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
All Replies
Wow… That’s some great machining! Hey I was looking to start a valve project of my own and was wondering what the thread sizes are that attach to the gun and to the tank?
Did you use a paintball tank?
Mark, great numbers. I know what you mean about barrel length making all the difference when shooting for high numbers like that (pun intended, sorry); the only problem is, when I go chasing pigs, I don’t want to have to hitch up my gun on a trailer behind my car 🙂 Not that I haven’t thought about it, mind you, but it’s just so inconvenient when a deer or pig runs in front of your howitzer.
aloha,
walt
The muzzel blast on this thing will turn over a Mini-Cooper at 10 feet!!
If I shot all the way across the basement, that would work good.
Your right, soft lead is the right way to go.
Mark
Try 15 feet. You’ll loose about 10fps at that distance.
i dont think my valve could keep up with yours, might be close but you have taken the throne away….the king is dead…long live the king !
i have long thought about using a those wolf barre liners…but never got around to it
44″ is too long for me, but way fun just for the heck f it….you should try optain some balloon gas, its usually a mix of helium and air, perfectly safe for the guns, i wouldnt be surpriced if you get nearly 1000 fpe with it !
you should try and move the chrony back 6 feet or so….that should disapate the air trailing around the bullet….it shouldt change much in power, just to rule out any false chrony reading….also fluerecent lighting should be turned off…only old style glow bulbs if you wanna make entirely sure….
btw that kind of power is the same that a 44mag with factory ammo is putting out…not shabby at all
but man those are some number….big congrats !
BUTCHER45:
The muzzel blast on this thing will turn over a Mini-Cooper at 10 feet!!
If I shot all the way across the basement, that would work good.
Your right, soft lead is the right way to go.
Mark
Amazing. Simply amazing.
Consider getting a hold of some softer lead slugs for a possible increase in power.
Also, realize that if you put the chrony 10 feet away from the muzzle, you are only going to loose about 1-2fps max. This helps eliminate the airblast factor, without the need for screens and shields and such.
Thanks! for all the comments & encouragement!!
I am afraid, You guys are gonna think that Iam full of B.S. , but I just got 790 FPE!!!
1089 FPS, 300 grain hardcast bullet, 3200 PSI fill, very COLD tank,
790 FPE !!!
New changes:
1 Bored out the valve orifice to .340 inch
2 Sized the bullets to .455 (to cut drag in the barrel)
3 Trimmed the bearing surfice of the bullet (cut .450 bands in bullet to reduce friction)
4 Cooled the tank all nite in the cold garage
5 Increased tank size from 22 cu inch to 48 (keeps the pressure higher, for longer)
6 Shimmed the valve return spring (increased the valve spring preload)
7 Built a new “streamlined” valve seal.
8 Polished the internal surfaces of the valvestem.
9 Streamlined an area inside the valve.
I always wonder if the crono is reading correctly, but the amount of muzzel blast and the recoil both verify the 790 figure — THIS THING KICKS HARD!!
This cold tank thing is worth 50 FPS!! Without the cold tank , I think, this would be a 720 FPE shot.
Other shots this weekend (before the above mods):
780 fps, 500 grain, .332 orifice, 675 FPE (these bullets have a lot of surface dragging in the barrel)
1019 fps, 300 grain, .332 orifice, 692 FPE
There is no sign of “valve lock” , that is, not being able to pop the valve open. That means that I could open the orifice up a little more, but I think this is it — I am gonna quit here.
Pictures are of my crono setup:
The gun barrel goes into white plastic guides to keep it aimed.
There is an aluminum “blast shield” with a hole to shoot through.
The crony is mounted in a wood box, with a small hole to shoot through.
Also, I shoot through cardboard.
All this to keep the muzzel blast off the crony.
This crony looks beet up, but I have a brand new green one that I swap in once in a while, just to check this red one.
This is so far “over the top” that I am afraid you will think I am making this up. I know some of the moded DAQ guns, do 615 FPE. This gun is “inline” — the airflow is straight, while in the DAQ guns the air has to “turn around” 180 degrees. It makes sense that you can get more power with the “inline” configuration. Also, no one out there is using a 44 inch barrel, the longer you push it the faster the bullet goes.
Cygnus: Your right , combine your valve with a 44 inch barrel, and the numbers would exceed mine. Using barrel length, bullet weight and velocity you posted, I calculate your average barrel pressure was 1500 PSI.
This gun is only developing an average pressure of 1300 PSI, but it pushes for 44 inches insted of 30 inches.
Teflon Tron said:
Tron you were right! bullet friction was holding the numbers down.
Mark
Well said!! yes indeed a light bullet as that caliber is concerned.
very proud of you Mark!!!!!! keep going 🙂
nice work MM….wow 44″ that is long
@walt_in_hawaii if you where to use my valve with a 44″ barrel you should be able to get simelar power in the kit i sold you
i hit 605 fpe with 500 grain…MM have you tried using 500 grain slugs…you might be into the 700 maybe even 800 fpe with those !
Ya, I agree with Tef, try some 405gr solid 45-70 bullets, that should make some serious power!
For me, the most impressive part is that all of that power is coming with “only” a 300 Grain Bullet.
Nice gatling but I guess your rifle is more powerful 😉
Did you build the gatling gun yourself?
Wrote 650 or more fpe?
How’d you guys feel shooting these Air Rifles? Is it Pressive, or what? !!
:1
Matt, it is indeed pretty cool. I can only imagine what Mark has going on!!
like 150% of what I have :):)
Gonna figure out a way to get there mind you I ONLY have a 30″ barrel 😉
What is real cool is shooting out to 200 yards and making one 8″ hole in the snow with about 10 shots into it!
I can spank a 10″ rock out that far pretty dog-gone reglar…..
Waiting to see what Mark gets out of his……….
OOps! I’m sorry. 466fpe. Compared to a stock .22 of like 35fpe? Shit….
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CorMaster:
I think the gun side of the valve is 7/8-14
The tank side is 5/8-18 for a paintball tank.
The tank side is 18 MM – 1.5 for an AirForce tank
My valve is set up with paintball tank threads — 5/8-18
Mark