.22 Cal. CFX Project

.22 Cal. CFX Project

Joined: December 22nd, 2009, 5:40 am

February 19th, 2010, 5:59 am #1

My Theoben gas ram arrived today.The installation was a bit time-consuming because the Theoben gas ram goes into the rifle backwards with the gas ram body sliding into the piston sleeve. I also had to wrap the gas ram body with masking tape (as per directions) to ~20.5mm dia. in two strategic places (with a bit of trimming) so it sits perfectly centered inside the piston sleeve and out of the way of the sliding cocking arm. The rod end of the gas ram comes with a couple of washers and a panhead hex screw that sits against the retaining block (at the end of the receiver tube).

This rifle put wadcutter pellets through a 3/4" piece of pine - something that my Crosman NPSS could NOT do. It punched a perfectly round hole in the wood that looked like it was made by a drill. I am guessing it's because of the way the gas ram is situated - putting more mass into the moving piston thereby putting more energy into the pellet (F=MA). It also feels calmer and sounds quieter than the Whisper gas ram I had in there. I am going to put the rifle through the chrony this Saturday and see what numbers I'm going to get.

I also have the GTXg2 trigger in the rifle and it is such a sweet trigger. In my honest opinion, it is waaaaaaaaaaaaaay better than the GRT-III triggers I have on the other 2 CFXes I own. I suspect I will be changing out those triggers to the GTXg2 in the near future.

Oh, one thing I almost forgot to mention: I removed the extra scope rail that is mounted to the dovetail on the receiver tube. I then took my 1-piece scope mount and tapped an 8x1.25 threaded hole through the existing set screw hole in the scope mount. This allowed me to take the larger 8x1.25 set screw I took off the extra scope rail and use it directly on the scope mount to the receiver tube. My experience has been with the original tiny set screw that comes with the scope mount to be inadequate for these high powered air rifles. I took off one set of rings one day and the tiny set screw was actually bent as the scope mounts started creeping backwards along the dovetail. I couldn't take the set screw out, so I just tapped the new hole right through it. With medium scope mounts, a scope with a 44mm objective bell sits 1/8" above the top of the receiver tube, leaving just enough room for a flip-up cover. I did this with all 3 of my CFXes. No more bent scope mount set screws and my scope no longer creeps backwards. And most importantly, no more torn set screw hole on the receiver tube.
Last edited by LongIslandArcher on February 19th, 2010, 8:21 am, edited 1 time in total.
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Joined: January 5th, 2010, 1:56 pm

February 19th, 2010, 2:07 pm #2

I notice that the gas ram is being offered in two types, one for .177 and the other for .22. What is the difference ? I have a .177 CFX fitted with a Air Venturi gas ram. It is now doing about 840 fps with RWS superdome pellet. Do you think it can do more with the Theoben gas ram ?
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Joined: December 22nd, 2009, 5:40 am

February 20th, 2010, 12:52 am #3

I don't know. I currently have the Theoben installed in the .22 cal. CFX. I have to put it through the chrony soon. I was hoping to do it tomorrow (Saturday) but I might be busy with other stuff.

When it still had the Whisper gas ram in the .22 CFX, it was shooting 11.9 grain pellets at 725 fps, 14.3 grain wadcutters at 650 fps and 16 grain Predators at 680 fps.

I have the Whisper gas ram installed in the .177 CFX. The .177 CFX with the Whisper gas ram shoots 7.0 grain pellets at 925 fps and 7.9 grain pellets at 870 fps.

The gas ram or either caliber is the same.
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Joined: October 21st, 2001, 3:36 am

February 20th, 2010, 5:20 am #4

My Theoben gas ram arrived today.The installation was a bit time-consuming because the Theoben gas ram goes into the rifle backwards with the gas ram body sliding into the piston sleeve. I also had to wrap the gas ram body with masking tape (as per directions) to ~20.5mm dia. in two strategic places (with a bit of trimming) so it sits perfectly centered inside the piston sleeve and out of the way of the sliding cocking arm. The rod end of the gas ram comes with a couple of washers and a panhead hex screw that sits against the retaining block (at the end of the receiver tube).

This rifle put wadcutter pellets through a 3/4" piece of pine - something that my Crosman NPSS could NOT do. It punched a perfectly round hole in the wood that looked like it was made by a drill. I am guessing it's because of the way the gas ram is situated - putting more mass into the moving piston thereby putting more energy into the pellet (F=MA). It also feels calmer and sounds quieter than the Whisper gas ram I had in there. I am going to put the rifle through the chrony this Saturday and see what numbers I'm going to get.

I also have the GTXg2 trigger in the rifle and it is such a sweet trigger. In my honest opinion, it is waaaaaaaaaaaaaay better than the GRT-III triggers I have on the other 2 CFXes I own. I suspect I will be changing out those triggers to the GTXg2 in the near future.

Oh, one thing I almost forgot to mention: I removed the extra scope rail that is mounted to the dovetail on the receiver tube. I then took my 1-piece scope mount and tapped an 8x1.25 threaded hole through the existing set screw hole in the scope mount. This allowed me to take the larger 8x1.25 set screw I took off the extra scope rail and use it directly on the scope mount to the receiver tube. My experience has been with the original tiny set screw that comes with the scope mount to be inadequate for these high powered air rifles. I took off one set of rings one day and the tiny set screw was actually bent as the scope mounts started creeping backwards along the dovetail. I couldn't take the set screw out, so I just tapped the new hole right through it. With medium scope mounts, a scope with a 44mm objective bell sits 1/8" above the top of the receiver tube, leaving just enough room for a flip-up cover. I did this with all 3 of my CFXes. No more bent scope mount set screws and my scope no longer creeps backwards. And most importantly, no more torn set screw hole on the receiver tube.
nt

Last edited by bigbore on February 20th, 2010, 5:20 am, edited 1 time in total.
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Joined: December 22nd, 2009, 5:40 am

February 21st, 2010, 3:22 am #5

I did a side-by-side comparison of the two triggers:
1) the adjustment screws on the GTX have rounded ball ends so it won't wear away at those points it contacts.

2) The GRT's adjustment screw right by the trigger blade is also a few millimeters further back than the one on the GTX. Being that I am an architect and am familiar with leverage, moment arms, forces applied, etc., I know how the location of this screw can affect trigger pull. The GRT is supposed to come preset to "engage" 2nd stage, but I really had to make a huge adjustment to it. The GRT comes back to a point where the 2nd stage should engage and I should have a nice solid positive stop before a little bit more pressure applied shoots the rifle. It comes to a quasi-2nd stage where I can't really tell if it's a trigger pull hiccup or the actually stop at the 2nd stage and before I know it, I've already sent the pellet downrange. And each trigger pull was different; sometimes it would stop at 2nd stage and other times, it doesn't and it blow your shot. So I started backing the screw out a quarter turn at a time and taking test shots with each adjustment to see where 2nd stage should be. I had to back the screw out almost 3-1/2 turns before I was comfortable. I can now see half the screw head sticking out from the hole it sits in.

With the GTX, I actually went about half a turn before I felt a nice comfortable 2nd stage, and it stayed there till I gave the trigger just another half pound of pull weight to shoot the rifle. This was repeatable shot after shot.

3) I took apart the GRT and found that that screw by the trigger blade has a spring underneath it and I guess it's to keep the screw from loosening up by keeping pressure on it. The screws on the GTX is held in with stuff that looks like red loc-tite, but isn't. It just keeps the screw from loosening and backing out on its own.
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