In the previous article on the UMAREX/VFC VP9 (SFP9), I covered disassembling and customizing the frame.

This time, we'll mainly be showcasing the customized shooting performance.

Before checking the actual shooting performance, I'll explain how to replace the gas injection valve, which is often difficult to insert in overseas-spec magazines.

Magazine gas injection valve replacement

First, let's look at the gas injection valve on the original magazine.

This valve is extremely difficult to fill with gas, so we'll replace it with one compatible with domestic gas. The replacement product is a Japanese-spec gas injection valve for WE (Western Electric) that is widely available and relatively inexpensive.

You can remove it with a flathead screwdriver after draining all the gas from inside the magazine.

Let's take a look at the removed valve. Actually, if you can't get a domestic-spec injection valve, simply removing the O-ring at the inlet will make it much easier to fill with gas.

The trick to removing it is to pierce it with a sewing needle, such as a pin, and lift it up.

Let's compare it to the domestic gas-compatible valve that you purchased.

The O-rings attached to the screw threads are of different thicknesses.

Next, let's look at the inlet.

Domestic valves do not have O-rings. While these O-rings allow only high-pressure gas to enter, they are a major reason why it is difficult to fill them with gases at pressures similar to those of alternative refrigerants (HFC-134a).

Simply assemble this into the magazine and you're done.

Here's a point to note when installing: Because there's an O-ring on the screw thread, you won't feel like it's fully tightened even when you're turning it. Be careful not to overtighten, as this can crush the O-ring too much and cause it to malfunction or get damaged.

While the details of O-ring design will be explained separately, if the compression rate is not 30% or less and the filling rate is not less than 100%, it will not function properly. If it is overtightened, the space for the O-ring will become narrow, exceeding the compression rate and filling rate, causing it to break.

To get a feel for it, it's a good idea to remember how tight the original valve was.

Correction regarding valve replacement

Later, a gas leak from the valve was discovered (my apologies for the oversight). The cause was that the O-ring at the neck of the valve was the wrong size.

Let's compare the sizes of the O-rings.

The original part is thicker than intended, so the O-rings for the Japanese specification of the WE model did not provide a proper seal.

So I put the original O-ring back on and applied Tokyo Marui high-viscosity grease just to be safe.

Next, when assembling, be careful to install the O-ring so that it does not deform too much.

The feeling is that you tighten the valve until the resistance changes, then stop. I left it for about two hours after filling it with gas, and this time it was fine.

As a reminder to myself, I added this as an addendum, deliberately leaving the mistakes in the article without rewriting it.

This completes all the customization.

Next, let's check the actual firing performance.

Live-fire performance verification

As usual, I filled the magazine with HFC-134a gas and brought the magazine surface temperature to 28°C (about body temperature). The ambient temperature was approximately 23°C.

As usual, I'll be using S&T Bio 0.2g BBs and checking the hop-up setting at 0.

The initial muzzle velocity out of the box was around 75.8 m/s, so it has dropped a little. However, when I checked it out of the box, the ambient temperature was around 25°C and the magazine surface temperature was 29.6°C, so you could say it hasn't changed that much.

In many cases where the muzzle velocity doesn't increase despite custom modifications such as increasing gas flow, narrowing the inner barrel diameter, and extending its length, applying hop-up tends to increase the muzzle velocity (becoming more flow-intensive).

Based on my experience, when the barrel is extremely short (around 110mm or less), increasing the amount of propellant gas or air often doesn't increase the muzzle velocity because there isn't enough acceleration zone for the projectile.

In that case, increasing the hop-up setting to increase the gripping force on the BB often increases the pressure inside the inner barrel, thus increasing the muzzle velocity (flow velocity?).

I'll try setting the hops to the maximum setting and see how it goes.

As expected, the initial velocity has increased.

Despite the increased hop-up tension (the force with which the BB is held) being higher than the original due to the longer hop-up application, the muzzle velocity has also increased, which is exactly as intended.

Next, regarding stability, this is the initial velocity of the 11th shot fired in a continuous burst (hop-up 0).

Even after firing all 22 rounds in the magazine, the muzzle velocity remained above 70 m/s (the slide stop also engaged properly).

With the original setup, the muzzle velocity drops to around 66 m/s after firing all 22 rounds, so it seems that stability has improved.

If you're interested, please also check out my review of the chronograph.

Fuel efficiency

Next is fuel efficiency.

I will weigh the empty magazine again to confirm.

Fill the gas tank to the maximum.

This means it contains about 21g of gas. Naturally, this is almost the same as when it was straight out of the box.

Next is the weight after firing 22 rounds from one magazine in a row.

With 6.5g of gas consumed for 22 shots, the average gas consumption per shot was approximately 0.3g, which is the same as out of the box. Considering the increase in propellant gas volume due to the change in the flow valve spring, it could be argued that the fuel efficiency has improved.

Next, here's a video showing how it works.

UMAREX/VFC VP9 Operation Custom

Out of the box

UMAREX/VFC VP9 Out of the Box

You can probably tell that the trigger response has improved thanks to the reduced hammer spring load and the resulting friction adjustments. Also, although it's hard to express in a blog post, the trigger feel has improved dramatically. The grinding feeling is completely gone, and the weight of the trigger caused by the hammer spring is gone.

