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My plan was to have the gun brought to spec (and re-anodized) regardless of which conversion I purchased. It will be a shooter.
As for as 'desirability' I should have been more clear - are they more or less durable than forged? I assume less - although it is an A2 style lower and the extra aluminum may help.
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My understanding is that they are not as tough/strong as a forged lower. The material Oly used back then was pretty soft to begin with on these receivers and forged receivers are always inherently stronger as the forging process make the material stronger by sealing cracks/inclusion and breaking up impurities or crystalline structures that may be inherent in the original billet.
How all this translates to the day to day life of an M16 lower, its hard to say but a forged lower should theoretically be stronger and have less change of a structural failure than a non-forged lower.
If I remember correctly, Oly considers all these early milled receivers "defective" and if sent in for work will automatically replace them (assuming they are still in semi-auto form). They were even replacing transferable M16 variants about 10 years ago until the ATF told them to stop.
Edited to add....I have never heard of a Oly milled receiver failing so while they may not be as strong as a forged lower they may still be plenty strong enough for the application at hand. Considering there are plastic AR lowers out there now, I can only imagine a 30 year old milled aluminum is still 10x as strong as a modern poly lower.