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What makes a good collapsable stock? One that's rigid, offers a good cheekweld surface, has a solid, simple locking mechanism and the ability to hold up to bumps and drops inherent to battlefield conditions.
 
Solid lockup can be had across the board, but look for a secondary friction lock if you get annoyed by rattling. Though, that rattle also equates to a tiny amount of play in the system and could have an effect on the rifles accuracy when taken to extremes.

Sling attachment points should suit your carry and shooting style. Tube tops should be smooth and fit your face. That goes for the hairy among you, interruptions in the cheekweld surface will pull beard hair and cause a loss of concentration. Of course, weight and size are constant considerations, and modularity fits here, too. Some stocks have removable storage that can be pulled to save ounces if not needed.

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Metrics:
We gathered data from the test samples. You can compare them to the specs posted on the manufacturers sites but specs between manufactures can vary innocently due to differing methods and configurations. Size and weights are straight forward, but we'll explain slop and deflection. Play is the amount of travel the stock has back and forth without using the adjustment mechanism. Deflection is the amount the stock moved vertically when we hung a ten-pound weight from the rearmost point on the stock. Measuring deflection gives you an ideahow rigid a stock is. Similarly, the amount of play in the stock also relates to its rigidity. As for a visual comparison, the photo above shows all the stock's shoulder pads to scale.

The Drop Test:
We are not a government lab. We don't want you to think that we walk around in lab coats and and have robots stirring our coffee. For our "GearScout Grinder" tests, we come up with some real-world scenario that challenges equipment and figure out a way to approximate it using the resources at hand

In this case, we figured a likely way guys might damage a collapsible stock would by from dropping a rifle while dismounting from a tall vehicle like an M-ATV or the back of an LMTV. We came up with a 3 foot drop figuring it was punishing enough to provide meaningful data without worrying we'd smash all the stocks on the first drop.

We didn't want to risk trashing the extension threads on GearScout's own lower receiver by subjecting it to hundreds drops. (Note to self: get a donor receiver for the next test!) So, we made a simple 8lb test fixture from a three foot section of black pipe. We used the weight of a loaded M4 with light, laser, optics, BUIS and sling as a our basis to get to 8 pounds. To make the fixture, we had a machine shop cut a hole in a pipe endcap and we used a pair of castle nuts to secure the extension. In hindsight, we realized this fixture will impart a stronger impact than a real rifle that weighs the same since the moving mass of the bolt carrier group would be buffered by the buffer assembly. While the mass is the same, the impact impulse is more violent than would be experienced by a functioning firearm.

To keep things fair, we used brand new 6061 aluminum receiver extensions, provided by DS Arms, for each stock's moment of truth. The extensions all held up as expected. An interesting aside, I hear guys talk about the need for stronger 7075 aluminum tubes and can now say that tube strength isn't really an issue, at least in dead drops. Butt stroking and taking a hit from the side may be a different story, but as for drops, the tubes weren't a definitive point of failure. We saw the extension adjustment holes did become a factor when testing the Troy Battle Ax. The Battle Ax's adjustment pin was so strong that it sheared the softer aluminum between adjustment holes. It may have done better with a 7075 tube. Or, it may have chipped the metal instead of shearing it away... it's hard to tell.

Once the stocks started dropping, it became apparent that they weren't going to just go until they exploded into plastic bits. This partial death added an unexpected data point to our collection and interpretation effort. A few "broke" outright but many gave up slowly as adjustment pins bent and polymer caved after repeated drops. So we decided to collect two data points to describe the damage timeline. The first we'll call the point of compromise, the second we'll call failure.

Compromise means the point at which something bent or broke but didn't immediately collapse the stock. The stock would still hold an adjustment and could fight on, though, with some hindrance to operation. Failure meant the stock either simply collapsed or it could no longer be relied on to hold it's position.

Looking at the photo gallery for each stock, the unmolested stock is shown first. The last two photos in each set is shows the shape the whole stock was in at the end of the test followed by a closeup image showing where the stock failed.

