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Full auto blowback is going ahead!

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Full auto blowback is going ahead!

Unread postAuthor: inonickname » Fri Mar 20, 2009 11:22 pm

Well after some discussions with my metals teacher I've gotten permission to build the blowback design Here. This includes the use of lathes and a full size mill (manual, not cnc) along with various other tools and machines.

This is built on the following conditions:
-Cannot be in a "firing" state on school grounds
-Must never be used to shoot/harm/threaten living beings
-Must bring in own materials, OR use materials in the sheds (there is plenty..)- i.e. no ordering in new materials
-Springs, nuts, bolts, air fittings, valves, o rings et cetera must be sourced by me.

Obviously these are all quite easy to satisfy, so it will be built! :D

About the design:

Hammer valve, actuated by a bolt in blowback configuration
Bolt "selects" ammunition and reloads via bolt position
Trigger and sear with side bolt for manual re-cocking
Only uses 2 springs, with an easy to tune design
Modular and serviceable
Can use magazine, hopper et cetera
Can fire bb's or pellets
No need for airtight mag or hopper.

Here's a quick concept drawing:
Image

From left to right:
- Front plate, barrel and hammer seat (hammer cover not pictured)
- Hammer valve
- Bolt
- Side bolt (manual recocking)
- Body

Now due to the limitations of google sketchup (can't push/pull curved surfaces) the air inlets on the bolt and hammer are missing, but they will be there!


Can anyone see problems with the design (see link above for workings). Note that the hammer valve has been centralized (thanks to JSR)

Thanks guys
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Unread postAuthor: POLAND_SPUD » Sat Mar 21, 2009 10:11 am

it's good that you use sketchup.. nicely done but it would be nice if you put a pic showing it fully 'assembled'... or include the file so that we could all see it in 3D

Now due to the limitations of google sketchup (can't push/pull curved surfaces) the air inlets on the bolt and hammer are missing, but they will be there

actually it can be done quite easily in a different way.. lol sorry but I don't know how to switch sketchup from polish to english so I can't tell what this tool is called :oops:


do you guys have machine tools in high schools?
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Unread postAuthor: inonickname » Sat Mar 21, 2009 10:20 am

Yes, easily sufficient enough to finish this..

Our school is moderately funded tool wise, so there we have:

-Mill
-Tap and dies (past 3/4" i think)
-Lathes (total of 6, and several woodworking ones)
-Multiple drill presses
-Center drills, carbide drills, index drills..all of that
-Pipe benders et cetera..

There's also other cool things..such as vacuum formers.. Apparently depending on the budget a CO2/plasma cutter, TIG welder and cnc equipment is on the cards..so it should be good.

Is the tool you're referring to on a newer sketchup? I haven't bothered to update...I'll do some google searching anyway. (will post new diagram when I figure this thing out)
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Unread postAuthor: psycix » Sat Mar 21, 2009 2:47 pm

I assume this will be machined out of aluminum?

I'm looking forward to it. Make sure to make the thing tweakable in every possible way.

Also I wonder:
The cut on the right side of the block to house the side bolt, does it go all the way into the big hole to connect to the hammer? Because that would mean air would leak from the sliding tube.
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Unread postAuthor: Moonbogg » Sat Mar 21, 2009 4:17 pm

Thats google sketch up? I didn't know google sketch up had 3D capability! Whoa, thats crazy. I love what your doing, this is great. Keep kickin ass.
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Unread postAuthor: POLAND_SPUD » Sat Mar 21, 2009 4:49 pm

ohh that's cool you have machine tools in high schools... hmmm you never stop learning :roll:



ok now as far as the tool is concerned... as I said I don't know how to switch sketchup to english version (I suppose there is such an option) but I made a screen shot....

it shows what you have to do in order to cut holes on curved surfaces... basically all you have to do is to create an object which you position where you want to cut a hole and then you use the tool selected (in the pic) from the EDIT menu and then you delete the substracting object... if you try this you'll see what I mean
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Unread postAuthor: SEAKING9006 » Sat Mar 21, 2009 8:04 pm

