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Confused about 30S VS. 30 Slide Weight.. Physics Q

Discussion in 'General Glocking' started by BenjiEDF, Feb 2, 2013.

  1. BenjiEDF


    Jun 15, 2012
    Confused about 30S VS. 30 Slide Weight.. new question: stay on topic. For physics nerds and gun enthusiasts only please.

    I just bought a 30S and am taking her to the range tomorrow and I ran across this post while surfing:

    The new Gen 4 30 owner says his recoil assembly is marked as 0-1-9... My new 30S uses the exact same RSA!?!? but the slide is almost 4 ounces lighter? This seems really weird to me, I would think that the heavier slide of the normal 30 would have much more inertia to overcome and would use a spring with less coil tension but it uses the same one? How can a significantly heavier slide use the same RSA as the slim G36/30S slide? I always figured engineers at Glock and other manufacturers were math geeks computing these type of ratios... I must be missing something here :embarassed:
  2. MSims


    Jun 19, 2012
    Actually its about 3.4 ounces and it uses the same recoil spring cause a G30s is bascially a parts model they slapped together since they wont be making anymore the G36 anymore... Plus it needs to handle that snappy recoil and the spring can handle it... Enjoy shooting it and enjoy your follow up shots... Lots and lots of practice... You shouldve gotten PERFECTION and thats the original G30 that is a smooth shooter overall especially when you really need it in SD when you need to use your follow up shots for tight groups.... But like i said practice makes perfect... Might as well have gotten the G26 or G27... Enjoy ;)

  3. BenjiEDF


    Jun 15, 2012
    :upeyes: Apparently you can't read...
  4. Tiro Fijo

    Tiro Fijo

    May 31, 2011
    I would assume that there is a "window" for a certain rate of load on a RSA.
  5. cowboy1964


    Sep 4, 2009
    When did Glock say they were dropping the 36?
    Last edited: Feb 2, 2013
  6. G26S239

    G26S239 NRA Patron

    Mar 17, 2008
    I used to have a 30 as well as the 36 I still have. The recoil spring assemblies are interchangeable. Of course the G30 is easily adaptable to fire the 45 Super and the 36 is uncomfortable to fire +Ps in, to me it is anyway.

    MSims do you have any sort of supporting documentation behind your claim that the 36 is being discontinued? Or is that an assumption on your part?
    Last edited: Feb 2, 2013
  7. G26S239

    G26S239 NRA Patron

    Mar 17, 2008
    Last edited: Feb 2, 2013
  8. I like chocolate milk...:supergrin:

    I'd bet the G30 slide is overbuilt (for 10mm) and the spring and slide of the G36 was engineered to work together...much like the same spring for different slide weights of the G19 and the G23/32 does...

    Last edited: Feb 2, 2013
  9. butcher_block


    Jul 22, 2007
    that is what i would think
  10. English


    Dec 24, 2005
    The first problem is that you don't understand the physics of recoil. The source of recoil is the momentum of the bullet and other ejecta. Because momentum is conserved that has to be equal and opposite to the momentum gained by the slide and barrel in its initial recoil. It then gives up that momentum to the frame and the shooter.

    Your next problem is that the recoil spring gains energy, as distinct from momentum, from the velocity reduction of the slide. It then returns the major part of that energy to the momentum of the returning slide. (Momentum is a vector and energy is a scalar!)

    By using a heavier slide, the momentum of the slide remains the same but its energy is reduced. The recoil spring then absorbs the same energy as the lighter slide since both slides travel back to the stop against the frame. It is worth illustrating this with a simplified example in which the lighter slide is half the weight of the heavier slide. For simplicity we will ignore the mass of the barrel and treat it as a blow back action pistol.

    Our initial equation of momentum is:
    Mv =mV where M is the mass of the heavier slide and V is the velocity of the lighter slide.
    Since m is M/2, V has to be 2v.

    Thus, since kinetic energy is proportional to half the mass times the square of the velocity, the energy of the heavy slide is proportional to 2mvv/2 or mvv. The energy of the lighter slide is proportional to m2v2v/2 or 2mvv. That is, the energy of the lighter slide twice that of the heavier slide.

    If we pick a random but conveniet figure for the energy absorbed by the recoil spring of mvv/2 we can see that the remaining KE of the heavier slide at the end of its rearwards motion (mvv - mvv/2) is is proportional to mvv/2. The remaining energy of the lighter slide (2mvv - mvv/2) is proportional to 3mvv/2 and so is three times that of the remaining energy of the heavier slide.

    This means that, if anything, the lighter slide needs the stronger spring, but the reality is that there is not a 2:1 difference in the slide weights of the G36 and the G30 and so the KE difference is much less than a factor of 3 and the same recoil spring assembly can be used without an engineering problem as the impact between slide and frame is cushioned by the flexibility of the polymer frame.

