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Education / Training Mendoza RM-2800 .22 cal. repeater – Part 2

Mendoza RM-2800 .22 cal. repeater – Part 2

by B.B. Pelletier

Part 1

Following the advice of some readers who noticed a similarity between the Mendoza RM-2800 and the RM-2000 I tested for you back in May and June of last year, I tested this rifle with most of the same pellets. We can expect the barrels to be the same on both rifles, but the advertised velocity of 950 f.p.s. leads me to believe the 2800 will be faster than the RM-2000. So, I ‘ll report velocities of pellets for both guns.

One thing I forgot to do until late in the RM-2000 test was clean the bore, so that was the first order of business for this rifle. The procedure is 20 strokes through the bore in each direction with a new brass brush loaded with J-B Non-Embedding Bore Cleaning Compound, and then cleaning patches until they come out clean. The bore was not too dirty on this rifle, so it cleaned up fast. Now, on to velocity testing.

Eley Wasps
I chose these because the RM-2000 was most accurate with them. I never chronographed them, though. In this rifle, they varied from a low of 411 f.p.s. to a high of 702. While a variation like that would normally be attributed to dieseling, I don’t think it is in this case. Even at 702, the velocity is too low for this rifle. I think it leaks air at the breech seal. Testing with other pellets helped confirm that.

Crosman Premiers
Crosman Premiers were next. They ranged from a low of 291 f.p.s. to a high of 608. They do feed through the magazine, and the slowest ones were those fed from the mag.

RWS Super-H-Points
I tried RWS Super-H-Points next. They went, 393, 398 and 400, respectively. I did not finish a string with them.

RWS Hobby
RWS Hobby pellets were the last ones I tried. They went 381, 405 and 397 f.p.s. That concluded the test of this rifle. Please note that the few higher velocities I recorded came with the first two pellet tested.

So much for my grand plans!
These velocities are unacceptable. They don’t represent what this gun is capable of, so something is clearly wrong. There aren’t many easy fixes for a breakbarrel when this happens. In fact, the best one that comes to mind is Vince’s shimming of the breech seal that will be reported later this week. That may be even more important in this case because of Mendoza’s sliding pellet carrier, which needs a seal on EACH SIDE of the moving carrier. That’s two chances to leak air, which is what’s happening…I think.

If this were an easy fix – something anyone could do – I would do it and report the results. Because of the requirement to disassemble the repeating mechanism to fix the interior breech seal, I’m going to pass. I can probably do the work without much problem, but most airgunners don’t have my experience or my tools.

If you look back at the test of the RM-2000, you’ll see the pellet velocity was much tighter than with this rifle. I think the seals on the pellet feed mechanism are not doing their job.

So, the test of this RM-2800 is over. I have an Air Venturi Avenger 1100 on order. That’s a Mendoza breakbarrel without the repeating mechanism. I’ll test that for you when I receive it.

I’m sorry things turned out this way. I’m going to return this rifle to Pyramyd AIR.

32 thoughts on “Mendoza RM-2800 .22 cal. repeater – Part 2”

  1. BB, I was wondering what the best method of removing the plastic front sight of my Sierra would be. When I get it back from Crosman, I’d like to mount a plain (smooth) muzzle break. Thomas

  2. BB – What does that kind of velocity spread translate to on the target at 10 meters? I ask because my Crosman Quest is stringing shots vertically 2 inches or more, and I’m wondering if there’s a leak at the breach seal. I clearly need to get a chrony to verify, but I was just curious.

  3. Airdog………

    Lay a sheet of toilet paper over the breech then fire the rifle with a pellet.
    If the breech seal is leaking, it will blow holes in the toilet paper or blow the toilet paper off the breech.

    If the toilet paper just lays there when fired, then your breech seal is O.K.

    Most stringing is caused by improper shooting tech. My Storm took some figuring out. Requires a loose and consistent hold to shoot without stringing.


