Originally Posted by lcjones
Do not shoot +P in the Glock (any Glock). It is a very good gun but barrel strength is not one of its great qualities.
Glock barrels are cold hammer forged, and use a type of polygonal rifling. Why? Because of strength, mostly.
Cold hammer forging steel around a mandrel (shaped like the inside of the Glock barrel) is one of the best ways to make a barrel. It relieves stress and aligns the grain of the steel.
The poly rifling is for strength, extra velocity, and longevity. How, you ask? Thanks for asking.
Broach cut rifling makes for a very accurate barrel. It also creates sharp corners where the lands meet the grooves. These corners are susceptible to increased heat transfer/degradation/metal fatigue. The poly rifling maintains its strength, as it does not have weak corners.
Broach cut rifling can allow minute amounts of hot gas to escape past the bullet. Poly rifling seals tighter.
Broach cut rifling cuts into the bullet deeper, causing more deformation and drag to the bullet, and slower velocity. Poly rifling allows for a tighter gas seal, and the rounded flanges cause less deformation to the bullet. It imparts less drag and leads to higher velocities.
HK used poly barrels in early variants of the G3. Some of these were imported on HK91's very early on. They are considered "unobtanium" these days. HK's with Poly barrels are not just collectible due to how rare they are, but also because the barrels last several times longer than the broach cut barrels, and are much less susceptible to rust/corrosion.
Glock barrels that you see blown up are products of the same stuff that blows up every gun barrel. Squibb loads, lead build up, bad ammo, etc.
The Glock 17 barrel can handle whatever you want to dish out, in my experience. The .40's have unsupported chambers, which can be problematic if used in conjunction with light (135gr) +P loads. This is partly because the .40 brass does not have a reinforced case head, and was developed to work with 180gr bullets at 950-980 fps. NOT 135gr at 1350 fps.
I used to be in the fortunate position of getting as much of the black tip Uzi SMG ammo for free as I could carry away. I fired uncountable thousands of rds of it through Glocks with no issues at all.