Very strange AR-15 failure

[Helen Keller]

had a factory bushmaster do the same thing.

[Schuetzenman]

Id disagreed the fact that forged is stronger. I think milled is less likly to crack or break because

Then you would be terribly wrong and you show your lack of knowledge. I do have some experience in this area as for 23 years I've been getting injection molds built. Ask yourself why every AR15 receiver maker talks about Forged receiver blanks. Single plane orientationis strong potentially in only one direction. Grain structure being folded over makes the metal stronger as now the grain goes in many directions so it is strong in many directions.

[NAPOTS]

Scheutz, forging can also reduce the presence of internal defects can't it?

[Partisan1983]

Then you would be terribly wrong and you show your lack of knowledge. I do have some experience in this area as for 23 years I've been getting injection molds built. Ask yourself why every AR15 receiver maker talks about Forged receiver blanks. Single plane orientationis strong potentially in only one direction. Grain structure being folded over makes the metal stronger as now the grain goes in many directions so it is strong in many directions.

I am not trying to start a debate or a fight, but in a way you are both right.

It all depends on the type of steel, how it's made and how it is heat treated.

I only have 8 years experience playing with metal, but there are many variables to take in account (it's surface hardness or 15N test for example, it's HRC and it's tensile) Those are just three test's that I think of right off the bat.


Again I am not trying to start some debate or fight over milled verse's forged, I am just putting my $.0000000002 cents in after taxes.

[Schuetzenman]

Scheutz, forging can also reduce the presence of internal defects can't it?

Depends on the defect. An inclusion of slag no, a void yes.

To Partisan1983's point just the native physical properties of the steel or aluminum alloy vary widely. If they didn't there would be 1 grade of steel and 1 grade of aluminum. Different attributes are imparted by the composition, yes how it is hardened AND how it is drawn back and normalized are all part of the big picture on performance. Forgings origianlly were the most common way to short cut to a useable shape for final machining. The forging dates back to early metal working, the Black Smith. In modern times we have CNC milling and turning centers so often now bar and slab stock of metals can be shaped directly after a blank is cut from the parent stock. This should save money as the forging process, a hot dirty and dangerous process is skipped.

A milled object is better than a CAST object or should be in most situations. However, a forged blank milled to a final shape, would under most situations be superior to just a milled from stock object.

[abpt1]

I thought that all milled (CNC ) stuff was billet that is AFAIK rolled or pressed

ok ok I was thinking cast vs forged .......When you were saying milled i was thinking cast ....it was a early post lol ....your right....

[NAPOTS]

If you can leave pre-stresses in the surface of the material, like you do with shot peening, you can "cheat" when it comes to reducing stresses.

[Silicon Wolverine]

ive personally seen (and repaired) 4 AR extractor broken in this exact way and each of them was traced to high usage of wolf steel cased ammo. im not saying that was your cause, but it is historically a cause of that type of failure IME.

SW

[5.56NATO]

Yes. A 16 inch carbine.

If it's a standard shorty ar, meaning non pistion rifle, the chance of this happening is always present as the case does not get enough time to collapse back to normal size after expanding and seizing on the chamber wall upon fire. There are so many bandaids they've tried it's amazing - heavier buffers, stronger extractors, extractor spring doodads, pig tail gas tubes, but the real solution is either a piston design [I]that gives the case enough time to collapse before extraction takes place[/I ]or a standard shorty design that somehow lengthens the time before the gas pulse causes extraction, or you do the right thing and only use 20in bbls in any standard ar rifle. All my humble opinion of course. I won't run a shorty if I have the choce.

[gpwasr10]

I got one of these awhile back and have been happy with it...

http://www.bravocompanyusa.com/BCM-S...rade%20kit.htm

[TEN-32]

While researching twist rates, I found this information which supports what 5.56NATO said.

GAS SYSTEMS OF THE AR-15 FAMILY

There are three types of gas systems for the AR-15 rifle: carbine, midlength and rifle. This is referencing the gas system, not the sight radius (distance of the front sight from the rear sight.) The gas system is composed of the gas port (located under the front sight base), which the gas block covers and redirects the gas back into the upper receiver through the gas tube. The handguards cover up this tube which is just made of thin aluminum. The M16 utilizes a rifle length gas system, and has 12" handguards. The midlength uses (you guessed it) a midlength gas system (9" handguards), and the carbine (M4, CAR-15) uses (that's right) the carbine length gas system (7" handguards.)

Carbine

An intersting note in regards to gas systems, is that the carbine length system was designed to be used with 11.5" barrels (Colt Commando.) When the M4 stuck a 14.5" barrel on there (and commercial manufacturers used 16" barrels) it makes the short gas system extremely harsh on the carbine, leading to the symptom of "hard extraction." To overcome this, a bolt upgrade is needed. The bolt in a carbine should have a black insert under the extractor spring. This helps the symptom, but commercial manufacturers went further and fixed the PROBLEM, not just the symptom when they created the midlength.

[Schuetzenman]

AS that quote states, 7" gas system of the carbine his harsh on the bolt and extractor. Reason, is what has been stated. The expanded case does not have time to shrink back away from the chamber walls so the bolt is moving back while the brass is still gripping the chamber walls, so the extraction force is very high compared to the 12" full rifle, which is the original design of the weapon and gas system.

I only have a mid length 16" barreled AR and it is converted to piston system so the recoil is slower and extraction is easy on the case and extractor. All this thread points out why I will never have a 7" Car gas system weapon unless it's NFA class for barrel length. Make mine a Middy.

[abpt1]

AS that quote states, 7" gas system of the carbine his harsh on the bolt and extractor. Reason, is what has been stated. The expanded case does not have time to shrink back away from the chamber walls so the bolt is moving back while the brass is still gripping the chamber walls, so the extraction force is very high compared to the 12" full rifle, which is the original design of the weapon and gas system.

I only have a mid length 16" barreled AR and it is converted to piston system so the recoil is slower and extraction is easy on the case and extractor. All this thread points out why I will never have a 7" Car gas system weapon unless it's NFA class for barrel length. Make mine a Middy.

So on my pistol ar that has a 10.5 bbl I should upgrade my extractor or get a piston ?

[gpwasr10]

So on my pistol ar that has a 10.5 bbl I should upgrade my extractor or get a piston ?

I'd just do a SOPMOD bolt upgrade and call it good. I have thousands of rounds through my 11.5/5.5 Bushy with that mod.

[Schuetzenman]

So on my pistol ar that has a 10.5 bbl I should upgrade my extractor or get a piston ?

The 7" carbine gas system was made up for the short barrels, your pistol is in that class so it shouldn't be quite as hard on the bolt / extractor. I bet it has quite the muzzle flash and as such that's powder burning in the air, not in the barrel. I expect this means the rounds don't achieve the peak pressures that would be achieved in a 16 inch barrel.

[5.56NATO]

I'd just do a SOPMOD bolt upgrade and call it good. I have thousands of rounds through my 11.5/5.5 Bushy with that mod.

I have a few k thru an m4 too, and a lot of case heads showed pulling anyway.