Ersatzjack
Corporal
"That silly Franz... he thinks we are winning."
Posts: 1,093
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PAK38
Apr 14, 2008 10:59:52 GMT -5
Post by Ersatzjack on Apr 14, 2008 10:59:52 GMT -5
Okay as I promised burt on these boards (at my insistence and not his) here is my report on his Pak38 build. burt operates airsoftcorner.com in New York State and I heartily recommend him for airsoft needs. He has been the linchpin go-to-guy for our unit the 3rd Panzergrenadiers. At an event out in New York last year I traded him a Mauser I built for his prototype Pak38 gun. I had seen it working at the event belching out water balloons and was impressed with it's range and accuracy and this was before he modified it for breech loading. The original looked like this: It was low on cosmetic appeal and high on function. burt then modified it for breech load. Then we drove it home with us and started the facelift to include it in our armory. I really like these things about it. 1) the thin wheels he found were in great shape and help its mobility. I've been looking at wheels at antique stores and he found a pair of beauties. The design of the frame is also ingenious. When positioned properly you can have one gunner control the elevation and traverse with ease and while the wheels have to move to traverse the shot they don't move much and they move easily enough so that the firing arc is about 35-degrees to the front before you are talking about spinning the carriage. This allows one guy to work his small arm and the other to shoot. Loading is easy enough but not automatic. The AP round is a highly effective Nerf pocket football. Have to keep your eyes peeled when firing these as they really move out. The anti-personnel round is a paper wrapped (that's the sabot) water balloon and it also works pretty well (better in dry hot weather than snowy mud however but what doesn't work better in those conditions.) We also experimented a bit with a corn kernel blast but are still tinkering with that. Recommended pressure is 60-PSI and you can operate it off a bicycle pump (not recommended) an air compressor (fixed positions) or as we have adapted it an air tank rig. This allows mobility and a movable piece of cover. Neat! Two man crew is what is used. The construction is all PVC, even the air chamber and so we watch that the pressure doesn't ever go over 100-psi. The bore is about 2-inches in diameter and so I call it a 50mm Pak. Back to the cosmetic changes - First off, the welding on the gun left something to be desired. Remember, I said that it was a prototype and I'm not complaining since I bought it for a fair price but my future son-in-law helped me re-weld (he did it) it overall. Several tubes had broken off you see. burt had used electrical conduit piping for construction and this is thin and hard to weld. But it is strong enough if welded well and also decreases weight. It is holding together now and time will tell. The next step in the facelift was to repaint and reshape some of the armor shields to better approximate a Pak 38 and I added a drop down plate in front so that rolling it up to cover we'd have latitude for different heights of cover. I plan to add 9-foam peanut filled sandbags to the mix so that the gun can be easily emplaced. Hauling the real thing has lost its appeal. The wheels were covered on one side only to limit weight and cost but still make the gun look more anti-tank and less artillery-like. Then I added the unit insignia and a net in the framework to hold odds and ends. The muzzle break was cut and kill rings added (had to have some of those) to finish off the look. The ammo boxes attached are US surplus and I just pretend otherwise. I like how it turned out. It is very fun and really adds to skirmishes. It was a very reasonable investment from my point of view but my theory is hobbies are money-pits and not businesses. I like it. I also know that burt is perfecting a new design and wants to improve on his offering and I'm sure he will. It was worth it for the design work and wheels alone. Here are some pics:
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gryphon
Master sergeant
shchi e kasha, pisha nasha.
Posts: 250
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PAK38
Apr 14, 2008 11:39:44 GMT -5
Post by gryphon on Apr 14, 2008 11:39:44 GMT -5
That is an intimidating thing to spot rolling through the cornfield in order to shell your position, I can tell you. What a great toy. Your crew can deploy this gun MUCH faster than I anticipated, BTW, Yikes! Where are those cursed Katyushas when you need them? Your rework looks fantastic - I love the pics of the PAK in the snow at Porkhov on the AAR thread as well. Can't wait to make an SMG shock assault on the PAK gun emplacement at Crane Lake in August....
