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PostPosted: Fri Feb 28, 2014 6:29 am 
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I like the big bore thing, but thought I'd offer some thoughts before you get too far ahead.
For example I'd make the barrel around the pellet, and use the lowest friction pellet. I think JSB is probably the lowest friction one available, plus they're more precision than most so you should always be able to get the same size. Say for example you choose 30cal and a JSB has a .308 head exactly. I'd make the bore .308 (top of the lands), then cut the shallowest lands possible that will still work. Picture a Marlin micro-groove barrel but much shallower. This way the head is just kissing the lands to keep it straight, but there's minimal friction. Then the shallow grooves are allowing max sealing at the pellet skirt and again at minimal friction. I'd also consider using. If possible I'd also make the grooves rounded rather than sharp so the head is not only barely touching, but there is little of it touching. I'd also polish the bore and use Tungsten Disulfide dry lube on the pellets.
The reason for minimal friction in your case isn't peak fps like most people, but to get the heaviest projectile up to 499fps. If that turns out to be easy to hit 499 with CO2 then it'll mean more shots per fill, but I think 499 will be very very hard to do with CO2 so you'll need all the help you can get.
Also consider the bore diam because a 60gr pellet at 30cal is easier to push than a 60gr in 25cal due to the larger surface area. This is why a 12GA makes as much power as a 30-'06 at 25% the pressure. The drawback is with a bigger bore you'll need a bigger air reservoir to compensate for the larger bore volume.
Yet another thought is sabots. In firearms sabots are lower friction and give you surface area for limited psi to push on, but I'm not sure about friction compared to a lead pellet since the sabot is straight walled. If the bore is cut to match a sabot and again with minimal grooves and it's dry lubed it might be an option.
If it were me I'd probably go 25cal JSB with the barrel sized to the pellets head and rifling so shallow it barely works. If that works well enough that you have power to spare I'd consider 30cal.
Also, in your pix it looks like the bolt retracts after seating the pellet? This creates air space behind the pellet and will cost you power so you might consider making it so the bolt doesn't retract. I'd also consider making it so the pellet depth is minimal, like just barely clearing the port. I'd also make the probe so it's fat to take up air space using the O-ring as far forward as possible, yet the probe is shaped to not restrict air flow. Make sense?
Of course using 3000psi air is a better option imo, it would be able to shoot heavier pellets per given caliber, and would not need as big of an air valve or have all the other air related problems you have. It should also be quieter. Picture a large volume of CO2 to hit 499 vs a much smaller 3000psi charge to hit the same #, so at 3000 you'd need less total air which means less muzzle blast.
Picture a Benj Marauder pistol with a 30 or even 357 barrel...


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PostPosted: Fri Feb 28, 2014 11:18 am 
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Thank you for your comments.... The .300 cal barrel that Sean Pero and I designed is built pretty much as you described, the groove diameter is .300" to match the OD of the head of the JSB pellets (which are NOT .308"), the land diameter is a rather shallow 0.294", it is 6 lands and they are much narrower than the grooves with only a 26" twist as it was designed specifically as an airgun barrel.... These are commercially available from seanpero@gmail.com ....

While you are quite correct that a larger boresize gives a greater push for the same pressure (relative to the area, not the diameter), the lightest pellets available in .30 cal are the 44.75 gr. JSB, and the plan is to use those to maximize the velocity while staying under the 500 fps required by law.... As to sabots, I'm not really interested in making my own ammunition, but would point out that the concept of being able to use lighter "pellets" with plastic components to up the velocity is already done in the smaller calibers, but with rather dismal accuracy....

If you have followed the development of this gun, referring to the previous thread which detailed my valve development and the reasoning behind it, you will see that starting small (.22 cal in fact) and working up (first to a .25 cal rifle, now the pistol) with the hopes of going larger IF the power is there is exactly the route I have taken.... I agree that a PCP, with the use of higher pressures, would make the job much easier, in fact the difficulty would be staying below the 500 fps limit.... The whole point of this build was to see what I could accomplish using CO2....

