Folding Stock Adapter Comparison Pt. 5


1. Doublestar ACE FSA, 2. SB Tactical BTFA, 3. Sylvan Arms FSA 4. MDT Carbine|Carbine FSA,
5. UTG/Leapers FSA, 6. XLR FSA 7. Law Tactical FSA (and clones) 8. Hera Arms

The core of the ACE is the folder to which various application specific adapters are attached.

Unlike all of the others tested so far, this unit was not purchased by me for this test. It would have been but they’re perennially out of stock. I think I have a notion of why. Such being the case, this unit was loaned to me by another member of SnipersHide rather than being purchased. You gotta love those guys at The Hide. Famous for their relentless and savage dogpiles as they are for the just stunning levels of expertise available in their number. The dogpiles usually happen because someone was talking out of their ass or just being a dick. Oddly, the stunning expertise seems to get displayed frequently for the same reasons. It’s funny that those same blunt, savage, in your face people are also almost destructively generous with their time, money and toys. Case in point: Someone noticed I was unable to get an ACE, wanted to help me finish this project and wanted to see what I might have to say about the DoubleStar ACE so, they loaned me theirs. They don’t know me from Adam but they sent me over a hundred bucks worth of goodie without a blink. I’d do the same. It’s a culture of gentlemen over at The Hide and so it’s highly intolerant of ungentlemanly conduct. Generosity is also a characteristic of gentlemen and you’ll find that there too but, in smaller quantities. Enough about the blasted forum and its population. We have goodies to review.

There’s a lot of choice in building your ACE folding stock adapter. In a way, too much choice. DoubleStar offers an aluminum unit and a steel unit and a partially-steel push-button unit and an entirely steel non-push-button unit. They also offer lugged and un-lugged versions. They have gobs of receiver blocks to sift through and there’s some overlap in application suitability. My advice, either use the recipe below or call them to help pick what you need. It’s important to know also that their use of aluminum varies between 6061 and 7075. The pushbutton units use 6061 for the generally unstressed parts and 1018 mild steel for the stressed parts. The non-steel units are 7075 aluminum and the steel non-push-button units are pure 1018 mild steel. I told you it was an embarrassment of choice. One thing to note is, given the strength of 7075 aluminum, you’d be hard pressed to need steel in its place.

I had fully planned on going pure steel and lugged because I’m brutal on my equipment. I’m the kind of guy that would happily fold my stock, hang the rifle from a 10ft tall brick wall by the folded butt stock and then climb up that bastard if I felt the need to be on the other side of the wall. That being the case it’s helpful to pick gear that will survive my attempts to destroy it. Imagine my joy to see that my benefactor in this case chose the same way. He’ll be happy too because I was not able to damage it in my testing, though I did not actually use the rifle as a ladder out of courtesy to him.

You remember back in Part 2 where I remarked about the UTG unit, “If someone were really smart they’d take this design and make it out of steel…”? Well, it’s not literally what appears to have happened but you can see how someone might spot a thematic resemblance. It’s the details that shine brilliant light on the differences and show that whatever resemblance there is between the two units, it is superficial in the extreme.


You an see the locking block poking out of the bottom, engaging with the folding arm. The locking bar and swing arm are both steel on the push-button model. The folding arm has a receiver notch to accept the locking bar so it engages on 3 faces.

Both UTG and DoubleStar make their units square shaped. Both use quite huge locking blocks. Both have extremely positive locking in the open position. That’s pretty much where all that similarity shit stops. The DoubleStar unit is clever in places; but not very clever, and they are clever with precision. The UTG unit’s design uses cleverness to avoid the need for precision. Don’t get it twisted, the DoubleStar unit’s clever parts are nothing like the really super clever bits of the MDT and XLR units but pretty darned close and a damned sight more clever than the UTG unit. Both units took extremely straightforward approaches to the hinge and the locking blocks but the DS requires precise machining due to 90deg angles in the lockup notch and locking bar, while the UTG design actually eschews that requirement by using tapered locking surfaces which are vastly more likely to gall. When you look at each detail and compare the two you get the sense that a Russian engineer did the UTG and an American Engineer did the DoubleStar. It’s the same kind of differences as between the AR-15 and the AK-47. They both do the same job but with different mindsets. An illiterate Russian farm boy would find the UTG version fit their philosophy and an illiterate American farm boy would find the DoubleStar fit their own.


A DoubleStarUSA lugged Pig Nose. Attaches to the butt stock and the swing arm.

DoubleStar’s unit is actually the most compact lengthwise of any unit tested so far. It’s only about 1/2-inch of length of pull being added, unlike the inch to 1.5 inches of the others. The locking mechanism is well shielded from gunk and dirt infiltration while in the closed position unlike the UTG which has it’s lockup area fully exposed. While we’re on the topic of the locking mechanism. Jeebus! Talk about over-strong. Both the UTG and the DS are over-strong but the DS is way way over-strong. When you look at the barrel on a Desert Eagle you get the same sensation of, “oh, that’s quite a bit beefier than it probably needs to be” as you do when you see the locking block of the ACE and the notch into which it fits. In the closed position you could probably drive a truck over it and not do too much damage. In the open position, there’s substantially less of the locking block engaged but it’s still enough that you’d be hard pressed to break it without the use of tools.

