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Posted: 3/20/2003 6:45:41 PM EDT
| I tried out some Thermolds tonight that I bought new last year. Had three problems with them: (1) they would not properly seat in the mag well - I would have to slap them into place, (2) the bolt would drag slowly when attempting to chamber a round (by either releasing the bolt catch or using the charging handle) and the round would not go fully into battery, and (3) when I attempted to strip the ammo by hand out of the mags, the follower would stick and not allow a round to move completely aganist the feed lips. The number on these Thermolds was 21H and 22H and the other four mags from this lot worked fine. Any suggestions? |
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I imagine the followers sticking had to do with their newness. I've seen some that lock easily in the magwell and the bolt easily drops on a new Thermold, but others, notably an Armalite, where the bolt would hang up and shave off a little of the top of the feed lips with each drop of the bolt. It would probably take many times retracting the bolt and letting it fly forward to get some of these mags to break in on those particular lowers. The top rib on the Thermolds is a pretty close fit to the bottom of the magwell on some lowers also. I don't know if any other members have filed or sanded a little off the tops of the top rib, to allow the mag to seat easier. I'm sure someone will chime in on that issue. |
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Remove the upper rx from lower rx, and insert the Thermold. See the problem? That extra plastic where the bolt catch is trying to engage the follower. Compare that area, the top rear of the Thermold, with the same area of a USGI mag. Using the 1/4" dia cylindrical mill with your Dremel(r) tool, carefully grind that area to match the contours of the USGI. You will now find that the bolt catch is not hanging up and keeping the mag from fully inserting. It may not be necessary to grind away the side ribs at all. And now you will find the bolt catch operates smoothly. |
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You don't have to go as far as Free-man recommends, although it will work just fine. The only problem with the dremel solution is that if you are not careful you can ruin the feedlips. All I did was take my pocket knive and scrap it across the feed lips a couple of times and it cleared up the problem just fine. Don't use the blade to cut the plastic, just scrape it 2-3 times. Many people don't even bother with this as new mags wear in after shooting 20-30 rounds anyways but its not a good idea to use a match to wear-in your thermolds. |
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I am not talking about grinding on the feedlips, sorry if I was not clear and you misunderstood. The molding at the rear of the top of the Thermold is such that the bolt catch cannot work properly, and will keep the mag from fully seating as the bolt catch is holding the mag body down. There is too much plastic there. You will see it as just a little U shaped cut on the back top of the Thermold, yet the USGI has a rectangular cut. What you need to do is contour the rear of the top of the Thermold to be like the USGI. |
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Quoted: This problem is very rare isn't it? I have quite a few Themolds (all are Wilson, NC) and have never had a problem with any of them. I use them in my Armalite, Bushy and Cavalry arms rifles. Rare? Not at all...actually it is rather common, especially for NIW Thermolds. |
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I did the same thing when I got my first batch. I couldn't dent/crack one by stomping my heel on it with my issue boots, but when I told by buddy to do it he cracked it the first time! (small hairline crack along the spine) Still works though! Try that with a USGI mag! -JD |
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Just went to the range yesterday w/ two new Colt AR's and a few new Thermolds. The problem described here is exactly what happened to me. The Colt Carbine accepted and shot all of the Thermolds OK, but the Colt M-4 Carbine would not feed the round into the chamber. I tried Dremeling the mag a little bit and tried it again in the M-4. Same result.All of my Sterling, USGI and Orlite mags worked fine in both guns. I think I'll continue to use them in the Carbine until they are broken in and then try them in the M-4. |
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