I replaced the stock plastic bushings in the mechbox with bearings. What bearings do is reduce the friction between the gears and the bearings. Less friction means they spin easier/faster.
Having said that, whenever you "upgrade" your gun you run the risk of it dying that much faster.
Another way to increase your ROF is to run a higher voltage battery... HOWEVER... doing so also increases wear and tear on the gears which will result in the blowing of a gear.
When upgrading, it's usually not a matter of IF you'll blow a gear, it's a matter of WHEN it will happen. From experience, I know you tend to run into more problems the more you upgrade your gun. More powerful springs lead to more gear wear and motor stress.
If upgrading your spring, you also MUST upgrade your bushings. Oiless metal bushings are durable and may last you for years. However, friction will be the same between metal and plastic bushings. Bearings will allow your ROF to go back up after the addition of a more powerful spring, but they will generally NOT last as long as a new set of metal bushings.
And when a bearing blows, you WILL need to replace a set of gears.
Basic "Level 1" upgrade: Systema M100 Spring (330-350fps), Systema Oiless metal bushings or bearings, new gear shims, original OEM gears.
Basic "Level 2" upgrade: Systema M120 spring (400fps), Systema Oiless Metal bushings, shims, High Torque gears,
Possibly a 9.6v battery and/or tightbore barrel.
WTF are you doing "Level 3" upgrade: 10.8v battery, high torque 2 gears, Systema M130 (or higher) spring, bearing spring guide, metal bushings (don't even try bearings), shims, possibly a tightbore barrel.
The level 1 upgrade gives you decent durability, it's pretty cheap, and a decent performance boost.
Keep in mind that if you ever plan on using your PR in a skirmish in THIS country, many locations have a 400fps limit. Some even run a 300fps limit. Honestly, unless you're running a sniper rifle there's NO REASON you need an airsoft gun that shoots in excess of 400fps. Unless you're using it to keep coyotes or dingos off the ranch.
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