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Inside The .45 GAP

by Dick Metcalf   |  January 4th, 2011 10

The .45 GAP gives performance equal to commercial .45 ACP personal-defense and law enforcement loads with 185- and 200-grain bullets but in a shorter overall case format


The .45 Glock Automatic Pistol cartridge (.45 GAP) is an intriguing cartridge with a great deal of potential. A joint development project by Glock and Speer/ATK, Glock initiated the concept, which grew from its experience as the current largest provider of U.S. law enforcement autoloading pistols.


The impetus for developing the new .45 GAP cartridge was a call from law enforcement for a .40-caliber-sized duty pistol that provides the ballistics performance
of the .45 ACP.

The largest selling individual model in the Glock line is the duty-size Model 22 .40 S&W, which is built on a 9mm-platform frame dimension. The duty-size .45 ACP Model 21 Glock requires a slightly larger frame and slide. A significant number of Glock’s law enforcement customers, responding to the growing popularity of the .45 ACP cartridge among performance-conscious police and enforcement agencies, had expressed a wish for a “9mm-sized” or “.40-sized” Glock in .45 caliber. Not a compact Model 21, which would still need to have a .45 ACP-size grip dimension, but a .45-caliber that could fit into a 9mm/.40-size grip and still have the performance of a .45 ACP.

Glock took the notion to Speer, and the result is the .45 GAP, which has a cartridge case length of .775 inch–essentially the same as the 9mm Luger (9x19mm) cartridge case. The maximum cartridge length is 1.070 inch, which is actually a bit shorter than the 9mm Luger, to accommodate the wider profile of .45-caliber bullets at the front of the magazine well.

These dimensions mean that the .45 GAP cartridge is ideally suited to compact and subcompact pistol frames and permits .45-caliber performance in firearms no larger than typical 9mm firearms. For shooters with small hands who find modern .45 ACP pistols too large for a secure grip, a .45 GAP pistol has a grip no greater in diameter than a duty-size 9mm or .40 S&W.


The .45 GAP (C) is slightly shorter than the 9mm Luger (L) but provides performance equal to the .45 ACP (R) with 185- and 200-grain bullets.

Okay, how did they do it? How did they get full-length .45 ACP performance in what many are already calling a “.45 Short”? The simple answer is: intelligent use of new-generation advanced propellants, which allow the production of higher velocities from smaller cases without excessive pressure, compared to previously available propellant technology.

It’s actually an application of the same principle that has permitted the development of the new generation of “short magnum” cartridges in high-power rifle ammunition–new propellants that provide the same (or greater) velocity and energy from short-action cases, as previously available only in long-action cases.

So in exactly the same way that the new .300 WSM cartridge can power a 180-grain .30-caliber rifle bullet at the same velocity as the old-generation full-length .300 Winchester Magnum, without excessive pressure, the .45 GAP allows 185- and 200-grain bullets to match muzzle, downrange, and terminal performance of the .45 ACP when fired in equivalent barrel lengths.

Be aware that catalog ballistic figures for the two .45 cartridges might appear to contradict this at first glance. That’s because the standard industry-reference test barrel for the .45 ACP is five inches, which means that published .45 ACP velocities appear slightly higher than the .45 GAP because it is specced from a standard 9mm/.40-configuration four-inch test barrel.


.45 Glock 185-Gr. Gold Dot

However, when both cartridges are fired from a four-inch barrel, the performance is virtually equal with 185- and 200-grain bullets. To achieve this parity, the .45 GAP is loaded to the same maximum average pressure as the .45 Auto +P: 23,000 psi. Compared to 9mm Luger and .40 S&W pressures of 35,000 psi, the new cartridge achieves its performance at moderate pressures. (See the accompanying chart.) On the other hand, the .45 GAP cannot reach the velocity and energy levels as the .45 ACP with 230-grain bullets, without exceeding safe-pressure limits–at least with currently existing propellants. If you want to use that classic heavier .45 ACP bullet weight, you still need the bigger ACP case.

