It's called a Tavor.  lol

And it sounded like it would be a 3D printing project , thus paperwork wouldn't be a problem for any other printer owner.  Which F-ing cool!

Not really they just use the same magazine. The AUG wearing a nato stock would be a ar15 bullpup by that logic too.

Quoting is getting cumbersome with the size of the replies, so I will just reference the number...

1 and 3)  The reason I suggested grooves is that the carrier travels in a tubular receiver with no room for springs, so the grooves were to have room for springs, yet still maintain an overall tubular shape as a guide for the carrier.  I assume that you other means to guide the carrier.  Since the springs extend so far forward, much of my problems with the design go away.  I would suggest that the front part of the draw bar be the location of your charging handle.  The AUG has the ability to switch to left eject, and with the location of the charging handle so far forward in their (and your) design, you really don't need to swap the charging handle to the other side.  It is easy to reach over to draw it back when it is that far forward.  That saves you some complexity. I would suggest attaching the handle to a deep cup over the end of the draw bar of sufficient length to ensure stability when pulling back on the handle.  One constraint I see is the added width to envelope the 10 and 4 springs. I would suggest a non toothed barrel nut like some of the newer rails have.

2) The AUG with a 20" barrel is 31.1", and when I put it up to me face, the left port cover is pretty much under my cheek.  I can't see how your ejection port will be significantly farther forward at 31.9" with a 20" barrel.  3/4" isn't much.  Ask some other AUG users.  I can't speak for any other bullpups, however.

4) Now that I have read a little on the draw bar, ad examined the AK spring, if take the forward end of the AK spring guide and add a mushroom shape (basically and annular groove about 1/8" back from the end, with the forward side of the groove having a 90 face (shaped like the end of an AUG left spring guide rod) you can use the same type of FA as the AUG.  You can still use it, just with the strong side hand when shooting left handed.  I know generally keeping the strong hand on the grip is preferred, but you don't when using the FA on an AR15.  Don't forget that the reason the AK spring is stable is due to the front of it being well contained by the hollow in the piston.  Your eyelet will probably need to be tube of at least several resting coils long if you don't control at least one half of the spring.

5) not really related to 5 earlier, but if you really think you need a deflector (I still don't see a reason, but I am not going to convince you) If your ejection port was a little longer than needed (towards the rear), it could snap in there, and when removed, the same snap in notches would secure the rear non ejection side port cover.

6) Here is a thought.  I know that you are firm in the diametrically opposed springs, from your first thread.  And you have stated that you don't want to switch spring locations.  Will having the springs at 10 and 4 for right hand ejection allow true 3 o'clock ejection, or more like a 2-3 oclock ejection port?  If the latter turns out to be the case, when switching to a left hand bolt, you would have an 8-9 o'clock ejection port?  It sounds like your receiver is going to be at least a little wider than an AR15, there could be interior contours to guide the case slightly up or down, depending on the side.

One think I have to say is that I really like that most people on this forum are so familiar with the AR 15 and we can discuss very complex details and not need a ton of back story. I have seen and was inspired by the Longziz. No one has posted any links to any of the guys working on the 3d printer side. One of my other inspirations was the Defcad Bullpup, aka the Shanpup, code name Hanuman, by Shanrilivan. There is a forum on defcad devoted to 3d printing lowers.

http://imgur.com/a/33bOp#0

1. I am going to work on getting good pictures of the drawbar concept. My model is a little messy. Once i do it should make more sense. You hit the nail on the head with the barrel nut. That is where i would likely put a bulkhead and an eyelet.

2/5. I admit I didn't really take the time to put my dummy on the rifle how everyone may hold it. I kind of had him standing straight up in a neutral position and canting his head down. I'm not saying the deflector would be a serious hunk of aluminum like it is on the AR (especially if I am getting my upper machined) it could just be an optional snap on/screw on feature like you are saying .

4. I only mentioned the ak spring since it uses 2 piece wire form guides. I like the idea of pushing the drawbar to charge if it is stable enough.

6. The ejection port is directly opposed to the ejector …I like the design option to change the ejection angle and guide the cases somewhere different but I wonder if it would work without changing the ejector/extraxtor location on the bolt. Does anyone have any experience with this?

When I get more done I think it will answer many questions…as well as bring up even more.

How does the BCG reciprocate in that design?

