Mendoza RM200 airgun review - PART 1

[Speedturtle]

As you all know, one of my "santa" here at AirgunOne gave me his Mendoza RM200 0.177 Air Rifle as a gift. This airgun is unique in a lot of ways so a short review will not suffice. I will subdivide my review on this rifle in 4 sections. Part 1 would be discussing the external aspect of the airgun and my initial impressions on it. Part 2 would be the dis-assembly process and discussion about the internal parts of the rifle itself. Part 3 would be the home-tuning process, and Part 4 would be the modifications I've done on the rifle based on what I know about modding an airgun using locally available materials.

PART 1. The Mendoza RM200 airgun.

This airgun is nice! Measuring about 41" in overall length (from end of the barrel to the tip of the rubber pad), the airgun is not that heavy.







Housed in a Walnut colored hardwood (I don't think it is a real walnut because when I took the rubber pad off the wood is very light in color) the contours of the stock was nicely curved and finished beautifully. There are some minor blemishes on the wood (I think it was from the wood grain itself) but can be simply corrected or repaired if you do some sanding and refinishing on the stock.





I like the way the wooden stock fits my small right hand. Without a scope the rifle balances at 5" away from the edge of the trigger guard. With a Leaper's 3-9X50 AO Scope the balance shifts at about 2" closer to the trigger making making me hold the rifle with the edge of my palm actually touching the edge of the trigger guard.



The steel parts used on the rifle is of a higher quality than what I have noticed on my Crosman airgun. First, the barrel is made of a harder kind of steel. (I noticed this when I chopped the barrel. ). The blueing was very nice. Since this is my first time to see a different brand of airgun up close I'd said this kind of steel blueing is definitely high quality to me. Both the barrel and the compression tube has a deep blueing on it. The compression tube fits nicely on the inletting of the wooden stock.



I noticed that on this airgun Mendoza has engraved a lot of information on both the barrel and the compression tube. Compared to my Crosman G-1, the information on the RM200 was machine-engraved and not silk-screened. This one has the RWS logo pressed on top of the polymer compression tube end cover that also serves as a scope stop.



The safety pin can be slided on both sides so I could probably say it is "ambidextrous" just like the wooden stock.





With regards to the trigger of the RM200, this is one of the uniquely designed trigger unit to be used on an airgun. The first thing that came into my mind when I saw this kind of trigger system is the Accutrigger with it's 2 trigger blade system. I don't think they are the same but the principle behind the mechanism has some similarity. The first trigger blade (the one on the right side) will have about 1/8" of trigger travel before it will align itself with the 2nd trigger blade (the one on the left). The pull weight of the 1st trigger is not that heavy. There is a stop pin attached to the 2nd trigger blade and when you fully press it both the two triggers will release the sear. If you try to only press the 2nd trigger blade to fire the airgun it will not allow you to do it. Why? Because the 1st trigger blade is still blocking the sear engagement. Both trigger blades has to clear the path for the sear to release it's hold on the center rod of the piston unit. Only after that can you fire the airgun safely.

Another unique feature of this airgun is the built-in OIL PORT located on the central part on top of the compression tube. You will see a sign (like an oil dropper) stamped beside the port to let you know that that is where you will add some oil to lube the rear of the piston unit. When you cock the rifle you will notice that this port is covered by a RED color. I have no idea why it is colored red. Probably to let you know that the airgun is "hot" and is ready to fire. When we get to part 2 of the review you can see some ingenious ideas applied on the piston unit about this oil port and piston lubing.

INITIAL FIRING IMPRESSION.

Flip, (The one who gave me this nice gift) told me from his PM that he only had about 300+ pellets fired through it. When I first tested the RM200 I noticed that it is still dieseling a lot. Further discussion with Flip allowed me to learn that the RM200 was actually designed with dieseling in mind to increase its FPS rating. I guess that's the reason why it has an oil port on the outside of the compression tube - to add some oil to let the airgun diesel when used. Personally, I I didn't the idea about the additional oil on dieseling since a controlled dieseling is very hard to achieve in an airgun. Later on, on part 4 of my review I will discuss the mods about this dieseling idea on the RM200.

