What headstamps are using small pistol primers? I've been loading 10mm for about 15 years and never even knew there was a small primer case for them. Now, .40S&W uses a small pistol primer, sure you don't have some of them mixed in? Only 0.142" difference in length between .40S&W and 10mm Auto cases.
All I've ever used for my 10mm loads is Federal Premium brass, I got a big bag of once-fired many years ago, over 1000 cases and still using them. Some are on their 4th reload (of mine).
Whatever brass you use, start low on the pressure. I loaded a long time for a 2nd Gen G20, which has a non-fully supported chamber and full power loads would bulge the case in the ramp area. I finally sold the gun after owning it for 24 years and bought a Ruger SR1911 in 10mm. I don't miss the Glock.