Are billet receivers advisable for precision long range 6.5 Grendel build?

[Eoch]

Are billet receivers (upper/lower) advisable for a good quality precision long range 6.5 Grendel build? I have no experience with this cartridge yet and would like advice if billet receivers are the way to go for a precision rifle for 600 and 1000 yard prone shooting? Or will the regular mil-spec uppers/lowers work fine? I’m a high power sling shooter and we have only used non-billet receivers which have worked fine in .556. Thanks!

[LRRPF52]

Welcome aboard.

I personally like the feel of a tightly-fit billet rifle for heavy barreled configurations.

There seems to be more confidence in the gun when it feels like one, solid piece, as opposed to a rattle trap of parts.

[just_john]

Eoch - Firstly, welcome to the Clan, from the Great Nation of Texas!

You will find a lot of discussion across this forum regarding billet vs forged.

The core is this: a billet is just a block of metal ( in this case aluminum ) that someone can load into a CNC machne and create fancy looking uppers and lowers. The advantage is that this methodology does lend itself to very intricate patterns and that there is absolute repeatability in this machined result. The issue is that there are metalurgical anomolies within any "billet" material which "could" cause failures IF something goes wrong.
With a forged part, a "near melting temperature" heated block of material ( in this case aluminum ) is set inside a die set and those dies are "slammed" together with extremely high level of force one or more times to form a particular shape. Then that result is machined to form the inside passages and the result is a usable upper or lower. The advantages of forging is that this "slamming" process forces the molecular structure into a "grained" pattern which results in a MUCH stronger material that is completely void of any metalurgical anomolies that "could" cause failures if something goes wrong. A key example is rifle barrels - have you ever seen a billet barrel? NO, all the better ones start out as hammer forged to get the greatest yield strength.

Most of the time, the difference does not matter. But, if a case ruptures on ignition, the strength of the material around that chamber is all that is between a 50,000+ psi ( think IED! ) and your head.

I have built a LOT of AR's / MSR's and will not use a billet upper or lower. Yes, I do have to do some extra machining to get the best fit, but, to me it is well worth the trouble.

[PVBoom]

Forged is better strength. As far as I am concerned, I want a forged upper for the obvious reasons.

[LRRPF52]

Guys, the upper receiver is not a stressed part to contain the pressure event, the barrel extension, bolt, and barrel are.

Billet receivers made from 7075 T6 usually have more material on them as well.

Yes, it is true that forged 7075 T6 uppers have more density because of the forging process. They start with a plate of aluminum, then crush the shape of the receiver onto it basically.

Since the AR15 forged receiver is meant for lightweight, the wall thicknesses are about as low as you would want to go, especially for the M4 upper, which has very thin walls above the extension tunnel, unlike the original carry handle models with the fixed rear sight and protective "handle" for the original trigger charge handle prototypes.

When I look at the Seekins, Mega, LaRue, Precision Firearms, etc. billet receivers, they have added mass around the barrel extension tunnel, much more than the Mil-spec minimal dimensions for a forged upper.

Even with the skeltonized billet receivers like from 2A Armament, there was a guy who had a catastrophic malfunction with a faulty round of ammunition, and his receivers didn't fragment like a lot of forged receivers do.

The argument about forged strength vs billet strength has no real practical value in terms of pressure containment.

The added material offered by billet receivers does bring a practical value for someone building a rifle with a heavy bull barrel, comparable to the added strength from A2 uppers that Service Rifle shooters use.

The precision fit of a billet set also offers that solid feel of the gun that you just don't get with most forged receiver sets.

[Joseph5]

Another thing to remember is that the billet that a receiver is cut out of was forged to a size to begin with. It may not be forged to the extent of a forged receiver but billets are forged to size and shape and then cut to length.

[Eoch]

Quote from LRRPF52: "The added material offered by billet receivers does bring a practical value for someone building a rifle with a heavy bull barrel, comparable to the added strength from A2 uppers that Service Rifle shooters use."

