Installation of regulator into Air Arms S500 Special FAC

Installation of regulator into Air Arms S500 Special FAC
(This example is appropriate for the Air Arms S4XX and S5XX series rifles)
Please use extreme caution when dis-assembling the high pressure
cylinder!
All air MUST be released before beginning the installation process to prevent accidental discharge of
high pressure air, and risk of personal injury. All installation procedures are at the risk of the installer.
To vent the high pressure air from the cylinder, loosen the fill valve slowly about 1/4 turn until the O-ring seal is
free and the air escapes. Be prepared for a mildly loud POP as the O-ring comes off its seat. Be sure your
fingers are away from the base of the fill valve too, no one wants an embolism in their finger, right? :-O
Loosen the two set screws on both sides of the barrel bracket and slide the bracket off the end of the barrel.
Remove the two screws from the end of the Striker Body. (Note this is a S500 FAC assembly and does not have
anti-tamper devices plugging the screw holes. If your model is not FAC, the plugs will need to be removed.)
Remove the four screws from the Valve Body in front of the trigger. These screws will be easier to remove if the
trigger guard is removed first.
The Breech and Barrel assembly can now be lifted from the rest of the rifle body. Be careful not to lose the white
plastic seal washer, it can fall off easily.
Dis-assembled parts.
Remove the Power Adjustment knob by loosening the set screw in the valve body directly under the knob.
Taking this knob out is not required, but it will make removing the cylinder easier. There is a small spring and a
dowel pin under the set screw. Place them aside so they are not lost.
Remove the Cylinder Pressure Gauge. This is a very tightly torqued screw, so be careful not to strip the hex. It
will come out and there is no thread locking compound used here, it is just very tight. Again, removal of the
pressure gauge is not required, but it will make removing the cylinder easier.
Before removing the cylinder, make a small mark across both the cylinder end and the valve body. This will give
a reference point to tighten the cylinder to at re-assembly. Again, a very tightly torqued connection.
To remove the cylinder it is necessary to hold the cylinder very tightly. Here, two automotive hose clamps are
used with a thick rubber strip underneath. Tighten them as much as possible. This helps grip the cylinder, and
prevents scratches. We don’t want any damage to this beautiful rifle, right? ;-P
Install the stock bolt into its mounting hole and place a box end wrench over the bolt to provide good leverage for
loosening the cylinder. Protect the whole assembly with a rag as it is clamped in a bench vise.
This is what you see as the cylinder is removed.
Mark the POT with the length of the spacer provided with the regulator. This is the maximum length the POT
could be and still allow proper installation of the regulator. The POT actually will be cut a bit shorter than this
length. Remove the POT by loosening the set screw in the side of the Valve Body, just where the POT is
attached.
To get the correct placement of the breather hole for the regulator in the cylinder, place the spacer and regulator
at the end of the valve body. Measure the distance from the face of the valve body to the breather hole in the
regulator.
Place a piece of masking tape on the centerline of the cylinder along the bottom of the cylinder. Draw a straight
line on the tape along the centerline, and transfer the dimension of the breather hole to the cylinder.
Carefully center punch and drill the breather hole using a 1mm or 1/16 inch drill bit. This is best done in a drill
press with the cylinder firmly clamped in place, but if you are careful not to let the bit wander, it can be done with
a hand drill.
Clean the burrs off the inside and outside of the hole. It should look like this when finished. It is extremely
important that the inside burrs are completely removed and the inside surface is smooth. Any remaining burr will
ruin the O-ring seal on the regulator and the air will leak out the breather hole. Finish sand the inside of the
cylinder with 600 grit silicon wet sand paper or finer, until the surface is clean and shines. Clean any remaining
grit or debris from the inside of the cylinder.
Using a coarse thread wood screw in a hex driver (held in place with a small piece of paper here), insert this into
the center hole of the white plastic piece inside the cylinder and thread it in a few turns. Using a piece of wire
with a loop formed at the end (sorry, no picture) grab the head of the screw and pull the plastic insert to the end
of the cylinder.
Once the head of the screw is close to the end of the cylinder, finish removing the plastic piece with needle nose
pliers. I don’t even know what this piece is! It is not called out in the Air Arms parts list, and for our purposes, is
not required. It won’t matter if this is left in place, however.
Mark the POT at a spot that creates a final length about 3mm (3/16 inch) shorter than the regulator spacer. The
POT also keeps the valve spring in place and has a shoulder inside to do so. DO NOT cut the POT shorter than
the shoulder location.
