GTA
Airguns by Make and Model => Benjamin Airguns => Topic started by: Psipumper on November 22, 2017, 08:02:10 PM
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After modding my original 392PA to 31 fpe , I decided to buy a new 392 to experiment. The new gun is the "Clone". The new gun was built in Feb. 2017. My goal for the clone is to make maximum power at 8 pumps. Out of the box was 630 fps using CPHP pellets. Unlike my first gun , I started with adjustable piston and headspace on this build. Adding the adjustable piston increased fps to 665 fps.Machining valve cone shape to match : 685 fps. Adding .078 diameter bolt probe: 698 fps. The next step surprised me. I added square O rings on the valve :721 fps. I haven't done anything to the valve internally except the two spring. Actually lost a few fps with that. Going to do the third O ring next, then on to the valve internals. Any guesses on the final fps @ 8 pumps?
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937fpe.
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Fps or Fpe ? Maybe a small nuclear boost.
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. Any guesses on the final fps @ 8 pumps?
775 fps
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Fps or Fpe ? Maybe a small nuclear boost.
FPS, based on what you did with your 392PA. I should have asked how many pumps did it take to achieve 31fpe with the 392PA
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Yes. The original gun I did required 16 pumps to get maximum power. It would lose velocity at lower pumps due to the valve volume being increased by lathe machining. At 8 pumps it clocked in at 733 fps. At 16 pumps =946 fps for it. Alot of people frown on pumping above 8 so the new gun is geared towards that. The photo below was a ear ringing blast from the original gun. LDC installed afterwards.
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Happy Thanksgiving
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I got my 392PA on 8 pumps getting 571 with the JSB 25.39 for 18.39 FPE.
That explains why you need to get the pumps so high, increasing the volume inside the valve.
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Somewhere around 900 fps would be great on 8 pumps 8)
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I got my 392PA on 8 pumps getting 571 with the JSB 25.39 for 18.39 FPE.
That explains why you need to get the pumps so high, increasing the volume inside the valve.
What numbers do you get with the Crosman 14.3 pellets at 8 pumps. They seem to be the standard pellet for speed testing or at least the most used. I don't use them much for anything else.
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Somewhere around 900 fps would be great on 8 pumps 8)
721 fps now. Mostly what I have left is a delrin exhaust valve, 3rd o-ring, new hammer, and valve porting. It is not going to make 900 fps . It would be great though.
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Okay, my new prediction is with 8 pumps, a 14.3g pellet & no nuclear acceleration, 701fps.
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I am looking forward to seeing the results. I would think you could get it close to 800 fps on 8 pumps. Good Luck!
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subbed to this thread (-'
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subbed to this thread (-'
Me to Rob :)
Ray
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Without looking up the other thread what are the square orings for?
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Without looking up the other thread what are the square orings for?
The square rings are used in place of the two standard o-rings located on the outside of the air valve. Since the square cross section better occupies the o- ring groove, the headspace air volume is further reduced. I ordered them from " The O-ring store " online. Part numbers: SN70113 and SN70016.
This mod is something I would recommend for all guns as the improvement is substantial and would be more pronounced at higher pumps.
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Just doing the basic internal mods to the valve, this is how my stock 392 turned out.
(https://www.snapagogo.com/images/2017/11/25/842ADEBF-AF89-45AB-B3BA-8893DA875683.md.jpg) (https://www.snapagogo.com/image/5pm7u)Uploaded at Snapagogo.com (http://www.snapagogo.com)
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I added the third o-ring to the valve. Five shots @ 8 pumps =735 to 741 . Average 738fps. So the third o- ring added 17. Delrin exhaust valve next.
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You can't just leave us hanging like that! :'(
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Used a highly modified 392 valve on this build.
7" stroke and .750" diameter Disco tube.
Got the following with 14.3 CPHPs and a 24" barrel
05 pumps=625 FPS
10 pumps=826 FPS
12 pumps=891 FPS
15 pumps=960 FPS
20 pumps=1034 FPS
With a 7.25" stroke x .775" diameter tube, 800+ FPS on 8 pumps should be a cake walk with a 392.
