The USP Compact developed by KSC is the benchmark for the Hard-Kick・system boasting a larger bore cylinder enhancing the Blowback action without sacrificing much muzzle velocity. The new trigger assembly is also advanced in that it no longer uses a direct impact hammer design; a rocker assembly similar to the Marui Desert Eagle has been fitted.
Blowback Report
The USP uses a new type Cylinder that is considerably larger than all of the KSC pistols on their lineup; even larger than the current Mk23 on the market (pre-2005 version). The bore has been increased to where KSC had to trim half of the blowback assembly housing to enable this system without interference from clearance issues.
What does all this mean? The Blowback on 134a is among the faster OEM Blow Back cyclic speeds, up to par with models such as the Marui G26, KSC G26, and KSC M945C. On Predator gas and Taiwanese Green Gas・the cyclic action is too fast for comfort and durability is severely compromised. The one-way piston cup is not strong enough to sustain the pressure of green and will often blow out of place which seizes the piston movement. Resetting the cup will remedy the problem but as the cup keeps blowing off it will stretch in size and will be more prone to blowing off more
frequently.
The KWA line which is often mistaken with the KSC line, while coming from the same mother factory, has an O-Ring in place of the Piston cup. However, because the O-Ring size is considerably smaller than the inner diameter of the cylinder, the blowback is sub-par and feels a bit anemic.
The true remedy is to find the O-Ring that is EXACTLY the same size in thickness and diameter as the OEM piston cup.
Accuracy:
The USP Compact uses the standard KSC Ball Bearing on Rubber Bucking Rotary type Hop-Up units utilized in over 95% of the KSC Gas Blowback Line with exceptions such as the Non-Hardkick Steyr TMP/SPP. The USP while not marginally more accurate than a Glock 19, Glock 26, or KSC M945 Compact, has a tighter adjustment collar than most of the current KSC pistols, a common fault with the rotary hop-up in which it moves on their own after a prolonged shooting, resulting in the USP less likely to have dramatic hop-up trajectory fluctuations.
IInteresting Features:
Live De-cocker: The safety lever double duties as a fully functional safety lever and if you push it downward, it is a live de-cocker. This prevents having accidental discharges by manually trying to drop a bobbed hammer.
Trigger lock out feature: This mechanism is on the bottom of the gun and once locked it prevents the hammer from moving by locking the hammer strut in the de-cocked position.
Tuning Parts Impressions:
Within the last few months KSC USP upgrade parts production have been・luggish at best. Only ONE hammer spring and recoil spring have been released.
Proud is apparently a Hong Kong Based company that made the springs for the USP and after using their products I have mixed feelings. Their Enhanced recoil spring is a standard linear coil spring that is NOT considerably more effective than the stock flat coiled counter part. I suggest not buying this spring unless you somehow lose the factory stock spring.
The Proud Enhanced・Hammer spring is a different story, this spring is definitely harder than a 150% hammer spring and causes the hammer to hit the valve knocker HARD. Too hard to the point where you KNOW durability has been compromised. We read a 4 fps gain from the hammer spring alone. The constant use of this spring will eventually damage your valve knocker
assembly, hammer, hammer strut, and hammer strut lower housing.
Hurricane Valves. After examining the OEM valves in the USP, they are in fact identical valve to the standard production Glock series, and M945 Series. They are identical in depth, diameter, thread pitch, and valve construction. The Hurricane Glock 19 valves were installed and immediately we recognized a jump in the Blowback action. A minimal 3-4 fps were gained by these valves, not a hearty velocity jump but the blowback action was considerably increased.
The KM TN 6.04mm (77mm) Inner barrel. This barrel is your standard Head/1950 Teflon coated barrel replacement for this particular pistol. The barrel was a no-nonsense drop-in fit with substantial gains in FPS and more importantly shot consistency. The velocity gain on this part was 7fps. I highly recommend this part.
Shooters Design CNC milled aluminum slide. If you have ever replaced a slide on a Glock, this will be no different unless you somehow bought Shooters Design FIRST production slides. They copied the plastic slide exactly, forgetting the fact that you have to pry the slide apart to remove the Blowback assembly. This problem was quickly remedied and the Gen.2 should be the only ones available. The Blowback housing was a drop in
affair, the barrel was a little more complicated to remove from the factory piece but the Shooters slide and outer barrel made re-installation much easier due to a simple threaded barrel drop spring plate instead of wrestling with a lever detent on the OEM outer barrel. The Slide having tight tolerances, slide movement was gritty at first but after manually cycling the action for a bout 15 minutes it cleans itself up.
G&G KSC USP Metal Slide Matte Black Finish. After trying the SD slide a friend bought the G&G Slide for his USP and after an hour of filing, it finally fit well. The Blowback housing had to be filed on the lobes that hold it in the OEM slide, then the blowback housing popped in. We installed the barrel assembly into the outer barrel and that was a cinch. Naturally the next step was to reassemble the slide and frame, it slid on perfectly without any filing. The horror came after that, the magazines wouldn't fit. Apparently G&G incorporated a faux extractor design much like the Mk.23 but didn't leave enough clearance for the magazines to fit so ALL of his magazines had to be filed on the extractor side about 2-3mm in depth. All in all this was a great finish on a slide, nice faux extractor, great price, but it being cast not CNC and the other fitment faults, I suggest the SD slide over the G&G slide.
Recommended Tuning Tips:
Piston O-ring as mentioned above. Pictured is the correct size in comparison to original one way piston cup.
Glock 19 OEM Recoil spring. After trying out many configurations (WA cut springs, Glock upgraded springs cut/uncut), this one worked the best in
regards to a balance or cycle fluidity and tension. The Glock 19 recoil spring is longer than the recoil spring guide in throw length and has more compressed tension than the proud and OEM spring. The Glock spring is also sized perfectly regarding diameter so when the spring compresses it doesn't collapse and bend causing friction on the bottom of the outer barrel and inside the frame.
Hurricane Glock 17/18C/19/23F valves
As mentioned above it does increase velocity and the heavier recoil works well in conjunction with the higher tension recoil spring.
KM 6.04 TN Inner Barrel (77mm) This is definitely the best bang for the buck on this pistol. The barrel increases velocity, as well as shooting consistency.
Shooters Design CNC USP Slide. If it is durability and Real steel feel that you desire then this part fulfills the requirements perfectly while retaining the ability to completely restore your gun to OEM standards.
