Lakeside Guns LM7 Discussion
There is some more discussion on the LM-7 over at Eric's site at the link above. Eric asked me to post this at a few other sites too, to help him answer some of the questions people are asking about this new system.
Eric (Lakeside Guns) sent me an LM-7 to T&E for an upcoming article in Small Arms Review Magazine. He recently asked me to accelerate my testing a little if I could to help answer some questions being asked prior to working on any particular article. He has asked me to give this a comprehensive evaluation and to report here exactly on the findings I have without “sugarcoating” anything. I hope the following is helpful.
I have been watching this project evolve for a long time and it has made giant leaps from its original conception. I have fired a few of these in the past during little outings that often happen at some of the larger trade shows so these are not completely new for me and Eric has given me several hands-on “walk-throughs” so I would be familiar with the design.
The upper, like everything else Eric is involved with looks great. The fit and finish is excellent and the workmanship is top notch. I have over a dozen AR-15 and M16 variants in my reference collection so our testing is not limited to any specific lower or component group, which may be out of spec a little itself. The first and obvious thing to try was the fit between upper and lower receivers. I have so far tried it for fit on DPMS, Doublestar, Colt, RRA, Bushmaster, Sun Devil, Sendra, E.A. and Olympic lower receivers. Just like every other upper / lower combination, some are tight and some are loose but all dropped on and pined up. The Olympic took a few taps on the rear pin to lock everything up but that is really not uncommon with so many manufacturers of so many parts. No combination required any cutting, drilling or sanding of any kind.
In function testing the first test was in semiautomatic. On every receiver tested, it has never failed to feed, fire, extract and eject on every squeeze of the trigger. The failure rate so far is zero (0). In full auto we initially found something quite different. Some guns it would run great on, and some guns it would not. Issues ranged from the hammer following the carrier back into battery to the carrier not tripping the auto sear and allowing the hammer to fall. In every instance the feeding was flawless, the only issues we have encountered were related to the above symptoms. Before you pass out from holding your breath, go ahead and release it, breath again and read on to learn what is causing these problems and how they were solved.
First, the problem with the failures to trip the sear and release the hammer are directly related to the fit between the sear trip portion of the bolt carrier and the auto sear. In every case, it was very close to being in battery and dropping the hammer but just needed a “little” more forward travel to completely engage the sear. In hand cycling the guns, (all of them) if the carrier was dropped from the rearward position, the forward momentum was enough to trip the sear. If the action was slowed down, such as with outside consumption of energy like belt pulling, round chambering, debris buildup, etc it had a residual effect of not leaving enough speed (energy) to trip the sear. This was not on all guns, only a few. It seems as though the numerous fire control parts are all over the map as far as manufacturing specs and while the differences are subtle, when combined with several other parts they start to become critical differences. Using these parts in .223 with the mass of the original bolt carrier and forward driving force of the original buffer springs, most of these inconsistencies are minute enough not to cause malfunction because of the residual energy in that system to overcome them. In a Rimfire system with greatly reduced weights, spring force and residual energy the differences seem to become more important. Not to fear though, after a little measuring and fitting this particular problem was an easy fix.
Eric designed the rear trip portion of the bolt carrier to be adjustable so it could be fine-tuned and timed to any individual firearm. We used some shim material placed between the carrier and the sear trip, and in no time the sear was tripping and the guns were coming into perfect timing. Each gun had a different size shim necessary to time it to perfection, again another example of the inconsistency of “spec” parts. Problem 1 solved.
As mentioned above the second problem we encountered with a few of the guns was that the hammer would occasionally follow the carrier and the gun would not fire. Upon careful inspection we found that the hammer was occasionally not being cocked upon the rearward travel of the carrier. We found a few different reasons for this. One was the difference of thickness between the face of the hammer and the face of the hammer spur that catches under the auto sear. If it was “tight” the hammer was compressed enough to catch the sear every time. If the space was a little longer, the hammer would engage the sear only when the bolt traveled back fast enough to give it a little extra “bump” to drop it under the sear. Of course, it SHOULD just snap into position upon rearward travel of the carrier, with every cycling of the action. This was resolved in some guns by simply changing hammers with a little tighter tolerance. In one gun it seemed the spacer that works in conjunction with the plunger (the LM7 version of the buffer system) was just a little too long to allow the bolt carrier to travel rearward enough to consistently engage the sear. We removed a little material from the spacer, increasing the length of the rearward travel available to the bolt and the hammer locked every time. Problem 2 solved.
After several hours of troubleshooting, measuring, shimming, and cutting we were finally ripping giant bursts. Since it was after 10:00pm when we finally got to this point and since it was only 20 degrees above zero and still falling, the shooting time was short but successful.
From this round of testing it is obvious there are several factors to consider here. The most important thing to note is the Rimfire system needs every ounce of residual energy (what little there is left) to operate reliably. There are several things that can rob this necessary energy. Consistently the guns ran better with links than belts. It is much easier to strip the rounds from the links and the links feed much easier than the cloth belts leaving more of this important residual energy. For obvious reasons, used belts work better than new ones. It takes less energy to strip the round from a belt that is broken in than one that is just being used for the first few times. This may mean lots of semi shooting to break in new belts. (The length of the action to shoot in semiautomatic is shorter than in full automatic in respect to cocking and releasing the hammer, this is why it runs so good in this mode every time.)
All of the testing we have performed in this phase has been utilizing the Federal Bulk Pack ammo which some have suggested may be a little “light” for this gun. Later we will be using several different types of ammo and recording those results. In respect to the residual energy so important to operate this system reliably, hotter ammo can do nothing but improve the reliability.
A general conclusion so far is that many people will be very happy very soon. Like any other high-tech machine, whether a racecar or a machine-gun, a little “fine-tuning” is necessary to ensure optimum operation. Most people with experience in machine guns are familiar with this process knowing how important it is to have timing as close as possible for both safety and reliability reasons. (Anyone who has ever “tuned” a lightning link will know exactly how this works.) When you add in the factor of all the different manufacturers of lower receivers and all the different fire control parts, it is unlikely that something could be designed as a simple “drop-on and run” component, especially when the relationship of all these parts makes such a difference in function. The fixes were easy, and it was only the troubleshooting that was time consuming. I believe that if provided with a little shim stock (a cheap feeler gage set works great for this) sear timing will be a minor task. If the end user has a spare hammer or 2 to try and / or needs to trim a little off the spacer of the plunger mechanism (a few strokes with a hacksaw works in seconds) the cocking issues will be solved too. More to follow.
Jeff W. Zimba
Proprietor – Small Arms Research
Production Manager – Small Arms Review Magazine
P.S. 1 of the test guns utilized a registered DIAS and it worked fine. I thought a few of you would be happy to hear that!