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Are A2 stock spacers supposed to be loose and rattly? (Page 1 of 2)
Posted: 3/29/2026 5:33:13 PM EDT
[Last Edit: 556Cliff][Edited]
Maybe @coldblue can shed some light here?  I have yet to find a combination of A2 butt plate and A2 stock spacer that doesn't rattle after the screw is tightened down. At one point I thought I had a solution by putting O-rings between the spacer and the back end of the buffer tube, but over time the O-ring gives (or takes a set) and the stock becomes loose. Since then I've been looking over shim options on McMaster-Carr to space the A2 spacer.  Most A2 spacers are close enough in length that there's not a lot of difference that can be made up by switching between brands (I've tried). The depth for the "nipple" end of the spacers between the different brands of A2 butt plates themselves varies quite a bit and that seems to be where most of the problem is.  So you can't just get one thickness of shim to take up the space... At minimum you might need shims from 0.02 all the way up to around 0.08 to fill up the free space. It's crazy to me that this is even a thing, but it is... I can't imagine that anyone has a combination of A2 butt plate and spacer that isn't a rattle trap. The plastic spacers tend to not rattle as obviously as the aluminum ones, though they're still most likely loose, they're just so much lighter in weight that you can't hear it. |
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Originally Posted By Toolman76: I use a foam washer between the extension and spacer. So you noticed the issue too.  I'm looking at nylon washers currently, but I can only get them in 0.031" (1/32") thickness, which may or may not work out for the majority of A2 butt plates I have. There's actually not a lot of washer or shim options with a 3/4" outside diameter and an inside diameter in the (preferably) 5/16" to 3/8" range that also has a lot of thickness options to play around with. If the nylon washers don't work out, my fall back will be 18-8 stainless shims, but the inside diameter is too large for my liking at 1/2". It's just kind of ridiculous... I shouldn't have to put this much thought into something that should've been ironed out back in the 80s. Plus I'm out the cost of whatever amount of money it takes to buy shims/washes to shim the A2 stock spacers. 
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You could try McMaster Carr and enter “washer” as a search term. You can select the OD and the ID that you’re looking for to see what comes up. I did and pasted the result in the link below. Maybe this will work? |
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Originally Posted By jdtbone: You could try McMaster Carr and enter “washer” as a search term. You can select the OD and the ID that you’re looking for to see what comes up. I did and pasted the result in the link below. Maybe this will work? Thanks, I’ll give it another look through. Even if I’ve already typed in my search terms and spent hours on the McMaster site on and off over the last 2 years to come up with just 2 options so far.  I’ve basically narrowed it down to possibly having to order custom shims from some place to get the thicknesses I’m looking for (which I don’t want to do). |
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Originally Posted By jdtbone: Whoops. Missed your McMaster Carr comment in the OP. RIF. Maybe glue the spacer to the stock extension? That would definitely keep it from rattling, but the free space would still need filled up so that tightening down the screw bottoms the butt plate out on something solid. |
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Originally Posted By mcantu: what does your spacer measure? the TDP has it at 0.81" tall with the "nipple" portion being 0.225" I'll have to get back to this thread with measurements. Not sure if I can get my calipers back from my brother or not yet. I did have measurements from all my spacers at one point, but never kept the notes I made. Currently I have A2 spacers from Fulton Armory, Luth-AR and I have a Brownells brand spacer (all aluminum). |
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Originally Posted By VinceU1: Have a friend 3D print a custom length spacer. That’s like the perfect use of a 3D printer. The problem is that I just don’t have a solid enough idea on what sizing is actually needed to fill the empty space correctly. And because of the differences in butt plates, there’s no one size spacer that would fit all. |
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Originally Posted By Glynn863: Never had the issue, but I only have one A2 stock, and it's a Colt. I mostly have Colt A2 stock bodies and a couple of their rifle buffer tubes, but even with those in the mix I still had to shim the spacers. I've never used all Colt for my stock parts though, so I do wonder if a Colt buffer tube, Colt A2 spacer, Colt A2 stock body and a Colt A2 butt plate would all fit together with no spacer rattle as they should. |
