Mendoza RM 2000: Part 2
by B.B. Pelletier
Okay - back to business. When we last looked at the .22 caliber Mendoza RM 2000, we saw the beauty of its adjustable sights and the marvel of the magazine loading system that enables this breakbarrel to be a repeater. Let's look at velocities and some necessary preparatory maintenance.
One of our readers wrote a comment that his RM 2000 got about 500 f.p.s. with 15.8 JSB Exact pellets. The description on the website says the gun gets "...smashing velocities up to 850 f.p.s. in .22 caliber." Of course that would be with lightweight pellets, but I would expect around 700-750 with .22 caliber Crosman Premiers and somewhere in the mid- to high 600s for the JSBs. That said, let's see!
The first pellets I tried were the Premiers. They averaged 713 f.p.s. with a spread of 38 f.p.s. The rifle is still producing a lot of smoke on every shot, so this wide variation is due to excess fuel burning in the compression chamber. If you wonder what that means, read the recent 3-part post about dieseling. This velocity is on the low end of what I expected from the stated velocity provided by the manufacturer. Going next to the 15.8-grain JSB Exacts, I got an average of 643 f.p.s. with a spread of 54 f.p.s. Again, this was slightly below the expected velocity, and the spread pointed to fuel-burning.
But, the real shocker came when I tried 11.9-grain RWS Hobbys. I expected to get up into the 800 f.p.s. realm, or at least close to it, but instead the average was only 726 f.p.s. That's only a little more than the heavier Crosman Premiers! However, the extreme spread was down to 35 f.p.s., indicating the rifle likes this pellet better than the others - or at least that's how I read it. The last pellets I tried were 21-grain Beeman Kodiaks. To my surprise, they averaged 618 f.p.s., with a spread of 34 f.p.s. The gun vibrated noticeably with this pellet, so I think there is some piston bounce, but look how close in velocity they are to the 15.8-grain JSBs. That tells me I need a better fitting pellet in about the same weight as the JSBs, because they obviously don't fit the bore well.
All shots were loaded single-shot, because most of these pellets will not feed through the magazine. I resolved to test some Premiers through the magazine for you, as well. Unfortunately, when I was blowing the smoke out of the barrel during testing I happened to look through it and, for the first time in my life, I saw a dark airgun barrel. Usually darkness is a sign of smoke remaining in the barrel, but that wasn't the case this time. This barrel was dirty in a very visible way! I had forgotten to clean it with JB Non-Embedding Bore Cleaning Compound, like I have been lecturing you for over a year. So, everything stopped while I cleaned the barrel.
What a lesson!
This was the most difficult airgun barrel I ever cleaned! The brush just didn't want to go through the bore. Boy am I glad I have a Dewey one-piece steel cleaning rod, because I think the effort would have broken a three-section aluminum rod. Up to pass number four, the force needed to push the rod through the bore took all my strength. The brass brush bent at the breech several times, so great was the entry force required. After pass number four, it became slightly easier, but I was able to feel a rough section just a few inches in front of the breech. That feeling went on until pass number 15, when everything smoothed out and became light and easy. I wish I owned a borescope, so I could look at these new bores and even take some pictures before cleaning them, because the feedback I get from the rod tells me they really need the cleaning!
Performance after cleaning - another lesson!
Crosman Premiers were first to be tested, and what a lesson they taught me! Velocity ranged from a low of 622 f.p.s. to a high of 832! Yes, nearly 200 f.p.s. spread. The median shot hovered around 724 f.p.s., so not a lot of change. BUT, when I loaded them through the magazine, the velocity was always higher and more consistent. That suggests that the Premier is too small for the bore of this rifle and it needs the extra resistance of squeezing through the end of the moving shuttle/breech to generate power.
Having established that, I figured fat pellets would be the best medicine for the RM 2000. RWS Super-H-Points are medium weight at 14.2 grains, but they have a wide skirt. Maybe that is why they gave a velocity of 754 f.p.s. with a spread of only 18 f.p.s. Beeman Ram Jets, on the other hand, are heavier, at 14.8 grains, but not particularly wide. They averaged just 670 f.p.s. with a 43 f.p.s. spread. Not the pellet for accuracy in this gun. Hobbys went an average of 724 f.p.s., which was a little slower than before but they only had a 25 f.p.s. spread - down 10 f.p.s., which is significant.
What have we learned so far?
- The RM-2000 likes fatter pellets.
- Crosman Premiers feed well through the magazine.
- The Bug Buster 2 scope cannot be mounted if you want to use the magazine.
- The RM 2000 is well-lubed from the factory.