I bought a .22cal RAW HM1000x about 6 months ago. Martin said it was tuned to shoot JSB 18gr at speeds around 970-980 fps. However, I found the rifle wasn't accurate as received. Also, I bought it with 2 barrels - a 20" and a 22".
Over the past 6 months, I've tried various Air Arms, H&N, JSB, Daystate and other pellets at energies between 30 - 45 foot pounds. I've tried different regulator settings, different hammer springs, and an SSG. I've shot from a bipod, from sandbags, and from a rest. The average accuracy is 1 - 2" groups at 25 yards. 50yd groups are all over the place. In no case could I get even close to 1/4" groups at 25 yards which would be my minimum standard. For reference, my .177cal RAW will shoot 1/8" groups at 25 yards with several different pellets and 1/2" groups at 50 yards. After giving up on pellets, I tried shooting slugs from ZAN, FX, and JSB at various speeds, but the accuracy was worse. I just received some NSA slugs tonight that I will try this weekend, but I'm not holding out a lot of hope
My conclusion is that both barrels are bad. I've been talking with Martin the whole time, trying different ideas that he had, but nothing has worked so far. He recently said that the .22cal barrels have not been very accurate the past few years, and that he has gotten a lot of them back. I'm likely going to be sending these back to him too, but I want to make sure Ive exhausted all of my options first.
Both bores are polished, and the crowns are very clean, even, and without any burrs. The only issue that i can find is that each bore is slightly tighter the first 1 - 2 inches (at the breach end) and then the pellet pushes through the bores without any resistance the rest of the way. They are both unchoked. I'm thinking the tighter breech may be what is ruining the accuracy. Is it worth trying to open this up by polishing it with a mild valve grinding compound?
Any ideas would be greatly appreciated.
Thanks!