Parts question.

[cougar20th]

So new R7 owner.

Most everything so far makes sense to me. But what is the black piece that is in the frame where the transfer port to the valve is? And what does it do?

[Jackson]

I think you are talking about the magic nipple. The idea is that it forms a seal on the transfer tube but the transfer tube should have a light file mark on it to create a leak that slows down the recharge rate of the valve chamber. The idea being that this keeps liquid CO2 out and improves 12 gram efficiency.

[cougar20th]

Interesting

[russc]

There's basically two schools of thought in Nelson tuning - tune for gas, or tune for liquid/vapor. Tuning for gas is what you see in the R7, Carters and Phantoms. Big powertube bores, vertical cartridges, large-ish valve body volumes. The other school of thought minimizes expansion between the cartridge and the valve, resulting in a vapor mix of gas and liquid going down the power tube and expanding on the way out of the barrel.

In both cases, sending excess liquid (as in, it isn't doing useful work for you) down the barrel kills your efficiency. That's why liquid/vapor tuning can be helped with devolumizing. To stop liquid from making its way into the valve body upon first piercing the cartridge, we put the magic nipple in the transfer port to act as a bit of an orifice and damp that initial flow.

I personally have a preference for gas-tuned Nelsons, you tend to get a flatter velocity vs, shot # curve as you go deep into the cartridge. The downside is it tends to be a little more cold weather sensitive since you need to expand the CO2 in the gun.