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Sigforum K9 handler |
I’m pushing 8 years or so with MRDS. I’m on my second gun at no fault of the pistol or optic. I think that the durability of the system as a whole will depend on how well the system is maintained. Once per year, we replace the optic batteries. When we replace the battery, we replace the mounting screws. I bought a box of 100 for $11 at Fastenal. At each range session we check torque. Supervisors check torque on quarterly inspections. We change recoil springs at 5 years or 5000 rounds whichever comes first. So far, so good. The long term will depend on maintenance I think. | |||
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Prepared for the Worst, Providing the Best |
Thanks for the feedback Jones...that's good info. Are you replacing the screws purely as good practice or have you guys actually had problems with them breaking? You're running RMRs, right, so the screws have to come out every time for a battery change? I have little doubt that a quality optic like an RMR can hold up to years of use. I'm curious what drove the change in the middle of that 8 year period. Was it just a scheduled update, or was there some improvement in tech offered by a newer optic or handgun that made it worth the jump? | |||
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I'm also interested in hearing about screw replacement. If they're torqued to spec, are they prone to failing after so many shots due to exceeding the steel's fatigue life? | |||
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A big part of the trouble with reusing screws is getting them properly cleaned. I use acetone and have found that getting all of the old threadlocker off the screws can be a chore. Not getting the screws properly cleaned can cause the new threadlocker to not properly set. Replacing the screws at the cost of cents is absolutely worth it. Fastenal and McMaster Carr are great sources. And since someone asked about stress on the screws causing/allowing them to break, I have not seen that on optics properly mounted with a good pocket, recoil bosses, or preferably both. | |||
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For the price of screws I'm with DaBigBR just use new ones. Primarily because the product(s) needed to properly clean them and prep them for loctite take time to use. You have to value your time at $0 to justify doing it. I personally have never seen broken screws on an RMR with recoil bosses. But I have seen them repeatedly on guns like the Sig 320 that has RMR pattern thread mounting holes but leaves a gap at the front of the optic so the screws take the abuse. I would never trust that setup and the aftermarket has stepped on to fix it via a plate. All FWIW. “So in war, the way is to avoid what is strong, and strike at what is weak.” | |||
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knock on wood I've never had a screw break or sheer off, but I'm not racking the slide on a barrier using the optic either. I've found using vibra tight VC-3 instead of med lock-tite doesn't require the screws to be cleaned everytime I change a battery, as it is designed for several uses and I've never had a screw back out. I also index screws with a marker. An easy inspection of the index marks insure the screws are not backing out and the few times I've checked torque, it's been a GO. I like the idea of spare screws for the optic however, just in case. The only optic mounting system I've had issue with is the FN 509 MRD. Lock-tite or no (FN says you don't need it) the screws blackout after a few hundred rounds and had to constantly rechecked. Too many plates, spacers leads to more points of failure. Guns with direct mounting Sig P320/DPP or my Shadow Systems MR920 with the RMR and provided spacer have been rock solid. Those Shadow Systems mounting screws are 2-3x longer than the typical mounting screws from gun maker or optic co. which I think is the cause of many problems with screws breaking or backing out. Joe Back in Tx. | |||
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Most of the strain on screws is going to come from the slide cycling under live fire and not manual manipulation, even very aggressive manual manipulation. | |||
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Yea, we'll have to disagree unless you have some imperial evidence. The stress on the screw depends on whether the screws were over torqued which appears to be the main factor, all else being equal. Tight optic fit to slide etc. Joe Back in Tx. | |||
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| Sigforum K9 handler |
We’ve had no problems with screws. As mentioned, for what the new screws cost, it simply not worth reusing the old ones. I too am in the camp that on systems without recoil bosses that the screws are under stress. The MOS system fits neatly into that category. I look at screws like batteries. I know I can get over two years on a single battery. But, for what they cost, we just change them out as a precaution. It’s a life saving tool and I’d much rather err on the side of prudence than being frugal. As to the switch, my first gun had to go visit the state police for a few months so I got a new one to replace it. When it came back, I just kept the replacement gun and the first gun is still in service with another officer. My replacement gun is probably going to have to be rebuilt this summer. Trigger is getting really crunchy. Gun still holds “A” box at 50 so I can’t complain. | |||
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| Prepared for the Worst, Providing the Best |
Roger that. Again, good info and thanks for the response! | |||
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If you are asking if you need to rack the slice on a barrier or something similar to have problems with the screws. Then I can say for sure you do not. I have worked on several 320's with broken screws whose history is completely known and the only stress they had was recoil. Over under torquing is also not an issue here. FWIW. “So in war, the way is to avoid what is strong, and strike at what is weak.” | |||
