Air Gun Home :: View topic - Rotary Indexing Magazine (RIM) for Disco / 22XX

rsterne · Moderator

I recently purchased a .22 cal. Rotary Indexing Magazine from http://www.qbmags.com.... specifically the DISCO-RIM2.... This is to turn my 2260 PCP Carbine Grouse gun into an 8-shot repeater.... The RIM2 comes with two magazines, and I chose the Aluminum ones.... I read later that some prefer the plastic ones, which are cheaper, because they provide more contrast to the pellets, and I can see that might be the case.... so next time I would probably save the $12 ($73 US instead of $85) and buy the black plastic magazines (RIM2P)....

I don't want to dwell on the wait I had to receive the parts.... prefering to give Jay Joyner (who was very helpful) the benefit of the doubt that this order was delayed due to other pressing work.... but I have to let you know that from the time I placed the order until I was invoiced via PayPal was six weeks, plus another 2 weeks before it was shipped and another 2 weeks in transit.... Jay originally told me he was about a week behind, so taking him at his word you could probably expect about a month from placing the order until it shows up at your door.... Unfortunately, that was not my experience.... good thing I wasn't in a rush....

The DISCO-RIM2 consists of a black anodized aluminum holder that slides onto a Crosman steel breech and tightens into place with one clamping screw (7/64" allen key).... plus two RIMs which hold 8 pellets each (you can also buy it with just one magazine).... They are not self indexing, and must be advanced manually.... Indexing them is easy, you can do it either direction, and from either side, (they have a positive detent at each position).... and they slide into a nicely machined T-slot on the holder, retained by a small latch.... You have to pull back the bolt before installing or indexing the magazine.... I found that the easiest way to locate the holder precisely before tightening it was to position it just ahead of the loading port, slide a magazine in place, push it forward until the magazine lightly contacts the front of the loading port, and then tighten the clamping screw…. The magazine slides out the right hand side…. So, installation is a breeze…. All machining appears to be CNC and is of the highest quality….

The magazine and holder stick up quite a ways above the breech, and require high mounts for the scope to clear…. I used Leapers RGPM-25H4 mounts, and the scope tube cleared by about 1/16”…. but the turret was below the top of the magazine and this limits to some extent where you can position the scope for eye relief…. I have a Leapers 4 x 32 AO scope on this gun, and with it slid back until it just touched the holder, eye relief was acceptable, although I would have preferred mounting the scope ¼” further back…. Some scopes may not be so forgiving, depending on the eye relief and the position of the turret….

A word of caution here about the length of the bolt…. Jay cautions that there may be insufficient clearance between the front of the bolt and the front of the loading port on a 22XX or Disco for the magazine…. and supplies (at extra cost) a bolt that has been shortened at the back to allow it to slide further back and increase the clearance…. I have a standard 22XX .22 cal bolt in my gun that has had the probe extended by 0.100” and the back of the bolt shortened by the same amount.... and it barely fits…. If you had a Disco bolt (which has a 0.085” longer probe) you would definitely have to either buy Jay’s shortened bolt or shorten the back of yours…. Even so, room is pretty cramped and you have to hold the bolt back so the skirt of the pellet doesn’t hit it and tip up….

I found that the JSB Exact 18 gr. Heavy pellets I always use in this gun fit perfectly in the magazine and functioned pretty well…. I was able to load Kodiaks, but barely…. They don’t hang up as far as the breech rotating is concerned, but they are 0.5mm longer than the 8mm Jay recommends…. The JSBs are 7.7 mm long…. Since the pellet simply falls out of the bottom of the magazine and into the loading tray in the breech it is possible for it to tumble and jam…. While with the right pellet and technique this can be minimized, there are sure to be certain gun attitudes where this is more likely to occur…. And when it does, it’s a b!tch….

The website warns that certain pellets have a tendency to tumble while others don’t (it highly recommends JSB 18 gr. Heavies)…. What it doesn’t say is how to clear a jam when it occurs…. Once the pellet is tipped up, even assuming you didn’t bend it by shoving the bolt forward…. you can’t either rotate or remove the magazine from the gun…. You have to reach in under the magazine with a piece of fine wire (paper clip?) and fiddle with the pellet until you get it lying down so that you can slide it into the chamber with the bolt…. While this is exactly the same problem you experience when loading pellets by hand in a 22XX, it’s VERY difficult to clear because you can’t get under the magazine….

