Here’s my review/opinions of a single, used Canadian Thermold magazine.  I put the summary first for those of you who are impatient.  

Summary
This magazine functioned flawlessly with four kinds of ammo in three different AR-15s.  However, because the magazine would not drop free from any of the lower receivers tested, I would limit use of this particular magazine to the range.  In all fairness, I have some USGI magazines that won’t drop free either and they are used at the range only.

Overall, I was impressed enough with the magazine to consider buying more of similar quality, at least as range alternatives to the more expensive USGI.  I’ve also changed my mind on Thermolds in general and will take a harder look at the USA-made Thermolds.

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A little backgound
ComputerGuy wanted someone to evaluate and test a used Canadian-manufactured Thermold magazine.  In response to his solicitation, I posted that I was one of the people who stayed away from Thermold magazines only because of the perceived inferiority to USGI aluminum magazines.  Thus, Cody (aka ComputerGuy) sent me a free magazine to evaluate.

I currently own 31 USGI 20-round magazines and 24 USGI 30-round magazines.  Before receiving the Thermold magazine, I did not own any Thermolds.  In fact, I had never even touched one.  The only other AR magazine I own is a 10-round Bushmaster.

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Why did I not like Thermolds before this test?  
These are the issues I’ve heard, read or been told and were the reasons I never considered buying Thermolds.  

Unlike USA-made Thermolds, Canadian-made Thermolds do not contain Zytel nylon.  Therefore, some users have reported feed lips melting and/or warping under heavy use (typically full-auto where temperatures inside the chamber become very high) or the magazines (feed lips in particular) becoming brittle in extreme cold.

It’s been reported that dropping a fully loaded Canadian Thermold magazine can cause several rounds to pop out of the magazine.  This appears to be generally attributed to the difference in plastic used in the Canadian magazines.

Some users have had to shave a slight amount of plastic off the magazine where the first magazine rib touches the bottom of the magazine well.

Some users have reported magazines can swell and/or feed lips can crack if left loaded for a long time.

The magazines work fine when they are clean.  If the inside of the magazine becomes dirty, particularly with sand or other grit that can adhere to the plastic, the magazines may fail.

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First impressions
The Thermold magazine I received was used, but not abused.  I was impressed with the finish, which had only slight surface wear in a few places.    

The magazine was very easy to disassemble and reassemble.  The Thermolds all include an anti-tilt follower, although with a slightly shorter front leg than the “green” followers in USGI magazines.  A vulnerability of aluminum USGI magazines is the metal tabs used to retain the floor plate.  The Thermold’s base plate is retained by a plastic tab at the front and rear of the magazine.  The tabs appear to be very sturdy.

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Materials used during evaluation
Rifles used during the evaluation included a 16” Bushmaster carbine, an Eagle Arms lower with a 20” Bushmaster upper and a Rock River Arms lower with a RRA upper (note this upper has a 20” Bushmaster barrel).  

Ammunition included 120 rounds of Winchester Q3131A, 150 rounds of Wolf, 80 rounds of IMI M855 and 20 rounds of Federal ballistic.

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Magazine fit
The magazine was somewhat tight in each lower receiver.  It fit flush in the magazine well and did not require any modification (i.e. shaving off some plastic).  The magazine did not drop free from any magazine well, even when the magazine was fully loaded.  

The Thermold did not scratch the magazine wells and didn’t appear to show wear as quickly as USGIs.  For example, I could easily scratch with my finger nail the surface of an unused (1970’s manufacture, still in the original box) USGI 20-round magazine, while the used Thermold retained it’s nice black finish.  (I’m not sure “finish” is the right word, since the whole thing is plastic.  But I think you get my meaning.)

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Feed lips/round retention
Comparing a USGI to the Thermold, I noticed that the USGI magazine seemed to retain the rounds slightly tighter.  Manually removing rounds from the Thermold was easier than removing rounds from the USGI.

I repeatedly (i.e. ten or more times) dropped a fully loaded, used USGI 30-round magazine on its side from a distance of 2” on to a wood workbench.  I should note the spring on this magazine is not a new spring and the magazine has been well used.  The magazine retained all rounds.

Performing the same test with the fully loaded Thermold yielded different results.  After the first drop, the tip of the first round had moved slightly up.  The second drop caused the first round to move even more.  The third drop resulted in the first round sticking out of the magazine at an angle of approximately 35 degrees (I actually measured it).  The fourth drop caused the first three rounds to pop out and the tip of the fourth round (now the first one in the magazine) to slightly protrude from the magazine.

