Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login

Log In

A valid email is required.
Password is required.
Site Notices
6/21/2017 8:25:40 PM
Arrow Left Previous Page
Page / 2
Posted: 2/15/2009 3:37:06 PM EDT
[Last Edit: 6/14/2009 10:26:09 AM EDT by RDTCU]
My first AR pistol is finally done!
Operating system similar to a ZM LR-300. It fires and cycles 5.56 every time. Forward charging handle. 80% lower. And yes, no buffer tube.
More Info and pictures HERE

New Pictures:


Link Posted: 2/15/2009 4:32:42 PM EDT
damn nice job. Looks like fun!
Link Posted: 2/15/2009 4:46:12 PM EDT
Awesome! have any in progress pics?
Link Posted: 2/15/2009 4:59:48 PM EDT
nice
Link Posted: 2/15/2009 5:08:17 PM EDT
Very nice looking gun there!
Link Posted: 2/15/2009 5:14:16 PM EDT
interesting recoil system you got there. would be interesting to see other rifles/pistols built in that style.
Link Posted: 2/15/2009 5:20:34 PM EDT
I'll didn't take that many pics during the build, but it went through a few changes throughout the process.
More pics added to the album in the original post!


Link Posted: 2/16/2009 8:23:01 AM EDT
[Last Edit: 2/16/2009 8:46:16 AM EDT by RDTCU]
Update, let the little sister shoot it, and she loved it...
You don't pick up on the echo with the earmuffs on, but if you're just using your hands and drop them after the shot, it's ridiculous. The conical brake definitely tames the blast to the shooter, but does nothing for the fireball you get with cheap ammo...
Link Posted: 2/16/2009 7:54:18 PM EDT
Link Posted: 2/16/2009 8:49:02 PM EDT
[Last Edit: 2/16/2009 8:50:32 PM EDT by upl8te]
Is that your design? Would you feel like showing more of the design?
Link Posted: 2/16/2009 11:05:09 PM EDT
Beautiful. Sturdiest looking piston I've seen on an AR. Does the charging handle move with each shot?

Nice work!
-Johnny
Link Posted: 2/17/2009 4:15:20 AM EDT
[Last Edit: 2/17/2009 6:48:44 AM EDT by RDTCU]
upl8te,
The lower is a standard 80% lower finished to spec, sans buffer tube. I machined the rear plug from SS roundstock. The upper is a DPMS slick flattop with the gas tube hole opened up for the larger gas key. The bolt carrier was a Bushmaster spare i had, chopped behind the firing pin and cleaned up with a lathe grinder. The barrel was a cheap (but accurate enough) Dez Arms 10.25 pistol barrel that came with a carbine sized gas port which had to be opened. The forened is a bushmaster carbine forend clearanced for the recoil system, the barrel nut also had to be clearanced. Gas key tube and gas tube are chromed, hardened die cast ejector sleeves, scraps from work. The gas block is a MI upper height rail block, with the gas tube hole bored offset and plugged. The SS muzzle brake is my own design, made from round stock (2 pieces, with the outer lip roll formed around the end). Next time i disassemble it (for duracoat) i'll be sure to take more pictures of the components.

bgoodjohnny,
Technically it's not a piston, it's a DI system with an extended gas key and a straight gas tube. I think a true piston would be too violent for the shortened bolt and would lead to bolt tilt and receiver wear. The beefy gas tube and gas key function as somewhat of a guide rod as well to reduce bolt tilt. Also, the charging handle is non-reciprocating and has a latch similar to a standard AR charging handle to keep it in place while the action cycles. I don' t know that i would want something reciprocating at high speeds if i were to put my thumb up the side of the handguard...
Link Posted: 2/17/2009 4:33:33 AM EDT
I want one, but SBR'ed with a folding stock.
Link Posted: 2/18/2009 2:13:01 PM EDT
Originally Posted By RDTCU:
upl8te,
The lower is a standard 80% lower finished to spec, sans buffer tube. I machined the rear plug from SS roundstock. The upper is a DPMS slick flattop with the gas tube hole opened up for the larger gas key. The bolt carrier was a Bushmaster spare i had, chopped behind the firing pin and cleaned up with a lathe grinder. The barrel was a cheap (but accurate enough) Dez Arms 10.25 pistol barrel that came with a carbine sized gas port which had to be opened. The forened is a bushmaster carbine forend clearanced for the recoil system, the barrel nut also had to be clearanced. Gas key tube and gas tube are chromed, hardened die cast ejector sleeves, scraps from work. The gas block is a MI upper height rail block, with the gas tube hole bored offset and plugged. The SS muzzle brake is my own design, made from round stock (2 pieces, with the outer lip roll formed around the end). Next time i disassemble it (for duracoat) i'll be sure to take more pictures of the components.

