First 308 AR build and questions about Juggernaut's Rail

[haewired]

Aloha everyone,

I've always wanted to add a 308 AR rifle to my collection so I thought to look here for some advice!  

Here's my Bill of Materials:

1. JMT Tactical Polymer lower / Larue Tactical Straight Bow MBT trigger / Phase 5 Tactical Extended Bolt release / Radian 45* Safety selector / Magpul MIAD grip / Extended Mag Release
2. JP Rifles PSC-19 Side Charging upper / Radian Raptor LT Charging handle
3. Full Mass Bolt Carrier Group / JP Enhanced Bolt
4. Magpul Gen2 UBR stock / Heavy Buffers XH buffer / JP Polished Rifle length Spring (The spacer has been removed from the UBR Stock for the A5 length)
5. Criterion Hybrid Contour 18" 1/10 Barrel, Nitride finish, Mid length gas length / JP Adjustable Gas black / AAC Blackout Muzzle Break 51 Tooth
6. Juggernaut tactical 15" Free Float Barrel
7. I have a 16" Bear Creek Arms Barrel, yes I do but how can I say no to a $50 on sale stainless steel barrel with a guaranteed MOA accuracy?  It does need to be crowned though.

This is also the first time I'm finishing a 80% and polymer lower receiver no less.  I've already learned that you must be patient with sandpaper, putty knives and files with polymer lowers.  Fitting parts is a bit of a pain especially when it comes to marrying the upper with the lower.  Pretty much every cutout needed some material removed ever so slightly, that's where the putty knife and sand paper came into play.  Folding the sandpaper over the edge gave me the tool I needed to make some room in tight spaces.  You'll see in the pics where I had to sand in some spots.   Not sure if there are other methods or tools out there ha ha ha.

My biggest issue with the lower is when the bolt locks back with a empty magazine, the magazine will not drop freely.  Any other time the magazine will drop out but not with pressure behind the bolt stop which surprises me since the tolerance is so close.  Pulling out the mag is a bit stiff so  I wonder if anything can be done here, or is it common with the 308 AR Platform?  

Right now I want to Cerakote my upper and I'm still waiting for my rail from Juggernaut Tactical.  It seems like they're a bit slow and I'm wondering how the rail secures to the barrel nut / receiver.  There's no manual I can look at and there's nothing on Youtube.  Anyone have any experience with this?  Will I need shims to clock the rail?

I've learned a lot by lurking in the forum so I wanted to thank you guys for sharing your experiences and knowledge and hopefully someone will learn from mine.

Thanks!

Edited April 30, 2019 by haewired
after thought

[haewired]

5 hours ago, haewired said:

My biggest issue with the lower is when the bolt locks back with a empty magazine, the magazine will not drop freely.  Any other time the magazine will drop out but not with pressure behind the bolt stop which surprises me since the tolerance is so close.  Pulling out the mag is a bit stiff so  I wonder if anything can be done here, or is it common with the 308 AR Platform?  

After some more observations, the Hex Magazine and the JP Side Charging upper PSC-19 had some tolerance issues.  The upper part of the magazine would bind itself into the upper receiver causing it to stick.  With the bolt catch holding the bolt back it cant assist with the magazine to fall out.  So I took some sandpaper again and shaved down the areas in the magazine making contact till it falls on it's own when the bolt is locked back and the catch fully engaged. 

I don't know if the JP upper's dimensions will affect all magazines.  It's something I'll have to find out as time goes on when I collect more magazines. 

[SimonSays]

Congrates on the self diagnosisand repair. On that JMT lower, I like the look of the smooth area around the mag well and the Cast Iron look above the controls. I'm interested in how the finish will turn out. I'm glad you're doing a polymer. I just can't decide between a metal or polymer 80% for my next build. I'm leaning heavy towards 7075 Aluminum.

I'll be watching this ...

Edited May 1, 2019 by SimonSays
Punk-she-ation

[haewired]

Thanks Simon,

I don't know how well polymer will hold up to the punishment from the 308 with it's "Extremely durable fiber polymer materials ".  To be honest I was really interested in trying out a 80% build and I thought the JMT looked pretty cool and would be a good "beginner" 80% lower.  Little did I know that it needed filing and sanding to get everything to fit.

