So, in part this is an acceptance of that challenge, and in another sense it is just the result of the reality that I am extremely busy and I have two other projects in the pipe and I cannot devote much time.
Anyway, the usual disclaimer:
DISCLAIMER.- The operations performed in this rifle void all warranties. Nor I, nor anybody else, has control over what each individual decides to do, so no warranties are given, or implied. It's up to each tinkerer to be safe in his/her endeavours.
The modifications performed were safe within the objectives and the context of the gun in question.
Which may not be exactly the same as yours.
All machining operations carry some risk, be safe, be careful and always err on the side of caution.
When working with open flames, specially the high temperatures one, extra care needs to be taken with all liquids and gases present in the area. Do NOT risk it.
Having added that, let's tackle the "little" 280:
The 280 is a gun that is not popular at all in the USA. In part, it is the traditionally American drive towards "more is better", and partly the result of a mismanaged marketing strategy by the former exclusive importer of DIANA airguns into the USA.
Now, with DIANA looking at more options and even doing some small direct shipments to pre-qualified individuals, there is an opportunity for savvy airgunners to enjoy the petite airgun that is available in two models:
There is a Classic version that is the "no-frills" one, and there is an elegant version called the "Premium" (as most upper-scale models in the DIANA lineup are.
We'll work here on a "Classic" version.
One of the reasons why this entry will be short is because we are basing the whole "re-tune" of this gun on the work performed for the "12 ft-lbs gunsmith's tune of the LGV" , and which will also be the base for our final approach to the 430L, to be done in the near future.
We started by testing what the gun can do off the shelf, and pretty sure, it IS a "12 ft-lbs gun". in OoB / OEM form, the gun yields between 11 and 12 ft-lbs depending on the pellet.
For sure, with proper running-in and proper lubing these guns could yield a foot-pound more, but we are not going to go there, this is a special job undertaken as a "light tune" to see how much a gun can be improved within a limited budget.
So, WHAT IS a "limited budget"?
Basically the gun is a $350 gun, landed in the USA, which essentially puts it into the HW-50 "region" though the gun itself is about a lb heavier and yields a couple of ft-lbs more at the muzzle, it is a "medium gun" region by all measurements.
Customer desired a "lightly tuned" one to 10 ft-lbs or thereabouts, because he basically shoots in his garden; and we setled on: basic trigger work, change of powerplant, and overall smoothing which, we agreed, would put the budget at $500
During the course of the project, he decided to add a SIGHTRON Si FT scope, and that drove the total "ready to shoot" cost to $685 plus Sh&Ins (and pellets, ;-) )
So, we started with this (catalogue photo):
We disassembled the gun, having established a benchmark, de-burred and smoothed everything in there, changed the piston seal and lubed.
With better guide the gun jumped in performance almost ½ ft-lb, while the cocking effort did not change (nor did we expect it to), but it was still twangy and the shot cycle clearly reflected the place in the "price ladder". I felt the gun could be much more refined.
So we brought in a Titan #1 spring and started the process. We will not go into the detail, as it has been written in the abovementioned entry.
By the time the little rifle was doing 10¾ ft-lbs. we stopped, and measured the cocking effort:
When we removed the "unnecessary hardware" the obvious muzzle piece missing looked real bad, so I decided to make a Harmonics tuner with a new design that fits into smooth barrels and is adjustable by ½ mm's.
In the end, the gun looks like this:
And how does it shoot? Like this:
At longer ranges:
I was surprised at the good results offered by the GTO (non-lead pellets); in the lead class, the 8.44/4.52/Pledged pellets perform the best.
Do note that about 1 in 10 shots is still a "flyer". The gun still is settling down and the Harmonics Tuner will have to be re-tuned once it does. The HT's final position, will also depend on how the gun is shot, whether sitting off a silicone knee-pad, or off the bench, things will be different.
For those of you that like numbers: the JSB Express were coming out of the muzzle at 770 ± 2 fps and the JSB Exacts were coming out at 758 ± 1 fps, so the consistency of the engine/machine is already there.
More seasoning to the barrel is needed (more shooting), some tests and then the final decision about the pellet of choice and the final adjustment of the HT and that should be a nice little gun, with power to spare for most things inside 35 yards. At 8# 14 Oz, "all in" it is a lightweight gun, somewhat "whippy".
LOP is short, that is why I added a temporary recoil pad to take it to 14½", otherwise I "scrunch" into the gun.
That has also been removed.
For ME, personally, it is not a gun I would HAVE to have. But it is an interesting class of airgun that could have a lot of success in some markets. Sadly, it is not slated to be kept in the lineup.
Though the project took a lot more time than expected, I learned a lot and I loved the end result.
Keep well and shoot straight!