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Originally Posted By mech4matsnova: 3 are Colts from the 90s, one a Bushmaster, and one a Stag. The Stag came with a nylon spacer, athe others all have anodized aluminum Originally Posted By mech4matsnova: Originally Posted By 556Cliff: Do you happen to know what brand the stocks are? 3 are Colts from the 90s, one a Bushmaster, and one a Stag. The Stag came with a nylon spacer, athe others all have anodized aluminum I had a factory Bushmaster assembled rifle with an A2 stock that I bought new back in 2003 and it had a black plastic spacer. I don't recall it rattling, but at the time I was just getting into ARs so I might not have noticed. |
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Originally Posted By mcantu: what does your spacer measure? the TDP has it at 0.81" tall with the "nipple" portion being 0.225" Stole the calipers back for some measurements. Had to give them right back after I was done though. Fulton Armory spacers in the order I measured them. Overall length first, followed by the nipple end length measurement. 0.816 - 0.226 0.814 - 0.225 0.818 - 0.229 0.815 - 0.224 0.816 - 0.228 Luth-AR spacers. 0.814 - 0.223 0.814 - 0.222 0.814 - 0.222 0.817 - 0.225 Brownells spacer. 0.825 - 0.223 |
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Originally Posted By 556Cliff: I had a factory Bushmaster assembled rifle with an A2 stock that I bought new back in 2003 and it had a black plastic spacer. I don't recall it rattling, but at the time I was just getting into ARs so I might not have noticed. Originally Posted By 556Cliff: Originally Posted By mech4matsnova: Originally Posted By 556Cliff: Do you happen to know what brand the stocks are? 3 are Colts from the 90s, one a Bushmaster, and one a Stag. The Stag came with a nylon spacer, athe others all have anodized aluminum I had a factory Bushmaster assembled rifle with an A2 stock that I bought new back in 2003 and it had a black plastic spacer. I don't recall it rattling, but at the time I was just getting into ARs so I might not have noticed. My Bushmaster is from 2009. The Stag is from 2012. None rattle or are loose, you have to apply light force to get the stock moving on the tube on all of them. |
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Originally Posted By 556Cliff: Stole the calipers back for some measurements. Had to give them right back after I was done though. Fulton Armory spacers in the order I measured them. Overall length first, followed by the nipple end length measurement. 0.816 - 0.226 0.814 - 0.225 0.818 - 0.229 0.815 - 0.224 0.816 - 0.228 Luth-AR spacers. 0.814 - 0.223 0.814 - 0.222 0.814 - 0.222 0.817 - 0.225 Brownells spacer. 0.825 - 0.223 well, those are all in spec. What's next to check? The buttplate? The buffer tube OAL? |
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Originally Posted By mcantu: well, those are all in spec. What's next to check? The buttplate? The buffer tube OAL? Originally Posted By mcantu: Originally Posted By 556Cliff: Stole the calipers back for some measurements. Had to give them right back after I was done though. Fulton Armory spacers in the order I measured them. Overall length first, followed by the nipple end length measurement. 0.816 - 0.226 0.814 - 0.225 0.818 - 0.229 0.815 - 0.224 0.816 - 0.228 Luth-AR spacers. 0.814 - 0.223 0.814 - 0.222 0.814 - 0.222 0.817 - 0.225 Brownells spacer. 0.825 - 0.223 well, those are all in spec. What's next to check? The buttplate? The buffer tube OAL? Everything is suspect at this point. The only thing I’m sure of is that of the 4 different A2 but plates I have, the depth for the nipple end of the spacers is different between all of them. I suppose the buffer tubes themselves could be too short and/or the stock bodies too long. With the RRA butt plates I’d need a shim that’s possibly as thick as 0.08… That’s a quite a bit. Colt and NOS surplus A2 butt plates possibly need a shim as thick as 0.03 to 0.04. Another A2 butt plate I have from Fulton Armory can possibly get away with a shim as thick as 0.02. And that’s still leaving some free space for compression… As much as 0.01. |
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Originally Posted By mcantu: What if you remove the butt plate from the stock and assemble it to the spacer/buffer so you can see where the movement is? If you mean with no stock body present, I've done that test and there is of course no movement of the spacer since it's sandwiched between the end of the buffer tube and the butt plate all pinched together with the screw. When the stock body is in the mix and you tighten everything down with the screw is when the rattle happens. With the trap door open you can actually watch the spacer move fore and aft when tipping the lower forwards and backwards. Blue arrow pointing at the visible section of the spacer so everyone knows where to look. 
