Tensioned steel shroud RMAC build

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thammer

thammer

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Jun 8, 2015
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Ohio, United States
Using a thick walled DOM steel tube since weight is good on a bench gun. Not much practical use for a carry gun but the premise is the same. Used 4 heavy bellville washers at the breech in hopes they will absorb any shrink/expand from temperature fluctuations plus 3 internal spacers as well. At 88fpe it balances a 177 pellet on the suppressor during the firing cycle and you could literally swing it like a baseball bat even weighing near 20lb with no flex. It's essentially a solid 1" thick barrel actually probably stronger under tension. 27" hammerforged TJ 1-26" twist barrel shooting 44.75 JSB at 940fps. Double 500cc 250bar bottles. 

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Delrin Slip fits over the barrel and centers the shroud very tight fit with 3 orings. The end is reduced to just let the bellville washers slip fit over that. The seat shown in the thick walled shroud captures the first washer and compresses them squarely against the breech. You can torq it down just shy of the shroud touching and let the washers absorb fluctuations of temp change. There will be 3 more 2" spacers that slip fit like the one holding the washers spaced evenly down the barrel to absorb vibration down the length of the barrel inside the shroud almost completely deadening it.



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Using a thick walled DOM steel tube since weight is good on a bench gun. Not much practical use for a carry gun but the premise is the same. Used 4 heavy bellville washers at the breech in hopes they will absorb any shrink/expand from temperature fluctuations plus 3 internal spacers as well. At 88fpe it balances a 177 pellet on the suppressor during the firing cycle and you could literally swing it like a baseball bat even weighing near 20lb with no flex. It's essentially a solid 1" thick barrel actually probably stronger under tension. 27" hammerforged TJ 1-26" twist barrel shooting 44.75 JSB at 940fps. Double 500cc 250bar bottles. 



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In bold above -

If you do not "have" an "interference" fit and have to use a press, and or have to heat one tube, or freeze the other tube, to install the sleeve over the barrel, it's NOT anything close to a "solid" barrel.

From an Engineering standpoint anyway ! Though, you can call it whatever you want.

Mike
 
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Using a thick walled DOM steel tube since weight is good on a bench gun. Not much practical use for a carry gun but the premise is the same. Used 4 heavy bellville washers at the breech in hopes they will absorb any shrink/expand from temperature fluctuations plus 3 internal spacers as well. At 88fpe it balances a 177 pellet on the suppressor during the firing cycle and you could literally swing it like a baseball bat even weighing near 20lb with no flex. It's essentially a solid 1" thick barrel actually probably stronger under tension. 27" hammerforged TJ 1-26" twist barrel shooting 44.75 JSB at 940fps. Double 500cc 250bar bottles. 



Click to expand...

In bold above -

If you do not "have" an "interference" fit and have to use a press, and or have to heat one tube, or freeze the other tube, to install the sleeve over the barrel, it's NOT anything close to a "solid" barrel.

From an Engineering standpoint anyway ! Though, you can call it whatever you want.

Mike
Click to expand...

Takes a rubber mallet to assemble and a press to take apart with the inner core tensioned and the outer core under compression. Perhaps a solid barrel would be more stiff so I'll retract the statement since I couldn't properly test to get the results. 
 
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This project is likely far more important to me than most simply because I shoot unregulated guns. An extremely accurate rifle may or may not balance a pellet and it not matter. If the gun is consistent with the harmonics it is likely fine. With an unregulated gun harmonics can change throughout the string. High pressure short burst of air changing to lower pressure with longer bursts to maintain the same speed throughout. Each shot changing. This is my attempt to mitigate that by deadening as much of that vibration as possible. 
 
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Whoa!!! That's awesome! Great work Troy!!! One less thing to worry about when you're competing at 100 yards. Will you be shooting the gun "free recoil" like you just did there?
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Thats the plan. That scalloped stock is beautiful but hell to use a rear bag. With the front bottles on a bag and the rear rider being flat with the plane I plan to shoot free recoil with a thumbs up approach. Should help with any muzzle flip that could occur at 90fpe. 
 
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I've not gotten to try at distance yet. Range time will come this weekend but here is five shots at 33yards with unsorted FX 44 grain pellets with a pellet for size reference. I've also just began to play with the swan harmonic tuner. Each hole in the tuner is filled with 64 grains of lead. Definitely showing potential for sub MOA! The string is vertical which should corolate to velocity differences and will hopefully shrink once sorted by weight. 

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