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Lower parts kit


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I'm in the process of building a 308 AR using an SI Defense upper and lower.  What do I need to know and look out for in terms of compatibilty for lower parts kits.  I was looking at this http://www.rainierarms.com/?page=shop/detail&product_id=1762


But am unsure as to if it will work in this build or not.  Are there other things I need to consider parts wise also?


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Montana - hey, brother, can you make a precise measurement of the length of that SI pin for me?  It's looking ALOT like the length of the RRA pin.  If you can get vernier calipers on that thing and list the length, I can confirm or deny.  <thumbsup>

Edited by 98Z5V
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  • 6 months later...

Ok so I’ve finally gotten all the parts together for my AR-308 build and this is what the pile looks like.  Let me know if I’ve missed something or if you’ve had experience with an item and would like to point something out.

Upper and lower receiver:  SI Defense matched set

Barrel:  20 inch Rainier Arms Ultra match

Hand guards: Apex rifle length system w/appropriate rail mounts

BCG: 762 Industries Nickel Boron match grade BCG

Gas block: JP Enterprise stainless (black) adjustable gas block

Muzzle brake: Precision Alignment M11 w/accu-washer alignment system

Charging handle: Mech Armor Defense TacOps-1 (I was going with the BCM medium gunfighter but after reading Robocops review on the Mech Armor Defense TacOps-1 it was a no brainer which one I was going with.)

Stock: Magpul Gen 2 PRS (7.62)

Grip: Hogue rubberized A2 (I went with this over grips with palm rest because the palm rest just didn't feel right that and due to the size of my hands didn't provide a benefit aside from something flat to rest on the ground.)
Trigger: DPMS National match 2 stage

Gas tube: Rifle length nitromet gas tube

Bipod: Atlas Precision

Optics: SWFA SS HD 5-20X50


Standard equipment: forward assist, ejection port cover, buffer and buffer spring, DPMS standard butt stock extension tube, DPMS steel 20 round magazine.

Edited by crazybull
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Charging handle: BCM Medium gunfighter




Optics: SWFA SS HD 5-20X50


The "Gunfighter" fails to be epic when you put such a large scope on the rifle. It's just too damned cumbersome to reach around the scope and grab that small portion of the CH.


I vehemently suggest considering the Mech Armor Defense "TacOps-1" for any build using a full sized scope. If you were using a red-dot or an ACOG style, the "Gunfighter" would have been enough. You will eventually want more from your CH.


Also, take a look at the Phase5 Extended Bolt Release

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I'll take a look at the Mech Armor Defense "TacOps-1" but for the BCM gunfighter with respect to a large scope will it make a difference that I will be doing one handed manipulation with my left hand that and I have some small mitts?


Also is the Phase 5 Extended Bolt Release better then the MagPul BAD leaver?  It certainly looks better built.

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First you should read


Then you'll want to go


As for the Phase 5 vs all others.... The 308AR is often too large in the receiver to accept the BAD lever or the Tactical Link. This isn't the case with ALL receivers, as there is no set standard for the 308AR. They can be hit or miss when fitting. The billet receivers are almost always larger than the forged version.


I have the Phase 5 on my Gen1 SI-D receiver, and I recently installed another on the Gen4 SI-D receiver.

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Ok,  I've got almost all my parts in the last bit that I'm waiting for should be delivered today sometime.  I also want to say good call on the charging handle Robo that thing is a beast.   I order it and Monday the company owner called me up just to confirm that my upper is compatible with it (got to love customer service like that, we ended up just chatting for about half and hour and to top it off he's located in my state so I'm helping local businesses). 

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Once I get it all together I'll post some pics.  but right now FEDEX is pissing me off.  The last of my stuff was suppose to be delivered Saturday.  Come sunday morning and no visit from santa I checked the tracking online and all it said was N/A.  Today is Monday and still nothing according to FEDEX their home delivery service is only open Tuesday - Saturdays.  So with some luck come tomorrow I'll have my loot and I can get this thing together for we start getting to much snow for me to want to go to the range.

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  • 2 weeks later...



Well here it is I completed it a few days ago and just dropped it off with a friend of mine that does Cerakoting.  I'm going to have him uniform the black on it so that theres not a dozen different shades of black and of course match the barrel also.  Once I get it back in about 5 weeks I'll post an updated pic.

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