Incidentally, do not let my earlier casual use of the increasingly common term “.45 Short” mislead you. The .45 GAP is emphatically not a cut-down, or shortened, .45 ACP case. It is an entirely new design with a completely different internal case design. The GAP rim is slightly rebated compared to the .45 Auto, and the extraction cannelure width is optimized to case length and web profile, resulting in a 10-degree difference in the lead-in angle.

The internal case wall profile is significantly different from .45 Auto cases to permit seating .45-caliber bullets without bulging. The most obvious difference is that the .45 GAP uses a Small Pistol primer to put distance between the primer and breech/action elements present in 9mm-frame pistols. It is unsafe to cut off .45 Auto cases to make .45 GAP cases. The most significant issue is the difference in primer size. A Large Pistol primer that fits the .45 Auto case will over-ignite safe powder charges developed in proper GAP cases with small primers, and high pressure will result. The .45 GAP case has a much different internal taper, so cutoff .45 Auto cases will bulge when bullets are seated to recommended lengths.


Maximum Average Pressure Comparison

Another common question I’ve heard asked when shooters first learn of the .45 GAP is whether it can be fired in .45 AC
P chambers. The answer is one of those not-so-simple ones: No, but sometimes it might. Both the .45 ACP and the .45 GAP headspace on the case mouth, so the .45 GAP won’t reach the chamber headspace index in a .45 ACP chamber.

On the other hand, the taper of the two cases is essentially the same so a .45 GAP might not slide too far forward in a really tight-chambered .45 ACP for the firing pin to reach the primer. But the .45 GAP rim is rebated, remember, so a .45 ACP extractor may not hook on, unless it’s got a really deep lateral reach. The real answer to the question is…maybe. If you drop a .45 GAP into a .45 ACP pistol it might go bang. Sometimes. And maybe extract and eject, too. From some guns. It is not a good idea–under any circumstances.

Ready And…Waiting
Speer’s initial .45 GAP commercial loadings include 185- and 200-grain Gold Dot premium hollowpoint ammunition for service and defense and the same weights of economical Speer TMJ bullets loaded in the Speer Lawman line for training, practice, and target shooting. Federal Cartridge, Speer’s big-brother company under the ATK banner, is initially introducing two .45 GAP loads as well: a 185-grain Hydra-Shok loading in the Premium Personal Defense line and a 185-grain TMJ loading in the economical American Eagle line.


Velocity & Energy Comparison

The terminal performance of the 185- and 200-grain Gold Dot and 185-grain Hydra-Shok .45 GAP loads is impressive. I have witnessed part of the six FBI test protocol stages and the IWBA heavy clothing protocol test to which ATK engineers have subjected these loads. Depending on the test protocol barriers, penetration was 12.3 to 18.3 inches of ordnance gelatin for the 200-grain Gold Dot and 10.6 to 18.7 inches for the 185-grain Gold Dot. This is for all practical purposes identical to the performance demonstrated by .45 ACP ammunition of the same bullet configuration–from a cartridge that is actually slightly shorter overall than the 9mm Luger.

Also, Speer emphasizes that the point of impact (POI) difference is negligible between the two bullet weights and between the Gold Dot and Lawman loads of the same weight. At 50 yards, the maximum shift in POI between the 185- and 200-grain bullets is just over .5 inch. With bullets of the same weight, the Gold Dot and Lawman loads print within 1/20 inch of each other. (See the diagram.) This commonality of performance characteristics between Speer’s “practice” and “premium” loads in the same calibers is a hallmark of the Speer handgun ammo line across the entire caliber range the company offers. In the case of the new .45 GAP loadings, this commonality extends to the Federal 185-grain American Eagle and Premium Hydra-Shok offerings as well.

