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General Discussion To Gateway To Airguns => Airgun Gate => : Wade.S February 06, 2010, 05:17:33 PM
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I have a Mendoza rm 600 in 22 cal that I have had for about 2 years. I love the gun and it shoots great, however it is way underpowered. I put it on a chrony a short while after I got it and it was shooting at 640 fps. I checked it today and it shot at 488 fps, the temp was just above freezing today however. The paperwork on the gun states it shoots at 950 fps. I have read some reviews in which they refer to dieseling, I have been using pellet rifle oil which is silicone based. Should I be using a different oil? Could I have a bad o'ring or a broken spring? The gun shoots and groups well, the only problem is a lack of power. Any ideas?
Thanks, Wade
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Don't know anything about Mendoza guns, but lets bump this post up and see if someone can help you. snookman
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I have a Mendoza 600 in .177 caliber and have experienced the same fps loss you refer to however it was due to the fact that the chamber oil that the rifle uses for it's "controlled dieseling" had burned off. A few drop of silicone chamber oil in the oiling port and the fps came back up to where it should be.
You mentioned that you are in fact using silicone chamber oil in your rifle as per the instructions so I would imagine it's possible then that you may have either a seal or spring problem or perhaps both. You could of course try another chamber oil and see if that makes a difference.... I think RWS makes one that's available..... before you resort to taking the rifle apart....
As for the advertised 950 fps..... I doubt it ever ran that hot... those are advertising numbers used to entice buyers. It was probably shooting in the mid to high 800's.....
Jeff
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Longislandhunter, thanks for you insight. I have looked for the RWS oil and have not found it yet. Do you know where I might be able to order it from?
Thanks, Wade
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Pyramydair used to carry it but it seems they no longer have it... I did find this stuff on P.A. though....
http://www.pyramydair.com/s/a/Chamber_Lube_1_oz/1015
I've never used it so I can't say how it will work in your Mendoza. The chamber oil I'm using is from "Airgunsmith" ... check out their website, here's the link..............
http://www.airgunsmith.com/
and here's the link to their chamber oil......................
http://www.airgunsmith.com/gunlube/airgun_lube.htm
hope this helps ya out
Jeff
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I'm going to have to break down and get one of these. From all I have read, they use the oil to diesel and get the high numbers. I would not be surprised if it does 950fps but the reports from owners who kept using the oil was that the guns were inconsistent since the lube burns off and the velocities produced have high fluctuations. Most say they just let it run out and then the guns settle into the 650fps range which is still good and, coupled with the accuracy of the Mendoza's, seems to be fine. What I don't understand is the use of "chamber oil" which is mostly (if not all) silicone. That has a very high flash-point, which is why it is used for chamber oil. I always thought the oil for the Mendoza guns was more or less petroleum based so that it diesels.
If you want to try some silicone oil, check at a hardware store or a model shop which sells R/C cars where it is used for shock absorbers. I think someone recommends their number two weight? Just be sure it is pure and not blended with petroleum. A couple of drop in through the transfer port may help the piston seal. Mendoza's have a fiber washer in there which may have dried out. Supposed to be what carries the lube.
Good luck! One day I will pick a Mendoza up. Would like one of the older Crosman models with the target sights.
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Why don't you try borrowing someone else's? I have RWS airgun oil that I use in mine and you can try (for a fee$$$$$$).
I still think we should take your gun apart and look for a seal/spring problem. A damaged seal will drop the fps, as will a sacked-out or broken spring.
Does anyone know where to get an aftermarket seal? What size/rate spring it is?
Does anyone tune the Mendoza's? Any links or #'s would be appreciated.
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Good questions. I've never seen references to a replacement spring, etc. Might call UmarexUSA. They sell Mendoza's.
As to the silicone oil, it's pretty cheap. I found a small spray can and it will last me forever.
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"I'm going to have to break down and get one of these."
Redfeather,,,,, just saw on the Umarex website they're selling display model 600's in .177 and .22 for $69 bucks. Just thought I'd mention it in case you're interested in picking one up.....
Jeff
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Did see that. They say they are out of .22's though. And I liked the older models wearing peeps. One will turn up, sooner or later, when I've got the itch.
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I called (umarex) on that one it is a 177 but she described it and scratched up pretty bad and passed on it.
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WadeS,
I called Darrell's Airguns in Portland. He said he used to sell Mendoza's. He thought it was a spring problem and sounded confident he could resurect yours. He said he thought about $110 + shipping to put in a new spring, seal and lube it.
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It sounds like a broken spring. I have a mendoza rm200. The spring broke but it took a while for me to notice because the fps dropped but the gun became more accurate. They are pretty easy to fix yourself. I got a spring from Pyramid air for $15. They are currently out of them. I use the RWS silicone chamber oil in mine, bought at a local gun shop. It's easy to build a spring compressor. Just be careful not to take the trigger apart when you open it up. Replace the trigger pin you need to remove with a shorter pin which will hold the internal trigger parts together and allow you to remove the trigger assembly from the gun.
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Thanks, BWANA. This is the route I am going to try! Hopefully this weekend I will get the gun taken apart to see if it is the spring.
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Wade, Once you get the stock removed, you will want to remove the plastic cover at the end of the receiver. Do not slide the pin holding the cover on until you have a replacement pin about 7/8 inches long. I made mine out of a piece of plastic which was about the same diameter as the pin. Use the new pin to force the old pin out. It should slide in easy. Center the new pin in the trigger housing. This will allow you to remove the trigger assembly without spending an hour putting it back together. I found out the hard way. Good luck.
Mendoza RM200, Crosman 1377, 760, Raven, Quest 800, Quest1000, G1
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Well, we found the problem. WadeS and I took his AR apart tonight and the spring was broken into four pieces. When it came out, it measured 9.5" long. When we arranged it the way it should have been, it was 13". Also, the pieces had wound their way into each other, creating a double-coil spring for about 1/3 of it's length. No wonder his velocities have been in the high 400's to low 600's. The spring seems to have been broken from day 1. The seal and cylinder look fine. $15 from PA should bring back mucho power.
Thanks BWANA for the advice on the trigger.
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WadeS e-mailed JM the stock Mendoza spring dimensions and ordered what JM spec'd. Thursday we installed the spring with the preload spacer like JM instructed. His guide rod was a little too large and the spring was too tight. We chucked it up and removed about 0.006" diameter and polished it. That was just right. We smoothed all the edges, tarred the outside of the spring, moly-greased the spring inside and guide and piston sides and reassembled it. Chorno + 630fps :emoticon:
Yesterday we picked up some more washers and I turned the ID to the correct size. We tried 18 washers for about 1.75" of spacer length. It turned out to be coil-bound so we took out 3 washers. The chrono = 645fps :emoticon: :emoticon: :emoticon:
I think that's about it for this gun. We were hoping for mid 700's. I wonder what the stock Mendoza spring would do, with no oil to combust.
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WadeS and I went out and rezero'd our .22 guns tonight after work in preparation for a squirrel trip saturday. We were both using RWS Superpoints. Wade's Mendoza is definitely easier to shoot good groups than my TF-89 but lacks the power. Below are two 5 shot groups from each of us at 15 yards. Wade's second picture is of 4 pellets through the same hole with a "flyer".