  4. Airdog,

    Twotalon gave you a great test. Ten meters is really close, so you would have to have velocity shifts as great as those I got with the 2800 to string that much.

    I suspect you aren’t applying the artillery hold correctly, or worse, you are trying to shoot off something other than your hand.


  5. Airdog..

    Should have elaborated a bit more as to shooting tech. Your rifle is essentially the same as mine.
    Light hold of the butt plate to the shoulder. Light touch of the stock to the cheek. Light grip with the trigger hand with the hand as far as possible to the rear that will still allow you to reach the trigger. Off hand just in front of the trigger guard, either on open palm or back of hand as BB has described before.
    DO NOT grip the stock with your off hand in any way!! DO NOT let your fingers touch the sides of the stock.
    And do not flinch the shot!!

    This works well with my storm. Shoots cpl and 8.4 Exact well this way. I shoot with open sights, as I don’t like the scope.

    Blue loctite the stock to gun mounting screws. If you don’t, they will keep shaking loose and the rifle will keep getting squirrely on you.


  6. There are few discovery 22 videos around. I’m still waiting for mine to ship. 🙁

    I stand corrected on the mendoza 600 somewhat. The advenger has a nice checking and a steal right now if one were looking for .177 springer. As for me I prefer the .22.

  7. Thomas, the front sight of the Sierra does not have to be cut off. Use a block of wood and a hammer to tap it forward. Reinstalling it is just the reverse of taking it off.

    Airdog, are you using a scope and how many shots on your gun? My observation is that the Quest variants use a harder compound for the breech seal – and when the gun is new the breech actually closes on that seal and not metal-on-metal. This can lead to inconsistent vertical lockup that really manifests itself when you use a scope.

    Eventually the seal seems to “mash down” to the point where the breach IS locking up metal-on-metal, and it becomes more consistent because it is locking up in the same place every time.


  8. Twotalon, I believe that the breech seal test you describe can be inconclusive. If the seal is leaking downward, I don’t know if this will pick it up. If it gives you a positive indication you know the seal is leaking… but a negative result wouldn’t tell you that it’s not.


  9. Thanks Vince.

    You are right. There is a chance that the leak test might not be conclusive, particularly without chrono testing.

    Had forgotten about the tip you gave me about replacing the crappy plastic seal with an O-ring. Works so well that I forgot about it.


  10. Vince, Thanks for the advice. I was very dissappointed with the rear factory sight (cheap and warped plastic) on my Sierra, that I removed the whole thing. Plan to put some allen heads back on it after its return from Crosman. The front sight gives an annoying blur through the scope at the highest magnification, and very clear in the lowest setting. Still trying to figure out which scope mount to get for it since the factory mount had to be adjusted ‘way too high’ in the back. BB recommended a B-Square type, but the #’s he gave me were individual adjustable rings, and I’d prefer the scope rail mount for it’s sturdier grip in the dove tails…..especially when recoil comes to mind. I would like to put the factory scope back on it. I was using a cheapo wal-mart BSA classic, and was getting better results. With the Crosman scope, I’d like to re-cal it,…or what I’ve heard as “centering the reticles” before, and start over. Thanks again, Thomas

  11. Thomas, I’m not sure exactly what your scope mount requirements are but you might consider the Leapers Accushot mounts. I was considering the B square too, but the PA techs told me that they’ve had some problems with screws stripping and that the many parts required to make the mount adjustable require some attention. I never found out for myself since I went with the one piece Accushot mount they recommended (based also on my good experience with a two piece set) and have been very pleased. The mount has a built-in scope stop pin, three big Allen screws that mount solid as a rock and even some kind of tape on the inside of the rings to hold the scope tighter. Best of all, it’s cheap!


