Opinion on the magnesium alloy uppers not lowers, uppers...???

[TED]

I personally would not buy a magnesium alloy lower. I would worry about it breaking.

However, since the bolt locks into a barrel extension and not the upper itself, what might be your thoughts about using a magnesium alloy upper?

Thanks.

[TED]

BTW, I see that someone else is offering an aluminum lithium allow upper. Any thoughts on those would be welcomed as well.

TED

[MorphCross]

When it comes to Alu-Li I would jump all over a set of Hodge 2099 Alcoa Forged. However as I am not made of 'Greenbacks' 7075-T6 is good enough. A Magnesium upper or lower is a whole heap of nope.

[Potss]

MAG Tactical used to make magnesium lowers. They break like poly lowers do, at the receiver extension threads most commonly. The tech was bought by fostech when MAG went out of biz. As far as I know not much has changed. So for fun guns and maybe race guns they are fine, but it isn't a question of it they will break but rather when.

As for other alloys, V7 makes a tremendously nice, light, and strong 2055 Alu-Li lower and upper.

[GH41]

I personally would not buy a magnesium alloy lower. I would worry about it breaking.

However, since the bolt locks into a barrel extension and not the upper itself, what might be your thoughts about using a magnesium alloy upper?

Thanks.

What are you looking to gain using magnesium? The only magnesium receivers I have seen came from Mag Tactical and I understand they morphed into Fostech. I wouldn't buy either of those.

[MegademiC]

My thought is if you have an over-pressure event, your face is basically on the upper, which becomes a pressure vessel.
Standard Al uppers fair well in these events. I wont buy anything that does not handle pressure at least as well as 7075. I dont know about the lithium alloy, but my understanding is that Mg alloy is not as strong as 7075.

[GH41]

My thought is if you have an over-pressure event, your face is basically on the upper, which becomes a pressure vessel.
Standard Al uppers fair well in these events. I wont buy anything that does not handle pressure at least as well as 7075. I dont know about the lithium alloy, but my understanding is that Mg alloy is not as strong as 7075.

Generally speaking Magnesium has almost twice the strength as aluminum pound for pound. Actually a little stronger than steel if the part is the same weight. Don't blame the alloy. Blame the bad reputation on the people that make junk magnesium cast receivers.

[Gödel]

Generally speaking Magnesium has almost twice the strength as aluminum pound for pound. Actually a little stronger than steel if the part is the same weight. Don't blame the alloy. Blame the bad reputation on the people that make junk magnesium cast receivers.

Pound for pound comparisons don't make a lot of sense when the parts are going to be similar in volume, not weight. So unless the magnesium part is the same weight as the aluminum upper it's replacing, you can't compare their strength-to-weight.

By volume, 7075 aluminum is nearly twice the strength of typical magnesium alloys, and actually has a higher strength-to-weight ratio as well. There is no way a magnesium upper made to similar dimensions could be as strong as a good aluminum one.

[lysander]

Generally speaking Magnesium has almost twice the strength as aluminum pound for pound. Actually a little stronger than steel if the part is the same weight. Don't blame the alloy. Blame the bad reputation on the people that make junk magnesium cast receivers.

Pound for pound... HOWEVER:

The ultimate and yield strength of the better wrought Mg alloys are about 15% to 20% lower than 6061.

Cast Mg alloys have less than half the yield strength of 6061.

You can blame the material, if they were cast, then magnesium is a poor material. If they were forged, then you can blame the manufacturer as forging magnesium is not quite the same as forging aluminum, and improper forging can lead to problems.

[Gunfixr]

An answer to the op: since it is established that the magnesium lowers tend to break at the receiver extension threads, and that is arguably the area getting the highest stress, would it not be likely that a magnesium upper would break behind the barrel nut threads, just in front of the receiver proper, in that thinnest section that carries the full weight of the barrel/handguard assembly, as well as receiving some impact every time the bolt carrier goes forward?
I believe that area is even thinner than the receiver extension threads area. This is probably why the upper never materialised.

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