CYMA CM048m - Patrol Base

[JVacation]

Could help to get in there and clean it up as well as re-shim.

O-ring nozzle is good as long as it fits properly (length and not too tight)

You could also try polishing the inner barrel.

(Presume you already cleaned the barrel...)

Had a response from PB today saying that it's very rarely that they receive them firing them hot. I take it they come from Taiwangun then and they do the downgrade for PB as their "low" option (310).

If the airseal work doesn't help significantly what strength of spring would you recommend? 

 

[Ebeneezer Goode]

If the range is a bit meh and there's a deviation in fps, sounds like a leak. I'd send it back to them and get them to check and fix. Seals will probably sort it.

 

[Rogerborg]

I think cracking it open and checking airseals and putting a oring nozzle on first is a good starting point

Yup, an o-ring nozzle and replacing the stock [clarification] piston o-ring resulted in a rock solid air seal on my CM.516.  A bit of silicone grease and I was seeing a had-to-check-it-twice 1.3J out of an M100 spring and a ZCI 229mm barrel.  Air seal is king, I had to drop to an M90 and even then it's nudging 1.14J.

 

[Ebeneezer Goode]

Seen the same issue on my LT M4. A bit of reassembly did the trick.

 

[SSPKali]

Yep, the air nozzles on the Cyma AKs is the one weak point but easy and cheap to fix.

One other thing to watch out for is the only chrono that matters is the one at the site you are playing at that day! 
 

My MP5 was 335-337fps on 0.20g at home but 351-352fps at the site. Bugger. Same with my GBBR but that was easier to dial down the gas valve.

Snipped a coil off the spring and all good now. I figure mine is reading about 5% under (or theirs is over, but that argument won’t get you anywhere) and work from there.

 

[JVacation]

Has been a funny few days. Started off doing the airseal which for some reason dropped the fps by 5 or so but was more consistent. (Could be due to friction of the oring) 

I noticed that the CM048m Nozzle length is the shorter nozzle instead of the longer one. The longer one worked perfectly fine but I think having the intended length is probably best so I swapped to the shorter one. I also then started upgrading springs as the one in the gearbox from stock (I take it whoever supplied PB with the cyma aks puts these terrible springs in to get under 350fps). I was recommended a m105 by ak2m4 and to our surprise it was shooting at 400fps. I also bought a ZCI M100 at the same time to drop in if the 105 was too high and that is still a bit hot at 370. I'm thinking I should now get a m95 or m90 and go from there. 

Once I got it where I like it I will do a bit of a in depth guide for the gun as a whole on recommended parts and etc.

 

[JVacation]

M95 has seemed to do the job. Currently shooting 349 on 20s with no hop applied and 293 on 28s. Just under the limit but I think the hop will help bring it a little bit down more. 

Will play with it this weekend if all is well and will type up a in depth guide next week. It's a shame companies like patrol base do this to cyma aks by putting in such weak springs. I may have to start offering a Cyma spring upgrade service... 

 

[Rogerborg]

Good to hear you got it sorted, and M95 sounds about right with o-ringed and lubed airseal.

Was the stock spring noticeably short?  The one in my CYMA M4 had clearly been cut down, it was only just barely under tension with the piston forward.

 

[JVacation]

Good to hear you got it sorted, and M95 sounds about right with o-ringed and lubed airseal.

Was the stock spring noticeably short?  The one in my CYMA M4 had clearly been cut down, it was only just barely under tension with the piston forward.

Didn't look like it was cut short it was just incredibly weak. Felt like it could either be a really poor grade m90 or even a m80. I think what currently happens is that Patrol Base order RIFs through TaiwanGun as they have a bit of "partnership" going on. Which do the work of reducing the fps as quickly as possible down to their low fps setting of 310. Replacing the spring is probably a bit quicker and more reliable than cutting the spring. Closing this particular gearbox on the cm048m was considerably easy - A magnet on the anti reverse latch and the trigger liked to play ball.

In terms of springs the gearparts range at ak2m4 are very solid for the price. For some reason they are much easier to install than other springs as the coils on one end are much tighter than the other. I also installed a ZCI m100 during my testing which just loved to try and pop out towards me where as the gearparts preferred to stay put.

 

[JVacation]

Had a game day with it yesterday. Was rather enjoyable and peformed quite well. Only thing I did notice is that once I set up the hop for 0.28 and did the chrono in the morning there was quite a bit of a fps drop. Do you think it's worth putting in a stronger spring so that when the hop is set for 0.28 its where it should be.

I saw an example of this in one of negativeairsofts video regarding a arcturus ak where it was perfect for 0.2 but when set to 0.28 it dropped a lot.

Cheers

 

[Rogerborg]

It depends on your site's chrono policies, and everyone's got their own ideas of the One True Way.

If they chrono with the weight that you're intending to use, with hop on, sure.

Some sites are still using 0.2g, some apparently even want the hop turned right off. If you're unlucky enough to play at once of those, you'll have to tune to their quirks.

There's a notional legal consideration that if it's capable of auto, and shooting "any missile" at over 1.3J, then it's not legally speaking an airsoft gun.  You'd be hard pressed to find any tool of the State who knows this, let alone cares about it though.