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Barrels

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: jackssmirkingrevenge » Mon May 21, 2012 12:02 am

wyz2285 wrote:Is the bad accuracy because it was too powerful or there are something to do with the barrel :?


It could be many reasons, I would say that 100 yards is simply beyond the capabilities of 0.177", even shooting relatively heavy pellets at 1050 fps.

For a "normal" air rifle shooting 8 grain pellets at 900 feet per second, 50 yards is already stretching it.
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Unread postAuthor: wyz2285 » Mon May 21, 2012 2:18 am

I have seen a lot of .177 shooting well at 75m, some of them actually can still be accurate after 100m :?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: jackssmirkingrevenge » Mon May 21, 2012 3:12 am

On a windless day shooting prone with a bipod with my FX Monsoon I can keep a 1.5 inch group at 120 metres, that's shooting 16 grain pellets at around 900 feet per second. A little wind or more challenging position is enough to throw me off though.

There are so many factors affecting accuracy that putting it down to the barrel is very difficult. You can clearly see the pellets are corkscrewing at the end of their flight, it's likely that they are being deformed by the air blast.

At those power levels I would probably be using something like this: http://www.airgunwarehouseinc.com/py-p-284.html
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Unread postAuthor: Gippeto » Mon May 21, 2012 10:26 pm

jackssmirkingrevenge wrote:On a windless day shooting prone with a bipod with my FX Monsoon I can keep a 1.5 inch group at 120 metres..


Bloody impressive with an air rifle. 8)

What's a windless day? :cry:
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Unread postAuthor: jackssmirkingrevenge » Mon May 21, 2012 11:32 pm

Gippeto wrote:Bloody impressive with an air rifle. 8)


The FX makes it east, it's amazingly consistent. I thought there would be a trade off in accuracy because of the semi-auto action but this was not the case, after all the reloading system is completely independent of the trigger and valve and acts after the pellet has left the muzzle so it doesn't interfere at all.

Also, don't ask me to do it in any other position than prone with a bipod ;)

What's a windless day? :cry:


A very rare event indeed :D
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Unread postAuthor: wyz2285 » Wed May 30, 2012 9:48 am

My weihrauch barrel arrived :D cost me 105euro total :roll:
Blued, chamfered, .177 cal 600mm.
The threading is on the muzze side, Gippeto you were right :) not a problem as I wasn´t planing on using it for barrel mount, handy for supressor mount through.
Now I have a problem, there is a pre-existent o-ring on the breech side of the barrel, apparently used to seal the barrel/breech connection. It looks good so I thought a new way to mount the barrel, as shown in the diagram. There is also a groove on the barrel that will help me to mount it. Any thoughts?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: warhead052 » Wed May 30, 2012 12:02 pm

Find a way to secure it nice and tight with the groove, and have it set up like the second diagram in the picture. I wouldn't modify it if I could help it.
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Unread postAuthor: wyz2285 » Wed May 30, 2012 1:23 pm

Yap, sounds good and simple. Also the barrel is damn heavy, so to keep the gun balanced I may make it in a bull up configuration.
@Gippeto I'm having problem with the chamber as I was try to have the o-rings to isolate the threadings from the chamber pressure, but as the threading's depth, the chamber wall is unnecessarily thick, that would add a considerable weight. I will do a simulation about yield strength to see if the threadings are ok when exposed to chamber pressure.
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Unread postAuthor: Gippeto » Wed May 30, 2012 4:11 pm

cough**cough.....

http://www.network54.com/Forum/275684/m ... %26quot%3B

Have some thoughts on the reciever too, but not enough time atm.
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Unread postAuthor: wyz2285 » Wed May 30, 2012 4:20 pm

Actually I have thought about having the head of the screw to take the load, didn't went any deeper through. Now I have to go back to study screw shear strength again :roll: Gippeto can you send me that link about screw shear strength? The old one isn't working anymore, says pahe not found.
Thanks for the helps.
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Unread postAuthor: Gippeto » Thu May 31, 2012 8:35 am

Shear strength is an easy one, but not the only one you'll be needing.

To calculate shear failure, you need shear strength of the material and the area of the material.

For shear strength, use 60% of yield strength...ie if yield strength of the material is 100 000 psi then shear strength is 60 000 psi.

Although I build very much the same as Walter, I prefer to use the screws minor diameter for calculation. A common screw for me to use is either an 8-32 or 10-32 low head socket head cap screw with a yield strength of 160 000psi. These have larger head diameters that help with bearing stress on the tube...which we'll cover in another post.

For calculation, the shear yield strength of these screws is 96 000psi.

Minor diameter of an 8-32 is .140" for an area (pi*r*r) of .0154in2

Multiply area by shear yield strength.... .0154in2 * 96 000psi to get 1478.4 lbs which is the force required to cause a yield failure in shear.

The load on the fasteners holding the "plug" into your tube is calculated by multiplying the pressure in the reservoir by the surface area exposed to pressure. I use a safety factor of 3...so I'll use enough screws to ensure that the screws will yield at a minimum of 3x my maximum working pressure.

Making sense? :)

Bearing stress is next. :wink:
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Unread postAuthor: wyz2285 » Thu May 31, 2012 9:21 am

Yap that makes sense, I will do a FEA simulation :) by the way the unregulated part chamber maxim pressure will be 250 bar instead of 200, but I have checked the chamber yield strength, safe enough.
Edit, going to simulate the yield strength of 4 8-32 socket head screw in shear, also the bearing stress on the chamber wall.
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Unread postAuthor: wyz2285 » Sun Jun 03, 2012 9:38 am

Made a simulation about 4 10-32 screw on chamber, safety factor about 1.5.
Increased to 6 10-32, minium safety factor 4.66 :) chamber wall 2.5mm thick. Now I only have to calculate/simulate to see how deep the screw should be :)
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