Big-Block Glock: The Guncrafter Industries .50 GI Conversion

Big-Block Glock: The Guncrafter Industries .50 GI Conversion

If you want your Glock to have momentum en masse, look no further than the Guncrafter Industries .50 GI conversion.

Quick question: which do you favor—kinetic energy or momentum? If you favor KE, then a 9mm +P+ with 115-grain JHPs is your measure, your option. But if you favor momentum, then something chambered in .45 is what you want. Like a .45 ACP with a 230-grain bullet at 850 fps, or a .45 Colt with a 255 grainer at 750 fps. We’re talking the equivalent of high-compression small engines versus big-block V-8s. (We won’t speak of alcohol-burning race engines at 12,000 rpm.)

But what if you want even more momentum?

How about we halve the 9mm+P+ velocity and more than double the 9mm weight? Or even exceed the .45 weight? A 300-grain JHP at 700 fps should be just the ticket. How do you get that? Here comes Guncrafter Industries to the rescue with the .50 GI.

The Guncrafter .50 GI conversion upper on a Glock G21 lower.

Massive Momentum

The .50 GI is all of that in a self-loading pistol. In this case, a Glock that left the factory in .45 ACP but somewhere along the way to me lost its .45 identity and now sports a .50 GI conversion upper.

As conversions go, this is dead-simple. Unload your .45 Glock, this being a G21. Remove the complete upper assembly and set it aside. Pick up the .50 GI upper and run it onto the frame just as you would if you were reassembling your .45. You’re done. In my case, as I mentioned, there’s no .45 upper so it’s a simple assembly job.

Oh, and in case you were wondering: Yes, it’ll work on your G20 in 10mm. Plus, the G40 and G41.

Guncrafter simply made a barrel and slide that’d accommodate the .50 GI, then added the standard Glock internals and provided a recoil spring to handle the extra slide mass and momentum generated by the .50 GI. Everything works just as you’d expect. And if you feel the need for some other kind of sights, they’re standard Glock dimensions, so swap to your heart’s content.

Now you see the benefits of proper engineering and planning. The Guncrafter slide is set up to take regular Glock sights, so you can swap in whatever ones you want or favor.

The .50 GI case uses the same rim diameter as that of the .45 ACP, so you could simply drop in or fit a .50 GI barrel to your G21 should you wish. Guncrafter makes conversion barrels for those who want to go that route. Your choices are a 4.6-inch barrel, a 5.3-inch barrel threaded 5/8-24 … and a 6-inch barrel if what you want is a bit more velocity. The case is larger in diameter to hold the .500-inch diameter bullet, while the full-up length of the .50 GI cartridge is the same as that of the .45 ACP, so converting Glocks is easy.

The .50 GI loaded round has the same length limitations as the .45 ACP, since it goes into the same magazine. This is a flat-nose 300-grain FMJ and, at 700 fps, knocks down steel and brooms pins with brio.

Just as an aside, converting 1911s isn’t so easy. The single-stack magazine simply can’t hold the .50 GI; there isn’t room side-to-side. So, to get a .50 GI 1911, you’ll have to get a custom 1911 from Guncrafter. I’ve tested those in the past, and you’re in for a treat if you spring for one. But this is about the Glock.

Since the G21 uses a double-stack magazine, fitting the .50 GI into a mag is easy. They just hold fewer rounds, but hey, that’s the not-very-great price you pay for a bigger bullet, right? Oh, and a minor detail, but one you should pay attention to: Mark your mags. If you have a Glock in .45 ACP that you’re putting your .50 GI onto, then you have Glock 45 magazines. Be sure and mark your 50 mags so you can tell them apart, because it isn’t easy otherwise.

The dedicated .50 GI Glock magazines are modified by Guncrafter, because a wider-diameter case needs a different feed lip spacing and geometry than a smaller one does (were that not the case, every magazine would be the same). Now, theoretically, you could take .45 Glock mags yourself and cut them to match the feed lips of a .50 GI mag. You have to be either extremely bored or really, really incorrectly cheap to do that. I mean, you’re going to use a thousand-dollar milling machine (the cheapest to be had) to machine $25 Glock mags, rather than buying ready-to-go modified-to-.50 GI magazines for $60? Even if you don’t screw up any mags learning how to do the cut (and you will, I have no doubt), you wouldn’t break even until you had machined your 29th magazine. And in talking with the owner of Guncrafter, Alex Zimmerman, I found out it’s more than just passing an end mill cutter over the feed lips. Nope, don’t be fooled, buying is a much better bargain.

While the Glock .50 GI conversion uses a Glock frame, the magazines are modified to properly feed .50 GI cartridges. The modified magazines hold nine rounds of .50 GI, compared to the 13 of the .45 ACP mags.

Feeding Momentum

Loading ammo, on the other hand, is easy. The .50 GI runs at much the same pressure as the .45 ACP, which means your brass will last … well, a very long time. The resizing force needed is minimal. The cases and bullets are large and easy to handle, and you’ll only lose cases by not finding them at the range or being ham-handed in loading and crushing one.

