SpudFiles

well, i was looking at the pellet guns availiable on the market, and sure they were accurate, but they cost a fourtune, so, i thought, why not build my own? i have a few questions....

first off, for someone with a .177 cal smoothbore air rifle-

what kind of groupings do you get with pellets?

second, for those with a rifled .177 cal air rifle, where can i get myself barrelstock!

the pressures involved in a high quality pellet gun are amazing, something n the order of 100's of psi. i belive you should talk to captian-LaW (tired, cant remember name, 4:20 in the morning).

just a idea on the pressures involved, if you have a combustable liquid in the piston area/breach, it will explode when fired

A-98 wrote:just a idea on the pressures involved, if you have a combustable liquid in the piston area/breach, it will explode when fired

I think (hope) he means making a pneumatic as they are much more feasible to build, easier and with more power potential.

You'll never achieve the 3500-odd psi that commercial PCPs have in their chambers, but with a long enough and tight barrel and big enough chamber, as well as a modded sprinkler/quick exhaust valve, you can approach good enough performance.

You can get a rifled barrel from airgun spares stockists like chambers but I don't think it's worthwhile - after all, diablo shaped pellets are designed to be stable in flight without being spun. I would suggest however that you get a 5.5 or 6.5mm barrel and use 0.22 or 0.25 pellets, as 0.177 will give you less performance - PCPs are less efficient with air as the calibre goes down. Make sure you use average weight pellets though (eg 8 grains/0.5grams for 0.177, 16 grains/1 gram for 0.22) as heavyweight pellets work best with rifling.

Well as for the grouping with a smoothbore, I get pretty darn good groups with mine. From 25 yards I can hit a pop can all day long (I'd try farther by my backyard is small). And from 15 yards I can shoot a pop can open, I mean shoot out the little tab that covers the opening.

A-98 wrote:the pressures involved in a high quality pellet gun are amazing, something n the order of 100's of psi. i belive you should talk to captian-LaW (tired, cant remember name, 4:20 in the morning).

just a idea on the pressures involved, if you have a combustable liquid in the piston area/breach, it will explode when fired

If I am not mistaken, that is called dieseling? Not sure how safe that would be on a standard pneumatic piston ie lifespan of your gun, unless of course you build the cannon with the intention of dieseling.

i actually don't know if myn is smooth bore or not, i have never really checked. but from 15 meters i can hit a penny, and i can hit pop cans form 30 esally, by the way, i have a scope.

Well I'm pretty proud of my accuracy since I just have ironsights. I actually haven't shot mine in a while. I cut a coke can in half a while back and just got bored with it.

To make a pellet gun, you definatley want to build a diferent type of gun than al the cannons you can see. A powerful pellet rifle can send a 0.5grams pellet past the speed of sound (36 joules, 380 m/s). The thing is, the air is very hot when the pellet fires. The air that propels the pellet is frickin hot and thus travels quicker. a normal penumatic runs with 100 psi...my experience is that pellet shot at even 300 psi with my piston rifle wont get past 230 m/s. (a BB airsoft 0.2g wil go 350 m/s)
You need to come up with something better......got an idea?
well......i'll tell you...you need a very small chamber...pressure rated to about 4000 psi. (burst at 12,000 psi) fill the chamber with propane...and make it a mini hybrid. run at 5X/5bar mix, so you are still far fom the DDT, an you will get running pressure very high, with high temperature gases, and so the gases will travel faster than sound in "normal" air.
you need a burst disc, your barrel must leave 6-7mm of steel wall around the bore. (so that you don't get shrapnels in ya face.)

That the basic idea. with a long enough barrel, you can get even faster speeds than high pressure PCP's.

P.S.: you need lathe.

CpTn_lAw wrote:a normal penumatic runs with 100 psi...my experience is that pellet shot at even 300 psi with my piston rifle wont get past 230 m/s. (a BB airsoft 0.2g wil go 350 m/s)

Using my HVBB project I managed to push a 1 gram pellet to around 235 m/s at 400 psi.

that is what i say, even at very high pressure using pumps that are not made for such pressures, you can't propell a pellet past the speed of sound...with hot gazes , you can.

im not really looking for high power, just something i can "hit those cans" down with effectively. i did find a peice of tubing on mcmaster that was .251 inches ID, thus the right size to fit .25 cal diablo pellets. i dont know if im gonna get AWSOME accuracy out of this thing, but whatever, it will be cool. i might even be able to rifle the peice of tubing myself....

anyway, thanks for all your help, youll see this little bugger out here sometime. im thinking of making it piston-valve actuated int he over/under fasion. the chamber will be 3/4 inch galvanized steel, the piston a 1/4 inch brass tee, and of course, the .25 cal barrel. ill slap all this onto a nice homade wodden stock, a blowgun, and wala! pellet gun. might not get the 500-1000 FPS power my friends pellet gun gets, but hey, i can sure have some fun plinking.

plus, it makes him cringe when i say im building myself a .25 cal airgun...... ecven if its got halph the power his .177 cal rifle has...

EDIT: i just did a GGDT test of a diablo .25 cal pellet traveling at 250 FPS (i did the calculations on my "predicted" gun). if the gun is elevated at a 1 degree angle, (easily acheved by adjusting my scope) i can get an accurate range of 135 feet out of it. the pellet hits its appogee at 60 feet, and hey, thats good enough for me.......

A piston would be overkill, just get yourself a QEV - even a 1/2" one will suffice. Make sure you can pump it to at least 200 psi, as you get smaller chamber pressure helps more than chamber volume. If you want accuracy, make sure you have a pump that can give you consistent pressure.

plus, it makes him cringe when i say im building myself a .25 cal airgun...... ecven if its got half the power his .177 cal rifle has...

Have a look at what GGDT has to say, you can easily get at least double the power of his gun

with my smoothbore Crosman i can get darn good groupings, although i have never used it with paper targets. Anyways, just buy a Crosman pellet/bb gun for $35-50, they're lots of fun, quite accurate for the price, and about as rugged as possible for something made of 95% plastic (that means no wood to oil or polish or worry about scratching. My point, great gun, good price, 'nuf' said.

trust me, you will like pressing the button, hearing a sharp "crack" , and very next to this, hearing the pellet hit target!
we were in the forest in a cool spot, and we fired my pellet rifle with powder, the guys were amazed of the velocity achieved by a .177 pellet.
you can make on easily....take galvanized steel pipe if you don't have access to a lathe (like me), use a 1/2" tee (female/female/female) one in put for propane, one for compressed air, one to connect to the union, and reducer from 1/2" steel to 1/4" copper (perfect fit for .25 pelets)

for jackssmirkingrevenge: the longest barrel i can get is 28 inches long.... but i did have a heavier pellet wieght on my test, i also didnt do the valve thing right.... i realized i had the piston like at a weight of 500 pounds........

also, i have a bike pump that will hit 300 PSI....

and i guess your right, a 1/2 inch QEV will work much better than any mimi-piston valve i can create. plus, its easy as pie, and pretty cheap.

and captain law.... i have tried .25 inch copper, and it doesnt fit my 1/4 inch steel slingshot ammo (wich is basically a .25 cal BB....). well, it fits it, but not well........ and i have to sway away from the whole hybrid things. ever scince i birned all the hair off my face with my combustion my parents wont let me make anything that has burning stuff in it.

by the way, id did make a mini combustion once that shot .25 cal bb's, and for the low FPS i was amazed at the power. it could consistently punch holes in sheetrock........ and the barrel was a pen tube..... im hoping ill get better preformance with a pneumatic with a .251 ID, 28" long barrel......