Keep in mind, we used a sample size of one for each test subject. Rifles rarely get dropped exactly vertically onto a hard surface. It's rare for a stock to fail in the field, yada, yada, yada... but we offer our test as a way to see just what will kill a stock. Since our protocol was uniform across the test subjects, our data should give you an idea how each stock deals with a similar and repeatable impact. Also, since our test is using a surrogate instead of a real rifle, our numbers are not going to relate to drop test results you may find from .gov and .mil testing. Our test was much more brutal, so the drop numbers will be low.

B5 Systems Enhanced SOPMOD Stock
The Enhanced SOPMOD has attracted a lot of attention because it's nearly a clone of the more expensive Lewis Machine & Tool SOPMOD stock. The stock looks just like the stock Crane spec'ed for the SOPMOD kit but costs 2/3 the price. A broad top with integral battery tubes and heavy duty polymer construction make this feel distinctly untoy-like feel. There's no friction lock, but the tube fits tight enough that there isn't any rattle. In fact, it's hard to operate out of the box, but I feel it loosening up with some use. There's some refinement missing when you look closely, like rounded edges and stippling on the adjustment lever, but for raw talent and performance, this can be overlooked.
Tube: Mil-Spec only
Length C/O: 8.4"/11.6"
Weight: 342gr
Play: 1mm
Deflection: .84mm
Sling Attachment: QD, slot
Price: $120
Drop Test Performance: The B5 adjustment pin bent on the first drop and then held in place for another 7 drops before it broke free. Looking at the adjustment holes in the receiver extension, we could see that the pin head dragged all the way down, gouging the aluminum until it closed.
Manufacturer comment: "We already use a harder pin than Crane spec'd but maybe we'll look at using an even harder pin."
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DS Arms M4 Stock
The DSA stock is a gen 1 design, it's a part that meets a performance level at the lowest price. If you end up with one of these on your rifle, and it works, don't knock it. Just don't expect it to withstand a lot of abuse or offer any of the frills of a higher end stock. But, for the price, it's not a bad option if you just need to get a build done and plan on upgrading at a later date.
Length C/O: 7.8"/11.2"
Weight: 200gr
Play: 1mm
Deflection: 0.7mm
Sling Attachment: Slot/loop
Price: $50
Drop Test Performance: The DSA adjustment pin broke and the lever fell off on the first drop, but the head of the pin stayed in place for 2 more drops before the stock finally collapsed. The pin held its position long enough to score 3 drops, but the stock would need to be replaced  ASAP after taking only one hit.
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ERGO F93 Pro Stock
I just got the memo; The F93 design is the predecessor to the Magpul UBR. The design was sold to ERGO after Magpul updated the MSS design to created the UBR. The F93 is a still magnificent bit of engineering and it gets close to the functionality of the UBR $100 cheaper. It's not nearly as refined; you'll have to deliberately engage the locking lever in a forward position to keep the stock from opening. (That fact is something worth mentioning in the stocks instruction manual... if ERGO included one.) But it's stiff as hell and the price (and weight) reflects an integral receiver extension.
Tube: Integral
Length C/O: 8.75"/12.6"
Weight: 657gr* includes integral Rec. Extension.
Play: 0.65mm
Deflection: 0.89mm
Price: $166
Sling Attachment: QD, 2x Sling
Drop Test Performance: The F93 pretty much broke on the first drop. We checked to make sure the lever was in the forward, locked position before dropping it. The latch system cracked, allowing the catch to slide past the adjustment teeth. There was enough meat left in the latch to hold on for one more drop, though.
Manufacturer comment: GearScout spoke to ERGO's leadership at SHOT Show last week and they were eager to get a look at the failed latch. I was ready to get clubbed and dragged away as I approached their booth. To their credit, they took a look at the damaged latch and issued a sigh of confirmation. They explained they'd already been talking about improvements to the stock since we'd posted our teaser video before SHOT. They are already reformulating the polymer used in key, high-stress areas of the stock to address the broken latch the F93 suffered in our drop test. They also plan on including some instructions on the stock's use.
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LMT SOPMOD
The original Crane SOPMOD stock was designed with direct input from the special operations community and has become a standard fixture on serious rifle operators throughout the US Department of Defense. The pedigree is hard to argue. It's a substantial feeling stock with great cheekweld and few frills. The battery tubes are a nice addition, but are easily ditched if weight is a concern. The locking mechanism means  you have to pull the stock off the receiver extension to get in to them, though.
Tube: Mil-Spec
Length C/O: 8.25"/11.5"
Weight: 328gr
Play: 0.6mm
Deflection: 0.8mm
