Recent twitter post from PEO Soldier

https://twitter.com/PEOSoldier/status/1661454518435848193

PdM Next Gen Squad Weapons recently took delivery of #XM7 Rifles and #XM250 Automatic Rifles for Production Quality Testing. Testing has begun and will finish in August. Be sure to check back for updates as we progress through PQT. This summer is really heating up!”

Potential design flaw for NGSW XM7?

Recently its been discovered that the SPEAR-LT (5.56 civilian/leo version of 6.8 SPEAR XM7) has issues with barrel shifting upon load / impact.

Basically if lateral pressure is applied to the barrel it will lose zero - and stay off target even once the pressure is no longer applied. Ie you whack the barrel going in a door, the barrel can get canted to the left and stay a bit canted.

Why is unknown yet, but most likely culprit is some flaw in the barrel to receiver interface.

YouTube

SIG Sauer Firearms MCX Spear LT Barrel Deflection PART THREE

This is the 3rd and FINAL installment of the MCX Spear LT and the barrel issues that we saw. In this video, we explore MCX barrel deviation and provide valu...

2nd source:

https://www.instagram.com/reel/CsmmB6-tnFa/

Claim that this is a 7.62/6.8 SPEAR with same issue (but little further context given)

https://www.instagram.com/reel/CsrOkiwoKup/

Google drive detailed Analysis (excellent)

https://drive.google.com/file/d/17d-jDJePHyNIDEIONoofD7VI7Ys8qJfk/view

Excerpt; problem seems more acute with left pressure vs right

And another test with near identical results

AS I understand it the barrel doesn't shift, the handguard does and it only effects POI IF using sights mounted to the handguard.

Harrison Beene (harrisonbeen) said:

AS I understand it the barrel doesn't shift, the handguard does and it only effects POI IF using sights mounted to the handguard

From the video test, it seems the barrel is indeed shifting.

He has the green laser mounted to the receiver (not the rail) and then has a laser boresight in the weapons chamber, showing where the barrel is oriented. At the start of the test both lasers are zero'd dead true one on top of the other. Then by moving the barrel the red boresighted laser shifts permanently/semi permanently to one side or the other, while the green laser mounted to the receiver stays in its initial centered zero. 

It is unknown to what extent this issue exists ie just some guns, just the 5.56 guns, or the entire 5.56-7.62-6.8 SPEAR family. 

I'll update with any more info I can find.

*edit* a new video shows the barrel is very easy to move.

YouTube

Sig Spear Wobbly Barrel #sigsauer

I can't tell from that if the barrel is moving in the receiver or if the handrail is moving in relation to the barrel.

I can make my rifle do that if I loosen all the screws.

I get it, there are 10s of thousands of people that hate the SIG deal, the caliber choice, the ideas etc.

In 2007 I spent about $40,000 trying to show the military that if the 6.8SPC barrels were made to the correct specs(different from what the mainstream is still producing) they could propel 110gr bullets to 2800fps out of a 16" barrel just like Holland, Murray and Lawton said it could. Sure I proved it, did it matter, no it didn't because Mattis couldn't get approval from congress even though he thought the 6.8 would be a great improvement.  Now I don't waste time thinking about what the military should do, I just make whatever wildcat I think would work best for me and shoot it.

Everyone thought the SCAR was the best thing since sliced bread, same with the 416, didn't last long did it?  All the guys that think we need something besides a 5.56 in a DI M4 are still shooting a 5.56 in a M4. The questions I have now is, just because the military awards contracts does it really mean the military will finally change or are they just testing something else for a few years and wasting a lot of tax money.  2-How long does some other caliber/rifle need to be fielded for it to be considered a change?

Sig Sauer USA  aka ''designed on computer tested on the customer'' so what is new, the product they launch is typically trash for the first 2+ years before they come up with an improved version.

Mr. T (MrT4) said:

the product they launch is typically trash for the first 2+ years before they come up with an improved version

Well whats odd here is this is the 3rd iteration of the MCX, which has been on the market since ~2015. And the SPEAR is based on work done for the NGSW, which we know has been getting tested for a few years now. 

...

It's funny you mention 'designed on the computer.' 

The Air Force was recently saying much the same - that computer simulation is not an adequate replacement for real world testing.

https://www.thedrive.com/the-war-zone/air-force-boss-gives-reality-check-on-over-hyped-digital-engineering-revolution

gatnerd said:

The Air Force was recently saying much the same - that computer simulation is not an adequate replacement for real world testing.

The situation did not really change...

https://en.wikipedia.org/wiki/NASA_X-43

"NASA's first X-43A test on June 2, 2001 failed because the Pegasus booster lost control about 13 seconds after it was released from the B-52 carrier. The rocket experienced a control oscillation as it went transonic, eventually leading to the failure of the rocket's starboard elevon. This caused the rocket to deviate significantly from the planned course, and it was destroyed as a safety precaution. An investigation into the incident stated that imprecise information about the capabilities of the rocket as well as its flight environment contributed to the accident. Several inaccuracies in data modeling for this test led to an inadequate control system for the particular Pegasus rocket used, though no single factor could ultimately be blamed for the failure.^[6]"

We should keep in mind that even a 6 DoF model can't predict every time something as simple as the the flight of a bullet, so being able to predict something more complex is pure hubris...

EmericD said...

We should keep in mind that even a 6 DoF model can't predict every time something as simple as the the flight of a bullet, so being able to predict something more complex is pure hubris...

To expand on this, if the physical test uses a bullet exactly as designed, at least to significant tolerances, and the air it was flying through was still and at constant temperature and pressure, and gravity was constant throughout the flight and the starting point (say muzzle exit) was consistent shot to shot  and all of those factors were covered in the model, you'd expect the model to be accurate. Bit of a tall ask for test range and conversely it's a bit of a tall ask for a model to account for all of those being variable. I wouldn't say bullet flight is simple.

In order to make it possible to run the model in a reasonable periods of time, a lot of these factors are assumed or abstracted and measurements aren't always correct. Then you've got very small effects that can build up over time and change the end result - this was a big thing in weather modelling in the '90s, where they changed from one set of starting conditions to get one set of results to a set of variances from measured conditions to get a range of results and they can comment on probability. This kind of modelling is dependent on computing power, so it becomes more accessible as computing power increases. Getting a good idea of how much to change the starting conditions requires test evidence though.

Simulation allows you to look at areas you can't test, or can't measure, either easily or at all. Ultimately you've got to test to prove that the end result matches (or not)

If anyone tells you that you don't need testing and can do it all on computers is trying to sell you something. Probably simulation software. 

RovingPedant said:

Simulation allows you to look at areas you can't test, or can't measure, either easily or at all. Ultimately you've got to test to prove that the end result matches (or not)

If anyone tells you that you don't need testing and can do it all on computers is trying to sell you something. Probably simulation software.

Every engineer o sciencist knows that since they allready learn it at the university.
As mentioned this is nothing new.

The problem is nowadays decisions tend to be made by people who are lacking in basic sciencific and technological understading. But they do understand "its soooooo much cheaper". Which is also exactly how far their understanding reaches. So they use the only benchmark they can comprehend for their decision. At the same time they are very poor business economists (if they weren't they wouldn't have to work for the government in the first place) because they never understood full cost calculation and holistic approach.
Since we also live in times where very seldom someone is held resposible and evasion of responsibility has been up lifted to an art form by the decision makers there effectively are no consequences for stupid decision. Negating any learning effect and any chance of personel changes in the decision making proces.
That is the root of the problem. The fact that simulations are limited is merely a environmental conditon.