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

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Motorhead

Motorhead

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Nov 1, 2018
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California, United States
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 have gone through about 1300 of them since I got my Ghost HP in October and most are 16.1g. I have some pre-covid, some pellet shortage ones and some from a month ago. They are all different! The pre-covid head sizes are 4.52 to 4.54, with most being 4.53. The skirts are over size and have to be pushed into the Ghost mag with an allen key and a good bit of pressure. The other two batches are 4.50 to 4.52 and if they don't drop in they only need a little push. Covids are mostly 16.1, but a lot are 16.2 and 16. The last order are mostly 16.1. The pre-covid are about 10 F.P.S. slower. Straight from the tin I had a 17F.P.S. ES. Sorted I have 10 or less ES.
 
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I am in the middle of building a .177 slug slinger Rapid....
But my Titanium Rapid setup.... .22cal
I use Short Valve-body and Tapered Titanium Valve-stem...
Better airflow and efficiency..
valve2.jpg

I also use a Double-Tap Spring Guide/interia weight combo....
It uses Tungsten inner weight and striker end...
It does a great job of eliminating Hammer/valve bounce...
20201009_203624.jpg

This gives me 70+ fpe......
 
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Just received a HUMA regulator order from the Netherlands, in there a RAW HM regulator. Needed to build an o-ring sealed sleeve being the Theoben uses No Fast fill adapter / gauge at that location. With the Huma not having the protruding spool/bevel stack the OEM reg has, we picked up a tad more plenum volume adding just a tad more Punch !!

Original set up with OEM reg at 150 bar was this:
JSB 13.4 @ 977, Now with Huma @ 1010
NSA 12.5 @ 980. Now with Huma @ 998
* Not tested the 10.3 or 15 or 16 grain at this time.

So with a tad more plenum it did wake up & watching chrony the ES is running tighter as well.
If a downside ... Now you very much hear a quick HISS as plenum is refreshed.
 
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Ca_Varminter said:
I am in the middle of building a .177 slug slinger Rapid....
But my Titanium Rapid setup.... .22cal
I use Short Valve-body and Tapered Titanium Valve-stem...
Better airflow and efficiency..

I also use a Double-Tap Spring Guide/interia weight combo....
It uses Tungsten inner weight and striker end...
It does a great job of eliminating Hammer/valve bounce...

This gives me 70+ fpe......
Click to expand...
So staying with a conventional poppet and heavy hammer.
The 70+ fpe obviously is in .22 caliber ?
And the Receiver a Stretched large plenum configuration similar to the RAW "X" series.
 
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Motorhead said:
So staying with a conventional poppet and heavy hammer.
The 70+ fpe obviously is in .22 caliber ?
And the Receiver a Stretched large plenum configuration similar to the RAW "X" series.
Click to expand...
Yes...
It gives me 70+ fpe in .22 w/ 28 grn pellets.
The receiver was designed and machined by Chip Smith...
image_471.jpg

This concept was done Way before RAW was Born...
It started as a conversation with Chip back in 2009.....Then conception and prototype by late 2009!!
 
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Gordy's Receivers basically was Chip's design made out of Aluminum...
Chip and Gordy are old friends their shops were very close to each other...
They shared tooling and fixtures... If Chip had overflow work, Gordy would help out..
When Chip was making the Titanium receivers, many people on AirgunAdvice.net wanted a cheaper version... made out Aluminum.
So Chip gave the CAD drawing to Gordy, and let him tweak it as he saw fit..for the aluminum version!!
 
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