GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: jus Tom on November 03, 2014, 07:00:16 PM
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A neighbor offered to get out his chrony today, so I grabbed up my .22 Nitro Venom and X20S and went over to check out some numbers.
Been wondering what kind of velocity I was getting on the NV since changing the seal, accuracy is much improved and it seems smoother but pretty stout cocking, so I figured it should be shooting higher numbers. Anyway, we got the Beta Chrony set up on the tri-pod and began testing using 14.3 pellets. I was surprised, disappointed actually, to find it only registering in the 630/640 fps range. My X20S was putting out the same pellet at 730fps.
Doesn't seem right ? I did all the needed de-burring and took care installing the new seal, lubed lightly with JM moly paste, as mentioned my accuracy has improved but I would've expected better velocity also.
Any thoughts appreciated.... thanks.
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I would guess and say that the nitro piston may be tired or the moly is slowing it down
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To answer John B,, I bought the gun new from PA hoping for something closer to the 950fps advertised, I realize those aren't real world numbers, but 300fps less seems something could be wrong.
To mafatone, all that I read about re-sealing speak of using moly paste lightly on the walls of the compression chamber.
This gun had massive amounts of oil showing inside the action when I first start shooting, hundreds of pellets later and it was still smoking and giving poor accuracy which led me to doing the re-seal.
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Just remember that after the rebuild, you have to brake it in all over again. It might just need to be shot some more then test it again.
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Re-breaking in ? It's probably had a couple hundred shots through it since the new seal.
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Exactly. Moly is a paste. The piston seal won't move freely enough. I know people have used moly with great results and no disrespect to anyone but I would never dream of putting that in any of my guns. I use moly for ball joints and front end suspensions. It's heavy grease.
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Breech seal?
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How tight was the new seal when you put it in? Did you check the fit compared to the original? Too tight or too loose and you lose velocity. I have carefully sized a seal only to have it become too loose after break in due to honing the cylinder. Then put the next one in tight and still have low velocity because of friction. I've come to believe that sizing a piston seal is an art learned by trial and error.
I too have gotten away from moly paste on the piston seal and use Krytox oil. It's very slippery, durable and never, ever diesels. Moly grease is for spring ends and trigger groups.
Jon
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Beta Chrony set up on the tri-pod and began testing using 14.3 pellets. I was surprised, disappointed actually, to find it only registering in the 630/640 fps range. My X20S was putting out the same pellet at 730fps.
Doesn't seem right ? I did all the needed de-burring and took care installing the new seal, lubed lightly with JM moly paste, as mentioned my accuracy has improved but I would've expected better velocity also.
Any thoughts appreciated.... thanks.
My NV 0.22 was shooting CPHP 670 fps out of the box. Did you have velocity data before the rework?
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Apparently there is more trial and error than mentioned in the many posts I read before undertaking the re-sealing.
I didn't hone the cylinder, just cleaned good then lightly turned some 400 grit on a snug fitting dowel by hand and cleaned again. The new Tesla seal was quite a bit tighter than the factory, which was burned badly (I assume) from the dieseling off excessive oil that was in the gun.
I lightly applied the moly paste to the seal edge and then lightly again to the walls of the cylinder. And NOW after reading so many great reviews about ARH moly paste, it's NOT good for the seals / cylinder walls....interesting.
To answer DOKF,, I did not have previous numbers, if you were only getting 670, maybe I'm expecting too much.
I can see another tear-down being inevitable.
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Breech seal?
I second that motion. Could need a breech seal or a shim under the existing breech seal.
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Did a tissue test, it never moved. Tore the gun down again too. Seal was perfect, cleaned it off, applied a bit more paste and put it back together. No neighbor around today to borrow his chrony, took 25 shots to get it back to zero.
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To answer DOKF,, I did not have previous numbers, if you were only getting 670, maybe I'm expecting too much.
I can see another tear-down being inevitable.
I was also disappointed initially with the velocity numbers on my NV 0.22, but by comparison to the other rifles I have by Crosman, I now realise that I may have been expected too much. And was fooled by the marketing hype.
I am interested in your progress; keep us posted on what you find.
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Temperature plays a big part in velocity with these guns. Somewhere buried deep in this forum are some numbers I recorded last winter. Mine would get a good 742 on a hot summer day. Come fall I was complaining of a leaking gas ram the numbers were that much lower. On seal drag, I like 'em nice and loose but at least contacting. I use the Crosman seal with great luck.
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Would like to see the marketing hype go away.....far, far away! Too bad the manufacturers won't tell it like it is (regardless of caliber) using the "most commonly" used pellet? The consumer is still going to buy what they will and they'll have real number values and what to expect of their guns. That's probably too easy? ???
Back to my gun.....the temperature that day was in the low/mid 50s, so it could've played part in the performance I suppose. Yesterday, after the tear down and re-lube the temps were warmer, close to 60. My first couple shots were 5 inches high and I wondered if the re lube was affecting accuracy by increasing speed that the pellet is rising? or could it have been the slightly warmer day? or combination of both? After 20/25 shots it was back to normal POI.
The Tesla seal is not sloppy loose compared to the factory seal I took out, but it's not so tight either that it takes much force to push it in.
I've done all the added improvements to this gun that I can and it really is a joy to shoot. It's minute of small critter accurate, smooth cocking and shooting, quiet and very eye appealing, I may just have to accept what it is and what it will do. AND, get my own chrony!
