There SHOULDN'T be any benefit to a gas check in this system. The major selling points of a gas check are:
1. Velocities (generally) in excess of about 1600 fps. It's actually more pressure-based, but an easy mental divide is handguns (if all else is adjusted correctly) won't need one, and smokeless rifle speeds will. The check acts as a driving key of harder material that prevents the softer bullet stripping out in the lands
2. Useful when using softer alloys than idea for the pressure/speeds encountered for the sake of bullet expansion.
(Given the blunt nature of the likely projectiles, a slower rate of rifling twist will help with 1 and 2)
3. If you don't have exact control or knowledge of matching up your bore and bullet dimensions, it's OK to err on the side of gas checks.
Seems to me that the pressures are high enough to justify bullet "lube" which serves as a gasket, but I'll admit that this "BB gun on steroids" is a bit outside my wheelhouse.
I remember Lewis and Clarke's air rifle took 1200 strokes to charge it. It had a point so you could stick it in a tree to hold it while pumping. That's a lot of maintenance. I bet the OP's air rifle would take 3000 strokes. If it's possible to hand charge it, and since he has an electric pump, I don't know why you would want to do it by hand.
Concealed carry is for protection, open carry is for attention.
I actually have a high pressure hand pump that looks like the kind you'd pump a bike tire with. It takes about 300 pumps to get to full. One asthma attack later and I spent the money for the electric pump. It's good as a backup or for top offs though.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
How long is that barrel? Just curious. After all, more barrel, more potential for velocity as long as the gas volume (pressure) remains high.
Also, I wouldn't worry too much about forcing those bullets through at 3000 psi, it means there's about 589 lbs of force behind those big bullets pushing them out the front. That should be enough to get them going.
Btw, what does the rifle weigh?
Never argue with stupid people, they will drag you down to their level and then beat you with experience -- Mark Twain How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
It's a 25.5 inch barrel. It was a 27 inches but things happened lol. I've not weighed it yet but it's heavy, probably 12 lbs but I'm going to trim some weight from it in different areas. Opening up the plenum to increase volume alone will drop some weight from it. It works fantastic, I just need to get the shot count and velocity where I want it to stay.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
It looks like a really fun project and sounds very promising.
Take a few more data points, the more the better. You'll find your optimum plenum volume in short order. You already have at least two, take a few more around 2 to 3.5 kpsi at different volumes (4 in^3, 6 in^3, and so on noting the velocities). I don't think you'll have to take too many since 5 cubic inches at 3 kpsi seems to be working great already.
How many shots per tank are you hoping to get?
Never argue with stupid people, they will drag you down to their level and then beat you with experience -- Mark Twain How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
I'm thinking that I'll be able to get 4 to 5 full powered shots once I open the plenum to 8 cubic inches of volume. I should be able to keep the velocity over 1300fps per shot. The nice thing about running a regulator is that all of the shots above the regulator pressure stay nearly identical in velocity until you drop below regulator pressure. Also, here's an updated pic shown without the tank. I'm going to put a carbon fiber tank on it. Apparently they weigh about 2lbs less than the current aluminum one that I have.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
That thing is just beyond cool! the new tank might make a great forend.
I like your comment about the design in your head. You might be shocked or maybe not that many engineers work that way and just polish up the design later. I am an engineer / machinist wannabe and just love to see wild notions go to functionality.
What's the size of the carbon fiber tank you plan to use? What's the physical volume (i.e. 1/2 L) and how much pressure can you run it up to? What's the final weight gonna be, any estimates? Maybe, 9 or 10 pounds?
Sorry for all the questions but inquiring minds want to know.
😏
I'm guessing your target velocity is around 1300 fps with those 250 grain bullets, is that correct or are you shooting for something else?
Either way, that's a lot of smackdown going down range.
Never argue with stupid people, they will drag you down to their level and then beat you with experience -- Mark Twain How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
I'm not sure on the final weight just yet but I'm guessing around 8 or 9lbs once I get the lighter bottle. The current bottle is .45 liters and can be pumped up to 4500psi. If I shoot this regulated, then the tank size will directly determine my shot count.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
I want to go on record. I want serial #2 when you go into production 😎
(assuming your keeping #1 🤣)
There's definitely a huge market for airgunners and air guns. I never knew it until I got into it and started watching YouTube videos of all the different PCP rifles and hunts. I've been enjoying my airguns more than I do my powder burners lately, maybe just because it's different or maybe because they have come a long way. I would like to sell these but I'd have to find a company that could pump out the parts via CNC because I made this one all manual machining and it took more time than would make it affordable.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
Reminds me of that Battlestar Galactica episode, The Lost Warrior (1978) were all the inhabitants ran around with a Pneumo (air rifle or air pistol).
Oh yes, good times.
Anyway, have you decided on what regulator pressure to use?
Never argue with stupid people, they will drag you down to their level and then beat you with experience -- Mark Twain How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
I think I'm pretty well set at the bottle pressure being 4500 and the reg set at 3000. I just need to increase my plenum volume to 8 cubic inches and I should be in the goldilocks zone. That should give me 4 to 5 shots at around 1300fps. Plenty to hunt. If I want to punch paper I can cut the regulator to 1800psi and get quite a few more shots in.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
When I fire it unregulated at 2500psi, it is dumping about 31 cubic inches of air in 1 shot which is where I got the 1417fps. I fired it today at 3000psi, regulated only dumping 5 cubic inches and it achieved 1397fps with a few more shots left over. I'm going to have to come up with the proper pressure and plenum volume to achieve the highest velocity and also highest shot count because it's a pain to pump back up.
