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Discussion Starter · #1 ·
I had an idea the other day for a replacement front pin for the XCR. Being one of the people with multiple uppers that get switched instead of pulling the barrel and changing calibers, I feel like the front pin is the weakest link in the XCR. With it's weird retainer clip that looks like a paperclip bent into a fish shape.
So enters my idea, what if the front pin was replaced with a hollow female thread rod, and used allen bolts threaded from both sides, basically just making a giant antiwalk pin like many after market triggers use.
I don't have any access to machining tools so I'm going to try and find something at local hardware store..
Has anyone else tried something similar? Any thoughts on potential negatives of doing this, that I hadn't thought of?
 

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How many retaining clips have you lost?

A hollow pin is likely to snap under recoil if not VERY heavy wall and of heat treated steel. Sounds like a really bad/unnecessary idea.
 

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So enters my idea, what if the front pin was replaced with a hollow female thread rod, and used allen bolts threaded from both sides, basically just making a giant antiwalk pin like many after market triggers use.
How is the front pin a weak link in your use case? If I understand this idea, you would need tools to remove the pin if you want it to work like this. Is this much more convenient for you? The current design securely fastens the upper and lower together and can still be pushed out by hand so you can do a tool-less swap of the upper. I would have liked to have a captive pin in the lower instead but I suspect that would have resulted in a pin that was thinner and longer and less secure than the set up we have (which acts like a captive pin anyway). I don't see how we can design a captive pin without modifying the lower, or the upper for that matter.
 

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Discussion Starter · #4 ·
How many retaining clips have you lost?

A hollow pin is likely to snap under recoil if not VERY heavy wall and of heat treated steel. Sounds like a really bad/unnecessary idea.
Only lost one, but on my lower that has a problem with it staying put, I've nearly lost the replacement several times. The potential for a snap seams reasonably likely when thinking about it.. I've squeezed the little fish clip to tighten it up and it helps but eh.. I just wish there was a better attachment for the front pin.

I consider it the weakest link because of how easily it seems to be lost and the potential for the front pin to slid out and because lost, allowing the upper to just slid off. As per murphy's law it would be the worst time possible for that to happen.
 

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Only lost one, but on my lower that has a problem with it staying put, I've nearly lost the replacement several times. The potential for a snap seams reasonably likely when thinking about it.. I've squeezed the little fish clip to tighten it up and it helps but eh.. I just wish there was a better attachment for the front pin.

I consider it the weakest link because of how easily it seems to be lost and the potential for the front pin to slid out and because lost, allowing the upper to just slid off. As per murphy's law it would be the worst time possible for that to happen.
Ah...I can see where you're coming from then. I've never lost one or heard of anyone else having an issue.

But rather than a hollow tube...why not replace it with a appropriately sized/grade solid bolt and nyloc nut? You could get fancy (but weaker) with a sleeve and a solid bolt...the sleeve being the exact size of the lower's width....

Just brainstorming...haven't actually looked at this issue with a lower in hand.

But as chowchow said...it's no longer a tool-less affair to swap and if you cinch in down too tight...you may not be able to hinge it if you need fast access to the FCG (say a popped primer or debris).
 

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Discussion Starter · #6 ·
All excellent points, and I feel chowwows about loosing the toolless aspect being the biggest.. and I had thought of a solid bolt first but then thought the hollow tube might be sleeker.. I may play with options if it continues to be a problem... Also I wonder about drilling a small hole through the take down pin so a codder pin like holds in the trigger pin could be used..
 

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I recently experimented with tightening up a loose set of receivers which had a little slop. Produced several years apart so there was just enough movement to trigger me. I used liquid electrical tape to add a thin layer of material to the rear receiver contact point and eliminated all of the slop. Since the front pin isn't exposed to high temps you could try adding some material to it to tighten them up. I've always had tight front pins, even on my high round count gun.
 

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Discussion Starter · #8 ·
I had not even considered the pin being undersized. I've just been under the assumption the little clip was my problem. Later when I've got some time to play with it I'll swap pins from another gun to see if it solves the issue.
 

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For the record....some of mine are STUPID tight.....like, need a bullet to push them out.
 