All six Speer and Federal .45 GAP ammunition loads are available right now. However, guns for the new cartridge have been slower in coming. Prototypes of the new Glock Model 37 .45 GAP pistol were initially previewed at the 2003 SHOT Show and were shown to industry journalists and demonstrated at some public shooting sports events as early as spring 2003. But then engineering delays arose, relatively late in the Glock preproduction sequence, stemming from translation problems between the geometry of the 9mm-configuration frame and necessary slide dimensions for the .45-diameter cartridge. Not to put too fine a point on it, the .45 GAP cartridge was relatively easy to shorten to 9mm length, but it was still just as big around. Initial Model 37 prototypes were built with a Model 22-type .40/9mm-dimension frame and slide.

The actual production Model 37 pistols, now anticipated to be in shipment by the end of 2003, will still have Model 22-type grip frames but will likely feature slightly thicker slides, more on the scale of the Model 21 .45 ACP. At the same time, other gun companies are working to bring out their own .45 GAP offerings–with even odds right now whether Glock’s Model 37 or an Xtreme Duty .45 GAP from quick-moving Springfield Armory will actually be the first to reach dealer’s shelves. And Winchester is known to be close to completing its own .45 GAP ammunition offerings as well.

I think the .45 GAP cartridge has a lot of leg, and I expect to see a lot of different model guns and additional loads from a wide range of ammomakers. By providing .45 ACP performance with a 9mm-dimension pistol package, it rides the same wave that originally made the .40 S&W a preferred alternative to the full-length 10mm. I’ve had the opportunity to shoot the prototype Glock Model 37 used by ATK to develop the Speer and Federal loads with all six varieties of ATK ammunition, both in the factory ballistics tunnel and on an outdoor range. Subjectively, I can feel little difference between shooting it and a .40-caliber Model 22. But it sure hits like a .45 ACP–it blows the dickens out of ballistic gelatin and slams down steel pepper-popper targets with authority!

  • Jay Dooly

    Great article. I own 2 Glock 45 GAPS and absolutely love the guns and cartridge. It is the perfect fit for my hands, I also reload the GAP for fun.

    • Jay Dooly

      OOPS! I own 3 Glocks and not 2!

  • Rockin Rob

    I also own 2 Glock 45 GAPS and the feel in your hand will sell you the firearm. It also fits my wifes hand, so I had to get one for her. We both love them.

  • Pistol Pete

    I own a Glock 37 and a Glock 38 in .45 GAP. They are both quite accurate and very controlable. I use the 37 as my Home Defense pistol, and the 38 as my CCW pistol. I also took the Glock 37 handgun hunting last week and took five of the Exotic Rams, using the Corbon 200 grain JHP at the Caryonah Hunting Lodge in Tennessee. I'll carry either pistol with the Speer Gold Dots or the Corbon. The Corbon hollowpoint is huge and resembles the old CCI "Flying Ashtrays."

  • Liam

    I have a Glock 37 and love the cartridge and the gun; the gun fits medium sized hands and the ctg is everything the .45ACP is in a more comfortable package

  • Evan

    I have a SA XS in 45GAP with a 5" barrel. and it sings like a top when it starts humming.. From my personal standpoint it recoils LESS than a 40..

    • ljw

      how

  • martins

    @j dolly, have you ever try fitting in a 9mm round into you 45GAP?

  • Kirk

    Bought one just recently and it's wonderful. I have a Glock 19 and love it but sometimes you just got to have a .45 around. My wife likes it too and finds it comfortable to shoot with. I have chosen Buffalo Bore's 160 grain Barnes TAC-XP Jacketed Hollow Point as my designated carry ammo. The Speer Gold Dot 200 grain load would be my second choice as a carry load. The .45 GAP is a good comprimise for those wanting a .45 caliber in a 9MM/40 S&W size pistol.

  • Pistol Pete

    I’ve got all three of the GAP Glock’s. The Model 37, the 38, and the Baby Glock 39. I took five head of Exotic game with the Glock 37 at the Caryonah Hunt Club. The results were impressive. The Baby Glock 39 is also my new Carry gun. I wear it in a De Santis Cozy Partner IWB holster and carry it with Corbon 200 grain JHP ammo. The same load I used on the five Exotics in Tennessee.

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