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All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Big Bore AirGun Gate => Topic started by: shorty on August 12, 2015, 06:31:57 PM
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Did some work on the .22 conversion to .357 yesterday and "ALMOST" got the wonderful 100 fpe (ALMOST).
I opened the exit port on the valve a little more to .200" and hit 678 fps with 95 grain air venturies HP's.
I am finding it very challenging to get the +100 fpe and 750 fps + with this short barrel of 16.5" but, I did hit the goal of 90 fpe that I set out to do.
I ran a string yesterday after the valve mod with 81.3 JSB's and was a little disappointed but it is what it is.
6 shots
3000psi
Everything maxed
FPS
712
716
716
710
708
700
End 2500psi
I really started using a heck of a lot more air and reduced the shot count when I added weight to the hammer. Possibly a mistake. Adding the extra travel to the hammer instead of the extra weight to the hammer was by far much better.
What I really need is a 20" to 24" barrel now. Anyone have or know of where I might find a .357 barrel blank at those lengths cheap <$75? If it holds true for 12 fps to 15 fps for every inch, a 22" barrel should get me around 780 to 800 fps with the JSbs pushing the 100 fpe mark pretty good.
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Figured I would show some pics. Nothing special besides the end of the barrel.
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A longer barrel would definitely help but you should be able to get there with 17". What are your transfer port and valve specs?
Tom
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Yep 100 fpe should be real easy in 357 with that format. With the short hammer throw of the marauder you either need lots of spring or a heavy hammer or both. I hit 187fpe with a .257 marauder power plant so .357 should be a breeze to hit 100fpe. Share your specs.
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Guys, I know this thing should be getting more but it just ain't. It's most likely due to not knowing (and someone) showing me what needs to be done. This gun has been all trial and error (first time ever doing this). I really would like to hand it over to someone (yes you Travis) but, I keep telling myself I can do it. I ain't wasting my one call yet LMBO.
Here's the spec's guys:
16.5" barrel - possibly 15.5" where the projectile sits in the chamber.
Valve hogged out to .5" all the way to the valve seat.
Valve cap opened to .495"
Dual dimension poppet spring - .5" to fit in the hog out part of the valve and transitioned with one coil turn to poppet head - approximately 8 lbs force.
Poppet throat .25"
Valve exit port .20" slightly tapered to back of valve.
TP sleeve .20" - nylon
Barrel port .20"
Double oring sleeve on bolt.
Scalloped bolt probe and shoulder pulled back to fully expose barrel port.
Hammer has lead filled sides
Hammer has counter sunk HT- approximately 3 turns negative
Dual wire hammer spring at 2" - Approximately 20 lbs per inch spring.
Boy, when laying that all out, it sounds like a lot of evolution and time. I don't think I missed anything though. You all are right though, this should be hitting over the 100 fpe by now. I started wondering if it was the darn chrony but, we should always trust our measuring equipment.
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I'd open the exhaust, barrel and transfer port to .225 provided there is room. Make sure all transitions are smoothed with a ball cutter/grinder so the air can flow smoothly. This is important! Then you should get there. Your valve throat dia. will be the limiting factor. Of course more throat dia requires a larger poppet which requires a more hammer strike. yada yada yada.
Tom
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Wish I could open to .225". No more room left on the stock valve. Although the ball cutter/grinder for smoothing out transitions may help. It would be hard for me to believe an extra 100 fps can be had from that alone. I can see maybe 10 to 20 fps more but that's still barely over 100 fpe. I'll give it a go though.
Thanks for the idea.
You know, I never touched the gauge port. Has anyone experienced an increased FPE/FPS with a larger gauge port ? I wouldn't think you would get much if not any but thought I might ask.
The only last thing I can think of is that my dual dimension poppet spring is coil binding and preventing the poppet from opening all the way up. The reason for bringing it up is because I gave the hammer the extra travel before adding weight to it and I was only hitting 695-700 with just the extra travel with great air usage. I then thought, why not add the weight to the hammer and see if it will increase the FPS/FPE. Adding the extra weight only increased the FPS/FPE marginally and killed the air usage. I then went with the .2" porting from valve to barrel and only got what I got yesterday and today about 10 to 20 fps faster.
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Your declining shot string says you need more flow not strike. Smoothing cross drilled ports is worth ~ 60 fps on a 30 cal. That could get you over the hump but it seems your valve is holding you back. Not sure about access to the poppet face, all my valves have nothing in front of the poppet. Can you run without a return spring and front housing? My Marauder knowledge is limited.
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Definitely going to try smoothing all the transitions the best I can this weekend. I didn't think you can really get that much.
Need the front valve cap and poppet spring though to get some kind of manageable shot string. With all the mods except the hammer weight,extra hammer throw, and .2 porting, I was getting 650 to 680 and back with the peak around 2400-2500 with the JSB's starting from 3000 to 2000.
Now it's looking like only 6 shots. Starting to dwindle now. Still get 2 or 3 shots before peak which has got to mean something. I just don't know.
