my AR15 build, advice? suggestions?

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jason41987

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hey everyone... ive been considering a new generation rifle, and well, none of them really offer anything the AR15 doesnt, sure, some offer a quick change barrel but at the loss of zero... whats the point of that if you have to re-zero your sights... still, AR15 winds out in my opinion, so ive decided to build one..

for the lower receiver, theres not going to be anything special, i may put an extended bolt release on it, but im about 50/50 on that... one thing i will do is install some means for quicker take-down, such as a push button pin, or an extended captive pin thats easier to grab and pull

the upper receiver is going to be different from most AR15 uppers, its going to be closer to that of the rock river PDS rifle... the recoil spring will be moved, the top charging handle will be removed, i will purchase a forward assistless upper receiver, a smooth stripped carrier, and i will install a side charging handle, probably on the right side of the receiver, and this will function as a forward assist as well, ive though about a left side folding charging handle, but its just simpler to go this way, less moving parts, simpler, lighter...

since i will no longer be using the top charging handle, i will replace the head of the top charging handle with a captive guide rod/recoil spring assembly that will mate with the newly designed key on top of the bolt carrier.. the bolt carrier of which will be removed behind the firing pin area...

since i have a new recoil spring location, a shorter carrier, and side charging, i will be able to remove the buffer tube entirely, and install a folding stock adapter, which will allow me to use any AR15 stock as a side-folder as well....

ive never seen a reliability advantage towards piston systems, but im about 50/50 on whether or not i want to install a short-stroke piston system, if i do itll be for quicker cleaning, only having to open the front of the gas block, remove the piston, and run a small bore cleaner through it, and with the recoil spring directly behind the piston itll take care of the carrier tilt issues as well...

so besides all of that, ill have a 16" length barrel, havent decided on weight yet, chrome lined, probably 1 in 7" twist, top rail all the way across with flip up front and rear iron sight, more ergonomic grip, and an angled forward grip and thatll all be about it... probably a regular birdcage flash suppressor and magpul stock..

the idea of moving the recoil spring and shortening the carrier isnt new, but does require moving the charging handle, the rock river PDS has a short recoil piston and moved the charging handle to the gas tube, im simply mounting the charging handle directly to the carrier itself...

something i could do if i wanted to keep the top charging setup would be to use an AR18 type recoil spring assembly but the side charging will let me eliminate the forward assist as well, so it kills a few birds with one stone going that way

so, what do y'all think?
 
jason41987 said:
hey everyone... ive been considering a new generation rifle, and well, none of them really offer anything the AR15 doesnt, sure, some offer a quick change barrel but at the loss of zero... whats the point of that if you have to re-zero your sights... still, AR15 winds out in my opinion, so ive decided to build one..

for the lower receiver, theres not going to be anything special, i may put an extended bolt release on it, but im about 50/50 on that... one thing i will do is install some means for quicker take-down, such as a push button pin, or an extended captive pin thats easier to grab and pull

the upper receiver is going to be different from most AR15 uppers, its going to be closer to that of the rock river PDS rifle... the recoil spring will be moved, the top charging handle will be removed, i will purchase a forward assistless upper receiver, a smooth stripped carrier, and i will install a side charging handle, probably on the right side of the receiver, and this will function as a forward assist as well, ive though about a left side folding charging handle, but its just simpler to go this way, less moving parts, simpler, lighter...

since i will no longer be using the top charging handle, i will replace the head of the top charging handle with a captive guide rod/recoil spring assembly that will mate with the newly designed key on top of the bolt carrier.. the bolt carrier of which will be removed behind the firing pin area...

since i have a new recoil spring location, a shorter carrier, and side charging, i will be able to remove the buffer tube entirely, and install a folding stock adapter, which will allow me to use any AR15 stock as a side-folder as well....

ive never seen a reliability advantage towards piston systems, but im about 50/50 on whether or not i want to install a short-stroke piston system, if i do itll be for quicker cleaning, only having to open the front of the gas block, remove the piston, and run a small bore cleaner through it, and with the recoil spring directly behind the piston itll take care of the carrier tilt issues as well...

so besides all of that, ill have a 16" length barrel, havent decided on weight yet, chrome lined, probably 1 in 7" twist, top rail all the way across with flip up front and rear iron sight, more ergonomic grip, and an angled forward grip and thatll all be about it... probably a regular birdcage flash suppressor and magpul stock..

the idea of moving the recoil spring and shortening the carrier isnt new, but does require moving the charging handle, the rock river PDS has a short recoil piston and moved the charging handle to the gas tube, im simply mounting the charging handle directly to the carrier itself...

something i could do if i wanted to keep the top charging setup would be to use an AR18 type recoil spring assembly but the side charging will let me eliminate the forward assist as well, so it kills a few birds with one stone going that way

so, what do y'all think?
Click to expand...
Sounds like you're trying to make an AR/AK mutant. Got me all kinds of intrigued. Do you have links for these parts you're using?
 
