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 Post subject: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 3:53 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
Lately I've had a lot of extra time, so why not build something cool? :lol:

The barrel is a Kral product. Bought on a discount due to a bad crown.

Did all the valve hot rodding. The exhaust port is angled a little in the appropriate direction. Bored and faced the valve. Concave delrin poppet With an alloy steel dowel pin stem.kept the spring perch at the factory settings. Something worth sharing, the porting and screw hole locations in the frame surrounding the valve are not always realiable to measure and assume they're all at 90*
It was best to secure the valve and mark the port in place. I drilled the original off center. Had to repair it and drill a new port on the bottom of the valve.

Adjustable hammer spring, little different from factory. At coil bind the gun shoots h&n 19.94gr at 492-489 fps. Nice surprise. Quite a nice bark to it. Just for fun, the Jsb 33.95gr do 379 fps

Haven't done a full string yet but I bet she's a gas hog.

The shroud is 4130 at .75", I tried to blue it but it kept going brown... I may leave it. I do still want to blue all the steel bits, trigger and front sight as well.

Got all urethane orings where needed.

Oh and a fancy bolt knob. I didn't go with a flow through bolt because the factory probe is the perfect size displacement to match all the port maths :lol:


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 Post subject: Re: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 3:56 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
More pics


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 Post subject: Re: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 3:57 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
And some more


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 Post subject: Re: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 8:29 pm 
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Joined: Sat Sep 03, 2005 9:25 am
Posts: 3844
Location: Ontario, Canada
Looks good. Lots of power! What is the barrel length? Did you keep the OEM valve return spring or go with something lighter?


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 Post subject: Re: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 9:33 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
Thanks!
I kept the original spring. I don't see any reason to change it.
The barrel is 9" from breech to crown. I think the shroud bushing adds 1/2"
Nice weight to it anyway.
Another thing on the list is a trigger overpull adjuster/spring perch. Anyone fiddling with mk1s knows of this spring. :lol:


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 Post subject: Re: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 11:29 pm 
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Joined: Thu Aug 05, 2021 5:36 pm
Posts: 26
Wow! That is great! Now you've got me thinking I need one too! I think you are right about it being a gas hog. Have you thought about an HPA tank instead of CO2? You sure do beautiful work.
JD


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 Post subject: Re: Mk1 .25 project
PostPosted: Thu Sep 09, 2021 11:55 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
Thanks JD.
I have thought of the hpa tanks. I just personally hate the way they look. I've been toying with the idea of putting a regulator in the handle and making a small air cylinder to thread into that. It would be a small vessel though... But 3000psi regulated at 850 is sweet.

I have another, one of my older builds which I run bulk co2. It does good. I'm using a custom plug with a foster nipple on it, so no gain in volume there.


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 Post subject: Re: Mk1 .25 project
PostPosted: Fri Sep 10, 2021 7:52 am 
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Joined: Tue Feb 18, 2014 7:24 pm
Posts: 943
Location: Dowling ,ontario
Nice work on that. I love the quarter bore especially in pistol form. I’ve never had my hands on an MKI but have always thought of getting one, they seem to come up for sale from time to time so I might have to splurge on a winter project.

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 Post subject: Re: Mk1 .25 project
PostPosted: Fri Sep 10, 2021 10:21 am 
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Joined: Sat Sep 03, 2005 9:25 am
Posts: 3844
Location: Ontario, Canada
I remember back when Dennis Quackenbush was making the .25cal conversions for the Cr2240. I guess that would be a 2540. I met Dennis back in 2001 at an airgun show in Minneapolis area. Great guy.

http://www.quackenbushairguns.com/2240.html

http://www.quackenbushairguns.com/2240.html
https://www.pyramydair.com/blog/2012/06 ... ol-part-2/

A .25cal Mark 1 is definitely a step up from the 2240 platform. I'm looking forward to reading about accuracy and any velocity tweak you do. Maybe you will find setting the pistol for slightly less power gives much more shots per powerlet. I bet it has quite a bit of muzzle flip! Tin cans beware!


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 Post subject: Re: Mk1 .25 project
PostPosted: Fri Sep 10, 2021 1:47 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
Yes the quarter bore! I love my 25-06, the do all rifle from gophers to deer ( and debatable for elk).

They do still come up for sale quite often. I usually have an eye on one somewhere, picked up some gems this year just on Kijiji and gunpost.

Yes I remember Dennis Quackenbush, He was one of the guys who really knew co2 guns. Had some nice stuff going anyway.

As for any velocity mods, the only thing that really needs to be done is to seal up the transfer port. I have an idea but it will be fiddly to get it right, and its not the oring on the valve port.
I'll probably use delrin, countersink the barrel port to fit the delrin tubing, and maybe flatten the valve port. Use barrel set screw to add tension and voila. Might work.
Gotta take it out and see how it shoots. The shot cycle does seem a little nicer at 450fps though, that's where it sits now.


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 Post subject: Re: Mk1 .25 project
PostPosted: Fri Sep 10, 2021 3:08 pm 
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Joined: Wed Aug 04, 2021 9:12 am
Posts: 37
Nice job on the .25 cal. Mk I. :supz:

This is a .30 cal. Mk I that I built about 35 years ago. It uses a tap loading system for breech loading. It has a 10" long barrel.
The barrel is turned about 1/4 turn, allowing it to move forward, the lead ball is dropped into the loading port, and the barrel moved rearward and turned back 1/4 turn to seal the breech.
Shooting at ~ 350 FPS.

Attachment:
MK1-30-04.jpg
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 Post subject: Re: Mk1 .25 project
PostPosted: Fri Sep 10, 2021 4:28 pm 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
Wow that's nice! I get what you mean with loading, very innovative. I have not yet looked at a tap loading gun...
Looks like its a shooter as well.
So at 10" of barrel, is that measured from the crown to the frame, or to the preech?


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 Post subject: Re: Mk1 .25 project
PostPosted: Fri Sep 10, 2021 5:23 pm 
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Joined: Wed Aug 04, 2021 9:12 am
Posts: 37
killercrow wrote:
Wow that's nice! I get what you mean with loading, very innovative. I have not yet looked at a tap loading gun...
Looks like its a shooter as well.
So at 10" of barrel, is that measured from the crown to the frame, or to the preech?

Thanks.
That target was shot at 10 yards.
The 10" is from breech to muzzle.


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 Post subject: Re: Mk1 .25 project
PostPosted: Sun Sep 12, 2021 1:38 am 
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Joined: Thu Oct 13, 2005 4:20 pm
Posts: 2010
Location: Spruce Grove AB
Ok, it must be the tapered barrel. It just looks long.
I like it though.
Did you machine the shroud yourself or are you using a tapered shaft? Golf club shaft?


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 Post subject: Re: Mk1 .25 project
PostPosted: Sun Sep 12, 2021 3:43 pm 
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Joined: Wed Aug 04, 2021 9:12 am
Posts: 37
killercrow wrote:
Ok, it must be the tapered barrel. It just looks long.
I like it though.
Did you machine the shroud yourself or are you using a tapered shaft? Golf club shaft?

Actually, the barrel isn't tapered.
That is the OD of the .30 cal barrel, which has been painted gray.

On another custom Mark I that I built, with a 12" barrel, the shroud is tapered.
Machined using the offset tailstock method.
Inserted a piece of heavy wall aluminum tube between the appropriately altered original shroud ends, and machined to suit.

Attachment:
MkI 12.jpg
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