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PostPosted: Wed Jan 20, 2021 9:20 am 
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Location: Southern Ontario
So, I am no stranger to tuning/modding as many of you know. Normally however I stick with porting and valve springs, and in the case of the revolvers I do it's the magazine/valve/barrel interface.

Anyways, working with that stuff has yielded consistent results in the past. Right now I am running into something new. I am working on the 38T .22 carbine, everything is tight, all the CO2 is coming out the barrel with the pellet. I am hitting 500 on the nose on the first shot, then it drops to 480, then 460, then 440.... and so on. I need to wait quite a while for the pressure to come back up so obviously there is NO consistency between shots.

My question is, is it possible I am dumping too much gas with this setup? Like maybe the longer barrel and magazine seals would have been enough? I wondering if I can actually go back to stock spring in this one, like maybe I'm holding the valve open too long. Luckily this is a variant 2 so I can tinker with the hammer tension a bit before going into the valve again.

Anyways, ideas? Thanks.


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PostPosted: Wed Jan 20, 2021 2:03 pm 
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Joined: Thu Dec 24, 2020 2:26 pm
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I’m glad the Gland Gaskets and Quad Seals are working for you.

I would go back to regular power Valve spring, I’m thinking your first shot is using too much air, making the pressure drop to quick.

Let us know what happens.

Jerad


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PostPosted: Wed Jan 20, 2021 2:22 pm 
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Thanks Jared, but I haven't received them yet to test them. I'll likely go back to the stock spring tonight and hope it all holds together.


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PostPosted: Wed Jan 20, 2021 2:41 pm 
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I played with a couple of these in the past, I don't remember what I did exactly but there was a way to increase the valve volume. Longer barrel will help if you get a good seal on the cylinder. I agree that the heavier hammer spring is probably causing unwanted flow of gas. Did you use a different spring altogether or just adjust the tension?


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PostPosted: Wed Jan 20, 2021 2:48 pm 
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killercrow wrote:
I played with a couple of these in the past, I don't remember what I did exactly but there was a way to increase the valve volume. Longer barrel will help if you get a good seal on the cylinder. I agree that the heavier hammer spring is probably causing unwanted flow of gas. Did you use a different spring altogether or just adjust the tension?


You can pull out or swiss cheese the little spacer in there to get some more volume in the valve. It's relatively roomy for what it is. I changed the valve spring entirely, I normally do that rather than increase the tension on the hammer to keep the double action somewhat light.


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PostPosted: Wed Jan 20, 2021 3:13 pm 
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Right, I did Swiss cheese that spacer. The old trapmaster had something similar also. Gets you more volume anyway.
Trial and error! Beef up the valve spring a little, if you have options. I remember how tedious this model is to break down and reassemble. Makes modding and testing a little painful.
This gun has the flow thru exhaust valve does it not? If so, you can add ports and hog out the stem a little.


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PostPosted: Wed Jan 20, 2021 3:19 pm 
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Yes it does, but that this is hardened on these so it's chore. I've done it, and I remember hating it. I'm hoping that just putting a normal spring in there will help, I just want it to be consistent in the 450's or so. And yeah, the take down is a pain in the buttock for sure lol.


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PostPosted: Wed Jan 20, 2021 3:22 pm 
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Actaully wait a minute, help me out here crow. If theory is I'm flowing too much gas why do I want to increase the volume?


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PostPosted: Wed Jan 20, 2021 4:23 pm 
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Well in theory you kind of want a balance of valve volume and exhausted gas with a given shot cycle. It's easy with, let's say a 2240 you put in a nice heavy spring, your gun gets louder with minimal if any power gain. Basically you are opening the valve more and for a longer duration but it is just flowing straight through from the source. Co2 is heavy and the pressure is ~850 psi. Also with more flow, your temperature drops drastically, lowering pressure. So, for the 38t, if you do the volume mods, and are hammering it harder, and have a lighter valve spring... There are a lot of variables there, I would say lighten your hammer. It'll reduce lock time and may increase efficiency. The volume increases by themselves without playing with any springs night well be enough. And on the hardened valve stem, I used a Dremel with the tiny diamond bits and was successful enough.


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PostPosted: Wed Jan 20, 2021 4:25 pm 
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Also, I don't know if you have a longer barrel or not, but more volume and a short barrel will probably not yield a lot of gain.


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PostPosted: Wed Jan 20, 2021 4:27 pm 
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Yes, yes this is the info I was looking for, thanks man. Barrel is slightly longer now.....


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PostPosted: Wed Jan 20, 2021 4:37 pm 
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Location: Spruce Grove AB
Haha that is sweet! Nice looking build you got there. I have seen a few old carbines built like that, not sure if they were 357 or 38spl, I guess they were dangerous to shoot as the powder flash from the cylinder to barrel space could remove your fingers.


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PostPosted: Wed Jan 20, 2021 4:44 pm 
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You know... Depending on how much you feel like putting into this project, regulated hpa might be a possibility. If there's any room inside that stock anyway.


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PostPosted: Wed Jan 20, 2021 5:08 pm 
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Thanks, this has been in the works for a while until I came up with a donor 38t for it. It's super cool, though I had to remove my custom made 10 shot steel mag and go back to the 6 to get it to seal to the barrel enough. It spins much smoother with it, so not the worst thing to do

I think in the past I have taken that spacer thing all the way out, I'll try that when I put the other spring back in. Hpa would be cool, but I'd need to get set up for it and that's an investment I don't want to get into. I could probably fit a tube in that stock though.

So yeah, first time I saw a rossi circuit judge I was like, I can do that....lol. Vigilante conversion is next.


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PostPosted: Wed Jan 20, 2021 6:11 pm 
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Location: Spruce Grove AB
Did you make the 10 round cylinder yourself? What about the indexing finger thingy, I would think you must have shortened the stroke somehow?
The spacer in the valve, I can't remember exactly what it's purpose is. I think it holds the valve seat in place? Might not work without it.
You can also open the port in the valve body between the 2 chambers if I'm remembering right.
Anything else... I think I might have played with shimming the hammer spring the be heavier but I might not have left it that way. I built it for someone here on the forum, most likely wllm995 :lol: I'm not sure.
If you put a cylinder in the butt stock, even co2 would be pretty sweet.


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