JoshF Posted January 24, 2009 Share Posted January 24, 2009 (edited) Can anyone give me accurate measurements for witness holes on 170mm and 140mm STI magazines? I'm thinking like 15, 20, 28/29 rnds marks.. I got 140mm 40S&W mags marked for 10,15,19 and I'm a little spoiled by them. I know a lot of people consider these "trade secrets" so If you can live with PM'ing them to me I'd be very thankful. Thanks Edited January 24, 2009 by JoshF Link to comment Share on other sites More sharing options...
joecichlid Posted January 25, 2009 Share Posted January 25, 2009 Josh, there is a little problem when trying to use a measurement to drill the whitness holes. That problem is the width of the magazine bodies. If they are just a little out of spec it can throw the hole totally off by a round when you get to the last hole. I found that out the easy way, take a look at my mags sometime. If there is an easy way to do it I would like to hear it too. Joe W. Link to comment Share on other sites More sharing options...
MadBomber Posted January 25, 2009 Share Posted January 25, 2009 I would love too have witness holes in my mags that were accurate. Having said that, how is that going to change when the next whiz bag follower/spring combo pops up? Do you through away your old tubes and start over? At 50-60 dollars a tube? As Reagan used to say, "Trust, but verify"! Count your rounds and know what is in there. Witness holes only work if everything remains constant. I always count my rounds in my mags. Link to comment Share on other sites More sharing options...
Tzygä Posted January 25, 2009 Share Posted January 25, 2009 I think gunsmiths need to know what kind of follower, springs and pads you are using to give exact measures. Link to comment Share on other sites More sharing options...
JoshF Posted January 25, 2009 Author Share Posted January 25, 2009 The Witness hole location is VERY close mag to mag long as you stay with the same manufacturer. If you think about it the holes are counting top down so followers really have nothing to do with this except where the final mark is (max capacity). I copied another set of mags from a friend on my 140mm STI tubes and they are PERFECT. Actually I tweaked his measurements just a bit to improve them. Does nobody have these measurements they'd be willing to share? PM works... I can keep a secret... kinda... Link to comment Share on other sites More sharing options...
Matt Cheely Posted January 25, 2009 Share Posted January 25, 2009 Problem is, most people had to cut up a perfectly good mag to get their measurements. Got $50 to get some measurements? Link to comment Share on other sites More sharing options...
BBoyle Posted January 26, 2009 Share Posted January 26, 2009 Can't you just take an empty tube and tape a round in the top and then fill it up from undrneath with the 20/21/22/28/29/30 rounds that the mag will hold and measure from the bottom. Then just add half the diameter from the cartridge to get you measurements. I would think it would be easy you just have to make sure you stack the rounds right in the mag. Link to comment Share on other sites More sharing options...
kimel Posted January 27, 2009 Share Posted January 27, 2009 Hmmm...that might just work. Link to comment Share on other sites More sharing options...
Flatland Shooter Posted January 27, 2009 Share Posted January 27, 2009 Can't you just take an empty tube and tape a round in the top and then fill it up from undrneath with the 20/21/22/28/29/30 rounds that the mag will hold and measure from the bottom. Then just add half the diameter from the cartridge to get you measurements. I would think it would be easy you just have to make sure you stack the rounds right in the mag. That's how I did mine. I shaved down a piece of wood to slide into the mag tube and tapered the top to keep the last round in place. Then I marked on the wood how far into the mag it went. Used the marks to align the last round's primer for my witness hole. It did not turn out perfect (one mag shows about 1/2 of the primer) but at least I can tell at a glance if its full or not. Bill Link to comment Share on other sites More sharing options...
ipscjoe Posted January 27, 2009 Share Posted January 27, 2009 I might be thinking a bit out of the box, but couldn't you take the guts out of the mag and carefully stack the bullets inside the mag (upside down), then mark the spine of the tube where you want the hole?...... Just wondering.... Joe Link to comment Share on other sites More sharing options...
redwoods Posted January 28, 2009 Share Posted January 28, 2009 There was a previous thread on this. I read it a while back and found out if you want to do it yourself you can try this.... Take a mag apart. Drop 10 or 15 rounds in it (depending on how many rounds you want the hole to show) Put the follower and spring back in Put the pad on without locking it on Make sure the rounds aren't loose Put mag upside down and slowly take pad off and spring/follower out Measure from bottom of mag to closest round and note what side it is on Measure the back of your round to the primer to find out how much to add to the measurement Use a special drill bit because the mag is stainless steel Randy Link to comment Share on other sites More sharing options...
Larry273 Posted January 28, 2009 Share Posted January 28, 2009 sounds like a good use for that mag that just won't work right (we all have one) which can serve as a test mag----worst thing that can happen is that there are a couple of "speed/lightning" holes that serve little purpose on the back of that mag---in either case, it will serve as a template for the rest of the mags Link to comment Share on other sites More sharing options...
JoshF Posted January 28, 2009 Author Share Posted January 28, 2009 Thanks guys for all the suggestions. I've already measured the 140mm mag by filling it to 10,15,22 and then removing the basepad/spring everytime to measure. I just got varying measurements when I repeated it. I finally did it enough the numbers are close so I'm going to take one of my junk mags which has a crack behind the feedlip to test with. We'll see how close I get. I've already done all my 140mm 40 mags so I got the drilling part down. I have access to a mill to do this with which makes things MUCH easier as the stainless is REAL hard. I'll post numbers and pics as soon as I get a chance to hack one up, it's worth loosing a tube or two getting numbers I can use and share. Link to comment Share on other sites More sharing options...
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