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!
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PostPosted: Fri Feb 28, 2014 7:10 pm 
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I decided today to test this gun with my .300 and .357 cal rifle barrels from the Disco Double.... By using a mix of breeches and bolts from the two guns I was able to test the .30 cal normally, but the .35 cal I had to remove the breech each time to cock the gun.... The bottom line is that all the transfer ports and barrel ports are the same size (0.219") so the results are consistent across the calibers.... I tested both barrels to determine the velocity at various preload settings, and found that the .30 cal still had plenty of hammer strike available, the knee of the curve is about 3 turns out from coil bind.... but with the .35 cal the knee of the curve is very near the maximum hammer strike I can get with the Disco spring and the lightweight hammer.... Here are the results....

Image

Anyway, the CO2 has enough power to drive the 44.8 gr. JSB .30 cal pellets at 495ish, and backed down to 470ish (21 FPE) I can get 16 shots before it drops below 450 and a total of 20 down to 325 fps.... The efficiency is 0.97 FPE/CI (403 FPE on 12.4 grams of CO2, I actually weighed the cartridge before and after).... So, you can make a .30 cal CO2 non-PAL rifle, but cutting the barrel in half would drop the velocity too far to make a decent pistol, IMO.... It would seem that the most logical thing is to stick to the .25 cal barrel for a CO2 pistol....

With the .357 barrel (28") I was just touching 390 fps and the velocity started to drop slightly as soon as I reduced the preload below coil bind, so a Disco spring will just barely max the gun out on CO2 in that caliber with the light hammer.... With the velocity under 400 fps, I didn't bother shooting a string.... For this to work, even as a rifle on CO2, would require larger ports, a larger valve throat, tranfer port, hammer, spring, and who knows what else, because once you start going that large the problems just snowball.... I don't even know if you could get a 22XX based rifle up close to 500 fps on CO2 with that big a caliber, but it is WAYYYYYY out of reach for this pistol build....

I then put the .25 cal pistol barrel back on, removed the RVA and reinstalled the fixed rear cap and added a spring guide with about a 0.050" spacer and ended up at 470-475 fps with the Kings.... I even heated the gun up with a hair dryer to over 100*F and the velocity dropped to ~400 fps and increased as it cooled back down to room temperature.... If I leave it sit to come to 68*F and then shoot a series of shots rapidly it starts at about 470, rised to nearly 480 at the 3rd shot (as the gun cools) and then starts to decline from there.... So, I've got the valve self-regulating with the velocity peaking at about 60*F.... How's THAT for kewl !?!

This has been an interesting build.... I now have a non-PAL repeating pistol that delivers nearly 24 shots (3 magazines) at ~12 FPE, and stays safely below the 500 fps limit over the entire range of temperatures.... and there are no "external adjustments" on the gun that can put it over 500.... I really like the functioning of the action with the left-handed bolt, and the Center-Point Holo-sight makes it easy to acquire the target.... All in all, it's a very usuable pistol.... The best thing is that, once again, I learned a lot.... It seems that if you tune a CO2 gun for the "knee" of the curve at room temperature, you are somewhere in the self-regulating zone for the valve.... What that means is that the velocity is stable over a wide range of temperatures, dropping only at extreme higher and lower temperatures.... I've seen this before with CO2, but now I know where to look on the tuning curve to find it, or at least get close.... The added benefit, of course, is that a gun tuned that way is very economical of CO2, getting more shots per cartridge, although the shot count will drop with temperature....

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!


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PostPosted: Fri Feb 28, 2014 11:22 pm 
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Thank you for the graphics, really nice :D

I got about the same result with my 2540, and with your post I know I'll stick with it!...but I'd love to get one of these multi breech you have in .25 cal.!

