Post Apr 20, 2017 by HMGTravis

Greetings to all!

This week we dive deep into the world of the HMG® StG and uncover some new and exciting developments with the project.  For those of you concerned: Yes, the StG is still happening and no, we did not quit and start baking StG shaped cookies.

Fair warning, this is a lengthy article.  So strap in and lets rock!

First lets talk about the biggest light bulb that dinged on for us!  As some of you may have seen in both the Military Arms Channel StG video as well as our own social media videos, the HMG® StG has always seen some instances of weak/poor ejection.  Although the platform worked and the rifle functioned, it was never 100% where we wanted it to be.  The first thought was gas port size on the barrel.  we assumed that we were simply not getting enough gas pressure.  After experimenting with different size ports we discovered that the system was getting PLENTY of gas but we were still losing bolt carrier velocity and coincidentally bolt velocity as well.  This led to decreased rifle performance, especially with some lower end power ammunition.

Through the power of technology and excessively expensive high speed cameras(the ultra rare and limited production iPhone 6) we were able to identify that there was a slight leak in our gas block.  The fix was easy and suddenly the pressure issue was no longer!

Unfortunately though even with this extra boost to the system we were seeing two things still continue to happen:

(1) We were unable to get consistent reliability in firing across calibers with a single recoil spring.

(2) The hammers in the HK packs were seeing ALOT of wear on the bearing surface where the bolt would ride.

So back to the drawing board we went.  We were chasing symptoms and not the root cause.  The answer funny enough came from the CETME’s…..  We have found through making the CETME-L rifles that the hammer springs were inherently weak and would often times take a set over time, thus causing light strikes on a regular basis.  The answer to this was simply find a new spring to fit, and viola!  No more light strikes(coincidentally enough this new spring actually improved the trigger reset substantially.  This coupled with a new firing pin spring and disconnector spring quite literally makes it a brand new feeling trigger pack. Order Here)

Then it hit us….  What if the recoil spring was never the issue and instead it was the hammer spring?!  The HK packs have quite the stout spring, and the tilting bolt design is one that any degradation in velocity can cause the system to fail.  It was an easy hypothesis to check, we replaced the stock HK hammer spring with one that had a bit less tension.  Low and behold that gun ran like myself to the dessert line at the Bacchanal buffet in Vegas(if you haven’t been… 1st: Haze yourself 2nd: Fly there and eat until you have to roll back to your hotel room.  Seriously.)  OK….  Maybe not the best comparison but it ran beautifully.  No longer did we have the weak ejection, nor the poor or erratic performance.  Needless to say it was an exciting moment!

New production spring left, HK rifle pack on right.  The HK one though smaller has far greater tension than the newest ones we are using!

With that issue ironed over lets spring into the next big achievement!(I’m the worst I know).  Since NRA of 2016 we have been showing off guns that externally were 100% production quality. What I mean by this is that the parts we had been using to make guns to show/for our testing purposes had been the same that would be used to manufacture StGs for the masses.  Internally however there was something that we had been missing….  The steel used to produce the internal bits, although metallurgically nearly identical to production steel, was technically not the same. Thankfully this is a non-issue now!  We received the batch of steel we had been waiting for that would enable us to manufacture these firearms faster and more efficiently than we had been doing thus far.

The question I’m sure some are asking is “How does this new steel allow us to make guns faster?”.  “I mean you just put blocks of steel into a CNC machine and press a button and some amount of time later a part spits out the other side right?”

Not so fast Chief Gotta-Go-Fast….  We accomplish this decrease in production time through the use of extrusions!  What are these?  Let me explain.  Lets say we wanted to manufacture a whole butt load of these rails(pictured below).  Well one option to do so would be get a steel square bar and just start machining, just slinging chips every which way until we get to our final product.

Would this work?  Yes, you would indeed eventually end up with the desired product.  In doing so however you would however waste a considerable amount of machine time and raw material which equates to a much high COGS(cost of goods sold) and eventually translates to higher cost to the customer.  So to prevent this waste we can use extrusions!  At its simplest definition it is a forged bar of steel that is the basic overall profile of the part you are making.  In this case think a somewhat circular bar with the profile of the picatinny rail on three sides.  If I was to get a bar of this I would now only have to cut to length, machine the slots on the rails/the other features.  Now my machine time is considerably less as well as the raw material cost(over time).

We utilize this concept with our bolts, bolt carriers, and trunnion.

These are coupons from the extrusion bar.  You can see that the extrusion sample is just the basic overall profile of each part.  Now we cut to length, and do the fine machining until we get our desired outcome!  Far more complex than that but its the basic gist.  When we started this project we never thought it would be this popular.  Some of you may think it’s silly to think this but honest to god we had no idea.  Once we got through our first SHOT Show and saw the popularity the rifle had we knew we had to rethink the way parts would be made, else it would take us forever and a day to manufacture.  Unfortunately getting extrusions that are both accurate and precise takes a fair bit of time.  This is by far one of the most exciting developments for us.  Not to mention unloading nearly 30 tons of steel was a sight to see….

SO….  We have consistent reliable performance, and we have some steel that has the tendency to get us all hot and bothered, how do we put this all together and properly test it?  We had to devise a way to perform every function of the firearm and work every little moving piece thousands of times to try and find failure.  Better for us to than the final customer!  So lets break down the simple function of the rifle.

• pull charging handle to the rear
• release charging handle
• pull trigger to rear
• release trigger to reset position

And rinse/repeat.  Well doing this by hand is not only tedious but it is not a precise test due to us being humans.  I may not pull the charging handle with as much force every time, or may not pull the trigger to the absolute rear.  There are far too many variables to test.  So how do we do it?  Enlist the help of our robot brethren!  Our head engineer and pneumatic system wizard gazed into his CAD software crystal ball and came up with this test piece!  LINK TO VIDEO

This contraption allow us to test these functions, as well as configure to test other moving bits, thousands of times per day with nothing more than air/electricity and the push of a button!  One bit of comedy with this testing device.  Ultimately we want to bring this to a range and shoot it.  The immediate thought was “oh snap….  is this a machine gun?!”.  By technical definition we are firing more than one bullet with the pull of a trigger(the trigger being the remote start button).  After some research we found that the actual issue or potential red tape was that by programming this to run a predetermined amount of times we were in essence storing trigger pulls to be used in the future with the push of a button(there is actually an ATF ruling on this).  To be safe we went ahead and filed the necessary paperwork to make it a conversion device.  All that to say we may be one of the only companies in history to register a robot machine gun conversion device.  I have never been so proud.

Things are moving in a great direction here!  We are getting closer and closer to pushing guns out the door.  I realize that is always the answer but it is 100% the truth.  For those of you planning to visit Atlanta for the NRA show come by and see us!  We are in booth 5120 and will have a plethora of StGs/CETMEs/Targets to show off!  It’s easy for us this year being in our backyard!  Truly hope to get the chance to meet more of you!

Oh!  Almost forgot.  We literally just received our retail packaging for the magazines.  I think they look fantastic!  Hope to see them in a store near you soon 🙂

Have a great rest of the month and as always stay groovy!

-Travis