bgoodjohnny,
Technically it's not a piston, it's a DI system with an extended gas key and a straight gas tube. I think a true piston would be too violent for the shortened bolt and would lead to bolt tilt and receiver wear. The beefy gas tube and gas key function as somewhat of a guide rod as well to reduce bolt tilt. Also, the charging handle is non-reciprocating and has a latch similar to a standard AR charging handle to keep it in place while the action cycles. I don' t know that i would want something reciprocating at high speeds if i were to put my thumb up the side of the handguard...


Thank You for the info.
Link Posted: 2/18/2009 9:07:31 PM EDT
Coolest. Build. Ever.

Thanks for the answers, you've given me something to think about in my spare time.

-Johnny
Link Posted: 2/18/2009 9:25:25 PM EDT
totally f'ing awesome!
Link Posted: 2/18/2009 9:35:51 PM EDT
I suggest filling a patent on the design and finding someone who will buy the design from you. Could be some big money since Para is getting like $2500 for theirs.
Link Posted: 2/19/2009 4:20:45 AM EDT
[Last Edit: 2/19/2009 4:28:14 AM EDT by RDTCU]
I've seriously considered a patent, the one hangup is that the gas system is already patented by ZM/YHM/Para (as far as i know), and my forward charging handle will only work on that type of system, if you're planning to lose the stock. Don't know many people that will drop $1500plus on a ZM upper just to have someone they don't know hack it up just to move the charging handle... If you're keeping the stock, i suppose it could be adapted to work with a piston system, i'll have to give this some thought. Thanks for the encouragement and suggestions!
Link Posted: 2/19/2009 4:38:08 AM EDT
I picked up a ZM bolt/carrier some years back, hoping to do something similar. The ZM extended key rides higher than the standard, so the hole through the receiver is offset higher. The channel in the upper where the key rides, must also be deeper than the normal upper. The ZM charging handle is correspondingly different. My thoughts as to why ZM's setup is "taller" than the norm, may be that they wanted all of this to clear a standard barrel nut.

I have a DPMS upper with more meat on the top, in hopes it can be machined to accept the ZM carrier. Looking at your mod, it may be more effective to mill the key's base down so the axis lines up more with the normal setup.

... or RDTCU, since I have a shortened carrier, wanna make a "Rhino" honker for me?

buckmeister
Link Posted: 2/19/2009 4:58:18 AM EDT
[Last Edit: 2/19/2009 4:59:42 AM EDT by RDTCU]
buckmeister,
As in .470 Rhino???
or a Rhino piston system???

Anyway, the gas key i used is shorter than a ZM setup, but the bushmaster barrel nut had to be significantly clearanced, but not so much as to compromise strength. If i was worried about it i could turn out a steel nut to replace the aluminum one. I also had to mill a shallow groove in the charging handle slot in the upper to clear the gas key where it sits, because i could not take the key any lower. As far as i know, ZM uses a proprietary barrel nut, as their forends are model-specific and a standard forend will not work. You didn't happen to grab a ZM gas block while you were at it, did you? The gas block/gas tube will give you some trouble and will have to be fabbed from scratch if you don't pick up a ZM one. I would also recommend using your high upper just for simplicity's sake, 'cause if you go much lower, you open up a whole can of worms with clearance issues, i just wanted to see if it could be done.
Just a note, my bolt is slightly shorter than a ZM, so the buffer plug would have to be a little longer to permit it to lock back...
Thanks for the interest!
Link Posted: 2/19/2009 3:00:12 PM EDT
Took it to the range today, and i was completely suprised. I'm using a 4moa Burris Fastfire dot sight (pretty much a 25yard pistol sight) so sighting it in at 100 yards was.... touchy. Using a rest, some of my groups were surprisingly small, around 3" 5 shot groups. the last few groups were all in the 5" ring with one or two fliers. I was amazed since the dot covers up half the 8" target and i have no stock. Only complaint is the standard mil-spec trigger, of course, but i didn't anticipate it being so consistent to begin with, or i might have dropped on a better trigger! A couple people at the range were commenting so i let them pop a few off and they got a kick out of it.
Link Posted: 2/19/2009 6:54:00 PM EDT
I'll take one "Rhino" DI extended key, please. I have a DPMS Hi-Rider Flattop Upper Receiver. Missed out on the ZM gasblock.