The cocking force is light. This airgun can be used by young adults. It only uses a single cocking arm to slide the piston unit towards the sear. One of the nice feature of the RM200 is that it uses a locking pin to lock the barrel to the compression tube. Compared to my G-1, I think this kind of locking mechanism performs better in terms of locking consistency. You can hear a positive locking noise every time you bring back the barrel prior to firing. I noticed that the RM200 has a lot of spring twang in it. The perceived stock vibration is very evident but not harsh. The rifle tends to jump on a clockwise motion when fired. I think this airgun is a nice candidate for a home-tune to control that twang and spring recoil!

The initial chrony results are:

Lo - 581.9 FPS
Hi - 616.0 FPS
Ave - 601.3 FPS
ES - 34.15
Sd - 10.44

10 shots total:

10 - 606.7
09 - 602.6
08 - 593.4
07 - 605.0
06 - 615.7
05 - 616.0
04 - 600.2
03 - 595.1
02 - 581.9
01 - 596.6

Using CPHP's the RM200 exhibits a 3/8" groupings at 10 yards indoor. The Gamo Match wadcutters came in second at 1/2" at 10 yards.

Here's the funny stuff. Prior to tune she does not like the more expensive type of pellets like the JSB exacts and the RWS superdomes. After the tune the RM200 can literally make one ragged hole at 10 yards using the JSB exacts! This sounds exciting (though for me I find it a bit of a problem since the only way I can buy the JSB pellets is to order it online and it's expensive for me just to use for paper punching!)



All in all I see a lot more potential on this airgun. Combined with some custom works on the spring guides and some additional weight on the moving mass I'd like to achieve a clean 600 - 650 FPS rating on her with very little recoil and vibration. stay tuned and thank you for reading!

[Flip]

Willie, very nice review. I’m looking forward to part 2. I’m happy that you are enjoying the project and at the same time experiencing the fruits of your labor. She is looking real good in the photos. I’m sure you will be telling us about that new addition to the barrel in the upcoming reviews.

[Speedturtle]

Originally Posted by Flip

Willie, very nice review. I’m looking forward to part 2. I’m happy that you are enjoying the project and at the same time experiencing the fruits of your labor. She is looking real good in the photos. I’m sure you will be telling us about that new addition to the barrel in the upcoming reviews.

Thanks Flip! I really enjoy working into this airgun since this is my first time to be exposed in a different design aside from Crosman break-barrels. As a giveaway, the addition to the barrel is a shroud made out of PVC pipe! More to come on Part 2 and this part will be a little bit technical.

[tirths]

I expected the power would be a bit higher side by looking at the length.

[Speedturtle]

Originally Posted by tirths

I expected the power would be a bit higher side by looking at the length.

Hey tirths, are you talking about the barrel length or the overall length of the RM-200? The RM-200 has a 2" piston stroke and the compression tube diameter is close to about 1". I'm supposed to post the part 2 soon but I'm tangled in between packing our stuff and transferring it to the new house that we will rent.

To give you an idea why the RM-200 is only rated in reality below 700 FPS is that the transfer port is a bit big for a caliber 0.177. Also it is not a straight cavity, it is more like a funnel, centered to the tube then being redirected towards the barrel bore so it is angled by about 15 degrees relative to the compression tube. IMO this also robs it of some power. Second, the piston seal is very hard and is not fitted properly to the compression tube that is why there are air leaks behind it robbing it again of some power. They (Mendoza engineers) decided to compensate for it by simply "allowing" the airgun to really diesel more by burning more lube than is necessary. I decided to go the other way and honed the cylinder. Then, I discard the felt material that holds the lube behind the piston seal and just put a light coat of moly grease on the compression tube.

Do you remember why I am so interested about the piston seal you posted? I am actually planning to modify the RM-200 piston unit and chop off the original piston seal holder (a screw-on type) convert the piston seal to the small apex parachuting type and use the IHP piston seal adapter that you have in India for the mod. This way, the airgun can make perform better since the seal is working properly - that is, to seal the chamber and make use of every available compressed air to push the pellet to the bore.

As soon as we are settled on the new house I will start posting new stuff about this nice and unique airgun.

Thanks!