Diana 35 shooting way lower now

[Mossonarock]

My D35 I acquired last year is shooting much lower in elevation than it used to. I've maxed out the elevation of the peep sight and it still shoots an inch low at 10m. I don't want to open it up again considering how difficult that trigger group is to reassemble. I suppose I'll have to. I'm wondering if maybe all it needs is more oil on the leather or if maybe the spring broke. Any ideas? It wouldn't surprise me to find that both is true. I know I should have replaced the very sad and sagging spring last year when I acquired the gun and had it all opened up to clean and relube it. I'm sure the barrel does not need to be bent.

[TooJung2Die]

This is why a chronometer is such a valuable tool. If you don't know how fast the pellet is moving you don't know what is causing the problem. I thought my Diana 45 was shooting great because it was loud and kicked hard. A chrono test showed it was only shooting 500 fps and the piston was slamming. The leather seal wasn't holding pressure even though it still looked brand new.

[Mossonarock]

I haven't checked it on the chrony b/c its always been low. Also, my chrony hasn't been working reliably. When I first got this gun, it was pushing pellets at about 150fps. Then I removed the steel shot from the compression chamber, lubed the leather piston seal, and cleaned and relubed the rest of the gun. I don't remember but I think the fps might have gotten up into the 400s- still very low and I'm sure the damaged leather piston seal and worn out spring are the culprits. I still had to adjust the rear sight high. However, now all of a sudden the shots were going up to four inches lower and when adjusting the vertical on the rear sight all the way up the shots are still an inch too low. I know I need to open it up and replace the spring b/c I should have done that in the first place. The leather seal should have been replaced too but I don't have the means to do that. Really, I'm just being lazy and don't want to open up the gun. I'll try the chrony this evening and see if it wants to work today.

[Mossonarock]

I finally managed to get some functionality out of my chrony
Shooting RWS Meisterkugeln 8.2gr
Hi: 413 Lo: 362 Avg: 386 ES: 51 SD: 17
In order they were shot:
413
408
397
401
362
370
373
383
382
376

A year ago, same pellets: HI: 424, Lo: 382, Avg: 402, ES: 42, SD: 13
It doesn't look like a lot of difference to me. So, why would the shots be so much lower now to the point that I can not adjust the vertical on my peep sight high enough to get poi on poa?

[Back_Roads]

 Take a few shots into a backstop, with  paper towel or the like as as catch mat. shoot at it from a foot or so away and check for chunks of leather seal coming out of the barrel along with the pellet, that would tell you you really need a new seal.

[lizzie]

This is why a chronometer is such a valuable tool. If you don't know how fast the pellet is moving you don't know what is causing the problem. I thought my Diana 45 was shooting great because it was loud and kicked hard. A chrono test showed it was only shooting 500 fps and the piston was slamming. The leather seal wasn't holding pressure even though it still looked brand new.

Good points, but in this particular case (and I have had similar experiences in the past), you can get a pretty good idea if there is a sudden change, (iow a change relative to previously), and that will often tell you there has been a significant change internally, unless it's an optics issue. I had the same experience recently with my Diana 45, and need to send it off for a check-up and probable tune. It also happened shortly after I acquired my FWB124, which still had the oroginal seal. In both cases, they were shooting very well, consistently, accurately, then I started seeing a gradual drop in the poi, and noticing that the pellet penetration on my wood target had changed.

[lizzie]

Take a few shots into a backstop, with  paper towel or the like as as catch mat. shoot at it from a foot or so away and check for chunks of leather seal coming out of the barrel along with the pellet, that would tell you you really need a new seal.

Those old leather seals are usually pretty good, unless they have been abused / neglected, and gotten brittle.

[Mossonarock]

Well, we can see the before and after statistics and there's only about a 15fps difference in avg fps from a year ago. I can't imagine that being the cause of inches in poi drop. The ES and SD are also very similar. I thought it was interesting that the first couple shots were the fastest but quickly went down by about 50 fps then seemed to gradually climb back up. I'm not sure what the chrony may be indicating.

In my original post about this gun when I got it a year ago (sorry I have a hard time finding that old post or I'd link to it), I talked about how the compression chamber had loose steel shot and crushed lead shot in it. The leather seal had steel and lead shot imbedded into it. Obviously, someone thought they could make the gun shoot like a shot gun. yeah, this leather seal is abused. The whole gun was. I know it would benefit from replacing the seal and the spring. However, those issues existed before I got the gun and the chrony results do not seem to suggest any huge recent changes. I would need to at least send off the piston to a tuner to have the seal replaced. I'm not able to extract that pin Diana used to keep the piston seal screw in place. Otherwise, I would have made my own seal and replaced it a year ago.

A year ago, I could do some good 10m shooting with it. Not so much now.

[TooJung2Die]

I would need to at least send off the piston to a tuner to have the seal replaced. I'm not able to extract that pin Diana used to keep the piston seal screw in place. Otherwise, I would have made my own seal and replaced it a year ago.

If you do decide to replace the seal don't put another leather one in there. You will be happier with a synthetic seal instead. I put a Vortek leather seal replacement kit in the Diana RWS 45 because the leather seal wasn't performing even though it looked perfect and fit tight. It now actually shoots better than RWS claimed it was capable of back in 1981!

The leather seal was riveted to the piston so it had to be drilled out and the hole tapped to accept the o-ring seal kit. I was anxious about drilling and tapping but it was easy. I bought the synthetic parachute seal kit in addition to the o-ring kit in case the o-ring didn't work. It still has the original o-ring in there many years later. It is lubricated with Krytox synthetic oil.

I thought about the possibility of reducing the gun's value by modifying it but decided in the end I'd rather shoot it than look at it. I'm very happy with the result.