RWS workmanship

I just got a used RWS Diana 350 magnum in .177 and for the most part it is a great rifle. It's kind of a beast but not too much to handle. My first impression was that this was a finely crafted gun, but up close there are a couple of things in its fit/finish that are disappointing. First, the rear sight has a lot of play and wiggles side to side. I'll probably mount a scope anyway so this is not that important, but I would have expected more from a gun that cost what this one does. Second, the recoil pad is smaller than the end of the buttstock. At the bottom it's flush with the wood but as you go up you can feel that the stock get wider and wider than the rubber, until the top where about 1/16" of wood sticks up beyond the pad. Again, not a deal breaker, but it's something I notice every time I shoot the gun.

Anyway the 350 magnum seems to shoots hard and accurately and otherwise does a great job. There's my 2¢.
 
The 350 Magnum is a quality gun with an accurate barrel and you will really enjoy shooting it. I have a Diana 350 Magnum in.22 with the T06 trigger. The fit and finish on my rifle is excellent and the accuracy is extremely good for such a powerful springer. Some owners have reported having a slightly offset bore on the breech end (mine is on the vertical axis) but it does not affect accuracy, power or loading. In fact until I read about it, I had not even noticed it.

If you do put a scope on it make sure it is specifically rated for a spring piston rifle (the scope lenses are braced from both sides) and get a good one-piece droop compensating mount. I use a Beeman 5039 mount (same as Sportsmatch AOP55). It has never moved or lost zero and has more than enough elevation adjustment to handle the droop. I also put a Beeman universal muzzlebreak on mine to cover the sharp front sight and make it easier to cock.


 
Very interesting about the offset bore. Do you mean the bore is centered at the muzzle but slightly off at the breech? I'll check mine this afternoon; did you just measure to your bore from the edge of the base block on all sides? An odd thing about my gun is that to center my shots I have the rear sight way over to the left. It looks bizarre but a bore offset on one end would explain it. Now I can't wait to get home.

Edit: I don't think my 350 Magnum's bore is offset. I Googled the condition & saw examples of the breech end of the bore visibly off center inside the breech seal. Mine looks centered, if it is a little off it's verrrrry little.
 
As mozeely suggested, I think it’s just that the breech seal recess is milled a bit off-center, which should make no difference in performance.

Most modern airgun barrels are made from special heavy-wall tubing, i.e. the manufacturer doesn’t drill the bore, they only add the rifling and other detail machining. I’ve been wrong before, LOL, but I’m not sure it’s physically possible for the bore to be off-center.

I don’t own any modern Diana rifles, but fit-and-finish is quite good on pre-1980’s models. Lateral barrel-receiver alignment - not always a strength of older HW’s - is without exception perfect, the breech-tensioning design is IMHO the best of any classic barrel-cocking springers, and Diana’s sights were always sturdy with fine, smooth adjustments.
 
I reduced the windage slop in my rear sight a lot, making the gun way more fun to shoot. The sight consists of a base piece which screws to the top of the barrel, and fits up inside a top piece which pivots up & down to adjust elevation. There was a lot of side-to-side play between the top and bottom pieces so I widened the bottom piece by putting a small piece of electrical tape an each side of it. That tightened the fit so the top piece with the sight blade attached to it still moves up and down but no longer has 1/16" of side to side movement.
 
I just got a used RWS Diana 350 magnum in .177 and for the most part it is a great rifle. It's kind of a beast but not too much to handle. My first impression was that this was a finely crafted gun, but up close there are a couple of things in its fit/finish that are disappointing. First, the rear sight has a lot of play and wiggles side to side. I'll probably mount a scope anyway so this is not that important, but I would have expected more from a gun that cost what this one does. Second, the recoil pad is smaller than the end of the buttstock. At the bottom it's flush with the wood but as you go up you can feel that the stock get wider and wider than the rubber, until the top where about 1/16" of wood sticks up beyond the pad. Again, not a deal breaker, but it's something I notice every time I shoot the gun.

Anyway the 350 magnum seems to shoots hard and accurately and otherwise does a great job. There's my 2¢.

'Never seen a Diana rifle with either of these issues. Owned seven. Still own five, gifted two to children and grandchildren.