Precision, Performance and Style
By: Jimmy “Bones” Beckett Photos: Walter Sidas
Sometimes being a gun tech means building things you don’t want to. Other times you have customers request some pretty interesting things. They may even give you free rein on a build within a certain budget. Recently, my buddy Jabber came to me with an idea to update the SR 25K. Although not a fan of the HK 417 style guns, he still wanted that heavy look, so we went with an A&K SR 25K from Airsplat. Jabber laid out some requests for this build. He wanted accuracy and range but it also needed to meet his chrono requirements and there was one more thing; he didn’t want anything too complicated.
With this build we take an A&K SR25K carbine and turn it into an updated and Gucci’d-out SR, complete with all the fi xins. Not only is it aesthetically pleasing but it’s built for semi only and national events. We will be changing parts both inside and outside to bring this blaster up to par.
THE TOOLS NEEDED
• P2 screwdriver
• Flat head screwdriver
• 1.5m Allen driver
• 2mm Allen driver
• 2.5mm Allen driver
• Wire cutters/strippers
• Gear grease
• Silicone oil
• Blue thread-lock
• Soldering iron
• Dremel with cutting wheel
A. RIS (Rail Integrated System): Madbull Noveske NSR 11 in. $120.99
B. STOCK: TI 7 $34.99 HSMAL1646
C. VERT GRIP: Magpul RVG $34.99
D. OPTIC AIM: ShorDot $132.61 [Y07B04][15365/JTCR1] E. SCOPE MOUNT: Larue SPR 1.5 $31.25
F. IRON SIGHTS: GDT AR15 AR 15 45-Degree $22.99
G. LIGHT: M600C $39.99 JA-6002-BK
H. OTHER: G&P D-Bal $179.99
I. FLASH HIDER: Madbull $29.99
J: OUTER BARREL: Madbull Noveske Crusader 12.5″ $63.50
GEARBOX VERSION: Extended V2
MOTOR: Echo 1 Max TQ $59.99
GEARS: SHS SR25 gears $22.95
SHIMS: Hurricane $4.99
BUSHINGS: 7mm Modify $9.99
CUT-OFF LEVER: Stock
SELECTOR PLATE: Stock
WIRING HARNESS: Stock
CYLINDER HEAD: Tweak V2 (modified) $12.99
PISTON: SHS extended piston $15.99
PISTON HEAD: Modified vented polycarb. $14.99
SPRING: Guarder M120 $19.99
ANTI-REVERSAL LATCH: Tweak $6.99
SPRING GUIDE: Tweak with ball bearing $14.99
INNER BARREL: AS tactical 6.02mm $24.99 AC-UPI-AS-IB300
HOP-UP UNIT: Systema hop-up $40.00
BUCKING: Guarder clear $8.99
CONNECTORS: Deans $3.99
Approx Total $1,109.62
PROS & CONS
+ Full metal construction
+ Great finish on all parts
+ Good performance
+ Lots of rail space
– Limited battery space
As per the choice of the end user we decked this out with some cool accessories. This gun certainly has some heft to it but it is pretty sleek. The larger mags give this some attitude and the choice of optics on here really makes this replica look good. Add to this the fl ashy silver outer barrel from Madbull and this thing really pops! As far as handling goes it’s pretty smooth. The low profi le RIS makes the gun easy to move and having an ambidextrous mag release is nice, too. With the new motor, gears and spring this thing responds very nicely in semi and the new barrel and hop-up give it great accuracy.
The SR25 style rifles are often overlooked in my opinion. It’s the larger cousin of the M4 style rifle and the most noticeable difference is the size of the mag well and receiver. The real one is designed to shoot a 7.62 round as opposed to the M4’s 5.56. This makes the gun a pretty easy build in airsoft because so many of the accessories will fit between the two gun types. You get a vast array of options, although there is one drawback with the internals; they use a different set of gears, piston and cylinder to fit in the larger V2 gearbox. This one used an Extended V2.
The model we acquired for the base is a pretty nice gun. It has a Crane-style stock, and full free-floating RIS, a RIS gas block and short barrel. The gun shoulders nicely and fires like any other AEG in this base price range. When we are finished with it, it will certainly attract some attention on the field.
