Cast and tempered aluminum has been used for many years and on millions of engines and tools (such as impact wrenches).  Quality aluminum alloys are cast, tempered and machined.  An hour of in-city driving is probably more stressful on an intake manifold, alternator casing, water pump housing, etc., than 10X or 100X hours of range use on an AR-type rifle.  The AR design dampens its own recoil.

I realize there is considerable bias against cast lowers.  But are forged-and-milled lowers really any better in a way that makes a difference?

If someone with metalurgical knowledge can answer this, or point to some real data, it would be worth knowing about.

Based on auto experience and observation, I think the bias against cast lowers is more a matter of snobbery than substance.

Not shure if this will help but I am QA at a aluminium wheel plant. We dye pen wheels with a uv sensitive dye and look at them under a blacklight. Any holes/cracks/scratches show up as a green glow. On our forged wheels you only see a few but when you look at a cast wheel "take in mind this is after the machining has been done" It looks like someone went crazy with a hammer and chisel. They are ate up. As far as lowers my thinking is that forged is better as it has more metal and less voids, hence a slightly stronger product.
My $0.02 worth.

When cast parts fail then tend to fracture, often times irreparably.  When forged parts fail they usually distort or bend.

When I investigated this for my first purchase there were some instances of failures in cast uppers and lowers that had "chipped" pieces out of either the lower or upper.

I NEVER found pictures of forged failures on the AR family.

This is not to say there are none, just couldn't find any.

That spoke VOLUMES to me and I bought an Armalite.  I now only look for forged receivers.

My preference and it COULD be snobbery. [;D]

Thanks.  This is the sort of informed responses I was hoping for.  

Is there such a thing as hi-grade cast aluminum?  Almost anything can be made poorly--but not everything can be made well.

Thanks again for the input.

In all honesty, a cast lower should do just fine for an civilian AR-15's needs. It is the upper reciever you should be worried about.

DPMS has cast and forged available and I have heard the cast is heat treated or something to about the same duability. I believe the quality of the machine work is more important than cast or forged. The same people who try to tell you it makes a difference will also tell you that the plastic Calvery arms lower is a great high quality unit that works and is very durable, and it is! The fact is it just is not going to make a difference, this is not a very stressed or impacted part of the gun, it's kind of like worrying about wheather or not the cigarette lighter handle in your car is forged or cast. I wonder if anyone can show us a failed cast lower form a good manufacturer that would not have failed if it had been forged. I think the only difference would be if you were selling it to someone who though it made a difference.

Materials Engineering to the rescue!

Castings can have some problems that a forging might not have. Inclusions (see shit) or bubbles in the aluminum during casting can weaken the structure. In addition, due to cooling of the molten aluminum to solid you might get dendtritic growth. This is where an alloying element cools at a differential rate from other elements of an alloy resulting in "fingers" of one component growing radially inward from the surface of the casting. However, I am not sure if this is a problem with the alloy they use with the receivers. As mentioned earlier cracking can be a problem if the cooling of the cast body isn't totally uniform. If a crack is already present then only a small force (relative to starting a crack in an unflawed body) will lead to failure. There night also be some grain size issues unless there is additional heat treatment.

Forgings get added strength from a process called work hardening. This strengthens the structure by introducing dislocations into it. These dislocations have difficulty moving past one and other and lead to higher tensile strength. IIRC these dislocations also retard crack growth.

Hope that helped.

Forgings are harder/denser than castings.

Castings will stand up to the usage that 95% of us give an AR15 (bed buddy's) [;)]

If you are going to use your AR15 as a shovel, paddle a canoe, roll in the dirt, a wantabe weekend warrier, etc., get forged.  If you are going to shoot paper 1 shot at a time and kiss your gun, either will be fine.

Cast lowers are easily coverted to full-auto and work just as well as a forged lower.

If you are going to get a cast lower, buy it based upon the warrenty - that way if a problem were to ever occur, you get it fixed without paying out money.

In fact the warranty is important for any AR15.  The warranty is a sign of how the company backs up their products.  Some of the well known companies are horrible with servicing their products.  Buyer beware!

I've got a couple of DPMS cast lowers and a DPMS forged lower.  The big advantage of the forged lower is cosmetic.  The lettering, logos, etc. are all stamped on the forged lower so they are very crisp with good detail.  On the cast lowers they save some steps by including what lettering they can in the molds which reduces the level of detail that is possible.

Slightly off but related subject:

i've been shopping for preban Eagle Arms lowers. These were all forged, right?

Correct, Eagle Arms lowers are forged. EA is a division of Armalite. Their lowers are supposed to be made on the same line, only difference is complete EA rifles don't have chrome-lined bores.

Question Why would cast be easier to convert to full auto rather than the forged Lower?

Nothing wrong with cast lowers as long as they're not cast!

Mark said Easy to conver not Easier to convert.

I think he meant they work just was well.

Personally for $20 difference in cost I just can't get past the ugly part of the cast parts.

[rofl2]

Cast metal is easier to mill.  Forged is harder.

Both work just as well in semi or full auto.

Man, you people baby your guns and act like snobs sometimes.

My guns are spotless on the inside but I don't go around hoping people can see that is it a brand new Bushmaster or Colt. I love the people that spend $1,800 on a flawless preban and are too afraid to shoot it.

I love my ARs but I can't see spending so much money on cosmetic items such as logos. From what I save on my ARs and wolf ammo I can shoot a whole lot more than a $1,800 gun, with $0.30 a shot ammo.

Exactly[:D].  when you're talking about something that's going to cost you at least several hundred dollars more to complete, why the heck would you want to save the $20?  I don't care if they're safe or not. They look crappy--at least the Olys that I keep seeing at shows look crappy[;D]

With most any lower receiver one of the areas that concerns me is the magazine well.


With forged lowers from quality manufacturers the magazine wells tend to be pretty consistent thanks to the broach that cuts them.

Compare to the cast lowers which from what I can tell have the magazine well formed from part of the casting process, when the part is cooling some of that variation mentioned in Gorto's post becomes apparent.    I look down into the magazine well of my stainless steel DPMS lower the walls are not perfectly uniform and parallel to one another.   What does this mean?   The magazine well isn't always "drop free" with all magazines, it's a little tighter fit with some mags than with my forged lowers that use broach cut magazine wells that run more consistent.




Take it for what it's worth.    From what I can see, cast lowers are easier to machine because they need less of it thanks to much of the voids already being formed from the casting process.