Taking a 12 fpe THEOBEN MFR .177 to 30 fpe !!

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Ran the JSB BEAST 16.2 threw it today ... after @ 2 cold shots to get valve freed up .. 933-935 shot after shot. ( 31.1 FPE )

1st cold shot 897, second 921 & third 933 & stable.

Not bad being rifles been sitting in safe pressurized since last Weds ( 7 days ) only dropping @ 35fps on a stuck valve. That is just @ 4% & very acceptable.
 
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Motorhead said:
Sure enough a statement of fact, not a question but a reality in this project finished up before the holidays.

Started with a UK spec STOCK 12 fpe Theoben MFR in .177 caliber and made it a heavy pellet ( 13-16 grain ) as well Slug ( 12.5 grain ) into a mean little Ice Pick shooter.
Modifications are 100% replacement parts / pieces. Taking the MFR back to OEM spec simply putting the factory parts back inside :p

Essentially a complete heart & lung transplant sort of thing ... Fabricated & Replaced the following items:
NEW Poppet Seat
NEW Poppet Valve/Stem ( Balanced Configuration )
NEW Anti Bounce SSG assembly
NEW Light Weight Hammer
*NEW Longer LW ( 23.7") 12 groove no choke barrel. ( Extracted the last bit of performance )
Replaced HPA cylinder with a 250bar 500cc

Anywho ... 150 bar set point & 17" factory barrel results.
JSB 10.3 = 978 fps
JSB 13.4 = 895 fps
NSA 12.5 slug = 892
Overall +/- making @ 24 fpe being double the factory spec ... yea we found some more power ... But
:-\


*Lets re-barrel & get some more length and see what we get .. So took a 15mm LW 12 groove standard no choke and made it fit with a 23-3/4" Finished length.
Retested changing nothing else but adding 7 3/4" more barrel we get ...
JSB 10.3 = 1074 fps
JSB 13.4 = 977 fps
NSA 12.5 slug = 980 fps
& the JSB 8.4 just for giggles at 1129 fps, yea bit too fast ..Lol
Overall now +/- 26-28 fpe range.

Shoot a JSB 16g beast or H&N Sniper Magnum 16g it goes a tad over 30 fpe :p
Pretty crazy power from such a small plenum, It shoots pretty quiet for the output, but is using more air than a .22 at similar output. To be expected with smaller bore area.

Accuracy is about a quarters diameter at 80 yards with JSB 13.4 monster originals, Tad tighter with NSA 12.5 slugs. Very much Minuet of ground squirrel !!!

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I bet it will shoot crossman piranhas out to 40yds pretty well also, for cheap ammo. Most Evanix .177 do about 30fpe with light 7.9g. My little bullpup and the rainstorm i had both stack them. It seems they need to be smokin to shoot.
 
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Scotay42 said:
I bet it will shoot crossman piranhas out to 40yds pretty well also, for cheap ammo. Most Evanix .177 do about 30fpe with light 7.9g. My little bullpup and the rainstorm i had both stack them. It seems they need to be smokin to shoot.
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never seen ANYTHING shoot a piranha pellet accurate enough to be worth while ... even if Ok at 40 yards, whats the point being this .177 high power THEOBEN MFR just starts getting more interesting and fun way past that distance ;)
 
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Motorhead, Really cool set up you got there. I always wanted to do something like that with the .20 cal Eunjin pellets that are heavy and long. I cant believe its 14 years ago I was tinkering with the Theoben design. Here's the balanced Ti valve set up I was running in 2015 with a reg in the Ti tube and larger plenum. Builds like yours have got me back into this. I've never done a SSG for the Thebeon so now you gave me a new project!

BV.jpg
 
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Just for the record ...
What i've seen with balanced valves, is that there closing speed is much Faster than a conventional poppet type. As such the impact and seat damage also increases by a large margin. Using the OEM Acetal valve body I found to be less than ideal having them pound down the sealing surface until leaking or just altering the flow & changed enough to effect power and consistency.
In the case of already having the T.I. parts made, suggest that you try and build a new valve body from PEEK or perhaps one of the Glass filled acetals that will increase hardness and durability.
* I've had really good luck and seeing minimal wear with a Valve body of 7075-T6 and PEEK poppet. Tho not sure how T.I. would do in hard aluminum for Stem wear and it not seizing ?
 
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Motorhead said:
suggest that you try and build a new valve body from PEEK
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Yes, I've got valve bodies in Peek as well. And the opposite with 7075 bodies, steel shafts and Peek poppets. Theoben stuff is just so versatile I love them. I'd really like to start doing some effiecency testing like you guys on Gateway do. I have never done any of that. What would the numbers be on this .177 be?
 
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csdilligaf said:
Yes, I've got valve bodies in Peek as well. And the opposite with 7075 bodies, steel shafts and Peek poppets. Theoben stuff is just so versatile I love them. I'd really like to start doing some effiecency testing like you guys on Gateway do. I have never done any of that. What would the numbers be on this .177 be?
csdilligaf said:
Yes, I've got valve bodies in Peek as well. And the opposite with 7075 bodies, steel shafts and Peek poppets. Theoben stuff is just so versatile I love them. I'd really like to start doing some effiecency testing like you guys on Gateway do. I have never done any of that. What would the numbers be on this .177 be?
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Some gateway info if interested ... https://www.gatewaytoairguns.org/GTA/index.php?topic=171589.msg155930096#msg155930096 At post #31 follow the next link ... It gets rather frustrating for a spell, then resolves with a tad more hammer weight.
LOTS of info there if you like too & can fabricate :p
 
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Well Guys here is another chunk to chew on.......
Chip do you remember you and Ernie were working on various design and weights of the Inertia weight...
You did this video....

Well I have been over help on the UK Rapid Forum site..
KevG came up with a Novel design.....
He calls it the Double Tap spring guide!
It combines the hammer spring guide and the Inertia Weight!!!

So of course I had to do my own twist on things.. I used Tungsten for the head and striker weight.
20201012_134920.jpg


I also made a video comparing the different combination for testing..
From Left to Right
1. Hammer alone
2. Hammer and standard Inertia weight
3. Hammer and the Double Tap guide w/o the striker weight
4 Hammer and the Full Double Tap guide...Not Bad!!
 
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Ca_Varminter said:
Well Guys here is another chunk to chew on.......
Chip do you remember you and Ernie were working on various design and weights of the Inertia weight...
You did this video....

Well I have been over help on the UK Rapid Forum site..
KevG came up with a Novel design.....
He calls it the Double Tap spring guide!
It combines the hammer spring guide and the Inertia Weight!!!

So of course I had to do my own twist on things.. I used Tungsten for the head and striker weight.
20201012_134920.jpg


I also made a video comparing the different combination for testing..
From Left to Right
1. Hammer alone
2. Hammer and standard Inertia weight
3. Hammer and the Double Tap guide w/o the striker weight
4 Hammer and the Full Double Tap guide...Not Bad!!
Click to expand...
Indeed in a conventional poppet and hammer set up having PRELOAD against poppet stem ... Balanced valves you want LOW hammer weight and free flighted. Completely different set up & requirements for each / both valve types.
 
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