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So is anyone or had anyone used the polymer ar15 receivers for an ar15. I know several people personally that have used the plumcrazy lowers. I was thinking about the lighest weight build possible and I'm thinking of using a polymer upper and lower a carbon fiber handguard, a turned down 9mm barrel of about 4 or 5 inches in length and a pilstol buffer with shockwave arm brace. Maybe even make up an aluminium flash hider.

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They are generally only about 4 oz or so lighter and I'm just not sure the reduction in durability is worth the weight savings over aluminum, especially with a 9mm build which tends to be a little harder on things. Having said that, I had a New Frontier polymer lower for a short period and it did not fail, but I was not very hard on it and the upper was 5.56.

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Yeah I know the polymer isn't going to save a ton. But an oz here and there. And I've seen blackthorn has some polymer uppers. I'm not sure they would be durable enough but I'm not going to shoot thousands of rounds through it. I'd probably use it to teach my kids, hell I may just use it as a 22lr. That would proably be smarter. My goal is a light weight short length of pull with a gun my 7 year old could hold up for long enough to learn to shoot. I got a bunch of kids and as they learn him safety and can recite the 4 rules I'll start teaching them how to shoot.

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Could always do a MagTac lower. Strength of aluminum and lower weight of polymer. Good trade off. I've used two for builds and have no complaints on them other than the proprietary FCG pins.

A complete plumcrazy lower is 99 bucks.

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Do NOT use a polymer lower. Ever. It's generally only accepted as being useful as a dedicated .22lr, but even then, they will break eventually. It's not a matter of "if", but "when". If you're looking for weight savings, especially on a direct blowback, stick with an aluminum receiver and consider skeletonized.

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Yeah I know the polymer isn't going to save a ton. But an oz here and there. And I've seen blackthorn has some polymer uppers. I'm not sure they would be durable enough but I'm not going to shoot thousands of rounds through it. I'd probably use it to teach my kids, hell I may just use it as a 22lr. That would proably be smarter. My goal is a light weight short length of pull with a gun my 7 year old could hold up for long enough to learn to shoot. I got a bunch of kids and as they learn him safety and can recite the 4 rules I'll start teaching them how to shoot.

No blackthorn anything, ever. I'm not sure they have ever been known for doing anything adequate or decent.

 

In the case of .22, have you considered the S&W M&P15-22? Great .22 trainer if you want to get them used to AR feel and controls.

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Yeah I know the polymer isn't going to save a ton. But an oz here and there. And I've seen blackthorn has some polymer uppers. I'm not sure they would be durable enough but I'm not going to shoot thousands of rounds through it. I'd probably use it to teach my kids, hell I may just use it as a 22lr. That would proably be smarter. My goal is a light weight short length of pull with a gun my 7 year old could hold up for long enough to learn to shoot. I got a bunch of kids and as they learn him safety and can recite the 4 rules I'll start teaching them how to shoot.

No blackthorn anything, ever. I'm not sure they have ever been known for doing anything adequate or decent.

 

In the case of .22, have you considered the S&W M&P15-22? Great .22 trainer if you want to get them used to AR feel and controls.

I know blackthorn I total crap. But they have the only polymer upper I can find. And I'm sure there's a reason. But....I'm planning to get a cmmg bolt and barrel. Wouldn't the upper just house those what issues could present themselves? And as far as polymer breaking I know personally 3 people with plumcrazy lowers, one guy has 5 between his father in and law and himself. And I've heard of no breakages. And they are all .223.

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I would absolutely not advise using a polymer lower for a pistol build of all things. There is much more stress on the reciever at the buffer tube threads as there is no bracing it to your shoulder. The force of the buffer hitting the end of the tube is going rearward on the threads instead of being absorbed in to your shoulder.

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I would absolutely not advise using a polymer lower for a pistol build of all things. There is much more stress on the reciever at the buffer tube threads as there is no bracing it to your shoulder. The force of the buffer hitting the end of the tube is going rearward on the threads instead of being absorbed in to your shoulder.

Very good point. I'm not sure that it would matter with the newer metal reinforced polymer lowers, but still a good point.

 

For yet another perspective, if both the upper receiver and the lower receiver fail, Monty still hasn't lost much money in the grand scheme of things. I am very interested in keeping things light, but not as obsessed with it as some might be. I try to manage my expectations by finding some middle ground between light and a durable serious-use weapon. I don't have anything just for fun anymore. I like a little adventure every now and then though, so I'd probably do another polymer lower AR if I allowed myself some play cash. too many important things in front of me right now, so I abstain from anything that is not an absolute necessity. I say go ahead and do the build. Whether it goes well or not, we will learn something from it.

