Steel vs Aluminum - Benefits and Cons of use for specific AR parts

[JediGuy]

This question is coming from the SOLGW steel magazines that are available, but that just got me thinking.

Considering the thickness of 7075 receivers, is there any potential downside to a stronger material like steel being used in certain parts?

Obviously it is used in small parts within the receivers.

What about parts that “stick out” like a magazine?

To move to different types of aluminum, are there potential downsides to using a 7075 optic mount?
As an example, if an impact placed enough pressure on an optic, would it be preferable to have some part of the optic mount made of 6061 to ensure the mount failed before part of the receiver?

I get this is likely theoretical, but it’s out of my lane, and I am curious.

Lysander’s explanation of why inserting the cam pin the same way all the time is counterproductive was great, and that sort of info is what I’d love to have for this topic.

[tehpwnag3]

I have a few steel AR mags that work well and are just a tad heavier than aluminum. They may last longer, be more durable, but I haven't noticed much difference. In my oversimplified opinion, if the application was appropriate for both materials, I would want the lighter and/or longer lasting material. I want ALL the pros, none of the cons haha.

[vicious_cb]

I have a few steel AR mags that work well and are just a tad heavier than aluminum. They may last longer, be more durable, but I haven't noticed much difference. In my oversimplified opinion, if the application was appropriate for both materials, I would want the lighter and/or longer lasting material. I want ALL the pros, none of the cons haha.

You mean like polymer?

Steel mags were a fad in the late 2000's with HKs. Turns out they were heavy as s***, were damaged just as easily and rusted on top of all that.

[Mjolnir]

You mean like polymer?

Steel mags were a fad in the late 2000's with HKs. Turns out they we're heavy as s***, we're damaged just as easily and rusted on top of all that.

Steel mags are heavier and corrode and the feed lips while stronger are not as malleable when they are dropped.

I’d prefer polymer over steel or stainless steel-reinforced lip polymer mags.


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[markm]

Steel mags are more than a tad heavier when you put three of them in a pouch. It's real weigh difference. I ran some Brit steel mags for range use for years. Never an issue with any lowers.

As far as optic mounts, I'd always opt for the strongest material. I'm tired of pic rail mounted stuff bending and breaking. The receiver is pretty strong.

[vicious_cb]

To move to different types of aluminum, are there potential downsides to using a 7075 optic mount?
As an example, if an impact placed enough pressure on an optic, would it be preferable to have some part of the optic mount made of 6061 to ensure the mount failed before part of the receiver?

I get this is likely theoretical, but it’s out of my lane, and I am curious.

Lysander’s explanation of why inserting the cam pin the same way all the time is counterproductive was great, and that sort of info is what I’d love to have for this topic.

Look up C405/7055 aluminum.

[Firefly]

I only have steel mags because they were free, came with the gun, or looked cool and made me feel tough.

Pmags all day. USGIs for putting away.

[tehpwnag3]

No, not at all. OP referred to steel vs aluminum parts, so that was my basis. While I love and prefer Pmags, I wouldn't want a FF rail made of polymer. Likewise, I wouldn't want a barrel made from aluminum.

You mean like polymer?

[lysander]

In good engineering you use the best material for the job, and by "best" that also includes cost and workability.

There is "strength" and there is "stiffness".

Both 7075 and 6061 have approximately the same stiffness for the same shape, so the question is, "How much strength do you need for an optic mount?"

The answer is, in most cases, not really a whole bunch, at least when you bulk up the shape to get the necessary stiffness, the stress is low enough that 6061 can handle it without issues. So, 6061 has more than ample strength for such and application. 6061 wins due to cost, with no loss in serviceability.

Steel is about twice as stiff for the same shape, so theoretically you could shave off half the material, but steel is about 2-1/2 times as heavy for the same volume. So you still wind up with something heavier.

And, with an optic mount you want no movement at all between the mount and the weapon, so in any case the optic needs to be strong enough to handle the recoil all on its own.

[tehpwnag3]

Some of the comments about weight made me curious, so I pulled out a scale and a couple 30rd mags, one stainless steel and the other aluminum. Each was weighed empty and then loaded with 30rds of LC XM855.

Empty
Al: 107 grams (3.8oz)
SS: 168 grams (5.9oz)

Loaded
Al: 468 grams (16.5oz)
SS: 528 grams (18.6oz)

Comparing empty mags, my steel mag weighed about 50% more which is quite dramatic and definitely adds up. However, fully loaded, the weight differential is about 12%. Still, lighter is better IMO.

For comparison, I also weighed a M2 Pmag (no dust cover):

137 grams empty (4.8oz)
498 grams loaded (17.6oz) (can only attach 5 photos here)

It would appear the polymer mag sits right in between the aluminum and steel mags.

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