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PAK38
Apr 14, 2008 11:52:22 GMT -5
Post by Garrick Udet on Apr 14, 2008 11:52:22 GMT -5
So I thought I'd chime in on the PAK thread as the assistant gunner assigned to the PAK for the 3rd Panzergrenadier's action in Porkhov. Overall the Gun looks great! I had only seen pics of it (both before and after the facelift) and seeing it up close and personal was like night and day. Not that the pics look bad, it's just that it there is something great about seeing it as a 3 dimensional object. It is lightweight enough to be transportable by 2 men even through the toughest terrain. Porkhov proved this last weekend as it was hauled through snow, mud and swamp during the second scenario. 3 men is best in rough terrain, especially after a long day of fighting. The breach loading is great! Very easy to get a round chambered. Charging the gun takes about 30-45 seconds (we never put a stopwatch to this), with a 60psi output from your air source. Here's a pic I took of the portable air system: Construction was fairly easy and cost me around $80 (if you don't count the first regulator I destroyed trying to get fancy). That does not include the HPA tank shown in the picture. Materials for the air system: - 1 Micro-Matic mixed gas regulator with a C02 tank input and 0-200psi adjustable output
- 1 PMI Remote Line adapter (Made for paintball)
- 2 1/4" -> 1/8" Brass couplings (female to female)
- 1 1/2" Male -> 3/8" Female Brass Reducing coupling
- 1 3/8" Male -> 1/8" Female Brass Reducing coupling
- 1 1/8" Male/Male Brass tubing coupling (these come in variable lengths, but the one I used was only about 1/2" long)
- 1 Spool Teflon pipe thread tape
Also shown is a 1/4" quick connect female compressor adapter, this was quickly ditched as it did not fit the male end that was on the gun. The problem was quickly remedied after I discovered that the threads on each end would be compatible and I just connected the coiled line output to the input hose on the gun. The netting installed on the gun was a perfect place to rest the tank and air system as you could easily work the on/off switch on the air and watch the the pressure gauge on the gun rise to the desired level. We were able to achieve about 4 shots off of a 48ci 3000psi HPA tank with a enough air left to pressurize the gun half way. This is ok since the on/off on the air system would allow you to switch air tanks on the fly and use every last psi you've got! As stated above the gun operates at 60psi. All in all this type of field gun is a great addition to any German unit's armory!
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PAK38
Apr 14, 2008 13:23:21 GMT -5
Post by CharleyNovember on Apr 14, 2008 13:23:21 GMT -5
How many shots do you think you could get off of one of the portable air tanks you use with normal shop compressors?
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PAK38
Apr 14, 2008 14:03:57 GMT -5
Post by Garrick Udet on Apr 14, 2008 14:03:57 GMT -5
How many shots do you think you could get off of one of the portable air tanks you use with normal shop compressors? The tanks attached are High Pressure Air (HPA) filled to either 3000 or 4500psi (depending on the tank). They are the same tanks I use to play paintball and are regulated to an 850psi output. To get a fill to full pressure you need an air source that can output to those pressures. Almost all paintball stores and fields (unless they are seriously podunk and only use CO2) will be able to fill to at least 3000psi, the shops in Minneapolis that I frequent both can fill to 4500 psi. This takes a serious compressor. I suppose you could rig your shop compressor with a 1/8" quick disconnect to attach to the tank's fill nipple, but you'd only be able to fill the tank to what ever your shop compressor's maximum output pressure would be. In my experience most small compressors will max out at 125-150psi. You'd have to fill approximately 8-10 small bottles to that pressure to be able to fully charge the gun for one shot. As was stated above, the input on the gun itself is a valve stem like you'd find on a car or bike tire. According to the Ersatzjack armory, you can charge the gun with a bike pump, but it takes some time and physical effort. Not the kind of thing you'd want to be doing in the heat of battle. The regulated output on the portable air system means that the gun crew can flip the on/off switch to 'on' and be able to focus on aiming the gun and/or fighting off any encroaching enemies while the gun in charging. Because the output pressure is set to the same pressure needed to charge the gun, there is no risk of overcharging the gun, nor is any gas wasted once the pressure is equalized (assuming there are no leaks). We took the practice of only charging the gun immediately prior to firing and switching off the air system once the gun reached a full charge as to not waste any air. We used HPA this weekend due to the cold temperatures. If it had been 60+ degrees outside we also could have used CO2. In cold weather this just isn't practical. Also, CO2 is cold coming out of the tank as it is in a liquid form when compressed to those pressures. When it exits the tank @ around 850-900psi, it converts back into a gas, this gas is usually pretty cold as well. I would be wary about using it as it could cause the PVC in the gun to contract causing leaks on the seals. This is speculation only as I don't believe it has been tried yet on the gun. Most likely though, if the temps are over 80 degrees, it should be fine to use CO2 although compressed air would be my primary choice. Also, I know that SCUBA tanks can be rigged up for use in Paintball and filled to 3000 psi. Getting a small Scuba tank would be the equivalent to 3-4 small HPA tanks or 2-3 large HPA tanks. The downside of using a SCUBA tank on the gun would be that it would be harder to fit in the netting that was installed in the gun carriage.
