Canadian Airgun Forum

So here we are with the new head design. Full piston assembly weighs 263 grams. Aluminum is a little heavier than delrin, but in this case I didn't make a steel dovetail so saved on that.

Pretty self explanatory. Got about 3/4" of thread engagement with the rod. Should be plenty. At that rate I can adjust stroke by installing a shim/washer under the shoulder of the bolt. If I need to for any reason that is...

Now I just gotta drink some more coffee and go test it

So I got it all back together, reglued the delrin rings (tricky stuff), I wasn't happy with the bond first time around. I was able to pick it off with my fingernails. Got proper seal engagement, all tuned up.
Adjusted stroke to 3/16" longer than stock. Now my auto safety engages
Shot over the chrony 6 shots at 664-667fps, with 25.4gr jsb's.
25 ft lbs with a lighter piston.
Just out of curiosity, the crow mags at 26.24gr shot at 650 fps
For the same energy output.

Then I thought hey, lots of guys in the states shoot the light ftt pellets, so I trimmed a couple with an Olfa knife down to 21gr, and it shoots them at 750-767fps, it's a little sporadic. Loud snap at the muzzle and the gun seems to jump forward. Feels funny. I don't like it. I do like 27 ft lbs though.

Even the extra 3/4 grain extra of the crow mags give the recoil a noticeable harder rearward recoil.

So what I think I've done is created a higher initial pressure, with a narrower peak duration. More sensitive to and responsive to lighter pellets, at the cost of more violent recoil.

I think the jsb's feel perfect. It recoils like a power tuned crosman phantom. Lot more heft to the magnum rifle though.

Just wanted to add I'm using .2" extra spacing. If I can't hit anything with it I'll remove a bit and try again. Not really trying for max power.

Woo update time!

She's a shooter. It surprised me anyway. I didn't expect much really... I can hit a beer can at 25 yards consistently. And an ether can, and some other junk

Tried for an offhand group at 25 yards, shot an honest 2.5" CTC. Not bad if you ask me. Next time I'll shoot off a rest and see what it does. For me... Just need to be able to hit a starling size target ..

Lots of work, and knowledge gained. Well done. Impressive.

_________________
Best Wishes
Daryl

It was really a lot of work to get things right. But now I have the winning formula. I think so anyway. I've got a couple hundred rounds thru it and so far so good.

I went ahead and ordered enough material for 10 more. But my order has been on hold for over a week now.
But I mean... Who wouldn't want a better shooting 350 mag?

Agreed. Makes you want to buy a lathe! Love seeing what other people come up with.

Sorry about the measurements, didn't notice the PM from Apr 4th. Hope they are legible in the gmail file.

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Got me a shipment of chrome moly tubing on the way. Finally. Might have it by the end of this week.

And if I don't feel like making it all into pistons, I'll have some sweet PCP building materials

Got a package in the mail today, ordered a small selection of h&n pellets, did a little chrony shooting in the garage.

Field target trophy, 19.91gr. 728-728-733-736-729
Silver point, 24.38gr. 681-666-669-672-661
Barracuda hunter, 27.47gr. 650-655-653
Barracuda hunter extreme, 28.24gr. 663-649-650
Not very consistent. Well the hunters look good.
Very strange ever string starts higher... Besides the Barracuda hunters. I'm not taking any real break between strings. Take shot, write it down.
Also I notice the skirts are a bit loose compared to the jsb's.
I'm liking the heavy weight velocities though. Now I'm tempted to order some jsb heavys.. but 34gr? I donno. I bet Id get 600 fps. Add weight to some hollow points?
I also got the grizzlies, at 31gr, they almost fall thru the barrel.

This is a .25, isn't it? The Predators run 26gr. Got any? The reason I suggested them, is they shoot well in
every rifle and handgun I own, no matter the calibre, from .177 to .25.
The Hunter, as well as the Hunter extreme pellets in .22 shoot really well in my HW97.

_________________
Best Wishes
Daryl

Yeah it's the .25.

Just doing some experiments here... I don't have the predators but I have crow magnums, I weighed them at 27gr. Advertised as 26.24gr.
Crow mags, 27gr. 668-671-662
Jsb 25.4gr. 686-681-677

Then I made a couple custom pellets stuffing lead trimmings into the hollow point.

29gr, 640
30gr, 630
32gr, 588
34gr, 560


Ok did the averages and fpe. Makes me want to graph this data.
Field target trophy, 19.91gr, 731fps, 24fpe
Silver point, 24.38gr, 670fps, 24fpe
Jsb kings,. 25.4gr, 681fps, 26fpe
Crow magnum,. 27gr, 667fps, 27fpe
Baracuda hunter,. 27.47gr, 652fps, 26fpe
Baracuda extreme,. 28.24gr, 654fps, 27fpe
29 grain custom, 640fps, 26fpe
30 grain custom, 630fps, 26fpe
32 grain custom, 588fps, 25fpe
34 grain custom, 560fps, 24fpe

Pretty cool, have a feeling the jsb's are a much better fit. Too bad they don't have a better selection. I guess there's predators and hades... at 26 and 26.5gr. now how to add weight to a domed pellet... Haha.

There. I remember reading somewhere somebody mentioned there was no performance benefit from a .25 version of this platform Over a .22.
Straight shooters gets 605fps with 25.4gr jsb monsters for 21fpe.

Also had a thought, seems this gun heats up fast. Must be the seal itself, as the first shot after a 30 second cool down cycle gives better efficiency than waiting only 10 seconds.
So it slowly drops in velocity as I keep shooting.
Too much pressure? Seal not worn in yet? I am using the vortek seal. Not sized at all.
That must be the effects of breaking in.

Now I'm thinking I need to replicate this little makeshift ladder test with the heavy piston.

Very cool project! Nice results, especially if it's taken some of the jumpiness out of the rifle.

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Website: https://airgunarcheryfun.ca/

The .25 Hades pellets I have are marked at 26.54 and got: 26.3, 26.5, 26.6, 26.6 and 26.8gr. - average 26.56gr. - pretty close to advertised weight.
If more were weighed, I assume JSB's average weight would likely be spot-on.
Considering the 27gr. to 28gr. pellets gave the highest FPE, that weight range is likely best (most efficient) in that rifle.
The most important thing, is how do they shoot?

_________________
Best Wishes
Daryl

It is a lot nicer to shoot than it was initially. If I could, I'd measure the recoil somehow but I'm not sure how I'd go about that.

The goal is to get out and do some field testing this weekend. I'll shoot some paper too... Guess we will see.
I would like to get my hands on some different jsb pellets. I thought I saw some wadcutters and pointed jsb... But now I can't find them. Must have been my imagination

I agree with Daryl for desired weight. Other than the Hades being close to the weight you're looking for, how will they shoot for accuracy?

Mine were about the same as domed, in .22 at 15.89. I had no expansion at 700fps, at 800fps they opened up well.

Once you find your final adjustments, lets hear your accuracy results with the different weights.

Since opening mine to grab some measurements, fps increased from 800 to 820fps at 23.7ft/lbs. Wasn't greased as lightly as I thought. It's still in a happy place for accuracy.

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