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Well that makes me feel even better! LOL
Sorry. I'm generally a realist....but unfortunately, it usually comes across as overly negative. I pray for my country and its countrymen and her prosperity, but I am concerned for our future.
 

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Like everyone else just said, these are just parts not firearms. See if Robinson arms can send you parts your way and listen to what they have to say.

Do not take anything I say the wrong way or as any indication of arrogance, I only offer this as perspective. Considering that the receivers were intact, no explosion or shrapnel was launched your way, that the rifle was still working with the broken oprod and likely broke before you noticed anything, and said broken parts remained inside of the gun, indicates to me that the gun is "fail-safe" and not "catastrophically failed". With these kinds of things, you have to consider the design and circumstances of the firearm. The fact is that the XCR upper is made of 7075 aluminum alloy in a more compact space at a thickness at least twice that of the Colt AR that Sheff pictured that appears to have suffered an out of battery detonation; very few rifles can make the same claim.

Not to be pedantic, but here is what a lot of CZ scorpion Evo users are waking up to:



I don't have any numbers but there are growing complaints that the Scorpion is susceptible to OOB detonations around reddit and Youtube. The most compelling theory is that the disconnector is off-timed and that it's letting people pull the trigger before the case is in battery. Personally, I also see the fact that the receiver is polymer and that the bolt rides on a spring-loaded guide rod as contributing factors to OOB.

This also reminds me of the ongoing case where a former sheriff got a DP-12 and is now suing everyone involved with the sale and operation of the gun after it seemed to explode on him. He got shrap directed at his body when he was test firing it, and while I do agree scrap would hit him that way, I don't understand how there would be an OOB based on what I know about the DP-12's design. There is a lot of steel in the bolt to close off the chamber and the slide closes tightly. It seems the Plaintiff doesn't really know either, as he sued not only the DP-12's manufacturer but Federal ammunition and the guns store he got the gun from, and has made demands for the companies to reveal trade secrets and design details to determine how any of them could fail. Considering that no independent examination of the offending shotgun has been made yet, no one can be really sure, but I somehow doubt Federal ammo or the gun maker had anything to do with it.

Here's a video on Forgotten Weapons to give you a primer on how dangerous guns can be to the user and what designs are made to make them safer:

To be frank, all guns can be dangerous and we are taking our lives into our own hands when we use them. With guns we are using controlled explosions to direct small metal objects at targets at high speeds. We take them for granted when they work for hundreds or thousands of rounds with no incident. If you are really spooked by the fact that firearm parts can break down during operation, it might be time to find another hobby or tool that doesn't rely on controlled explosions.
@Chowwow. I’m not sure why you think the polymer body contributed to the OOB explosion occurring in the Scorpion in your post. We don’t actually know what caused that explosion or the other similar cases. There are multiple theories, one of which relates to a potential design flaw in the semi-auto bolt.
I have had some odd failure to feed and failure to eject instances with my Scorpion, and have not been able to isolate the cause. I believe that it may relate to the play in the magazine, but I don’t know. It’s concerning.
 

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@Northern When I started looking into 3D printing 9mm firearms, I was made aware that one important design consideration was making sure that the bolt and barrel were in line and rigid to prevent OOB explosions. It's really important to keep in mind when building guns with plastic uppers (and for that matter, any gun with any caliber), that's why the FGC-9 has a second metal rod that travels with the bolt so it can help keep the system rigid and in line. Metal uppers don't have as much of a problem with this and are rigid enough to keep the bolt in line, which is why the recoil spring on the MPX can reciprocate and the bolt doesn't need a constant guide rail. So when I saw that the Scorpion had a (albeit rigid) polymer upper with a bolt and guide rod that was relatively easy to slide off, I cringed a little. I didn't think the receiver would last over time and when I first heard about the OOBs, I initially thought it was the chickens from that receiver design that were coming home to roost. It's likely a host of small issues that are adding up to this:


Any number of small things can add up to make it so the bolt won't go home in that one crucial second. Honestly, I don't own a Scorpion yet and I can't attest to any of these claims, but when I do or get any other plastic gun I'm going to be a lot less reckless with it.

Back on topic, this is just one way of thinking that we as gun owners can use to examine a gun and decide if it's right for us based on its design, and not just its looks or features. It also goes to show that even popular and proven firearms with simple designs can come with significant risks.
 

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I have to say I'm pretty impressed with the XCR, I got a 5 gallon bucket of 5.56 at an estate sale. It looks like some of the reloads were either pistol powder or a compressed load. 6 blew up out of ~250 reloads, with one case separation. I checked headspace and chamber with a bore scope. I'm convinced any of these would have blown an AR upper apart, especially the btfo primers.
 

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@Chowwow but we do not actually know that that is what is causing the OOB explosions in the scorpions, right? I thought the more likely cause relates to some feature that was removed when redesigning the bolt for semi auto, which results in the firing pin engaging out of battery. There is no specific reason to believe that the polymer upper was giving way, allowing the bolt to move out of alignment, right?
 

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Just wanted to add that I survived my Scorpion shooting sesh today! Yay!
My friends have survived a ton of them with mine (they shoot it way more than I do). And mine's got a VERY short trigger and reset.....ala Miller. I'd expect if it's an issue with the chamber not fully closing before a detonation, a short trigger might exacerbate the problem.
 