  12. B.B.

    So what’s the best way to acquire this god-like knowledge of gunsmithing? I’m not a tinkerer by disposition, but I’m feeling moved to extend my knowledge of guns by knowing what goes on inside them. I was reading the biography of a very high-level guy who was in the military, went on to get a Distinguished ranking in the NRA, and then went to a community college to get a degree in gunsmithing before starting his business. Are there certifications like this for gunsmiths?

    Otherwise, I suppose the best way, especially at the amateur level is to get in there and do it aided by the internet–which I make heavy use of. I don’t know if there’s much else to say. Is there a good starter book or a good (easy) gun to work on?


  13. Matt61,

    This “god-like” knowledge is anything but. It’s the result of many years of practical experience working on guns.

    Buy an inexpensive breakbarrel spring gun that you can work on. Make a mainspring compressor and learn how to dismantle the rifle safely and quickly. Use the 13-part series I did on tuning a spring gun as your guide – BUT NOT AS STEP-BY-STEP INSTRUCTIONS.

    The gunsmith is someone who does not need step-by-step instructions. He knows instinctively how things go together and come apart. Experience is the best teacher for this.


  14. Thanks Two-talon, Vince and BB for the advice. I’m definitely trying to make use of the artillery hold. It’s frustrating because with my Viper I just need to hold it loosely and everything’s on a dime. The Quest is finecky, but I will try the tp test. What’s funny is that the more guns you have, the more you can lose track of how each gun demands to be held. That’s why I’ve grown to love my AR2078 so much. It’s like a girlfriend who never demands too much. 😉

  15. Airdog, I know what you mean. By and large my criteria is this – if a gun doesn’t shoot reasonably well the way I naturally hold it, it goes. I’ve sold guns because I couldn’t get them to group very well, and the buyer then raves about how accurate it is!

  16. B.B.

    Thanks. Yes, I’ve been meaning to look at the series on spring gun tuning. I think that detailed disassembly would be a good goal for me. Building and modifying sounds like another level that would take specialized tools.


  17. airdog, tell me more about your AR2078. I was considering that gun for the longest time. It certainly looks sharp. But I finally decided against it since it apparently does not have the accuracy of the Daisy 853 and seems to be something of a gas hog. What do you thing?


  18. Has anyone noticed that the artillery hold for rested shots with the rifle on a hand instead of a bag is a little shakier than setting it directly on the bag? My IZH 61 has not performed in benchresting as I expected although it continues to excel with every other kind of shooting. That may be a feature of this particular gun, though as noted in the blog report.

    Also, there might be other circumstances. I haven’t found the exact right height and support materials for my bag, and I was distracted by getting hit with brass casings and by the report from the monster revolver down the line, so I’m not realizing the full potential of the bench rest. I was just wondering about other impressions.


  19. Matt – I’m very pleased with the AR2078. I actually ordered mine with the regular QB78 barrel so I could put on a Beeman muzzlebrake, so I now have an extra 177 barrel. (The AR2078 barrel is 1 mm thicker.) Off a bench the gun can keep 10 shots within a half inch at 10 meters. There are occasional flyers, but I didn’t even bother to clean the barrel. As far as being a gas hog, you get 50-60 consistent shots with 2 powerlets, but I bulk-fill mine from a 20 oz paintball tank anyway. Once you bulk-fill it’s cheaper than any gun using powerlets.

  20. BB, Matt61, /dave, BG_farmer, among others,

    Bad day… only one squirrel… But i am having some golfer trouble up at the farm, but am testing the incendiaries at home. I filled a Advil container with black powder cartridges and it was like a firework, didn’t move enough material. I ought to try a nalgene (if thats how you spell it) bottles worth (higher pressure + more sudden release)! I could always move over to some HE’s such as Acetone Peroxide. Like the Hav-a-Heart, explosives are much cheaper than airguns. Lets see- draino + Hydrogen peroxide + coffee filters. Thats like $15. Got a couple phone calls. Although, im not the worst in town. This guy up the street has ten acres, in my town, this permits him to shoot deer with his 50 bmg (true – he does). I have six, thats good math correct? I am about a quarter mile away from the guy so ill know who to!
    He has it silenced! Still loud.

    the McMILLAN tac-50 is tempting!