You are correct, the ZM key is longer (semi-midlength). The carrier has remnant "ears" which make it longer than yours. I like the ZM spring keeper, which you incorporated on your version. I have a Badger railed forend with a barrel nut arrangement I think would work (too bad its a carbine length "tube"). Details on you charging handle would be welcome.

buckmeister
Link Posted: 2/21/2009 9:06:30 PM EDT
[Last Edit: 2/21/2009 9:10:08 PM EDT by RDTCU]
buckmeister,

Took it down for blasting and Duracoat.
More pics added to show the charging handle assembly...
ALBUM


Link Posted: 2/22/2009 3:58:18 AM EDT
It never made sense to me why people go to piston systems if they're going to keep the buffe/spring etc in the stock. They might as well just do up a system like this, or like the Olympic OA93 system and eliminate the buffer tube assy completely.

PS this would be really cool with a tax stamp and a side folding stock!
Link Posted: 3/1/2009 3:22:32 PM EDT
Finally finished the bare parts and shot it some more. Less shiny = more evil...

Album




Enjoy!
Link Posted: 3/5/2009 1:09:29 AM EDT
[Last Edit: 3/5/2009 1:15:26 AM EDT by Tony-Ri]
I like how you took the hardest part of finishing the 80% and turned it into a starting point for a unique design.

The BCG assy looks like an AK raped an AR and that's the demon spawn...

How did you make the ultra-extended key, and where exactly is the return spring? Ok, I see it now under the handguard.
Link Posted: 3/5/2009 3:07:12 AM EDT
omg that thing is sexy!

sling attachment and that bad boy would hide well under a coat!
Link Posted: 3/5/2009 3:39:19 AM EDT
Tony,
What do you consider the hardest point of an 80%? The buff tube hole IS tapped and the stainless plug is threaded into it and has a set screw. I machined the gas key base from 4340 stock and the "snout" is a 3/8" case hardened rod sleeve machined to fit and tigged on. The extended gas tube is a 1/4" version, but the same thing. even when the bolt is fully back, the key still engages the gas tube by about 1", so it functions as somewhat of a guiderod for the shortened bolt. The gas key is a real GAS key, in that gas does actually enter the bolt carrier.
And is "demon spawn" always bad when it comes to guns?

dHutch,
Look under the buffer tube plug on the back. That little round black thingy is a QD sling swivel socket....
I made a single shoulder loop sling that works nicely, and you can use it with tension for more stability off-hand.
And you would need a long coat if it's straight down.

RDTCU

And this thing even works with Wolf!
Link Posted: 3/5/2009 6:11:13 AM EDT
B...e...a-utiful, I want one
Link Posted: 3/6/2009 11:58:56 AM EDT
I really like this idea! I've never liked the fact that 5.56 AR pistols had a buffer tube. I've read and reread your posts about the design and I have a few questions. You say "The gas key is a real GAS key, in that gas does actually enter the bolt carrier." What I don't understand is why not seal it up and have it act as a piston? I understand that pistons cause carrier tilt, but wouldn't the extended gas tube(from the gas block) stop most of that? I'm not certain how the bolt works in the AR. Does the bolt get reset inside of the Carrier Group by gas or just from the BCG slamming backwards and the bolt drags on the barrel extension to some degree? If the bolt resets from the rearward motion of the BCG, couldn't you drill some vent holes in the extended gas key tube to vent the gases out side of the receiver? If the bolt is reset from the gases then how do piston guns reset the bolt? Thanks for the new ideas! Wish I had access to a machine shop and knew what I was doing in one...
Link Posted: 3/6/2009 12:13:20 PM EDT
[Last Edit: 3/6/2009 12:31:40 PM EDT by RDTCU]
reosed,

