This has been dealt with thoroughly on several other threads - I will summarize it here:
E-Lander mags are shipped with new Tavor rifles. They have been extensively tested in the Tavor and the M16/M4 by the IDF and also by independent testing companies and found to work flawlessly and to be consistently within spec. Keep in mind that the IDF tends to require more and harder testing than most other militaries.
I personally tested these magazines for almost two years before the decision was made to import them. I found them to be consistent and to have perfect function in every rifle I tested them in, except for one Spikes lower/Delton upper and one DEZ Arms rifle that had a slightly tighter fit, but not enough to cause any concern.
When we had been shipping these magazines for a while, we began to receive a handful of complaints about hard seating in certain rifles. We began to look for data on this, to determine if it was limited to specific rifles, but found that people were reporting that the same magazine worked fine in one rifle, but seated hard in another, often of the same manufacture. Compounding the problem, we soon learned that people were reporting that the mags seated hard in a certain brand of rifle, but we found that many of these were actually lowers that were built up by some one, so the guy who claims hard seating in a RRA rifle may actually have a RRA lower with lower parts from Blackthorne, an upper from Model 1 Sales, and a bolt carrier that he is not sure where it cam from, so we quickly learned that we could not establish a pattern in most cases, thoug we do no know that certain brands of rifles tend to have higher numbers of seating issues - even so, some of these companies have changed hands or changed suppliers, and we cannot determine if there is a certain range that have a higher tendency to have seating issues.
Immediately, there was a range of tests performed in Israel to see if an error had been introduced in manufacturing. Magazines from all series were carefully measured and also checked with the measuring built by Colt that are used in the factory for quality control. All magazines were found to be right on the specifications. Next a range test was conducted using the mags from the various series and multiple M16 and M4 military contract rifles built by Colt. They were also tested in Gilboa and Tavor rifles. All magazines worked flawlessly and had no seating issues. I fact, this has never been reported in all the time these magazines have been in use in Colt military contract rifles.
At this point, I contacted those who had reported seating issues and asked them to return the actually magazines that they had issues with. Meanwhile engineers and executives from E-Lander flew to the US to investigate the reports. I met with our CEO and the engineers from E-Lander and we investigated the returned magazines, comparing them to other magazines of various series pulled from stock. They were compared to the military specification drawings from Colt, which are the standard for M16 magazines, and the standard to which E-Lander mags are built. We measured all of the returned magazines, plus all of the magazines pulled from stock, both loaded and unloaded, and found that they were right on the ideal specs in all dimensions, according to the drawings. We also found that they were extremely consistent from magazine to magazine and from series to series, with the 10 series being exactly on, while the 12 series was just off from the 10 series with an almost immeasurable difference in one dimension, but still right on the ideal specs, according to the MIL-SPEC drawings. For each dimension, the drawings have a target dimension and then an allowable variance. Imagine if a certain measurement was 10. The variance may be 3 on one side and 2 on the other, so any measurement between 8 and 13 would be considered within spec. The E-Lander mags would consistently be 10.
We then measured US-made magazines. We found them to be just outside of spec in certain critical dimensions.
We then tested fit in a variety of US-made rifles - we found no issues with seating in any rifle we tested the magazines with - these were the same magazines that were returned to us for seating difficulty. We spoke with rifle manufacturers and industry experts about the issues. We submitted mags for testing to manufacturers such as LMT, Mega Machine, Alexander Arms, etc. - both new magazines and some of those that were returned. We also sent some of the returned mags to certain gun writers who are knowledgeable enough to do thorough investigations of their own.
Here is what we determined, due to our own testing and also largely from information provided to us by manufacturers and industry members:
• Colt military contract rifles are all gauged to guarantee that they are within spec. Most rifles built for the civilian and law enforcement market in the US are not. There has never been an issue with seating in the Colt military contract rifles in use in Israel, nor with Tavor, Gilboa, or FN SCAR.
• There is actually a wide variation in dimensions between rifles in the civilian market in the US. Even among the large manufacturers, parts are sourced from a myriad of suppliers, and things change, sometimes quite often.
• With civilian market rifles in the US, by the end of last week, we had had at most .07% of the thousands of magazines we have shipped reported as being difficult to seat in particular rifles. When we consider that some shooters have not tried them yet, and some who have may not report issues to us, we feel confident in saying that so far, we have had less than 1% of the magazines we shipped having reported seating issues.
• Clearly, the magazines are built to the ideal dimensions, according to the MIL-SPEC drawings, for use in MIL-SPEC rifles. By MIL-SPEC, I don't mean the term as it is thrown around by many AR-15 manufacturers - I just looked at a rifle that was advertised as MIL-SPEC by the manufacturer, yet it had a fluted non-chrome-lined barrel, stainless lower parts, non-standard selector, "MIL-SPEC" buffer tube with too many positions, no lock washer on pistol grip screw, AR-15 bolt carrier, etc. (and by the way, it didn't go bang, either). When I say MIL-SPEC, I mean built to the military specifications as provided for M16 magazines and found to be identical in two versions of the Colt factory drawings that we were using. The E-Lander magazines are truly built to MIL-SPEC dimensions.
• Clearly, the magazines are not built to the ideal dimensions for the US civilian market. There is just too much variation between rifles, for a variety of reasons I won't go into here. While they work fine in almost all rifles, we want them to work fine in all rifles. Of course, this won't ever happen, because there is stuff out there that is just way out of spec, but most rifles are close.
• Dimensions on the rifle that can be critical to magazine compatibility are:
Magazine catch location
Magazine catch hole location
Magazine release button size, shape, and location of threaded hole
Upper to lower fit
Radius in upper for magazine fit
Bolt carrier dimensions
Groove location and depth on bottom of bolt carrier.
Any of these can affect the fit of the magazine, or several that would not affect the fit by themselves can stack together to affect the fit.
• We can go one of two ways - we can say, "We know our mags are in spec and so it has to be your rifle; tough luck." Alternately, we can find a way to solve the issue for those few rifles that the mags seat hard in.
We don't think the first response helps anyone - it does not help us, and it certainly does not help anyone else. I know that people hold the military specifications to be the holy grail for ARs, but if you have a rifle that does not necessarily meet the specifications, but still works fine, is there really a big problem? Not as long as you have mags that work, right? So the second solution is the one for us. We cannot change the rifles, so we must adjust the magazines slightly.
• As I said before, we measured US-made mags and found them to be just out of spec. Why would this be? I think it is because they already know what we are just learning - that ideal military specifications for magazines may not be ideal for non-MIL-SPEC rifles in the US civilian market. Remember that many people experienced drop-free issues with the Gen 1 Pmags, until Magpul made a change. I can promise you that Magpul is not a company that releases out-of-spec stuff. So we can be sure that those Gen 1 Pmags were in-spec, yet there were issues with certain rifles. On the other hand, the first Pmags work flawlessly in every rifle I own.
• The solution we found is to move the top edge of the magazine catch window on the magazines slightly up from the ideal specification (but keep it within spec, because the primary customers for these magazines are military). If this is done, the magazines should still work perfectly with the military contract rifles, yet seat easier in the few commercial rifles in the US that they now seat hard in.
If you find that you have a rifle that the mags seat harder ion than you prefer, you can use a couple strokes with a file to raise the top of the mag catch window slightly, but only very slightly - don't remove too much.