Stephane


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PostPosted: Sat Mar 01, 2014 4:05 am 
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Cool... I'm guessing you're like me in that the journey and knowledge gained is more important than the outcome. I usually experiment with something that is interesting, then once finished I lose interest. Depending on what it is of course, but that's the beauty of guns, they're still fun even when you run out of stuff to do to them.
No I haven't been following your posts, I just jumped in with this thread yesterday. All I know is I think it was a 2240 at one time.
My main complaint with CO2 is the temp/pressure relation, and that temp drops per shot which compounds the problem, but it sounds like you have it mastered which is something I didn't think possible without a regulator which would drop pressure even further. Whatever the case cudo's on your work.
My next step, if it were my project, would be to bulk fill the gun with CO2. Maybe make a longer tank as well, might as well if you have a 12" barrel. I imagine the new tank length could give you 10 times the CO2? Not only cheaper to fill, but 10x the shots would be well worth the effort imo. For a target only gun maybe a flex hose to the fill tank would be an option too, like a common 20lb CO2 tank... Imagine the shot count there! I'm guessing 10,000?
The valve assy is my next thought: The volume of air stored in the valve for the shot is very important, obviously, and both a larger bore and longer barrel need a larger volume of air to match. My question is have you been playing with the volume? I'm guessing the valve assy is like a Crosman 13xx, it might even be the exact same valve... If so then it might be ideal size for .22 using a 10" barrel, but with a larger bore your charge is petering out faster, and that continues further with every inch of barrel length. Lets say for example a 30 cal bore has 50% more volume than a 22, so right there you need 50% more air volume. If your barrel is twice as long then you need double. With a 30 bore twice as long you'll need 3x the volume. The port size isn't as affected, in fact you might not even need to increase it much if at all, and for testing I'd leave it alone anyway.
The 13xx vlave has a lot of room to increase internal volume, not that much, but maybe 50%? That increase would tell you if volume is what you need to get a 30, or larger moving... I'd cut barrel length too, I'd probably draw the line ~15". What are your thoughts?


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PostPosted: Sat Mar 01, 2014 5:43 am 
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Chevota:
Your comments like all others here are always welcome, but they have all been talked about in most exquisite detail and at length before.
I don't mean to chastise for your involvement, but will suggest you explore some of Bob's threads for all the detailed info he humbly shares with us.
There is a lot in them to absorb and I'm grateful for all of it. You will no doubt find the lengths he has already gone to explore the limits and push them quite informative and entertaining. This thread is just one example of what is already recorded here.

I just hate to see dead horses beaten is all, so invite you and any other new eyes on the topic to do that reading.
It's one reason this forum is such a great resource for airgunners.


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PostPosted: Sat Mar 01, 2014 11:13 am 
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Chevota.... As I suggested, you should really read the previous thread, it was mentioned near the bottom of the previous page.... Here is the link again as you obviously missed it.... post406307.html

As you will see, the valve volume has been addressed (now 3 times as large as a 22XX valve, which BTW is NOT the same as a 13XX valve, they are completely different diameters).... I also gave my reasons for not bulk filling (the convenience of the cartridges and the greatly reduced chance of liquid CO2 inside the valve which leads to wasted CO2 and wild velocity swings).... Your comments, while not unwelcome, could easily be answered with a bit of reading about the research and development which has already taken place on this project....

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!


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PostPosted: Sun Mar 02, 2014 1:52 pm 
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Bob at any point of your build did you consider a twin Co2 cart operation. Just curious.

Thx Kim

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PostPosted: Sun Mar 02, 2014 3:45 pm 
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No, because I didn't want to pressurize the tube and have to pin the valve.... However, I might just do that, or go to a bulk fill so that I can try out the .30 and .35 cal barrels I have as the current 5 cc valve doesn't have enough volume for their larger barrel volumes, IMO.... I'll probably go bulk as the front piercing pin would still restrict the flow into the valve too much.... Either way I would use a Disco valve or similar....

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!


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PostPosted: Sun Mar 02, 2014 4:19 pm 
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My apologies.... Didn't mean to annoy anyone with repetitive info/thoughts. You obviously know what you're doing so I'll observe your progress quietly :) Best of luck and enjoy your efforts!


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PostPosted: Sun Mar 02, 2014 5:45 pm 
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rsterne wrote:
No, because I didn't want to pressurize the tube and have to pin the valve.... However, I might just do that, or go to a bulk fill so that I can try out the .30 and .35 cal barrels I have as the current 5 cc valve doesn't have enough volume for their larger barrel volumes, IMO.... I'll probably go bulk as the front piercing pin would still restrict the flow into the valve too much.... Either way I would use a Disco valve or similar....

