HFT 500 power drop-offs

[Archer50]

Hi Folks, I hope someone can help here.

In every hundred shot string from my HFT 500 - ie every fill - three or four pellets drop out of the group by around 2 inches at 30 yards. Checking on the chrono, these correspond with drop-offs of about 40-50 fps in MV, and I presume the rest of it is something to do with changed barrel harmonics. Each drop-off only affects one shot, and then things are right back to normal. I get similar drop-offs whatever pellet I try, and they still happen with weighed pellets, so I'm pretty sure its something to do with the gun itself.

My gun is thoroughly cleaned and degreased, the hammer rail and valve stem polished within an inch of their lives and every seal checked. Cleaning the barrel makes no difference.

Anyone got any ideas what this might be, and how to fix it?

Alan

[Roger5]

40/50 fps that's quite a drop, are you using a pump or a dive bottle, just wondering if you might be getting muck round exhaust valve. Rog

[Archer50]

Thanks Roger. I think the only thing I can do is a back to basics strip down, clean out and rebuild. Because I've checked just about everything else I'll have a particularly close look at the transfer port and make sure it's completely clean and clear. Unless one of the seals is duff and I've not spotted it, I think it's got to be dirt somewhere. The really puzzling thing to me is that every time, it is just one shot, then straight back to its very consistent normal.

Still, on the bright side, at least I don't have to send it back to Daystate

Alan

[Archer50]

Spent a happy couple of hours dismantling, inspecting, and cleaning literally everything. Nothing was worn, loose or out of adjustment, I didn't find any dirt or grease anywhere that matters, and there was no sign of damaged/worn seals, so I just muttered a few prayers to the God of Airguns and put it back together again.

I'm hoping it's going to be like an old VW Beetle I had in the 1970's: no matter how much I tinkered and fiddled, it was forever stalling and flooding, so in the end I totally dismantled the carburettor (any of you youngsters don't know what that is, drop me a PM ) and put it back together. I didn't find anything wrong whatever, but the problems vanished.....

Alan

[Roger5]

Good to know you've sorted it, now what's all this about a carbanoobi wotsit. Rog