Need help with design and measurements (.45 bigbore)
First post on this forum, so hello all.
I’ve been dreaming of my own big bore airgun for quite a long time now. Now that I have access to a lathe and a milling machine (not CNC though 🙁 ) maybe my dream can finally become true 🙄
The design that the talon gun uses looks rather simple and most of the workpieces not too difficult to turn. However, not having a factory-made talon gun myself (and not having the money to buy one, yet), I haven’t been able to disassemble one and look at the design more profoundly.
So, here’s what I’ve come up with: http://www.aijaa.com/v.php?i=3647467.png
The barrel’s inner diameter is 12 millimeter/0.45″ hydraulic tubing (700mm/28″ long), and the regulated air reservoir holds 800 PSI of pressure.
My main concern is the valve design, as it involves rather elaborate physics. How large should the valve stem inner diameter be to allow free air flow? Or the hole through which the air escapes from the reservoir? What about the stem excursion? In this picture the maximum free excursion is 10mm/0.40″, will it ever go that far?
I will be using as heavy hammer and as strong spring as possible. I’d just love some help with the valve measurements so that the gun would work in the first try.
Any help is appreciated 8)
All Replies
Viewing 12 replies - 1 through 12 (of 12 total)
i have a few spud cannons i made i dotn use a flamable source i just use a 2 inch dump valve hooked up to a chamber or compressed air i compress it to 150 off my shop compressor with the original bbl that was 12 inches it would jut go flop but then i made the bbl48 inches and it now launches a potato over 400 yds very very fast, low pressure very big bore (2 inch) and a long bbl it give it time to get all pressure in bbl i have a sprinkler valve on order now for it so it is just an electronic button to launch it
mine looks like this minus the spinkler valve currently
http://www.spudtech.com/detail.asp?id=52
ok sorry to hijack the thread just giving my input on big bore low pressure
.357 / 9mm, is a nice intermediate caliber.
This barrel is cheep , $27 +shipping. It has 10 grove rifling that works good for airguns.
http://www.e-gunparts.com/DisplayAd.asp?chrProductSKU=957250&chrSuperSKU=&MC=
There are lots of bullets available, from 80 grains on up.
Its much less trickey to get power in this caliber.
A chronograph is a necessary tool to get a homebuild tuned up and working correctly. A chrono costs about $100.
The machining is only 1/3 of the project, the rest is tuning and finishing.
Yes .118 is enough for the rod. The seal on the rod needs to be constrained from movement in both directions on the rod. I use a hardened screw insted of the rod. That way ,I can thread the seat, and screw it on (I also super glue it) to the hardened screw. Then You turn the screw and seat into the valve stem. This allows adjustment of the tophat height using the hardened screw.
These guns require a very large volume of air in a very short time (like 5 milliseconds) to get any power. If you use a hose to carry the air to the gun, you will not get the quick, high volume blast of air that is necessary to generate power. The same for the requlator. If the regulator is not specificaly designed to deliver high volume very quickly, you will not get much power.
800 PSI is just too low for a bigbore. Build the valve to go directly into the paintball tank and use the full 3000 PSI.
My valve only opens about .2 inch. It is mechanicaly limited to .2 inch. More than this and it becomes harder to get the valve to close, and the tank dumps all of its air on the first shot. Theres a lot of tinkering involved in getting a valve to work correctly.
Valve theory / drawing:
http://talonairgun.com/forum/viewtopic.php?t=4705
Mark
Very helpful as usual, thanks!
My plan really is to use a secondary, regulated chamber of air of 800 PSI that is about the volume of the barrel + pellet chamber. The air to the chamber is transferred through a hose, and all the 800 PSI air in the chamber is available immediately through the valve. So there’s no risk of losing all the air from the bottle with a single shot, as the air does not flow quickly enough through the hose (yet quickly enough to fill the chamber during reload). Does this sound reasonable? I read somewhere that there was a regulated bigbore using lower pressure (below 1000 PSI) air and it did deliver, thanks to the long barrel.
Why not scale down a notch.
.357 / 9mm, is a nice intermediate caliber.
This barrel is cheep , $27 +shipping. It has 10 grove rifling that works good for airguns.
http://www.e-gunparts.com/DisplayAd.asp?chrProductSKU=957250&chrSuperSKU=&MC=
There are lots of bullets available, from 80 grains on up.
Its much less trickey to get power in this caliber.
A chronograph is a necessary tool to get a homebuild tuned up and working correctly. A chrono costs about $100.
The machining is only 1/3 of the project, the rest is tuning and finishing.
Yes .118 is enough for the rod. The seal on the rod needs to be constrained from movement in both directions on the rod. I use a hardened screw insted of the rod. That way ,I can thread the seat, and screw it on (I also super glue it) to the hardened screw. Then You turn the screw and seat into the valve stem. This allows adjustment of the tophat height using the hardened screw.
