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Mk1 .25 project https://www.airgunforum.ca/forums/topic89460-15.html	Page 2 of 3

Author:

killercrow [ Tue Sep 14, 2021 10:34 pm ]

Post subject:

Re: Mk1 .25 project

Very nice work.
I still have a lot to learn.

Well I tried a slow rust blue procedure I found on the Google, seems like a winner, only takes a couple hours to do the bluing...
But it is looking better so far. The shroud is soaking in oil at the moment.

Just wanted to share some chrony results. Starting with a new co2 cart, shooting 25.4gr Jsb Kings, with the hammer preload at the half way mark.

30 shots. Not too bad.

Also a picture of the trigger overpull stop. Works nice.

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Author:	Leonardj [ Wed Sep 15, 2021 6:04 pm ]
Post subject:	Re: Mk1 .25 project
Thanks. What I found to result in a very nice, and quite durable finish for the Mark I is Birchwoood Casey Aluma-Blue. The preparation of the alloy pieces is important. I found that bead-blasting them first, then cleaning any dust, etc. off with lacquer thinner, prior to application of the Aluma-Blue gave the best and most durable result. Resulting finish is a satin black. Attachment: MkI BWCB.jpg [ 83.03 KiB \| Viewed 564 times ] One trick that some folks have done to increase the hammer strike dwell time, is to replace the two cocking knobs with slightly larger, heavier knobs. You can tailor the power without having to disassemble the gun.

Author:	killercrow [ Wed Sep 15, 2021 7:59 pm ]
Post subject:	Re: Mk1 .25 project
Hey thanks for that tip, I had no idea anything like that would work on these frames. I will get some asap! I have tried the trick with a heavier knob on one side of the bolt. I think if anything, I might lighten the hammer on this one. Seems the valve is opening pretty easily, using factory spring and preload. Is that a bolt knob hammer adjuster?

Author:	Leonardj [ Thu Sep 16, 2021 12:36 pm ]
Post subject:	Re: Mk1 .25 project
killercrow wrote: Is that a bolt knob hammer adjuster? Yes. I drilled and tapped the adjuster, added a long set-screw, and then topped it off with the cocking knob. It allows me to back off the pre-load on the hammer spring between shooting sessions, without the need for an Allen wrench.

Author:	killercrow [ Mon Sep 20, 2021 3:00 am ]
Post subject:	Re: Mk1 .25 project
I did a little more playing with the mk1, goal was to seal the transfer port to the valve. I milled a flat into the valve exhaust face. Then drilled the frame port to .23"ish and spun up a little delrin insert to fit into that port. With a flat faced flare to accept the valve whence inserted into the frame. Hope that makes sense. Since I don't have pictures at this point in time. It works. No detectable blow-by while firing. And I managed to pick up 20 fps on the max setting with the 20 grainers. So obviously the hammer spring probe gets cut a little short. It's just nice to gain a little efficiency. And hobbyman! You need one of these pistols. I promise you won't be disappointed.

Author:	Leonardj [ Mon Sep 20, 2021 11:55 am ]
Post subject:	Re: Mk1 .25 project
Too bad you didn't get some pics of your transfer port sealing mod. Always interested in seeing how others tackle their Mark I & II mods. This is how I have been eliminating transfer port blow-by for decades. Spot-face the valve at the exhaust port to take an o-ring. It makes installing the valve a bit fiddly, but it works great. I posted these pics a few years back. Attachment: Mk1 Valve Mod.jpg [ 23.48 KiB \| Viewed 512 times ] Some folks have even tried putting seals at the valve body fixing screw locations, but I proved through testing that this was not an issue - there is no leakage at the fixing screws.

Author:

killercrow [ Fri Sep 24, 2021 1:42 am ]

Post subject:

Re: Mk1 .25 project

I'll get some pics the next time I take it apart. I'd like to find a way to fix the shroud more permanently to the hammer spring retainer. Got some ideas, when I have the time I'll get to it.
I actually have done valves like that with the oring. It is very likely I got the idea from you.

But I did some target shooting today, setup a bench with sand bags, did some 20 yard shooting. Not sure how this is for a pistol, but I feel like it's pretty decent. Especially with the poly mags on the left. Right target is with Jsb Kings.

The target dots are a toonie traced with a sharpie :lol:

so... 1-1/4"?

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Author:	Leonardj [ Fri Sep 24, 2021 12:49 pm ]
Post subject:	Re: Mk1 .25 project
The poly-mag group is looking good. Try a few more different pellets and you may be able to tighten that group up even more.

Author:	Daryl [ Fri Sep 24, 2021 4:25 pm ]
Post subject:	Re: Mk1 .25 project
I believe that is really good for that pistol. I did my best shooting at 20yards, with my PP700SA using H&N pellets, the 19.09gr. and 21.3gr RN Match, by the same company. The Predators also shot quite well.

Author:	TCooper [ Fri Sep 24, 2021 8:11 pm ]
Post subject:	Re: Mk1 .25 project
Nice shooting with the Mk1 at 20 yards, especially with iron sights off a sandbag. Optics might help shrink the groups a bit. When I'm just shooting to test pellets and group size I'll sometimes use a Black & Decker Workmate for CO2 pistols. I clamp the front of the trigger guard in the Workmate. You can load and shoot without removing the pistol. The older model 200 WM is quite sturdy.

Author:

killercrow [ Tue Sep 28, 2021 4:36 pm ]

Post subject:

Re: Mk1 .25 project

Thanks guys.
I like the idea of clamping the gun to the bench, or with the bench... I'm sure I could figure something out for that.

Daryl, is that pp700 in .22 or .25 ? How does it shoot?

So I got it apart again, here's what she looks like.
The oring snags on the port bushing a little when installing the valve. If I do another I won't go so far with milling the valve.
Otherwise, removal of the valve is unaffected. I can push the bushing out with a small punch through the barrel set screw hole. It works good, no leaking anywhere. The only advantage I think might be the ability to adjust the port diameter. It would be easy to make more bushings with smaller I.D.

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Author:	Leonardj [ Wed Sep 29, 2021 1:17 pm ]
Post subject:	Re: Mk1 .25 project
Thank you for the pics. They help to clarify your earlier explanation - at least for me. Yet another solution to a leaky transfer port. Well done.

Author:

killercrow [ Thu Sep 30, 2021 11:03 am ]

Post subject:

Re: Mk1 .25 project

Figured out how to use blue wonder on large surfaces too. Getting better anyway. Prep work is key.

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Author:	Gippeto [ Fri Oct 01, 2021 10:55 am ]
Post subject:	Re: Mk1 .25 project
Prep work is always key. Looks good! Regards, Al

Author:	Emery [ Wed Oct 06, 2021 6:06 pm ]
Post subject:	Re: Mk1 .25 project
Hello, New here and need help! Need new valve seal and how to replace for Crosman Mark 1 - .22 cal. Any help, suggestion, recommendation would be greatly appreciated. Em…. Canada.

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