The POT can be cut using many ways, a lathe being the best. But if a lathe is not available, the POT can be
effectively cut by chucking it in a drill press and using a hack saw blade to cut off the remaining portion (sorry,
forgot to take a picture of that set-up). Below is the cut POT re-installed into the Valve Body.
To fit around the POT when installed, a slot must be cut through the length of the spacer. Mark a slot along the
full length of the spacer approximately 13mm (1/2 inch) wide and remove the material using a hack saw.
De-burr all sharp edges and corners of the slot. The finished product should look similar to this.
This is what the spacer should look like when placed around the shortened POT. Notice the internal shoulder
inside the POT that retains the valve spring. Also notice the chamfered inside edge of the POT.
Coat the inside of the cylinder and the outer surface of the regulator with silicone grease. Align the breather hole
with the witness mark on the cylinder centerline so the hole will align with the breather hole in the cylinder.
Gently press the regulator into the cylinder with your thumb until it passes the inside threads of the cylinder.
Then position the spacer in front of the regulator and press the two together further into the cylinder until the
threads are exposed enough to thread the valve body into place.
Regulator and spacer in place, with the breather hole aligned to the hole in the cylinder, ready to thread the valve
body into place.
Regulator installed and valve body fully threaded into place. Use the hose clamps, rubber strips, and protective
rag in the bench vise to get a good grip on the cylinder for tightening. Be sure to align the witness marks made
earlier during final tightening of the valve body. This ensures the proper torque on the connection.
Note; the breather hole does not necessarily need to line up with the hole in the cylinder. There is enough space
between the regulator and the inside diameter of the tube to allow proper venting.
Tightening the valve body until the witness marks align ensures proper torque on the connection.
As long as the rifle is dis-assembled this far, now is a good time to inspect the barrel crown. Remove the barrel
shroud in a manner similar to the removal of the pressure cylinder, using the hose clamps and rubber strips.
In this case, it was noticed that the crown of the barrel was not good. Notice in the picture that the crown is off
center, and a sharp edge can be seen on the right. Not common for a Lothar Walther barrel. Looks like a recrown is the next project for this rifle!
The remainder of the re-assembly is performed in reverse order of the dis-assembly. Once re-assembled charge
the pressure cylinder and see how we have done! If your results are near what was accomplished with this
modification, I am certain you will be satisfied.
Now for the best part of the project, a comparison of the shot strings before and after installation of the regulator.
Big difference here and a good one at that!
Air Arms S500 Special FAC
Huub Regulator 2b
Setpoint - 140 bar
990
980
970
960
950
940
New in Box - FTT 8.64 gr From
180 bar 1/2 Power
930
Velocity (fps)
920
New in Box - FTT 8.64gr From
190 bar, 7/16 power
910
900
Reg Installed - FTT 8.64 gr From
200 Bar, 7/16 power
890
880
870
Reg Installed - JSB 8.44 gr From
200 Bar, 7/16 power
Regu
860
850
Reg Installed - JSB 10.34 gr
From 200 Bar, 7/16 power
840
830
820
810
800
790
0
5
10
15
20
25
30
35
40
45
50
# Of Shots
As you can see, with all other shot strings, the velocity continuously drops off from the start. Some more than
others and that may be due to different power settings, but all the same, the difference between stock and
regulator installed is dramatic! Shots were fired until the power dropped off dramatically. In the first two cases
with the regulator installed (red and blue) there was a loss of efficiency due to hammer bounce. A 1/4“ID X
3/8”OD O-ring was placed on the hammer slide in front of the hammer decreasing the amount that the firing pin
opens and reducing hammer bounce. This is commonly referred to as an O-ring tune. A much more efficient
curve with over 35 consistent shots and standard deviations of no greater than 2.2 were achieved!