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Links to the only decent options I've found so far for shimming the spacer (internal diameter is just a bit too large for my liking). https://www.mcmaster.com/98126A653/ https://www.mcmaster.com/98126A576/ https://www.mcmaster.com/98126A453/ What I'm considering buying next since I "think" it might work with the majority of the NOS surplus butt plates that I have. > Link. |
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Originally Posted By mcantu: How long is the buffer tube? It's supposed to be 10.098" I’ll try to get a measurement on that today. Assuming that’s overall length (threads included)? Do you have a measurement for the stock without butt plate? I assume an overall length on the stock would also include the protrusion that interfaces with anti rotation socket on the lower receiver. |
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Originally Posted By jdtbone: Are Belleville washers too thick or too much of a spring force? I considered Belleville washers, I’d have to look at them again, but I think there were some that were thin enough. In the end I wasn’t sure about adding spring pressure into the mix so I decided to go with flat washers/shims. |
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Originally Posted By 556Cliff: I considered Belleville washers, I’d have to look at them again, but I think there were some that were thin enough. In the end I wasn’t sure about adding spring pressure into the mix so I decided to go with flat washers/shims. Originally Posted By 556Cliff: Originally Posted By jdtbone: Are Belleville washers too thick or too much of a spring force? I considered Belleville washers, I’d have to look at them again, but I think there were some that were thin enough. In the end I wasn’t sure about adding spring pressure into the mix so I decided to go with flat washers/shims. There is some spring pressure on the stock assembly but not very much: the rear takedown pin detent spring. Have you looked closely at your lower? Is it in spec? Swap the tube/stock assembly to another lower and see if you still have the problem. Its unlikely but Id want to rule it out. |
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Originally Posted By mech4matsnova: There is some spring pressure on the stock assembly but not very much: the rear takedown pin detent spring. Have you looked closely at your lower? Is it in spec? Swap the tube/stock assembly to another lower and see if you still have the problem. Its unlikely but Id want to rule it out. Originally Posted By mech4matsnova: Originally Posted By 556Cliff: Originally Posted By jdtbone: Are Belleville washers too thick or too much of a spring force? I considered Belleville washers, I’d have to look at them again, but I think there were some that were thin enough. In the end I wasn’t sure about adding spring pressure into the mix so I decided to go with flat washers/shims. There is some spring pressure on the stock assembly but not very much: the rear takedown pin detent spring. Have you looked closely at your lower? Is it in spec? Swap the tube/stock assembly to another lower and see if you still have the problem. Its unlikely but Id want to rule it out. With the buffer tubes and A2 stock parts I typically use on my personal builds, I've experienced the same amount of spacer rattle regardless of the lowers. I've had to use my old O-ring shim trick with A2 stocks installed on Colt, Aero, Anderson and Tactical Machining lowers. Also, sometimes I've had to do builds for my brothers and their friends and they will buy el-cheapo mystery parts a lot of the time... Mystery A2 stock kits that they have had me install (including UTG) have required the spacers to be shimmed. |
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Originally Posted By mcantu: How long is the buffer tube? It's supposed to be 10.098" Originally Posted By mcantu: How long is the buffer tube? It's supposed to be 10.098" Got some measurements... I have no calipers big enough for checking the length off of these parts unfortunately, so I used a combination square. I have an old 7075 Colt rifle buffer tube for comparison (purchased from SAW) and a few 7075 rifle buffer tubes from Brownells. Both brands measure exactly the same, at 10" and just a hair shy of 1/8". I wish I could be more precise than that. 10" and 1/8" would be 10.125", so it's got to be in the ballpark of within spec. The overall length of my Colt A2 stock bodies (including the protrusion at the front of the stock) measure 10" and 3/8" which would be 10.375" (no idea what the spec is for these though ).Originally Posted By mcantu: If you snug everything up on the entire stock assembly (screw, butt plate, stock, spacer, buffer tube) while it is not attached to the receiver, does it still have the movement? Just trying to narrow down when the problem happens I checked this out too. With everything snugged down and the buffer tubes not attached to the receiver I get the same results... Of course I can't go as tight on the screw, but the spacers still rattle. With my usual NOS surplus A2 butt plates it takes a stack 3 to 4 0.01 shims (depending if you put them between the spacer and the back of the buffer tube, or between the back of the spacer and the butt plate) to take up the free space that allows the spacer to be loose. So at this point I'm thinking the parts that are most suspect are the stock bodies and the butt plates. Seeing the variations in different A2 butt plates has me thinking it's those more than anything. Only other thing I can figure is that maybe the loose spacer was part of the design??? That’s why I was hoping coldblue could chime in. |
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Originally Posted By 556Cliff: I'll try to get a measurement on that today. Assuming that's overall length (threads included)? Do you have a measurement for the stock without butt plate? I assume an overall length on the stock would also include the protrusion that interfaces with anti rotation socket on the lower receiver. including the nub: 10.375 |
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Originally Posted By mcantu: along the top: 10.113 +/- 0.015 including the nub: 10.375 Alright, so my "including the nub" measurements are on point at 10.375". My along the top of the stock measurement is exactly at 10" and 1/8" (which is 10.125"). That leaves only the A2 butt plates as the suspect part and all four of the different types I have would have to be out of spec (including the Colt). So the only thing left that needs checked against the specs is the depth of the spacer pocket indicated in the below picture.
