Okay, would someone please remind me of all the drawbacks to gas rams vs. springs? Cause at the moment, I can't come up with a single one! But I guess I'll start at the beginning.
The Theoben ram from Airgunwerks (David Slade) arrived on Saturday by Priority Mail. Not much to look at, the gas struts on the hatch back on my Subaru are a lot bigger. Since this was a mis shipment from Theoben UK, the instructions in the package were for a Webley Patriot. Interesting, but not much help. Instructions are available from the UK site, for everything EXCEPT Gamo's. But by reading through all the different ones, I was able to get an idea of the general technique. And since it can only go in one way, the only real question was what to do with the rear spring guide; shorten it, or remove it completely? The Gamo strut goes in with the rod to the rear, and there are a couple of large washers staked to the end of the rod, sized to just fit the spring cylinder. I first tried cutting the guide down so the washers ended up just in front of the trigger group, the this had the rams cylinder hitting the washers. The only other answer was to remove the guide completely, using just the steel plug, and this ended up being the answer. The ram cylinder gets a few wraps of tape at both ends, for a snug, centered fit in the piston. And that's it for the install. My next one will probably take me 15 minutes, and most of that will be cleaning all the old lube out!
I've heard that the rams take more cocking force, and that like a spring, it gets stiffer as you approach the end of the stroke. That's not the case here. Cocking is very linear, virtually no difference from start to finish, and either the same or slightly lighter than the spring. Note: this had a JM Tarantula spring in it.
Oh, you want to know how it shoots! I gotta say, I really didn't know what to expect. Theoben claims less recoil, faster lock time, and smoother shot cycle, but we all know about sales hype. Almost everything I've read has said just the opposite. In this case, it's not hype. I was expecting something more like my Diana 350, what I got was more like my IZH 61! Recoil is noticeably less, very smooth, and with something I can only describe as SNAP! I don't KNOW if the lock time is actually quicker, but it sure feels like it is. Also, the rifle feels lighter.
Not sure what Theoben is going to claim for power, but it's definitely more than the UK limit of 12 fpe. I'm not sure my numbers are representative at the moment, because I think I need a new piston seal. But they're still quite respectable. Prior to my spring collapse, I was getting about 900 fps with Superdomes. After the collapse, I was getting a 768 fps avg. with a 60 fps spread for about 11 fpe. With the ram installed, I got 883 fps, 15 fps spread, for 14.4 fpe. I think a new piston seal and some improvement in the sealing system on the rotary breech could see a serious increase here. Or install it in a break barrel. I also need to retest with more pellets. I haven't had the chance to do any accuracy testing yet, there's a busted Suburban in the middle of my indoor range right now!
So there you have it. The ram was $145, and considering the results so far, I'd have to call that a bargain. This is a "tune" that requires only the expertise needed to build or buy a spring compressor. I finally built a compressor out of a pipe clamp and some scrap Ipe I had on hand. Worked fine, now if I could only get a ram for my 350, I'd be set. Later.
Dave
