Tuning the .22 Bantam Sniper HR, can't get fps over 900

[xyon]

My Bantam came with the reg set at 125 bar and was doing 870 fps with jsb 15.9gr exacts. As an experiment I tried adjusting the hammer travel, but that was the peek velocity I could get.

Now I have upped the reg pressure to 150 bar and I can just get 900 fps with 15.9gr pellets.

I have added an a hammer spring tension adjuster that I have made as, the factory setup was not adjustable for preload, only travel. With this I can see the velocity plateau at 900 fps as I increase the spring preload. I was hoping for more power at this reg pressure. I'm wondering what fpe others have got from there Bantam?

I shot a 20 shot string with the fps at 880 and it was using 1.5bar per shot, which is not very efficient (480cc bottle).

 

[L.Leon]

Mine as received with regulator set at 150 bar is sending AA 16s at 918 FPS and JSB Exacts 18s at 891 FPS.

 

[Long_Gun_Dallas]

Hm. That seems pretty low. I thought that gun was supposed to have ample power? At any rate it sounds like you need more hammer weight to get any extra power. I'd say try a 7gm weight first at 150bar and see how that does for you.



*edit* I was thinking of the magnum. 

17" isn't a whole lot of barrel. But I think you should be able to get around 950fps with 18gr assuming you can smooth out the ports some and run a lil higher pressure. Something like a 4gm weight might suffice. But if you want to run 150bar, 7gm ought to be the ticket, I think

 

[bzizzi373]

With factory barrel I was able to get 15.9 JSB's at 950 FPS, 18.1 JSB's at 920 and 25.4 JSB's at 820 FPS

 

[xyon]

Thanks guys for the replies. I might just have to disassemble the rifle and have a look at some porting. I did read somewhere that the valve closing spring is quite stiff on these. I was hoping to shoot the 18.1gr JSB a little faster than the 850 I got as they were very accurate at 30M but at 70M were scattering. Another option is to just shoot the 15.9 at 870 fps and be happy with that

My CARM magazine just arrived yesterday, so I will test that as soon as I can.

Edit: The factory magazine may not be as bad as I said, I just shot another group with it and it wasn't too bad maybe not quite as good as the single shot tray.

 

[L.Leon]

@xyon, 70 meters is a long poke for JSB Exact 18s, especially if there’s a little wind. I use 3 mags between two Brococks and have not had accuracy issues because of them. I’ve shot comparable groups single loading as with the mags. What is a CARM magazine?

 

[xyon]

Hi Leon, I've edited my post,as I don't want to post incorrect info. I just shot 2 9 shot groups, one with the CARM mag and the other with the Brocock at 30M and they were both pretty good. I'm not sure what was going on before, the last group I did with the Brocock mag was a at 50M and was quite a bit worse than the one I shot with the tray. The carm magazines are made by Darko Dell'Orco https://www.carm-magazines.com/

 

[L.Leon]

Thanks xyon, I’m loving my Bantam Sniper, I just came in from busting pieces of chalk at 50 yards in the dark, with a green light attached to my Athlon Helos. My rifle is accurate with the JSB Exact 18s, Jumbo 15.9s, the AA 16s and the Crosman Premiers (a few more fliers). Attaching the light is the only way I can get in any after work shooting. It has proven to be a good rig for me in the field.