New Pellets in Holland

[SeanMP]

Just to give some perspective on this new caliber

The top shooters are hitting a quarter 28/30 at 100m

The worst are managing 25/30

[rsterne]

Looking forward to hearing about your two-block setup, Sean.... I've been giving the design some preliminary thoughts as well.... I'm leaning towards a Hayabusa-based design.... Regulated plenum of about 115cc with a single-ended valve (ie effectively 115cc valve).... That will keep the average pressure during the shot within about 5% of the regulator setpoint with a 100 FPE output.... It could be run from a 22CI tank (acting as the forestock) and/or tethered to a 4500 psi regulated bottle or SCUBA tank.... In case you forgot, here's what it looks like....



It would be a simple matter to use a lower block with the valve and hammer inside and attach the 1" CrMoly tube to the front of it for a plenum.... Alternately, eliminate the regulator, turn the tank around, and screw it directly to the front of the block and run unregulated.... Lots of possibilities....

Bob

[SeanMP]

The idea is not fully baked yet Bob but the concept is to have two modular blocks.

The top block would as usual carry the bolt and be the breech socket, like your Hayabusa picture

The bottom block would be the valve body and would carry the hammer, spring , RVA. The forward end of this block would be threaded to accept the tube or paintball adapter. So far so good but I need a brilliant solution for securing the valve return spring.

These two blocks would be held together by 6 fine socket screws and the TP would be sealed by an Oring laying in a seal groove machined in one of the halves. The idea here is I would then have no restriction on the size of the ports and a rifle could be retuned by changing out the lower module.

Once the upper and lower were mated then another block could be added to the front containing the regulator (I ripped off this idea from Anschutz) Then the original threaded section becomes reservoir. And the added block is now where the tube or adapter screws on.

The reason I'm trying to work this out are to simplify. I've eliminated a separate valve body and all associated retaining screws and seals. I can change a stem or stem return spring by unscrewing a tube. I can reprofile the gun entirely by swapping a bottom or top module.

[rsterne]

The only downside (maybe) I can see to that design is the volume between the regulator and the valve seat.... I really like the modular approach, and the ridigity of the assembly, however.... Might I suggest a Marauder trigger assembly bolted to the bottom of the lower block, they really are a very fine unit.... I've been playing with regulated guns long enough now to realize how important volume downstream of the regulator for the valve to draw on is.... I aim for 1 cc per FPE.... Here is a graph showing an example of how the plenum volume affects the potential power of the gun....



That graph is for a 50 FPE design point on a gun running 2000 psi with an efficiency of 1 FPE/CI.... You can compensate for less volume by running a higher regulator pressure, of course.... Running 1/2cc per FPE will require roughly 7% more pressure to compensate (compared to 1cc / FPE, in that example)....

Bob

[SeanMP]

Good info Bob

The regulator add on module thought was for precision target. 6 fpe or less. But if I can get my design down it would be easy to just increase the volume in the plenum (within limits...not bigbore) by increasing the length of the block I suppose. I'm going to guess that a paintball adapter socket is 7/8" dia and 1" long that would give me 38cc in the socket and an additional 38cc for every inch of cavity in the block.

And I definitely had the Mrod trigger in mind. They fit well with the modular concept. But....thats if crosman is playing along

[rsterne]

The inside bore of a paintball fitting is 0.694" or so.... I use an 11/16" mill and with a bit of runout on the chuck it's perfect to seal on the O-ring.... However, if you're using a sandwiched block, it could be whatever diameter would work structurally and enough room for an O-ring on the parting face.... I used 1" thick material for my breech on the Hayabusa, and that is what I use for the tank block as well.... The first part of the socket yields no volume, of course, as it's full of the regulator male fitting on the tank....

BTW, I only get 9.85cc per inch of length for a 7/8" hole....

Bob

[SeanMP]

Lol...thats what happens when you try and do calculations at 11pm the night before shift change.

I used the diameter not the radius...whoops!