Thanks for all the thoughts.
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Having a personal chrony really helps diagnose and maintain air guns. Well worth the investment!
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I bought a chrony because I thought it was a must have once you surpassed owning a certain number of airguns. I only use it from time to time when I suspect a problem or when I try new things with my tinkering. I do a heck of alot more plinking than I do hunting. I pretty much know the capabilities and ranges of my guns. When I go to the woods after squirrels, I take a gun that I know is up to the task. I don't attempt to shoot animals out of that range and I can assure you, not once has a squirrel ever told me that I hit him too fast or too slow. I like a smooth cocking and smooth shooting airgun. I'm not so much worried about how hard I hit my targets as long as I'm consistantly making good groups. There was a thread at one point about how boring the FD-PCP was because hitting ragged hole was almost automatic. We were all joking about it but, there is some truth there. If I'm not challenged at all then it's just not as fun. Lately we've really come to enjoy shooting low to mid powered airguns with open sights. Betty Lou even made a comment the other night that I was cheeting because I put a home-made peep sight on my APX NXG. Then I put one on her 1377 carbine and she was knocking Daisy wadcutter pellets off of a drywall screw at 25 feet with 5 pumps. She don't think it's cheeting now. I guess my point is... if a gun is shooting well and there is a big grin on mine and Betty Lou's face... we really don't care that it's capable of 20 fps faster.
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I don't know if the Nitro Piston was upgraded but the part number was.
I installed a new one in George's NVD and it made a great improvement.
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There was a new part number for the gas piston. One difference was the addition of threads in the base. This change allows a 4mm pan head screw to be inserted and the ram reversed using the screw as a centering point inside the piston. I have both rams and see no difference in performance between the two.
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Would like to see the marketing hype go away.....far, far away! Too bad the manufacturers won't tell it like it is (regardless of caliber) using the "most commonly" used pellet? The consumer is still going to buy what they will and they'll have real number values and what to expect of their guns. That's probably too easy? ???
Back to my gun.....the temperature that day was in the low/mid 50s, so it could've played part in the performance I suppose. Yesterday, after the tear down and re-lube the temps were warmer, close to 60. My first couple shots were 5 inches high and I wondered if the re lube was affecting accuracy by increasing speed that the pellet is rising? or could it have been the slightly warmer day? or combination of both? After 20/25 shots it was back to normal POI.
The Tesla seal is not sloppy loose compared to the factory seal I took out, but it's not so tight either that it takes much force to push it in.
I've done all the added improvements to this gun that I can and it really is a joy to shoot. It's minute of small critter accurate, smooth cocking and shooting, quiet and very eye appealing, I may just have to accept what it is and what it will do. AND, get my own chrony!
Thanks for all the thoughts.
My best piston seal with the highest velocity was so loose I could plug the TP, drop the piston down the bore and it would bounce against the air cushion. Try using pure moly powder burnished into the piston and bore and mixing that powder with the Honda 60 paste as thick as you can mix it for the areas behind the seal and the last 1/2" of the skirt. The smallest amounts rubbed in works best.
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I think a lot don't realize that Moly is a powder that can be mixed with grease or oil and can also be used as a powder and can be burnished into the metal piston and seal. It will NOT diesel. I like using the powder in the trigger group and let it work it way into the parts. Moly can also be added to some of the new super lubes. If you take a dowel and a rag or paper towel on the end that just fits the tube, put some powder on the rag and move it in and out it will burnish into the metal making it really smooth. The grease that saids moly for auto ball joints, is NOT what you use on Air Guns!
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I never bought it so I don't know, but from what I see, the little screw top tubs of moly on some popular websites looks like grease to me. I agree the powder moly would be great for the air gun.
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There are a few that is selling the powder on ebay. What I use to mix my own is Midway Moly disulfide dry lubricant A big container is 8oz. and lasts a very long time. It is used for lubing shell cases and lead bullets. Getting it that way you can mix how strong you want it. If mixed with thin oil the oil will act as a carrier to get it into tight spaces like the cocking linkage and the barrel block if did not change over to brass washers then use the Moly in a little grease. I use the Moly/grease on the spring ends and the top hat. Now the bad once you burnish it into the metal it is HARD to get out and nothing will stick to it!
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The dry moly inside the tube and on the seal sounds like an interesting experiment. I know someone that has and uses the dry moly in his reloading of match ammo, he offered some to me when I was telling him about using the ARH moly paste but I declined at that time, guess I'll have to take him up on his offer now.
BTW,, my piston has the threaded hole on the bottom and now I know why....thanks for the info.
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There are a few that is selling the powder on ebay. What I use to mix my own is Midway Moly disulfide dry lubricant A big container is 8oz. and lasts a very long time. It is used for lubing shell cases and lead bullets. Getting it that way you can mix how strong you want it. If mixed with thin oil the oil will act as a carrier to get it into tight spaces like the cocking linkage and the barrel block if did not change over to brass washers then use the Moly in a little grease. I use the Moly/grease on the spring ends and the top hat. Now the bad once you burnish it into the metal it is HARD to get out and nothing will stick to it!
You were right. Moly paste is 70%-80% moly. The moly grease is only 20%-30% moly. Thanks for the information. Maybe I was thinking of that tar stuff that I would never use. Either way thanks.