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Discussion Starter · #10 ·
I wouldn't be opposed to tighter like that. The current pin can be pushed loose when gripping the mag well of the gun.
 

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For the record....some of mine are STUPID tight.....like, need a bullet to push them out.
I have one which can be removed by hand and one that definitely needs some help. Both seem to lock the receiver up tight so there's no movement at the front
 

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So I went to the Home Depot looking for replacement retaining clips for the front takedown pin and found them and the proper name for the part: they are zinc-plated 7/32" hitch pin clips. Something tells me they are not quite exact to the default clips that RA provides but they clip on securely and work to retain the front takedown pin while allowing you to back it in and out by hand. You get 2 clips for $1.04. I haven't shot with the Home Depot clip on but I know the clip's area of responsibility doesn't interact with the rifle's recoil. They are a bit tighter but, again, they still fit and I suspect they would be less likely to pop out and get lost while swapping out the upper.

Pictured below are the default clip (left) and one of the replacements (right).

Font Material property Gas Technology Temperature
 

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Discussion Starter · #13 ·
Thank you, I'll have to go by my local hardware store and pick up a few for spares. Certainly easier than trying to reinvent the wheel.
 

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Yeah, so the diameter of the groove where the clip sits in on the takedown pin is .218" according to my calipers, which is just about 7/32" that the clip is designed for. I needed a small flat head screw driver to extract the clip out after, but it still did the job. I figure that the original clip is wider to allow for the pin to pull out but the replacement is able to stretch open a bit for you to pull out the pin, and I figure the tightness will help a little to prevent the pin from walking out due to recoil.
 

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Yeah, so the diameter of the groove where the clip sits in on the takedown pin is .218" according to my calipers, which is just about 7/32" that the clip is designed for. I needed a small flat head screw driver to extract the clip out after, but it still did the job. I figure that the original clip is wider to allow for the pin to pull out but the replacement is able to stretch open a bit for you to pull out the pin, and I figure the tightness will help a little to prevent the pin from walking out due to recoil.
Or the stretch fatigues the metal and it breaks.....double edged sword and a materials engineer (specializing in spring steel with FEA and FMEA) is likely what's needed to determine which is actually better. Trial and error may have to suffice in this case though...
 
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Or the stretch fatigues the metal and it breaks.....double edged sword and a materials engineer (specializing in spring steel with FEA and FMEA) is likely what's needed to determine which is actually better. Trial and error may have to suffice in this case though...
Good point. I took my rifle out with the new clip and it seems to have held tight; I'll keep it on that way and see how things go from there. From what I understand about spring steel (if the clip is actually made from that) as long as the spring isn't being consistently compressed and stretched, it will hold it's strength for a long time whether relaxed or compressed. That's why people can get away with storing their magazines full of bullets without wearing the spring, or old toys that haven't been played with are still springy; as long as the spring isn't seeing that much activity, it will last. Frankly, it's a low-stress job that the clip has to do, so unless you are constantly pulling the takedown pin in and out everyday, I would not be worried about it.

Come to think of it, the hammer pin has a retaining clip too, it's an R-clip/hairpin cotter. I better look around Home Depot again for other replacement hardware we could use. It beats waiting for RA to ship them to you, tends to be cheaper too.
 

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Good point. I took my rifle out with the new clip and it seems to have held tight; I'll keep it on that way and see how things go from there. From what I understand about spring steel (if the clip is actually made from that) as long as the spring isn't being consistently compressed and stretched, it will hold it's strength for a long time whether relaxed or compressed. That's why people can get away with storing their magazines full of bullets without wearing the spring, or old toys that haven't been played with are still springy; as long as the spring isn't seeing that much activity, it will last. Frankly, it's a low-stress job that the clip has to do, so unless you are constantly pulling the takedown pin in and out everyday, I would not be worried about it.

Come to think of it, the hammer pin has a retaining clip too, it's an R-clip/hairpin cotter. I better look around Home Depot again for other replacement hardware we could use. I beats waiting for RA to ship them to you, tends to be cheaper too.
Yes, cycling causes fatigue in spring steel. However, every time you fire the weapon, you are potentially loading a clip like that...granted, not in a substantial way...but it still has the potential.

All springs are not created equal. Just something to keep in mind.
 
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