Raw Data
8.64 gr FTT - 1/2 power
180 bar start
1
982.8
125 bar stop
2
976 Energy= 18.07948 ft-lb
3
974.4
958.50 L
4
971.2
982.80 H
5
977.6
970.64 AVE
6
973.8
24.30 ES
7
965.5
7.72 SD
8
965
9
961.6
10
958.5
11
957.1
12
960.1
13
953.2
934.30 L
14
949.1
960.10 H
15
951.6
948.15 AVE
16
948.3
25.80 ES
17
942.6
7.79 SD
18
934.3
19
943.2
20
942
21
934.2
22
932.4
23
930.5
910.50 L
24
924.6
934.20 H
25
925.9
922.80 AVE
26
923.6
23.70 ES
27
917.7
8.30 SD
28
915.5
29
913.1
30
910.5
31
908
32
907.3
33
902.8
880.20 L
34
897.4
908.00 H
35
894.8
894.33 AVE
36
892.1
27.80 ES
37
890.5
9.59 SD
38
886.1
39
884.1
40
880.2
8.64 gr FTT - 7/16 power
190 bar start
1
953.2
130 bar stop
2
965.4 Energy= 17.57
ft-lb
3
962.9
943.00 L
4
962.8
965.40 H
5
960.7
956.74 AVE
6
959.5
22.40 ES
7
954.9
6.86 SD
8
954.7
9
943
10
950.3
11
942.8
12
947.4
13
942.8
926.60 L
14
944.1
947.40 H
15
940.4
938.45 AVE
16
935.9
20.80 ES
17
936.7
6.19 SD
18
934.3
19
933.5
20
926.6
21
936
22
926
23
922.4
910.60 L
24
919.9
936.00 H
25
918.8
919.19 AVE
26
918.2
25.40 ES
27
911.3
7.78 SD
28
917.6
29
911.1
30
910.6
31
908.7
32
902.2
33
901.6
881.10 L
34
902.3
908.70 H
35
897.3
894.90 AVE
36
881.1
27.60 ES
37
892.1
8.86 SD
38
889.8
39
888.7
40
885.2
8.64 gr FTT - 1/2 power
200 bar start
1
928
125 bar stop
2
907.3 Energy= 15.8
ft-lb
3
912.4
900.80 L
4
909.3
928.00 H
5
904.5
907.75 AVE
6
904.1
27.20 ES
7
901.4
7.53 SD
8
903.6
9
900.8
10
906.1
11
905.1
12
906.8
13
906.7
895.20 L
14
901.9
906.80 H
15
899.9
901.18 AVE
16
897.3
11.60 ES
17
900.4
3.73 SD
18
898.8
19
899.7
20
895.2
21
896.8
22
896.5
23
898.6
850.40 L
24
890.6
898.60 H
25
888.2
879.20 AVE
26
882.9
48.20 ES
27
866.2
17.10 SD
28
865.6
29
856.2
30
850.4
8.44 gr JSB - 1/2 power
200 bar start
1
883.1
130 bar stop
2
874.4 Energy= 14.2
ft-lb
3
873.2
865.8 L
4
872.2
874.4 H
5
871.8
871.0 AVE
6
870.4
8.6 ES
7
871.7
4.1 SD
8
870.7
9
872.2
10
865.8
11
867.4
12
867.4
13
865.8
863.5 L
14
864.8
867.4 H
15
866.1
865.2 AVE
16
865.8
3.9 ES
17
863.7
1.4 SD
18
865.8
19
863.6
20
863.5
21
861.4
22
868.7
23
860.5
856.2 L
24
861.3
868.7 H
25
860.5
860.7 AVE
26
861.1
12.5 ES
27
861.3
3.2 SD
28
856.8
29
859.2
30
856.2
10.34 gr JSB - 7/16 power
200 bar start
1
834.8
130 bar stop
2
839.6 Energy= 16.14396 ft-lb
3
842.9
834.8 L
4
838.4
842.9 H
5
840.5
838.4 AVE
6
836.7
8.1 ES
7
838.8
2.2 SD
8
838.7
9
837.5
10
836.4
11
840.5
12
836.2
13
836.9
834.7 L
14
837.4
840.5 H
15
837.1
837.4 AVE
16
835.5
5.8 ES
17
838
1.7 SD
18
840.1
19
834.7
20
838
21
837.4
22
837.3
23
841.1
834.3 L
24
839.6
841.1 H
25
836.1
837.7 AVE
26
838.4
6.8 ES
27
837.3
1.8 SD
28
836.9
29
834.3
30
838.9
31
841.3
32
835.5
33
836.9
832.8 L
34
844.4
844.4 H
35
836.5
836.7 AVE
36
835.9
11.6 ES
37
834.8
3.3 SD
38
835.8
39
832.8
40
833.5
41
835.2
42
831.6
43
829.9
810.0 L
44
824.5
835.2 H
45
825.2
823.2 AVE
46
823.9
25.2 ES
47
820.9
7.8 SD
48
817
49
813.9
50
810