Dual Tank Benchrest Rifle

[rsterne]

I made the rest of the valve parts today.... the cages/spiders that support the valve spring and balance chamber piston and allow air into the valve, through eight 5/32" holes (over twice the valve throat area).... and the adjustable pistons for the balance chambers....



I haven't cut the O-ring groove in the 1/4" pistons yet, but they are threaded and loctited to the 1/8" shafts, and are a loose fit in the 5/32" center hole of the spider, to avoid any alignment issues.... When the valve is closed, their normal position will be back towards the seat, with the distance between the end of the piston and the inside of the balance chamber in the poppet adjustable with the 5-40 Nyloc nut.... I filed flats in the piston so that I can use a 7/32" wrench on it to hold it when adjusting the locknut.... I can adjust the clearance from less than 0.070" to over 0.200", which varies the volume of the balance chamber, and so the amount of "blow-open" tendency of the valve....

The valve stem protrudes 0.200" from the end of the valve, and has at least 0.250" of travel before the spring goes coil bind.... The balance chamber has an O-ring for a bumper to absorb any impact and reduce the peak stress on the spider.... Under normal operation, the hammer will strike the valve stem, the lower pressure in the balance chamber will help to lift the poppet off the seat, the poppet will hit the end of the balance chamber piston and the two will travel together, against the spring force, and rising pressure inside the balance chamber, until the travel reverses and the valve closes.... It will be interesting to see how much affect adjusting the balance chamber volume has on the hammer impact required and the valve dwell....

Bob

[rsterne]

I finally heard from Lothar Walther, my barrel is ready to be shipped.... Now that I know I will have barrels, it is time to dust off the parts and drawings and try and figure out what I still need to do.... which is LOTS !!!!

Bob

[sb327]

Glad to see you back on this one.

Dave

[rsterne]

It only took 2 years to get the LW barrel....

Bob

[JuryRigger]

Watching! 
Jesse

[Scotchmo]

Then you’ll need your mold:

183-39-RN BT R6

[rsterne]

Yes, indeed.... I have emailed Al to check on it....

Bob

[rsterne]

I needed a scope mount for my .183 cal Benchrest rifle, capable of shooting up to maybe 800 yards.... Here is what I printed.... The Picatinny Rail has a groove in the bottom to match the ridge in the center of the wedges, and the outside of the rail fits inside the wider groove in the wedges.... It is a beautiful slide fit in all of the wedges.... The curve on the bottom of the wedges fits a 1.25" OD barrel.... and the height clears the objective of a 50mm scope by 1/16" to the bottom of the scope cap with all of the wedges....



The wedges, from front to back, are 30 MOA, 60 MOA, 90 MOA, 120 MOA, and 180 MOA (yes, a full 3 degrees).... If the rifle is sighted at 100 yards with the lowest rail, using the other rails should put me on the paper at about 265 yds, 415  yds, 550 yds, and 760 yards.... This is assuming a MV of 1000 fps and a BC (RA4) of 0.27.... I think those should be appropriate for the 39 gr. BBT I will be shooting at about 1000 fps....

Bob

[bear air]

That's some amazing distances Bob.

[rsterne]

May as well have a goal!....

Bob

[subscriber]

Bob,

If you can shoot 760+ yards with 3 degrees of elevation, how far can you shoot with 30 degrees?  I assume that max range would be achieved by shooting around 30 degrees above horizontal, on level ground.  Perhaps you could calculate max range and the required elevation for grins?

[Scotchmo]

Bob,

If you can shoot 760+ yards with 3 degrees of elevation, how far can you shoot with 30 degrees?  I assume that max range would be achieved by shooting around 30 degrees above horizontal, on level ground.  Perhaps you could calculate max range and the required elevation for grins?

[subscriber]

Thank you, Scott

[OTmachine]

Pretty impressive!  But, then again, it is Bob.

[rsterne]

Realistically, if I can ever hit anything at 500 yards I will have achieved more than I could ever imagine....

Bob

[subscriber]

Bob,

I am impressed by both effective range and maximum range.  Effective range depends on the size of the target and whether you are marking or puncturing an inanimate target, or need to kill it.

Then there is the matter that you designed and made the air rifle.  That is impressive right there; even if you are shooing "only" 100 yards.