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 Post subject: Re: Shop goings-on
PostPosted: Fri Feb 16, 2024 11:46 am 
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I'm diggin' the closed-off side ports with the new barrel. the look has a certain industrial/steampunk appearance to it. Leave it to Ned to to a replacement/repair and turn it into art.


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 Post subject: Re: Shop goings-on
PostPosted: Mon Feb 19, 2024 11:04 am 
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Thank you Patrick. You are forgiven for disliking the Shield Driver sight :lol:

Off-center firing pin holes- As mentioned in a recent post (Page 8 of this thread, Dec 22), this is practically a given in guns shorter than a Commander. Manufacturers could totally make this go away but I think that because "most of the time" it's not extreme enough to lead to misfires, they get away with it. The barrel is shorter but nothing is changed about the slide bore that locates the front of the barrel when in battery, so as the barrel locks up, it tips 'down" more than in a G-Model. As it does the rear end also tip up a little-- low firing pin strikes are common in these, although again, it has to be radically off center to cause misfires. I have not purposely tried it but I would guess that off center plus a 9mm-sized firing pin that is quite common, plus the Speer ammo with small primers, would be the misfirin'-est combo.

In any case, when it has to be fixed, outside of a radical mess=around with the barrel, the fix is a bushing. How far doe the FP hole have to move sometimes? A lot:

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This FP hole is on-center with the chamber within a couple thousands, not gonna reveal my exact method but it puts the hole right-effing-there. The question becomes, do you but in a blank bushing and then drill the FP hole perfectly aligned with the bore axis, or do you make the bushing hole on center and then make the bushing with the FP hole in the center of it, the install the bushing? I prefer the latter.

When things are this eccentric, it's beneficial to use a 9mm FP, otherwise there is more likelihood of the FB binding in the misaligned holes. In the pic you can see that after installation, I went in the firing pin hole from the back with a flat-bottom drill to make sure that the back of the bushing and the original hole present a flat enough surface to the firing pin spring to land squarely in, otherwise it might contribute to binding.


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 Post subject: Re: Shop goings-on
PostPosted: Mon Feb 19, 2024 11:28 am 
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My head hurts just thinking about how this was done,and what the FP has to go through, to squirm through the breechface to the primer.


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 Post subject: Re: Shop goings-on
PostPosted: Thu Feb 22, 2024 10:29 am 
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The .50 GI pin gun ( https://forum.ltwguns.com/viewtopic.php?f=6&t=9890 ) with the compensator made of Delrin, as expected, has suffered some erosion. It’s a two-chamber comp and I had already installed an aluminum flanged bushing on the first blast face, that was really taking the brunt as expected. Well that eventually got damaged when an ejected case bounced off of something and landed in the rear chamber—just as the trigger finger had been given the “fire” command. Damage was not catastrophic and it would have been good for another season of pin shooting but—I was asked to bring it back up to par. This is the process in small part.
Boring the first chamber back to a known dimension—just cleaning it up 90%, really. The flame erosion pattern was interesting and you can kinda see it here—the axial washouts correspond with lands, and not grooves, in the barrel (these are eight-groove barrels). This pic makes it look like the Delrin is threaded but those are just the pass-though holes for the cap screws that hold the comp to the barrel extension, that have been marked by the screws.
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Starting the aluminum sleeve that will line the rear chamber.
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Lots of chips….. 7075 aluminum.
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Sleeve finished and installed at a light press fit… now two slots are milled for little keys to be dropped in and sandwiched between the Delrin comp and the aluminum barrel extension. These will keep the sleeve from rotating and from moving upward, which I don’t think it would do but when you fire bullets through things by the thousands, the unexpected does happen.
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More to be done, but sofar, so good. You can see some of the remaining flame erosion where the aluminum and Delrin meet at the top. I just didn’t want to bore out enough Delrin out to clean it up. I see it like a patch on a Spartan’s helmet—“OK, this guy has seen some battles.”. And it is very true of this .50 GI pin gun!
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 Post subject: Re: Shop goings-on
PostPosted: Thu Feb 22, 2024 5:35 pm 
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The front blast face was also getting significant erosion, again as expected, but I think it can also be taken as an indicator that the second chamber and blast face are doing some work. If gas and particulates are hitting it hard enough to erode it (even though it's just Delrin), it's pushing the muzzle forward / down to same degree. So the blast face resurfacing plate is not 7075 aluminum, it's the soft gummy stuff. But it will hold up better than Delrin and anyway I made a spare. It is held on with four, 5-40 alloy button-head cap screws and aircraft locknuts. I think we're good for another 5-10,000 rounds of .50 GI goodness. Bowling pins beware.

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 Post subject: Re: Shop goings-on
PostPosted: Thu Feb 22, 2024 11:34 pm 
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It's like Christmas when I see a new post in this thread from Ned. What has the mad scientist come up with now...


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 Post subject: Re: Shop goings-on
PostPosted: Fri Feb 23, 2024 6:55 pm 
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Thanks Bill! Great having you as an onlooker.

Delrin comp epilogue-- for now. The sleeve is rock solid in its installation into the Delrin body. It can't move in any direction, nor rotate. But is was easy enough to add a little more insurance, so, a couple of those 5-40 button heads were installed, one on each side. Drilled and tapped into the aluminum sleeve and the Delrin around it, they go in with some red Loctite, and get ground off flush inside with the Moto Tool. Not the neatest work there but very soon the whole area will be covered with burnt powder soot and lead buildup. I thought about various ways to mechanically lock down the front of the sleeve and arrived at this since this way IF the screws were to come loose, they would fall out of the comp and not into it. As a final hedge, I made a little piece that got heated up with the torch and brought down precisely on the screws' locations, melting the Delrin and deforming it over the screw heads. Those screws are staying put, pretty sure. But again-- everything in a gun, especially in a comp, takes a vibratory jolt every time the thing is fired. That's why guns crack, why screws come loose.
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A few more little things to squeeze in over the w/e and then we return to our regularly scheduled program.