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Yes, your small gauge port opening is limiting you also. This happened to me also when i converted my 22 Disco to .308. It took me a few days to finally have the DUH moment......lol! The air goes from the tube, THROUGH the gauge port (PSI reading) and down into the valve. The opening on my 22 Disco was small and acts more like a meter. Try opening just a little bit to see what you then get then go more from there if need be. Better to open just a little bit like a 1/8" then to go ALL out and have to then order a new part. START SMALL 1st. Also be careful and you don't want to make the gauge port wall TOO THIN.
Usually 75% of caliber (.357) is a good recommended starting point for the ports. Which is .267" TP diameter. Your at .200". You for sure need more flow. And i understand that you don't have room any longer where you are. I was just throwing that rule of thumb in there for reference.
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Not that I'm trying to push one of our products on you but your in need of a WAR valve you do not have enough internal volume in the stock valve and your at the end of what you can do with the stock valve.
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I'll add that the return spring does not influence the curve. I know I'm going to catch flack for that statement but I've spent countless hours with them and never was a flatter curve observed with a spring than without. If it wasn't for hand pumpers the Slayer would not have a return spring. Actually 90% of valve development was done without the spring, adding the spring requires more hammer to overcome. Once adjusted the curves are the same with and without. Flame away. :)
Now for port size. 75% of bore is great when you are going for power with heavier slugs but you will get better efficiency and a flatter curve with a slightly smaller port. This is why I recommended .225. I've found that the valve throat area should be ~105% of your port area. I've gone smaller and bigger before settling on 105% Anyhow your valve is the limiting factor if you can't get more exhaust and throat volume. As for the gauge block, why they would put a bunch of restrictive gak in front of the poppet is beyond me.
Tom
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The stock MRod valve does not have enough material to further open the ports.... I see the biggest limitation on power as the very short barrel.... however, I still think you are getting significantly less power than you should with the specs you have.... My first Disco converted to .357 cal (24" barrel) had only 0.219" ports, and with a 3000 psi fill I got 121 FPE with 78 gr. EunJins and 138 FPE with 132 gr. Cast bullets.... Those were not "one shot wonders", but the average for a 4-shot string with the stock 135 cc reservoir.... When I fitted the Disco Double kit, and increased the reservoir to 250 cc, the shot count doubled at the same power level.... There was no restriction in my gauge port, air could get into the valve much easier than it can get out....
Bob
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Are you slugging your barrels?" Is the bullet to loose in the bore? I agree you should be well above 100FPE already.
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or, tight in the bore?....
Bob
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I have never slugged the barrel as you guys would have. Everything I put through the barrel seems to me like a good fit. I have no other way of explaining it.
When I first got the barrel I did push through the air ventury 95 grain. It took a some pressure to fit the whole slug in, and then when pushing it the rest through with a wooden dowel seemed fairly smooth and tight. It wasn't so hard to push it that I was grunting and thinking it was going to get stuck. And it wasn't so light to push through as if it was going to smoothly drop out of the barrel. Rifling marks on the slug where light and shallow. Nothing like I see in pictures from you guys.
I do have a star barrel at 20.5" that is just about to go in the scrap heep because I did measure that one at .345/.348 bore and rifling at .352/.354 ( As close as I can measure). When I push the 95 grain through this one, I have to actually tap the wood dowel instead of push it 1/2 way into the barrel and then I can finally push it with alot of force. It really deforms the slugs and JSB's fairly bad.
I do observe 2 things:
1) Ever since the increase hammer weight, I can hear hammer bounce (burp) at 3000 psi. A lot with a 10 lb spring but little to none with my short dual wire spring. Same FPS/FPE between the 2 springs.
2)Every time I pull the upper off and put it back on I tissue test for leaks. Always the first shot has a small puff. After that, nothing and nothing. I think the nylon TP expands to air tight fit with that first dry shot.
You guys really got me thinking here and I thank you very much for your help and support. I know you guys say I can get more but I keep going back to sigmanders (yellow forum) 9mm marauder and I am extremely close to his numbers even though he has an 18.5" barrel.
I would like to get those magical numbers over 150 fpe one day and add a 500cc bottle. I guess that would be the next continuous goal.
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I do observe 2 things:
1) Ever since the increase hammer weight, I can hear hammer bounce (burp) at 3000 psi. A lot with a 10 lb spring but little to none with my short dual wire spring. Same FPS/FPE between the 2 springs.
Hammer is too heavy is why you get bounce.
Good luck with your venture
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Well,
After polishing and making all airways "smoother", I have finally found the culprit. It was the bolt seal to the barrel. Crazy how just a small leak is so critical with delivering the expected power.
I can clearly say I am now in the big bore club with a 131 fpe .357 marauder born from a 22 synrod.
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Congrats! 8)
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Nice job Shorty!
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Well,
After polishing and making all airways "smoother", I have finally found the culprit. It was the bolt seal to the barrel. Crazy how just a small leak is so critical with delivering the expected power.
I can clearly say I am now in the big bore club with a 131 fpe .357 marauder born from a 22 synrod.
Awesome! Yes, a little air past the bolt probe oring makes a big difference. The same thing happened to me with a project gun and when the oring was replaced, the very same projectile and fill pressure went 100 fps faster. There was a nice POOF, but i didn't think it would affect FPS by that much
SEAL THEM AIRGUNS COMPLETELY.....lol!
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Sweeeeet