How to tell if it's forged or cast?

[Evil Monkey]

How do you tell if an AR15 receiver is forged & milled or cast?

I go on Gunbroker and check out the various Oly Arms plinkers and Bushmasters, etc., and I can't tell the difference.

Is there something wrong with the cast receivers as well? Those cast plinker models are quite cheap for an AR15.

 

[browningguy]

Once final machined and finished it's practically impossible to tell a forging from a casting by looking at it. Theoretically, there is nothing wrong with a cast receiver, it's just a matter of how well it is done.

Some of the guys on the board can probably tell you which brands use castings.

 

[3rdpig]

All of the current Oly receivers are forged, I don't think they've made a cast receiver for several years. Look at the lettering on the receiver, cast recievers usually have raised lettering, forged receivers have engraved lettering.

On the Olympic FAQ page they've got some pictures and descriptions to help you identify cast or forged.

http://www.olyarms.com/?rootView=page&page=faq#

 

[Slamfire]

Assuming that a forged receiver and a cast receiver are machined to the same tolerances, (big assumption) then there is not much of a difference between the two in this application.

The upper receiver and the lower receiver in the AR platform don't carry that much load. The barrel and bolt are steel, because they must hold the cartridge thrust, and the upper and lower only have to hold those things in alignment. I don't think that is a strength critical application.

I have not looked up material data on aluminum, but my recollection is that extruded aluminum is stronger than cast. Maybe you can find something on MatWeb.

 

[MrDig]

Thoughts on Metalurgy

Forged steel is a little stronger than cast steel, this is due to the forging process. it actually adds carbon to the metal, this is technically the difference between Iron and Steel. Steel is Iron with a higher carbon content. Steel is graded by its carbon content 4140 carbon, 440 Stainless, etc. the higher the carbon content the better the steel to some extent.
If steel is cast 4140 or forged 4140 it still has a carbon content that grades it 4140.
I took some cheap scrap iron and stuck it into a oak feuled coal fire and heated it and folded it, and hammered it until it looked like a knife. I used 20 mule team borax to flux the folds so I got good welds each layer. the result is I have a pretty cool knife and I learned some thing in the process.
Steel is Steel, 4140 is 4140 if you have a 4140 cast steel 1911A1 frame and slide it will function like a 4140 forged steel frame and slide. Both will need finish work that makes it impossible to tell visually which is which. they will have the same tensil strength, and brittleness and be significantly harder to work than lower grade steel. I will dig up a steel grade reference from my metalurgy books to post.
If all other things being equal you took a cast 4140 part from a pistol and a forged 4140 identical piece, I can assure you if pooly fit and finished the Forged piece could easily under prefom the cast part.
This is the inherent difference the fit and finish, That has nothing to do with cast or forged it has to do with craftsmanship.

 

[Evil Monkey]

Thanks guys that was helpful.

So there's nothing wrong with cast receivers if their grade is the same as forged receivers? I heard that they cracked easily.

 

[Don't Tread On Me]

I believe the last cast receivers made into an AR was Olympic Arms "plinker" which was a budget priced carbine.


I *heard* that they started using forged on this model a while ago.


I'm not sure there are any cast receivers out there anymore. I could be entirely wrong though.


Stick with a good name brand like RRA, Colt, Bushmaster, Stag etc...and you will have no problems.