MEGGA VALVE, 458 PROJECT– === 790 FPE ! =================
I BEEN BUILDING THIS .458 CAL. AIRGUN
WITH A 44 INCH LONG BARREL.
GOT 903 fps WITH A 300 GRAIN HARDCAST BULLET.
THAT WASNT ENOUGH, SO I BUILT A NEW VALVE THIS WEEKEND.
I’AM STILL IN THE TESTING STAGES WITH THE NEW VALVE.
THE OLD VALVE HAD A .437 DIAMETER STEM.
THE NEW VALVE HAS A .520 INCH DIAMETER STEM.
I.D. OF THE HOLE IN THE STEM IS .397 INCH.
ORIFICE DIAMETER (SO FAR) IS .305 INCH.
PORTS IN THE STEM WERE CUT WITH A .25 ENDMILL, THEN FILED OPEN.
THE SCREW FOR THE VALVE SEAT IS 6-32.
SOME OF THE STRENGTH OF THE VALVE IS LESSENED BY THE INCREASED VALVE STEM DIAMETER, SO THIS VALVE IS BUILT FROM 85,000 PSI TINSLE STRENGTH STEEL.
I GOT 543 fpe WITH THE OLD VALVE AND 300 GRAIN BULLETS.
HOPING TO ACHIEVE NEAR 600 fpe, MAYBE NOT! , BUT I’AM GONNA TRY.
THERE IS A TALON ss VALVE IN THE PICTURES AS A SIZE COMPAIRSON.
THE “PELLETS” ARE 21, 300 AND 500 GRAIN.
Mark
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Vulture is taken 🙂
a name yes indeed Mark????? 🙂
Did you give it a name yet?
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That’s justTO MUCH! :10
Not in the way it sounds. mean “FUCK’N AWESOM!
Deer\Large game with a .40 cal. AIR Propelled BULLET!
You know, You guys doing this mind blowing stuff; All that is REALLY NEEDED is the ability to make\overcome the single shot action crap.
I’d say 3 shot semi auto. for sure.
:4
Even too much for the inner home protection. (for hunting of course) I’d love to have an Air Rifle that could devestate a criminal in my home yet not go through walls into sleeping of hiding family members.
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Planning on putting a full shroud on that puppy ?
That’d be as mad as a sack full of ferrets.
Congratz Mark!!!
Lots of power for sure!!
great stuff on that , major power blowing out of that thing .
how come you dont use a delrin disk seated in side the valve and have a all metal stem , could shorten the stem by half if the seat was plastic insted . , less to move and push the air back .
everyones got different ideas , ?
Holy Smokes! Look at that barrel ). If you miss the deer on the first shot you can always just bang him over the head with the barrel ).
EXCELLENT WORK!!!
Voltar_1
Your explanation for the cold tank makes sense.
Yes, I fill the tank, let it cool , then top off, so the pressure is highest.
Again, thanks for the tip on the barrel!.
73 cubic inch sounds about right for a big bore.
I am only using the small 22 cubic inch tank , because its quick to fill and discharge.
The front “endcap” is long to support the thin barrel. It incorporates two plastic bushings to “float” the barrel. The bushings are a tight slip fit. Theres about a foot of unsupported barrel, hope it doesnt “whip” when fired.
The rear barrel bushing has 6 setscrews holding the bushing to the barrel.
Theres three 1/4 -20 set screws holding the bushing to the frame.
Next – I gotta build the grips.
Go for it Voltar!!
Mark
Mark, this is fantastic!!!!!
okay now you got me fired up :):)
cold tank, same pressure? air is more dense so more energy packed into the tank. Making more power makes sense for sure.
The trick of course is to get the cold tank up to a full pressure vs a hot fill that cooled. That would give roughly equivalent energies.
You have done very well on this project and have every right to be very proud of this accomplishment. Extra fun when all that is purchased is a barrel and tank eh?!!! 😉
So what do you attribute the power to? any tips??
oh yes and if the shot sounds clean and crisp that is a very good sign.
I just received a couple 73 cu inch 3,000psi tanks by mistake and may need to adapt one to my .458 and see what that will do.
Cheers
Walter…..
Voltar_1
Thanks !!
This hobby is an obsession!
I blew off work on monday and tuesday to work on gun (they are gonna fire me). Actualy, I was sick, but still got in some time on the gun.
Did many tunes on the gun/valve.
Just took a few test shots:
925 FPS, 300 grain, 2700 PSI fill, 570 FPE — warm tank
962 FPS, 300 grain, 3100 PSI fill, 616 FPE — warm tank
1002 FPS, 300 grain, 3200 PSI fill, 669 FPE — cold tank
I am pretty sure of these numbers.
My crono setup has a “blast shield” 12 inches from the muzzel.
The blast shield is a thick aluminum plate with a 1 inch hole to shoot through. Then I shoot through cardboard, and then over the crony.
With the cardboard and the blast shield, theres no blast hitting the crono.
Its funney, theres something about a COLD tank.
I been doing a lot of test shots.
My compressor is in the unheated garage.
If I fill a tank, and let it sit untill it is cold (35 degrees today), the gun shoots harder.
I have seen this over and over.
If I shoot with a warm tank, the crono numbers are lower.
I know the pressures are the same, but a cold tank hits harder.
The 1002 FPS number was with a very cold tank.
Been using a 22 cubic inch tank.
When I shoot, the tank pressure drops from 3200 to 1000 PSI — a 2200 PSI drop. Its not a tank dump, because the shot sounds short and crisp.
I havnt tried any heavy ammo yet, but Iam sure the FPE numbers will go up.
Most of the power is comming from the long barrel, 44 inches, almost 45 % longer than most.
At 1000 FPS, this thing will be flat shooting out to 85 yards!
Mark
Well done Mark!!
love the numbers!
What a huge valve stem….. mine will look small beside yours 🙂
Walter….
Yeah, the rear thread did look a tad small. Is that because the paintball tanks are cheaper and easier to find? I’ve thought of putting a small vertical chamber at the rear; it only has to hold enough air for 1 shot, after all; and relocating the main supply chamber forward under the barrel with a thin supply hose running back. Fine for a .22 but the big bores need so much airflow, even in .308 I think I’d run into problems so never thought seriously about starting that project.
Good stuff, Mark. Good luck on your hunt next year.
aloha,
walt
walt_in_hawaii & Shadoh:
The valve body is long because the valve stem is .520 in diameter.
There are no “o” rings sealing the valve setm, its just a close fit and the longer the valve stem the better air seal you get. You need 2 or 3 diameters (of the diameter of the valve stem) to get a good seal.
This valve has a paintball thread on the end — 5/8-18.
I couldnt make the .520 bore go all the way through this 5/8 section — it would be too weak. So the bore is .400 through that section. That means that the .520 part of the valve stem must end inside the long valve body.
Thats why the thing is so long.
selphb:
The barrel comes from “Track of the Wolf”. Its a barrel liner for a 45-70 trapdoor. 5/8 inch diameter O.D. and 44 inch long — 1 in 22 twist, only 3 lands.
The hammer is brass and weighs about .33 pounds (150 grams) and has a HUGE spring pushing it. The wire on the spring is .105 thick! The hammer stroke is 2.125 inches long. It takes a real man to cock this thing — thats why the cocking knob is so big.
rabbits:
This is gonna be my deer rifle for next november!
Mark
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Voltar_1
Wrote 650 or more fpe?
How’d you guys feel shooting these Air Rifles? Is it Pressive, or what? !!
:1