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gryphon
Master sergeant
shchi e kasha, pisha nasha.
Posts: 250
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PAK38
Apr 14, 2008 14:27:55 GMT -5
Post by gryphon on Apr 14, 2008 14:27:55 GMT -5
Garrick, your regulated HPA rig is perfect for this setup. Please, please, don't EVER use compressed CO2 to operate this gun; after just one or two shots, that PVC expansion chamber will be chilled down and the plastic itself will become dangerously brittle. You would be lucky if a joint blew first, beacuse the body tube itself could just as easily blow up and throw jagged plastic shrapnel like a big grenade. Some of us old-time Paintball Tank Crew types discovered this the hard way about a decade ago. Stick to air. Seriously, Compressed CO2 + PVC expansion chamber = real chance of death or maiming.
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YankeeDiv26
Staff Sgt.
Frustrated Mac Owner
BDM<33
Posts: 2,462
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PAK38
Apr 14, 2008 14:54:48 GMT -5
Post by YankeeDiv26 on Apr 14, 2008 14:54:48 GMT -5
Wow, great work by all it's owners. That sure is intimidating to see rolling down the battlefield. The hpa rig setup and general concept could be applied well to a multitude of roles. Once again, very well done.
I remember seeing that at the bulge but never looking closely at it. I thought it was just a prop.
<YD>
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PAK38
Apr 14, 2008 15:16:37 GMT -5
Post by Garrick Udet on Apr 14, 2008 15:16:37 GMT -5
Stick to air. Seriously, Compressed CO2 + PVC expansion chamber = real chance of death or maiming. That's what I had thought, thanks for the confirmation. I know the Ersatzjack armory has at least two HPA tanks and if I get my 92ci 4500psi tank fixed I'll have 4 HPA tanks for use by the next event. Even so, with these 6 tanks I think we'd only be able to muster 25-30 shots. I know used SCUBA tanks are cheaper than good fiber wrapped paintball tanks and they hold a helluva lot more air. I might have to look into what it would take to pick a couple up and get them hydro tested. I'm no SCUBA guy so I have no idea what the regulator on one of those things is like, but my guess is that you could remove the SCUBA regulator and attach an aftermarket Paintball tank regulator. EDIT: After a little research I discovered that SCUBA tanks themselves have no regulator attached. You can purchase a fill adapter that will output air from the tank to fill an HPA bottle. The output pressure of the SCUBA tank is whatever pressure is in the tank (i.e. at a full fill the tank will output 3000psi). I think the overall scenario design for Porkhov was good as it had one PAK heavy scenario. We had a nerf rocket all set to scare the Bolshevik out of one of you Ruskies in the first scenario, but only once did any of your men approach the line of fire, and when they did they were quickly eliminated by our front line skirmishers as we had the PAK deployed to the rear as a defensive contingency.
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PAK38
Apr 14, 2008 15:17:59 GMT -5
Post by CharleyNovember on Apr 14, 2008 15:17:59 GMT -5
riiight..not what I meant. I understand all about HPA having come from a paintball background and having owned a podunk field (We ran off about 8 really big HPA tanks to get fills) I'm talking about filling one of these: homerepair.about.com/od/toolsmaterialsyouneed/ss/airtank.htmWe used it with our "tank" gun and I can't remember how many shots we got. However the great thing is you only had to have one shop compressor and one portable tank to take around with you. Unless the field you play at provides HPA fills. Our expansion chamber was much smaller then the PAK we got about 150-175 feet shots with our gun. This is what it looked like from the inside it was breach slide loading. I'd like to build something like what you guys did but I notice the expansion chamber is much longer aswell as the barrel. I was thinking of building something smaller as I got the same distance you guys did with a smaller barrel and expansion chamber.