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Sorry for leaving you hanging. Rolling again. I was not able to get the delrin exhaust valve to seal. Tried remaking with white delrin but still sealing issues. I decided to skip the delrin for now. Average results are:
Undercut stock exhaust valve stem =742 fps.
Angled transfer hole with Dremel tool = 767.
Changed transfer hole to a D shape = 765.
New improved hammer = 771.
Reduced valve volume with plastic spring spacer=782 fps.
Final of 782 . I think the delrin is possible but the valve guide hole is too sloppy of a fit. I am going to sleeve the stem hole and build a smaller .093” stem delrin valve then retry 800 fps in the future.
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Impressive numbers.
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No comments? How about this photo. Double lifetime guarantee.
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WOW, that front assembly is bad-ss .. that could be a commercial product tomorrow and sell like crazy
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Beefy! I like!!
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Sign me up for one. That's awesome
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Super heavy duty assembly - makes my bit of 1322 two-screw reinforcement look rather puny! 8)
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WOW, that front assembly is bad-ss .. that could be a commercial product tomorrow and sell like crazy
I had some reservations for that reason. We know where we saw it first gentlemen. I would sell the rights to market . I will send you the blueprints to make them for your personal use.
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I found some more potential power. Valve diameter was .750 in front of o-ring. The rest of the valve is .767. Soldered it up to turn down to .775.
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Every little bit helps...
What kind of solder is that? Think it's up to handling the stress?
I've never thought to measure that part of the valve. I have thought of putting a back-up ring above the o-ring both on the valve and piston to reduce headspace. As I understand it, these are used to help prevent your o-rings from extruding. I think they would have to be on the opposite side of the o-ring that I am referring to to serve that purpose, again, if I understand correctly.
And since you're going all-out, you might consider putting a small pin/rod on the front end of the check valve to fill the space between the check and the tip of the cone.
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The solder is 60/40 rosin core. I didn’t do a very neat job but if it sticks good enough to survive the lathe machining , it will hold up in the gun. I think those backup rings require the groove to be machined wider to add them. Appreciate the advice on the air inlet hole space.
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The solder is 60/40 rosin core. I didn’t do a very neat job but if it sticks good enough to survive the lathe machining , it will hold up in the gun. I think those backup rings require the groove to be machined wider to add them. Appreciate the advice on the air inlet hole space.
Good point on the solder. Let us know what you gain from that.
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The new bar is 825. I checked today and the results were impressive. Kinda cold outside but the gun was kept and pumped indoor. 5 shots = 797,796,797,801,797. I decided to take a few shots with fewer pumps. 3 pumps was 552. 4 pumps was 625. 6 pumps 726. I tried a JSB 18.13 at 8 pumps for 730.
I am beginning to like this clone. This PA platform is a blast.
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I like the idea of getting the most out of the least, especially on a pumper.
Whenever I mod a valve I usually stuff it a little instead of increasing the capacity.
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The new bar is 825. I checked today and the results were impressive. Kinda cold outside but the gun was kept and pumped indoor. 5 shots = 797,796,797,801,797. I decided to take a few shots with fewer pumps. 3 pumps was 552. 4 pumps was 625. 6 pumps 726. I tried a JSB 18.13 at 8 pumps for 730.
I am beginning to like this clone. This PA platform is a blast.
Nice numbers. What do you have planned next?
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I like the idea of getting the most out of the least, especially on a pumper.
Whenever I mod a valve I usually stuff it a little instead of increasing the capacity.
Yes, high efficiency is what is significant about this gun. Makes the “air conserving pumper” concept obsolete. 625@4 easy pumps every time. No guesswork.
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Just wondering as I move along if I am providing enough explanation or not. I have some good stuff coming to address one of the biggest design flaws of the PA. Many of the mods are already on the internet and I didn’t won’t to repost the details of them unless someone asks a question. Some of my mods are a first ,at least for “as seen on the internet”. I feel guilty for providing stuff that my be hard to obtain for the do it your self person.
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Just wondering as I move along if I am providing enough explanation or not. I have some good stuff coming to address one of the biggest design flaws of the PA. Many of the mods are already on the internet and I didn’t won’t to repost the details of them unless someone asks a question. Some of it is a first at least for the internet.
I think you're doing a fine job. I am guilty of not doing this myself sometimes, but try to remember to take pics as you go. Especially when doing unique mods.
