[shuffster]

Hi guys, I am new on here. I purchased a gen 3 21 LE trade in this past week. Took it to the range this morning after changing to a stainless guide rod and about half the time the slide locked back.
I made sure my thumb stayed out of the way and kept good grip, stance, etc. I changed my grip several times but nothing helped.
Could the guide rod be the problem since this didn't happen at all with the original guide rod?
Thanks

 

[jimmyalbrecht]

The slide locked back, but there was no misfeed, double feed, or stovepipe? Did the shell eject? And I think it might be the slide stop lever. Maybe the spring is not strong enough and the recoil is causing it to pop up and lock the slide. It could also be a bad magazine. The spring may be pushing the slide stop lever up when in tries to push the round up. Have you tried different magazines?

 

[voyager4520]

If it didn't happen with the original guide rod, I'd try lubricating the steel guide rod. What I do is take an old expired soft plastic ID card that I use for gun cleaning, I wrap an oiled patch around it and run it through the gaps between the spring coils.

Have you ever taken apart the frame, say to install a different slide stop? If it's a used gun, the previous owner may have. They may have reassembled it incorrectly or used the wrong parts.

The slide stop spring is probably in the wrong position, the spring needs to be under the locking block pin.

(inside the frame of course)

If the spring is in the correct position, it's possible that your grip was pushing the slide stop up into the slide without you realizing it. Another possibility is that you're using the wrong slide stop. The correct slide stop to use in the G21 is Glock part # 5306 for standard, # 1034 for extended. The slide stop will have a different number from the actual part # stamped onto it.

 

[bryanbrescia]

^ bingo, its critical that the spring on the slide stop is underneath the locking block pin

 

[shuffster]

Voyager4520 you nailed it. I posted this and took a shower and remembered putting it back together and knew exactly what the problem was then your post confirmed it. Problem alleviated thanks for the help!