I heard of this problem. They had a 40 cal spring in the 9mm but it was to stiff. It was changed for a weaker recoil spring. I have heard that there were still some issues with weaker cheap ammo until it was broken in. If you look or call Glock they will tell you that 115 grain ammo is to weak. They designed it for 124grain. That's why people get casings in the face. So I've heard hope it helps.
I have a gen 4 glock 19. It is an incredible gun and shoots like a dream. I have had a few problems with spent cases hitting me in the face with Winchester white box. Nothing to worry about it doesn't hurt just catches u off guard. I wouldn't let that change ur mind on buying one. They are great!
I have yet to shoot a semi automatic weapon that would not occasionally throw a spent casing in my direction. That is why many ranges and safety courses require that all shooters wear a cap and safety glasses. I usually take an extra step and wear a full brim hat. I don't like hot casings going down my shirt.
I have a g17 gen 4, and yes in the beginning it did sometimes throw the brass back at me. But after 250 rds it seems fine now. Brass gets ejected to the side. Even with the 115g ammo.. My lgs said that since it has the latest ejector it may have just been a break in issue.... Love the gun!
I have a Glock 17 Gen 4 and, yes, it does throw brass back in your face if the ammunition is not high powered stuff. All the +P and 124/147 grain stuff I've put through my Glock has a predictable ejection pattern. All of the 115 grain loadings (Federal, Remington, Winchester, PRVI) I've tried have some ejection pattern issues.