Extruder Barell
Hi Guys, had a thought today regarding barells. There was a company here in Australia in the early 90’s making extruder, or tapered bore barells for the .22LR rimfire. The idea was that the bullet was squeezed down from .22 to .20 or to .17 calibre on exit. This increased velocity by some margin, due to the higher pressure from the extruding process upon firing. These barells where made by Myra gunshop in Broken hill Australia. How effective they were i dont know in rimfire, there was someone in a forum saying they werent accurate. They have sinced ceased trading, i think the inventor died a while back. I even read the Germans had developed the idea in WW2 for there anti tank guns. The idea is sound, and does work, but aparently much too expensive to be practical. Anyway enough of the history of the idea, my thinking is would the same principle work in a PCP rifle? I have read that some of the .25 guys are getting pretty much the same velocities with heavier pellets in .25 as we get in .22 with much lighter pellets. Aparently the greater surface area of a .25 V a .22 makes the .25 more efficient. So if it where possible to make/buy a .25 barell that tapered to .22, or .177 would it generate higher velocitie by building up more pressure? I dont think there would be any problems with the pellet swaging down in the bore. I have been kinda thinking of ways to experiment with this idea, but tapering a bore is a big problem. I was thinking to take an old shitty .177 barell and bore the breech end to 5.5 and taper a forcing cone like in a shotgun. Any body have an idea that this will or wont work? or how it could be done? Imagine a .25 40gr pellet swaged down to .177 fired at around 1000FPS,i think the sectional density and BC would be awsome ! Any idea’s would be most welcome !
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A .177 barrel might be to thin to take the higher pressure needed to extrude lead. However, A deeply ribbed pellet could be the answer.
Maybe Jerry could make more deeply ringed pellet in .25 cal. that could squash more easily to .22 cal.?
I would think that you would get an extreme amount of barrel leading in a rifled bore. Extruding is usually done with smooth highly polished dies for wire. Other shaped extrusions are in a very straight form with no twist.
Frm what i can gather from old Shooting mags, the myra extruder barell increased velocities in the standard .22LR round. With initial velocity of 1280 FPS through an extruder Barell produced velocities of 1480 FPS. This is not stories these are verified results, the system does work. But as far as i can acertain the accuracy was not there. Not point in higher velocities if you cant hit anything. The idea to incorporate into a PCP would be a little easier than in a rifle shooting solid bullets. Remember a Diabolo pellet is a waisted design having only 2 friction points with the barell. And generaly of hollow design. I dont think there would be anywhere near the friction in a tapered bore with a pellet as there would be with a solid bullet. The idea is as there is a larger surface area to begin with the pellet accelerates better in the bore, in the time it travels down the bore, i believe there is still X amount of pressure acting on the pellet most of the way down the bore. Actualy a longer barell will produce higher velocities as a result. The longer the pellet is in the bore the more time it has to accelerate in the barrell.
My question is this.. if you constrict the opening of air discharge at high pressure, does it increase the pressure? let me explain. Like a water hose, constricting the opening of the hose produces higher water pressure, so you get a longer stream of water. Would the same princeple work with air? If so then the tapered bore theory will work.
i agree with jerry, i think the whole idea was abonded, it started in ww2 and the us exparmented into the 70’s with it then gave up. i would think you would use most of the energy in the barrel if it would make it out of an air gun. i would like to see if the choke was a little longer on a barrel if it would help, i think it is only 1/2 inch long, maybe a inch long might help. could help stablize the pellet more
Get yourself a .22 sizing die and then try to pound a .25 through it. I expect you’ll see right away that this is not going to work. PCPs don’t have near enough energy to extrude slugs over that range and the energy in shaping metal would take directly from the energy to create motion.
As far as I have read and understood, the Lothar Walthar barrels are
choked/wedged.. I am not sure what the diameter is at the choke but I
am sure some of the guys here will know….
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About the water. The pressure doesn’t increase. Only the velocity. It only seem to as it is now a much smaller stream. You would have to do the math to get it exact, but the higher velocity carrys more energy, so it seems to be at a highter pressure visually.