Juggernaut tactical replied to my inquiry about installing their rail.  It sounds like the barrel nut has flats and can be torqued down with a open ended wrench or crows foot.  They may be slow with filling orders (it seems to me) but at least they're good about answering emails.

So far it looks like I'll be the first one on the forum to experience installing the Juggernaut Tactical Rail.  I also can't find any information concerning the JP Rifles side charging upper PSC-19.  When I'm done with this project, I'll write up my reviews for these items in case anyone's interested in the future.  Times like this it would be really nice to find some kind of information about thinks like this, but there's also a first for everything.  It seems that the AR 308 world is very small especially custom builds. 

So far my build is coming along.  Now I have to take them apart to Cerakote them to FDE.

[98Z5V]

Looks like a good build - this will be nice.  

[Belt Fed]

It's looking good, while I am not a fan of polymer lowers yours looks pretty stout.  a rash of them was sold for the 15 platform a few years ago and they were junk. I seen a couple of them break. you don't see many polymer 15 lowers sold anymore. the aluminum ones got dirt cheap.

[EugeneStoner]

Very cool rifle, please provide a range report when you can.  Thanks to this forum I'm thinking about trying my first .308 build and have started researching components.  In the course of this I came across completed hybrid polymer lowers (they are "hybrid" as they contain some brass reinforcement) from Tennessee Arms. Do you or anyone else reading this have any experience with these?  I know there are several other more mainstream options for lowers (e.g. Aero Precision M5, etc.) but I think these inexpensive polymer lowers look kind of cool and their low cost is also attractive.

https://www.tnarmsco.com/ar-308/

 

 

[DNP]

The clock ticks and “The Rule” applies. 

[haewired]

Thanks everyone!  The most painful part of any exotic build is the wait time for unique parts and coatings.  It's all slowly coming back together though, and hopefully it'll be done by Next week along with a brief range report.

On 5/8/2019 at 5:07 PM, EugeneStoner said:

Very cool rifle, please provide a range report when you can.  Thanks to this forum I'm thinking about trying my first .308 build and have started researching components.  In the course of this I came across completed hybrid polymer lowers (they are "hybrid" as they contain some brass reinforcement) from Tennessee Arms. Do you or anyone else reading this have any experience with these?  I know there are several other more mainstream options for lowers (e.g. Aero Precision M5, etc.) but I think these inexpensive polymer lowers look kind of cool and their low cost is also attractive.

https://www.tnarmsco.com/ar-308/

 

 

Like you this is my first 308 build.  I'm interested in the hybrid lowers from Tennessee Arms, I'll have to check them out.  I'm interested in the Juggernaut Aluminum lower as well.  

On 5/8/2019 at 5:20 PM, DNP said:

The clock ticks and “The Rule” applies. 

What's "The Rule"?  I looked under forum rules but I didn't see anything specific?

[haewired]

7 minutes ago, haewired said:

Thanks everyone!  The most painful part of any exotic build is the wait time for unique parts and coatings.  It's all slowly coming back together though, and hopefully it'll be done by Next week along with a brief range report.

Like you this is my first 308 build.  I'm interested in the hybrid lowers from Tennessee Arms.  I do like the concept of a brass threaded ring in the buffer tube ring and the price is definitely right.  I am a bit curious why there's a blanked out field under the safety.  Other lowers I'm interested in is the Juggernaut Tactical, I like the way it looks and the bolt release is pretty cool.  

What's "The Rule"?  I looked under forum rules but I didn't see anything specific?

 

[98Z5V]

17 minutes ago, haewired said:

What's "The Rule"?  I looked under forum rules but I didn't see anything specific?

For reference:

THE RULE

If you post, inquiring about a product, be it new or old, and no one responds with a review within 48 hours, you are hereby required to buy said product, and review that product, so that this rule doesn't apply to the next person with the same inquiry. "The Rule" shall not apply to the announcement of new or upcoming products, unless there is some context inquiring as to who will be the first to assume ownership of said product. At that point "The Rule" will once again apply to the poster, who will be obligated to be the first in the stated question.

[haewired]

On 5/8/2019 at 8:44 AM, Belt Fed said:

It's looking good, while I am not a fan of polymer lowers yours looks pretty stout.  a rash of them was sold for the 15 platform a few years ago and they were junk. I seen a couple of them break. you don't see many polymer 15 lowers sold anymore. the aluminum ones got dirt cheap.

