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Angstadt Arms might not be a familiar name in the firearms world, but in just a few short years, this company has carved out a respectable reputation for making specialized AR-15-style weapons that use Glock magazines. When the company released the UDP-9 rifle at the 2013 SHOT Show, it was one of only a few AR-style platforms that used Glock mags. Three years later, many more players have stepped into the Glock mag AR niche, so Rich Angstadt upped the ante by teaming with Kyle Grob of KGmade suppressors to produce the integrally-suppressed 9mm UDP-9i.

Although integral suppressors are hardly new, the Angstadt-Grob firearms set themselves apart from the herd with a unique and inventive design that allows the user to reduce bullet velocity by adjusting 15 barrel ports to divert gas from the barrel into the suppressor. The user-adjustable porting is unique … but so are Grob’s other design features.

Why reduce velocity on a 9mm? To eliminate the sonic crack produced by 115-grain FMJ ammo and allow shooters to use this much-less-expensive and far-more-available ammo instead of having to buy naturally subsonic, 147-grain cartridges. There’s also the benefit of tuning 147-grain loads to lower velocities with even less sound signature, although the power and limited range make them strictly a specialty use round. (For those who want an ultra-quiet 9mm factory load, try the 165-grain HUSH from Freedom Munitions.

My testing shows the HUSH has the performance of a .38 Special when shot from a 16-inch barrel.) The HK MP5SD always comes to mind when thinking of integrally suppressed 9mms, but it lacks adjustable barrel ports, thus reducing the velocity of 147-grain loads to being marginally effective—or worse. With the UDP-9i, you have the choice of bleeding off gas or retaining full power.

A connector links the magazine follower to the bolt catch. Angstadt’s connector is intentionally made to be lightweight and loose fitting, because magazine spring tension is at its least when empty, and the follower needs to press the connector upward to make the bolt catch work. Changing to the Wolf extra-power spring will improve reliability.

The UDP-9i is available in pistol (UDP-9iP), carbine (UDP-9iC) and rifle (UDP-9iR) configurations and is sold as a complete firearm or as a suppressed upper receiver (compatible with Colt 9mm and most dedicated Glock lower receivers). The pistol and carbine (actually an SBR—Short Barrel Rifle) versions have a 6-inch barrel followed by a 5.9-inch baffle core. The rifle uses an 8-inch barrel and 8.1-inch baffle section. Because of the added velocity of the longer barrel and the additional suppression afforded by a longer baffle stack, I selected the rifle version to test for this article.

“Using LAW Tactical’s folding stock adapter on the UDP-9i rifle reduces its overall length to 24 inches when folded and 20 inches on the SBR version, making these firearms discreetly stowable in unassuming carry cases or backpacks.”


Angstadt Arms’ UDP-9 series is blowback-operated; and, except for lacking a forward assist and an ejection port dust cover, it is patterned like the AR-15. It has similar disassembly, controls and operation—including the bolt locking open after last-round function (this function is not universal among Glock AR-type weapons).

The Streamlight TLR-2HL mounts and dismounts quickly for easy movement from pistol to rifle. At 800 lumens, it easily throws enough light to identify targets at (and beyond) typical engagement distances of the UDP-9i.

Interchangeable parts between the UDP-9 and the AR-15 include the hammer/trigger groups, charging handle, buttstock and grip. This makes them configurable with AR-15 parts. None is more useful to me than LAW Tactical’s folding stock adapter, which allows the buttstock to be folded sideways, making the rifle far more compact than otherwise. The LAW adapter fits both AR-15s and AR-10s and mounts between the receiver and the buffer tube. It is rugged, well made from stainless steel, and it allows the folded stock to be instantly swung into the firing position for immediate deployment. (firing a single shot with the stock folded is possible—but not recommended). Using LAW Tactical’s folding stock adapter on the UDP-9i rifle reduces its overall length to 24 inches when folded and 20 inches on the SBR version, making these firearms discreetly stowable in unassuming carry cases or backpacks.

The LAW Tactical folding stock adapter in its open position. Note the bolt carrier extension, which comes with the LAW kit, and the latch that holds it in place when the stock is folded.

The suppressor does add some weight compared to the unsuppressed UDP-9, but it is comparable to other 9mm carbines—6.5 pounds for the rifle version and slightly less than 6 pounds for the SBR. The upper and lower receivers are milled from a 7075-T6 aluminum billet and fit tightly without any gaps or wobble. Standard finish is black hardcoat anodizing, with Cerakote optional. The 12.5-inch-long handguard is from Odin works and has a top rail and keymod on three sides.

The UDP-9i uses a heat-treated extractor and ejector for necessary durability in these high-stress areas. The internal parts are typical with the industry standard AR-15, but the fit and tightness of Angstadt’s assembly are unsurpassed. The trigger on my sample has a 7-pound pull weight, measured using a Lyman electronic scale, but it has no takeup or overtravel, making it a decent trigger, despite being on the heavier side.