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I've built Poly80 lower. No issues at all. Very nice lower. 

 

As far as Blackthorne goes....

 

https://duckduckgo.com/?q=blackthorne+hesse+vulcan&t=opera&ia=web

 

The consensus says CRAP!

 

Their 50BMG is an infamous bomb in your face. 

https://duckduckgo.com/?q=blackthorne+hesse+vulcan+50+FCSA+Reade&t=opera&ia=web

 

I MIGHT use one of their products as fill in a concrete foundation pour, but that's about it.

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Just saying when you mill a 80% polymer lower you come to understand how tuff some of this stuff is.

All in all for lowers , the failures came in the early days when they did not have their recipes for their polymer correct but aluminum alloy lowers had the same problem.

My 9mm rocks and I am confident that the polymer will hold up.

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I would absolutely not advise using a polymer lower for a pistol build of all things. There is much more stress on the reciever at the buffer tube threads as there is no bracing it to your shoulder. The force of the buffer hitting the end of the tube is going rearward on the threads instead of being absorbed in to your shoulder.

Very good point. I'm not sure that it would matter with the newer metal reinforced polymer lowers, but still a good point.

 

For yet another perspective, if both the upper receiver and the lower receiver fail, Monty still hasn't lost much money in the grand scheme of things. I am very interested in keeping things light, but not as obsessed with it as some might be. I try to manage my expectations by finding some middle ground between light and a durable serious-use weapon. I don't have anything just for fun anymore. I like a little adventure every now and then though, so I'd probably do another polymer lower AR if I allowed myself some play cash. too many important things in front of me right now, so I abstain from anything that is not an absolute necessity. I say go ahead and do the build. Whether it goes well or not, we will learn something from it.

That is a very good point about the pistol buffer tude taking abuse in a "pistol" ar.

 

I think I've decided to make this a 22lr instead of 9mm. I've already got a full metal ar15 that takes glock mags so that may not be the best option.

 

And I know the rep that blackthorn has. But it will just be the polymer upper that will house a cmmg bolt conversion. The only problem I for see a shitty polymer upper causing on a 22 would be the ejection port causing failure to eject. I think I'll do a 10" barrel turned down pretty to lighten it. And a folding shockwave armbrace. A carbon fiber handguard tube at 10". Then if the HPA passes I'll cut the barrel down some and attach a silencer to protrude out of the handguard about an inch or two. Should be a very light "pistol" great for squirrel hunting.

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I don't trust poly ARs.  I'm not saying they can't be good, just that I don't trust them.

 

Considering that you can get an Anderson lower for $39 if you wait for a sale (like AIM has right now), I'll stick with those.  I have built 3 ARs on Anderson lowers and they go together perfect and work perfect.  No reason to pay more unless you just want a name to impress your friends.

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I don't trust poly ARs.  I'm not saying they can't be good, just that I don't trust them.

 

Considering that you can get an Anderson lower for $39 if you wait for a sale (like AIM has right now), I'll stick with those.  I have built 3 ARs on Anderson lowers and they go together perfect and work perfect.  No reason to pay more unless you just want a name to impress your friends.

...Do you have a Glock? ;)

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...then there's THIS:

 

https://fightlite.com/collections/belt-fed-uppers

 

It ain't light, but with a registered auto lower, it'd be a LOT of fun!

Yeah I'm looking for cheap. But if I ever win the lottery or they repeal the Hughes amendment I'll find the money for that 9mm belt fed upper to go with my legal machine gun lower.

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They are generally only about 4 oz or so lighter and I'm just not sure the reduction in durability is worth the weight savings over aluminum, especially with a 9mm build which tends to be a little harder on things. Having said that, I had a New Frontier polymer lower for a short period and it did not fail, but I was not very hard on it and the upper was 5.56.

 

Those exact things have broken specifically in the 9mm builds. No locking lugs to take the force.

 

Look Up the Cav Arms lower. It is reinforced in particular areas and has an integral A2 style stock. The result is something much stronger and lighter.

I don't trust poly ARs.  I'm not saying they can't be good, just that I don't trust them.

 

Considering that you can get an Anderson lower for $39 if you wait for a sale (like AIM has right now), I'll stick with those.  I have built 3 ARs on Anderson lowers and they go together perfect and work perfect.  No reason to pay more unless you just want a name to impress your friends.

 

+ you could drill a few speed holes in non-critical areas such as the sides of the magwell and eliminate an ounce or so without compromising strength in a meaningful way.

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