Flounder wrote:I am at a loss for the required information for the valve information. I plan to use Mcmaster Carr part number 6646K23 That I have seen used for several builds on the forum all ready. Any advice you can provide would be appreciated.

This should give you a very good approximation:

Thank you for that information. I had to poke around to find how to change Flow Coef to Cv instead of %.

On to another question. Has anyone tried using a slide gate valve for a breech? I have found a few but they only have a 40 psi rating. I think that would be ok since I am running relatively low pressure in this thing, but I was hoping for input from the people who have been doing this a long time.

should be okay, you still wanna make sure your ammo is ahead of the valve outlet while keeping the dead space to a minimum. a lot of designs like the coaxial gun in the website banner used built in ram rods to push ammo into the correct side pipe fittings

A lot of other breech designs incorporated these camlock fittitings which weren't exactly high pressure fittings either I'm sure a 40psi gate valve is at least as strong

Flounder wrote:Has anyone tried using a slide gate valve for a breech? I have found a few but they only have a 40 psi rating. I think that would be ok since I am running relatively low pressure in this thing

I can't think of any examples but you should be fine, peak pressure in the barrel is usually significantly less than the chamber pressure and in any case it only spikes for a moment. GGDT will actually give you an indication of barrel pressure if you select the correct Y axis on the graph bottom left.

using GGDT I came up with a peak of less than the 40 psi limit. I also sourced an old oxygen tank today for free while out at a paintball event. I may end up using that for my pressure chamber instead. Hope to have a firing unit next weekend and then start building the carriage for it the following week if my work schedule permits it.