Stocks are far better than MIL-SPEC A2 style and use the collapsible Magpul MOE and Magpul K2 grip. This grip is more vertical than most designs; it places the shooter’s hand at a more-natural angle when using a shorter length stock. It also has a compartment for stowing an extra battery for your reflex sight—not a small matter when you are out in the field, away from home. The stock is adjustable for length of pull to fit body armor and for better stowage, but its more subtle value comes from the rubber buttplate, which keeps the rifle from skidding out when leaned against a vehicle or wall. The integrally suppressed UDP-9i uses a heavier-weight AR-10 buffer spring; the standard model does not. Those who only buy the suppressed upper receiver with the intent of mounting it on their lower will need to change the recoil spring for best performance.


The KGmade suppressor provides significantly greater volume for containing gas than a detachable suppressor. Clever engineering is evident in its use of two containment areas for the expanding gas rather than simply building a monocore suppressor and pinning it to a shortened barrel, which is typical of integral suppressors. The primary expansion chamber surrounds the barrel, followed by a sealed baffle stack that is attached to the muzzle.
Here’s how it works. Gas is vented into the primary chamber in two ways: by removing the screws on the barrel ports and through vent holes in the rear of the baffle stack.

A titanium sleeve covers the entire unit, completely sealing in the gas that is vented into the primary area. Sound reduction is achieved by the action of both the baffled section and from venting some of the gas from the baffled section rearward into the primary chamber.

The integral SBR suppressor with the shroud removed. Note the barrel ports, each of which can be used fully closed or fully open with the set screw removed. Intermediate screw settings don’t work, because they loosen under use. Also note the ports at the rear of the sealed baffle stack that direct gas into the barrel area, as well as the superb workmanship evident in removing the welds from the baffle stack. (Photo: KGmade)

This gives considerable volume for the gas to expand and cool; and KGmade states that “first-round pop” is eliminated by this design. The baffle stack is made with eight symmetrically arranged M-type baffles made of hardened 17-4 stainless steel. They are circumferentially-welded together and then pinned and welded to the muzzle. It’s a durable design for heavy firing schedules and full-auto use. KGmade machines its M baffles from a solid bar rather than using less-expensive stampings. Bullet velocity is adjusted by removing hex head screws that cover 15 1/8-inch-diameter ports just ahead of the chamber.

Gas is siphoned off into the primary suppressor chamber surrounding the barrel by fully removing one or all of these screws. KGmade states that venting every port will drop the velocity of 115-grain FMJ range ammo by 125 fps from 1,200 fps down to 1,075 fps—slightly under the 1,110-fps threshold for the speed of sound at sea level.

The standard stock and grip are from Magpul and far better than MIL-SPEC components. The grip’s stowage compartment holds batteries for optics.

Accessing the barrel ports is not quick, but it is needed only infrequently. First, remove six hex-head screws that attach the handguard and pull it off. Unscrew the suppressor’s end cap by hand and pull the suppressor shroud forward, off the barrel/suppressor assembly. An O-ring seals in the gas at the chamber end of the shroud, and extra rings are provided.


Because the baffles are inaccessible, don’t shoot unjacketed or unplated lead bullets—because lead accumulates in the blast baffle. FMJ bullets with exposed lead bases also deposit lead, but at a lesser rate. Jacketed bullets with encapsulated bases, such as the Winchester Winclean, are best for this application. KGmade recommends soaking the barrel and baffle unit in Kano Kroil penetrating oil and then using an ultrasonic cleaner after 2,500 rounds, as well as less-extensive cleaning through the bore with a rod and patch after every 500 rounds. Be careful not to get cleaning patches caught inside the baffle stack, because retrieval will be difficult.


Accuracy was tested at 50 yards shooting from a Caldwell Rock BR bench rest and using a Leopold Mark 4, which has the magnification and image clarity to ring out a gun’s accuracy (although it’s obviously not what you would use on a 9mm rifle). The tests showed that the UDP-9i favors heavier-weight loads, with best/average five-shot groups of 1 inch/1.4 inches—turned in with SIG Sauer 147-grain JHP loads and 1 inch/1.6 inches from Winchester Winclean 147-grain BEB. These groups were not easy to shoot, due to the standard, 7-pound trigger and tactical stock (rather than target-style stock). However, they were repeatable and not just a fluke. Of course, drop-in AR-15 triggers with lighter weights can be installed.

The large “winter trigger guard” makes accessing the trigger easy when the shooter wears a thick glove.

The UDP-9i was reliable, and the bolt locked open with the supplied Glock mag, but it was inconsistent when using other mags—both Glock OEM or aftermarket. This is caused by the magazines’ dimensional and spring tension variations. I found that one particular 30-round Glock mag worked if it was pulled slightly rearward. That put more contact between the mag follower and the connector bar; but another 30-round Glock mag worked fine. Remington UMC and Winchester USA 115-grain FMJ loads, which produce supersonic velocity with the ports in place, dropped to subsonic velocity after removing them—thus validating KGmade’s tests.