Most/many SR shooters today have converted to flat tops for 4.5X scopes under the 2017 NRA rule change. I have old eyes and made the move too, but miss the simplicity of the A2 upper/sights. Never thought about that extra material in the original A1/A2 design, but makes total sense.

[85_Ranger4x4]

If you are figuring on blowing up your gun more meat will help. I have also heard billet is better for long and/heavy barrels.

I have three forged M4 flattops and am happy with them though.

[Frontier Gear]

Another thing to remember is that the billet that a receiver is cut out of was forged to a size to begin with. It may not be forged to the extent of a forged receiver but billets are forged to size and shape and then cut to length.

This is correct. LRRPF52 is correct as well.

More important than forged vs billet are these two things:

1. How thick is it?
   
2. What alloy is it?
   

There is a huge difference between 6061 and 7075. However, for the purpose of a receiver, I don't think that it matters a whole lot. My biggest concern with the alloy type is actually where the charging handle "clips" on the upper receiver. 6061 is soft(er) and "wears down" a lot faster than 7075. That looks like a wear point to me. If that little shelf wears down from the charging handle hook and spring, then you pretty much need a new upper receiver.

Both forged and "billet" receivers start out as aluminum plate and are forged into that plate. In this case, the purpose of forging the receiver is to get the rough shape as close as possible to the finished dimension in order to minimize machine work. The added strength benefit is marginal. Let me explain why. I worked in an aluminum foundry for over ten years. Here is how aluminum plate is made.

All aluminum plate is cast. Depending on the mold the thickness can vary, but it averages about 1.5 FEET thick. From there is it heated back up to 900 degrees (it melts around 1,200) and then rolled (forged) down to it's final thickness. So in the case of an AR receiver, this would be about 1.5-2 INCHES thick. That is a LOT of forging. After rolling to final thickness, it is then heat treated and quenched. The "T6" in "6061T6" aluminum is actually the heat treatment, not the alloy type. Immediately after heat treatment it is then stretched. The stretching aligns the plate and actually helps to harden it. This is what is meant by "work hardened". After stretching, every square millimeter is scanned by ultrasonic inspection. They inspect the complete thickness of the plate for any abnormalities or voids. If it passes inspection it is then put into an aging furnace that further strengthens the metal.

My point being that the very small difference that is accomplished between "forging" a receiver from a 2 inch thick plate verses machining one from a two inch thick plate is not even worth mentioning as compared to the process that the plate has already gone through. Again, for our purposes.

1. How thick is it?
   
2. What alloy is it?
   

Another side note, "Aircraft grade" aluminum is simply a marketing scheme. Airplanes are made out of a lot of different types of aluminum. It depends on what part you are making. Is it a wing or a seat back try?

[hill37]

Frontier Gear, could an extruded aluminum tube be made thin and strong enough for a magazine body?

[Frontier Gear]

Frontier Gear, could an extruded aluminum tube be made thin and strong enough for a magazine body?

Probably, but I guess I don't see the point in that. Extrusions are usually done to make manufacturing easier, such as with hand guards. It would be a pain to machine out that huge hole through the middle of the hand guard and leave such a thin wall. Extruding the basic hand guard shape and then machining in the rails, Mlok or Keymod cuts (along with any decorations) and machining it's attachment point is much easier. Also, extruding is expensive and requires special machinery, not to mention the cost of heating the metal to it's melting point. Sheet metal forming is easy and can be done with fairly common tools.

Magazines are formed from sheet. Sheet goes through the same process as plate. It is just rolled down to a much thinner final product, but it starts out just as thick. Sheet is also stretched, but it is not ultrasonic inspected (not much point to that at this thickness). So a magazine formed out of a sheet should be much stronger than one that was extruded. The variables being the construction methods and quality of the workmanship (welds, etc...). Also, anytime that you stamp aluminum sheet (as many magazines are), you are stretching it and therefor making it stronger. This is one reason why aluminum makes such good boats. If you hit a rock, the aluminum actually gets stronger as it starts to deform. That is up until it's point of failure.