Glock 21 to 20 guide rod questions (plus 17)

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  • lazarus

    Ultimate Member
    Jun 23, 2015
    13,737
    So, seems like all I need is a barrel and mags. I have mags for the 20. Hunting down someone's old barrel from when they got something fancy.

    What's up with the guide rod and recoil spring? I've seen a couple people mention swapping them with some mention that the G20 slide is a bit heavier than a 21 slide (any truth to that?), but that the G20 and 21 actually have the same recoil guide rod and spring rate.

    Also, is the G17 the same guide rod and spring? I am referring to the gen 3 for all of these here.

    I am wondering in part because I've got a Wolff SS guide rod for my 17, that I don't use in it and I think 18 and 19# springs (at least an 18#, but I think I'd gotten 18 and 19 and not a 17 and an 18#). I've seen mention of using 21# in a caliber conversion, but I figure a 19# is at least a start.

    With the current ammo shortage its not like I am planning on investing in thousands of rounds. I am looking to get 100-150 and barrel and once I can get to a range, just mostly function check it. A fun, not so rainy day, project.

    I'll worry about ultimate reliability and/or not battering the frame/locking block pin apart later (unless of course 50-100 rounds is going to bend things up).

    Some day I'd build a 20 slide, but those funds are better spent elsewhere.

    So I guess to lay it out

    1) all I REALLY need is swap the barrel and the mags
    2) Is the G20 and G21 slide the same weight wise?
    3) Do the G20 and G21 use the same recoil guide rod spring rate?
    4) Is a G17 guide rod the same as the G20 and G21, so I can use my G17 SS guide rod with a heavier weight spring (and also what weight, but would stepping it up even to just 18 or 19 be okay, if not ideal)?

    Thanks!
     

    GunBum

    Active Member
    Feb 21, 2018
    751
    SW Missouri
    Answers in order. :D

    1) Yes and no. Unless your extractor doesn’t reach far enough. Then you may also need a different extractor. It is also recommended to use a 20lb recoil spring.
    2) No. the 21 slide is a little bit lighter. A very little bit.
    3) Change to a 20lb spring and don’t worry about it. At least that’s the internet lore, and it seems to work.
    4) See answers above
     

    lazarus

    Ultimate Member
    Jun 23, 2015
    13,737
    Answers in order. :D

    1) Yes and no. Unless your extractor doesn’t reach far enough. Then you may also need a different extractor. It is also recommended to use a 20lb recoil spring.
    2) No. the 21 slide is a little bit lighter. A very little bit.
    3) Change to a 20lb spring and don’t worry about it. At least that’s the internet lore, and it seems to work.
    4) See answers above

    Thanks!

    I'll poke through my box 'o gun parts and see what weight springs I have. I think its an 18 and a 19. I likely want/need things from Wolff, so maybe I'll just order a 20#.
     
    Thanks!

    I'll poke through my box 'o gun parts and see what weight springs I have. I think its an 18 and a 19. I likely want/need things from Wolff, so maybe I'll just order a 20#.

    I would get the Wolff 20# spring for full power loads. If you're using a 20# spring on lower power/most factory 10mm rounds you will damage brass. For those loads, I stick with the factory 17# spring.
     

    nedsurf

    Ultimate Member
    Feb 8, 2013
    2,204
    Also to consider, there are tungsten guide rods for the Glock 20 that adds front end weight that seems to help with the stout recoil of full power 10mm.
     

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