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@Sean K. yeah I was just kidding, I shoot mine weekly and it has maybe 5000 rounds through it, total. My recent discovery is that the rate failures to feed seem to be caused by some bad Czech mags, which I have to change to have US made followers and bases anyhow. Very fun gun, and every friend who shoots it, and my son, feels like a pro shot after a session, it’s just so damn fun and easy. Especially suppressed!
 

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@Sean K. yeah I was just kidding, I shoot mine weekly and it has maybe 5000 rounds through it, total. My recent discovery is that the rate failures to feed seem to be caused by some bad Czech mags, which I have to change to have US made followers and bases anyhow. Very fun gun, and every friend who shoots it, and my son, feels like a pro shot after a session, it’s just so damn fun and easy. Especially suppressed!
No, I figured you were joking....

I like mine but don't love it. Thinking I'm going to like my AK-V better....but haven't actually shot it yet.
 
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I do like it a lot, it just does not hit all my buttons the way my XCR-L does. I just got n Hbi handguard that will simplify its appearance and … reduce the overall plastic quotient lol.
 

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@roflcopters Holy shit, case head separation too? That's why I don't fuck with old ammo, sheesh!

Just wanted to add that I survived my Scorpion shooting sesh today! Yay!
May you treat every day from now on as a gift!

Seriously though, I think that CZ accounted for my concerns with bolt travel rigidity when they made it T-shaped like they did. But I'm just throwing my 2 cents out there; I heard it could be an issue with the disconnector and the kinds of ammo that people are using too. Time will tell I guess.

Arfcom is full of fanboys.

I don't think you understand what the ban means in Canada. For your edification: The Terrible Trouble With Trudeau's Canadian Gun Ban and that was prior to Trudeau's latest election victory.
I stand corrected.
 

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Discussion Starter · #33 ·
Thanks for the replies and suggestions but again - getting replacement parts in Canada is all but impossible (legally) and the consequences for attempting to circumvent that are absolutely astronomical and will only get worse.

Canada is a lost country doomed to authoritarian socialist rule. Those of you in the US should be paying close attention - you're next.
 

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Thanks for the replies and suggestions but again - getting replacement parts in Canada is all but impossible (legally) and the consequences for attempting to circumvent that are absolutely astronomical and will only get worse.

Canada is a lost country doomed to authoritarian socialist rule. Those of you in the US should be paying close attention - you're next.
Trust me, we know.

How would you have stopped it if you had it to do over?
 

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So a little more bad news to add to the thread....I looked over all my XCRs (Ms and Ls) and found one out of 11 or so op rods with a crack (to be fair 2 of those were spares). It was on one of the one piece mini length op rods for my 9" bbl XCR-L in 7.62x39 (stnd length upper, Type 3 buried block). Probably has 5K or so rounds on it, AFAIK....I bought the op rod from Nate, but I don't remember now if it was used or new. I think it was new. I plan to post up some pics of it (along with some other stuff I'll explain in a moment soon).

The crack in this op rod got me thinking about this issue and I remembered the newer XCR-M and L I bought in the last 2 years have a relief cut (or a notch, if you will) cut where the tube and 'foot' meet on the op rod. I assumed this was a stress relief for a stress riser where the two surfaces meet on the part. This was confirmed by Tech at RobArms in an email as being the reason for the relief cut. I was told that they haven't had any breakages of the one piece op rod since adding the relief cut.

I have 4 of the 2 piece, welded foot version op rods.....none of them are cracked and there is no apparent peening on the front of the foot portion of the op rod. The welded version is only welded on the sides....so there's no 'stress riser' at the front of the foot where it meets the tube.

Upon consulting with Tech....I asked about making the relief cut on the 1 piece design to alleviate the stress riser. I was told NOT to do any such relief cut on the welded ones (again, makes sense since there's no riser and no evidence of peening suggesting an impact at that point on the op rod during cycling of the firearm) and only to do so on the 1 piece ones.

At first, I tried using an appropriately sized end mill in my drill press (b/c I still suck and don't own a manual knee mill even though I've wanted one for years)....but the spindle just has too much run out, so I gave up on that and bought a single cut 5/32" carbide bur from McMaster Carr with a 1/4" shank for about $14 and put it in my Makita electric die grinder (air powered ones bog down too much in my experience). The relief cut takes a few minutes to make with this method and the edges of the cut need cleaning up with a fine tooth round file (I have a 1/8 and a 3/16" that worked nicely) to alleviate any stresses at those points. I just use gun blue to refinish the cut since re-parkerizing the part isn't really an option for me and generally takes care of any corrosion issue. Easy enough to do if you have the one piece, non-relief cut version.

I'll be posting pics of my cracked one (which I may....for shits and giggles...try and weld up and see if it can be repaired) as well as some of the notches I cut with the carbide bur.

Long story short....if you have the 1 piece design without the relief cut....might want to keep an eye out for a crack in this area and/or modify your 1 piece with a relief cut as I have on mine. And it might be wise to order a spare with the relief cut (all of the new production units will have it already). They run $70 with the appropriate piston head attached from RA direct. The M versions of op rods (for the various gas system types and lengths) are not on the website...at least as of the other day...Holly will be talking to Alex about adding them, but the L versions are listed in the parts section. So, if you need one for an M...you may need to contact Holly to order it until the website is updated.
 
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Just a few pics to go along with my write up.

1st pic is one of the op rods I modded. 2nd is of the cracked one (I did the relief cut on it first since it was a practice piece and is junk until I weld it up...if I go that route). Last one is the blueing liquid I use to refinish the notches.
 

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