Upper Receiver Flex Testing - Part Two

[bigbore]

< shouting Brit accent >
I'd like to see......
< / shouting Brit accent >

A MUR w/DD Lite rail next to a the LaRue receiver w/LaRue rail.

I wonder if the mounting system of the DD makes any difference.


I wish there was a way to apply any of this testing to actual effects on functional firing weapon; what difference does any of it really make?

With my yellow glasses - I see folks who must be putting much more than 20lbs on the end of a fifle length float tube. Standard receivers, loads loaded as hot as possible, and I cant think of a problem ever being had.

I would have to imagine a yellow glass shooter slung up prone, is puttin way more stress on a tube than any soldier with a carbine, even under stress.

This testing is neat, but in what way does any of it apply to anything a simpleton like myself can relate to?


It would be cool if you could do your testing with hot uppers, or mount something like a laser level on the receiver and a aiming point on the front sight of a match rifle to see how much its flexing from a sling.

[jmart]

I wish there was a way to apply any of this testing to actual effects on functional firing weapon; what difference does any of it really make?

With my yellow glasses - I see folks who must be putting much more than 20lbs on the end of a fifle length float tube. Standard receivers, loads loaded as hot as possible, and I cant think of a problem ever being had.

I would have to imagine a yellow glass shooter slung up prone, is puttin way more stress on a tube than any soldier with a carbine, even under stress.

I asked myself that very same question when I started reading this thread, but the more I thought about it, it seemed the tension a sling would place would be more of a compression than a bend. The bulk of the force's vector is coming back along the axis of the tube (down the sling and toward the shooter's bicep), comparatively little is going downward.

I do share your same curiosity though about how much flex needs to occur before reliability and/or accuracy detriorates. Between this thread and the "migraine inducer" Larue billet receiver thread over at you know where, it would be neat to figure out between the two what the correlation is between flex/dimensional errors and accuracy/unreliability.

[Nitrox]

I'd like to see a high rise upper added to the test. DPMS has made them over the years but it looks like RRA is the only game now.

[K.L. Davis]

Okay... as of last night, I have an Oberland Arms receiver.

This morning I got word that a production VIS and MUR are on deck as well. I have not heard from LT... probably not back in the shop until monday.

I will hit up DPMS and RRA to see what they want to submit, and I have a couple of emails that may possibly bring in a couple of others. I will see if DD wants to send a new handguard to test the mounting method... but it would have to be ran against a "traditional" mounted free float on the same upper -- running the test on two different manufacturers introduces a variable.

So... the reason I started this testing a couple of years ago was just to see if there was flexing in the upper receiver -- the camps where split and you either thought there was, or thought there was not. I like to think that this testing put that to bed... and most manufacturers and end user organizations that I talk to now, subscribe to the results of the test.

I don't have any direct correlation to the amount of flex v. mechanical problem... but I do know that some of the shops that have replicated or continued the tests claim that it is at least a factor in bolt breakage -- anything that I can add to this is purely anecdotal. I am also told that when the test is taken to 400 degrees, the flex is very severe!

We all know from our days in basic training, that the traditional sling to the FSB can flex the barrel enough to move POI... but the test here was to see if loading the handguard caused the front of the receiver (and therefore the relation to chamber/bolt) to flex -- interestingly, but easy to understand, is that the problem is manifest under "up and down" loads and not nearly as noticable under any sort of "side to side" load.

I would say this... cutting off the carry handle reduced the structural integrity of the upper, no doubt about it -- does it matter though? This is just me thinking, but we have had a really bass ackwards approach to this for a long time -- think about how much you would be willing to pay for a good bolt action receiver? The upper receiver is functionally the same thing, but if someome was selling $35.00 flat tops on "The EE", they would fly off the shelf (if they had M4 cuts) -- and in spite of that, we are willing to pay $200.00 for a lower. Hey, if the hammer pins holes are straight, the mag well in spec and the receiver extension lines up -- that is all we can expect from the lower... I guess because it is the serial numbered part and carries "The Name", we throw the extra cash at it?

Again, I am not going to replace every flat top receiver just because it may flex or whatever, but if I had a choice for a new build -- that was going to be used in the defense of life... I would opt for the best upper I could get my hands on.

Which one is that? Hopefully, in a couple of weeks, you can make that decision based on what you read here.

[bigbore]

We all know from our days in basic training, that the traditional sling to the FSB can flex the barrel enough to move POI... but the test here was to see if loading the handguard caused the front of the receiver (and therefore the relation to chamber/bolt) to flex -- interestingly, but easy to understand, is that the problem is manifest under "up and down" loads and not nearly as noticable under any sort of "side to side" load.

I was talking about NM Service Rifles with the sling attached to the float tube. There are some big guys putting a LOT of pressure on those tubes - even though its not forced directly down, things are still bending. Same can be said for the match uppers with float tubes built an flat top uppers. Amount of flex as temps increase - these guys arent shooting more than 10 rounds at a time. Seeing scores shot with ARs - I dont for a minute believe the flexing alone has any noticable effect on accuracy.

think about how much you would be willing to pay for a good bolt action receiver? The upper receiver is functionally the same thing,

Apples and oranges of a comparison for this testing. It would be nice to compare the consistancy of the internal spec dimensions of receivers. A nice black (so it matches the lower) upper with M4 feedramps, for $35, that the barrel extension fits in like a hot dog in a garbage can, and bolt carrier that rotates around when closed is another thing...