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Originally Posted By 556Cliff: Alright, so my "including the nub" measurements are on point at 10.375". My along the top of the stock measurement is exactly at 10" and 1/8" (which is 10.125"). That leaves only the A2 butt plates as the suspect part and all four of the different types I have would have to be out of spec (including the Colt). So the only thing left that needs checked against the specs is the depth of the spacer pocket indicated in the below picture. https://i.imgur.com/rywTWHsl.jpeg |
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Originally Posted By mcantu: 0.195 +/- 0.010 Originally Posted By mcantu: Originally Posted By 556Cliff: Alright, so my "including the nub" measurements are on point at 10.375". My along the top of the stock measurement is exactly at 10" and 1/8" (which is 10.125"). That leaves only the A2 butt plates as the suspect part and all four of the different types I have would have to be out of spec (including the Colt). So the only thing left that needs checked against the specs is the depth of the spacer pocket indicated in the below picture. https://i.imgur.com/rywTWHsl.jpeg Well, measuring the spacer pockets was interesting... NOS surplus A2 butt plate had a passing measurement of 0.191 Modern Colt A2 butt plate had a failing measurement of 0.182 Fulton Armory A2 butt plate had a failing measurement of 0.173 RRA A2 butt plate had a failing measurement of 0.233 And just for fun I checked an NOS surplus A1 butt plate that had a passing measurement of 0.202 Now I'm just more confused... Because all of the A2 butt plates (even the Colt and Fulton that have shallower spacer pocket depth) require shims to keep the spacers from being loose when everything is tightened down. So either the loose spacer is by design, or it was a major oversight that never got noticed over all these years. Either way and no matter the combination of parts, I have to shim the spacers. |
Not my video, but he noticed the same thing. AR15/M16A2 JSE Surplus Upper/PSA Lower/Fulton Armory A2 Buttstock Install w/ Spacer Shim! |
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Originally Posted By mcantu: You sure it's not noise from the trapdoor? Yep I'm sure. It happens with no trap door installed and no buffer and spring in the buffer tube. I just ordered the nylon washers from McMaster to see if they will do the trick (at least for the NOS surplus A2 butt plates that I mainly use on my personal builds). |
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There's a variety of wavy discs available that will keep the spacers from rattling. ACE should have a small selection. McMaster |
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Originally Posted By LawnDartGoalie: There's a variety of wavy discs available that will keep the spacers from rattling. ACE should have a small selection. McMaster I looked them over a few times too. Sure it would keep the spacer from rattling, but it wouldn't really give the solid backing to the butt plate directly against the buffer tube as (I'm at least thinking) was intended... Though I really have no idea what was intended since even if all parts are measuring up to the spec the spacers still have enough room (between 0.03 and 0.04) to move around. This one has me stumped. I've noticed the issue with every A2 stock that I've come accross since about 2015 at least, I'm thinking it's so weird that this loose spacer syndrome isn't more prevalent. There's a lot of ARs with A2 stocks and most guys just aren't noticing/reporting any spacer rattle. |
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They probably wanted the clearance as small as possible incase the shooter had to mortar a round, or bash the stock on something, but not so small that the parts could stack and open a gap between the shell and the butt plate. I may have missed if it's already been suggested, but peel washers like the ones used on the earlier A2s would fit in the butt plate. Attached File |
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Originally Posted By LawnDartGoalie: They probably wanted the clearance as small as possible incase the shooter had to mortar a round, or bash the stock on something, but not so small that the parts could stack and open a gap between the shell and the butt plate. I may have missed if it's already been suggested, but peel washers like the ones used on the earlier A2s would fit in the butt plate. https://www.ar15.com/media/mediaFiles/548699/peel_washers_jpg-3741505.JPG It has me wondering about the A1 stock and if there is any space between the inside of it's butt plate and the end of the buffer tube... I just don't have any A1 stocks lying around to check it out.  I considered the peel washers too, but they have the same 1/2" inside diameter as the stainless shims I have. I have the stainless shims in 0.03, 0.02 and 0.01 thicknesses. So I can determine what I need with the 0.01 shims and then stack what I need. They're actually really nice, but they'd be perfect if they came with a 5/16" or 3/8" inside diameter. |
Are A2 stock spacers supposed to be loose and rattly? (Page 1 of 2)
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