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Part 2
Okay, switching gears to the context of military/LE use and technical mumbo jumbo.
Not every gun on the market is tuned per say. Many are thrown into generic configurations that work well enough for most shooters. Remember, a gas port specification by itself doesn't mean anything.
Taking an HSDI gun, it is timed for it's specific intended use : high round counts of M855A1, AA53, AB49, 70gr. Optimized, etc. across a full range of temperatures and altitudes. It is intended for a level of backwards compatibility to work with military theater provided logistics and the predominant configured parts across the US for in-extremis repairs.
Besides terminal ballistic performance HSDI guns provide, it also provides tame enough kinematics.
Some people in the corners of the BookFace have criticized this point, but they are not my opinion. It is basic physics.
You start with a tamed down gas port. It can be tamed down because of a really solid gas block seal (something KAC rifles are exceptional at!), a solid gas tube to gas block seal, an in-spec gas tube (particularly the flared boss that fits into the carrier key), a solid and flat carrier key to carrier deck contact surface, and triggers with a military strength hammer spring. Now, you no longer need an extra power or proprietary buffer spring or excessively biased buffer weight. The QPQ carriers travel a touch faster than standard phosphate carriers, the exact speed of which (in inches per second) I do not know, but the difference can be felt from a complete HSDI gun to an FN Pro line gun. I do know it is less than a 14.5" mid gas gun with a 0.076" port and an H2 buffer in front of a standard action spring. Also with this setup (especially 14.5 mid) it is less sensitive to suppressor usage (carrier speeds start lower than most guns, end slower as well). Bolt life is exceptional as a result of QPQ treatment, but the jury is still out on whether the reduced friction coefficient or the hardening of the metal is the more dominant factor. This is beyond my level of understanding.
All put together? The guns shoot softer than many of it's competitors. In other words, the buffer is bottoming out on the buffer tube with less force than other guns set up differently. Split times can be matched by any gun with similar triggers, yes, but at the expense of either group size or muscular tension/control required to control a more 'violent' system. Post firing actions like follow through and recovery/reset are easier - this is one of those things you need to try first hand to experience. A well-tuned JP rifle can deliver the same or better performance in this regard but at the expense of reciprocating mass (important when factoring in external debris).
Moving on to the SEP Program, the Army did test HSDI guns. They also did test several other competitors aside from the M4A1 and M27. This is part of the reason there is no publicly available (such as on NDIA) data. Those that are aware of the program know the top line conclusions, but even if you FOIA (all documents related to 2007 SEP Program rifle durability and user assessments - Picatinny NJ) the data collected is considered sensitive particularly if a competitor got a hold of another's data. Normally a company will get a result back and all other entrants will be blacked out to them. Now, if you want to know more, call the HSDI number and ask. You may not learn everything, but you will learn more.
It is no surprise a well timed, free floated gun with an American answer to the HK barrel would perform better than either the M4A1 or M27, particularly firing hotter, older lots of M855A1. I do know that the HSDI gun was more reliable (not hard to do, but not taking away from what Jim has done). All that broke was the right side of an extended ambi charging handle. It happens. What were the metrics you ask?
There are normally several in the standard 24K round assessment. Dispersion (100 yards), Mean Rounds Between Stoppage (MRBS), Mean Rounds Between Essential Equipment Failure (MRBEEF), rate of fire measurements (auto RPM), velocity (Army criteria for deadline is 200 FPS and over 7 MOA dispersion... garbage...) at the muzzle (FPS), throat erosion (in thousanths of an inch), firing pin protrusion (in thousanths of an inch), buffer spring length (inch + fractional remainder if I remember correctly), headspace (in thousanths of an inch) and one or two others I'm forgetting. The whole thing is done in 600 round cycles between a wipe and lubricant, and every 1200 or so is cleaned fully and inspected/measured. Normally you could fire two 600 round cycles in a day, but they often drag it out and fire one cycle per day for... Civil Service reasons...
I have tighter deadline criteria for my guns or parts than that, but that should give you a rough idea of the data will be found in the report.
Regarding military contracts, having a military or LE contract doesn't mean anything in itself either. It is no standalone metric of success or failure. There are many products that should have been in service for decades if it weren't for the bureaucratic legions that exist to maintain the status quo. The lack of a military contract means nothing when Army G8, to this day, has rejected TWO Deliberate Universal Needs Statements from the 82nd Airborne requesting free floated rails for the M4A1, and I quote, "We have no interest in modifying the M4" (Please confirm yourself by calling the 82nd Abn PAO and requesting to talk to their SgtMaj). If an organization can't even float their rifles formally, is the lack of them awarding a contract for a baller rifle an indication that it sucks? No! To imply that is to show mastery of the highest level of mental gymnastics.
ASR was won by the Barrett MRAD. Does this mean the AI ASR II (now AXSR) was a junk rifle? Not at all! One tiny little thing can cost a victory, be it a contract proposal error, a drop test, a wayward KO (acronym for a contracting officer, FYI!) with a conflict of interest, institutional inbreeding that kills good ideas in the cradle... any of it! SEP Program fell victim to the innate ability of the US Army to fuck up a threesome and hit the sweet spot of mediocrity.
Now, a separate measure would be who, if they are able to, purchases things with their own money, and who uses it if allowed? While I won't say much of who and where, if you ask around you will see HDSI guns or uppers out there. That I have one is no accident. Even then, who uses it and what they use it for shouldn't really mean anything to anyone by itself. Evaluate your own needs, skills, resources, and make decisions accordingly. Would you use an M40A6 because the Marine Corps had them? Not only no but hell no! One can get a WAY better rifle for the same money (nearly an AI!) and less piecing it together with all associated headaches. Just because I have one doesn't mean you need one - you may need something more economical, or through some crazy circumstances, you may actually need something even more durable or boutique (in configuration or rarity)! Lack of contracts being correlative of quality is a straw man argument at best, and not a good one.
Hell, KAC Mod 2s are some of the absolute best guns/uppers going right now. Take that sucker out of the box, add optic, ammo, sling, lube, pants are optional for this party, and go shoot! I love their enlarged bolt lugs and generous radii, and absolutely love the fact that the gas system is now second-echelon serviceable due to the castle nut architecture. I love that they are more available than the HDSI lineup, or even the FN Pro line (at this time). If a KAC Mod 2 isn't in the running, you're wrong. The KAC offerings are in the $2K+ range complete. The HDSIs are as well - neither is truly off base.
I can't build a gun off a KAC barrel because I can't get the extensions. I lose there but I gain on distributor availability over HDSI. I gain backwards compatibility with an HDSI in the event something goes wrong, and I can change configurations easily. Want a Proof barrel? HDSI will do it for you. KAC? Not so much - you're going to take it like Henry Ford said you will. And you'll like it.
So HDSI - can anyone do it? Yep, if they wanted to take the time and effort to make those guns. Does everyone do it, and do it in one shot? No.
Give it a shot, pick up the phone and investigate, and go shoot one... or not. Makes no difference to me.
Lastly, if someone thinks they can make a cheaper gun with the same levels of performance and longevity, then I ask, what are you waiting for? Help the rest of us out. I ain't scared of you!
S/F
