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Gear Review: Bootleg Adjustable Bolt Carrier

Function

Like many options on the market today, the Bootleg carrier works to decrease the amount of gas being used to cycle the action.  When attaching a suppressor, for example, the added back-pressure can result in increased bolt speed, increased muzzle rise/recoil, and excess gas being vented into the shooter’s face (ask me how I know!).  Although there are suppressor options on the market that focus on reducing backpressure, the fact remains that many options on the market do not, so a product that can help mitigate excess gas could be useful.

While there are many adjustable gas blocks available, many people do not like the idea of small set screws, detents, and springs being integrated into the gas block where you see a significant build-up of heat and pressure.  Other more niche products like adjustable gas keys are also available, but I have no personal experience with them and won’t comment on them.

The Bootleg carrier works by venting excess gas through the bolt carrier, and has four settings.  The first is for un-suppressed shooting, and the remaining three vent progressively more gas, allowing you to find the optimum place for your specific ammunition, barrel length, gas port size, buffer and action spring, and suppressor.

 

Gen 1 vs. Gen 2

I purchased my first Bootleg adjustable carrier a bit over a year ago, and have been using it in my personal 11.5″ upper.  The gen 1 models were not full auto capable (they will not trip the auto sear).  Although I never really see myself owning a full auto gun, I wanted to do some testing with a full auto gun I have access to, which is where the gen 2 model comes in.  In full disclosure, although I bought my original carrier, I was sent the gen 2 model specifically do to this testing.  The major difference between the two is the added material on the back of the carrier that mimics the shape of the standard full auto GI carrier.  Notches also interface with a forward assist.  This redesign allows the bottom of the carrier to trip an auto sear lever.  A couple other minor differences seen in the pictures would be the removal of the angled cuts on the rails that contact the upper receiver, and the added material on the left side of the carrier surrounding the bolt.

Gen 1 and 2 post-testing. Note the minor machining differences.
Note the re-profiled carrier and included notches for a forward assist. (gen 2 on top)

Testing Protocol

Use of full auto will be accomplished using a Colt factory machine gun lower.  Trigger is stock from Colt, as is the recoil system with an H buffer and standard carbine action spring.  A single upper will be used for the initial testing.  The specs are: 13.7″ Ballistic advantage barrel with a pinned low profile gas block and Keymount flash hider.   A Dead Air sandman-K and S, along with a Silencerco Saker 556 with the Key-Mo attachment system (because I need to be able to take it off) will be the suppressors used.  Rates of fire will be recorded with a CED pocket pro 2 shot timer in the “RPM” mode.  Two strings of fire will be shot with each suppressor in each setting.  Each string will be five rounds for a total of 10 rounds shot per setting and suppressor.

In addition to rate of fire data, each set of 10 rounds will be shot on a separate B-8 target from a distance of 10 yards.  This will allow a practical (albeit not perfectly quantitative) view into the control-ability differences between settings.

Data

A few notes about the numbers.  It appears that the most drastic difference in cyclic rates (and it felt this way shooting as well), is between setting 1 and 2.  I think that using guns with a tighter (ie. correctly sized) gas port like my 11.5″ BCM barrel would show different numbers than a budget 16 inch carbine gas system barrel that was severely overgassed.  Practically speaking, I would say a good rule of thumb with a quality barrel would be the default to position 2 when running suppressed, and only use the other settings if you were still feeling significant gas to the face, or using larger, high-back pressure cans with 5.56 ammo.  Using this carrier to deal with an overgassed barrel might mean the 3 and 4 settings would make more sense.

On the accuracy graph, two points to note. One: I forgot to score the last target using the Sandman-K, so no data was available.  Two: there was an unusually high score on the first setting using the Saker 556.  I would consider that the result of a fairly subjective test like the one being used.  I will be continuing to use these carriers, and I hope that over time more shooting will lead to a higher quality, larger-n data set.

Higher-Round Count Use

One concern that many might have would be centered around the adjustment mechanism and how it functions over time and higher round counts.  This has been the downfall of many adjustable gas blocks in the past.  For many who might use this product, it would not be unusual to see round counts in the 500 range on a single day during a training class or personal practice.  So, after running through the different settings with both uppers, I set the carrier to position 2 in my 11.5 gun, put on the Saker 556 (which has been a workhorse when doing higher round count testing), and got to shooting.  I shot half a case of American Eagle 55 grain 5.56 ammo without adding any lube, or adjusting the carrier in any way.  I wanted to see if function would change over time, and especially if the adjustment screw would seize up after half a case of ammo.

