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Posted: 12/5/2016 9:11:20 PM EDT
| I assembled my lower last night and used all quality parts, including BCM buffer Kit, Mega lower and IWC rotation limited QD end plate. The tab on the inside of the end plate slid into the groove on the buffer tube and the raised edge around the QD hole on the end plate fit into the hole in the back of the receiver, so from the receiver to the buttstock, everything should be lined up perfectly. I tighted down the castle nut to 40 foot pounds and staked it. If I turn the rifle upside down and look down the rifle from the buttstock to check the vertical allignment of the buttstock and the grip, the grip is at a very slight angle to the buttstock, with the grip tilting to the left of the buttstock. This suggests that there is either some normal play in the way these parts go together, one of the parts is out of spec, or something twisted while tightening the castle nut. Is it normal for that alignment to be rotated slightly? It's not off by very much but of course I noticed it immediately. Since I already staked the castle nut, I don't really want to take it apart at this point unless this poses a bigger problem with the function of the gun but I can't imagine it would. It's just aesthetically displeasing to me. |
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I assembled my lower last night and used all quality parts, including BCM buffer Kit, Mega lower and IWC rotation limited QD end plate. The tab on the inside of the end plate slid into the groove on the buffer tube and the raised edge around the QD hole on the end plate fit into the hole in the back of the receiver, so from the receiver to the buttstock, everything should be lined up perfectly. I tighted down the castle nut to 40 foot pounds and staked it. If I turn the rifle upside down and look down the rifle from the buttstock to check the vertical allignment of the buttstock and the grip, the grip is at a very slight angle to the buttstock, with the grip tilting to the left of the buttstock. This suggests that there is either some normal play in the way these parts go together, one of the parts is out of spec, or something twisted while tightening the castle nut. Is it normal for that alignment to be rotated slightly? It's not off by very much but of course I noticed it immediately. Since I already staked the castle nut, I don't really want to take it apart at this point unless this poses a bigger problem with the function of the gun but I can't imagine it would. It's just aesthetically displeasing to me. You needed to visually verify alignment before finalizing your torque and staking - more than enough tolerance in in-spec parts for things to be canted if you're not double-checking everything. Rifle tubes and stocks are idiot-proof, but not carbine tubes and stocks. |
| I guess if it's just due to play in the tolerances, I can live with it since you probably wouldn't notice unless you were looking for it. Of all the instructional videos and literature that I used prior to and during assembly, not one of them ever mentioned checking the alignment, so it never even occurred to me. Even if you lined everything up before tightening, wouldn't the force of tightening to 40 FP twist it back out of alignment anyway? |
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You might want to loosen the castle nut (spanner nut), then realign things up correctly. If your collapsible stock has a large flat spot up on top (at 12:00 O-Clock position), a lot of traditional CAR stocks and M4 stocks have a large flat spot on top at the front where the charging handle is manually cycled over the top, if the alignment of this flat spot on top of the stock is not on the same plane as the top of the lower receiver then you can bend and twist the charging handle which can result in either a broken charging handle or malfunctions when manually cycling the rifle.
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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Yeah, your pics won't show until approved by team members (post count under 50)
I see it, personally I would loosen, remedy, and re-stake, my OCD would force me. Honestly, I don't stake mine anymore. I dont plan on any hasty exits from helos/humvees in the immediate future. I have not had one come loose in 22+ years. |
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http://i.imgur.com/4nuYmN6.jpg Here's a pic that shows what I'm talking about. The butt stock is a Magpul STR, so no problems with the charging handle. Overall, I think it turned out pretty nice. http://i.imgur.com/AUKfkoZ.jpg (In the post preview, the images were there. Now they're just links.) I use a couple of small handheld levels when throwing things together. A million to one chance but you don't have a commercial stock on a mil-spec buffer tube do you? |
| Nope, it's a mil-spec stock. It's really not that noticeable, so I'm not going to worry about it too much. I would be worried if I bent or twisted something but it sounds like it's just the normal tolerances that allowed it to move a little while tightening. It actually probably gives me an ever so slightly better cheek weld. Yea, that's it.....a better cheek weld! Don't you all go out and cant your stocks now. |
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The spec is 40 INCH pounds. If you used ft-lbs you overtorqued by 12X. Seen this happen a few times on the site and will give you a canted stock. It shouldn't be a function issue though. It's 40 foot pounds. That manual with inch pounds listed is incorrect. |
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As you tighten the castle nut, it tries the turn the tube, since it's already backed up to the end plate. Even with 40 ft/lbs, you can EASILY gall the tube threads from the end plate locator nub. The tube can move a little (from tolerances of nub and tube) or a LOT (once the nub crushes the tube threading edges). This is also very common when disassembling or changing an RE (receiver extension or buffer tube). I keep extra RE's on hand and usually just toss the old one and replace with new one when reinstalling the set up.
Also, as another mentioned, I grip the tube with one hand while wrenching the nut with other (and yes, I realize that sounds like a dirty joke  )
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40 ftlbs is a hell of a lot of torque for a thin aluminum tube. I know from experience that going anywhere near that amount gave me a canted stock. When I removed it the tube threads were damaged at the end plate slot. This was a BCM tube.
I have never had a problem with a staked stock coming loose but I admit I use more than 40inlbs. Do we have confirmation that 40ftlb is indeed the spec? |
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40 ftlbs is a hell of a lot of torque for a thin aluminum tube. I know from experience that going anywhere near that amount gave me a canted stock. When I removed it the tube threads were damaged at the end plate slot. This was a BCM tube. I have never had a problem with a staked stock coming loose but I admit I use more than 40inlbs. Do we have confirmation that 40ftlb is indeed the spec? A pickle jar is tighter than 40 inch pounds. |
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Basic rule for installing a carbine receiver extension,
Pull the butt stock off the tube before the install, so you can use the bottom lug for the butt stock on the tube to align the tube to the lower receiver when you are tighten the castle nut. If you don't have a lower armor block, then you may need a third hand to help hold the tube to receiver as you are tighten the nut. Hence never trust the slot in the tube, and the tab in the back plate, to hold the tube in the correct position to the lower receiver as you are tightening the castle nut isntead. |
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If you want to make sure the back-plate does not damage the threads on the tube place a small amount of grease or Aeroshell on the castle nut and backplate where they meet when tightening/ torquing.
By using this trick it allows the castle nut to rotate on the backplate and not bind up once they meet and torque is applied. Otherwise when they come into contact the parkerizing acts like a strip of of sand paper and they bind together and cause the back plate tab to turn with the castle nut on the tube, and damage the treads and result in misalignment. |
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If you want to make sure the back-plate does not damage the threads on the tube place a small amount of grease or Aeroshell on the castle nut and backplate where they meet when tightening/ torquing. By using this trick it allows the castle nut to rotate on the backplate and not bind up once they meet and torque is applied. Otherwise when they come into contact the parkerizing acts like a strip of of sand paper and they bind together and cause the back plate tab to turn with the castle nut on the tube, and damage the treads and result in misalignment. Great tip! Thanks for that! |
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