Once I got the hang of it, I shot 8 shots on the bench with no hang ups…. and another clip with the barrel facing downwards at about 45 degrees, which is typically the way I hold and load the gun while hunting…. The gun seems to need to be held relatively level side-to-side…. and either muzzle level or low…. Raising the muzzle seems to cause frequent jamming…. I think that there is barely enough room in the loading port for the longer pellets (like the JSB Heavy)…. but short pellets may have an even greater tendency to tip up…. It is critical to hold the bolt back while indexing the magazine or the skirt will hit the front of the bolt and tip up…. I didn’t try the magazine in a Disco breech (which has the tiny breech screw tucked back under the bolt)…. nor does my gun have the breech screw covered in wax (yet!)…. Either may greatly reduce the tumbling of the pellet….

I have two things I will be doing to customize this breech to my gun…. The first thing I discussed with Jay, and that is to machine the front of the loading port in the breech slightly (about 1/16”) to allow the magazine and holder to be positioned further forward…. This will increase the clearance between the front of the bolt and the pellet skirt and should improve functioning with the longish pellet I use…. The other thing (which I didn’t discuss with Jay, but when he reads this I hope he may incorporate into the design) is that I will be machining about 1/16” off the top of the aluminum holder ONLY (not the magazine)…. This will allow me to move my scope further back (with the turret over the holder) but not so far back as to hit the magazine…. Please note that if you are using this magazine on a Disco, and using Jay’s shortened bolt, machining the breech would not be necessary…. and the pellet tumbling may be reduced as well, without the forward breech screw hole location I’m dealing with…. As far as the turret interference…. I’m just being fussy….

To summarize:

The RIM2 system is well machined and of excellent quality.
In a Disco, you will need the shortened bolt, and lengthy bolt probes, even with the back of the bolt shortened, will not work.
The system is relatively pellet sensitive, but seems to function quite well with proper pellet selection.
The attitude of the gun may also affect sensitivity. All these items are mentioned on the website.
If you have a pellet tumble, it’s VERY difficult to clear…. This could easily cause the loss of a follow-up shot when hunting…. I didn’t see any mention of how to clear a jam on the website other than my fiddling the bolt and in my case, that often didn’t work….
Within the design constraints of using a stock Crosman steel breech, this system works quite well…. Until someone makes a breech and bolt to use the Marauder self-indexing magazines, this may well be as good as it gets….

Bob

rsterne · Moderator

I did the mods today, and am happy to report the feeding is much less prone to tipping.... Rather than lengthen the loading port at the front, I simply machined the slot for the bolt handle 0.100" further back and shortened the bolt another 0.080".... When the bolt is retracted now (even with the extended probe) it is just aft of the back of the magazine.... When cycling the gun on the bench, through two complete clips while sighting in, I never had a single loading problem.... If the gun is even close to level, it now works flawlessly with the JSB Exact Heavy 18 gr. pellets.... I tried it in several other positions, and with the muzzle 45 degrees low it would occasionally tip up slightly, but retracting the bolt once and then feeding forward again cleared it, at least so far.... I'm sure that with the gun held in certain attitudes it could still present a problem.... but now that I am concious of keeping the gun relatively level I think I will be able to use it for Grouse hunting next fall.... which was the primary reason for the purchase....

Machining 0.080" off the top of the holder allowed me to move the scope back 1/4" and now the eye relief is perfect....

If you fit a RIM to your gun, make sure that the bolt retracts so that the front of the probe is slightly behind the back of the magazine.... I'm guessing that it will function even smoother with a Disco without the hole for the tiny breech screw directly under where the pellet drops....

Bob

Alstone · Moderator & Site Supporter

A very good write up Bob, I have read the bumph over here in the UK on the QB version as I was thinking of getting one, plus experimenting myself with rotary loaders I also had a problem with tipping pellets, but no mention of that in the advert. Mad

Nice job

Al