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Not really what I’m saying. Problems with screws can come from a multitude of mounting mistakes. For a properly fitting and installed optic (preferably one without a plate and recessed into the slide), most the recoil force is absorbed by the optic body. This is well known. The screws become compromised when they are over torqued causing sheering and this is true for many applications where screws/bolts or fasteners are used. Racking with the optic will cause force applied to screws in more than just the linear axis along the slide optic cut plane acting like a lever, pulling the screws upward away from the slide, further compromising the structural integrity of the fastener. Most optic screws are designed to handle the forces of recoil in a slide cut/linear plane, but not with an optic acting as a lever and pulling upward on the screws at the same time. These screws have fine threads and are very short, which minimizes the number of thread engagement. Torque values are in the 10-18 in lb range which is an indicator of their low sheer strength. Anyone that has seen or stripped the head of these screws is doing it wrong. And we all know it’s done all the time. Joe Back in Tx. | |||
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I don't get your point. I'm most familiar with RMR's. The design has the recoil forces absorbed on the recoil lugs and minimizes the force on the screws. And many/most milling projects provide positive contact to the optic body in the milled slot so in theory neither the lugs nor the screws face recoil forces. The existence or not of a plate has absolutely nothing to do with that. The racking of the slide off axis using the optic body certainly applies force to the screws but it is in the direction that they are actually strongest. The fact that the failure's I've seen is actual fastener failure at the head and not pullout is indicative of the failure mode. The torque values don't mean anything about the sheer strength. “So in war, the way is to avoid what is strong, and strike at what is weak.” | |||
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Lots of absolute statements without regard for mechanical engineering principles. No one mentioned screw pull out from the threads. I’ve been taking about fastener failure. Rotational and linear forces caused by racking the slide from a point higher than the axis will cause a weakened screw to shear quicker than just a linear force along one plane. This will manifest itself in the neck or head of the fastener shearing. That’s correct, most direct mounting solutions, the recoil is absorbed by the optic body, as I already stated. The existence of the a plate requires more screws = more points of failure. “Recoil” lugs are not necessary and are often used when plates are required for mounting. If you can’t acknowledge how over torquing a fastener could compromise the materials tensile strength and compromise the fastener, whether at the threads or neck/head of the fastener, then I’d say you’re just being argumentative. Joe Back in Tx. | |||
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OK, lets review. Not once I have argued about fastener torque. You need to torque these (and literally every fastener ever used) to the correct torque. If you don't bad things happen on guns or airplanes or cars or whatever. So if you screw that up then away we go, you get what you deserve. But assuming one can get that correct... There are simply no examples I have seen of the plate to slide fasteners failing. Yup its more points of failure but they are not loaded in an a way they fail. The design of the RMR (at least) uses recoil lugs, to argue that the are not necessary is simply stupid. The optic may do equally well when secured in a correctly sized pocket on the slide, but when its not the lugs need to be there. This IS the problem on the 320's I've seen. For the size of the fasteners we are discussing the pull out failure load is lower than the sheer load (look it up) so if racking on a barricade is an issue it doesn't fail as expected. But in the end. Mounting these properly works just fine and all is good. “So in war, the way is to avoid what is strong, and strike at what is weak.” | |||
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| Sigforum K9 handler |
“There comes a point in time in every project to shoot the engineer and start production”- Unknown | |||
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The RMR does NOT have recoil lugs, it has recesses for recoil also called positioning lugs. Again typically used in “universal optic cuts” ie where a mounting plate is needed. This is why direct milling/mounting is superior and recoil/positioning lugs, are superfluous in those instances. Over torque screw will ALWAYS reduce the tensile strength of the fastener, increasing the likeliness of shearing or other failures. Not that hard to understand.Words matter. “ The torque values don't mean anything about the sheer strength” - Not once huh? Recommendation - don’t drink and mount optics or internet.  Joe Back in Tx. | |||
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E tan e epi tas |
I’d imagine on an RMR where I had to remove the unit to replace the battery I’d likely replace the screws/do all the cleanup of the mounting etc. just like I was doing from new. Now since I am just starting to experiment with optics, mine don’t require removal for battery replacement so I don’t plan on removing unless there is some kind of failure/issue. I am also likely not abusing like in a duty environment. (I don’t mean abuse through neglect as much as I simply mean all the normal bumps, bangs, scuffles etc. that are gonna happen day to day in a duty holster). "Guns are tools. The only weapon ever created was man." | |||
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Ok I'll accept I may have not done well in articulating my point thanks for pointing that out. So I'll try again. What the screw(s) are made of matters for the strength and the necessary torque values. These RMR mounting screws are easily available in tensile strengths from 50K to 160K. Materials matter. “So in war, the way is to avoid what is strong, and strike at what is weak.” | |||
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