Polymer Receivers

[wch]

There's something about the innate strength and/or durability of AR-15 plastic receivers that makes me distrust the idea.
Anyone have experience with them, anyone with a list of pros and cons?

[Winger Ed.]

Modern generation plastics are pretty incredible.
Back in the 90's one of the auto makers built a running prototype car engine that didn't have any metal in it.

I had to make an exception for my Springfield XD, but I never warmed up to Tupperware guns either.
I haven't been around a plastic AR, but they would probably have been fired a million times before they went into production.

[VariableRecall]

Considering that someone has been able to make one-off lowers out of lego blocks and screws, you can make a lower out of just about anything you could imagine that's somewhat solid.
I suppose that the difference really is HOW long you want it to last.

Lego Block AR Lower Firing a full magazine without issue
https://youtu.be/Z4KQZ0LJwuY

Lego Block AR dissasembly
https://www.youtube.com/watch?v=OiqfTG2oF4s

[recumbent]

History of Monolithic Polymer ARs. Interesting video.
https://www.youtube.com/watch?v=RFxNvi7920c&ab_channel=ForgottenWeapons

[rancher1913]

well just consider all the real work is done in the upper, so the lower just has to support the trigger pins.

[Lloyd Smale]

not much stress on an ar15 lower. You probably could make on out of paper Mache and it would work.

[MrWolf]

I got one maybe 6-7 years ago. Shoots fine, no issues but I still prefer metal. No valid reason at all. Like others have stated only holds the trigger. Come to think of it think it is a full lower with an A2 stock style.

[DanishM1Garand]

https://youtube.com/playlist?list=PLj9u4Ts2NpEuyUMbu1Pe3yXtez7CwkW8c

Gun Jesus and Gun Satan did a project where they built a rifle on a new polymer lower. This lower uses the strength and weaknesses of polymer.

I built one on the precursor lower sold by Armalite made by CavArms. It is a sturdy little carbine. I would avoid any of the polymer lowers that are a direct copy of an aluminum lower. These are prone to break.

[Blanket]

buffer tube area is the weak spot

[Petrol & Powder]

well just consider all the real work is done in the upper, so the lower just has to support the trigger pins.

/\ YEP /\

It's sort of a fluke of American gun laws that the lower receiver of an AR-15 platform is the "receiver" (controlled part) and the upper receiver that contains the pressure of firing is an uncontrolled part.
In other countries, the pressure bearing parts are the "gun".

The lower receiver of an AR-15 doesn't have much stress on it.

[RU shooter]

Unless your gonna be bayoneting or butt stroking something to death IE full on combat use , their plenty strong for what they need to do for 99% of civilian use . Can they break ? Yep so can an aluminum lower if you torture or abuse it enough. As been said about the connection of the stock tube is the weak link but some companies have beefed this area up and inserted metal reinforcement

[HATCH]

The issues that people have run into using the plastic lowers has been the buffer tube area but that is mostly when used in pistol caliber setups.

[Texas by God]

I've used a few of the CavArms type with no problems. My .300BO is built on one and it is as solid as my conventional ARs plus it fits to the upper with NO rattle. I like the light weight, too. Ugly as a mud fence but 8# with 30 rounds and a scope.
I'm leery of the conventional type polymer lowers, but haven't owned one.

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[fcvan]

I have built a couple with both materials, nary a problem. I saw one that I found interesting, the lower, grip, and rear A2 style stock was 1 piece. It looked pretty healthy considering the buffer tube was integral in the fixed rear portion.

I considered building one with a fixed magazine and a pump action just to P.O. the CA legislators. Fed through the ejection port with a device made by a manufacturer in SO CA, who also did so just to P.O. the CA legislators. The rifle was as fast to reload as a detach mag, maybe slightly faster as there is no mag to detach. The drawback was I needed to use an 18" barrel cut/crowned without threads, spendy to order a custom with a rate of twist just for cast.

I may still build a pump upper with normal parts and weld on the flash hider, or machine one with closed ports. For now, whenever I am in CA, I just shoot the Mini 14, having removed anything 'black and fun' from CA after I retired . . . from Law Enforcement. Our 'SWAT' duty rifles were AR 15s (former team member) and the regular duty rifles were Mini 14s. Fun thing is, the agency was set to transition to AR 15s due to their price, ease (and price) of maintenance, and accuracy.

