Tommygunn Posted August 31, 2011 Report Share Posted August 31, 2011 I stripped the cylinder and piston of my CA M24 today to inspect it and give it a clean. I left the spring, spring guide and piston internal suface greased but I decided to use HPI 40 weight silicone oil (RC car shock absorber oil) for the mating surface of the piston and cylinder thinking that the oil would be more fluid than smeared grease. However, I chronoed the rifle today and it appears to have lost about 10fps since the other day. It was about 500fps and now it is shooting consistantly around 490fps or thereabouts. Is there an explanation? Tom. Link to post Share on other sites
Dan B Posted August 31, 2011 Report Share Posted August 31, 2011 I'm pretty sure that the greasing of the outside of the cylinder wouldn't affect the fps very much, if at all, due to it not really having anything to do with the air seal, only the smoothness of the bolt pull. Your spring may have just lost some of it's tension, or some other logical reason Link to post Share on other sites
Lightbulb Posted August 31, 2011 Report Share Posted August 31, 2011 Did you wrap the threads of the cylinder head with teflon tape? Opening it up might have led to a less good air seal. Link to post Share on other sites
Tommygunn Posted September 1, 2011 Author Report Share Posted September 1, 2011 Dan B, You have misread the title and my post. I said I have used oil instead of grease to lubricate the piston against the inside of the cylinder wall i.e. the cylinder/piston interface or mating suface. I made no mention of lubing the outside of the cylinder, although I do that to promote smooth action when cocking. Lightbulb, Never needed to. The o-ring(s) of the cylinder head/nozzle are in excellent shape and are well lubed up to keep them sealed and in good nick. I could try the teflon tape trick I suppose. Tom. Link to post Share on other sites
Tommygunn Posted September 1, 2011 Author Report Share Posted September 1, 2011 Lightbulb, I just tried the teflon tape and it made no difference to what I was previously experiencing. I just took the rifle apart and cleaned out the oil and replaced with grease and I'm pretty much getting the same results but with quite a bit of variance. I'm sure I was getting the fps variance before I switched to oil as well. I fired about 15 shots that gave me random fps readings of the following values: 0.2g BB 483fps - one or two times 490 to 495fps - a few 499fps - once 509fps - at least twice. Is it normal to get random fps results in near specific values? Does that seem a normal variance on the values? It's the high and low values which are most bothersome, or rather I would like to have the rifle shooting at the 500/510fps mark. Tom. Link to post Share on other sites
Dan B Posted September 1, 2011 Report Share Posted September 1, 2011 Oops, sorry about that! No more posting when tired for me haha! Link to post Share on other sites
Lightbulb Posted September 1, 2011 Report Share Posted September 1, 2011 Could be the battery of the chrono wearing out? They some times get less accurate if the battery runs low? Might be worth replacing those maybe? Unlikely but possible. Other than that there's not a lot to suggest really. 490 to 500 is still pretty good. Link to post Share on other sites
Tommygunn Posted September 1, 2011 Author Report Share Posted September 1, 2011 They were replaced just the other day. Tom. Link to post Share on other sites
hwagan Posted September 1, 2011 Report Share Posted September 1, 2011 How many rounds have you fired between applying lube and chrono'ing? Could be that any excess grease around the piston is getting fired through into the hop/barrel - Try firing say 100-200 rounds, clean the barrel and hop and air nozzle thoroughly and give it another go? Link to post Share on other sites
Lightbulb Posted September 2, 2011 Report Share Posted September 2, 2011 Grease coming through and getting on the hop is definately a possibility. Honestly though I would take it out and and check the accuracy. Unless its seriously affected I wouldn't worry about it too much. Link to post Share on other sites
Tommygunn Posted September 2, 2011 Author Report Share Posted September 2, 2011 I've got the grease issue covered and made sure I've not been excessive, mostly greasing behind the piston o-ring. I've also checked each time I've taken it down in the past day or so and no grease is being spat through, hop and barrel are clean. I have actually put in a fibre and nylon washer on the spring guide, about 3mm in total, to slightly tension the spring. Here are the results for five shots on a 0.2g bb. 505fps 501fps 504fps 498fps 506fps That'll do for me! I'll put it down to the rifle and spring being 8 years old. Tom. Link to post Share on other sites
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