Guncrafter Industries Conversion Glock Model 21 50 GI


Alex Zimmerman has a great idea. Gun Tests magazine first experienced it in a review of one of his Guncrafter Industries’ 50-caliber 1911s, which they found to be a well-made handgun, if a bit on the costly side. Zimmerman’s idea is to give the shooter something more without the cost of broken hands. Rather than a bang-up, hot and heavy blaster, the 50 GI is a throwback to older times when big bullets traveled at low velocities and got the job done at least as well as any small-caliber, high-velocity round.

Some 200 years ago the norm was single-shot or occasional double flintlock pistols, which commonly threw balls of up to 12-bore in size at velocities in the low- to middle-hundreds of feet per second. But wait!, cried the “engineers.” Those low-velocity rounds are all wrong, they said. They don’t develop the muzzle energy of these new-fangled, higher-speed rounds, which depend on velocity squared to get their (largely misleading) high numbers. Thus, in today’s terms, a 9mm high-velocity round can equal the “power” of a 45 ACP, at least on paper. In the real world, those with experience know this is not quite the whole picture. Many experts always go for the bigger bore with heavy bullets.

The grand master of elephant hunting, John “Pondoro” Taylor, did practical studies over many years to test his own theories along similar lines, and to his satisfaction proved his theories to be correct. He found that big bullets at reasonable velocities work better than smaller ones at outrageous velocities. Taylor derived a simple formula that may be applied to handgun rounds today, though Taylor never intended that kind of comparison.

Taylor’s “knock-out” blow (KO) is derived from the velocity (not squared), times the bullet weight, times the bullet diameter, divided by a constant to keep the numbers reasonable. Thus he put equal emphasis on bullet weight, diameter, and velocity. A 230-grain 45 auto ball load, at 850 fps, may be looked at this way:

KO (45 ACP) = 230.x .45 x 850/7000 = 12.6

A hot 9mm might use a 115-grain bullet at 1200 fps. Its Taylor value is thus:

KO (9mm) = 115 x .355 x 1200/7000 = 7.0

These two rounds develop essentially identical muzzle energy, just under 370 foot-pounds. Many experienced shooters maintain the Taylor value is a better indicator than muzzle energy of how these two cartridges actually work in the field.

Bullet nose shape or design is not a factor in the Taylor formula. There are other, similar, formulas that apply a form factor to the bullet nose, but for general non-complicated evaluation of rifle and handgun cartridges, some of us have found this simple formula works exceedingly well, and clears away a whole lot of the advertising spin that is commonly applied to new, exotic and soon-to-be-famous cartridges. If you get thinking in terms of bullet diameter, weight, and speed instead of published energy figures, you quickly get a feel for what any rifle or handgun cartridge can do, and you’ll also see through much of the misleading hype.

So what Alex Zimmerman has done is offer a package that maximizes handgun bullet diameter, and Taylor KO values, without blasting your hand away at the grip end. For this report Gun Tests got the loan of a 50-GI conversion kit ($595) for Glock 21 a.

The Guncrafter Industries 50 GI Conversion, $595, consisted of a slide, barrel, captive slide spring, and magazine in a hard plastic case. Comparing the conversion’s parts with the Glock 21’s equivalent parts showed us the Guncrafter Industries machining was at least as good as Glock’s. Further, the GI parts were stainless, with a pleasing matte finish to the slide. The slide and barrel were machined from stainless forgings. The sights appeared to be Glock parts, made of plastic and readily replaceable. The barrel had normal rifling, not the segmented style used by Glock. There are two magazine types available, a normal-looking one that holds eight rounds, and the extended one that came with our conversion, with nine-round capacity.

Installing this well-made unit was extremely easy. We simply took off the Glock 45 slide and barrel and slipped on the Guncrafter unit, loaded the 9-round extension magazine and went to work. We could actually get ten rounds into the mag, but it’s not recommended. The big 50 GI rounds came in two flavors, 275-grain JHP and 300-grain flat point. The 275-grain load at a measured 905 fps (875 claimed), gave 500 foot-pounds of muzzle energy and a KO value of 17.8. The 300-grain load, our favorite, chrono’ed at 735 fps instead of the claimed 700, which gave 360 foot-pounds, and a Taylor KO value of 15.8.

The gun felt exactly the same in our hands as did the regular 45, same balance and essentially the same weight. With the magazine loaded, the weight and balance were again pretty close to the 45 version. On the range, we noticed a bit more pounding to the hand with the 275-grain JHP load, but it was by no means uncomfortable or uncontrollable. If you didn’t know, we suspect you’d have a hard time telling if you were shooting a 45 load or a 50 GI. We were again hampered by the lousy trigger of this Glock 21, but we were able to shoot groups about equal to those from the 45 setup. Best were 1.9 inches with the 275-grain load and 1.7 with our favored 300-grain bullet. There were no failures of any kind, though we noted a slight sluggishness for the slide to go fully forward for the first few rounds. This went away with just a touch of wearing in.

Rapid-fire results were about equal between the 45 and 50 GI, with the nod actually going to the 50 GI. This is probably because we were aware we had a bit more power, and were a bit more careful. We slightly preferred the 300-grain bullet for rapid-fire. Ammunition is available from GI, and they also offer loading dies and brass. None of it is especially cheap, but not much in the firearms ammunition world today is. We found the ammo to be very well made, packed 20 to a box, and excellent in performance and consistency.

Our Team Said: The cost was reasonable, we felt, in that you’re getting something you can’t get any other way. Of course for the price of the conversion you could get another Glock, but you can’t get a 50 GI easier nor cheaper, so far as we know. If you have a Glock 21 or 20 and have a hankering for more usable power without going to a magnum blaster, this conversion might be just right for you. We hope there’s a unit in the works for the S&W M&P, or perhaps for another good modern auto pistol.


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