I don't have a preference of aluminum or polymer, both work fine. I do know a guy who blew up an AR 9mm on a poly. He didn't use the heavy buffer which allowed the bolt to blow back before chamber pressure was reduced. Mag well and adapter cracked and ejected the magazine and parts at his feet. He described his upper as being filled with brass confetti. He ordered a heavy buffer and fixed the lower with Super Glue Gel. He said 'isn't that what Super Glue is for?'

His catastrophic failure did not result in injury nor was it caused by defective parts, only due to improper assembly. I built one with a poly frame, proper buffer, a silicon buffer bump, and a slightly stiffer buffer spring. Runs like a champ and is my favorite plinking rifle.

[Big Tom]

I 3D printed a few to play with it - weakest link, as described here already, is the buffer tube attachment (the ones out of plastic that you buy most likely have some metal there to make it more sturdy. Here's a pic of a 3D printed one, cost of material is about $7. It worked fine, but I am more of a fan of something more substantial as well.

273347

[leadeye]

3D printing is something I've always wanted to try for hard to find parts on old guns. There are a lot of parts that just move around and keep things in place that don't get heat or stress, but are made of unobtainium today. Places like Jacks First does a pretty good job, but he doesn't have everything and what he does have isn't cheap.

[monadnock#5]

Strictly utilitarian works for me. I love my S&W 15-22.

[VariableRecall]

3D printing is something I've always wanted to try for hard to find parts on old guns. There are a lot of parts that just move around and keep things in place that don't get heat or stress, but are made of unobtainium today. Places like Jacks First does a pretty good job, but he doesn't have everything and what he does have isn't cheap.

I've heard that using 3D printed parts for such things as en-bloc clips have been fairly successful for rifles whose original parts are rare and hard to find.

[Lloyd Smale]

I 3D printed a few to play with it - weakest link, as described here already, is the buffer tube attachment (the ones out of plastic that you buy most likely have some metal there to make it more sturdy. Here's a pic of a 3D printed one, cost of material is about $7. It worked fine, but I am more of a fan of something more substantial as well.

273347

to bad you cant sell those. Youd make a killing right now.

[Big Tom]

I would not even want to get into that - they really aren't as sturdy as the ones made out of enhanced injection molded plastics - and if anybody really wants to get into it, a printer is below $200, plastic is below $20 for a 2 lbs roll (probably good for 3-4 of these receivers). The design files are readily available on the internet for free...

On a side note - if anybody needs small parts they have the exact measurements for, feel free to reach out to me. As long as they are legal to make and I got time at hands, I am more than happy to see if I can help.


to bad you cant sell those. Youd make a killing right now.

[mtnman31]

I've got a New Frontier Armory polymer lower I got a few years back. It has worked fine for me. It's been under 5.56, 300 Blackout, and .458 SOCOM uppers. No issues or problems with performance. My only complaint is that the opening on the raised boss for the bolt release is just slightly wider than it should be. The result is some minor back/forth slop with the bolt release. It's a minor issue considering the cost of the lower.

[white eagle]

I had a composite lower for my ar15
my son now owns it
I never had any issue's with it worked just fine

[abunaitoo]

A while back I remember trying a plastic AR.
Forget what brand.
I remember it did reduce the vibration and twanging sound.
Other than the weight, it was no different from my Colt H-bar.
Friend has a 3D printer.
It's so slow.
Kind of like watching a plant grow.
But would be nice to play with one.

[Bazoo]

The original bushmaster made a polymer AR for a while. I don't recall the name of it.

[Bodean98]

I used a polymer 80 lower until it broke. Buffer tube area. 300BO in less than 1000 rounds.

[bruce drake]

I used a polymer 80 lower until it broke. Buffer tube area. 300BO in less than 1000 rounds.

Its pretty easy to print off spare lower receivers. I keep one handy for whenever my other polymer receiver breaks or cracks. swapping out the FCG and stock parts is under an hour. 3d printing the recevier takes about 12 hours. set it and forget it like a slow cooker.

[CarlMc]

The design for the AR was optimized to be made from aluminum. If the design had been optimized for a variety of polymers available at the time, it would have looked a lot different. Modern polymers are pretty incredible, but the rule about designing for the material is still a rule. What we've all been talking about is taking an aluminum design and attempting to make it work for polymer. You can't duplicate the pattern in polymer, you have to redesign it from the requirements, which is far easier said than done.

[jonp]

I've run a few for several thousand rounds with no problems including a couple of 80% lowers I built. Too bad I lost them in a canoe accident

[djlwest]

A polymer lower does not bother me nowhere as much as a polymer upper.

