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: : : Daniel DeMerchant posted recently one of the major causes of noise in the M98, the sudden release of blowback gas as the O-ring on the hammer reaches the side slot. I have thought about this and discussed it with an engineer friend and here are several of my 2 cents on the subject. : : : My first thought was to port the receiver just ahead of the slot, allowing the gas to escape over a wider area; problem is it makes lots of entry points for dirt. : : : My next thought was to cut grooves on the inside of the receiver so that the gas could escape past the O-ring and be vented into the rear area of the receiver. There could be lots of grooves just ahead of where the O-ring would reach the side slot, and some longer ones to allow a gradual release of pressure. You would just have to be careful not to cut too many grooves or there may not be enough pressure to cock the hammer, especially with C02 pressure changes in different weathers. : : : So what you need is an adjustable vent of blowback pressure, just like with the RT! How about mounting the valve from an RT and adjusting it to release most of the pressure, leaving just enough to cock the hammer. The outlet from the RT valve could vent more gradually, perhaps in a silencer arrangement with wadding filled chambers, to deaden this sound. : : : My engineer friend suggested a wadding filled cover for the side slot, a much simpler idea than mine, and doesn’t actually make any changes to the receiver, especially if you already have rear cocking. : : : What is really required is a variable blowback in the valve so that only the required gas is released, you’d get greater gas efficiency and less recoil too. This would require a redesigned CVX valve, a bit beyond my scope. : : : Any constructive comments ? : : Your headed in the right direction. The gun tech at my local store has done some stuff with reducing blow back. However, he was trying to prevent the blow back from restricting the paint ball flow into the breach. I don't know if you've noticed, but the blow back will launch a paintball back into the hopper. I don't know if porting will reduce noise. I know my M98 is loud as heck. Mine shoots with a BING! BING! BING! I hate it, but I live with it. Maybe you can make some sort of muffle or silencer for it on the outside. Be careful. Don't start drilling holes unless your sure you know what your doing...or if at least you know you can fix it... : Hey... I am a friend of Dan's, we have been talking about this alot. : I just put a new rear velocity adjuster onto my 98 custom, I have noticed a big difference in blowback pop, and recoil! Dan's theory to me was... the stock setup relies on the velocity adjuster in front of the valve to reduce the air flow to the ball thus reducing velocity (but your rear bolt will always strike the valve with the same force (because the rear spring is not adjustable!), releasing a lot of blow back gas and causing major pop and recoil. : With the rear velocity adjuster, you open the front velocity screw up fully and rely on the rear spring (adjustable) to only open the valve as much as you need to get the right amount of air to the ball. : The gun runs twice as smooth. : I am currently running: : 98 custom : 14" ported barrel : rear velocity adjuster : star fire bolt : rocket cocker : 20 oz CO2 : coil remote : Viewloader 12v : I am extremely happy with my gun right now. it is quiet, super accurate, super reliable, very low cost. (I paid a total of about $250 for everything above.) : It's not a lot to spend to try it out. I would suggest it greatly. : John : P.S. check www.dickspaintball.com they have awesome prices on a lot of this stuff. I just got the package from the "SPECIALS" section that has --1 Ronin 4+1 pack, 4 PMI clear tubes, 1 20oz CO2 tank, and a 32deg. Coil Remote -- all for $55.00. : Good deal.