look up the rock river arms PDS, the rock rock river PDS uses a shorter bolt carrier and the same recoil spring assembly as i mentioned, the difference is the PDS is a piston system and has a non reciprocating charging handle in front of the receiver, on the gas tube, the difference with mine is my charging handle will be on the carrier itself, so i can still used direct impingement if i choose to, but im starting to think i might go piston as well, just to make cleaning quicker and easier (cleaning locking lugs less often, etc)

ill be modifying a pre-existing upper and carrier group to do all of this simply by maching a lip into the back of the receiver to hold the recoil spring when the receivers opened, so i can just squeeze a button and pull it out, and cutting the receiver to make clearance for the charging handle itself
 
jason41987 said:
look up the rock river arms PDS, the rock rock river PDS uses a shorter bolt carrier and the same recoil spring assembly as i mentioned, the difference is the PDS is a piston system and has a non reciprocating charging handle in front of the receiver, on the gas tube, the difference with mine is my charging handle will be on the carrier itself, so i can still used direct impingement if i choose to, but im starting to think i might go piston as well, just to make cleaning quicker and easier (cleaning locking lugs less often, etc)

ill be modifying a pre-existing upper and carrier group to do all of this simply by maching a lip into the back of the receiver to hold the recoil spring when the receivers opened, so i can just squeeze a button and pull it out, and cutting the receiver to make clearance for the charging handle itself
Click to expand...
I will look those items up, as I'm not familiar. You're right about one thing, easier to clean that gas piston system.

You must have some bank account!
 
3 questions that jump out at me.

1. Which carrier are you gonna use? The carrier will need to be much shorter without a buffer tube. Edit: i see you metioned this in a later post. If you use an existing carrier, the gas key screws arent reliable enough and a piston carrier has no way of mounting the guide/spring assembly.

2. How small will the guide and recoil spring be? The PDS carrier and spring set up looks like it takes a larger channel than the typical charging handle channel.

3. How will you stabilize the carrier when it is so short? The PDS uses a long shaft over the barrel. I think piston would be better for this.

I am not trying to be a buzz kill, i am just curious. It sounds like a great idea. I would love to see a finished product with specs.
 
since i was thinking of going with a short stroke piston system, i was thinking of making the key something like a backwards shaped cup... to hold the spring with a flat surface on the front for the short stroke piston to hit against.. you did bring up a good question though about the spring... will it be long enough? i dont know...

i was thinking of shaping the key the same was as its shaped on the PDS... drill some holes in the top part of the tube section so it can still be fixed to the carrier like a normal key which will give a section for the spring to fit into and help guide the carrier

im not sure if this is a good idea or not, but one of the ideas i had was to drill the section the spring fits into all the way through, and then thread the end the gas piston hits against so that i could drive a screw into it with some locktite and this flat headed screw would be the surface in which the piston itself impacts against which gives me the option of replacing the screw as many times as needed as it gets worn

the spring itself will probably end up using thicker, wider coils to make up for the shorter overall length of the spring and be captive on a telescoping rod

id like the face of the key where the piston impacts on to be in the same position above the receiver as commercially available piston carriers, this way i can use any third party piston system i choose... the diameter of the spring would be about the same as the PDS system... i wanted to use a larger diameter, more rigid telescoping rod inside the captive spring to add extra stability to the carrier
 
hmm.. this looks like a long-stroke system with a recoil spring over the piston, very much like the sig commando rifle... its a very good idea but how does it field strip?...

i think if youre going to have an extension mounted to the carrier that long, youre going to have the same downfalls as a long-stroke system with barrel whip and added mass that you might as well benefit from the advantages of the long-stroke system and just make it long stroke, essentially making it a sig 556 in an AR15 body which isnt bad

but im having a hard time imagining how having the recoil spring over the piston would make for a quick and easy takedown in the AR15.. in the sig, theres a mechanism to unlock it from the carrier, in the AR15, the part of the carrier youd need to do this too is hidden away
 
its tough to say if this idea is going to work or not... ill probably build a standard piston AR first that i can use to test out some of these new ideas with later, ill probably still go side-charging though..

just a question... did anyone ever device a viable, reliable, and working solution to carrier tilt with piston ARs?
 
hmm, ive been thinking about it more and i dont think stabilization of the carrier is going to be a problem, for one.. the carrier isnt so long anymore, i dont have to worry about tilt with that giant tail end of the carrier aiding in the tilt of a gas piston systems forces upon it... the center of gravity of the carrier will be much more centralized since its shortened... that being said the skis on the remaining section of the carrier will be full-length

so i just dont think carrier stability will be so much of as issue for those reasons.. also, in a conventional system the piston pushed back, the spring pushed forward at a lower axis causing it to rock and cause wear and damage, with this setup the recoil spring is directly behind the piston, and can absorb the forces directly... so i think thatll be a non issue

all im concerned about at this point is whether or not ill have enough spring length to effectively tame the recoil, and guide the carrier back into battery... when the carrier is fully rearward there still has to be more length between the two ends of the spring than the total length of the spring while compressed
 
this build does sound like a Sig556 with the folding stock. I have fired one before and it is pretty cool. The side charging handle is very weird. Being a standard DI AR15 fan, its great to see a different configuration. I assume you are a lefty since you want to put the charging handle on the right?