The process is the same as any other handgun cartridge, but those of you with progressive presses will find one small roadblock: the rebated rim. The rim is smaller in diameter than the case. This makes it possible to fit it to a .45 slide. If you’re in the habit of using an automatic case feeder to get empties into your press, you aren’t going to be able to do that here.

This is a problem with any rebated-rim cartridge, not just the .50 GI, and it’s a simple problem and situation: The rebated rim falls into the case mouth of the case underneath it in the feed tube and, as a result, can’t be shuttled out by the mechanism. So, you’ll have to feed the empties in by hand. It’s not a big deal, and you probably won’t be loading 5-gallon buckets of .50 GI.

The options for bullets aren’t as great as some cartridges, but you do have choices. And once you find what you (and your pistol) like, how many choices do you need?

Bullet weights that can be used range from 255 grains on the light end to 350 grains on the heavy end. Velocities are in the moderate range but, again, we’re after momentum here. A 300-grain bullet at a “mere” 700 fps generates a 210 power factor, and that’s more than a lot of .45 ACP+P loads generate.

The low operating pressure gives you more “head” room, should you want to pump up the ballistics some. It’s possible, with the proper powders and a willingness to endure recoil, to push bullets faster than you might think. The 275-grainers can be run up just over 900 fps, the 300s to the mid-800s, 325-grain bullets up to 800 fps and 350-grain bullets to 750 fps. Those range from a power factor of 255 up to 262. If you mean to thump, then those are real thumpers. As far as momentum goes, the brisk .50 GI loads are equal to a mild .44 Magnum, and that’s out of an auto-loading pistol that doesn’t have a sharp bark.


The late sci-fi author Robert Heinlein made famous the acronym TANSTAAFL: “There ain’t no such thing as a free lunch.” So, what’s the cost of the .50 GI? Aside from the conversion barrel or conversion upper?

First, there’s the brass. It’s available only from Guncrafter. As a proprietary case, Guncrafter controls who makes it for them—and makes sure only them. It can’t be made from some other case, and even if it could be, the cost of doing so would be greater than buying GI brass. At the moment, .50 GI brass from Guncrafter is $60 per hundred new empties. That’s twice what other high-performance brass would run you. Unless you’re in the habit of using your .50 GI pistol in “lost brass” matches (one where you aren’t allowed to pick up your fired cases), the initial cost really isn’t much since they’ll last through dozens of loadings.

This loading die set came from Hornady, but there are others. With low-pressure cases and tungsten-carbide sizing dies, loading is easy work.

Your bullet options will be limited, but not as much as the brass purchase. Guncrafter offers bullets as well as cases. A quick search shows a handful of other bullet providers. What you need are cast, coated, plated or jacketed bullets of .500-inch diameter, and ones short enough to fit in the case and under the cartridge-overall-length of the .45 ACP and .50 GI. This precludes some of the offerings for the various other .50 handgun cartridges.

You’re simply not going to be able to use the heavyweights you might load into a .500 S&W magnum into a .50 GI case. The weight range of usable bullets in the .50 GI is going to be 255 grains up to 350 grains. As with the brass, once you have a supply of bullets and brass, settled on a particular bullet and the powder charge to run your .50 GI, it’s like any other firearm. You get what you need, when you need it and load up as you want to shoot.

The caliber of this beast is quite clearly more than a mere .45 ACP.

Once you have the components and settled on a load, it isn’t like you’re going through the fuss of loading for benchrest. Nor do you have the R&D arcana of trying to craft .38-40 cowboy loads that actually work. Loading the .50 GI is simple.

Since the case has a .45 ACP rim, the shell-holder or press shell plate for a .45 will work. And dies? Mine are from Hornady when they made a run back a while ago. There are others who make dies, like Lee (available from Guncrafter), and since the case is straight-walled, you can opt for a tungsten carbide sizer, keeping things simple and speedy.

One place the .50 GI excels is in pin shooting. A 300-grain or heavier bullet, at 210 PF or more, brooms pins off with efficiency and speed. Be nice to the brass rats and, when they pick up brass, you’ll get your .50 GI empties back. If you want a thumper, but not one that’s also suitable as a backup to your Jurassic Park long-gun (and with recoil to match), then you need a .50 GI.

Pistolsmith Ned Christiansen with his .50 GI (correct, not a Glock) and the epic muzzle brake he built for it. Note that while there’s an empty in the air, the slide is closed and he’s back on target.

My friend and fabulous 1911 pistolsmith Ned Christiansen runs a set of .50 GI pistols on pins. One of them has a truly epic muzzle brake on it—not because he has to have it to deal with the recoil of the .50 GI (it isn’t much more than others). When you’re trying to win and stay the best, you don’t leave anything to chance.


Editor's Note: This article originally appeared in the May 2022 issue of Gun Digest the Magazine.

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