AR15 lower differences?

[204chucknorris]

I am looking into building my own AR15 in a new caliber versus a new upper for my current AR. So the question is if a lower is mil spec is it fair to say they are all equal? Understanding large pin versus small and or billet. It seems there are some large price variations between lowers or brands.

[FC]

There really isn't that much difference as long as they are mil spec.

[KillBilly]

There actually is a big difference between Machined and Forged Lowers

I prefer the Tactical Innovations Billet Machined lowers with the STBA™ - AR15/M16 STAINLESS TRIGGER BUSHING & HEX HEAD PIN ASSEMBLY (Stainless Bushings and Pins).. 

http://www.tacticalinc.com/t15bdxtrade-billet-deluxe-patented-billet-machined-lower-receiver-p-1082.html

[ducklab]

There is a large difference in machined/milled or forged as previously stated. Most lowers around the $100 - 200 range are forged. Most $300+ are machined or milled from one block of metal. Almost all off the shelf ARs (s&w, colt, bushmaster,stag,etc) are forged. Forged lowers are all made by 3 or so companies and sold to smaller companies and finished. By finished I mean polished up, possiably milled a little more precise in certain areas and logo put on. I cannot comment on milled becuase I have no experience but I can imagine they are alot more precise. As long as you get one from a reputable company they will be SPEC.

[Bean Counter]

Thanks for the.explanation, Duck 

[GregMcFadden]

precision of the lowers (forged or milled) depends on who did the machining.  They can both be machined to be more close to the nominal dimensions than is necessary for the firearm to funciton properly.

see here for an example of the process on billet.   

http://cncguns.com/projects/ar15lower.html

you do the same milling/broaching on a forged one, but you don't have the option of leaving extra material or radically altering the outside shape without paying for  new forging tooling ($$$$$)

the forgings look like this
http://www.tacticalinc.com/ar15-lower-receiver-forging-p-1108.html

before machining.  With the exception of the exterior machining operations, the interior ones are the same for both the forged and billet.  the tolerances that can be held are the same.   

the billet may be stronger (given all dimensions the same and same material) depending on the quality of the forging itself and the processing, but keep in mind that unless you are using your AR as a club, battering ram, etc.  the lower is a low stress part.   

Also keep in mind that some folks sell 6061T6 billet  lowers.  IFF you are worried about strength and weight, avoid these, as they will be one of two things : the same weight as the 7075T6 forged lowers and weaker, or As strong/stronger and heavier.

My general take is that the lower itself is a very low stress part.  Unless you abolutely can not live without the freakin awesome looks of the billet lowers (I really do like how most look, and if money was no object, would drop it on them in a second) you would be better off saving the difference between  a billet and a forged and using it on better optics for the finished rifle.

[Biggerhammer]

A quality billet lower will not cost you much more than a forged lower. A quality billet lower will cost you around $200.00

http://www.rainierarms.com/?page=shop/detail&product_id=1539

Mega Machine does some nice stuff but it's all about one's perceived look, there are many choices to fit ones style, feel, function and application.

[dontgetcrabs]

I think the small pin large pin lower refers to the trigger group pins not take down.

[Biggerhammer]

I think the small pin large pin lower refers to the trigger group pins not take down.

You're correct, I edited my post.