Solution- Super easy way to reversibly semi lock a Cyma 098 SR25

[The_Lord_Poncho]

All - I'm not sure if it is general knowledge, but from internet research it transpires that the usual trimming of an M4 style selector plate to semi lock isn't always successful on the Cyma SR25 (098). There exists an alternative very easy way to semi lock them which does not involve drilling holes/epoxying physical external blocks to prevent the selector switch moving to the auto position  - and doesn't require the gear box removed from the lower receiver. Essentially, a washer is inserted, sitting on the rear retaining pin, between the gearbox and the passenger side of the lower receiver. As long as its a snug enough fit, this has the effect of preventing the rearward movement of the selector plate.

 

The easiest way i found to locate a washer of the perfect size was to 3d print one from an existing free file on the net, and simply scale it up until it fitted perfectly- albeit with a little trial and error I'm sure this isn't necessary and standard metal washer(s) would work. As i went as large as i physically could, there was a little interference between the washer and the lip of the top receiver when snugging the two back together, that i rectified by shaving a tiny amount off the top outer of the washer (obviously super easy with a plastic 3d printed washer using a knife when it was in-situ). If people have access to a 3d printer, the file for the washer that i used was this one https://www.thingiverse.com/thing:3178444/files    an m6 washer, which I scaled up width wise/z axis to 195% (resulting in it being circa 3mm thick), and increased the diameter to 105% (resulting in the diameter being 13.1 mm, and the resulting hole in the middle of the washer being very slightly larger than M6.

 

Seems to work perfectly, with no movement of the safety selector possible past semi. I perhaps might worry that the selector plate could be damaged if someone tried to put ludicrous pressure on the selector switch, but i don't think that is likely - not least as the selector switch is pretty stiff anyhow on the CM098.

 

As an aside, if anyone is interested, the CM098 that I just purchased from Patrol Base arrived doing circa 300FPS on a 0.2BB. The spring was super short, and looked like an M90. The SHS M130 spring that I popped in took it to a consistent 430fps.

[Rogerborg]

On 05/01/2023 at 16:28, The_Lord_Poncho said:

The spring was super short, and looked like an M90

 

Same with my CM.516, I'm pretty sure either PB (or TaiwanGun, upstream) just lop some coils off of the stock spring.

[Shamal]

They are probably all cut to order from a mile long spring 😂😂

[Impulse]

The springs in the SR-25 are cut as they come out of the box at 460fps, so the springs get clipped when they're imported.