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 Post subject: Crosman Piston Swaps
PostPosted: Fri Aug 04, 2017 10:44 pm 
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Joined: Thu Mar 24, 2016 7:33 pm
Posts: 240
Location: Yukon
I have a 22 Crosman Phantom which is my go to grouse gun. It began life as a sub 500 fps but I swapped in the PAL version spring shortly after purchasing. (I do have an Unrestricted License) Anyways I love the way it shoots the big lead now and the impact on a soup can is dramatically harder than my PAL Quest 177.
Not having a crony, I just assumed I would be in the 700 fps as advertised for a PAL 22 Crosman.

Then today I pulled it apart to do a lube job when I realized I have the long 190 cm piston. So now I wonder what FPS I am actually shooting. Also I do have a spare short piston that I welded shut in a sub 500 gun (shoots much nicer now at 600 FPS or so) but now thinking I should swap in the short piston too. I never did remove the piston when I did the spring swap originally.

I am not really trying to get velocity over shoot-ability, but do wonder what the piston swap difference may be. I assume it would add quite a bit of velocity? The piston is 40 cm shorter. Perhaps the calking process would get too hard as I believe factory PAL versions have a longer barrel for more leverage.

Anyone already gone through this process and can shed some light?
cheers Tango


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 Post subject: Re: Crosman Piston Swaps
PostPosted: Sat Aug 05, 2017 5:12 am 
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Joined: Mon May 26, 2014 1:08 am
Posts: 480
Location: Thunder Bay
Hello Tango,

A short piston and full power spring should give you around 700 fps with crosman hollow points for about 15-17 foot pounds. The gun will also be louder, more hold sensitive, and probably less accurate. No problem cocking it with the shorter barrel.
I have read that folks like the setup you seem to have of the longer piston with the full power spring. It gives a shorter, snappier shot cycle with good accuracy and velocity.

My phantom started life with a short, unvented piston and a very weak spring for sub-pal. I installed a full power spring and shot it like that for a while. I later detuned it by installing a mid-power spring. It now shoots cphp at 610-620 for around 12-13 foot pounds and is less hold sensitive and more fun to shoot. Easier to cock and easier on scopes too. The Brits have been hunting grouse and rabbits with 12 fpe guns for years.

Try the short piston. It may shoot well for you. You can always change it back.

_________________
12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

I'm not multitasking. I'm doing something else until I remember what I was doing.


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 Post subject: Re: Crosman Piston Swaps
PostPosted: Sat Aug 05, 2017 11:51 am 
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Joined: Thu Mar 24, 2016 7:33 pm
Posts: 240
Location: Yukon
Thanks for all your info.
Maybe I should put the weak spring, short welded piston in for a test as well. So many options with crosman air guns. Its always nice to learn from others experiences. Sweet spots seem to always be somewhere between min and max versions with Crosmans making this all so much fun.
I see a chrony in my future, but the penetration test is always a good comparison in the mean time.


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 Post subject: Re: Crosman Piston Swaps
PostPosted: Sat Aug 05, 2017 2:46 pm 
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Joined: Mon Mar 27, 2017 7:06 pm
Posts: 840
Location: Meaford, Ont.
Crono is nice because you can crono average speed then do as one pleases and crono gun and see the difference in the work you did. Sometimes I think one is a little down in power so you can check it and see. I tend not to change scope till I double check that speed is still the same. Tells me if it is just me or scope loose or some problem. Nice to be able to shoot them in the house and I leave my crono setup upstairs in my mini 30 foot range. CHEERS!


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 Post subject: Re: Crosman Piston Swaps
PostPosted: Sat Aug 05, 2017 10:11 pm 
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Joined: Mon May 26, 2014 1:08 am
Posts: 480
Location: Thunder Bay
A chrony is an essential tool for anyone who tunes an Airgun. Besides telling you how fast the pellet is going, it can tell you a lot more.
What is the extreme spread in a 10 shot string? My most accurate Springer has an ES of 3 fps. Average es for an untuned Springer is around 15-30 fps. A high ES usually signifies a seal problem.
Is the first shot from a stored gun faster? If so, it's probably diesling caused by oil from an overlubed hinge bolt finding its way into the compression tube or transfer port. If it's slower, you may have a breach seal problem that resolves itself after a few shot cycles. Folks often lament (justly) that the first shot from a stored gun is rarely on zero. A chrony may point you towards the source of the problem.
I use my chrony with my airguns far more than with my powderburners.
Enjoy!!

_________________
12 springers and a couple of pumpers.
2 lathes and lots of scrap metal.

I'm not multitasking. I'm doing something else until I remember what I was doing.


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