In a gas ar, the largest cross section exposed to gas is in the chamber behind the bolt (inside the carrier). The pressure behind the bolt forces the BCG back and the bolt forwards, which unlocks the bolt and forces the carrier back from the impulse, eventually pulling the bolt with it. SOME force is exerted in the gas key, but not as much as on the bolt. If you look at a piston system, the piston cross section is rather large, equal to or larger than the effective piston area of the bolt. If i went with a piston system, with the larger piston/cup, on such a short system, the return spring would have to have a large ID to clear the piston, but it would be so large that it would have to be relocated higher, and running it concentric to the piston would become impractical. Basically you'd end up with a piston driven OA93, and that's exactly what i did not want. Not to say they aren't cool, they're just too high-profile for my tastes. And mine is easier to disassemble..
Link Posted: 3/7/2009 9:20:36 PM EDT
Originally Posted By RDTCU:
reosed,

In a gas ar, the largest cross section exposed to gas is in the chamber behind the bolt (inside the carrier). The pressure behind the bolt forces the BCG back and the bolt forwards, which unlocks the bolt and forces the carrier back from the impulse, eventually pulling the bolt with it. SOME force is exerted in the gas key, but not as much as on the bolt. If you look at a piston system, the piston cross section is rather large, equal to or larger than the effective piston area of the bolt. If i went with a piston system, with the larger piston/cup, on such a short system, the return spring would have to have a large ID to clear the piston, but it would be so large that it would have to be relocated higher, and running it concentric to the piston would become impractical. Basically you'd end up with a piston driven OA93, and that's exactly what i did not want. Not to say they aren't cool, they're just too high-profile for my tastes. And mine is easier to disassemble..


R U sure about that? What if only the piston shaft has to clear the barrel nut, and not the spring, too. It is stopped at the toothed face of the barrel nut by a collar that provides a square surface for the spring to seat/push against?
Link Posted: 3/7/2009 11:32:31 PM EDT
Bret,
Yea, the return spring stops at the front of the barrel nut, like a piston system, but the nut had to be clearanced a good bit for the 3/8" gas key tube, and if the spring went to the receiver, it would be all in the receiver barrel nut threads... The spring basically contacts the area of the barrel just in front of the nut, so the spring can't get larger where it is. The spring would HAVE to be larger so that it could run outside the piston/cup or it would be too short for the ~3.25" stroke that it has to make to lock back reliably. Ultimately the spring to barrel contact is a limiting factor just as much as the larger OD gas key tube is now. One alternative i suppose would be to run a tapered/conical spring that would clear both the barrel at the chamber AND the piston cup at the gas block. Another option would be to run a laaarge diameter spring around the barrel with an offset spring seat, which i seriously considered until i did some calculations on the bending loads the gas key and spring seat could see.
Of course if i had tried this on anything longer than a carbine length gas system, then yes, a piston would work just fine...
Link Posted: 3/8/2009 7:32:12 AM EDT
[Last Edit: 3/8/2009 7:38:48 AM EDT by Bretshooter]
Ok, that does make sense, but does the rod need to be 3/8" if it isn't hollow? And without the standard charging handle, don't you gain a little room to elevate the rod some?

The reason I think it is do-able, is that ZM uses a slightly higher receiver, but they also retain the standard charging handle position, albeit modified to work with their slightly raised rod. I would guess the front of it drops more to reach the carrier. But it doesn't look goofy-tall like the OA93.
Link Posted: 3/8/2009 9:34:16 AM EDT
The thing is, the rod IS hollow, and if you went with a piston for the smaller op-rod, your piston cup would have to be too large to fit a standard spring around. Also, you'd have to find a way to detatch the piston cup (or plunger) from the op rod to be able to remove the spring and carrier from the upper, because they all have to be solidly linked for the return spring to return more than just the piston... The key is also elevated as high as possible, as in i did remove some material from the charging handle track in the upper receiver to bring it up higher. any higher and i'd have some thin material under the rail, or eventually get into the rail grooves. Ultimately, it's about as high as possible with the largest spring possible without the recoil system being higher than the standard upper rail height. The whole point was to try to get the system as low profile as possible, but i had also modeled up an elevated DPMS upper should the standard height prove to be too low. You've got me thinking about trying a piston version on a longer gas system though...
I'm still trying to decide whether the 45acp piston upper i'm piecing together should be a pistol or a rifle, and whether or not it should have a similar recoil system...
Link Posted: 3/9/2009 5:48:55 AM EDT
It is hollow for DI, but doesn't need to be for Piston.