A nifty feature of the way the buffer tube adapters connect to the ACE folder itself is, you can raise or lower each end independently of the FSA itself. This means you can raise both ends thus effectively putting the folder as low as it can get and this really helps keep the knuckle banging while operating the bolt to a minimum. It looks to me like there’s more than enough material there that they could scallop or just bevel the hell out of the top corner opposite the hinge and knuckles everywhere would sing songs of praise. At least the corners are all radius-ed enough that when you do drag a knuckle over it quickly, it doesn’t take any skin off. Still, if this was my own unit I’d already be at the grinder buzzing that corner down a bit.


A DoubleStarUSA AR-15 receiver block. Works with fixed or carbine stocks, just pull off the fixed plate if you don’t need it. Attaches to the FSA body and the chassis.

Now you might not have gathered so far but, installation is actually the easiest of any unit because you can set up each piece individually so getting things clocked is a total non-issue. True it’s only marginally easier than something like the XLR unit (which was eye-poppingly easy to install) but little things matter and a little frustration, to me, is a high cost so I appreciate the simplicity of setup. There’s more steps because there’s more parts to join up but it’s easier than the others in the end. Only the XLR is actually anything near “as” easy. The Hera unit was close but the allen key size needed on the chassis end is smaller than it should be to properly torque things down.

The other place where this unit just crushes the superficially similar UTG unit is the push button unlock. It’s not super obtrusive, you barely notice it there at all until you want to fold or unfold the thing. Then it’s a firm but not hard press and the thing smoothly unlocks with absolutely no drama nor even any blood blisters. The way the UTG works, you could end up waving your rifle around pretty irresponsibly while trying to unlock it.

So with all of this going for the DoubleStar ACE, what’s the downside if any? It’s heavy as balls compared to all of the others except the Law Tactical unit. Easily twice the weight which ought not surprise anyone since steel is more than twice as heavy per unit volume as aluminum. That’s about it. Oh yeah, and as alluded to earlier the number of attachment options and materials options and other options for how you put it together can easily get confusing when trying to pick the 3 pieces you’ll need from their website. That’s all the negative I can find.

To make your life easier, if you want one like the unit being evaluated here then you want a FSM-PB folding mechanism with boss ($69.99) + a CAR-15 Stock Adatper (aka Pig Nose) with boss ($29.99), and an AR-15 receiver block ($32.99). That comes in at about $130 and then add shipping and you’re probably at $150 all in which makes this very much competitive on price with the MDT and Sylvan units but with the critical parts of the folding and locking bits made of steel.

Still, the confusion-enabling profusion of choice there cost it a point for coming with everything needed to install. You can easily fail to buy the right thing and since you make your own kit, so to speak, you’re at the mercy of your own silliness and bad judgement. DoubleStarUSA tries to be helpful about telling you what bits go with what other bits but the information is scattered so it’s hard to make sense of until you’ve spent more time than necessary doubting if you got it right. Being men, we stereotypically just won’t call and ask for help normally (though I did many weeks ago for the sake of this article).

How about wiggle and instructions and other factors that make points differences? As far as wiggle, just the tiniest amount of it which you can’t tell while using it and it’s only in the mating of the lockup surfaces, not the joint or anything else. The way the locking block works, I’m not sure how I’d go about trying to bring that tolerance to zero. That being the case, it lost one of 3 points it could have gotten for the tightness of the lockup. Instructions were not included with the loaner (at this point I don’t need them) but it’d be pretty hard to fuck up the installation even if you just gut-feel the install procedure. Still, I’m taking the 2 points for clear instructions because just picking the pieces can daunt some people. They really need to make a “precision rifle package” with those 3 bits in it so we can turn our brains off while we shop, like women seem to get to do.

After all is said and done, the DoubleStar ACE with push button release, lugged pig nose and receiver block pulled down an impressive 16 of 19 points, putting it in 4th place overall so far on value (points divided by cost) and just barely trailing the 3rd place entry. This sits right up there in quality/features/value with the offerings from MDT, Hera Arms and XLR Industries which were all beyond excellent. I’m tempted to give an extra point for the ability to independently adjust up/down the relationship of the folder to both the chassis and the buffer tube and for the unthinkable robustness of the lockup parts. That’s all really slick. However, in fairness, I didn’t give any special treatment to any other so far so I’m not going to start now. The only thing that stops it getting 5 stars in the arbitrary rating scale is the 90 degree corner that’s still just a little in the way of my fat fingers wrapped around my oversized bolt handle.

What is not in the way is the push button. It’s underneath the stock if you set it up for left side folding. If you set it up for right side folding, there could be bolt travel interference issues. I didn’t have any interference folding either way using an LSS stock on either a Mossberg MVP or a Savage 10. Long actions may be different. Keep in mind that only matters for lefties though and only if they want the stock and bolt handle on opposite sides when it’s all folded up.

What can we learn from what we’ve gathered so far? Easy. Steel rules the damned roost. You can have a super slick design but if you make it from crap materials (China, we’re looking at you) you’ve only made a very slick piece of shit. You can take a totally non-clever thing and if you make it from good materials and make it well with tight tolerances, you’ve made a very un-clever but high quality and therefore probably useful thing. You can also make a very un-clever thing out of shit materials so long as the design is optimized for shit materials (looking at you, UTG) you’ll still have a useful widget. For me, as much as I really like this DoubleStar ACE push-button unit I think for me the XLR, MDT and Hera units are a better fit just because of the physical shape allowing them to not interfere at all with my knuckles.

part 1.
part 2.
part 3.
part 4.
Mid-Series Check-in.
part 5.
part 6.
Declaring the Winners