Armalite Pistol?
 

Anyone here made an Armalite pistol I plan to make one with an inner barrel thats about 5 inches long, will the normal M4 cylinder work with this set up?

The idea really came to life when I noticed that I sucked at changing AEP magazines, I figured I might as well just make an AR pistol and share the mags with my primary

http://i6.photobucket.com/albums/y20...n/SP_A0132.jpg

Bottom one, still mechbox and motorless. Cut off the buffer tube thing completely. Yes I know if it was real it wouldn't work, so just imigine I'm shooting 9mm....

Project went from Pistol to SMG

Yes it'll work bur your FPS will be poor because it doesn't match the barrel length. You should get yourself a MP5K cylinder or perhaps drill a hole near the center of your M4 cylinder. Don't expect high fps from a setup like that though unless you use a really stiff spring.

You can always use a cylinder that provides you with more volume than needed. That isn't a big deal. More you can just find a 1/2 port cylinder, they're usually listed for MP5K.

MP5K cylinder idea sounds good seems easier

I wish I had a drill press and the craftsmanship to drill and work the hole as per Colin's idea...

You don't need to do that.

Might save your mechbox some stress, but you don't need to.

I'm thinking of an M100 at most for this build since I'll be using it in a machine pistol configuration.

Using a cylinder that pushes more air than necessary will degrade your FPS, compared to the proper cylinder.

Hey man, I'm planning the same thing, I figured that if I was getting 320fps with an m90 in an MP5k, then I should be able to get a similar fps with an AR pistol. I'm doing this for the exact same reason too, simplifying my gear to use the same magazines.

Check out my other thread, I'm looking to have an AR pistol holster made.

http://airsoftcanada.com/showthread.php?t=60190

While it does work to use a cylinder which provides too much volume, the spring hasn't reached optimal expansion speed by the time the bb has left the gun on such a short barrel. So the half ported cylinder allows the spring to reach maximum velocity before pressure is exerted on the cylinder, providing the best velocities for your bb.

I know that already. It's for a pistol, the guy was trying to cut corners, I don't think FPS would be a big deal in that case.

Unless you already have an armalite you want to butcher, why not just buy the m4 pistol? Probably easier and maybe cheaper than trying to find a short front end and a place to house the battery without a peq.
Almost bought one but took the mp5k instead to save on mags.

Once I tried a full cylinder in my MP5 and found a 30fps drop.

He was talking about a M4 cylinder, though. Figured he wasn't going to take the advice and put a full cylinder in.

In my case I do have an M4 I want to butcher. But who makes the m4 pistol for airsoft?

True, but the difference between full and MP5 type ported is about the same as MP5 type ported and the half port of the MP5k. So it might affect it. I have a couple MP5k cylinders sitting around doing nothing if he wants one, which would be a good idea if he wants a 5" barrel or close. Hell, maybe even putting the ported cylinder in there already in backwards with the short barrel might be the best idea.

I was thinking about that earlier. Anyone know if there are undesirable effects of mounting a cylinder backwards? Like a cylinder taper that I don't know about... xD

Yeah, if the numbers I found over at zshot are correct, there should be just enough volume to flip a 3/4 ported cylinder, assuming ~140mm barrel.

A stock cylinder in backwards would give an fps drop.

ICS makes one. I've wanted one for a while.

You can find it here

Is that because the cylinder tapers towards the front of the gun to allow for a better air seal?

Wow, that's one dog of a gun isn't it? Lack of buffer tube and strange front end (ignoring the RAS).

No, it's because there is less volume in the cylinder than there is in the barrel. A mild vacuum starts behind the moving BB, hence the term barrel suck. Really only if a long barrel is used, if a short one like a 229mm, you'd see a drop in fps.

Yeah. but if you're using a 4 or 5 inch barrel (101mm and 127mm respectively) then as long as you've got enough volume in that cylinder to push the bb out the barrel before the piston starts it's backwards journey, you should be ok, right?

Ya, should be completely fine.

Sweet. God damn I can't wait to be back in Canada to start this project...

Good luck with this, I've built a FMU Patriot
and owned that very same ICS M4 pistol and
the fps wasn't what they listed on that site.

As expected and said many times already—
you can get to 320fps but it's tricky business
when your dealing with such a shorty barrel.
Too much air to push and the bb exits without
reaching top speed. So you'll be finding the
balance between air volume/ length and
strength of spring is a bitch. Colin_S told me
about PDI springs being physically shorter
so they could reach expansion faster. I would
take his advice and the Guarder MP5K kit
plus a couple PDI springs.

Thanks a lot for the info about the PDI springs. That's a big help.

EDIT: Also, using regular pitch (as opposed to the traditional irregular pitch) springs will cause the spring to expand at a constant rate throughout the duration of it's expansion. Irregular pitch springs are designed to get increased spring expansion near the end of it's cycle, which for short barrel users, is too late at the bb has already exited the barrel.

For the lipo battery, I thing something around 1000mAh should fit correctly in there. Forget about 11.1v though. You will have barelly enought place for a 2 parts 7.4v pack, as in one cell on each side of the barrel.

I think you can fit a mini type in the fake buffertube if you cut the post on the body. Again you are stuck ar 8.4v, but you probably would be able to fit a 1200mAh 11.1v lipo in the same space.

The ICS one is awesome. Saw it at the warstore and nearly creamed the jeans. There are a few though I think. Worth looking into.

PDI springs aren't exactly shorter, they are various lengths. Across a few 150% springs I've measured, one was 6 3/8", one was 6 3/4" and one bruiser was a whopping 7" long! All the same brand and rating, but results right across the map. Hence my saying PDI springs suck, avoid at all costs.

I got a TM body left over from an upgrade and a chopped down barrel so i figured why the hell not, initially i was going to make just the upper and drop it into my CQBR but then i decided to go the extra mile and make the whole gun. As for the battery its going to be a PEQ2 solution. I've always wanted a PEQ2 unit anyways.

Well, Colin has seen many springs in his day
and if he tells me they tend to be shorter on
average I guess I'll believe him on that.

But, I've also heard PDI's had a rep for not
being consistent to what the rated fps claimed.
I can't confirm that with the newer ones being
sold, since my last 4 ICS builds all use PDI's
and all were firing very close to the rated fps.
Even my last ICS build which is my current cqb
m4, runs a PDI 130% and is getting 350 just
like PDI claims.

Doesn't matter, the idea is to use a shorter
spring. If you get one right out of the pack,
buy Stalkers shortest, or cut one down, great.
May be a good idea to get a few and try
different lengths anyway.

Good luck with your build.

Belongs to a friend of mine, battery is in the 'spare mag'.

http://img232.imageshack.us/img232/6415/dsc01715qv8.jpg

LOL I have a box of unmarked springs, my current plan is to toss in an old M110, if it works at say 300-330 I'll be happy, again its more of an ROF thing at this point. I've done high power builds but I've never messed with ROF. So I'm interested in learning all that good stuff.

Pic finally added need to get a mechbox from Huangs sometime soon