Semper Paratus Arms AR-15 Armorer Course AAR

Semper Paratus Arms 2 Day Armorer Course

May 16/17, 2017

Greater Seattle, WA area

Instructor: William Larson


I had seen the announcement for this course by watching Will Larson’s company’s posts on Facebook.


I was paying attention to this and was in the process of fitting it into my schedule when I saw that Primary & Secondary had a free slot giveaway in the class for LE. Somehow, I was blessed to win the free slot. Thanks to Larson and P&S for the opportunity.

The course was different in the description from other AR-15 specific armorer classes I’d looked at attending. How so you may ask? The instructor has the student bring their own or department issued AR-15 pattern rifle to the class. The others I’d seen, you just bring the required tools and a rifle is provided. It became evident the advantage of bringing rifles to the class as the 2 days progressed.

The day started off with an overview of Larson’s background and what gave him his knowledge. I had followed Larson from his posts on back in that forums heyday as “IraqGunz” where he posted many pictures of the problems with assorted guns sold as “Milspec” yet failing to be close. (For those lacking critical thinking abilities, that is as close as they can be to Milspec absent a full auto switch.) This class was all Direct Impingement gas system focused.


After establishing the “why you should listen,” the course purpose and terminology was defined. Next up was called “Establishing the Standard.” This was explaining “MilSpec” and what that means. During this entire portion, the instructor was bringing up many AR-15 weapon myth’s such as “jamming,” “Milpsec sucks,” gas rings must be aligned to work,” “staking of the carrier key and castle nut is overrated,” etc…, and then debunking them.

A common myth is that “Milspec means lowest bidder.” Larson explained that while this was technically true, it implies something that isn’t true. What is implied is that lowest bidder equals junk. Lowest bidder equals “junk” in word association. What does lowest bidder mean in association with government contracts? Lowest bidder who states they will produce/provide what the contract description asks for. So a US MIlitary issued MilSpec M4/M4A1 Carbine (Colt or FN manufacture), doesn’t mean its “junk” as the contract price for a M-4 Carbine is anywhere from $500-600 per, compared to a Bushmaster of similar listed specs at $800. Cost alone isn’t an indicator of quality. Quality is based on the parts and way they are built.


The reason one should be familiar with the MilSpec standards, is to know what a product’s specifications should be and that there is a reason for parts to be what they are. Larson showed examples of guns from his personal armorer experiences as well as student guns from past classes. The best part was getting to look at the guns brought to class, both personally purchased and issued duty guns. Seeing the results of doing homework before purchasing a gun and how this usually avoids having a gun with problems.


First thing we looked at in the gun, was the BCG. During the history of the BCG the instructor covered the precursor to the AR-15, the AR-10. The AR-10 was built by Armalite, a division of the Fairchild Engine and Airplane Corporation. Getting to see the history of rifle parts was very interesting to someone who is into history and therefore likes to know why we are where we are today. This showed how things have changed for the better as specifications where changed.


BCG’s must be staked, no room for discussion. Understanding that the spec’s show such a low torque value for the screws that hold the carrier key in, and how easy it was to break the torque, it drove home the importance of proper staking. A MOACKS was used to fix staking on BCG’s that were fixable in class. It was interesting that the carriers that weren’t staked properly generally had non-quality/spec screws in them as well. Having a BCG with poor staking and some aftermarket coatings prevented some BCG’s from being staked. Staking something that was already coated would of have fractured the coating which could lead to eventual peeling or flaking over time. This was something one should consider before they purchase a coated BCG – make sure its staked properly or you will be SOL for the cost of getting it coated.


The AR-15 family in common use today, is not the same as originally built (20” barrel with 1/12 twist and rifle stock). The AR-15 family today is really a gun limited by imagination and parts. No other rifle has truly answered the designers’ goal of “weapon system” that the AR-15 family has become. With the adaptability of the gun, comes issues though.


The Milspec for gas ports was the next topic. Rifle length gas, carbine gas, buffers, etc. all play factors. The right size gas port is very important and must be in place for a gun to function correctly. AR-15’s DI gas systems require dwell time to both function and stabilize the bullet. Charts were showing to explain why some longer barrels have smaller gas ports, while others have larger. This variance in size was due to the length of gas system – from carbine, midlength to rifle. Also discussed were some manufactures proprietary gas systems and the downside of that – parts availability.


Larson gave an example on why both knowing and following the spec by explaining, the MK18. The MK18 is a very misunderstood gun, although its understanding is increasing as time progresses. The MK18 is a Crane built gun for the Navy based on a specific request. Take the standard M4 carbine, make it as short as possible for ship operations yet still work with the standing SOPMOD accessories including the SOPMOD can which at the time was the KAC QDSS suppressor. When this was done, Crane was taking M4 Carbines in service and cutting the barrel down. This resulted in 10.3” barrel, which was the shortest possible combination of the carbine gas system and the KAC suppressor mount. Next up was making the gas system work, which was done by progressively enlarging the gas port until the gun ran both suppressed and unsuppressed. This resulted in a larger gas port that works with Milspec ammunition. The MK18 has been copied by many companies and “clone” builders. Sadly, most of them are not anywhere close to the spec.


The FSB and gas blocks were next. Larson explained how a FSB is spaced for the front handguard cap. If you remove the FSB to install a low profile gas block, most of the time a gas block is secured with set screws, not pins. Also covered was materials used – don’t use aluminum for example.


Chamber’s were covered – including what is a 5.56, .223 and .223 Wylde. The reality is, most companies that don’t follow the spec list they claim to follow, also don’t have a 5.56 chamber even when they market it as such. A 5.56 chamber reamer was shown and how to use it. Larson used this on a couple different 5.56 marked barrels in the class, which by this point based on the manufacturer of the guns, didn’t surprise the students.

Day 2 was short on powerpoint and long on the hands on work of tearing the rest of the rifle down. We took our rifles other than barrel, gas block/tube, and rail. We took lower receivers apart and parts of the upper. The parts that were not taken out, were shown how to install or replace. The course didn’t call for tearing barrels out, but students who wished to did get to have their rifle taken down for fixing things such as receiver extension staking, barrel replacement, gas tube alignment, barrel nut replacement etc.


It was interesting to see the guns students brought to work on. Some were put together with good parts by people who did the install correctly. Others were not. Those rifles were great examples of why things must be done correctly. From set screw gas blocks with no dimples so they were misaligned, to UTG parts being used by someone.

This is my first AR-15 armorer course, so I’m curious what other classes would teach. That said, I felt that by having the background of working on a litany of AR-15’s in his career and the course having a variety of AR-15’s in it I gained much more than working on a stock Colt 6920 style carbine for two days. None of my AR-15’s are “stock” so learning about the stuff to look for in buying, building or inspecting a rifle with parts that are performance or fight enhancing makes this worth it.

*** No dremel tools were used in the class, thankfully. ***








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