Sling Attachment: QD, Slot
Price: $199
Drop Test Performance:  The adjustment pin on the LMT bent after the first drop. We couldn't move the stock after that. So, we dropped it 5 more times before it collapsed. The failure mode is identical to the B5. Once the pin bent it gouged its way along the adjustment channel till the pin, or what was left of it's head, gave up. With a new pin (and a bitchin' set of tools), the stock could probably be put back into service.
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Magpul ACS-L
If you like a little more cheek real estate and some storage on your stock, but don't need battery tubes the Adaptable Carbine Stock-Light (ACS-L) is your stock. A shielded operation paddle lets you put your support hand under your stock without inadvertently opening or closing your stock as you send your shot. The single, reversible QD cup isn't set into the stock body and stands proud, but didn't get in the way during our quick trip to the range. But, it does worry me a little that it's so tall that it could be bent/levered accidentally.  It's also one of the longest stocks in our roundup, could be a pro or a con depending on your anatomy.
Tube: Mil-Spec or Commercial
Length C/O: 8.75"/12.15"
Weight: 357gr
Play: 0/1.32mm Friction lock engaged/not engaged
Deflection: 0.9mm
Sling Attachment: QD, 1x Slot
Price: $100
Drop Test Performance: The adjustment pin on the ACS-L began to bend and blocked normal stock operation after the third drop. On subsequent drops, the pin continued to bend and eventually broke, trapping the head inside the tube when the stock collapsed after the sixth drop.
Manufacturer comment: While we am certainly pleased that Magpul products took the top two spots in this test, we would urge shooters to think hard about what actually matters in terms of performance and feature set, rather than basing their decision on a factor that may prove inconsequential to them.  For some end users, drop test performance is a KPP that must be met, but customer reports of broken Magpul buttstocks of any type are incredibly rare, and almost always related to various types of severe misuse or abuse not duplicated in this type of study.  As such, many shooters place drop test performance lower on their list of priorities, behind factors such as adjustability, size, weight, sling attachment(s), cost, etc.
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Magpul CTR
The Compact/Type Restricted (CTR) (and it's friction lock-less sibling, the MOE) is very popular thanks to its light weight, compact size and shielded operation paddle. The successful design has spawned some flattering homages but the original stands tall with it's ambidextrous friction lock and uninterrupted top. The December '11 price drop from $100 down to $80 makes it hard to turn away from the original, too.
Tube: Mil-Spec or Commercial
Length C/O: 7.75"/11.2"
Play: 0/0.92mm Friction lock engaged/not engaged
Deflection: 0.68mm
Weight: 252gr
Sling Attachment: QD, 2x Slot
Price: $80
Drop Test Performance: The adjustment pin wrenched out of place after the first drop, giving the stock free reign to slide along the extension. But, the friction lock held up making the stock usable for a few more drops. Subsequent abuse saw it shed the adjustment lever and finally tear the body apart at the pin socket after the fourth drop.
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Magpul STR
The Storage/Type Restricted (STR) gives you a mid-weight stock with a place to shove a pair of AA or CR123 batteries on each side. The front AA rattles a little, but the CR123s fit well after adding half of a foam earplug to take up a little extra space in the almost ingeniously designed cap. I didn't find the seam between the top tube and the batter tube to trap facial hair. One PIA to note is the recessed main cross pin. You can't get your fingers under the battery tube to pull the ears down when installing or removing the stock. It's not a concern during operation, but only during maintenance. Ironically, I think this ended up contributing to the stock's good performance in the drop test.
Tube: Mil-Spec or Commercial
Length C/O: 8.25"/11.5"
Weight: 351gr
Play: 0/ 0.72mm Friction lock engaged/not engaged
Deflection: 0.7mm
Sling Attachment: QD, 2x Slot
Price:$100
Drop Test Performance: The STR did well, I think because the battery tubes pinned the sides of the adjustment lever in place and made for a slightly more rigid assembly than the other Magpul stocks using the otherwise identical system. The mode of failure was the same as we found on the CTR, it just took a lot longer to get there. It went eleven drops before the adjustment lever cracked and broke away and the adjustment pin shifted so that the stock couldn't be adjusted. The stock fully collapsed after drop fourteen, though it began creeping closed on drop twelve.
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Magpul UBR
