first build woes, don't know what I don't know

[MikeD]

figured I'd try my hand at an 80% lower and decided to go polymer due to cost so that I can get a handle on the process of cutting it out without worry about if I'm going to destroy it as part of the process.  Ordered a polymer80 80% lower and the LPK and buffer assy, they shipped it from Reno within 20 min of placing the order.  Got here in about 48hrs, good service.

Decided to try the Genesys upper receiver thinking that at some point I'll order a nicer 7075 80% lower, don't need FA since my BCG doesn't have it, high rail, plus they had it on sale for something like $130 shipped, worth a go right?

Nice piece (as best I know, but I'm aware that I don't know shite at the moment as well)  but it turns out the upper only really mates well with their lower - why?  see gap in the mating area on left side of the receiver

The upper has a 45* cut in the rear by the buffer tube.  Went back and looked at some pics of other manufacturers lowers - they all match the rounded/radiused style of the lower.  Looked at the Genesys alum 80% lower, 45* cut.  I know this is mostly cosmetic (isn't it??)  but it already bugs me that my plan is astray.  Now I'm locked into the Genesys lower if I want the parts to match up.  I didn't know what I didn't know, and the 45* cut in the upper never jumped out at me.  Damn

[MikedaddyH]

Look at things on the bright side. When you are done you will have two rifles ! An AR-10 and a LR-308 . But don't be too frustrated sometimes mistakes are the best way to learn. Ask questions , that's what we are here for .

Edited January 13, 2017 by MikedaddyH

[MikeD]

is that the deal??  AR10 mated to LR308?  which is which?

[MikedaddyH]

What

[MikeD]

well, that sucks.  but learned something, so that's a plus - an expensive plus, but a plus.  I'll put the upper aside then and hunt for the correct part now that I know better what I should be after.  Hoping that's the last mistake I make in this build...  Thx for the help

[shepp]

1 hour ago, MikedaddyH said:

What

Those pictures are golden, I'm saving those for further posting

[planeflyer21]

Just now, shepp said:

Those pictures are golden, I'm saving those for further posting

STICKY!!

Someplace near the entire top of the forum would be best.

[MikeD]

yep, would have helped me, but I could have helped myself by asking someone to eyeball my purchase prior to ordering

So now that this mystery is solved - I see M5, LR308, AR308, M5E1, and Gen 1 and Gen 2.  Can someone describe, or point me to a webpage describing, the differences and what is compatible with what?

And, do I prefer a high or low rail setup?

[MikedaddyH]

I have only one suggestion. Buy a complete upper ! Then assemble the lower yourself. JMHO !!!!?

 

[jtallen83]

By looking at my Matrix receiver set you would say it is an Armalite but they do not interchange with my AR-10 in any way. The only way to be POSITIVE of a fit is to buy a set from the same manufacturer.

[98Z5V]

This thread is the entire reason this forum exists, in the first place, seriously - perfect example.

 

 

 

Now, throw in some RRA for the "third major type" and it would be all set.  Know that the older Bushmaster BAR-10 is the exact same thing as the RRA LAR series.

Then, toss in some "DPMS Gen II" and some "PSA GEN 2" parts, and further muddy the waters... 

Oh, and whatever weird schit custom billet CNC makers decide to do, like the Iron Ridge stuff from a few years ago... 

 

[MikedaddyH]

Buffer

[guruofhotrod]

1 hour ago, MikeD said:

yep, would have helped me, but I could have helped myself by asking someone to eyeball my purchase prior to ordering

So now that this mystery is solved - I see M5, LR308, AR308, M5E1, and Gen 1 and Gen 2.  Can someone describe, or point me to a webpage describing, the differences and what is compatible with what?

And, do I prefer a high or low rail setup?

I don't think you'll find the webpage you're after but, there's a bunch of very knowledgeable guys here that can help keep you going in the right direction

And either High or Low profile is fine as long as you match the rail height on the handguard you select (on rare occasion there can be a slight height variation)

Edited January 14, 2017 by guruofhotrod

[MikedaddyH]

Buffer and spring

[unforgiven]

If you stay with matched upper/lower and same system like recoil = Armalite you stand a better chance not to have problems. If your new to the platform. Just my 2 mags.

[MikeD]

to those suggesting buying matched upper/lower, I understand the suggestion but I'm already well past that point with the poly lower, besides this is supposed to be a learning experience.

@MikedaddyH keep em coming, all great info that helps me at this point

[beantown]

21 minutes ago, MikeD said:

to those suggesting buying matched upper/lower, I understand the suggestion but I'm already well past that point with the poly lower, besides this is supposed to be a learning experience.

@MikedaddyH keep em coming, all great info that helps me at this point

I'd call the lower manufacturer and see what upper they recommend. I'd think a DPMS upper would be the lowest cost route at this point. That is, if it will fit. Down the road buy a lower for the AR10 pattern uppper and build another one. Have you thought about just selling the AR10 upper?

[MikeD]

I will prob sell the AR10 upper, I got it at a decent price so I won't take too much of a haircut when it comes time to sell.  Rather put the funds into the next build of an AR15 once this is done for the girl to shoot

I did email the peeps at polymer80.com about compatibility, and got the generic 'any DPMS upper' - but I also passed along the link to the AR10 Genesis upper asking if it would fit and they indicated no problems, so ymmv apparently 

I'm not too chapped about it honestly, a big part of this build is learning all the stuff to learn, and taking a small hit on the AR10 upper isn't going to hurt me and I learned from the experience, so all good.  Just need to find a reasonable stripped DPMS upper in stock somewhere, no luck so far.  If someone has a link to inventory that would be great

[rcnut]

found a DPMS upper on gunbroker.com item #612790588 it is a High Rise so if you got it you will have to make sure you get a high rise handguard for a DPMS style upper  ALSO there is item 613856506 there are a few options for you. good luck

[rcnut]

if your looking for a complete upper take a look at item #613624230

[98Z5V]

MikeD, you need to link up with Barrett, in this thread below, and sell him your upper receiver...  I'm just sayin'...

 

[guruofhotrod]

Riflegear has Aero DPMS type high profile stripped uppers on sale for $99.99

https://www.riflegear.com/p-5798-aero-precision-m5-308-stripped-upper-receiver-anodized-black.aspx

Should be a good fit for your lower - if you want the forward assist to function you'll need a bolt carrier group with the ar15 style serrations on the side (most don't have them)

[beantown]

42 minutes ago, 98Z5V said:

MikeD, you need to link up with Barrett, in this thread below, and sell him your upper receiver...  I'm just sayin'...

 

I see what you did there 98. 

 

[98Z5V]

That was all you, man - you're the one that caught it in the first place.  Beers to you.

[guruofhotrod]

1 hour ago, rcnut said:

found a DPMS upper on gunbroker.com item #612790588 it is a High Rise so if you got it you will have to make sure you get a high rise handguard for a DPMS style upper  ALSO there is item 613856506 there are a few options for you. good luck

I wouldn't recommend that first one (612790588) that's the really high rise and you won't find a third party rail or handguard for it (it's kind of a bastard in the LR308 world) the second one (613856506) looks good and has the standard LR308 forward assist provision that will work with any DPMS 308 type bolt carrier group (not that a forward assist has much of a purpose on a large frame AR) The assembled upper doesn't look bad either for the price.

 

Edited January 16, 2017 by guruofhotrod