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Ersatzjack
Corporal
"That silly Franz... he thinks we are winning."
Posts: 1,093
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PAK38
Apr 14, 2008 16:17:34 GMT -5
Post by Ersatzjack on Apr 14, 2008 16:17:34 GMT -5
I'll try and answer you CN. The tank you show pictured is about the size (maybe a might bigger) then the storage tank on my compressor. I fill the expansion chamber and let the compressor refill itself to start with a fresh supply of air. That's how you would use it right? So you fire once and then draw air from the tank, fire again and draw air again and somewhere during the second draw you would empty the tank I think. So I figure mobility using a tank like that and a compressor at home base would be three shots top. Using a smaller expansion chamber and a smaller barrel (maybe inside a larger one for looks) and shooting a smaller projectile I'll bet you could substantially increase your shots. Let us know how you solve it. I for one like Garricks idea of looking into a scuba tank solution. He is the airsmithy and I'll leave it in his capable hands.
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PAK38
Apr 14, 2008 16:26:04 GMT -5
Post by Garrick Udet on Apr 14, 2008 16:26:04 GMT -5
Ahhh Gotcha! This will require some Math (you've been warned . How high a pressure can it be filled to? If we figure the volume of the expansion chamber on the gun (I don't know the dimensions of it personally) but let's assume it is 3" wide (1.5" radius) and 48" long (2.25*3.14*48=339 cubic inches) I found a conversion site on the internet which tells me that 339ci is equal to approx 1.25 gallons. That would mean if your tank was filled to 60 psi, you'd get 4 shots off. If your tank was filled to 120 you'd get 8. Probably less since I'm assuming 0 PSI left in the tank after the last shot when in reality it would probably be slightly higher than that. * Disclaimer: I was not a math/physics/chem/engineering major in school If this math is wrong then it's because I'm not very good at it. If it's right, I got lucky.
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PAK38
Apr 14, 2008 16:50:15 GMT -5
Post by CharleyNovember on Apr 14, 2008 16:50:15 GMT -5
great guys thanks! I might look into building something like what you have. I have access to a 3k stubby and a 4500. Scuba tanks can be had pretty cheap around here and I know of atleast one place that will fill them for paintball guys.
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biged
Master sergeant
Posts: 468
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PAK38
Apr 15, 2008 5:40:58 GMT -5
Post by biged on Apr 15, 2008 5:40:58 GMT -5
For a single shot system. Pickup a CO2 cartridge tire inflater to charge your expansion chamber.
Pressure acheived by unloading a 12 gram CO2 cartridge into a expansion chamber (in cubic inches).
5 Cubic inches 840 psi 6 Cubic inches 700 psi 7 Cubic inches 600 psi 8 Cubic inches 525 psi 9 Cubic inches 466.666667 psi 10 Cubic inches 420 psi 11 Cubic inches 381.818182 psi 12 Cubic inches 350 psi 13 Cubic inches 323.076923 psi 14 Cubic inches 300 psi 15 Cubic inches 280 psi 16 Cubic inches 262.5 psi 17 Cubic inches 247.058824 psi 18 Cubic inches 233.333333 psi 19 Cubic inches 221.052632 psi 20 Cubic inches 210 psi 21 Cubic inches 200 psi 22 Cubic inches 190.909091 psi 23 Cubic inches 182.608696 psi 24 Cubic inches 175 psi 25 Cubic inches 168 psi 26 Cubic inches 161.538462 psi 27 Cubic inches 155.555556 psi 28 Cubic inches 150 psi 29 Cubic inches 144.827586 psi 30 Cubic inches 140 psi 31 Cubic inches 135.483871 psi 32 Cubic inches 131.25 psi 33 Cubic inches 127.272727 psi 34 Cubic inches 123.529412 psi 35 Cubic inches 120 psi 36 Cubic inches 116.666667 psi 37 Cubic inches 113.513514 psi 38 Cubic inches 110.526316 psi 39 Cubic inches 107.692308 psi 40 Cubic inches 105 psi 41 Cubic inches 102.439024 psi 42 Cubic inches 100 psi 43 Cubic inches 97.6744186 psi 44 Cubic inches 95.4545455 psi 45 Cubic inches 93.3333333 psi 46 Cubic inches 91.3043478 psi 47 Cubic inches 89.3617021 psi 48 Cubic inches 87.5 psi 49 Cubic inches 85.7142857 psi 50 Cubic inches 84 psi