The Utility/Battle Rifle (UBR) is one MFer of a stock. This beast is the stock of choice for those that want a fixed feel in a collapsible format. It's unique in that the cheek-weld surface stays put as you draw the stock out. It's also about as solid a collapsible stock there is thanks to the double cam-action locking pawls that snap into place like an alligators jaw. The setup comes with a proprietary receiver extension tube that mates up and locks the stock in place without staking or Loc-tite. If you want to dump a few ounces, the storage compartment is easily removed. You can also add an aluminum strike plate if you want to trade a little weight for some added aggression.
Tube: N/A (Proprietary)
Length C/O: 8.5"/11.3"
Weight: 666gr stock only/ 747gr w/proprietary rec. extension
Play: 0mm
Deflection: 0.65mm
Sling Attachment: 2x QD, 1x slot
Price: $265
Drop Test Performance: It's hard to place the UBR in the same class as those that use a standard receiver extension, but since the stock is obviously handicapped by its substantial weight and high price I don't feel it's necessary to do so. The UBR is unquestionably strong, so strong that even in its death throe it reached out and claimed the life of an innocent GoPro camera we tried to use to document the stock's demise. It took a ten foot drop to kill it; and that was after two-hundred 3-foot drops. The failure point was the rail channels that hold the upper part of the stock as it slides open and closed. The rail is made from polymer with a metal core that can be seen in the damage photos. When the polymer split, it allowed the upper portion to ride out of the track, seizing up the mechanism.
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Rogers Super-Stoc
The Super-Stoc is the lightest stock we looked at by a good margin. It's strongest marketing points are it's weight and adaptability. It'll fit a mil-spec or a commercial receiver extension with a few minutes of screwdriver work. It's got a shielded operation paddle, configurable and adjustable friction lock, and top mounted sling loop and a QD point, though it's the lowest mounting point in the group. This could make top heavy rifles, say those with tall optics, to want to flop when carried across the chest. But, you're getting a light package with slid rigidity at a great price.  One concern we had after some range time is the friction lock lever. It's fairly easily dislodged.
Tube: Mil-Spec and Commercial
Length C/O: 8.25"/11.6"
Weight: 188gr
Play: 0/1.0mm Friction lock engaged/not engaged
Deflection: 0.7mm
Sling Attachment: QD, 1x Slot
Price: $80
Drop Test Performance:  The adjustment pin began to shift after the first drop, though the stock still worked. The second drop caused the adjustment lever to break off and the third crushed the plastic backing that holds the adjustment pin in place. With the housing compromised, the pin was able to rotate out of the adjustment holes on the extension.
Manufacturer comment: Bill Rogers liked our test. He said the results largely lined up with his own testing. Though their sample size was much larger and their methods were different, the determination of strength and the mechanism of failure was the same. He pointed out, and I agree, that inches and ounces make a huge difference in these tests. A stock dropped from 3' will bounce unharmed all day, while raising the drop height by as little as 1" caused plastic splintering trauma.
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Colt Super-Stoc
This is the OEM version Colt is buying for their carbines. This version has no shim or adjustment to accommodate a commercial sized receiver extension tube. With fewer parts, this simpler OEM design barely edges out the convertible version in strength. These OEM stocks are easily identified by their Colt branding. Like the Rogers version, the friction lock is a point of concern. Out of the box, the friction lock lever felt a little too tight. Ten seconds with a screwdriver brought a much better feel to the lever. Though, a bump or drag still knocked the lever into the open position.
Tube: Mil-Spec and Commercial
Length C/O: 8.25"/11.6"
Weight: 186g
Play: 0/1.0mm Friction lock engaged/not engaged
Deflection: 0.7mm
Sling Attachment: QD, 1x Slot
Price: $N/A OEM only
Drop Test Performance:  Despite the numbers looking close, the Colt Super-Stoc did hold up a little better than the Rogers version. The mode of failure was similar --the plastic behind the pin gave out and the adjustment lever snapped off. The stock died slowly, with a shifting pin beginning after the first drop. We called failure when the stock showed obvious signs of movement down the tube after the third and fourth drop. Though, it could probably be shot like this it would no longer reliably hold a selected adjustment setting even with the friction lock in place. The Colt version of the stock has a little more plastic and a few less parts to bang around, namely the commercial tube shim, so it makes sense that it fared a bit better.
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Troy Battle Ax CQB Stock
