STI Duty One (ASG)


STI Duty One (.45 ACP)

Made in Taiwan for ASG, STI Duty One
Replica Of:
STI Duty One (.45 ACP))
Made In:

177, steel BBs, 20-shot magazine
Air Source: CO2, 12 g Powerlet
Recommended Pellet or BB:
Crosman Copperhead BBs (5.1 gr)
Weight (lb)/Length (in):
1.6, 8.6
Body Material/Finish/Grips:
polymer (slide is metal)
, black, polymer
Barrel Length (in)/Material/Rifled:
4.9, brass, no
Trigger Action:
SA only
Trigger Pull (lbs)/Adjustable:
8.0 (SA), no
Sights (front/rear):
front (fixed), rear (adjustable for windage)

Velocity (fps):
Sound Level (dB): 93
Thickness of Pellet Holder (in): N/A
Manufactured Dates:
98%, yes, yes
Serial Number:



Comments: The STI Duty One is made in Taiwan for ASG and carries trademarks licensed from STI. The gun is a very close replica, except for the trigger, of the STI firearm. The STI Duty One has the same internal mechanism as its ASG stablemate, the CZ 75 P-07 Duty. The fit and finish of the STI Duty One are generally very good with most seams being hidden and smoothed. Most of the controls function just as they do on the firearm, the only exception being the grip safety, which is molded into the frame. The STI Duty One operates by blowback and the slide locks back after the last shot. The blowback action cocks the gun for the next shot but does not load a BB into the chamber (BBs are loaded during the trigger pull). The blowback action on the gun is pretty strong and does not seem to steal too much gas as the gun gets more than 70 good shots from each CO2 cylinder. The muzzle velocity is about average for a blowback operated CO2 pistol measuring in at 329 fps. While this is a typical figure for this class of airguns, it is far below the 426 fps advertised for the gun by ASG. Shot-to-shot variation in muzzle velocity was good (std. dev. = 5). The single-action trigger on the STI Duty One has a long and spongy first stage (2.7 lb) and a short second stage (5.3 lb) that is a little rough (you can feel the BB being loaded as the trigger is pulled). The trigger is very slow to reset. The owner's manual contains a warning about how to pull the trigger. It recommends a swift pull with no hesitation in order to prevent two BBs being loaded at once. This problem was confirmed during testing. The front sight is fixed but the rear sight can be adjusted for windage.

The magazine for the STI Duty One has a locking position for the spring follower. After locking the follower down, BBs are loaded through the opening at the top of the magazine from the side labeled ".177". To prevent BBs from accidentally coming out the other side, place a finger over the opening on the side opposite the ".177" label. When the magazine is full, cover both openings at the top of the magazine with your fingers and then release the follower. (If you do not cover the holes at the top of the magazine, BBs will fly out of the magazine when the follower is released). To load a CO
2 cylinder into the grip of the STI  Duty One, remove the backstrap by pressing in on the button at the bottom of the backstrap. The backstrap must be removed in order to access and turn the piercing screw for the CO2 cylinder. While a CO2 cylinder is easy to insert into the grip, it is very difficult to get it out. The accuracy of the STI Duty One was poor with all BBs tested. Although the STI Duty One grouped best with Crosman BBs, even these produced groups over one inch (center-to-center). The STI Duty One is a decent plinker but the price is very high for this level of performance.

2010 ASG Airgun Catalog (.pdf)
Owner's Manual for STI Duty One (.jpg)
Exploded Parts Diagram for ASG STI Duty One (.pdf)

Performance: Measurements were made on 12/09/2011 at a temperature of 71 F and 5000' elevation. A ten shot string was fired from a bench rest at 15' using Crosman Copperhead BBs (5.1 gr). The highest velocity measured was 340 fps, the lowest was 323 fps (average of the 10-shot string was 329 fps, s = 5). The average velocity was far below the advertised value of 426 fps but the shot-to-shot consistency was good. A five-shot string fired with open sights grouped at 1.03". Click the thumbnail below to see a larger image. Click here for a description of the measurement methods.

Four different brands of BBs were tested with the STI Duty One. The targets below show the results for firing five-shot groups from 15' using a bench and open sights with Crosman Copperhead BBs (1.03"), Daisy Avanti BBs (1.42"), Daisy Precision Max BBs (1.53"), and RWS Match Grade BBs (1.89"). Crosman Copperhead BBs produced the best results. All measurements are center-to-center.


Right Profile: The accessory rail on the STI Duty One accepts standard Weaver mount items. The grip safety is molded into the frame and is non-functional.

Front View: The slide lock lever, magazine release, and thumb safety on the left side of the frame all function in the same manner as their counterparts on the STI firearm. Pushing the safety lever up engages the safety and pushing it down disengages the safety. There is no de-cocking mechanism on the gun other than using your thumb to slowly lower the hammer as the trigger is pulled.

Left Profile 2: The front sight is fixed but the rear sight can be adjusted for windage by nudging it left or right after loosening the set screw.


Right Side Markings: The trademarks on the STI Duty One are officially licensed by ASG from STI.



Left Side Markings:


Loading BBs: The STI Duty One uses a removable 20-shot magazine. The spring-loaded follower in the magazine has a locking position for loading. When loading BBs, place a finger over the back of the loading port to keep BBs from falling out. When releasing the follower, place fingers over both sides of the loading port to prevent BBs from being forced out of the magazine. Be sure to release the follower after loading BBs.


The internal loading mechanism of the STI Duty One allows more than one BB at a time to be loaded if the trigger is not operated properly. The owner's manual contains the following warning about this potential problem.


Loading CO2: The CO2 cylinder is stored in the grip. The backstrap comes off by pressing the button at the bottom of the backstrap. When the backstrap is installed, it completely covers the CO2 piercing screw giving the gun a more realistic appearance.


Owner's Manual

Exploded Parts Diagram for ASG STI Duty One (.pdf)




 Copyright 2011