on other 135 and 140 grain bullets do not even show velocities this fast. Even LeHigh's 10mm 140 grain Load data
shows the max speed of 1315 fps with this bullet. Most max velocities are in the 1300-1400 fps with a 140 grain. Also, a solid copper bullet will have more bearing surface on the bullet, so there is more surface area pushing back to generate more pressure. The ammo is also loaded with a nickel case. Nickel is a coating added to the outside of the case. Doing this, decreases the internal volume of the case, and increases the pressure.
+P ammo, nickel case, tight match chamber, longer barrel, solid copper bullet... add all this and you have a perfect storm of events leading up to a major over pressure issue. There's no "free lunch" in shooting with pressures and bullet velocities. Sure, everyone wants a fast round, but there becomes a point where you cross the line between too fast and something like this happens. Yes, the article said the bullet was under-sized and probably had bullet set back to cause the issue. But if they are truly running 1500 fps with a 140 grain, the powder inside the case will be so much that the bullet set back would be near impossible.
Shooters need to be informed about their ammo choices and know the effects on what's happening when they make changes to their firearm with that ammo. SMH.