This is the storage stock that spoke to us the most. It's smooth, overbuilt and has a nearly elegant design aura. (Remember, Parisians wanted to tear the Eiffel Tower down for years after it was built... ) There are no angles to snag and no recess to catch beard hair. But she's a heavy bitch. That aluminum-zinc butt plate is unique in the market and its durable as hell. But it weighs a ton. There is more evidence of Troy's dedication strength in the aluminum tube liner. The solid metal-on-metal contact with the receiver extension tube is also only seen here. The  metal tube liner rattles a little; we can live with that. But, I want a more tactile activation lever and a polymer door to cut the weight. And, a slightly easier way to open the storage door. It's a real pain in the ass to open even with a knife hilt. If you're wondering what CBIR stands for, it's Chemical, Biological and Impact Resistance. We asked.
Tube: Mil-Spec only
Length C/O: 7.5"/10.75"
Weight: 586gr
Play: 0.59mm
Deflection:  0.65mm
Sling Attachment: 3x QD (1QD included), 1x slot, HK hook
Price: $125
Drop Test Performance: The Battle Ax was a bit of a brain tease. When it failed, it was hard to figure out what happened because there wasn't any obvious signs of trauma on the adjusting mechanism right up until, and even after, the stock failed on the 3rd drop. The stock ate the 6061 aluminum receiver extension holes. At first I was happy to chalk this up as a simple case of the softer metal in the extension failing before stock. But, I used the same stock on a new extension and found it slipped between settings with a little thumping. So, the stock was damaged, just not severely. Ultimately, the short stroke of the adjustment pin, the pin's sharp top and the strong but inflexible metal channel inside the stock meant the design is simply hard on receiver extensions. While the stock didn't splinter or break in a dramatic fashion, it did suffer enough damage on its own to combine with the damage it inflicted on the extension to cause it to fail.
Manufacturer comment: Troy told us they are looking at the retainer pins to see if there were some tolerance differences in the last batch of pins. Their engineers really want to see the stock as well to compare it to older version. They tell ua they have not had any prior complaints about this to date. They are planning on trying to replicate our test and see if they can identify the issue on their end.
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VLTOR EMOD
The IMOD's big brother shares all of the IMOD's designs and adds a little more than an inch to the stocks length. It also adds a storage box (suitable for earplugs), a steel strike plate at the bottom and a modified, flat operation paddle. I'm not a fan of the flat paddle, it's not as easy deploy because you can really only use your finger tips. Broad top with the battery tubes makes a great cheek weld, just like on the IMOD, but those slots grab beard hair like Velcro grabs fuzzy.
Tube: Mil-Spec or Commercial
Length C/O: 8.8"/12.1"
Weight: 391gr
Play: 0.8mm
Deflection: 1.31mm
Sling Attachment: QD, 2x slot
Price: $95
Drop Test Performance: The pin on the EMOD bent on the first drop. The stock wouldn't adjust after that. The second drop must have sheared the pin because the stock slammed closed. With no signs of trauma, we took the battery tubes off to see if we could identify the point of failure. There were two slight cracks running up the side of the stock walls from the pin slot. That gave the extension enough room to slide over the bent, and likely cracked, pin.
Manufacturer comment: VLTOR responded, "Though your test is consistent, I (and others) may think that the test criteria is actually not "real world" scenario or Milspec standards. Also, an 8 pound fixture? Not an 8 pound gun? The fixture could easily create forces/reactions that a rifle would not when impact occurs." We agree.
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VLTOR IMOD
You have to admire the IMOD for its strength to weight ratio. The secret sauce is a metal plate that diffuses the load placed on the locking pin. It's been a popular stock for years for a reason. It works. It's super-compact, has a positive, large operating lever, albeit an unshielded one. This is only an issue if you support the buttstock with your offhand in the prone. Still, it's light, has removable battery tubes and comes with a rubber buttpad (my first IMOD didn't). Our only real gripe with the IMOD? It grabs beard hair, relentlessly.
Tube: Mil-Spec or Commercial
Length C/O: 7.75"/11"
Weight: 272gr
Play: 0.9mm
Deflection: 0.67mm
Sling Attachment: QD, 2x slot
Price: $120
Drop Test Performance: The adjustment pin bent on the third drop and the housing that surrounds and holds the reenforced metal pin sleeve actually gave out on the fifth. While the metal square is there to keep the pin from tearing through the plastic in exactly the same manner of failure as seen on other stocks in the test (like the Super-Stoc and and CTR), the polymer housing wasn't strong enough to prevent the reenforced assembly from tearing out of the body.
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Conclusion: If you can afford the weight and the price, the UBR is the Rolls Royce of collapsible buttstocks. No question. But, it's not a drop in replacement since it has a peculiar receiver extension. Moving down the line from there things get very messy and generically ranking these stocks is nearly impossible since there is such a wide degree of features and performance factors to evaluate.

