What is the difference between bore-up kits and standard?

[outrider]

I would like to upgrade my cylinder head and piston head to a silent piston head set for my AUG. I have a bore-up kit installed.

My understanding of the clearances involved would indicated that the ID (inner diameter) of a bore-up kit can not be any larger then stock. I also don't think the nozzle can be any bigger because it still has to fit into the same hop-up.

The only difference that I can see is the bore up cylinder is not slotted like the stock cylinder is.

Has anyone every used a micrometer to measure the ID of the cylinder or the nozzle?

Has anyone experimented with non-bore up parts with a bore up kit?

[TriChrome]

Bore-up kits are larger not in their external dimensions (so they still fit in the same gearbox shell, same hop-up, etc), but the internal dimensions.

The internal of the cylinder is bored out to a slightly larger dimension than stock. Subsequently the cylinder head and piston head is larger as well. The inside of the nozzle is bored out more as well, so the part of the cylinder head it sits on is larger than normal.

You can't use non-bore-up parts in a bore-up setup because of these size differences.

Also, on a semi-side note; don't believe people when they tell you a bore-up kit increases FPS. They do not increase FPS over a similar non-bore-up setup with a good air seal. If you're maybe running a 650+mm barrel with a closed cylinder, then is the only time you might see a little boost in FPS because of the slightly larger volume of the cylinder.

[ShelledPants]

You only need a bore up kit when the volume of a closed cylinder is less than the volume of your barrel. By boring up the cylinder, you increase the volume of air, allowing you to have a longer barrel without the risk of BB suck as the piston is pulled for it's next cycle.

EDIT: As TriChrome stated, you need a very long barrel for this to be useful.

[TriChrome]

By "BB suck" do you mean that there's actual reverse pressure in the barrel from the piston on it's back stroke which negatively affects the BB? I hope that's not what you mean because that's physically impossible to happen on Airsoft guns (the BB has cleared the barrel long before the piston starts to be drawn back again for the next shot).

And for bore-up kits, you don't need a long barrel to utilize them. They can be bought with ported cylinders from MP5K to M16 length. I run them in all my guns (mainly M4 and MP5 length), because I like the quality of the parts (and in 4 years of running heavily modified guns I've never broken one).

[ShelledPants]

Originally Posted by TriChrome

By "BB suck" do you mean that there's actual reverse pressure in the barrel from the piston on it's back stroke which negatively affects the BB? I hope that's not what you mean because that's physically impossible to happen on Airsoft guns (the BB has cleared the barrel long before the piston starts to be drawn back again for the next shot).

And for bore-up kits, you don't need a long barrel to utilize them. They can be bought with ported cylinders from MP5K to M16 length. I run them in all my guns (mainly M4 and MP5 length), because I like the quality of the parts (and in 4 years of running heavily modified guns I've never broken one).

I'm referring to the slight vacuum a bb would cause when it runs out of pressure exerted by the piston. It wouldn't cause the bb to stop, by any means, but it could have bad effects on the bb's backspin.

[Skruface]

Bore-up cylinder sets are meant to be used with M130 or higher springs.