    As a side consequence, the main source of felt recoil is the remaining slide momentum when the slide hits the frame. This is why the G36 and the G30S will have noticeably heavier felt recoil than the G30 and why Glocks have noticeably less felt recoil, pistol weight for pistol weight, than makes with lighter slides.

    To answer your question in another way, the heavier slide can use the same spring weight because it is traveling slower.

  11. CSP


    Mar 22, 2007
    The 36 and the 30 have always used the same recoil spring assy. I believe that English is correct and this is why the 30S uses the same one as well.

    I have been told, by GLOCK, that the G30S slide is heavier than the G36 slide as some additional mass was required to ensure function. I still want to see this for myself.

  12. BustedFlush

    BustedFlush Springy Member

    Mar 28, 2006
    Awesome post English. I've been "away" from GT for a while. Desiring news and updates of the Gen 4 models and the "new" 30S brought me back. Seems like GT members "invented" the 30S (aka 30/36 hybrid) pistol years ago, Glock really didn't do much. But if you want one you only have to buy one pistol now!

    I have always enjoyed your posts.

    BF :wavey:
  13. BustedFlush

    BustedFlush Springy Member

    Mar 28, 2006
    The specs for these models are on now, but they do not show slide mass.

    They do show the width of the slides for the various .45acp models. I think they must have the width dimension wrong for the model 30S, as Glock lists it as 32.5 mm, same as the other 30 variants.

    The width of the 36's slide is 28 mm. I suspect the 30S has the same width as the 36, but we won't know for sure until someone holds one and gets out the calipers.

    This is typical Glock when it comes to their website goofs. Come on guys, have a little attention to detail with your new product!
    Last edited: Feb 7, 2013
  14. Thekat

    Thekat Millennium Member

    Jan 21, 1999

    Yeah what's the deal with no more G36? Where did that come from?

  15. butcher_block


    Jul 22, 2007
    if the 36 is goig away ill pick up another one and then be set for life (the grip fits me like a glove )
    21 and 30 feel way wide and the std size frames feel to round to me
  16. GRT45

    GRT45 Transform & Win

    Jun 20, 2010
    In December, 2010, GT member Sonnytoo posted the results of careful measurements for several pistol models he owns and cleared up the mystery of the pistol dimensions posted on the Glock website. In a nutshell, the widths given on the website are not the slide widths, but rather are a width measured on the grip. That explains why the widths for the G30/G30SF versus G30S given on the website are the same.

    I archived his fact-filled post from 12/30/2010 and a relevant portion is quoted below. It has long been removed from online access at Glock Talk.

    Last edited: Feb 8, 2013
  17. DannyR

    DannyR Moderator Millennium Member

    Dec 17, 1998
    Roanoke, Virginia
    Width given is the widest part of the pistol--the frame, not the slide. Since the 30 and 30S share the same frame, they share the same width.
  18. ron59

    ron59 Bustin Caps

    Jan 3, 2009
    Smyrna, GA
    While English might be accurate with his technical diatribe (I didn't read it), it's all moot.

    You really think Glock takes any of that into consideration? Hardly.

    Check this: in the Gen3 guns, the 9mm and .40 caliber models of the same size use THE SAME RSA. Meaning, the G17 and the G22. Say what? The .40s have considerable more recoil than the 9mms. No, it's not .357Magnum recoil, but there is a considerable difference, I'm thinking probably more so than your G30 to G30S comparison.

    They could care less, they don't want to have to create/stock another combination, they just consider it "close enough for government work". You should too.

    And it's why many savvy 9mm-shooting competitors re-spring their gun ASAP.
    Last edited: Feb 8, 2013
  19. SiGlockBoy


    Mar 4, 2009
    Glock 29, 29sf, 30, 30s and 30sf all use the same RSA. In laymans terms, I believe the engineers concentrate on using a single RSA type for many guns due to simplicity of design and parts manufacturing. I also believe that they adjust slide weight to control the slide recoil speeds according to ammo and caliber. 17lbs +- 1lb is a very common spring rate for many semi auto guns in many different calibers from many makers.

    Have used the old 30sf/36 slide hybrid many times with my glocks. I still prefer the G36 for carry as the slide is thin in the waste so be the frame. If you like the gun to sit deeper you notice this.

    If you like the gun to sit high, you might not care so much.

    I do prefer to shoot my 30 or 30SF moreso as it tends to eat the recoil much better.
  20. BustedFlush

    BustedFlush Springy Member

    Mar 28, 2006
    Thanks for reposting. I've also had several of my better threads and posts pruned over the years.

    Glock's little diagram with the red lines and arrows is very misleading. It shows the width as being the slide width. Yet another Glock website mistake.


    I think any reasonable person viewing that second diagram would see the frame is wider than the slide, and that the slide is being measured.
    Last edited: Feb 8, 2013