But, one way we tried to make sense of the figures was to use our 8th grade math skills to come up with some ratios based on performance.  Our first ratio is the tried-and-true strength to weight ratio. We based this on the number of drops to failure with the resulting rank seen on the left, below. We then ranked them using number of drops to compromise with the results in the right column, below.

  Strength/Weight to failure Strength/Weight to compromise
1 Magpul UBR Magpul UBR
2 Magpul STR Magpul STR
3 B5 Systems SOPMOD Colt Super-Stoc
4 VLTOR IMOD Rogers Super-Stoc
5 Magpul ACS-L Magpul ACS-L
6 Colt Super-Stoc VLTOR IMOD
7 Rogers Super-Stoc Troy Battle Ax CQB Stock
8 Magpul CTR DSA CARM4RIB
9 LMT SOPMOD Magpul CTR
10 DSA CARM4RIB LMT SOPMOD
11 Troy Battle Ax CQB B5 Systems SOPMOD
12 VLTOR EMOD VLTOR EMOD 
13 ERGO F93 Pro

ERGO F93 Pro Stock

If we substitute price for the weight, we get the cost per drop based on drops to failure, below left, and number of drops until compromised operation, as seen in the right column. Note that there are only 12 stocks listed here because the Colt Super-Stoc doesn't really have a price since it's an OEM product.

 

Cost per drop to failure Cost per drop to compromise
1 Magpul UBR Magpul UBR
2 Magpul STR Magpul STR
3 B5 Systems SOPMOD Magpul ACS-L
4 Troy Battle Ax CQB Stock Rogers Super-Stoc
5 Magpul ACS-L Troy Battle Ax CQB Stock
6 DSA M4 CARM4RIB DSA M4 CARM4RIB
7 Magpul CTR VLTOR IMOD
8 VLTOR IMOD Magpul CTR
9 Rogers Super-Stoc VLTOR EMOD
10 LMT SOPMOD B5 Systems SOPMOD
11 VLTOR EMOD ERGO F93 Pro Stock
12 ERGO F93 Pro Stock LMT SOPMOD

So, these are four ways you can use our test data to help make an informed decision when you buy the next stock. These numbers relate to the stocks performance with regard to one dimension, durability. Your adoption decision will include features and criteria based on your intended use.

Our choice for best stock comes in response to questions related to specific use. If weight and price aren't an issue, the Magpul UBR is your stock. If you're after the lightest stock, the Rogers Super-Stoc has a killer strength to weight ratio. If you like storage, check out Magpul's STR. If you want a battle proven pedigree, the LMT SOPMOD and the VLTOR IMOD show they can take some abuse and keep fighting.