It took a little time to shop around and find what I needed to complete this build. Then it took about two weeks to get in all the parts from several different places. I laid them out around the gun to see what it would look like and I had a moment of excitement envisioning this build’s completion. I was really ready to get crackin’ on this one!
To get started, I broke down the gun. I opted to take apart the upper receiver first. I took off the fl ash hider, gas block, RIS and outer barrel, leaving just the upper receiver in one piece. I set aside the old RIS parts for use with other projects. Be sure to keep all your parts together and marked to save yourself some frustration down the road. Next I took apart the lower receiver and stripped the gearbox, wiping it clean. I wanted a fresh slate and so begins the build. It’s always a good idea to keep the stock parts. As a gun tech, I use them for a multitude of things, including but not limited to experimenting and modifying, replacing stock parts to keep a gun running and completing a gun created entirely of spare parts.
1 With the extended V2 gearbox in front of me I had to start with the wiring harness. I bent the two prongs on the harness just a bit closer together to get the best contact points. Be sure not to make them too close. It can cause them to arc and fi re on its own. Too far apart and there is no connection and your gun is dead in the water.
2 When your wiring is settled in place and tucked away you can add your bushings. The bushings offer durability. They are good for a high FPS setup. Since they are just a solid piece of metal, the chances of damage or breaking in normal use is very low with a high quality one. You may need to tap them into place to get them to seat properly. If this is the case, you can use a punch sized correctly or a nut driver to evenly disperse the weight when tapping it in to prevent damage.
3 With the bushings in position it’s time to get the gears in. For this we used a set of SHS SR25-type gears made specifically for this gearbox type. You will notice the piston gear is larger than the standard one to accommodate the longer piston with more teeth. Start with the center gear and work out. Shimming is a process that takes time. When done correctly it makes for a quiet and smooth operating AEG. When not done correctly it can lead to a short lifespan of your new expensive upgrades.
4 It’s piston time. To match the set of SHS gears, we grabbed an SHS extended piston. This is longer than the standard length piston for this big beefy gearbox. To get it ready we added a modified vented piston head. This polycarbonate model offers great air seal and durability. It’s a piston head that I have been using a lot lately with great results. Simply add some thread lock to the screw to keep this together and free from rattling apart in this high-performance piece.
5 We decided to keep the cylinder but switch the cylinder head. I used a Tweak brand cylinder head with the Sorbothane pad on the back. This pad helps soak up the hard impact of the piston on this new aluminum head. It also comes with two O-rings to give you a better air seal and lessen any loss in FPS. We did have to modify this to fit. We used a drill to extend the two holes on either side to allow it to seat in the gearbox. To prevent injury, be sure to lock the part down in a vice and not hold it in your hand. Take your time with this.
6 An aftermarket nozzle was all that we had in mind for the next step. We went with a Modify brand of nozzle. These are polycarbonate and have an O-ring on the inside for better seal. A dab of silicone grease or heavy weight oil on the inside does the trick to keep the air from escaping and also allows it to move freely. Add this to the tappet plate and slide it over the new tweak cylinder head. Now take the whole unit and place it into the gearbox with the tappet spring—but not before adding a little lube to the tappet and piston groves on the inside of the gearbox.
7 A Tweak aluminum anti-reversal latch will take the place of the old anti-reversal latch so we dropped that in and added the bevel gear in next. Now it was time to close up the box. I held the gearbox with one hand and with the other I slid the M120 spring and Tweak spring guide into place at the rear of the box. I then picked up and put the other half of the gearbox on to close it up. I used the back side of my large Phillips P2 to tap the shell closed. Once that was down I started replacing the screws, being sure to place them all snugly at home.
8 Time to get the box into the body and the lower finished. I started by putting the gun’s fire selector between safe and semi-automatic fire. I tilted the gearbox forward and slid the back end in first.
9 Once it was seated properly I added the rear body pin and floral pin.
10 Next I added the magazine release.
11 Now it was time to add the grip. I opted to use a G&G grip; the smooth shape and great ergonomic feel make this a must-have. I also added in the AMP 5000 torque motor. This is what drives the beast. I have had great results with these motors. They last a while and can pull anything.
