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Posted: 7/1/2025 11:24:40 AM EDT
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Thought I’d share some pics and thoughts on the two new 1913 pic rail stocks from Magpul and B5. The B5 MPS has a slightly shorter LOP when collapsed, but the Magpul UCS has a longer LOP when fully extended. The buttpad is longer on the UCS. Overall weight feels similar, but the MPS has more of a noticeable rear bias when holding both stocks in my hand. The UCS has a button/latch locking mechanism, while the MPS has the spring loaded hinge with ramped surfaces to lock the stock, although you have to push down to unlock instead of pull up like on the Sig (and many other) hinge designs. Both have non-rotating QD sockets. The MPS has one on each side with 8 detents, while the UCS has a single reversible one with 4 detents inside. The MPS has a bottom latch to lock/unlock the sliding portion of the stock while the UCS has a button on each side that must be depressed.   I mounted them both on my Kuna for a comparison.   The UCS has a downward cant when folded while the MPS is pretty much level. The MPS is left side folding only while you can invert the UCS hinge to make it right side folding if you choose.   The MPS has a built in cheek riser that adds 0.5” when raised. The UCS comes with two snap-on cheek risers of 0.5 and 0.75 height. Note that on the MPS, the cheek riser is on the fixed part of the stock. On the UCS, the riser is attached to the movable part of the stock    HTH anyone choosing between these stocks. |
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Both seem about the same in the folded position, and both lock up pretty solid in the unfolded position. One thing I’ve noticed is that you need to make sure that the USC latch is fully locked. Give it some force when unfolding to make sure the claw on the latch snaps under the mating ledge in the rear of the adapter. Otherwise, it’s not fully latched and just held in place mainly by the force of the friction between the two mating surfaces. The MPS doesn’t have this issue. It uses a ramped tab on the movable center part of the hinge that fits in a matching notch in the fixed top part of the hinge when it’s fully folded and unfolded. Pretty idiot proof with regards to being securely locked. |
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1. Will the UCS collapse and lock with the cheek riser installed? 2. I’m a lefty. Is the QD mount on the UCS reversible? Is the B5 QD on both sides (appears so)? 3. Is the B5 uncomfortable to cheek weld when extended? I would think you would want the flat surface to the rear, seems like with it extended, and even more so with it raised, it would be uncomfortable. |
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Quoted: 1. Will the UCS collapse and lock with the cheek riser installed? 2. I’m a lefty. Is the QD mount on the UCS reversible? Is the B5 QD on both sides (appears so)? 3. Is the B5 uncomfortable to cheek weld when extended? I would think you would want the flat surface to the rear, seems like with it extended, and even more so with it raised, it would be uncomfortable. 1. Yes 2. Yes to both. 3. That’s a bit of a personal preference thing on how you have it set up. I don’t run mine extended, so it’s not an issue for me. It all depends on where your shoulder is in relation to your face. People just find a comfortable position that works for them. The UCS is probably a better option if you want to run the stock extended back. |
If you’re still taking questions  Does the charging handle clear the B5 MPS when it’s folded? It looks like the buttpad may block the last half inch of travel but that could be the angle of the photo. Thinking about dumping the Kriss stock I’m using and going to one of these two. |
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Quoted: If you’re still taking questions Does the charging handle clear the B5 MPS when it’s folded? It looks like the buttpad may block the last half inch of travel but that could be the angle of the photo. Thinking about dumping the Kriss stock I’m using and going to one of these two. I don’t think it blocks the path enough to prevent manual charging or locking the bolt back, but it would be pretty awkward and uncomfortable to keep your hand from hitting the stock. Personally, I wouldn’t operate the charging handle with the B5 stock folded. Of the two, I prefer the UCS on the Kuna. |
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Quoted: I don’t think it blocks the path enough to prevent manual charging or locking the bolt back, but it would be pretty awkward and uncomfortable to keep your hand from hitting the stock. Personally, I wouldn’t operate the charging handle with the B5 stock folded. Of the two, I prefer the UCS on the Kuna. It does seem like the better option. Thanks man! 
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