The only thing left to do is check the ballistics, and I'll update this as soon as I can confirm it during my next airsoft game.

The feel of the BB when I applied the hop-up and hit it seemed fine, so I don't think it will have a strange trajectory.

This means the custom goal has now been achieved.

Ballistics confirmation

I checked the ball flight at Yanex at the end of July 2020.

The conditions were a temperature of around 32°C, a full tank of gas, and G&G Bio 0.2g BBs. Because it was hot, the initial velocity reached 79m/s (with proper hop-up).

This is a ballistic trajectory image.

I was surprised by the excellent trajectory, which was comparable to that of a slightly longer weapon.

Moreover, with just a slight adjustment to the hop-up setting to my liking, it achieved the optimal trajectory for 0.2g BBs, so it seems it can handle heavier BBs as well.

I believe the contributing factors are the good quality of the original long-range hop-up bucking, the improved long-range hop-up arm, and the slight extension of the inner barrel.

In my experience, this gas blowback handgun seems to have the best trajectory.

Finally, let's compare the appearance of the custom-built product with that of the product straight out of the box.

If you'd like to know more about the shooting performance right out of the box, please click here.

G&G Bio-Bullets 0.2g
It's inexpensive and accurate, so I use it for a wide range of purposes, from performance testing to airsoft games. It's been my favorite since it first came to Japan (around 2008). It lasts a long time for a biodegradable product.

G&G Bio-Bullets 0.25g
It's 0.25g. I generally use 0.25g BBs when playing airsoft.

Comparison of appearances

The only difference in appearance is that the steel sights, extractor, and takedown lever that came with the special combo are different, and the grip panels have been changed from size M to size S.

extractor

Site

Takedown lever

Next, let's look at the effect of lengthening the inner barrel.

Under normal conditions, the outer barrel and inner barrel are the perfect length match.

When you pull back the slide, the outer barrel retracts, causing the inner barrel to protrude slightly.

I've decided this is good enough for now, but it's quite noticeable, so I might paint the inner barrel black later.

Next is the grip.

S Size

Size M (out of box)

It's difficult to compare them directly with images, but if you look closely at each finger, you can see that they've become more compact.

Next, let's look at the operability of the magazine release lever with the S-size grip.

In my case, I don't have much strength in my fingers, so I press down the lever with both my thumb and index finger. With the M-sized grip, I couldn't reach the lever with this method and couldn't operate it, but when I switched to the S-sized grip panel, I was able to operate it smoothly.

This completes the customization process.

Summary

To reiterate, the improvements made this time are as follows:

Only the following two parts were used:

・RA-TECH 6.02mm Precision Inner Barrel, 97mm Length

・Strike Arms Flow Valve Spring Medium Long (Green)

The rest comes down to ingenuity and the priceless benefits of DIY.

I've explained it in quite a long text, but if you're familiar with the process, the actual work can be completed in less than three hours. It also costs almost nothing, so I highly recommend it.

In particular, overseas-made gas blowback pistols have their muzzle velocity adjusted to comply with Japanese regulations, but other parts are set up for high-pressure gas, so a little adjustment often makes them operate more smoothly. Also, even with domestic manufacturers' products, polishing and other work can make them even better than they were originally.

Since these are industrial products, there are always parts that simply cannot be mass-produced, so we identify those parts and address them manually.

This VP9 is quite well-made out of the box and has a great design, but I think it has the potential to be even better with a little extra effort. Also, as it is HK's latest polymer striker-type automatic pistol, it is very easy to use, and since it has been officially adopted by the Japan Self-Defense Forces, I was very satisfied with this product.

Ideally, I'd like to see a domestic manufacturer release one, but given the economic downturn and busy schedule caused by the coronavirus, that doesn't seem likely for a while. So, if you want to get your hands on a VP9, ​​this seems to be your only option for the time being.

That concludes my introduction.

The inner barrel I used is no longer available on major online retailers, so I'll recommend a different one.

・PDI Inner diameter 6.01mm Length 97mm
Since PDI is known for its high accuracy and reliability, their product might be even better than the one we initially chose.

・Maple Leaf Crazy Jet, 97mm in length
This is a barrel I often use in gas blowback guns. I'm not sure about the jet effect, but it's a well-made barrel overall.

The hop-up packing is quite good in its original form, so I think it's best to keep using it as is when making any modifications.

- AMG winter hammer springs (20-30% lower than stock springs)
I've heard that there are low-load hammer springs available from third-party manufacturers, but I couldn't find any in stock.

This is the main unit.

・UMAREX/VFC VP9 special comb DX/JP version
It comes with a steel extractor, a luminous sight set, and a slide takedown lever.

・UMAREX/VFC VP9 STD JP version
The extractor, sight, and lever are made of aluminum. The difference is purely cosmetic.

・Le Pair Magazine
It seems they've restocked, and the price is now reasonable. I recommend getting it while it's still in stock.

・Injection valve for domestic gases
I recommend it (but be sure to use genuine O-rings).