Here is a pic I found online. just sharing I guess. good luck with your build.

sig_556_classic_swat_2.jpg
 
no, im right handed, for the one time i actually charge it for the day i dont see any advantage of having it stick into my back on a sling by putting it on the left, and should i ever need to use it for forward assist, i have more strength and control in my right arm being right handed
 
im going to try to fabricate a key thats compatible with pre-existing short stroke piston systems, probably buy an adjustable regulator gas block for it and test out how the short stroke piston works..

if it doesnt work well, plan B is to construct a long, full length long-stroke piston thatll run in a gas tube, and vent out when the carrier has reached its full rearward position to take advantage of the long stroke reliability found in rifles such as the AK, M14, SIG, etc and the gas piston will be hollow with the spring running about halfway down the piston, so the carrier will look very much like the rock river carrier with a fixed piston on the end

i really see no point in installing a spring over the piston because then its going to be a pain in the rear for takedown, where if the springs inside the piston i can just open the receiver, unlatch the spring assembly and pull everything straight out the back... no carrier tilt to worry about either with this route
 
i havent been completely honest with my intentions... this upper receiver is something ive been envisioning for the last couple weeks, of installing the recoil spring in the position ive mentioned, and changing to side charging....

well, the real reason is proof of concept, not to me, but to the nay-sayers of the AR-15 design that want to tell me the AR15 cant do this, it cant do that.. well, id like to essentially turn the AR15 into something more along the lines of the modern rifles you hear people hype about, scar, ACR, etc..

so what im thinking.. monolithic upper receiver, there are a couple aftermarket quick-change barrel packages available, ambidextrous controls seem to be all the rage... so, in this world of aftermarket, ive actually found AR-15 lowers that have been designed to be entirely ambidextrous so there you go... and since i can take that buffer tube assembly out i could fabricate a folding stock adapter and mount the magpul stock in a side folding fashion to it just to prove i can get everything you might like in a SCAR or ACR, in a 40-50 year old design for about half the price and little or no added weight

so let me ask this.. do y'all think i should go ahead and do this for proof of concept?.. heck, maybe ill find some nice earth-tone color to paint it too, maybe dark tan, or olive drab..

actually, ive even thought of getting a folding stock that could contain the buffer tube assembly if i could find one
 
There are parts available to build what you envision. The idea of moving the gas piston of an AR from the BCG to the gas block results in no improvements to the fit, form or function of the AR. What it will do is add to complexity and weight as well as introducing off center recoil forces in the reciprocating mass. While minor in this case, each is a disadvantage. It's like designing a bicycle with retractable training wheels.

Using a right handed charging handle is also a step backwards for right handed shooters. It requires the shooter to use the trigger hand to operate. Modern technique means being able to use all the controls of a fighting rifle while the trigger hand stays on the grip for best efficiency. The R/H charging handle of an AR is more fragile, likely to loosen and cause malfunctions and makes field stripping the AR more complicated. A left handed non-reciprocating charging handle would be a much better choice, although the mounting of optics might hinder it's use.

There is a folding receiver extension that holds the buffer and action spring and must be in place before the AR can be safely shot.

None of the so called "modern rifles" offer any advantage over the AR, nor are they any more modern. In fact, I'd argue they are more archaic and are not as advanced or well designed as an AR
 
archaic.. i agree with all of that which is why its proof of concept for the most part.. do you have any links to these folding receiver extensions? id be interested in learning more about them..

as for the non-reciprocating charging handle on the left side, its something ive thought about, but would need some method of forward assist.. i thought about having the charging handle sort of on a spring you could push into a groove on the carrier to lock it in place while pushing it forward to act as forward assist.. and once you release, the charging handle pops back out of the carrier

so the left side non-reciprocating bolt handle is a possibility.. for an initial build, just to get a rifle together with the proven concepts as i work on testing out the other ideas i would keep the standard carrier and buffer assembly...

umm... so yeah, show me the folding extention, ill go that route initially
 
I saw a post over on m4carbine.net about the folding receiver extension. A little searching should turn it up. It will also give you exposure to a site with the best AR knowledge on the web.

