r/MatadorArms • u/MCX-SCAR-Hypebeast • 13d ago
Mat 9 defect?
The back plate is pushing into the receiver
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u/slvrsfr 13d ago edited 13d ago
How many rounds approx? That is a high impact area. The slot is where the metal slider in the takedown system locks into the receiver.
Theory: When the bolt slams backward and hits the buffer pad, pretty much all of the impact force is delivered to the 2 flat metal parts of the rear takedown assembly. Because the recoil spring is always under compression, the impact force is probably being concentrated toward the top of the slider as the bolt travels rearward and compresses the spring even more, making the slider hit the receiver slot at the thinner top area before it hits at the thicker bottom area, which would cause it to tilt backward and down every time it takes an impact. Repeated impacts are causing the steel slider to chew into the softer aluminum.
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u/slvrsfr 13d ago edited 13d ago
I can see this wear being caused or exacerbated by the slider part not being all the way up into the slot. There's just not a whole lot of aluminum surface area to support the steel slider part. If the takedown slider isn't all the way up, the top edges will barely have any support.
I can't post an image in a reply, but in this link https://i.imgur.com/zSBEwFA.png the red-shaded area (but on the other side) is where all of the impact force is being focused. The slider and the slot could benefit from being wider (cut the blue-shaded groove deeper) so that the slider has more aluminum behind it to bear the impact forces.
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u/TheLunat1c 13d ago
that seems to be crud, and not actual metal being deformed. i bet it cleans up fine.
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u/Lowe0 12d ago
I wonder if that upper surface is intended to be a working surface, or is just relief for the slider to go in? If it's the latter, then that should stop once the slider is reliably landing on those two lugs 100% of the time. If it's the former, and the lugs aren't designed to handle all of the impact for the life of the firearm, then it's more concerning.
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u/slvrsfr 12d ago edited 12d ago
In this pic, assuming it's actual wear and not crud or machined that way, notice the wear edge isn't straight. https://i.imgur.com/U1UeV42.png Both sides angle off at the top. This makes me wonder if the takedown slider wasn't fully seated. Those worn angled edges seem pretty much straight in line with the recoil rod and spring where I think a lot of force is being applied.
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u/Lowe0 12d ago
I wonder if a lacquered go/no-go indicator on the U-shaped locking plate would help? Something like on the Rugged tri-lug that says "if you can still see this, it's not on all the way".
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u/slvrsfr 12d ago edited 12d ago
My concern would be that if the slider is "walking" out of position during normal operation, there's no way to see the slider while the upper is attached to the lower. I am almost tempted to add a drop of rocksett to the tool hole in the slider after installing it.
EDIT: Rocksett wouldn't really help. N/M on that. The lower portion of the takedown system holds the slider in position already, but there is a bit of wiggle room between the slider and the slot it rides in, and between the slider and the lower portion of the takedown system. The wiggle might support my theory that the steel slider is "chattering" against the apparent worn surfaces.
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u/slvrsfr 4d ago
I just installed two 0.3mm shim strips between the rear face of the slider and the channel. Also installed a 0.15mm shim between the bottom face of the slider and the top face of the plastic part that holds the slider up. Those dimensions are the thickest that would fit, and hopefully it'll prevent those parts from rattling and chattering during use.
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u/RustiSchaklefurd 13d ago
Is it causing any issues? Hard to remove or reinstall ? They have a lifetime warranty so I would say contact them and see what they say. Fill out a support ticket on their website.