[richs]

I'm going to follow this too... I have a pair of E1-M28's with new cylinders, pistons and springs. Be watchful over the cylinder, both guns had failed with cylinder issues independent of the piston.
I added the BV3/BV7 upgrade kit, it has performed flawlessly. One note, the FPS remained > 530 with the entire kit installed, but with the STOCK spring in the kit, the FPS was ~400 - 420. With the stock spring, they are 'legal' at most arenas. If I can figure a way to pull the catch pin and pull the cylinder without complete disassembly, then a quick swap is possible.

 

[richs]

BV3/BV7 upgrades? Could you elaborate please?

That's what happens when your memory is reduced to flash-backs...
I meant "WELL Spring Rifle Upgrade Kit (for MB03/MB07)". The piston is a little shorter than the M28 piston (but it's aluminum, not plastic) but the spring is a bit longer to take up the slack. I have it in both M28's and they've been shooting great!

 

[richs]

Ok, here's the dope on the MB03/MB07 upgrade kit:

• WELL Spring Rifle Upgrade Kit (for MB03/MB07)
• Drop in upgrade kit for WELL MB03/MB07 Spring Rifles
• Includes Spring, Spring Guide, Piston

The boys at Airsoft Atlanta let me try several pistons, until I found this one fit almost perfectly.

The first pic shows the spring guides, notice the upgrade one is a bit shorter.
The next shows the pistons. Again the new one is shorter. I used a micrometer to verify they are the same diameter.
Next is the springs. The new one is the longer one, it provides 530FPS while using the old spring with the kit, the FPS drops to just at 400.
next shows both sets assembled, and the new kit is a total of 1/4 inch longer.

 

[richs]

Here's the upgrade in action:

1. Upgrade kit installed
2. Bolt installed in receiver
3. Bolt closed
4. Bolt cocked - sears holding fine\
5. Spring fully compressed in the receiver.

All I did to the kit was to NOT use the bearing kit included. Every time I attempted to use it, the sears would NOT catch. I suspect this may be the problem you've had.

 

[richs]

That may be the key, is to omit the bearing guide parts.

Yeah, now the only weak link is in the cheep metal of the cylinder. Both my M28's had bad cylinders, and were replaced with original Echo1 units I found on eBay. The stress of the heavier springs will take its toll on the pressed fittings for the bolt lever. I'm not looking to steal ~Ranger~'s thunder on his pistons, they are PERFECT replacements. Now if we can get him to make the cylinder in stainless steel, I'd be the first to order a pair of them.

 

[richs]

I have found that by using the ORIGINAL spring with the upgrade kit (instead of their longer spring) the FPS dropped to ~400 and the bolt was a lot easier to pull back. However, what I did find is the set pin (or Spring Guide Stopper) would be loose and would fall out if the body didn't hold it in. The pin uses the spring force to hold it in place, but with the shorter spring, it doesn't have the power to do that.