[DDriller]

As Texas by God said the Cav Arms lowers work well. Brownells has a new one out that looks nice the KP-15.

[Lloyd Smale]

where do you buy a 3d printer for under 200 bucks that will do one??

[Big Tom]

Check out fleebay. I have been using the "Anycubic" brand printers for 4 years now and they are inexpensive and produce decent results. (there is one on sale for $109 incl. shipping at the moment). For filament, I suggest using PLA, which is easy to use and about $20 per 2 lbs. Microcenter.com and Amazon.com are best sources for the filament.


where do you buy a 3d printer for under 200 bucks that will do one??

[bkbville]

if polymer worked for Glock, why shouldn't it work for Stoner?

(There are 3 types of pistols left in the world. 1911's, Glocks, and Glock copies.)

I have had a few synthetic lowers.

I first had bought a couple of New Frontier LW-15's (Light Weight 15) that worked quite well, and with a lot of different uppers - .223, 30BlackOut, and even .458 SOCOM. It took some weight off the rifles, which was nice, and actually had one with a plastic trigger group
and hammer that worked quite well - believe it or not (can't remember if that was the LW15 or not.)

The second one I had was an ATI lower that simply broke in half the first time I fired it. I don't know why, and neither did ATI. They took it back and refunded me. This was a disaster, and I think they got out of the business.

I still have another New Frontier LW-15 that is on my disturbingly ugly (New York State's fault - not New Frontier) AR, and that works
great. I don't, however attempt to test it's limits - but I don't do that with aluminum lowers either.

I'm comfortable with these, especially as I like light weight builds.

Now.. 3D printed? No way. Having done a fair amount of 3D printing - I'd just never trust the process on any (currently) affordable printer. They are imprecise (hard enough to make a round hole), and you would have to be very careful about material selection (PLA ain't going to cut it.) Someday? yes (and maybe today if you have all high-end stuff.)

I was more enthralled with the idea of casting a lower but I don't know what became of that.

[Texas by God]

DDriller, thanks for the heads up about Brownells kp15. The video is interesting and they look like a good start- if one can find the rest of the parts needed nowadays. The grip looks like an improvement but the loss of the butt storage and the extra sling holes don’t thrill me. But I would definitely build on one. It’s interesting that they recommend Not using the bigger AR15 compatible “thumpers”.

[Lloyd Smale]

Now.. 3D printed? No way. Having done a fair amount of 3D printing - I'd just never trust the process on any (currently) affordable printer. They are imprecise (hard enough to make a round hole), and you would have to be very careful about material selection (PLA ain't going to cut it.) Someday? yes (and maybe today if you have all high-end stuff.)Is this opinion based on an actual failure or experience or just an opinion? Im more interested in talking with someone who tried it and it failed then just conjecture. I have absoultey no experience with 3 d printing but do have a poly80 ar and the people on here that know me know I SHOOT. Mine has held up just fine. Not one bit of problem with probably 5k on a 556 upper. I own blackouts too and the differnce between them and 556's in recoil isnt enough to talk about.

[Big Tom]

You can get 3D printer designs that enforce the weak areas like the buffer tube attachment and upper pin holder areas. PLA is just fine for it (and yes, I have been 3D printing things for 5+ years now and that included a few lowers). I agree with the accuracy of the pin holes, but nothing a drill could not fix. You also need to be careful when installing the pins so you don't break the rather brittle plastic - but there are even modular designs that allow you to just re-print the part that you broke.

I am using my 3D printed lowers primarily for the .22 LR conversion kit ARs, but they could be used for .223 as well. Not sure about the more powerful rounds.

My personal choice is aluminum, then commercially re-enforces plastic lowers, then 3D printed lowers - and no plastic in the AR I used for home protection.



Is this opinion based on an actual failure or experience or just an opinion? Im more interested in talking with someone who tried it and it failed then just conjecture. I have absoultey no experience with 3 d printing but do have a poly80 ar and the people on here that know me know I SHOOT. Mine has held up just fine. Not one bit of problem with probably 5k on a 556 upper. I own blackouts too and the differnce between them and 556's in recoil isnt enough to talk about.

[Elkins45]

I have a GWACS integrated lower and love it, but it was designed from the beginning to be a polymer gun. The ones that simply copy the aluminum design in polymer tend to snap off at the receiver extension. With a 16” pencil barrel you can put together a nice rifle that’s less than six pounds.

[Lloyd Smale]

The original bushmaster made a polymer AR for a while. I don't recall the name of it.

that was the carbon 15 and i think the upper and lower were carbon fiber