But yes, they would sell because the folks buying them dont shoot more than 50rds a year off a bench at paper plates 50yds away

Again, I am not going to replace every flat top receiver just because it may flex or whatever, but if I had a choice for a new build -- that was going to be used in the defense of life... I would opt for the best upper I could get my hands on.

Is the best the enemy of good enough? What will you use to determine what is "the best"? How many of each can be tested to find who is more consistant?

I would hope this will break down as best, good enough, and decoration.

Best - I would determine by strength, and consistancy of "spec".
I would expect the "billet" pieces to come out as the best.

Good Enough - I would think Colt, and CMT - because of consistancy to specs.

Decoration - the gunshow specials where all the pieces fit with "room to spare".

[Nitrox]

Best = Value

Value = Need/Cost

Need, and Cost can be rated 1 - 10, 10 being highest.

[Submariner]

Is the best the enemy of good enough? What will you use to determine what is "the best"? How many of each can be tested to find who is more consistant?

I would hope this will break down as best, good enough, and decoration.

Best - I would determine by strength, and consistancy of "spec".
I would expect the "billet" pieces to come out as the best.

Good Enough - I would think Colt, and CMT - because of consistancy to specs.

After seeing newer and "better" gear in five years of classes and staying current with the boards, I came to much the same conclusion; " Is the best the enemy of good enough?"

The kind of testing that would be required to determine the "best" would add significantly to the cost of these parts. (Imagine two identical valves, one certified for use in a nuclear power primary system and another for a drain line on a surface ship; the former costs 2 to 5 times the latter, perhaps more.)

I cannot afford perfection in this arms race. Colt lowers, even the lowly Sporter I's, with uppers made from Colt barrels, Colt upper receivers, and Colt bolt carrier groups "work pretty good". At this point, money spent on ammunition for training and practice is arguably better used.

[Resq47]

Agreed, Sub. If I find myself going cyclic on the bigger, better, faster loop I go back to Kamm's law of diminishing returns. The difference between having an AR that runs and not having one at all is much larger than the little hoo-haws we deliberate on for waaaay too long.

That said, it's enlightening to see technical comparisons being done even if it's essentially esoteric.

[K.L. Davis]

To clarify... I hope to find the design variation that provides the most strength -- as for which is "best" that is ultimately up to the end user.

Steve, you know that you and I are both very pragmatic when it comes to this stuff... hell, I don't have nearly half of the high zoot stuff that is out there on my personal guns. But we have both seen the strange alignment of priorities that a lot of the end users subscribe to -- granted, a lot of them only shoot 50 rounds a year and the closest they will ever get to their gun being in "battle", is if it falls over in the closet and scratches their wife's favorite high heels.

But, it used to be barrels... remember how folks would say "I want this name brand lower; with a custom plated NM bolt; a 200 dollar stock and another 200 bucks worth of extra grips; three lights; 4.7 yards of rail on a 300 dollar fore end; at least three sighting options, one of which is optic and cost more than the rifle itself; I'll need a 100 dollar flash suppresor; a sling that comes with a video of how to use it... oh, and what is the cheapest barrel you have?"

Now, in some sort of knee-jerk reaction I guess, one can not show up on the range without a gun that has the latest ubertube...

That said, I am not sure that any of the crop of new uppers are any better... yet.

For those that don't know me... When I first really started into the gun thing, IPSC was a budding sport and the number of custom 1911 builders could be counted on one hand... the "martial artist" and the "roonies" were just starting to go their seperate ways and for most guys, extended safeties, beaver tails, better sights and a trigger job was about as exotic as you could get -- there was, however, a group that was putting weights on the end of the barrel... they even ported the weights and played around with cartridges once thought extinct, this small group of guys mounted over sized goodies on their guns and welded/filed/milled in different shapes... it really was an interesting time.

I worked part time as a gun plumber for a small shop in Phoenix then, the Hassayampa River Shooters and the Cactus Match League would meet in the evenings and we would have a great time... a few would sit on the picnic tables and preach the ways of our particular following, and young shooters would sit wide eyed and soak it in. I was doing pretty good with "custom" pistol building at the time... well beyond just sights and trigger work, I had ventured into welding up and fitting barrels, extractor tuning, lug cutting and ramping and releaving -- truley state of the art 'smithing.

Then, one night as I was sitting on the tailgate and discussing the virtues of my wares... a kid that had shot earlier that night (and not very well mind you) walked over and said "I have $200.00 to spend"... he held out his mostly stock AO 45 and asked "How do you recommend I spend it?" -- well. I answered honestly and pointed him to a guy that worked for Phoenix Arms and said "Go buy 200 bucks worth of his reloads and practice more"... you know that Charlie Brown whaa, whaa, whaa sound? I swear you could actually hear that after I told him this.

The next week, I did not have nearly the following of new shooters hanging around seeking wisdom... it seems that my suggestion, while it no doubt would have improved his shooting, did little to improve his appearance on the line... I learned a lot that night, but I have not changed. If something truley offers advantages that offset the price, I will wholeheartedly recomend that item... if, however, something is "fluff" or simply bragging rights, you won't find it in my favor. Therefore, I do these sort of tests so that I can make sound recommendations based on what I know to be facts.

In honor of a good friend recently lost... the first Rule of Gunfighting is: Have a gun.

That simple axiom speaks volumes.

[K.L. Davis]

Update...

The test should go down soon, I have two short deployments this month, but can probably find time between them to get it all taken care of.

I have commitments for product from:

Daniel Defense
Vltor (New VIS and MUR)
Oberland Arms (private owner)

and I am pretty sure that RRA and DPMS won't shy away.

The testing will include how much strain *can* be applied via a VFG. Should be lots of fun!