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PostPosted: Sat Jul 21, 2018 10:42 pm 
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Joined: Thu May 04, 2017 6:41 pm
Posts: 136
Location: Vancouver BC
It's the difference between frustration and fun that's for sure.

Now that I'm feeling more confident in this QB78 I'm ready to do move on to bulk CO2 or a regulated HPA rig like yours.

But after this bench test with the JSB 15.89 pellets I'm not so sure regulated is necessary for this plinker. I would love it if it could hit 45mm kill zone at 35-40 meters from a tripod, seated. I'll get a chance at that this weekend at the field target meet.

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PostPosted: Sat Jul 21, 2018 10:46 pm 
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Location: Caronport, Saskatchewan
Good deal! I'm jealous! Have a great time!

Sent from my LG-M154 using Tapatalk

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PostPosted: Sun Jul 22, 2018 8:21 am 
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Joined: Wed Oct 17, 2007 3:27 am
Posts: 2586
Location: Winnipeg, Canada
Pushtone wrote:
Good news! My QB78 likes JSB 15.89 grain, hates anything lighter.
I started with the JSB (Cometa) Exact Jumbo RS 13.43 gr. and got random scatter shot.
Then onto the JSB Exact Jumbo Express 14.35 and same thing, scatter.
At this point the Crosmans HP were performing much better. The CHPP would at least occasionally group with randomness in between good groups.

I was composing the rifles Craigslist ad in my head when I loaded the JSB Exact Jumbo 15.89 and... Holly Heck, one hole groups.
Very good repeatable groups. Now trigger control and hold mean something!

I had no idea it could be so night and day. I'll get some heavier pellets next and see if this is a one pellet rifle or just like the heavy ones.

Thx for the help


Check out the difference:
JSB 14.35 gr.



JSB 15.89 gr.



QB78D - modded valve, extended probe, one powerlet, stock hammer spring, no shimms,
4-16x40 scope at 16mag
Bench rest
10m
20 deg C
3-shot groups


Again here the full shot sequence for the 15.89 gr. Getting 27 shots on one powerlet. Now I can take it to sunday dinner at the folks and try 27meters next.


Kinda figured that. Good for you! The 18.1 heavy may be a bit more tighter at distances... 2.3 gr really doesn't sound enough to make a difference, but it sure does for me.

-D.S.

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PostPosted: Sun Jul 22, 2018 1:38 pm 
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Joined: Mon Aug 24, 2015 4:56 pm
Posts: 462
Location: Tecumseh, Ontario in South Western Ontario
A bent barrel/bore does have an annoying effect on POI. If the bend is to the left or right then not only do you have to adjust the elevation turret or hold over for different distances but you have to also adjust the windage turret or horizontal hold for different distances.

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PostPosted: Mon Jul 23, 2018 9:25 pm 
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Joined: Thu May 04, 2017 6:41 pm
Posts: 136
Location: Vancouver BC
Ed I think you got something there.

Got to shoot from 30 to 47 meters on Sunday and I think I was experiencing just what you describe. The farther the range the more it slides right and my barrel dips down and slightly to the right. Putting the barrel under the car tire is starting to look like a good idea again.

Another issue came up with the CO2 as well. Vancouver is getting its first warm weather. The 15.89 grain pellets which were grouping great in the 70deg basement at 10 - 18meters started forming open scattered groups when the temp hit 82deg. I've got 16 and 18 grain pellets on their way.

I'm gonna take to a HFT meet on Sunday and temperatures in Mission BC are expected to be 32deg!
I think I'll de-tune the hammer spring some more in light of the weekend temps. I only hope the seals hold.
I may even keep the co2 powerlets on ice in a cooler.

This gun has been an emotional up and down ride. Just when I think its a keeper an issue comes up that makes me think there a CL ad in its future. Still having fun and gaining experience though so I guess it's worth it.

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PostPosted: Wed Jul 25, 2018 9:24 am 
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Joined: Thu May 04, 2017 6:41 pm
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Location: Vancouver BC
I bent the barrel back to true.
Took more force than I expected but looks much straighter now and rolls on a flat surface without the hump in the middle.
I'll get a chance to shoot and different ranges on Sunday and see if the POI slides right with increasing range like before.

So now I'll be testing different pellets weights at extreme temps (32-35deg) but I'll also be testing groups at three different ranges, 20m, 35m and 55m.
When will the testing of this QB78 end and the shooting begin?

Here's my pourpose build barrel bending vise...
The barrel sits about 1mm proud of the wood block.
Attachment:
barrelbend2.jpg
barrelbend2.jpg [ 132.82 KiB | Viewed 223 times ]


Attachment:
barrelbend.jpg
barrelbend.jpg [ 106.67 KiB | Viewed 223 times ]

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PostPosted: Thu Jul 26, 2018 9:54 pm 
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Joined: Thu May 04, 2017 6:41 pm
Posts: 136
Location: Vancouver BC
I've had the barrel on the bespoke bending device twice now and it's getting a little closer every time. I can no longer see a bend in the barrel visually but when I roll it on a known flat surface you can see a slight Bend to the right because the muzzle tip lifts up just enough to see light underneath. from the breech to the barrel band is perfectly straight. the bending is happening pretty much at the barrel band.

I eliminated the vertical droop and it's hitting the bull's-eye with the scope turret dialed in to zero. Cool, I even discarded the paper shims in the rear scope mount the previous owner used to compensate for the bent Barrel. I'm noticing that the windage is getting closer to zero on the turret than before. So I'm thinking one more Gentle Ben to the right and I should be able to shoot 12meters with both turrets set to zero.

After that I'm hoping it will still Shoot Straight at 25 30 and 40 when I get it to the range on Sunday. hold overs are going to be hard enough I don't need hold lefts and hold rights to unless there's wind

All of this is a real pain in the buttock but I wanted a hobby gun and I got a gun and I am enjoying the DIY aspect.

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