12 With the grip and motor in place I added the stock tube and broke out the iron to add in some Deans connectors.
13 Moving to the hop-up, we went with a Systema hop unit. We also added a Prometheus strike arm. You will notice the arm is a different color and changes the angle at which the nub touches the bucking and BB. We also decided to use a clear guarder type hop-up bucking. The assembly on this hop-up is quick and easy like any M4 hop. Be sure to use a dab of silicone to lube the rubber to keep it in good shape.
14 Time for the Upper receiver. I started off by placing the Madbull Outer barrel into the port for the barrel on the receiver. Unfortunately this didn’t fit and required some Dremeling. I carefully marked the two positions that needed to be cut to allow the barrel to fit into the receiver. Then, with safety glasses on, I used my Dremel with the cut-off wheel to cut a notch on either side. Be sure to take your time with this and “measure twice cut once.” I like to cut a small portion at a time to verify that the piece fits and is on track so as not to do too much modification.
15 With everything fitting together it was time to get the barrel nut on. I carefully slid the nut over the barrel and added a few drops of blue thread-lock. Next I began threading by hand. I finished with an adjustable wrench to really get it tight. Also be sure that the holes are perfectly vertical on top so the rail is straight.
16 Now you can place the fake gas tube in the port and slide the gas block over the barrel and tighten it down with a 2mm hex head wrench.
17 Take the RIS and slide it over this now complete assembly and be sure the top RIS matches with the receiver. Use a drop of blue thread-lock on the six remaining 2.5mm screws.
18 Lastly, add the fl ash-hider by screwing it on counterclockwise and locking it in place with the 1.5mm hex screw located on the bottom. Now the base of the gun is assembled and you can place the upper receiver onto the lower and secure it with the front body pin.
19 Time for accessories, starting with the stock. I simply placed the new stock on and it already looks that much better!
20 Next I added the back-up iron sights. These are canted or placed at an angle, which allows the user to have a set of sights for close range shooting while retaining the magnified optic for longer range shooting and spotting.
21 After the sights were on we added the scope. It is an AIM brand short dot scope in a Larue SPR 1.5 mount with quick-detach arms. This pops right on with no issue and it really adds to the look.
22 Finally it was time to get the front accessories on. I started with the D-Bal PEQ again and it has a quick throw arm to pop it right on. The tan color compliments the grips and stock. Having both a visible and IR laser is important for those with and without night vision at night games.
23 Now I need to add some rail sections. The cool part about the Key Mod RIS is that you can move the panels. Simply slide the rail on and lock it down with the 2.5mm Allen wrench. I put one on the right side for a flashlight and the one on the bottom for the RVG vertical grip in tan.
24 Now it’s time to take it all in. She sure is nice looking.
Well now it’s time for the best part. Let’s take it out and use it, loading up a few hi-caps with some Airsplat .20g BBs to break it in. I started out with a 8.4V battery in it. The fire was slow but consistent. The gun was very quiet and I did enjoy shooting it. It’s pretty accurate with the light BBs but next it was time to really kick it into gear. I filled it up with a mag of .25g BBs. I also bumped it up to the 9.6V battery and ran this hi-cap clean. The ROF increased a little bit. It was pretty responsive in semi-automatic and wasn’t too bad. At the end of this hi-cap I wanted to kick it into high gear for the 11.1V LiPo. This thing was shooting pretty good. Rate of fire increased again and the semi auto fire was very nice. No double tap or burst. It was very consistent and I was able to pull the trigger very rapidly with no hiccups. Here are my chrono results.
BATTERY: Venom 11.1V LiPo, 9.6V 1600mAh NiMH and an 8.4V 1600mAh NiMH
CHARGER: Onyx 230
BB’s: Airsplat .20g and .25g
8.4V – 12.26 rps
9.6V – 16.73 rps
11.1V – 21.94 rps
.20g – 390 fps
.25g – 369 fps
This was a pretty cool build. It had been a while since I built up a gun with this base and I hadn’t done a Carbine style until now. The build is similar to many other M4 style guns. The difference here is the mag and the receiver. It’s a visually appealing gun and runs pretty well. Semi auto fire was consistent and quick. This gun works out well. The most important part of any custom build, though, is the end user, no matter who it is. Whether it’s you or a customer they must be happy or it was all for nothing. My work here is done for now.
AIM Sports, aimsportsinc.com
Ground Zero Airsoft, groundzeroairsoftusa.com
MadBull Airsoft, madbull.com
Phantom Industries, phantomindustries.com