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 Post subject: Re: Shop goings-on
PostPosted: Sat Mar 02, 2024 6:02 pm 
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Many, maybe most, of my customers are on the high-volume side. TC got this back together today and put 520 rounds of .50 cal 270-grain SWC's through i:
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 Post subject: Re: Shop goings-on
PostPosted: Thu Mar 14, 2024 9:16 am 
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Time waits for no…. Coltwood grips. The years have taken their toll on these 1968 grips. They have shrunk to the point of cracking and elongating the grip screw holes. As a former moldmaker I know that plastic does shrink—when we make a mold, everything has to be scaled up for example, ABS is usually 1.006, in other words, if you need a 2” dimension on the plastic part the cavity has to be cut to 2.012. But it also shrinks more, very slowly, “depending”. These sure did. 1968 .38 Super.

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 Post subject: Re: Shop goings-on
PostPosted: Thu Mar 14, 2024 11:28 am 
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A good idea at the time.....

But then, had G10 even invented by 1968?


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 Post subject: Re: Shop goings-on
PostPosted: Thu Mar 14, 2024 10:51 pm 
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Quote:
...But then, had G10 even invented by 1968?
G-10 was introduced in the 1950s, first used in printed circuit boards. Micarta, very similar, introduced in the eary 1900s.


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 Post subject: Re: Shop goings-on
PostPosted: Fri Mar 15, 2024 9:03 am 
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I had occasion a few months ago to put a couple file strokes on some gutta percha grips and did some research on it, interesting material and history and applications "way back". I remember an episode of The Wild, Wild West where a supposed sea creature was found to be made partially of gutta percha and I never forgot the term. In my little-kid mind I wondered, since it was a sea creature, if this gutta percha was maybe made from perch guts..?!

The gutta percha filings smelled like Vegemite. That is not a compliment to gutta percha. I did not attempt to taste the filings but they can't have been worse than Vegemite.


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 Post subject: Re: Shop goings-on
PostPosted: Mon Mar 25, 2024 4:30 pm 
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Getting old grip bushings out. I’ve done it a variety of ways but this time I wanted to try something I’ve been thinking of. I made a step drill out of a .191 (#11) drill, grinding a .125 pilot on it. .125 just passes through a grip screw bushing. Using this I can drill the bushing’s middle out and be pretty sure I’m dead center without an elaborate setup. Then, in with an easy out. The thing with this old Colt that kinda tipped it for me was that they were the original bushings and had very substantial, 8-point stakes. The bushings were not going to come out easy—and generally they are not made of very strong stuff—they are the mildest of mild steel, so the slots might well give way before the bushings turn. Anyway I did not want to drag those extreme stakes back out through the frame. Well this way they did get dragged through but at that point they had been drilled and the wall thickness left was so thin that they just collapsed in diameter and came out real easy.
Image
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 Post subject: Re: Shop goings-on
PostPosted: Sat Mar 30, 2024 9:39 am 
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On the previous page of this thread, Page 10, 3/4 of the way down, I put out some comments on frame to slide fitting. I'll say again (because I just did it again) that the recutting of both the frame and slide, the cutting is the easy part (but not that easy). When you have a frame and/or slide whose exterior is done the old way, basically sanded / polished / buffed by hand, you have a finish that can look really good but it's far from flat. There's nothing wrong with frames and slides done that way until you want to hang onto it somehow for further machine work; some of that work it honestly doesn't matter too much if it is performed on a frame or slide that is flexed .005 in an effort to hold it securely, let's say as an example, holding it to FRAG the front strap. But if you are holding them to cut slide and frame channels that you want to mate with each other all straight and parallel and with minimal clearance, you can't just clamp them up to something or in something, because they will flex. Then when you're done cutting, and unclamp them, they will unflex and your nice straight cuts will unflex with them! Sometimes the slide and frame rails are far from straight from the factory and sometimes it's for the very same reasons: when they clamped it for cutting, it flexed. On a recent one, the slide rails were uncommonly straight and parallel until the last 1 1/4" at the rear, where the rails took a distinct turn to the right! Both sides, all vertical surfaces went right in perfect unison, to the tune of .005, so everything was parallel but not straight.

It's easier when the slide and frame have been surface ground and are straight and parallel with, usually something like a half thou. many more recent brands are done this way. Could you take a wavy slide and frame, and surface grind them flat? Yes, but it's not practical. You will lose some rollmarks probably-- I say that having seen slides and frame whose thickness varies .010 or even more. That means you're going to grind them at least .010 thinner and that will lead to other problems. Because both parts are so hollowed out, in grinding they will be very sensitive to heat from grinding and a generous coolant flood is necessary. Other work-arounds are preferred.


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 Post subject: Re: Shop goings-on
PostPosted: Sat Mar 30, 2024 10:28 pm 
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Quote:
On the previous page of this thread, Page 10, 3/4 of the way down, I put out some comments on frame to slide fitting...
Yep. Understood. Brands don't seem to matter, although the few JEM frames that I've built on have been far more uniform than any others. Looking forward to trying a JEM slide.


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