Julien Boit Posted September 19, 2001 Share Posted September 19, 2001 Hey all, I was calculating spring rates in kilogrammes last time when i thought about it : If you calculate the force that the bullet produces, you should find a spring rate that would correspond to the momentum (in fact its opposite). Is it true, or am I wrong ? DVC Julien Link to comment Share on other sites More sharing options...
Bill Schwab Posted September 19, 2001 Share Posted September 19, 2001 Julien, I think you're on the right track, but your method doesn't take into account the weight of the slide. The momentum of the bullet is countered by -the spring rate -the acceleration of the slide -and other stuff (like the friction between the slide/frame fit etc) You can forget about the last (friction, etc) and get a pretty close answer. Geez, I'm having flashbacks of engineering school (scary stuff). Bill Link to comment Share on other sites More sharing options...
Julien Boit Posted September 19, 2001 Author Share Posted September 19, 2001 Hey bill, My goal was to have a "scientific" base to start to work with recoil springs. Of course slide weight was in a corner of my mind . My main problem is to find tools to measure things such as slide travel and speed. About friction, i should find back some datas in my old school books (I studied mechanics few years ago). Thanks DVC Julien Link to comment Share on other sites More sharing options...
Bill Schwab Posted September 19, 2001 Share Posted September 19, 2001 Julien, I hope I in no way offended you. Wow, tools to measure slide velocity, you're really getting into this...what's your ultimate plan/goal with this endeavor? Bill Link to comment Share on other sites More sharing options...
benos Posted September 19, 2001 Share Posted September 19, 2001 You fellas can measure and calculate till the cows come home, but the gun still has to FEED. (Get it - cows, feed) It's not possible to calculate the variables involved in that. be Link to comment Share on other sites More sharing options...
Detlef Posted September 19, 2001 Share Posted September 19, 2001 I knew someone would eventually ask a physics question....:-) Julien, I don't know what this should accomplish. What *is* the optimal spring weight??? I sure don't know...but Brian's answer is a good first one: One that makes your gun feed! So if in our calculation we find that the force of the spring is more than the opposite force caused by the exiting bullet, the gun won't open and you won't be happy. On the other extreme is the gun with such a light spring that you could well leave it out: No spring! It's actually worth an experiment. Hint: The slide will *not* be stuck all the way back! Anyway, also no good because no feed! In between, you'll have to experiment with the complex timing of slide travel and force development, and figure out what you *feel* suites you best. I am sure that the gun companies have all these hard measurements, but I have never seen them published anywhere. Here I go: Brian, correct me on this, I think a *10 lb* spring will keep a 10 lb weight suspended (how much?) when you stand up the spring vertically and put the weight down on it. So certainly initially the spring *force* is mass (10 lb) times acceleration (gravitational constant g): 10 lb * 9.8 m/sec^2 = 2 200 000 grain*ft/sec^2 (I did the unit conversion for you from lb to grain and from meters to ft). Since I run a 10 lb spring and my gun cycles, I would hope that the force caused by the shot is at least that, so here I go: Force is also change of momentum in time. Here's where things get ugly, that force at any instant while the bullet travels down the barrel will vary greatly with time, and I have no idea how that will look! Let's pretend that it's constant instead. The bullet exits with momentum 170 000 gr*ft/sec (you shoot Standard, don't you?), and it takes about 0.0005 sec to clear the barrel. So it changed momentum from 0 to 170 000 in 0.0005 sec, therefore Average "bullet" force = 170 000/0.0005 sec = 34 000 000 grain *ft/sec^2 Good, that force is larger than the spring force, so it can overcome it, kick the slide backwards and cycle the gun! Notice that thus far, slide mass/weight had not appeared anywhere! But that makes sense since we all know that the slide doesn't even begin to move before the bullet has exited! So now we are faced with having to *conserve momentum*: The bullet has gone forward with 170 PF, that means gun, shooter and all that's attached to it will *eventually* get that exact amount of momentum backwards. In a revolver that happens instantly, in a pistol the moving slide will delay some of the momentum transfer until it closed again (takes about 0.1 sec), until then it both pulls and pushes on the shooter in a weird way. So what did you really want to accomplish with all this? Don't run a spring that keeps the slide closed? We knew that! So...I think you're on the wrong track wanting to balance those opposing forces, one absolutely *has* to be larger than the other, but the other still *has* to be large enough to feed new ammo reliably. In between, it's up to you... --Detlef (Edited by Detlef at 2:51 pm on Sep. 19, 2001) Link to comment Share on other sites More sharing options...
benos Posted September 19, 2001 Share Posted September 19, 2001 Wow!, now that was the response I know we all were looking for, (and expected), from our moderator. And, the distance is one inch. If you put your cars coil spring on top of your super accurate bathroom scale and place all this in your handy hydralic press, take out the slack, and then compress the press one inch, the reading is your spring rate. be Link to comment Share on other sites More sharing options...
Detlef Posted September 19, 2001 Share Posted September 19, 2001 thanks, that's what I didn't know... Link to comment Share on other sites More sharing options...
Singlestack Posted September 20, 2001 Share Posted September 20, 2001 Uh, anyone care to translate Detlef's post to english? (Edited by Singlestack at 10:42 pm on Sep. 19, 2001) Link to comment Share on other sites More sharing options...
Julien Boit Posted September 20, 2001 Author Share Posted September 20, 2001 Wow , detlef ! I must confess, i didn't think about all those things involved ! Bill, no problem, you didn't offend me at all . Thanks all DVC Julien Link to comment Share on other sites More sharing options...
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