There is already a "lower" for converting an AR upper to a bullpup in the works. But it is a 22 based on a S&W. But there is potential here to use a bufferless upper like the Rock River instead.

http://bullpupforum.com/index.php?topic=3417.0

I was mistaken about about my charging idea.  I forgot about the rigid connection needed. DOH!
Making the deflector a snap in feature allows the port cover to snap in.  You will need some method of attaching the cover, so that solves two problems with one solution.
The ejection port is not exactly at 3 o'clock on the AR15.  But if there is room to have the ports at 3 and at 9 without running into the springs, there should be no reason to move them when swapping out carriers like I suggested  I was originally thinking you were using an AR15 shaped interior (tight tube) with closer springs and didn't think there would be enough room for 3 o'clock and 9 o'clock ports, since the AR's is more like 2-2:30.

ok, it is killing me.  Why a deflector?  I just don't see why it is needed.
And here is a thought.  With a wider receiver, the rear edge of the port is farther away from the bolt when it kicks the round out.  So odds are it will be hitting it on the way out, thus it will act as a deflector.  Better beef it up someway if it is a poly receiver.

You are keeping the carrier, but does the key need to be the same shape?  You could change the shape of the rear of it to use it for some functions.

If some idiot wants to put a potential grenade next to their jugular than so be it.


Me?   Naw I will keep the KABOOM potential out in front of my face.

I dont think the OP has seen enough carrier and upper receiver splitting KBs to decide his idea isnt so great.

Any recoil assembly that makes use of a folding stock would be an option for a host.

I don't think there is anything flawed about the AR system that would make is more prone to explosions than any other system. Or do you have some new evidence of this? If your point is to take care in designing the upper receiver to protect the user I agree.

If your point is no bull pup is safe, I don't know what to tell you.

His point is that kabooms happen, and when they happen in ARs, the upper is often split.  I've not seen a catastrophic kaboom in a bullpup, but that's probably due to the difference in numbers out there.  The RFB for example has two sheets of 0.06" steel between the chamber and the shooter's face, but that's .308.

If you're going to use nearly stock AR uppers, then my suggestion to protect the user would be to put a wall extending from the lower that projects up along side the chamber area of the upper.  This might mitigate some kaboom concerns, albeit at a weight penalty.

I a proponent of steel. This is a constant back and forth in the bike frame industry (4130 vs 7075). Steel is better at absorbing energy (toughness). This is helpful in the case of an explosion. I have 3 concepts for the upper and 1 of them is steel. the others are aluminum. Anyway its nice to know the thickness of another design thanks.

Ya i don't mind the double walls idea (as was mentioned the RFB does). I need to have layers anyway for the action spring i want to use. I should probably do some more modeling instead of vegging out on AR15.com.

@Bretshooter

I moved things around and I have come to the conclusion that springs at 9 and 3 are not as bulky as i thought after sizing them so its probably acceptable. they will just make the bolt release harder to get to…I think this is ok since you could just pull back on the charging handle instead of slapping the bolt release. It would be easier to show a new shooter how to work the rifle with one less button for them to remember (just trying to rationalize it :). I put some pics together. One of them i threw in the baseline hand guards for reference. The big red things are the ejection directions. Also the drawbars are missing some features so don't read into that too much.

So you would be using "drawbars" to connect the carrier to the fronts of the springs?  That would work, but it may be more challenging to disassemble/reassemble.

Ya making assembly easy is key. I'm thinking the drawbars would hook into the carrier catcher plate and you would un do them first then reach into the front and finger the loop loose and then pull the drawbar spring out the back. Undoing and redoing the connection by the FSB is what I can see being potentially difficult if designed wrong. Threading the assembly in thru to the fromt may be tricky but i'm designing the drawbar springs to have the correct preload so it would help keep the spring somewhat rigid when putting it in there. Similar to how the ak spring assembly keeps its shape. Plus the drawbars will essentially be a bundle of 4 wires wrapped in another wire when its being inserted.

Sounds a lot more complicated than it needs to be...

I misspoke. What i meant to say is " Plus the drawbar spring assembly will essentially be a bundle of 4 wires wrapped in another wire when its being inserted" The drawbars would just be regular solid steel wire form like in the AK. I was trying to say the cross section of the drawbar spring assembly will be the 2 drawbars (4 wires) and a spring (wrapped in another wire). Its nothing new i'm actually just describing all drawbar springs so I don't claim its my idea.

