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New Cometa Fusion Work
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Author:  eSteve [ Tue Aug 10, 2021 1:07 pm ]
Post subject:  New Cometa Fusion Work

It was shooting fine out of the box so I put 100 or so shots through it. It softened up fine. I liked shooting it. Then I chronied it before the work, using 3 different pellets:

RWS Meisterkugeln 7 gn
RWS Super-H-Point 7.2 gn
JSB Simply 8.1 gn

RWS MK 7 gn
Av 511.3 fps, SD 6.78

RWS SHP 7.2 gn
Av 471.8 fps, SD 9.00

JSB Simply 8.1 gn
Av 452.2 fps, SD 6.85

Ok, what I did.

I have a good spring compressor that works well with my other 3 rifles. It works well with the Fusion too, I just had to add one small washer to the screw at the push end. The 495 spring doesn’t really need the compressor, it’s still nice to use tho. It’ll be more necessary with other springs.

After opening it and disassembly I did some cosmetic smoothing. The end of the receiver and the safety had sharp edges and my fingers are there all the time, so I smoothed all that out. The forks on the other end had sharp edges from machining, I smoothed those out, I know I’ll be swapping barrels on this rifle.

Inside, the trigger assembly also performs as the rear spring guide, the piston and safety slide over either end of the top in a cylindrical way and work with the sear.

Out came the spring, I measured carefully. Not exactly the same dimensions as B-18 springs but close enough. Could be fun.

Then the piston. Similar looking to B-18 but that cylindrical flange reaching back for the sear, and a sort of button end, wider to meet the cylinder wall. The seal looked in good shape. I smoothed the flange and cocking groove, didn’t go too crazy. There was a steel liner, the first I had seen. The front spring guide (top hat) quite long, again, not exactly the same diameters as B-18, but this was going to work. I tested a B-18 spring in there, just a little wide to slide comfortably in the liner.

I decided to remove the steel piston liner and replace it with a plastic one. It was in there tight, I managed to push it out without wrecking anything. I just had to put the little flaps back in place, I could reinstall it to use again if needed. The steel was thick so I used thicker plastic than I had used for previous liners. Still, thinner than the steel, I needed a larger diameter spring guide. Lucky me, I have 2 spare B-18 spring guides. I filed one down, smaller than I would for B-18 but larger than the Fusion one. I smooshed it together, seemed fine. I’m only a little worried that the untested plastic, thicker and perhaps softer, will come apart in a mess inside my new rifle.

In the past, when I was first thinking about experimenting with preload adjustment on the other rifle, I had shied away from adding mass to the piston assembly. Wasn’t comfortable with that. But this new liner and guide decrease piston mass, I’m down.

I was bummed I couldn’t drill a stop pin hole while I had it open. I didn’t have the correct size bit in the case (of course) but I couldn’t mark the location for the hole without the new mounts anyway. I was still deciding about which mount to get, at the time.

I smoothed the cuts in the cylinder, they weren’t too bad. I lubed everything correctly, I hope. Thanks Rick for the moly paste. I smoothed and molyed the sear just the tiniest bit, otherwise not touching the trigger for now. And I smooshed together the whole thing with the stock 495 spring. Ta-daa!

Author:  TCooper [ Tue Aug 10, 2021 2:49 pm ]
Post subject:  Re: New Cometa Fusion Work

I had a look at the parts on the D&L Airgun web site. Springs are only $25 for full power. You can get a different calibre barrel and cocking linkage for $40 total. The piston seals looks a lot like a Crosman. Will a Crosman seal work in the Cometa?

Author:  eSteve [ Tue Aug 10, 2021 3:06 pm ]
Post subject:  Re: New Cometa Fusion Work

TCooper wrote:
I had a look at the parts on the D&L Airgun web site. Springs are only $25 for full power. You can get a different calibre barrel and cocking linkage for $40 total. The piston seals looks a lot like a Crosman. Will a Crosman seal work in the Cometa?
Yes, available parts. That was part of the whole deal for me. May not need the spring. But it's funny you mentioned the linkage. I saw it as a separate item there but it was also showing as part of the barrel assembly in that photo. But not listed as part in the description. I'm gonna have to confirm that. I don't think the Crosman seal will work. I've only eyeballed it but it looks that the piston dove on the Fusion is quite larger. And I haven't compared tube diameter yet either

Author:  eSteve [ Tue Aug 10, 2021 4:09 pm ]
Post subject:  Re: New Cometa Fusion Work

So what happened?

I chronied it with the same pellets. It’s funny with these jobs at the beginning, I find myself wishing I had done or not done that thing, or done them in a different order or chronied first. Humans are funny.

Anyway, the increases in velocity here are likely owing more to a lighter piston than smoothing and lube. And I only fired 5 or 10 shots before the first session, with the MK 7 gn. The first shot was the lowest by a bit, SD might have shrunk some with a few more shots first. But I think the other 2 sessions are a clear record.

Also funny, I haven’t cleaned the barrel. Probably the first thing I should have done. The factory lube seemed good tho. Maybe I’ll chrony again after I do.

RWS MK 7 gn
Av 531 fps, SD 6.16 - 20 fps increase velocity, .62 decrease Standard Deviation

RWS SHP 7.2 gn
Av 483.9 fps, SD 3.60 - 12 fps increase velocity, 5.4 decrease Standard Deviation

JSB Simply 8.1 gn
Av 481.4 fps, SD 4.69 - 29 fps increase velocity, 2.16 decrease Standard Deviation

It’s nice to have easy increases in velocity but what I like better is less deviation, consistency. One can see this rifle settling right down, from typical factory numbers.

I’ll be opening it again soon. I’ll have to drill a stop pin hole when scope mounts arrive. And for other tests. I’ll see

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