MDI SLR receivers come loose.
- Thread starter HotSoup
- Start date
r34skyline
CGN Ultra frequent flyer
They increased the torque spec is all they did as far as I know.
The negatives about the XCR barrel bolt were less about it staying tight and more to do with it just being a really poor way to mount a barrel where accuracy is concerned. The rest was just the lock-tite jokes about fasteners coming loose.
So there you have it, it's been known for years that bolts holding together black rifles is less than ideal, good thing these guys have been paying attention.
Weird seeing that my sl8 receiver bolts have never come loose on either...
Would i prefer a pin? Yeah. Does the bolt make this the end of the world? Not even remotely.
If I recall my SL8's correctly they use bolts with a knurled head that bites into the polymer a little.
You're right, it's not the end of the world, as was mentioned earlier it's less about it being a bolt and more about some guys having it come loose every 60-100 rounds that's the problem. I also personally don't like that they used a helicoil instead of tapping the receiver or something a little less backyard mechanic.
Obviously you don't know how a helicoil is installed, or it's function. First, the hole is tapped to the size that allows the helicoil to thread into it. Then you thread your bolt in. The purpose of the helicoil is to keep the stainless steel bolt from chewing the crap out of the aluminum threads over time from assembly/disassembly.
My only experience with helicoils is back in the 90's when I worked in an auto shop and they had to use one to repair a stripped spark plug hole. Seemed like a crappy way to repair something.
So what's the helicoil made of? If it's steel you're still going to have dissimilar metal corrosion occurring which will eventually make the inside of the receiver lose it's hold on the helicoil.
Or you could just use a captured pin to stop them from sliding apart. They still would have gotten the non restricted stamp if it was a single pin at the front that just stopped them from sliding apart. Hmmm, does anyone else use something similar and have a non restricted status? Hmmmm, I think someone does and it works quite well.
Or any number of better solutions that don't involve a bolt and insert which was probably the easiest. Obviously there is a problem with the helicoil/bolt solution or we wouldn't be talking about it. There are guys that are having this bolt come loose every 100 rounds so it's obviously not a good design.
Just use more lock-tite? Ya, just what we all want is a rifle held together with a bolt that either falls out or is all gummed up with thread locker that it is hard to remove and maybe eventually drags the helicoil out with it.
The simple truth is that if they used a single captured pin cross ways through the receiver we wouldn't even be having this discussion. The fact that we are is proof that there is a problem.
And just because everyone isn't experiencing problems does NOT mean that there isn't a problem.
Just like the XCR's barrel retention bolt, the SLR's takedown bolt is the pitfall of the design.
People trying to camouflage the flaw in the design by claiming it was necessary to obtain NR status are simply trying to fool themselves.
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And just because everyone isn't experiencing problems does NOT mean that there isn't a problem.
Just like the XCR's barrel retention bolt, the SLR's takedown bolt is the pitfall of the design.
People trying to camouflage the flaw in the design by claiming it was necessary to obtain NR status are simply trying to fool themselves.
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Hey , I understand where you’re coming from.
I was in on the very first pre-order, but I found out early, how the U/L were held together.
So I canceled, not from experience but I knew enough, that I didn’t want this set.
I do agree however, there’s a problem and the lack of trying to fix it , is hurting their business.
I was in on the very first pre-order, but I found out early, how the U/L were held together.
So I canceled, not from experience but I knew enough, that I didn’t want this set.
I do agree however, there’s a problem and the lack of trying to fix it , is hurting their business.
r34skyline
CGN Ultra frequent flyer
Helicoils are utilized in multiple locations on aircraft. They are hardly a backyard mechanic solution and are a good sacrificial piece. If the helicoil was inserted on an unfinished surface over time dissimilar corrosion could be a problem. Otherwise it's a non issue. Why they used a bolt that lacked retention features such as an oring or a knurled edge or simply a lockwasher is a bit beyond me. Maybe they can fix that going forward.
It would appear you don't know how galvanic corrosion works neither. It's not "dissimilar metal corrosion" BTW.
Helicoils are a necessity when you repeatedly screw-torque-unscrew steel bolts into aluminium.
The problem isn't the helicoil, the problem is the interaction of the receiver flex, horizontal separation forces and firing vibrations with the bolt. Having the bolt directly threaded into the aluminium would suffer from the same problems because the problem is the base design of the system. Having the upper and lower receivers holding together halh/half with one screw in the vertical axis is pretty much guaranteed to have screw retention problems. Every time the gun fires and cycles the forces are acting on the bolt to get it loose.
NEVER loctite a bolt in a helicoil.
The solution to this SLR bolt problem would be to design a bolt with dimples cut all around, and having a spring-loaded plunger besides it that would lock itself into a dimple. Like the front sight post and plunger on a front sight base.
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Patt08
CGN Ultra frequent flyer
So back to square one then lol.
Well I don't know about that. Seems like a pretty easy upgrade to do yourself with the current design actually.
Can someone post a closeup picture of the upper/lower screw/retention area?
So the plunger hole is already there, so that's good. I don't know if Macabee would be able to design/machine a custom long-headed dimpled bolt for that application altho it's something that would be easy to design. Someone knows the thread pitch and size of the screws? Depth/diameter of the hole for the bolt head?
I'm thinking they may not even have to make a new bolt... there may be readily-availabe fasteners that could work together for this application...
No, not a metallurgist or a machinist but I still know this is a crap design that was simply the easiest way they could come up with to stop them from sliding apart. Works great on paper but not in the field.
The solution is not a better bolt, it's getting rid of the bolt altogether and changing the design to utilize a cross pin or some other type of plunger or something that can simply be depressed or slid out like a captured pin on an AR.
Really awesome how we stick together on this site isn't it? A few guys have problems but the guys that haven't had issues YET act like it's user error and stand behind the manufacturer defending the design which is obviously flawed. Everyone should be pressuring MDI to change the design to something more reliable instead of looking for a home fix to work around the crappy design.
To the guys that haven't had problems yet. If the bolt on your rifle starts working itself free are you still going to say there is nothing wrong with the design and you'll just go buy some fancy bolt? Or are you going to be pissed and want them to fix your rifle so it doesn't keep coming loose? I would bet that all of you will be pissed and want it repaired, so why is it a non issue just because it's happening to someone else? They bought the same product you did except they were not as lucky as you.
There's no way of knowing whether or not every single one of these will eventually start having the same issue but my bet would be that it's only a matter of time till every single owner of an SLR receiver set is having problems with it coming loose.
Patt08
CGN Ultra frequent flyer
I know this is pretty much the most basic way they could go at it, but I don't think they can readily drastically change the mounting system without involving the RCMP and FRT process... so we have to work with the currect design.
They aren't gonna change the system with a cross-pin because they would have to replace every receiver set made and sold and would instantly go bankrupt and end up on the street.
But the main problem with the currect design is that there isn't a mechanical fail-proof system to keep the main bolt from rotating by itself. A spring-loaded plunger locking into the bolt head would solve that issue and wouldn't alter the mounting system configuration.
Heck, I'm not affected by this SLR problem because I didn't buy into the design, but I still want to help those that did and have a problem to deal with.
I ordered a Nord Lock washer NL5ss. I think the OD is good but will have to drill out the ID by a mm to fit the current bolt. I’ll update here with results. I also think a lot of us our on the same wavelength. If a custom shoulder bolt could machined to sit high enough to be locked in place by the secondary bolt that would work great. Might need a secondary bolt with flat bottom. Not sure why it’s not a socket head cap screw too.
