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Posted: 2/28/2006 12:14:05 PM EDT
[Last Edit: 3/10/2006 12:39:31 PM EDT by Gunzilla]
Moved to another forum
Link Posted: 2/28/2006 12:27:25 PM EDT
Good work. I did something similiar once, except not so controlled.

Link Posted: 2/28/2006 12:32:47 PM EDT
[Last Edit: 2/28/2006 12:38:44 PM EDT by comp1911]
Tagged for conclusion

Edit to add, a test of a MRP or equivilent "monolithic" upper would be good to see as a comparison!
Link Posted: 2/28/2006 12:37:23 PM EDT

Originally Posted By comp1911:
Tagged for conclusion

Link Posted: 2/28/2006 12:59:18 PM EDT
cool
Link Posted: 2/28/2006 1:27:03 PM EDT
Wouldn't happen to have an SIR system, or something similar in how it attaches to the picatinny rail as opposed to the barrel extension, would you?

Be interesting to see if it were truely isolating the forces acting on the barrel extension.
Link Posted: 2/28/2006 2:07:41 PM EDT
[Last Edit: 2/28/2006 2:17:48 PM EDT by mongo001]
In my case, I hung the 45lb dumbell on the forward part of the rail system and got a few thousandths movement at the barrel nut, but upwards to 50 thousandths at the forward end of the rail system. The dial on the forward horse was used to roughly measure the movement of the horse and this was subtracted from the totals of the other two. Rough, crude, but it did show that this particular rail system was pretty stiff.
Link Posted: 2/28/2006 2:32:06 PM EDT
[Last Edit: 3/2/2006 10:34:45 AM EDT by Capn_Crunch]
Removed
Link Posted: 2/28/2006 3:29:57 PM EDT
[Last Edit: 2/28/2006 3:30:29 PM EDT by BravoCompanyUSA]
Link Posted: 2/28/2006 3:36:31 PM EDT
[Last Edit: 3/1/2006 4:05:06 PM EDT by BravoCompanyUSA]
Link Posted: 2/28/2006 3:41:39 PM EDT
Posts like this are why i enjoy this site so much. Lots and lots of brain power and ideas exchanged
Link Posted: 2/28/2006 3:44:03 PM EDT
[Last Edit: 2/28/2006 3:45:09 PM EDT by comp1911]

Originally Posted By BravoCompanyUSA:
Gunz - Wow – very impressive !


Ok, a couple of questions;
I don’t have an engineering background, so these questions may be flawed. Please bear with me.

How do you interpret these results to the theory of the flex causing alignment issues with extension and bolt resulting in broken bolts ?

Maybe I am wrong (wouldn’t be the first time ), but isn’t 20lbs a huge amount of weight to replicate downward pressure in a real world scenario ? Or is the change in the indicators at 10lbs or less lbs enough to make the same conclusions?

Wouldn’t the farther forward you put the weight on the handguard the more flexing you would see ? On the tests it is at 7.5”. Carbine handguards are about 7” in length and a vertical grip would generally be located at about 2”-3” ?


thanks in advance !



You're correct in the fact that the further out the weight is hung (Force) the larger the torque about some point will be (Force X distance) or the "moment" in engineering terms. This will also impact the deflection. The addition of the carry handle is a classic bridge or truss type bracing that obviously effects the bending forces within the receiver.

It's been a few years since I've done a Statics or Mechanics of Materials problem but I might have to look at this one. Hmm free body diagram anyone?
Link Posted: 2/28/2006 4:26:12 PM EDT

Originally Posted By GreyGoose:
Posts like this are why i enjoy this site so much. Lots and lots of brain power and ideas exchanged



I totally Agree!

Gunzy, Great Job!

Link Posted: 2/28/2006 4:35:39 PM EDT
Excellent info, tagged for conclusion...
Link Posted: 2/28/2006 5:44:20 PM EDT
interested to see where this goes...
Link Posted: 2/28/2006 6:56:32 PM EDT

Originally Posted By uglygun:
Wouldn't happen to have an SIR system, or something similar in how it attaches to the picatinny rail as opposed to the barrel extension, would you?

Be interesting to see if it were truely isolating the forces acting on the barrel extension.



Posted that before you edited and updated the thread.


Thank you for testing such a handguard system, nice to see there are benefits to the designs.
Link Posted: 2/28/2006 7:57:25 PM EDT
[Last Edit: 2/28/2006 7:57:47 PM EDT by NYPatriot]

Originally Posted By Wackypeacock:

Originally Posted By GreyGoose:
Posts like this are why i enjoy this site so much. Lots and lots of brain power and ideas exchanged



I totally Agree!

