On Tuning a Stormrider

I like your style. Experimentation is the name of the game with optimizing for harmonics. If you’re looking for a good starting point in general, try 4/7 of the distance from the receiver to the muzzle. Next best is 3/7. Again, speaking of generalities relating to harmonic nodes. Experimenting will have the final say. 

Also, if you haven’t checked already, give the barrel a close inspection. Rough leade and crown are a near certainty with a budget rifle like this. Not judging, I have two SPA rifles myself so I’m speaking from experience. Unfortunately, they are also bad about damaging the rifling at the muzzle: 
https://www.gatewaytoairguns.org/GTA/index.php?topic=166821

The good news is they can be remarkably accurate if you deal with those shortcomings.

Nice work OS. I found that adding a moderator to my shrouded barrel cause a wide shift in POI. I have been working on a power tune and have gotten similar nodes as I turn the power up and down keep at it, nerd-vana awaits us all

Somtimes it helps accuracy by adding an additional barrel band. YO!

Yo’s comment made me look back and it sounds like you added a 2nd barrel band. Is that right? In that case, try it at 4/7 the distance from the OEM band to the muzzle.

Let’s say there is 14” from the original barrel band to the muzzle (or the end of the LDC in this case). Try placing the 2nd band at 14 * (4/7) = 8” from the original barrel band. If that puts it past the end of the air tube, try the 3/7 position.

Because natural vibration nodes tend to set up at divisions of 2, 3, and 4 of the unsupported length (25%, 33%, 50%, 67%, 75%), and the idea is to avoid these and instead place the barrel band at a probable antinode (location of high displacement). 4/7 or 57% is that probable location.

Yeah, I figured you were just asking to see if I knew the reason why.

Ive tried barrelband in some different postions, and also 2 barrelbends, I have a couple Diana stormriders, but the main problem with the "harmonics" is that is seems to shoot higher when the pressure gets lower, 200 bar= bullseye, then 180 bar a few mm higher, 160 bar even higher and so on, it has nothing with velocity do to, it seems to be the harmonics vs the pressure holding the valve when hammer hits, its hard to find a sweetspot as there are many setting one can do. 

I didnt put to much time to find out, as each gun has it own way, and its to time consuming , and I dont have high expectation of this gun shooting FX/AA good anyway.

What Ive noticed is, 2 barrel band are better then one, In my case, and I think a regulator should take care of the most problems in my case, but the regulator alone is half the price of the gun, so....

Im about to within a few month as I dont have much time now, I will glue on a carbonfiber-tube in between the receiver and the barrelband, it should stiffen up things quite good.

I think the main problem is the thin barrel. Ive also order som extra barrelbands in plastic from Ebay.

I can post my result when I dig into this again.

Ive done inlet and crown work, polished barrel, making sure the receiver is flat against the tube, and made sure the grubscews are firm onto the barrel. nothing helped much except extra barrelband.



But as other said, check inlet for burrs, check the crown with cottonswab for burrs, make sure the receiver is flush on the tube, and feel the grubscrews, they are poor material.

Maybee this above can help you some? It didnt help me much, but I have high hopes in the carbonfibertube on barrel

Yeah it’s nice that carbon fiber tubing is so inexpensive nowadays that there’s not so much hand-wringing to just give it a shot. Unfortunately there’s not enough meat in the receiver to accept the larger diameter but it may still provide some benefit to simply sleeve the exposed portion.

I’m curious, where is the good part of the bell curve? For example, you mention that the POI is continuing to climb as the pressure declines to 160 bar (~2300psi). This review on AGN says the optimal fill pressure is just a bit above that so what you’re seeing sounds normal. But manufacturing tolerances being what they are, who knows!

https://www.airgunnation.com/topic/best-budget-2000-psi-rifle/

it was some time ago, I dont remember everything exactly, but yes, speed starts low, then rises (bell curve), but after that it riser more and more, this is where my harmonics comes into play, I will get to the bottom of this, and I hope my carbonfibertube over barrel + extra barrelband will cure most of that problem. The difference in speed from 200 bar to lets say 150 bar shouldnt rise the POI so much as mine did, so for sure there is some harmonics problems.

I will also look into how to secure the receiver to the tube extra.

I also have to order new grubscrews, as the ones that came with the gun are soft.

I don't have a picture, but will take one tomorrow. My Stormrider is 100% unmodified. I see much better grouping than this. 

I'll get it done after work. I hadn't done much with mine other than shoot it a little. The stock is the reason mine is listed in the classifieds. I don't like plastic. Yours may do better than mine. I don't think I would have stopped if it wasn't grouping decent.

As promised. The first 3 shots of the first groupI shot out of the magazine. I don't know what pellets my son had in there but obviously they are wrong. I didn't reshoot it because that wouldn't have been right. The second 2 groups are JSB Jumbo's. These are the first 15 shots I fired. 3 targets, 25 yards, 5 shot strings.