I went back to dropping the USGI magazine and could not get it to fail.  I tried the same test with three more USGI magazines and finally did get a round to pop out of one very well used USGI magazine.  That particular magazine does not drop free from any of my rifles as the feed lips have begun to slightly stretch.

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Feeding and extracting
I manually fed 300 rounds of ammunition through one of the rifles.  (Just a note regarding safety.  To manually feed these rounds I replaced the firing pin with a firing pin modified to NOT protrude through the firing pin hole in the bolt.  As always, the rifle was pointed in a safe direction.)  Not one failure to feed or extract was encountered.  

Various ammunition types were used for this manual feed testing.  The magazine was loaded using a LULA and stripper clips.

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Range report
Shooting at the range was somewhat uneventful.  I didn’t encounter a single failure of any kind.  Most of the rounds were fired through the Eagle Arms lower/Bushy upper so I could get the rifle hot.  I think it would take a LOT of ammo from a lot of magazines to get the chamber temperature hot enough to melt the feed lips.  A better test would be sending enough ammo through an M-16 until the rifle to try to melt the magazine.  I doubt melting the magazine is a serious concern for most semi-automatic shooters.

I sold my Canadian Thermolds, not because I didn't trust them or had problems, I just wanted some cash for another goody. I found them to work great in my Colts. No problems at all. I think the percieved problems with them are all blown out of proportion, especially if used with a semi-auto. In SA you would have to have a LIGHTENING fast trigger finger and go through several mags before you could even HOPE for a heat problem. They are worth the money.

SorryOciffer

Very informative.  Great job BookHound!

I have both USGI and USA Thermolds.  My Thermold functions flawlessly and drops free from my Colt and Bushie.  In fact, I perfer Thermold.  However, because the ribs on the Thermold adds to the overall width, they may not fit mag carries designed to hold USGI.

very well done. load a USGI and the thermold and put them in a freezer for 6 hours, take them out and drop them on a concrete floor from 3 feet. I dont know what would happen but it would be interesting.

Thanks for the review, that was quite interesting!


Did you ever stick it in the oven?

If you liked the Canadian piece, you'll love the US made versions.  I too have a couple of the Canuk pieces, to go along with a dozen of the North Carolina jobs. I've had the same experience you report with the Canadian models, and all of them are a bit tight in the Bushie and early Rock River lowers at my house, However, a very recent RR lower, and my preban Colt lowers handle them perfectly.

Thr US built Thermolds, however, are a treasure.  I probably shouldn't type this, because now all you "US GI or nothing" people, having gotten the reality of Thermold's superiority pushed in your faces, will start wanting them and drive the prices up[;D][:D].

The only disadvantage of Thermolds is that the late ones (H21 and 22 marked)may need to have the top rear of the mags shaved slightly and/or the overinsertion rib thinned out, to properly seat in many of the aftermarket lowers. Once this is done, however, they're a treasure.  No spray painting needed, no tabs breaking off, no feed lips cracking.  I have a couple of US jobs that have been fully loaded for nearly two years with zero swelling or malformation.

OK, so now that I've spilled the beans, go for it guys.  Only need a couple more myself anyway, and if I can pick them up at the next show, y'all can fight over the rest[:D]

I didn't try freezing the mag or putting it in the oven.  I did get the AR pretty hot, so I'm thinking I'd never experience the reported melting problems in a semi-auto gun.  I just don't think it's an issue.

I am impressed enough with the mags to give some more a try.  I also am now very interested in USA-made Thermolds.

Overall, testing just a single used mag made me realize my initial hesitation was foolish.  People should always form their own opinions.  Plus, environments and conditions are different for different people.  So, what works for some may not work for others.

I'll give some more of these a try.

Great job on the mag review....I couldn't help but think you were the one that got snookered.

You get a $12.00 mag in exchange you get to spend over $30.00 worth of ammo and hours of your time shooting (no complaints there I'm sure) and then all the computer time posting your results.

I think Computer Guy really made out on this one, he got you to test it so he can sell more...Wow....the american way of business...you gotta love it.

For what it's worth... your a stand up guy and the board members as a whole are now better informed thanks to your efforts. I have to admit I'm a straight USGI guy myself....hummm , guess I'll have to call Computer guy and place an order.

good review!

Please leave his wife out of this!....[:D]