Why is a fwd assist needed? If it is needed, why not just go with the one it already has?
 
ill look into it, the idea should work for my proof of concept until i can fab the other parts..

my philosophy, as for what i prefer in a rifle is different from this proof of concept... my point... i think folding stocks is useful only for storage, and even then not really, i think left side charging handles dont matter so much, especially on a rifle with a bolt hold open feature, im right handed, right eye dominant, why should i care if my rifle is left friendly? i dont, monolithic uppers restrict modularity by not letting me swap forearms, and quick change barrels are a gimmick, since an in the field barrel change on an assault rifle, or semi auto carbine is just dumb to think about, and not worth losing zero, better to have interchangable uppers where i can select the forearm, barrel, muzzle device, optics, and accessories all pre-zeroed and set up for the task at hand...

so at some point, ill have two uppers, what i want, and one to s how off the extend of what an Ar15 can be made to do
 
How do you compensate for the mass of the longer carrier, buffer spring and buffer? All that has to fit inside the upper? It seems like the recoil spring that would fit inside the charging handle slot would have to be incredibly robust - you need to have enough force to unlock the bolt and reliably extract fired rounds but not so much that you batter the rear of the upper where the recoil spring assembly is anchored.

It seems like having more reciprocating mass above center of the recoil force would increase muzzle flip a bit also.

With the shorter carrier, do you lose some protection against an out of battery ignition? I thought part of the out of battery protection on the AR15 platform was the fact that the bottom of the carrier prevented the hammer from striking the firing pin until the bolt was almost completely cammed into battery.
 
maybe the lip behind the firing pin could be used as a safety mechanism, but that long tail end is mostly to make clearance for the hammer while being able to use the single buffer spring, if it wasnt there the hammer would just hit the buffer spring and never make it to the firing pin which does seem a bit inefficient to add that extra length and weight just for that purpose when you could significantly reduce the length of the action by relocating the spring behind the gas system like on 99% of the gas driven designs out there, or by using two recoil springs like the AR18 uses

having the recoil spring pushing forward while the gas system pushes back should keep the carrier straight and stable, considering the remaining section of the carrier will have skis nearly full length for it to ride on.. but yeah, the biggest question is where there be enough length inside for the spring, or would i have to extend the key section of the carrier further forward for more clearance and simply go with a long-recoil system?...

first id like to see if it works at all with a short recoil system that would allow me to use off the shelf piston systems, if there isnt enough room to do this, ill simply go with a long stroke design nearly identicle to the rock river PDS carrier, which will be very AK-47 like with the bulk of the spring inside the piston extension of the receiver

so yeah.. if the short stroke system doesnt work, that plan B definitely will, and current rifles in production prove it will... so either way ill be able to forget the buffer tube assembly in this upper build, and to go with the theme of copying the hype rifles on the market now, im trying to find a solid monolithic upper that doesnt include the forward assist that will become useless as soon as the carriers shortened, and id like to grind off the shell deflector and put a removable one on... this idea isnt neccessarily to copy the hype rifles, but to allow me to change deflectors as they get worn in time
 
jason41987 said:
...i think left side charging handles dont matter so much, especially on a rifle with a bolt hold open feature, im right handed, right eye dominant, why should i care if my rifle is left friendly?...
Click to expand...

If you think the only function of the L/H charging handle is to make the rifle lefty friendly, you haven't shot enough. The L/H charging handle is easier to operate for right handed shooters. Go shoot a FAL and you'll see

Do you know how many rounds need to be fired before a shell deflector is worn enough to require replacing??
 
ive never had a shell deflector worn, but wouldnt complain the option of being able to change the shell deflector for a few reasons...

i havent decided which side to put the charging handle on, but having it poke you in the back the entire time its on a sling doesnt seem worth having it on the left side the one time during the day you actually use it, and other time you may use a side charging handle is if you need to use the forward assist, which is even more rare, but on an AR15 which side of the rifle are you used to hitting for forward assist?.. the right.. and i dont fire FALs a lot, my preferred .308 caliber rifle is the M1A/garand, so again, besides the AR15 itself, which i only have to do once for every day of shooting, i havent used left hand charging rifles enough to get used to it
 
MistWolf said:
If you think the only function of the L/H charging handle is to make the rifle lefty friendly, you haven't shot enough. The L/H charging handle is easier to operate for right handed shooters. Go shoot a FAL and you'll see

Do you know how many rounds need to be fired before a shell deflector is worn enough to require replacing??
Click to expand...
It also, with an optic with no eye relief, means keeping your eye on target and your strong hand on the grip. Means faster mag changes, charging, without taking your eyes off the target.
 
again.. a bolt release feature, its not like you actually use a charging handle more than once per session of shooting, and that one time i can just as easily reach under the rifle and charge it with my left hand
 
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