*** Pressure will increase as ambient temperature goes up. CO2 is greatly effected by temperature.
Around 47 cubic inches is safe for pressure rated PVC. Steel pipe can handle up to 1000 psi.
Cubic Inches = ( Diameter / 2 ) ^ 2 * Length * 3.141593
A 2 inch ID pipe, 12 inches long is 37.699116 cubic inches.
///ed///
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biged
Master sergeant
Posts: 468
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PAK38
Apr 15, 2008 5:50:11 GMT -5
Post by biged on Apr 15, 2008 5:50:11 GMT -5
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PAK38
Jun 5, 2008 15:05:55 GMT -5
Post by trippy on Jun 5, 2008 15:05:55 GMT -5
Sorry for the necro post, but over pressuring something is dangerous, so:
Biged, you formula is wrong.
d(pi)l/2 (that's L, not 1) brakes down to pipe surface area/2 You want (pi)r^2l
The formula for your example d=2 ends up being right because you divide by 2 and r=1, so v=37.7. This was only a coincidence.
d v d(pi)l/2 1 9.4 18.84 2 37.68 37.68 3 84.78 56.52 4 150.72 75.36
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PAK38
Jun 5, 2008 15:12:11 GMT -5
Post by Guinness on Jun 5, 2008 15:12:11 GMT -5
trippy- Kind of hard to take the advice on something this serious from someone that can't spell- Sorry, but Ed's an Adult that has been doing this for quite a while, and since we can't see you and have no idea who you are, writing like a 9 year old will get you all the respect and attention that a 9 year old receives.
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PAK38
Jun 5, 2008 15:33:49 GMT -5
Post by CharleyNovember on Jun 5, 2008 15:33:49 GMT -5
Ow...Big G. I think he was just trying to help.
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PAK38
Jun 5, 2008 15:42:16 GMT -5
Post by Guinness on Jun 5, 2008 15:42:16 GMT -5
Oh I have no doubt that he was- but when you come on a board and raise doubts about formulas and calculations, not to mention said calculations from a Mod, it would be nice to be able to back that up with something more than what appears to be a gradeschooler saying "Hey, that am wrongz!" That's all- he could be the next Einstein for all I know- but the message is lost on the well....message itself
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PAK38
Jun 5, 2008 15:46:12 GMT -5
Post by CharleyNovember on Jun 5, 2008 15:46:12 GMT -5
Me not following math formulas at all would believe either of them cause honestly hell if I know... I just know what will and will not blow something up out of trial and error. But I do see your point G man.
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PAK38
Jun 6, 2008 0:06:18 GMT -5
Post by Tough Ombre on Jun 6, 2008 0:06:18 GMT -5
umm.. i dont even see problems with his spelling, and Garrick, i didnt see this being brought up but those portable air tanks hold between 120-150 PSI usually the one i have is rated only at 125 PSI. -Cary
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biged
Master sergeant
Posts: 468
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PAK38
Jun 6, 2008 5:09:07 GMT -5
Post by biged on Jun 6, 2008 5:09:07 GMT -5
It is just the volume of a cylinder. You can calculate Cubic Inches a bunch of different ways.
Cubic Inches = ( Diameter / 2) ^ 2 * 3.141593 * Length Cubic Inches = Radius * Radius * 3.141593 * Length
The formula for calculating pressure is:
(4200 is the volume contained in a 12 gram CO2 this number can change with temperature.)
4200 / Cubic Inches = PSI
///ed///
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Ersatzjack
Corporal
"That silly Franz... he thinks we are winning."
