I was wondering how strong is a cast lower compared to a forged.  How long would either really last?  Also, the plinker model from Olympic also has a cast upper.  how wise is that?  With all the pressure from the chamber, is that safe?

An AR type receiver has little load on it.

Its functions include:

• Holding the trigger, safety, and hammer group.


• Holding the Magazine.
• Holding the "Bolt hold open".
• A mounting point for the Pistol Grip.
• Aligning the upper receiver with the rear receiver extension/buffer tube

Note that stocks are all supported by the receiver extension/buffer tube threads.

The heaviest loads a lower has to endure is when the buffer is bottoming hard. Also in improperly assembled or out of spec parts a condition can occur where the back of the gas key will impact the top of the receiver just below the charging handle.

All the high pressure is handled by steel components. - The Bolt is locked into the barrel extension during firing, the bolt carrier movement is initiated by gas pressure inside the bolt carrier.

I make cast lower receivers, and I will tell you that a forged one is better, but it is not enough of a difference to cause worry, or none of us would use them.

If your paranoid about quality - the items that you should be worried about are the bolt, carrier and barrel. These should be from trusted sources of known quality.  There are people out there who will sell out of spec junk that was sold as scrap, or parts that have not been fully heat treated.

(edit) - The main wear point is the hammer and trigger pivot pins - worse case #1 you install "Anti-walk" pins which have an "e"-ring on them to keep them from moving. Worse case #2 - Pin holes are seriously loose, enough to warrant safety concerns about accidental hammer release. - Just ream the holes out to fit pony pins (Colt trigger group).

(edit #2) -  Note: I have only heard of one case that was bad enough to require the oversize pin job - and it was a Nam era M16 Forged receiver.

Thanks for the info.  So what is the main complaint?  Appearance?

The Prof speaks the truth.  Unless you are really going to abuse the rifle you won't notice the strength difference.