GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: J M on November 18, 2016, 10:32:53 AM
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Little history.
Yep I am Noobie.
I have a 6 mo. old Gen II .25 Marauder, and am in trying to tune. installed a WAR SSG, max velocity I can achieve with 3000 PSI Fill is 813 fps. Shooting JSB 25.39 pellets. Each successive shot drops in velocity rather than a "upward curve" before descending as I am told / have read? ( maybe that's also a fill issue ...to much pressure?)
I have opened up the flow adjuster 5 1/2 turns and tested to make sure its all the way open( via chrony ).
I have adjusted the pre load both ways including adjusting the spring so tight that the nut is not visible. when the rifle is cocked and I have also adjusted the gap from touching to tight to back off 1/4 and further.
Refill and chrony verify every few shots to see results.
When disassembling I noticed the transfer port sleeve is offset with the valve below by maybe 20 - 40 thousands obviously creating a slight restriction?
Questions.
1. is the shot string I'm seeing normal.... descending velocity from first shot or should I see an upward curve before it starts to fall off?
2. I was looking for a velocity in the mid 800's as I am told that seems to be the sweet range for accuracy out of a .25?
3. I can drill out the valve body to correct alignment or send back to Benjamin? (I assume the alignment problem has to be in the valve because all other ports / holes between the air tube and breech are good).
Sorry about being long winded.
Any advise, help would be greatly appreciated.
Mike
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First thing you should know is take what I say with a grain of salt, I am in no way an expert and there are better and more experience folks that I'm sure will join and help. 1. I'm assuming that Mrod does not have a regulator in in so no the shot strings isn't normal. With an unregulated PCP your first shot should typically be one of the lower velocities and go up the back down, that's your power curve. When you have the air reservoir full ie 3k fill on Mrod, it takes more pressure to open the valve and it shuts slightly faster, as you shoot and use air it makes it easier to open until you reach a peak and drop back off, that's the working pressure of the gun, this is what we use when choosing a set point when starting to work on regulating the rifle. 2. Looking to shoot the 25.39 JSBs in the mid 800s is very realistic even for an unregulated Mrod and if done right you should be able to get at least 24 usable shots. While we're at it, are you looking for power or do you care about shot count? 3. And this is the one I'm a little questionable about, and if possible for you to post some pictures it would help a bit. Yes you can drill out the valve body I know that much, and I have seen quite a few high flow valves that have done that as well as angling the port. Do you have a lathe or are you planning on using hand tools?
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First thing I'd look at is your breach seal...your symptoms seem to coincide with a missing breach seal. When mine was missing I had the same results...
I am currently tuned for around 32-40 shots at 800-815 fps range myself with a nice bell curve.
If I tune to the mid 800's I get about 24 shots as Ozarkairgunner noted.
This is on a .25 mrod with only an SSG installed (from my experience)
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Ozark yes. it is non regulated stock maurader, right now the priority is get a good shot string and accuracy is #1 priority.
I do have a picture of misalignment issue just need to figure out how to post it.
ackuric , not sure what you are referring to by breach seal ? are you talking about the o rings on either side of the transfer sleeve ?
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First thing I'd look at is your breach seal...your symptoms seem to coincide with a missing breach seal. When mine was missing I had the same results...
I am currently tuned for around 32-40 shots at 800-815 fps range myself with a nice bell curve.
If I tune to the mid 800's I get about 24 shots as Ozarkairgunner noted.
This is on a .25 mrod with only an SSG installed (from my experience)
DITTO
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If a seal is missing gun will be really loud. There is a seal on both ends of the transfer sleeve and one inside the back of barrel. Missing anyone of them would cause the low velocity. I think my gun when stock was pushing 25.39 kings around 840 fps. Maybe double check your pellets and make sure they are the 25.39gr kings and not the 33.95gr heavy kings.
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Ozark yes. it is non regulated stock maurader, right now the priority is get a good shot string and accuracy is #1 priority.
I do have a picture of misalignment issue just need to figure out how to post it.
ackuric , not sure what you are referring to by breach seal ? are you talking about the o rings on either side of the transfer sleeve ?
Breech seal is just inside the barrel, the bolt pushes the pellet head thru it and seals around the pellet skirt. There is a small indentation about 1/4" in, the Breech seal... o ring.. fits in. You can do a search in this gate or even a google search and get a world of information about it. When mine did it, it was blowing excessive pressure out around the magazine. Looks impossible till you do it one time, just be careful not to damage the new o ring and coat it lightly with silicone grease when installing. Till I could order the correct o ring, I went to Home Depot and got a pack of #5 o rings, 3/8" od x 1/4" id x 1/16". A pack of 10 was something like $2. If you don't have any silicone grease, Home Depot has it also, right around the o rings, think its called plumbers grease. DO NOT use any grease other than silicone based.
Charles
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Ahhh, defiantly missing the breach seal !
I'll see if I can measure and buy something here locally while waiting on some.
kind of excited to see results, especially since the comment about it making it loud ...I thought that was just the noise of the .25 ?
lastly is the mis alignment issue worth dealing with? should I redrill to center? I tried to attach picture
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Yep the breech seal was missing and I got one that would suffice from ace hardware. Works like a champ !
Thank you fellas for your guidance.
Apparently the misaligned valve transfer port was not the issue, but I'm thinking about opening it up to true it anyway. Anyone see anything detrimental with dong that ?