Canadian Airgun Forum

I am collecting the parts for a dual tank benchrest rifle.... it will have a pair of bottles reversed under the plenum, which will be regulated....

My tanks have arrived from AirgunArchery Fun in Saskatchewan....



They are gorgeous, and I love the long slender profile....

I have ordered the 4130 CrMoly tubing for the main tube, and some 2024-T3 for internal parts.... The general arrangement will be like this, a previous QB79 with two 88 gr. tanks....



Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Well proposed - it will be an interesting build, indeed.

_________________
Best Wishes
Daryl

Interesting!

Should work well, provided weight is not a major consideration.
From the bench, fine...
Will be watching this, just to see how it's stocked, and final operating pressure.
Do give us the final details on the valving, etc.

-D.S.

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"Ain't no half-way"
-S.R.V.

The bottles are 300 bar, I have ordered a Ninja HP regulator from Hajimoto set to 250 bar (3600 psi).... I plan on a LW barrel in .183 cal (4.6 x 30mm) and a 4 caliber long bullet from NOE....







Note the 5.9" twist, the bullet is designed around that....

The plan is to set the regulator, mounted in the top of the "Y" shaped tank block, partially into the front of the main tube (plenum)....



I will probably make the regulator adapter a bit longer so that I can mount a gauge on the left side.... The gun will weigh at least 15 lbs. (the barrel is over 6 lbs.)....

There will be no forestock, the bottles will provide a nice wide base for the bench....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Long range .177 - gotta love it. .273 is very hopeful. Seems to me, the 25gr. .172" Hornady Vmax bullet is .230 BC, but it's a flat based,plastic tipped spitzer.
I've used it on gophers to 500 yards, but at much higher velocities than air will provide.
Best wishes with this, Bob. 6" ROT - VERY impressive.

_________________
Best Wishes
Daryl

LOL - my bad. 4.6mm is .181 according to my app. I see your groove diameter is .183" & the mould, .184" on the driving band behind the waist. Odd number, not known in the powder burning arena, however there are .198"(Calhoon) and of course, the .204" Ruger.
That is a mean looking bullet - your BC expectation might be spot-on afterall.
.005" rifling depth is very interesting. What is the land width?

_________________
Best Wishes
Daryl

That will also be a good truck / UtV based varminter!,kelly

The 4.6 x 30mm is indeed an oddball.... Here it is compared to the 5.56 mm / .223....



The round delivers 330-400 FPE.... Bullets run from 26-42 gr., so my 39 gr. is right in the ballpark (but at a lot less velocity).... I don't know the land width of the LW barrel....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

4.6x30. Hmm - not in my Donnely's book, nor any other of my wildcat books. Interesting.
Bullets would be custom, of course. Power-wise, no better than the .17 WSM rimfire, except
it is reloadable, with custom bullets. That round appears to be a shortened, blown out .22
Hornet case with the rim turned off & new extraction groove cut, kinda like I did with my
.458 Alaskan chambering for a model 70 bolt action rifle, from a .450 Alaskan wildcat.

_________________
Best Wishes
Daryl

It turns out that I will also be getting a .22 cal LW pellet barrel with a VERY slow twist, compliments of Mike Niksch of Thomas Benchrest Rifles.... I helped Mike decide what to get for shooting 25.4 gr. JSB Monsters at 100 yards (he is trying to beat rimfires) and it is working well, so he is sending one as a thank you!.... Here is a 25 shot group he shot at 100 yards (looked like he pulled one)....



I decided I will make up an upper to either fit on this gun, or since I have a pair of SIG 450 cc, 250 bar bottles, I might make another lower for it.... In any case, I borrowed the concept from my Monocoque .257 and came up with this unique way of marrying the barrel and breech....



I have a meter long piece of 16mm ID (to fit the LW barrel) with a 20mm OD, and I have ordered a piece of 5mm wall CF tubing a meter long, 20mm ID x 30mm OD, to slide both it and the breech into.... Barrel in green, breech in blue, bolt in red above.... The breech will be 20mm OD, turned from 2024-T3, and sealed to the barrel with an O-ring.... The resulting assembly should be about the same stiffness as a 1-1/8" OD steel barrel, at a fraction of the weight....

Sidetracked, maybe, but this should be fun!....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Amazing group with an air rifle.

_________________
Best Wishes
Daryl

I have been thinking about a change to my balanced valve for this gun.... Here is a drawing, although the dimensions show a 5/16" throat (from my 6mm), which I can reduce to 1/4" for these smaller calibers, and reduce all the other dimensions proportionally if desired.... That would make the valve easier to open.... The balance chamber is 50% of the area of the poppet seat.... reducing the force required to crack the valve by that much....



The valve body is in black, the poppet and front spider are in blue, the balance chamber is in red, and the O-rings in magenta.... The valve spring (green) is outside the balance chamber instead of inside it.... This allows the chamber to be much shorter, and therefore a lot less volume.... The balancing force is basically only going to reduce the force holding the poppet closed.... Once it opens 1/3rd of it's diameter (it may never get that far), the poppet (actually the buffer O-ring on it) hits the end of the balance chamber, which can slide 1/8" forward, driven by the momentum of the hammer.... As the balance chamber fills with HPA from the valve throat through the vent in the poppet stem, the closing force increases.... This allows the dwell to be tuned with the hammer strike....

If I need a larger balance chamber, I can move the balance chamber forward by tightening the screw that holds it in place in the spider.... That would reduce the hammer strike required as the valve would have a longer "blow open" period.... The balance chamber dimensions can be changed if a larger alteration in operation is needed....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

I just received my Carbon Fibre barrel sleeve from Amazon.ca....



30mm (1.18") OD x 20mm ID, shown with my normal 20mm OD barrel sleeve inside it!....



Anybody need a metre long CF Crowbar?.... ::)

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Bob, I might have missed it, but failed to see the rate of twist.

_________________
Best Wishes
Daryl

The .183 cal is 5.9".... The .22 pellet barrel is very slow, I believe over 40"....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!