...
How many full power shots in all did you get before with only using 5 cubic inches (~82 ml, cc)? That seem to work pretty good.
Just wondering.
Never argue with stupid people, they will drag you down to their level and then beat you with experience -- Mark Twain How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
I want to go on record. I want serial #2 when you go into production 😎
(assuming your keeping #1 🤣)
There's definitely a huge market for airgunners and air guns. I never knew it until I got into it and started watching YouTube videos of all the different PCP rifles and hunts. I've been enjoying my airguns more than I do my powder burners lately, maybe just because it's different or maybe because they have come a long way. I would like to sell these but I'd have to find a company that could pump out the parts via CNC because I made this one all manual machining and it took more time than would make it affordable.
I understand but in general you probably are aware that folks will pay a premium for one of a kind custom things. Just giving you something to think about. 🤣
Japhy posed an interesting question. Why not a 30 cal? With 150-165 gr lead bullet you would get more shots, less recoil, less weight, and possibly high velocities. The twist rate would be the only challenge. A 100 yard deer killer and 300 yard gong ringer.
You could even go 357 cal, a 158 gr bullet....there are a number of bullets designed to work at lower velocities and there are NEF and contender barrels available.
When I fire it unregulated at 2500psi, it is dumping about 31 cubic inches of air in 1 shot which is where I got the 1417fps. I fired it today at 3000psi, regulated only dumping 5 cubic inches and it achieved 1397fps with a few more shots left over. I'm going to have to come up with the proper pressure and plenum volume to achieve the highest velocity and also highest shot count because it's a pain to pump back up.
...
How many full power shots in all did you get before with only using 5 cubic inches (~82 ml, cc)? That seem to work pretty good.
Just wondering.
The issue I'm having with what I did above is that it's not being reliable in that configuration. It keeps sticking the valve open and then it becomes a single shot so I've been taking it to 2500 psi which isn't pushing as fast of velocities but the valve doesn't hang open. I need to be above my regulator pressure though. I ordered some expensive ptfe orings which should get me back on track. It's amazing the variables that airguns have.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
With a starting pressure of around 2500 to 3000 psi, a 5 in^3 plenum and a 25.5 inch barrel, I figure your exit pressure is in the neighborhood of just under 1500 psi. That would be kinda like a 28 guage shotgun going off, I imagine.
I can also imagine the recoil is pretty noticeable and if you reduce the weight from a possible 12 lbs to 9 lbs, the recoil is gonna go up by about 33%, that'll get your attention.
Considering the volume of air you're pushing through, I wonder if a brake would settle things down a bit on recoil. 🤔
Just musing out loud. I can't wait to see what you come up with.
Never argue with stupid people, they will drag you down to their level and then beat you with experience -- Mark Twain How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
You should watch my facebook video. It's centerfire loud.
NOT a firearm so you can put a suppressor on it 😎
Well, apparently some guy got busted with an airgun suppressor on a firearm a few months ago so the feds went to Donnyfl, who is the leading manufacturer of airgun suppressors and shut him down saying that airgun suppressors are firearm suppressors because they can be placed on a real firearm. The strange thing is that they have been legal for decades and all of a sudden they aren't. Where have I seen that before? They aren't even threaded to fit firearms. A person would have to be able to make an adapter. Because I have the capability to do so, it's easier to just not take the risk and be accused of "intent."
We've been conditioned to believe that obedience is virtuous and voting is freedom-
Well I was having issues with my valve sticking open when taking it up to full pressure. Seems that nitrile orings don't like extreme pressures in a dynamic environment. I ordered some high dollar teflon orings that I wasn't sure I'd be able to install because they're so stiff but finally managed to with some choice words and a tapered mandrel. No more valve stick! I can finally get it dialed in now.
We've been conditioned to believe that obedience is virtuous and voting is freedom-
Replies
1. Velocities (generally) in excess of about 1600 fps. It's actually more pressure-based, but an easy mental divide is handguns (if all else is adjusted correctly) won't need one, and smokeless rifle speeds will. The check acts as a driving key of harder material that prevents the softer bullet stripping out in the lands
2. Useful when using softer alloys than idea for the pressure/speeds encountered for the sake of bullet expansion.
(Given the blunt nature of the likely projectiles, a slower rate of rifling twist will help with 1 and 2)
3. If you don't have exact control or knowledge of matching up your bore and bullet dimensions, it's OK to err on the side of gas checks.
Seems to me that the pressures are high enough to justify bullet "lube" which serves as a gasket, but I'll admit that this "BB gun on steroids" is a bit outside my wheelhouse.
"Nothing is safe from stupid." - Zee
Luis
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
the new tank might make a great forend.
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
(assuming your keeping #1 🤣)
It’s a °IIIII° thing 😎
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
It’s a °IIIII° thing 😎
You could even go 357 cal, a 158 gr bullet....there are a number of bullets designed to work at lower velocities and there are NEF and contender barrels available.
OH! The possibilities.
It’s a °IIIII° thing 😎
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
It’s a °IIIII° thing 😎
It’s a °IIIII° thing 😎