Empirical Evidence for AR Supremacy ???

[KurtM]

Well posted Glocktogo!

More to the point, the rifles I have seen fail the most in competition and in class, in order of failures. Colt, Armalite,Olympic, DPMS, Bushmaster.Almost all of these have been older ones. For a while Colt had TERRIBLE QC as did DPMS and Bushmaster (Ususally front sights not square to the barrel). Within the last 3-4 years ALL brands have been good enogh for a 1500 round class/ high 3-gun use. Frankenguns usually run as good or better than most as long as the builder took his time, knew what he was doing and had good parts. (note not necessarily Mil Spec.)

The most accurate in order J.P., Firebird, Clark, Noveske, Saber, DPMS

The best for the $$ DPMS, now...not 5 years ago

The "best" in My mind J.P. Enterprises/Firebird followed for a close second Noveske, Saber, and then La Rue. ( personal experience with all of them and for more than a couple of rounds )

The last three catagories are my subjective opinion, but back up with "tens of thousands of rounds" of experience

The Coolest whizz bang part for an AR...Titanium bolt carrier! As light as the Aluminum J.P. doesn't wear and cycles soooooo fassssst! with no felt recoil

 

[Spiff]

As for Shot Peening, there are two schools of thought on it, some say it is the only way to go, others Like Reed Knight ( which is no recomendation ) and J.P. don't like the process. I myself care not one way or the other, as it only SURFACE stress releives and does nothing for the bolt other than MAYBE stop a crack from propagating....BUT since we already MPIed the darn thing...cause you can't shot peen before MPI, we already know it isn't cracked....so why???

Quick note here - shot peening very slightly plastically deforms the surface of whatever it's being done on, leaving compressive residual stress on the surface - it's not stress relief.

Since fatigue failure is caused by crack growth, the whole point is to try to keep the cracks from propogating - the compressive stress tends to squeeze it back closed and keep it from getting longer. A crack doesn't have to be present to begin with...it can just form later from any weak point in the part. Inhibiting crack growth = greater fatigue life = more rounds downrange.

I have a feeling you already knew that....just for the benefit of anyone watching.

 

[CAR-AR-M16]

This is a recomended procedure from Crane Naval Weapons facility, for Dev group, and is recomended SOCOM procedure as well ( replacing the bolt ). I didn't say it wasn't a good idea, it was meerly used to show that even Mil Spec parts can and do fail, at a high rate, to get a memo from Crane. this last June while I was doing some shooting with the A.M.U. at Ft Benning I was shown a 3 pound coffe can of broken M-16 Bolts from just the few the A.M.U. uses in teaching.

Thanks for the info. I have seen where NSWC Crane was trying to develop an electronic round counter to be placed into the pistol grip, but I do not know the status of it. Here is some info on it for those who are interested: http://www.dtic.mil/ndia/2009infantrysmallarms/thursdaysessionxi8469.pdf

 

[Spooln-Rex]

This is probably one of the best threads i have read on here in a long time dealing with the AR dilema. Kurt said it best no doubt.

On a side note i completely agree with all the above as i have a DPMS..... i KNOW its not by any means a run into battle rifle. But for me and the 500ish rounds ive got through it, its been great and had one malfunction due to not seating the mag all the way when i first started getting to know the rifle. Other than that i'll probably take a class with it someday but i'll be upgrading the bolt carrier before then just for piece of mind.

Anyways well said everyone glad this didnt spin out of control like most the other threads in the past.

 

[TerryP]

Stephen, good thread you started.
I have often wondered some of the same things too.
As has been stated already it seems that the real payoff for spending the top dollar for an AR comes in when the rifle is pushed very hard, or the very max of accuracy is needed.
About the only thing better than looking at all the AR's is shooting them!

 

[Stephen Cue]

Stephen, good thread you started.
I have often wondered some of the same things too.
As has been stated already it seems that the real payoff for spending the top dollar for an AR comes in when the rifle is pushed very hard, or the very max of accuracy is needed.
About the only thing better than looking at all the AR's is shooting them!

Thanks, I agree shooting them is the best but building one is right up there.

I am building a varminter and a carbine now. Havent bought a barrel for the varminter yet but I probalbly go with a stainless 20" bull.

On the carbine I would like to have one of those cheap $400 uppers that the boys over at MASgunworks had, if they still have one when Im ready.

 

[jcbarlow]

Best AR thread on OKshooters I think I have read yet

 

[KurtM]

Ahhhhhh a whole different can of Mil Spec worms...why would anyone need to know how many rounds were fire from an M-9....hahahahahaha

As for Shot Peening...well lets just say I agree about the crack propagating thing (only due to the crack running into a rounded stress reliever, the shot impact area), but not the "compressive" part. It is a percussive residual, it can only be compression if there is containment...and on this semi-ductile surface we are talking about metal is neither added or subtracted, just moved around so there can't be containment. we are talking about a process that AT BEST only "disrupts" to a depth of .00005, as we are talking about a air hardening heat treated steel. Now this works great for "surface cracks", but does nothing for stress risers created by sharp machining angles and carbon/chromium inclusions in poorly amalgamated material (a "bad pour" in the metallurgy business) so it only deals with surface cracks ( yes they can grow ) and the MPI can't tell you about inclusions...It ain't X Ray.. so we are talking about a superficial treatment and a test that while making one feel good, don't really tell you about your bolt. (These are the exact reasons Reed and John question this process)

Now since we are talking about failure, metallurgy, and stress risers of which I have a bit of passing knowledge, and since you seem to have a good grasp on this subject....where do bolts usually fail?, the least common is to shear a locking lug, although it does happen , usually on full auto guns that see lots of mag dumps.. Where is it?

For extra credit, What Bolt part fails the most out of all of them...not to include firing pins being cooked by pierced primers? and consumables like gas rings and extractors.

BTW Glocktogo the DPMS rifle that Blew up...the only parts that was still usable in the upper were the Bolt Carrier, dust cover, and forward assist, I guess what I am saying is I wouldn't worry about your bolt carrier. Kurt Miller

 

[Shadowrider]

Okay I'll chime in here since I too have a good bit of experience with shot peening in the aerospace and oil field industries and also a good bit of experience with government procurement for the military. KurtM you are pretty close on the shot peening. I will point out that you can get compressive stress imparted far deeper than the depth you state. Shot size and material, part material and heat treat condition all play a role. But suffice it to say it makes a hell of a difference in multiple areas. Fatigue cracks propagate from a surface in tension. Never from a surface in compression. The point of shot peening is to impart this compressed layer to "fend off" a fatigue crack propagating in the first place. It doesn't last forever but it greatly extends the parts life. Secondly all parts to be shot peened should have no sharp corners at all. Everything should be radiused, particularly groove corners and all concave features. Otherwise you can impart a stress riser by the shot peening itself and it will roll edges like crazy.

As to the mil-spec issue others have stated it exactly right. If there is a requirement for a part to have a AISI 4140 steel heat treated to 145KSI strength and you make it out of AISI 4345 and heat treat it to 185 KSI to improve it? The source inspector will reject the entire lot. Even though it really is better in every respect. Simply because it does not meet the specification. If they wanted it better they would have required it in the 1st place. So mil spec is not always the best.

 

[Cue]

Thanks, I agree shooting them is the best but building one is right up there.

I am building a varminter and a carbine now. Havent bought a barrel for the varminter yet but I probalbly go with a stainless 20" bull.

On the carbine I would like to have one of those cheap $400 uppers that the boys over at MASgunworks had, if they still have one when Im ready.

Don't let that go to your head, your still a jackhole.