    Heres what the stuff does–>


    this all pertains to airguns through pest elimination, to my mind at least.

  21. henry, are you planning to blow up the squirrels? And is the rifle for them too? I would beware of a neighbor who is shooting a .50 caliber rifle only a quarter mile away. The Wikipedia article on this very impressive rifle said that it was used to make the longest sniper shot in history in Afghanistan at 2500 yards. I would keep my head low if I were you.

    Maybe you can use your terrain against the squirrels. You could construct a sort of greased slide down your mountain. Then you could unload the Have-a-Heart traps onto the slide instead of driving them around and send the squirrels down the mountain and into the lake. I doubt they would ever come back.


  22. BB,

    For those looking for some comments on the production discovery I have left some extensive comments.

    This is a very easy gun to disassemble and work on trigger. Other than that don’t recommend any mods. Doesn’t need them imho.

    And I can tell you it is awesome. Still haven’t a chance to long range test with air yet but have completed velocity tests.

    All tests were 10 shot strings over an Alpha Chrony. Some were done at initial filling and then again on shots 20 – 30.

    This gun is very sensitive to pressure. If you fill to 2200 psi (top of green line) you get lowered velocities at first but subsequently more shots. Here you get about 35 usable shots but first 10 are 25 – 35 fps lower than if filled to 2000 psi.

    If you fill to only 2000 psi you get most consistent velocities over the usable pressure curve but that curve is only 20 – 25 shots.

    Here is a summary of my velocity results. All were filled to 2000 psi and 10 shots fired then refilled.

    Here is the velocity winner of those tested: Beeman Silver bear hp 875 fps es 13.28 sd 5.29

    Close runner up on velocity: RWS hobby 836 fps es 54.72 sd 18.91

    Beeman H&N match 821 fps es 28.21 sd 9.48

    Gamo magnum 768 fps es 17.09 sd 6.78

    Gamo master point 749 fps es 26.55 sd 10.14

    Beeman ram jet 735 fps es 20.72 sd 9.11

    Beeman kodiak extra heavy 659 fps es 15.51 sd 6.55

    Jsb predator 754 fps es 13.09 sd 5.83

    Beeman silver jet pointed 762 fps es 14.68 sd 5.91

    Daisy Precision match wc 782 fps es 37.32 sd 13.89

    Gamo match wc 795 fps es 25.40 sd 9.74

    RWA Super H Point 760 fps es 15.76 sd 6.00

    Crossman premier hp 793 fps es 28.50 sd 13.11

    RWS Superpoint 791 fps es 16.36 sd 6.00

    RWS superdome field line 790 fps es 14.39 sd 5.38

    This is every .22 cal pellet I had on hand to test. Longer pointed pellets were easiest to load in breech, followed by the domed and worst was short wc like RWS hobby.

    This gun is powerful! I broke a gamo pellet trap shooting at 25′. This is the green trap with the four hanging resetable circles snd the center reset square. These are very heavy at at least 1/4 inch thick and after 50 to 100 shots one broke off at the top of the circle.

    It also appears to be very accurate. I haven’t tested with air yet at longer ranges but was quite pleased with CO2 at moderate ranges.

    I am very picky and have sent numerous chinese guns back to the sellers. This one is a keeper!

  23. Hello, has anyone tested round ball pellets in the mendoza 2000-2800 magazine? Please let me know, I can only get a one order chance!
    Thaksfor the reviews, very friendly and informative.

  24. beachunter,

    I cann't answer your question, but I can point you in a direction where you can get some help. You posted to a blog that was written in April of 2008.

    There is a small group of us looking at the posts to the older blogs. Please ask your question on the current blog which can be found at/blog//

    There are a ton of good folks there helping each other out. Hope to see you there as a regular.

    Mr B.

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