I power tuned my S410 Xtra. Now getting 35ft/lbs with JSB’s

Hello everyone!

I’m having lots fun with my S410 -SL Xtra FAC and by nature I have to tinker with it.

After a ton of research, reading and a few PM’s this is what I’ve done and wanted to share with you all.

– Polished #3, Striker rod
– Polished #50 Striker
– Polished #4 Firing Valve Assembly
– I slightly increased the diameter of the #9 Power adjuster Knob’s hole because mine was not aligned correctly with the transfer port.
– I decreased the diameter on the pellet plunger of #37 bolt stem from 3.02mm to 2.80mm to allow better air flow through the breech transfer port.
– Here’s the big change, but it’s a small adjustment. I lengthened the #6 Firing Pot out a bit. Just enough so the grub screw can hold it in place still. I also drilled a small dent so the grub screw seat firmly in place. It’s the firing pot that determines the amount of air used to push the pellet. I’ve found that my rifle requires about 30psi to a pellet at full power. Increase the volume of the firing pot = more air volume. When the time comes I will machine myself a new larger firing pot but that will happen when I get a mini metal lathe.

I never did search for the “power curve” of the JSB 15.9gr pellets but found it for the Kodiak 21.1gr @ 2800psi but I stop using the Kodiak’s. Also I want the max power on my first 10 shots for hunting purposes.

Here are some numbers.

Brand new no mods:
That is all the data I have when it was brand new.

Kodiak 21.1gr @ 2800psi
01-10 @ 857fps
11-20 @ 868fps
21-30 @ 849fps

Kodiak 21.1gr @ 2700psi
01-10 @ 865fps
11-20 @ 856fps
21-30 @ 832fps

JSB 15.9gr @ 2700psi
01-10 @ 960
11-20 @ 944
21-30 @ 908

Mod #1 – Polished Striker Rod, Firing Valve Assembly and Striker:

JSB 15.9gr @ 2750psi… note that I got some 1150fps spike. Something was not moving smoothly internally
01-10 @ 996
11-21 @ 953

JSB 15.9gr @ 2700psi.… note that power adjuster had moved a bit and not fully opened.
01-10 @ 957
11-21 @ 939.… I’ve tightened the hold down screw since then so it won’t adjust on it’s own.

Because my choice of pellet will be the JSB 15.9gr I will tune my rifle around that pellet.

Here are some interesting numbers at different PSI start fill.

Mod #2 – Polished Striker Rod, Firing Valve Assembly and Striker and pot extended.

JSB 15.9gr @ 2850psi
01-10 @ 999fps
11-20 @ 982fps
21-30 @ I did not record any numbers.

JSB 15.9gr @ 2800psi
01-10 @ 980
11-20 @ 977
21-30 @ 909

JSB 15.9gr @ 2750psi.… Note that power adjuster had moved a bit and not fully opened.
01-10 @ 982
11-20 @ 947 ???
21-30 @ 895 ???

JSB 15.9gr @ 2700psi
01-10 @ 974
11-20 @ 947
21-30 @ 896

JSB 15.9gr @ 2600psi… Note that I was getting awful 1150fps spikes in this 30 shot string
01-10 @ 937
11-20 @ 880
21-30 @ 1054

JSB 15.9gr @ 2400psi
01-10 @ 963fps

JSB 15.9gr @ 2300psi
01-10 @ 946

JSB 15.9gr @ 2200psi
01-10 @ 936

I was low on air, 2390psi left in my scuba tank so I hooked it up directly to the S410 and shot 5 shot to see what I would get at full power.

#1 – 976fps
#2 – 979
#3 – 979
#4 – 982
#5 – 975

Just for fun I tried the RWS 11.9gr pellets at low power with Mod #2 and I like the numbers:

RWS Hobby 11.9gr @ 2850psi 2 low power
01-10 @ 583
11-20 @ 578
21-30 @ 569
31-40 @ 570
41-50 @ 562
51-60 @ 580
61-70 @ 575
71-80 @ 534
81-90 @ 549
91-100 @ 531
Finish @ 1650psi… about 12psi per shot

FPS @ Low – 567
FPS @ Low/Med -796
FPS @ Med – 993
FPS @ Med/Hi – 1031
FPS @ Hi – 1050

So I’ve reached my goal of 999fps with 15.9gr pellets which gives me 35.24fpe

Cheers.