My school is also fairly good tech-wise. (VERY well stocked shop class, home of a first rate BEST robotics team.) Not only do we have most basic machine tools (planer, bandsaw, tablesaw, angle grinder, various sanding tools, drill presses, ect) we also have a CNC lathe and a CNC mill, though the lathe is used with an old PC running MS/DOS and proves to be problematic, and I have never for the life of me seen the mill hooked up to jack. But we DO use the lathe to make nosecones for rockets in one of the teachers classes. I have always wanted one of my own.
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Unread postAuthor: covey12 » Sat Mar 21, 2009 8:46 pm

yea, once i get in the navy my dad is gonna let me use the work shop, where you make anyting that comes to mind lol (only becuase hes incharge)
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Unread postAuthor: inonickname » Mon Mar 23, 2009 6:01 am

Well it's time for an update I suppose.. No metalwork until Thursday/Friday so I've been working on some of the less practical, aesthetic pieces.

A quick rundown on whats built so far:

Silencer:
-Anodized aluminum filled with a dense, soft acrylic gap filler. Plexiglass plugs in either end, barrel will have slots milled then rebored to prevent issues with ammunition dragging on burrs or the barrel getting deformed.

Handle:
-Cut from delrin. Trigger will be one of the 'el cheapo blowguns- you know the ones..odd hook on it..red trigger. It will be streamlined and incorporated into the handle. Also note that this will not use a sear, it will be a manual recocking job!

Stock:
-Arm support cut into a crescent shape from delrin.
-Odd aluminum 'U' channel used, may be bored out and modified to a telescoping stock.

Grenade launcher:
-Short length of aluminium tubing, with a 90-110 psi burst disk. Schrader fill. This has been tested but range proves poor (you get under 10 cm of barrel travel) but it should go along with the gun nicely. Testing has shown it's best to fill with flour (think airsoft room clearing) and fired.

Blowback mechanism:
-Not much done, but the chamber has been selected and polished.

Sights:
-Cut from plexiglass. Use notches (line them up) for aim. Notches have been made coarse (plexiglass goes chalky) for visibility.

Accessory rail:
-Yet another delrin block..Nothing much to say about it. Uses a U channel which has a bolt passed through it to secure the item.

Image
View of (back of) handle.

Image
Accessory rail..

Image
Stock.

Image
Grenade launcher, flash on 'el cheapo kodak camera produced some great glare.

Image
Barrel (may be replaced) and silencer.

Image
Parts lined up next to ruler. (30 cm)

Image
Mock gun setup (viewed from stock).


So..I reckon it's going fine so far. Having to manually recock for every burst will get annoying but it will keep the gun nice an' simple.

Any thoughts so far? Hate it? great..
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Unread postAuthor: Demon » Mon Mar 23, 2009 6:34 am

Great, looks very nice for now, i cant wait see it shooting!
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Unread postAuthor: POLAND_SPUD » Mon Mar 23, 2009 10:48 am

it looks very good... I can't wait to see it shooting
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 23, 2009 12:59 pm

Coming along nicely, let's just hope you get the mechanism to work :) to be honest I would build the valve and breech first and test it before making naything else.
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Unread postAuthor: SEAKING9006 » Mon Mar 23, 2009 1:07 pm

He speaks the truth, I made the error of building a prototype without properly determining C/B ratio and the effect all the dead space would have on it. Needless to say, a second prototype was designed immediately.
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Unread postAuthor: inonickname » Tue Mar 24, 2009 2:29 am

Well personally, building things like this is what I like doing with my time (rather than play station or whatever..have a wii which is nice). The materials I used are both readily available to me and (fairly) easy to work with more powerful tools.

If I run out of time/the mechanism fails I'll use the chamber to build a coax, I'm thinking rather substantial pressures seen as the walls are 5mm thick..

Thanks for the input, I'll keep you posted
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