Gunzy, Great Job!




+1

ARFCOM at its best!
Link Posted: 2/28/2006 8:24:50 PM EDT

Originally Posted By Gunzilla:
<snip>


Thanks, awesome work and tagged for future results
Link Posted: 2/28/2006 9:49:34 PM EDT
TAG
Link Posted: 2/28/2006 10:57:49 PM EDT
[Last Edit: 2/28/2006 10:58:22 PM EDT by Humminbird]
Gunzilla, thanks for making this test happen! Very interesting findings indeed. Test one goes a long way into proving my earlier theory that force acting on the barrel would not cause enough flexing in the front section of the upper to cause problems. However, I never even considered the possibility of the whole upper receiver flexing, so the results of the other tests come as a big surprise to me.

If at all possible, could you repeat tests 2 and 3 with the bolt carrier group inserted? You could use a micrometer to measure the deflection of the upper receiver top surface to see if there is a noticeable change in rigidity. The BCG has a lot of clearance inside the upper, but it could still add to the overal rigidity.
Link Posted: 3/1/2006 2:14:54 AM EDT
Wow, I nominate this post as "post of the year."
Link Posted: 3/1/2006 2:15:35 AM EDT
Did you ever conceder putting an indicator on the front of the barrel? It would give you another data point and may give you a rough idea of where the fulcrum is for the barrel's movement.
Link Posted: 3/1/2006 4:01:39 AM EDT

Originally Posted By Humminbird:
Gunzilla, thanks for making this test happen! Very interesting findings indeed. Test one goes a long way into proving my earlier theory that force acting on the barrel would not cause enough flexing in the front section of the upper to cause problems. However, I never even considered the possibility of the whole upper receiver flexing, so the results of the other tests come as a big surprise to me.

If at all possible, could you repeat tests 2 and 3 with the bolt carrier group inserted? You could use a micrometer to measure the deflection of the upper receiver top surface to see if there is a noticeable change in rigidity. The BCG has a lot of clearance inside the upper, but it could still add to the overal rigidity.



I can't imagine the bolt carrier group would make any noticable difference. Here's a couple of reasons why: First, only half of the bolt carrier has a bearing strip, which contacts the Inter diameter. Second, there is enough slop in tolerance that the bolt carrier would barely be affected by the flex of the receiver.

For a none free float system, I could only imagine that the flex of the receiver and barrel extension shift would be allot more. I wonder how much flex/shift would be needed to break bolt lugs?
Link Posted: 3/1/2006 4:05:27 AM EDT
[Last Edit: 3/1/2006 4:05:52 AM EDT by SULACO2]

Originally Posted By NYPatriot:
ARFCOM at its best!



Nice work, Thank you, Sir. A thought:

Would a level or other mechanical device, if placed on the "picatinny rail" section of the upper, be accurate enough to, prove and/or measure the amount of "arching" in the upper, in the "pinned" test?

Thanks, /S2
Link Posted: 3/1/2006 4:08:26 AM EDT
tag!
Link Posted: 3/1/2006 6:28:29 AM EDT
Excellent work, thanks for sharing with us!
Link Posted: 3/1/2006 6:46:58 AM EDT
[Last Edit: 3/1/2006 6:50:21 AM EDT by Humminbird]

Originally Posted By Wackypeacock:

Originally Posted By Humminbird:
Gunzilla, thanks for making this test happen! Very interesting findings indeed. Test one goes a long way into proving my earlier theory that force acting on the barrel would not cause enough flexing in the front section of the upper to cause problems. However, I never even considered the possibility of the whole upper receiver flexing, so the results of the other tests come as a big surprise to me.

If at all possible, could you repeat tests 2 and 3 with the bolt carrier group inserted? You could use a micrometer to measure the deflection of the upper receiver top surface to see if there is a noticeable change in rigidity. The BCG has a lot of clearance inside the upper, but it could still add to the overal rigidity.



I can't imagine the bolt carrier group would make any noticable difference. Here's a couple of reasons why: First, only half of the bolt carrier has a bearing strip, which contacts the Inter diameter. Second, there is enough slop in tolerance that the bolt carrier would barely be affected by the flex of the receiver.



If that is the case, then there is no reason to assume the flexing would cause any catastrophic misalignment of the lugs. If on the other hand the flexing of the upper is causing stress on the BCG, then the logical conclusion is that the BCG would also restrict the flexing to an extent.

The displacement curve will determine how much off the bolt lugs are with the barrel extension lugs. The BCG bearing surfaces are at the front of the carrir, so the displacement curve from the barrel extension to the rear of the BCG bearing surface is what determines the misalignment.
Link Posted: 3/1/2006 7:13:23 AM EDT
Tagged for info.