Wow, I didn't realize how high you had raised it.

Charging from the side of the receiver vs forward on the spring tube would make it simpler, and possibly allow for a smaller size.
Link Posted: 3/9/2009 6:49:47 AM EDT
Yea, but there are half a dozen companies out there making side-charging uppers, and charging an arm and a leg for them I wanted to do something that hadn't been done, but still be "practical" (as practical as an AR pistol can be anyway) without dropping lots of $$$. That was the primary motivation. But yea, it would have been simpler to buy a side charging upper.
With the piston though, there's still the problem of disassembly, as the piston would have to rigidly attach to the op rod to capture the spring (short system only), but be easily removable for disassembly. The way the system works now, i can have it from functional to upper off, carrier out in about 10 seconds with no tools. Just rotate the spring tube by lifting firmly on the charging handle 90 deg, pull back about 1", flick the spring keeper which drops out and then the carrier slides out.
Thanks for the suggestions.
Link Posted: 3/9/2009 8:31:59 AM EDT
I was think more along the lines of Fulton Armory style side charging. A recip handle that unscrews from the carrier for carrier removal. slot in upper for it's travel.

If your piston has a hex shoulder between the head and shaft, you could make it screw on, either at the head, or the shaft into the key area. Likewise an allen socket in the piston face would allow it to be turned for removal.
Link Posted: 3/9/2009 8:38:23 AM EDT
Originally Posted By RDTCU:With the piston though, there's still the problem of disassembly, as the piston would have to rigidly attach to the op rod to capture the spring (short system only), but be easily removable for disassembly.


Why only on a short carbine system?

Link Posted: 3/9/2009 8:38:26 AM EDT
[Last Edit: 3/9/2009 8:40:27 AM EDT by RDTCU]
All of those sound great, except that they all require tools...
plus i don't like the idea of a threaded shaft (op rod) in cyclical loading, especially if it has to be assembled/disassembled often.
For one you have unnecessary stress risers at the threads, and two, it WILL work loose, especially since it is reciprocating, unless you stake it, which kinda kills the ease of disassembly...
i did run a few Cosmos FEA simulations to give me some fatigue numbers on the components.

On your other question, on a carbine system, you're limited to overall minimum return spring length (or you'll get coil bind, baaaaad), but on a longer system, the spring could stop behind the piston without having to have the piston/cup rigidly attached to the op rod, just use a similar spring keeper to what i've got.
Link Posted: 3/9/2009 9:02:49 AM EDT
DO WANT


do you have blueprints?
Link Posted: 3/12/2009 7:41:14 AM EDT
bump
Link Posted: 3/12/2009 7:55:09 AM EDT
This is just badass, I enjoy the ingenuity. Like others I never wanted an AR pistol because of the buffer tube. Two thumbs up man.
Link Posted: 3/12/2009 7:59:23 AM EDT
cool build.
Link Posted: 3/13/2009 8:15:55 PM EDT
Very cooll!!!!
I have wondered for along time why no one was building these,after seeing the ZM weapons AR's years ago I knew it was possible,out of my skill range but with all the cool shit + skills/equipment that some here have available im amazed it hasent been done sooner
this would make a sweet SBR!!!
Link Posted: 3/17/2009 12:37:28 PM EDT
Link Posted: 3/18/2009 7:56:48 PM EDT
tag.
Link Posted: 3/21/2009 12:44:34 PM EDT
[Last Edit: 3/21/2009 12:45:17 PM EDT by imtheflash]
I own two AR pistols without buffer tubes. The skeletonized one with the wood grip was built by Allan Zitta. It's also chambered in 7mm TCU



Link Posted: 3/30/2009 10:26:50 AM EDT
Link Posted: 4/4/2009 6:50:24 PM EDT
You sir get the "Evil Black Rifle Pistol Award" of the year.

I would buy one def. although the charging handle would have to fold, because i would keep it in bed with me, as lovers do...
Link Posted: 4/17/2009 10:45:21 AM EDT
Arrow Left Previous Page
Page / 2
Top Top