Can't wait to see the "good stuff" you have coming.
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Just wondering as I move along if I am providing enough explanation or not. I have some good stuff coming to address one of the biggest design flaws of the PA. Many of the mods are already on the internet and I didn’t won’t to repost the details of them unless someone asks a question. Some of it is a first at least for the internet. I feel guilty for providing stuff that my be hard to obtain for the do it your self person.
Any plans to flat top the valve/piston?
Fairly easy and will yield good gain.
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I like the idea of getting the most out of the least, especially on a pumper.
Whenever I mod a valve I usually stuff it a little instead of increasing the capacity.
Yes, high efficiency is what is significant about this gun. Makes the “air conserving pumper” concept obsolete. 625@4 easy pumps every time. No guesswork.
I used to have a debounced C9. It had a hammer spring preload adjuster so you could fine tune the hammer strike to dump just the right amount of air to stay consistent . Iirc, mine took 6 pumps to precharge, then 3 pumps between shots all day long for 610 fps with .20 cal 14 .3s.
I've been imagining a debounced gun like yours doing 800 on 4 pumps. But maybe there's not any room in the valve to hold air between shots due to such high efficiency.
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Any plans to flat top the valve/piston?
Fairly easy and will yield good gain.
Flat top won’t help here because I have already reduced the the headspace to a very small amount. Regardless of the shape , zero air volume is zero. There are pros and cons to the flat top. Although it can be done, an adjustable piston is already available from Mac1. The factory cup seals well with replacements available. If you remove the cone shape and extend the flat top piston to meet it, the air hole at the top of stroke would not line up.
The one way a flat top piston would be better: A high volume valve that uses a spacer between the valve halves . This would return the position of the flattened end of the valve to use the air hole. Maybe.
Probably easier ways to gain more valve volume in the 392PA though.
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Nice numbers. What do you have planned next?
I am going to return to adding the delrin exhaust valve . Getting a good seal on delrin can be troublesome on a pumper. Maybe more trouble than it’s worth? If it doesn’t add 20 fps ,it’s too much trouble.
Then on to the final stretch to wrap up the clone project .
Revisit my original gun to add things learned from the clone.
Possibly start a new thread on the late model trigger .
I am asking around locally looking for a 392P or a 342 . I really don’t need one but I think I should repair one to have a look around.
Who knows, I may stumble onto a 50 yard tack driver.
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The best way to FT a 392 valve that I've found is to trim the front part of the valve 1/2".
Make a new FT valve cap that is 1/2" long so the original valve length is maintained.
This would make the valve a 3 piece.
The check valve is machined to .030" to the front of the FT minimizing dead air space.
Duro 90 poly O-ring seals on the valve and piston.
The FT eliminates the cone resulting in a gain in stroke plus minimizes dead air space.
Volume is variable using spacers depending on desired result.
Never had a problem getting delrin valve stems to seal.
Here are some examples from other guns. The principles are the same.
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I agree that a flat top piston is possible. Just a little too late to change course on this one. I will keep that in mind if I decide to build a max power altered gun.
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WOW ! This is a great post.... I had a lot of trouble getting the delrin to seal properly as well.... I needed to increase the spring pressure. I modified the original valve stem by removing the crappy Rubber seal that is destined to fail and replaced it with a piece of the delrin popet/ exhaust seal.... it's much more efficient at dumping all the air out. The Rubber seal is too soft and closes up too quickly leaving air in the valve...... in the picture you can see the new delrin seal installed and the old damaged seal sitting on the side with brass shrapnel all over it....
I hope you continue with this post , it's been very informative and entertaining.. also could you please make me one of those Wicked awesome barrel breaks ! ;D
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Charles, Did you ever get the Delrin to seal? What did you do to change the hammer?
Rob
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Charles, Did you ever get the Delrin to seal? What did you do to change the hammer?
I didn’t have any trouble with the delrin sealing after sleeving the valve stem hole to correct excessive clearance. I changed the stem diameter to 3/32 . Unfortunately, the change slowed the gun 16 fps to 782.
After trying a few things without success, I made a new larger diameter exhaust and regained lost speed to average 805@8 pumps. 647@4 pumps.