Bob


Bob I'm just about finished a project on a 22xx and will post soon.
I'm running it on HPA without having to pin the valve, I added an adapter to take up the CO2 cartridge I'm sure your well aware that you can do so, mind you its a stock bottle Reg @ 850psi output, its not the most elegant looking because I don't have a tank block but my setup is simple and works great, even with a very light hammer spring its still up there :shock: so I'm thinking of adding a reg instead of chopping the already light spring, this project of mine was more for efficiency, I'm looking to get the most shot count per fill. :wink:
just wanted to say you don't have to pin the valve unless your obviously looking to pressurizing the tube itself ?

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PostPosted: Sun Mar 02, 2014 6:17 pm 
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I had an idea for mounting a piercing pin on the front of a Disco valve so that I could eliminate the internal pin in the valve and open up the front end for more flow.... This would require sealing the front of the tube and pinning the valve (or using a Disco valve, mounted with three screws), but it would drastically increase the valve volume which would be desireable for trying larger calibers.... Here are the parts....

Image

The Disco valve front end is drilled out to 3/8" ID back to just shy of the spring seat, and that throat is drilled out to 17/64", the same as the spring ID.... Then the very front of the valve where the O-rings are, is drilled out to 1/2" for a depth of 3/8".... The piercing cap is machined from steel, with the pin mounted on a spider formed by drilling three 3/16" holes so that they are just inside the 1/2" OD portion of the cap which will be pressed into the front of the valve.... The cap is drilled from the back to 3/8" ID to match the bore of the drilled out Disco valve front end.... Therefore way more CO2 can enter the valve than can exit through the throat, effectively making the area around the neck of the CO2 cylinder plus the inside of the Disco valve front end, part of the valve volume.... If that still isn't enough volume, then I can remove the CO2 cartridge and go to a bulk fill by adding a male Foster to the front cap.... Here is what it looks like from the front....

Image

The cap still has to be pressed into place with a bit of green loctite for good measure to make it permanent.... If a two cartridge setup was desired, another piercing pin would be installed in the front cap and one cartridge loaded each way, as in a QB78.... using a longer tube of course....

Ace, you are correct, you don't have to pin the valve if you don't pressurize the tube.... However, with a two cartridge setup, or a bulk fill, you do pressurize the tube, and that is what I was talking about.... There are several ways of doing what you have done.... the HiPac style HPA conversion has a nipple end that seals against a 22XX style valve front.... you can use a "dummy" CO2 cartridge, fed from the bottom, side, or front end with a hose.... or you can use a tube (where the end seals to the valve) with a shoulder held in by a drilled front cap that feeds either HPA or CO2 directly into the valve.... All of those, except the HiPac, require a separate tank and a hose tethering the two together, which I was not interested in.... It is also possible to duplicate the function of a tank block with the tank either forward under the barrel, or back under the main tube, using pipe fittings, with either HPA or CO2, which sounds from your description similar to what you are using.... I didn't care about high shot count as this project was more of a max. power big bore experiment....

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!


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PostPosted: Mon Mar 03, 2014 10:23 am 
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Looks good Bob, be interesting to see how that turns out! I didn't think you'd be able to resist doing something with those two large bore barrels for long, although I was thinking you'd go down the pcp route.


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PostPosted: Mon Mar 03, 2014 11:30 am 
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The PCP idea is a backup plan, the problem is that with a pistol length tube and large calibers the shot count would be REALLY dismal.... On the other hand a longer tube and two cartridges would work fine....

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!


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PostPosted: Tue Mar 04, 2014 12:12 am 
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I redesigned the piercing cap and front plug today to increase the volume of the "valve" section....ie from the cartridge to the valve seat.... I have now doubled the volume from the extended valve to 10 cc....

Image

Basically I extended the piercing pin forward of the valve to move the cartridge forward in the tube, increasing the volume between it and the front of the valve.... I also made a new rotating plug for the front of the tube.... The brass section which carries the O-ring is free to rotate relative to the threaded cap but is fastened to it with an 8-32 screw through the center, which is in turn prevented from unscrewing by the setscrew.... Tightening the cap drives the cartridge onto the piercing pin, releasing the CO2 into the tube.... I'm hoping that by doubling the volume available for the shot I can get close to 500 fps with the .30 cal barrel, or maybe even the .35 cal....

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!


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