Posts: 1,093
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PAK38
Jun 12, 2008 22:03:59 GMT -5
Post by Ersatzjack on Jun 12, 2008 22:03:59 GMT -5
Just checked back and want to address some stuff in my usual layman's speak. First off, no one is gonna get overpressurized here because the air tank rig is working out real well after the field test at the last event. We used 48cu tanks filled to 4500psi and regulated to 60-psi. It will always be HPA and not CO2. With the described tank it fires about ten times before emptying. We thought that was pretty good. Just show up with 3-4 tanks per event and you have a real useful weapon. I don't foresee a larger tank being used because the small ones are just fine and don't load the gun down. You can just throw the rig in the netting and you are ready to roll. We might go to a 96cu tank but that will be the largest we try for. When we get that fixed I'll report back on the number of shots. Calculations are great but so are actual results.
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PAK38
Jun 20, 2008 0:01:08 GMT -5
Post by trippy on Jun 20, 2008 0:01:08 GMT -5
You're right, Guinness, it is a dangerous thing to call out a mod on a new board. You don't know me, and I could be some random kid making stuff up; however, any kid that has made it past eighth grade knows how to find the volume of a solid: base x height. In this case, base would be (pi)r^2, thus (pi)r^2xl. I was unaware I had to cite my sources for a fundamental math formula: www.math.com/tables/geometry/volumes.htmFurthermore, I apologize for forgetting the 'r' in 'your' -trippy
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Russian
Corporal
Magician
Posts: 923
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PAK38
Jun 20, 2008 0:27:01 GMT -5
Post by Russian on Jun 20, 2008 0:27:01 GMT -5
I find it harsh and a little daunting for the prospect of this board that when a new member joins, and says something to a mod, as if that were a position Holy Writ, that they dislike, a person is shot down. Seems to me that, either A) we all accept each other as equals here on the "inter-web", or we give positions for longevity/age. If the latter, then disrespect of a position shouldn't be so harshly taken down as to merit scrutinizing the person's spelling. Hell, if it's all about respecting people for positions and time on a forum, then I beat out most of the moderators for longevity here, right? No, that's foolish. So, we should all get off our high horses, and just accept that maybe, a "n00b" member may have something to say. Lighten up, eh?
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PAK38
Jul 15, 2008 17:22:21 GMT -5
Post by Garrick Udet on Jul 15, 2008 17:22:21 GMT -5
umm.. i dont even see problems with his spelling, and Garrick, i didnt see this being brought up but those portable air tanks hold between 120-150 PSI usually the one i have is rated only at 125 PSI. -Cary Yeah, shop compressor tanks only hold that much pressure. Carbon Fiber wrapped High Pressure Air (HPA) tanks for paintball can go up to 4500 psi. Now that I just bartered my 92ci 4500psi tank to Ersatzjack to knock some of the price off of my K98, I think we'll see it in action at Baltic. I am estimating 18-22 shots based on our experience at the last event where we got 10+ shots off of one 68ci 4500psi tank. The advantage of using a paintball tank is that they are much smaller due to the high pressure in the tank and generally have a more consistent output pressure due to a higher quality regulator. This last point doesn't matter too much as the 850psi output from the tank is then run through a secondary regulator that drops it down to 60psi. (all of this is shown in my earlier post from April)
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PAK38
Jan 20, 2009 18:43:04 GMT -5
Post by Uscha Bahr on Jan 20, 2009 18:43:04 GMT -5
We have a 38 project going too. Here is a solidworks drawing I did of the armour. Unlike our 222 project I dont have a model to referance nor do I have a set of dimensioned drawning so it was pretty much a generalization baised on pictures. We have a CNC waterjet cutting system so the final product will be exactly as drawn.
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PAK38
Jun 22, 2009 17:30:43 GMT -5
Post by partisan on Jun 22, 2009 17:30:43 GMT -5
the formula for volume i think is lenghXwidthXheight
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biged
Master sergeant
Posts: 468
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PAK38
Jun 23, 2009 5:11:01 GMT -5
Post by biged on Jun 23, 2009 5:11:01 GMT -5
Trippy did have the correct equation. I edited and posted the correct equations. (That's what you get when you cut and paste from a paintball thread topic about volume.)
Volume of a cylinder: Radius * Radius * PI * Length
///ed///
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