AR15 lower questions

C

CMOS

New member
OK my fellow displaced AR15.com colleagues, help me with this question.

Which manufacturers have CAST and FORGED lowers?

I know Colt and BM are forged.

I'm looking for a pre-ban AR and don't know much about CAST lowers. Any opinions about them?

Thanks,
Join NRA, GOA and vote!
CMOS

[This message has been edited by CMOS (edited June 29, 1999).]
 
Let's see I think casting is OK as long as it is done right with good materials. You may have more chance of finding defects, such as non metallic inclusions and porosity, however. Porosity, as we all know, will affect the strength of the materials, and those non metallics inclusions, if not treated correctly, will act as stress concentrator and act as crack nucleation sites. Both porosity and inclusions will cause aluminum to have shorter fatigue life (please allow me to remind you that Al does not have fatigue endurance in the first place). The grain structure of aluminum casting is also questionable if their molds are to thick or if they have really low thermal conductivity: large columnar grain will form, causing the product to have very poor mechanical properties. I guess the manufacturer can always mix titanium or other metals in the molten almuminum to provide lots of heterogenous nucleation sites for the solid phase to form, thereby, reducing the grain size of the casting. Afterward, the manufacturer can then heat treat the casting and artificially age it, making it stronger.

The reason forging is so good because the blow holes (porosities) woud be weld shut, and some types of inclusions can be made into stringers, in which with proper orientations, can acually act as crack suppressors instead of originator. Furthermore, forging will give you small, recrystallized, equiaxed grain structures, which is really good for the mechanical properties.

Bottm line: metallurgists don't really like CAST ALUMINUM for parts that will be subjected to high load levels, because of the fear that they were not done properly. Mandatory lecture is always about a busted cherry picker with badly cast aluminum lugs. But as far as lower receivers are concerned, I think it should be totally fine, PROVIDING THAT IT WAS DONE PROPERLY. If cast parts are not properly casted, all bets are off! On the other hand, if cast lowers are cheaper, and they're reinforced (say with thicker walls) at the critical parts, then I wouldn't worry about it and buy it. Another thing is that cracks will propagate SO fast in bad casting, it will fail in a brittle manner, i.e., without any warning none whatsoever.

I hope my confused ramblin' don't give you a headache. Just try to help that's all.

Johannes
 
the lower is not really under alot of stress

Ruger is rumored to cast dpms's lowers
Olympic had cast lowers
i think palmeto armory did cast lowers

cast lowers have cast in graphics instead of engraved letters & numbers
as long as the pin holes are where they need to be a cast lower should function fine.

dZ
 
Eagle/Armalite uses forged lowers. The quick go-by is that only cast receivers can have raised lettering, buy may have stamped or recessed lettering.
 
I have three old pre-ban Oly lowers that are cast. After thousands of rounds and many years I've managed to break nearly every AR part imaginable but I've never had a problem with the cast lower.

However, Oly did make a batch of cast lowers many years ago that were out of spec. They function just fine but you will need to modify your upper to allow the magazine to fit properly (not a fun prospect). Somehow these got into the hands of an unscrupulous wholesaler and he flooded the market with them. I don't know any serial #'s, but they are cast lowers with both "Olympic Arms" and the old "SGW" (Oly's old name) logo stamped on them. Watch out for those unless you get a really good deal and are willing to modify your upper!
 
No mods for me. I have already decided that I want a forged lower.

Thanks for all the responses.

CMOS
 
Castings can be just as strong as forgings, but that depends on the process. Just because it is forged does not mean it is ok also. Ivestment castings are quite good from a structural standpoint. My personal belief is that a cast lower from DPMS and a forged lower from Bushmaster would be equal in terms of strength and durability.

Johnboy
 
While Ruger (Pine Tree Castings) does cast the aluminum lower for DPMS, they are not the supplier of their stainless lowers. I wonder if the caster (of the SS) is the same as for Hesse Arms?

------------------
Vigilantibus et non dormientibus jura subveniunt
 
You must log in or register to reply here.
Back
Top