This suppressor offers lots of flexibility and will surely be appreciated by those who like to tinker with velocity- and sound-reduction parameters. Be sure to chronograph your loads. In addition, don’t assume the accuracy will be identical once you adjust the porting.

Two bolts—one with the extension needed for the LAW Tactical folder (left) and one without. Note that the key is staked properly. In addition, the carrier will work on fully automatic lowers.

It’s always interesting to see how different barrel lengths impact velocity, so I informally compared velocities of  10 different loads—from the UDP-9 SBR, with its 7-inch barrel and birdcage flash hider, to the UDP-9iR rifle, with its 8-inch barrel and 8.1-inch suppressor baffle stack. The results showed that the additional 1 inch of extra barrel and 8.1 inches of added baffle gave an average increased velocity of 57 fps. However, there was a wide range, depending on the load. Winchester 147-grain PDX and Atlanta Arms Ammo 115-grain Elite showed only a 24 fps increase, while Freedom Munitions 165-grain HUSH and Remington UMC 115 grain had dramatic increases of 142 fps and 89 fps, respectively. These results once again demonstrate how important chronographing is to understanding the performance you actually achieve with a given load in a given firearm, rather than relying on guesswork.

“…the Angstadt-Grob firearms set themselves apart from the herd with a unique and inventive design that allows the user to reduce bullet velocity by adjusting 15 barrel ports to divert gas from the barrel into the suppressor.”


The UDP-9i is a very adaptable short-range tactical weapon. Its ability to squelch sound and flash signatures makes it an obvious choice for LE/MIL use and home defense (with the proper loads). However, this rifle is also ideal for close-range eradication of small nocturnal varmints (such as rats, raccoons and opossums) that plague agriculture operations.

The LAW Tactical folding adapter is very rugged and firmly locks into place. Note the small latch button at right.

Nighttime operations require lights or an NVG, but because the latter is far too pricey, I mounted a Streamlight TLR-2HL light/laser device and conducted a jungle walk in the woods late at night. Paper targets were set along a trail at 15 to 50 yards into the woods, both partially occluded or in the open. The TLR-2HL is a highly versatile unit with which I have prior experience.

At 800 lumens on the “high” setting, and with a red laser, it easily illuminates and pinpoints targets at the engagement distances typical when using a 9mm rifle. Yet, it is compact enough to fit onto a pistol. I like its switching and mounting systems. These switches are activated with the index finger when used on a pistol or with an extended switch cord for easier use when mounted on a rifle. A small toggle switch allows you to instantly change from “light” to “laser” to both, while a rocker switch gives “momentary” or “constant on.” This unit can be quickly mounted and dismounted without tools to 1913 rails and Glock-style rails, making it easy to remove for handheld use. I found that this light worked very well at illuminating any of the targets within 50 yards—and it would have worked had I set them at 100 yards. The beam was even, without a hot spot.

Mounting under the barrel at the forward end of the rail, rather than on the side, works best, because the laser is easier to sight-in, and you only need to adjust elevation to pinpoint more-distant targets. The beam gets somewhat occluded by the end of suppressor shroud, which extends in front of it by several inches, but that’s unavoidable.

Finally, this unit weighs only 4.8 ounces, so it didn’t noticeably diminish the rifle’s handling characteristics, even when mounted far forward.

“The UDP-9i is a very adaptable short-range tactical weapon. Its ability to squelch sound and flash signatures makes it an obvious choice for LE/MIL use and home defense (with the proper loads).”


The UDP-9i is a versatile platform well suited to sport shooters, home defenders and LE/MIL, alike, and its ability to mount on a variety of dedicated Glock magazine-compatible AR-15-style lowers is a real benefit. Accurate with heavier-weight loads, this rifle is also reliable and very effective at sound reduction. The porting system works as advertised: No first-round pop was noticed, and the shooter has the option of using economy ammo to achieve subsonic velocity.

Adding the LAW Tactical folder adds an important element of concealment and discreet carry, while a light/laser, holograph sight and a sling make it mission-ready to help solve most CQB problems—from criminal aggressors to rabid raccoons.



Accuracy (inches)

Velocity (fps)



SIG Sauer 147-grain JHP




Remington 115-grain FMJ




Winchester USA 147-grain BEB




Note: Accuracy was tested with five five-shot groups fired at 50 yards from a Caldwell TackDriver rest and measured center to center. Velocity was an average of five shots measured 15 feet from the muzzle with an Oehler 35 chronograph and no barrel porting.



ACTION: Semiautomatic; blowback operation

CALIBER: 9mm Parabellum

OVERALL LENGTH: 16.1 inches with stock open and set at shortest length

BARREL: 8 inches; permanently attached to 8.1-inch suppressor

WEIGHT: 6.5 pounds (unloaded)


STOCKS: Magpul MOE collapsible stock; K2 grip

FINISH: Hardcoat anodized

CAPACITY: 15+1, 17+1, 33+1

MSRP: $1,995; $1,495 (upper receiver only)




Editor’s note: A version of this article first appeared in the April 2018 print issue of Gun World Magazine.