MN
Link Posted: 3/1/2006 8:18:28 AM EDT
Link Posted: 3/1/2006 8:24:20 AM EDT
Anecdotally, I have been told that an Army unit experiences more broken bolts on rifles with more stuff on the front end. The fact that they use RAS may be a factor. I don't know.
Link Posted: 3/1/2006 9:02:40 AM EDT
Tag for a more thorough reading.
Link Posted: 3/1/2006 11:37:56 AM EDT
Interesting. I'd like to see this test done possibly on a clamped lower as I'd be willing to bet alot of the flex is absorbed by the upper and lower mating.
Link Posted: 3/1/2006 1:09:07 PM EDT
I too find this very interesting. I just happened to have one of my AR's out last night, and I "tried" some of the force application. Without a front vertical grip, I found it hard to put much of any amount vertical force on the front of the gun. It would cause the rear of the gun to lift, and was impossible to maintain any kind of proper hold on the gun. I could put lots of force horizontal to the bore axis into my shoulder, but the force vectors were all wrong for this analysis.

While I do not own a vertical grip for the forend, I can clearly see how it would be possible to put a great deal of rearward force back on a vertical grip. This type of force adds a few different vectors to the equation. It would be interesting to see what the final stress looks like with the static component of the vertical weight (which I think would be more limited to the actual stuff hanging off the forend) combined with the more complex vectors of rearward "pulling" on a vertical grip.

In any case, I will pass this info onto a friend of mine who is ex-marine, who liked to set the last horizontal bar on the military cot with the barrel of his M16. He should trun the weapon so the flex on the receiver is into the lower, and not away from it.

Craig
Link Posted: 3/1/2006 2:43:44 PM EDT
KOOL!! you guys are to much!
Link Posted: 3/1/2006 5:31:55 PM EDT
TAG
Link Posted: 3/1/2006 5:57:24 PM EDT
so would two piece handguards do better in this test since they do not flex the upper receiver?
Link Posted: 3/1/2006 6:43:35 PM EDT
Good stuff!
Link Posted: 3/1/2006 7:22:00 PM EDT
"Fascinating."

-Mr. Spock
Link Posted: 3/2/2006 7:02:54 AM EDT
Unfortunatrely, you don't need 20 lbs of weight to simulate leverage on the handguard/barrel. All one has to do is to install a baseball bat like these guys did:



Link Posted: 3/2/2006 7:48:39 AM EDT

Originally Posted By Wackypeacock:
Unfortunatrely, you don't need 20 lbs of weight to simulate leverage on the handguard/barrel. All one has to do is to install a baseball bat like these guys did:

www.m203grip.com/M203grip-control.JPG

i37.photobucket.com/albums/e81/4majorchaos/MVC-866S.jpg



What?
Link Posted: 3/2/2006 7:49:13 AM EDT
[Last Edit: 3/2/2006 8:14:17 AM EDT by Dace]
I was wondering if you did similar tests on a non free floar rail, would it come out worse then a free float rail because you are pulling directly on the barrel?
Link Posted: 3/2/2006 8:01:59 AM EDT
I'm glad to read this. I was flamed a while ago on another thread when I talked about USASFC (US Army Special Forces Command) changing out all the regular M4 profile barrels to the new Heavy barrels because bolt lugs were being sheared from pressure exerted using the forward grip and barrels were bursting at sustained rates of full auto fire.

Would the fact that the knights armament SOPMOD kit is not a free float rail have any additional stess added to the upper or barrel nut area causeing the lug shearing?
Link Posted: 3/2/2006 8:12:56 AM EDT
Thanks for all the positive feedback... a couple of crude comments in IM, but all in all good feedback!

A KAC system was tested (non free float) and I will get the pics and results posted tonight... as well as try to address most of the questions that have been asked up to here -- my *real job* has me a bit busy at the moment however... but I will get done what I can this evening.

Thanks,
Gunz
Link Posted: 3/2/2006 8:28:15 AM EDT
I am wondering if you would be able to do the test with a surefire M73 / M85 style HG?

I would imagine that the result would be the same as the Knights, but since the locking system
is of the opposing lateral horizontal forces type, the result may be a little diferent.