Would it make it easier to use a solid guide/draw rod instead of a wire setup?  I know it would sure be easier to control for assembly/disassembly.

it may but my thoughts on that is it would be less stable and need more guidance i.e. eyelets i do like the idea of less fingerig by the fsb tho

back on the shell deflector and forward assist my other goal is a universal uppet for a bullpup and traditonal layouy. i will post some pics on what i mean on that when i can.

What about the M17s?

Less stable going in, but once in place?  Rods are solid, catch plate at rear fixes that end, and whatever was going to fix the forward end will still do it for the rod system, if I understand you correctly.
As for your eyelets, they could be part of a collar that clamps to the barrel nut after it is torqued into place, and be as long (or longer) than the nut is deep.

And I was thinking your 10 and 4 was working well.  Looking at your images, is that a carbine fore end or an M4?  Just trying to get an idea of how wide the over all design is.  Having the ejection angled allows for 3 and 9, but IF 10 and 4 leaves enough room for 3 and 9 ejection with the springs in tighter to the barrel nut, it may be a preferable arrangement.  And it would put the charging in the forward top right position, which is a very ambidextrous accessible location.

Or sell your AR and get one of these:

http://www.ar15.com/forums/t_6_43/408069_New_M17S___Tell_me_all_you_know.html

Hmm I think we are on different pages. I may have to invent some terminology. Think of in a standard AR the action spring reacts against two ends

1 muzzle end (via the buffer)
2  the shooter end (via the end of the receiver extension)

In the drawbar concept the muzzle end of the spring is near the FSB and is pulled back via the rear  internal drawbar. The shooter end of the spring is held via the front drawbar that is hooked into a modified hand guard cap.  

If you go with a solid rod the you only have one drawbar. The shooter end of the spring is no longer reacting near the FSB via the draw bar anymore you would have it react near the back of the receiver.

Here is what I was thinking.

I'm sure I would like shooting it. I just think its more fun right now (during the crappy weather) to work on designing a new type of rifle. I obviously am inspired by it with the "upper" and "lower" like an ar.

Take the pic of your rod on the left.  Now fix the rear of the rod to the carrier and have a plate behind the spring for it to push against. mounted to the front/middle of the upper receiver.
Then you could have an additional guide rod or tube, and it's fully constrained and captured, and if you set it up right, you won't have to preload the spring to assemble it.

You would still have 1/4 the work if you compromised and went with an overhead spring..  just saying...

There are no real, articulable disadvantages, other than you don't like it

Ha, I didn't say I didn't like it. I didn't know thats what you were describing.

It seems like you are describing an inside out drawbar spring where the front drawbar is a tube on the outside. If you connect that tube far enough forward, sure it could be stable and not require any eyelets for guidance. I'm not fully sure how you are saying you won't have any preload since the goal is to match the spring rate and preload of the AR. The AR has roughly 4.3" of preload.

For reference the springs I have to use are 23" long so that is why i'm concerned about stability.

The inside out drawbar may be more robust I have a feeling getting the tubes are rods are going to end up costing more than the wire forms. I will try to see if i can shrink the spring enough to get the inside out drawbar to sit in the notches of the standard barrel nut in that case it may be worth it since then i can make the design less bulky.  

I did look in to regular extension springs what i kept running into was a failure means you totally loose the spring force. The other name for the drawbar spring is "safety spring" for this reason. I'm also nervous about why i have never seen any other designs use regular extension springs like that. But no doubt that could work also.

I was saying that if you've got the spring captive on a rod, with a head or bolt on each end, you can remove it without unloading it.  When you install it, it only needs a small bit of interference and you're at your preload.  Similar to how a Glock or similar action spring comes out as an assembly, most of the preload is never released.

Sure I agree. The preload should be in the spring assembly already.  pre load in an extension spring means making it longer it should be easier to hook up.

This was in ref to your reply to RDTCU, I forgot to quote it.  I think I am up to speed on the draw bar springs.

Here is the 2nd goal. A universal upper.

What advantage does your "universal upper" have the current upper doesn't?

The recoil system would be built in to the upper. This, along with spreading out the pivot and take down pin reduce the forces into the lower allowing a plastic lower. Think the original M17S.

The recoil system has been built into standard pin length uppers already, albeit at the expense of full-automatic fire.

How does lengthening the pin distance lessen the force on the lower?  Plastic lowers are already in use, though the most successful is the CavArms/GWACS design with an integrated stock reinforcing the weak point in the takedown pin/buffer tube nexus.