[rsterne]

I've been giving this project some more thought, and I can see why most (if not all) of the competitors have their rifles tethered to a SCUBA or SCBA tank.... First of all, to get 950 fps with the 41.5gr. pellet (83 FPE) and have the valve close when the pellet is half way down a 26" barrel requires about 2800 psi at an efficiency of 0.90 FPE/CI.... That would use 92 CI of air (at 1 bar) per shot.... If you had a 22 CI, 3000 psi tank (2.6 CF), the pressure would drop 61 psi per shot.... If you started at 3000 psi, and shot 7 shots, you would be down to about 2600.... Using less pressure would drop the efficiency, and eventually you wouldn't have enough to get the velocity/energy required even with a dump shot (which is very wasteful).... Sooooooo, it's either not many shots, or a very big reservoir....

If you tethered the same gun to an 88 CF SCUBA tank, you might get about 200 shots from 3000 psi down to 2600.... If you regulated the output to 2800 psi, maybe 100 shots.... The best way to go, would be to tether to a 4500 psi SCBA tank regulated to a 3000 psi output and tune the gun accordingly.... The higher the pressure you use, the more efficient, because you can close the valve sooner.... That also makes the gun quieter, although these things will be LOUD anyway.... In the example above, the residual muzzle pressure would be about 1340 psi (ie nearly half the tank pressure).... Note that these numbers are all rough approximations, and there is no guarantee we can reach the required efficiency levels to produce them.... That said - GAME ON !!!

Bob

[SeanMP]

Game on indeed. I was out picking up material today so I grabbed some 12L14 to start poking away at the upper and lower block. I had to settle for 1 1/2" hex bar
How many shots does your Quackenbush get on a tube fill?

Looks like I better look at using 1" ID tube. That would give about 5 shots off the tether. Certainly viable as a hunter

With such a heavy long projectile that is bound to increase the dwell time allowing the pressure wave to build. Do you think this could have a positive effect on the efficiency?

[rsterne]

My DAQ .308?.... Before or after Len gave me hell for fiddling with the hammer spring?.... Originally I got 3 shots, 836, 782, 744 (averaging 163 FPE) starting from 3000 psi, ending at 1800.... After I had the gall to set the hammer spring, which shortened it by nearly an inch, I got 6 shots, 826, 833, 832, 824, 811, 792 (averaging 180 FPE) starting at 3200 and shooting down to 2050.... The efficiency went from 0.38 FPE/CI to 0.88 FPE/CI.... The DAQ tube is about 250cc....

My Hayabusa has about 115-120cc inside the plenum tube (1" OD x 0.065" 4130).... I figure I'll make a slightly shorter tube (1.4" less, the length of the regulator) and mount the 22CI (360cc) tank without a regulator to a similar reversed block to what I have now.... I'll make sure the passageways through the block are 3/8" so that all the air will be feeding the valve.... That will give me about 475-480 cc on deck....

I've been playing with the spreadsheet a lot, and it's telling me that we can't go below about 2600 psi and still get 950ish fps with a 26" barrel.... If the fill is only 3000, that makes for only a 400psi usuable range.... IF we can achieve 0.90 FPE/CI, I'm only looking at about 8 shots off tether within that 400 psi range.... Mind you, with such a narrow pressure range, the ES should be almost as good as a regulated gun.... Perhaps we'll be pleasantly surprised and be able to use a wider pressure range.... but with the spreadsheet telling me there is no way to use under 2500 psi I'm not going to even consider a regulator in the gun itself....

The spreadsheet takes into account the weight of the projectile, it's one of the main variables.... For the same valve duration, because the bullet is moving slower, the bullet hasn't moved as far before the valve closes, leaving more barrel remaining for expansion, which increases efficiency.... Have you decided on a barrel length yet?.... It's worth about 50 fps (with no increase in air used) to go from 24" to 30".... I'm thinking 26 or 28" sounds about right.... but I could go 30" if you want to (check your email)....

Bob