Thanks Rough
Link Posted: 3/2/2006 2:05:15 PM EDT
Tag for RAS data. Also I wonder just how hot is hot. I have hat smoke rool off my barrel, and would imagine that 220f is not that hot, and 5 or 6 hundred may be mor like it. If I had a non-contact thermomiter I would see how hot it was, but $500 for one is too much.
Link Posted: 3/2/2006 2:33:59 PM EDT
[Last Edit: 3/2/2006 4:21:43 PM EDT by BravoCompanyUSA]
Link Posted: 3/2/2006 2:48:02 PM EDT
Best would be to have a setup where it is possible to measure the force from the verticle grip while shooting under FA, as I think this is where most of the stress occurs. Like an electronic sensor that could record the magnitude and direction of the force (ie, is it straight down, or more down and back). I envision something similar to an inverted joystick that could measure forces mounted to a rail. That way, you could have "real world" data to experiment with. But I do not know how practical that setup would be from a cost perspective.

Great job so far, and I hope you are able to spend more time on this.
Link Posted: 3/2/2006 2:49:13 PM EDT
Thanks for sharing-
Link Posted: 3/2/2006 8:33:23 PM EDT
A few updates...

added some stuff to the first post, not much, but a little -- pretty busy this week. Try to answer some of the questions that have been posted.

*I am not interested in testing all sorts of different handguards... this is not about HGs, the intention is to try to veryify if the "receiver flex" stories are true and what can be done. Furthermore, I test what I have... some manufacturers are great about providing stuff, others are not -- I don't have the fluid capital to be buying one of everything you know

*The bolt in place may provide some support, but that is not at all good really... if that is the case, then the bolt assembly is taking stress that it was never designed to experience. Keep in mind that there are only two bearing surfaces on the bolt to receiver bore -- the third point is tension from the top round in the magazine.

*Could this flexing cause a bolt to break? I could not say at this point, but I have designed a fixture to flex the upper receiver and allow for the rifle to be fired normally, when I get the chance to take this to the range then I may know more.

*The best bet (I think) from this point is to measure the flex of the receiver with a simple laser and grid... this will allow a lot of freedom in how and where the flex is measured and give a much better idea of the actual deformation of the top rail.

*I agree that 200-220F is on the low side... I only wanted to see what effect that limited amount of heat did have on the test. When possible, I think a standard should be set by taking temperature readings on the upper after a three magazine dump in full auto.

*As for the amount of force used in the tests, twenty pounds may seem like a lot, but some seem to think that may even be on the low side? It would be easy to make a "dummy gun" that would measure the force applied to the front section of the receiver -- but what is the standard of the shooter? One has to error to the side of "worst case" and anyone that has been in that situation knows that their actions can be far beyond normal.

*To date, all this proves is that there is flexing in the flat top receivers and that the barrel nut mounted handguards are the least desirable setup as far as that flexing goes -- as to how that flexing effects the operation and integrity of the gun, that is still on the plate. The monolithic uppers seem to be a good option to prevent this and provide the much needed top rail section...

*The ultimate goal is to improve the system, nothing more.
Link Posted: 3/2/2006 9:59:25 PM EDT

Originally Posted By BravoCompanyUSA:

Originally Posted By FROST18E:
I'm glad to read this. I was flamed a while ago on another thread when I talked about USASFC (US Army Special Forces Command) changing out all the regular M4 profile barrels to the new Heavy barrels because bolt lugs were being sheared from pressure exerted using the forward grip and barrels were bursting at sustained rates of full auto fire.

Would the fact that the knights armament SOPMOD kit is not a free float rail have any additional stess added to the upper or barrel nut area causeing the lug shearing?



That has been one of the competing theories in some circles, but is that the conclusion we should come to after reviewing this data ?

Is a 20lb weight (pulling straight down) at 7"+ out on the barrel representative of what the carbine would experience while being shot by a soldier ?
Does the 10lb data more closely correlate with "real world effects" ?
Would the change in the indicator measurements be enough to cause misalignment in the bolt and barrel extensions that would cause damage ?

Gunz performed the testing and collected a lot of great data. The next step is this data needs to be interpreted so it can be applied in a "real world" sense. I will let men smarter than me do that.



I'm not saying that putting this stress on the barrel by pulling down on a vertical foregrip WILL cause this to happen. What I am saying, and know for a fact, is that this was the reason USASFC used to go to the heavy barrels. I was on an ODA in 1st group around 2001 (if i remember the date correctly) when we received brand new M4's for all the teams and about a month or two later had them all rebarreled to the heavy profile by the civvie armorers at group (contractors from General Dynamics). I've never shot one to the point this did happen. The most I've done is shot so many rounds that I had a cook off in the chamber.
Link Posted: 3/3/2006 5:45:29 AM EDT
Thanks gunz, don't forget to watermark your pics so the thieves at sigforums don't steal them without giving you credit
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