There was a full-auto ZM variant, it used a toggle that engaged a notch in the shortened carrier to activate the auto sear.

If you look around enough, you'll see that the pivot pin for the toggle is on the right side of the lower, above the FCG pins.

I can't find the picture I'm thinking of right now, but here's one.

I see they moved the forward assist up as well due to the short bolt carrier.  It was the Olympic buffertube-less action I was reading the user manual for last week and the full-auto had a shortened carrier with a short buffer tube to trip the stock auto-sear.

The best way I can explain why the forces would be lower (without getting too technical) is think of the pins as taking the force of the shot and the moment (torque) due to the offset (of the barrel) from the center of the pins. If you spread the pins out the torque stays the same but the force goes down. Maybe think of how high the forces would be if the pins were very close to each other.  This is a consequence of Newton's Second Law. Putting the springs in the upper eliminate the weak spot you are describing by the takedown pin.

Ah, I'm tracking now.  Seems the only modification to the AR BCG on the Olympic was to cut the tail off, & a custom gas key.  I think chopping off the end is an acceptable modification until someone starts making short BCGs for bullpups, and no matter what you do you'll need a custom gas key, just like any piston mod.

The direction i'm thinking would be to leave the gas system untouched. The recoil system was where I was focused. When I look at the tail of the carrier in my computer screen I keep thinking about how much shorter i could make it by chopping it. I think the simple rough up I did proves that the length of pull and overall length of a bull pup rifle that uses a run of the mill BCG could work.

I'm thinking thru how to protect the shooter during an explosion in the event of a barrel obstruction and I was focused on the upper and the shooter's face, but I'm now I'm thinking I don't like how the ar mag is held in and likes to explode out (near your wrist in a bull pup).  Does anyone think this is an issue with other designs that use the AR mag? The rock in mag (AK, FAL etc) seem like they are more suited to preventing a magazine blowout.

A mag blowout is the best possible outcome of a case rupture.  The gas has to go somewhere, and mags and ammo are the cheapest thing in the gun.

That's why black powder in a cup goes "poof" and black powder in a pipe bomb goes "BOOM"

Good point.

http://www.youtube.com/watch?v=pcepZLJSJ4E

I seen video of exploding ar's I wonder if in other designs the gases channel in a way so that the mag doesn't blow and the entire rifle doesn't become a bomb. I can't see how you would do this tho.

Seen that vid, possibly a case of spiked ammo.  

It looks like a turkish company is working along the same lines.

http://www.thefirearmblog.com/blog/2014/01/13/safir-arms-ar-57-upper-bullpup-rifle/

I don't really get why the ejection is shown on the left. I like the use of the standard mag catch but I would make it accessible on the left with an extra lever. The front pivot being in front of the grip vs behind it is something i keep going back and forth on. Having it behind the pivot means you have to have a separate grip/trigger assembly for the bull pup. Plus the trigger become more complicated. Having it in front precludes it from working with the standard AR lower. I may look into having three pins on the bull pup (the middle one would become the pivot in the 2 pin std config)

There is defiantly not room in there for a un modified trigger. The most important thing (bcg and recoil system are obviously missing from the pictures). It looks like the t-17 and t-18 could be the same upper if you look really close at the parting line…but its hard to tell.





Edit: just looked at putting a regular lower and the receiver extension portion gets in the way of the springs…so a std lower would be out anyway, but a modified lower without the section for the receiver extension could work.

In response to the poll--Of course a bullpup that uses an AR 15 gas system and unmodified BCG CAN work.  It will just be unnecessarily long, and result in a longer than necessary overall length and length of pull.

If you are not going to use the part that is only there to engage the recoil buffer and spring, why not chop it off to achieve a shorter overall length and length of pull?  Just so you can use standard, off the shelf parts?  If so, that's a valid reason, but IMO minimizing overall lengths is the major "pro" of a bullpup, and excessive lengths of pull is a major "con".  My $0.02.  YMMV.

The devil is in the details. This is what i'm finding.

Lets compare to the Tavor with an 18" barrel. The Tavor has a 15.75" LOP and and overall length of 27.625. My initial sketch shows a 20" barrel with a 15" LOP and an overall length of 31.9. If you had an 18" barrel the overall length would be about 29.9. This difference of overall length of 2.3" can be attributed to the BCG. To some the extra 2.3" would be unacceptable, but some may think its ok. I don't think its an open and shut case either way by any means.