These guns require a very large volume of air in a very short time (like 5 milliseconds) to get any power. If you use a hose to carry the air to the gun, you will not get the quick, high volume blast of air that is necessary to generate power. The same for the requlator. If the regulator is not specificaly designed to deliver high volume very quickly, you will not get much power.
800 PSI is just too low for a bigbore. Build the valve to go directly into the paintball tank and use the full 3000 PSI.
My valve only opens about .2 inch. It is mechanicaly limited to .2 inch. More than this and it becomes harder to get the valve to close, and the tank dumps all of its air on the first shot. Theres a lot of tinkering involved in getting a valve to work correctly.
Valve theory / drawing:
http://talonairgun.com/forum/viewtopic.php?t=4705
Mark
Airbrain,
Don’t worry about the accuracy yet. I’ve got a .62 smooth bore that can hit a 4″x4″ target at 40 yards all day long. The trick is in the slugs not in the barrel. So long as the barrel has a reasonably smooth interior finish you’ll be ok. For slugs, you’ll want to find something with high base drag to stabalize them. You’ll probably want to order a custom sizing die from Lee to get the fit just right also.
Airbrain:
GOOD DRAWINGS!
I would move the valve seat all the way to the left, so its not thinning out the crossection of material on the threaded end that screws into the tank.
For 3000 PSI in the tank theres 1800 pounds trying to push the valve out of the tank.
The 3 ports on my valve stem are about .2 inch in diameter.
Use the paintball tank, without the regulator.
heres another link that might help.
http://talonairgun.com/forum/viewtopic.php?t=1286&highlight=
Mark
That would be a good idea if I weren’t a student with little money and only limited chaces of using the machines. So I’ll go for the beast first 🙄
800PSI is low, but as I already have some paintball accessories that allow me very easily to plug a 800PSI regulated source in the gun, I’m going to use it. Surely it can propel a pellet to a reasonable velocity (i’ll turn my own custom pellets)
Using the numbers given by Mark (and reading other posts for inspiration), this is what I got
There’s three 0.118 holes in the middle of the valve stem where the rod begins. Are these measurements OK? Should there be more sealing surface? Is the rod thickness (0.118) and stem tube wall thickness (0.059) sufficient, given I’m using 316 SS and this valve will withstand 3000PSI of pressure in the future?
Well, it’s a steep learning curve and an obsession for most of us….But with tube like that for a barrel, I doubt you could get 5 shots in 2 feet at 10 yrds….. I once tried a smoothbore (mfr. defect) airgun at 10yrds, and that was the best I got.. Now some smoothbores can shoot well, but the barrels are choked and have other very fine details that make them shoot well.
Anyway, the tube would have to be .458-9 to shoot .45 ammo at all, so I think the best course of action would be to find a used talon, tinker with it and then build a monster later on..
Check out Cyngus’s post:
http://talonairgun.com/forum/viewtopic.php?t=195&highlight=457
Valve stem diameter = .437 inch
orifice passage to tank = .300 inch
You need a very stiff spring to open the valve.
no “o” ring is required on the valve stem, just make it a close sliding fit.
You are using 800 PSI source??
That sounds too low to generate any power.
A regulated source may not work too well, as a 45 barrel requires a huge volume of air, delivered in a very short time.
I sugest that you start small and work up to .45, to gain experiance.
Mark
Well, it’s a steep learning curve and an obsession for most of us….But with tube like that for a barrel, I doubt you could get 5 shots in 2 feet at 10 yrds….. I once tried a smoothbore (mfr. defect) airgun at 10yrds, and that was the best I got.. Now some smoothbores can shoot well, but the barrels are choked and have other very fine details that make them shoot well.
Anyway, the tube would have to be .458-9 to shoot .45 ammo at all, so I think the best course of action would be to find a used talon, tinker with it and then build a monster later on..
P.S: Langnasen may also be able to assist…
Thanks for the reply, Critter.
Yeah, I’m aware of the barrel problem. But being my first airgun and just a prototype at that, I’m willing to sacrifice some accuracy for power. After all, in the 18th century most barrels were smoothbore 😉
The gun would be used for mere silhouette shooting and plinking. Later I could buy a proper barrel or machine one from solid bar and let some airgunsmith do the rifling.
I’ve been reading Mark’s (MM123522) posts with great interest and it looks like my valve design is doomed to failure 👿
Well, the first concern is that you need a real barrel, not tubing. Sorry, but if you want to hit anything at all you’ll need a rifled barrel. I suggest you contact Don G. (shrpshotr28) about it, he can give you excellent advice. Second, the valve….I know close to nothing about valves, but I know the valve GOD, Sean… (blodnob) can tell you everything you will need to know.
P.S: Langnasen may also be able to assist…
Viewing 12 replies - 1 through 12 (of 12 total)
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Airbrain:
Check out this post:
http://talonairgun.com/forum/viewtopic.php?t=4153&highlight=
Mark