Range session #2 for the last few hundred rounds. Note the ever-present Dark Angel med kit.

After 500 rounds with the carrier set to a single position, I was able to easily re-adjust the gas back up to the unsuppressed setting after taking the suppressor off.  The adjustment feels very positive, and I would have little concern about the possibility of the adjustment moving inadvertently.

The Saker 556 going well past Fahrenheit 451.  I don’t use the factory mounting system, but the can itself is built like a tank and eats up high rounds counts easily.

Considerations

Just like any adjustable system, users will want to verify the carrier is set to the proper position for the ammunition being used, or whether or not a suppressor is attached.  When doing the testing and removing/attaching different suppressors, I did find myself forgetting to update the setting based on the condition the gun was in (suppressed vs. unsuppressed).  Whether your use would be at a match, class, or for duty use, an important addition to your prep would be to verify that the carrier was set to the proper setting to ensure reliability.

One additional note about reliability.  Like any other addition to your firearms, you will want to verify reliability with your equipment before trusting it.  I recommend verifying function with the exact ammo and configuration you intend to use.  Do not assume that a certain setting on the carrier will work for your particular set-up until you have actually verified function yourself.  For example, I have a 13.7″ gun with the excellent Vltor A5 action system installed.  With a standard BCM bolt carrier suppressed, an A5H3 buffer with the LAW folder (the metal insert adding additional weight to the carrier) would cycle perfectly.  When I added the Bootleg carrier, the decreased gas ended up causing the gun to not cycle completely, and I ended up dropping the buffer weight to get reliability back up to what I was used to, and expected. I also tested the carrier on a lower with the Maxim PDW system for several hundred rounds.  No reliability issues in my very limited test to report.

Other considerations are specific barrels.  One example is the Sionics 11.5″ reduced gas port barrel which prevents excess gas by restricting it through a smaller gas port in the barrel.  If you are buying a rifle with this barrel, for example, the bootleg carrier would most likely not be needed.  However, many AR barrels, even those from companies people consider to be ‘high end’ can be overgassed.  Adding a suppressor into the mix only exacerbates the problem.  The Bootleg carrier is a drop-in solution to solve many of those problems.

Conclusion

Like with pretty much any other part or accessory, the bootleg carrier is not for everybody.  I would not buy it as a replacement for an adjustable gas block on a competition gun like one used in 3-gun.  The adjustments are too course for fine-tuning a game rifle, and I would worry about reliability when choking the gas down that much without a can attached.  I would also not feel this is needed on a reduced gas port gun, or one only occasionally ran suppressed.  So, where would the bootleg carrier find a place?

One major advantage is the easy installation with no modifications needed to the gun.  Many times taking department or issued guns apart is verboden by policy (and often for good reason).  This eliminates the option of new gas blocks, gas block inserts, etc.  I would use it when higher round counts have let to excessive gas to the face when shooting suppressed.  During the full auto testing, I found myself blinking more as the gun went off with standards bolts and the cans on. Turning the gas down allowed me to keep my eyes on target as it was firing, which is obviously a big benefit.  For me personally, the Bootleg carriers now live in the 13.7 and 11.5 guns that see about 90% of my rifle shooting.  The ability to increase performance while maintaining the same standard of reliability, plus the ease of install, is well worth the cost of admission.

As always, I am open to answering any specific questions or clarifying anything in the article.  If you have additional testing you think would be worthwhile, let me know and I will try to do it.  Look for a future article covering use with 300 BLK guns.

 

 

Nate Osborne
Range Manager
Nathan Osborne began a serious study of shooting in 2012 when taking the "Citizens use of Deadly Force" class with Massad Ayoob. Being able to drink from the fire-hose in class started a desire to learn as much as possible, and hopefully be a source of quality information to others. In addition to attending and working as staff with the Massad Ayoob Group, Nate has taken classes with John Chapman, Earnest Langdon, Chris Costa, and others, and will never be able to go to classes from every instructor on his 'to attend' list. He is also a Glock and S&W M&P Armorer.

Nate currently manages a gun range in Northern Utah while finishing a master's degree, and running a weekly practical pistol match.

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