Where and/or how did they fail?  I would think the weak spot would be around the Buffer tube ring, the bolt catch area and maybe the trigger pin holes.

[98Z5V]

Lesson 65b is the other big one.

Lesson 65b - You snooze, you lose.

You see something for sale, or on sale - and you look at it long enough, study it, try to find a better price comparison, etc...    And someone else will already have it bought, or it'll be out of stock.  You see something you like, you better grab it.  

[Belt Fed]

6 minutes ago, haewired said:

Where and/or how did they fail?  I would think the weak spot would be around the Buffer tube ring, the bolt catch area and maybe the trigger pin holes.

Yeah, if they're going to break, most do there.

 

[haewired]

4 minutes ago, Belt Fed said:

Yeah, if they're going to break, most do there.

 

So I'll be the guinea pig here as I haven't seen any range reviews of any 308 polymer lowers here unless I missed them.  Well, we are about sharing experiences!  On that note, there are a lot of products and manufactures out there, and it seems like many of the parts I'm using hasn't been reviewed before.  Should I submit a review for any parts not reviewed in the past after my build report?  Or would it be too much?

[98Z5V]

1 minute ago, haewired said:

 On that note, there are a lot of products and manufactures out there, and it seems like many of the parts I'm using hasn't been reviewed before.  Should I submit a review for any parts not reviewed in the past after my build report?  Or would it be too much?

That would be great! - That's what most of us do when we're using a new part that hasn't been out in the wild yet... 

[DNP]

The rule applied to Eugene. In the post directly above mine. He owes us the report

[jtallen83]

On 5/8/2019 at 4:07 PM, EugeneStoner said:

Tennessee Arms. Do you or anyone else reading this have any experience with these?

 

[DNP]

^^^that still doesn’t count. Time went by. He gets a cheap one at least....right?

[EugeneStoner]

Ignorance of the rules and especially "The Rule" is no excuse but I promise I was not aware of it until this thread. I thought @DNP's  mention of it might have had something to do with my response to @haewired's build thread but decided to pretend I didn't see it and maintain a casual "business as usual"-type low profile and so on. Since that didn't work I promise to provide a range report on my build when I can. 

FWIW I did search the forum for relevant content related to TN Arms' composite lowers, TN Arms, composite lowers and other related search terms before posting but mineralman55's build thread didn't come up for some reason.  No big deal as I have already pretty much settled on a AP upper too at this point. I think I'm going to use the regular AP M5 upper (i.e. the generic DPMS Gen 1 High Profile pattern upper)  instead of the AP M5E though as while the enhanced version may be better in some respects than the plain M5 upper it also appears to lock you into using one of AP's handguards.  These look good too and are probably a great option but I want to do a "Plain Jane"  DPMS Gen 1 build.  If there is a compelling argument in favor of a different upper please tell me.

BTW @Belt Fed what manufacturer's composite lower is in this picture?

19 hours ago, Belt Fed said:

Yeah, if they're going to break, most do there.

  

 

Edited May 12, 2019 by EugeneStoner

[Belt Fed]

1 hour ago, EugeneStoner said:

 

BTW @Belt Fed what manufacturer's composite lower is in this picture?

 

I don't know, I googled the pic.

[DNP]

It’s a self enforced rule, but it’s fun. There were reviews here, so I don’t know how that one gets played. 

[mineralman55]

18 hours ago, EugeneStoner said:

These look good too and are probably a great option but I want to do a "Plain Jane"  DPMS Gen 1 build.  If there is a compelling argument in favor of a different upper please tell me.

Yes, the enhanced M5E1 uppers are very stiff, and because it can only mount one way, the timing is perfect every time. Alright, someone could rotate and mount the handguard 45 degrees off, but you'd have to be a real numbnutz to to that. 

[EugeneStoner]

6 hours ago, mineralman55 said:

Yes, the enhanced M5E1 uppers are very stiff, and because it can only mount one way, the timing is perfect every time. Alright, someone could rotate and mount the handguard 45 degrees off, but you'd have to be a real numbnutz to to that. 

Thanks for the response. 

[haewired]

All done!  Now I have to test it out!  the whole package without the magazine is 10.6 lbs.  A bit heavy, and the stock doesn't help here but she's balanced.