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Posted: 6/9/2009 8:24:30 PM EDT
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Let me first start off by saying that this is going to seem like common sense, but I want other people's opinions about the efficacy of the various fixes for a FTE.
Okay, I completed my first build of a 16" M4. I get a FTE probably twice a magazine. I did some reading and found that the carbines have too much pressure in the chamber to extract properly 100% of the time. As a result of the high pressure, the carrier and bolt move rearward too quickly before the case pressure can drop resulting in the case sticking to the walls of the chamber, the extractor slips off the rim of the case failing to extract and of course eject the spent casing and then as the bolt moves forward it forces a live round into the spent case in the chamber. 1) A solution that seems to be pretty common is to get a heavy buffer to slow the action of the rearward moving carrier thereby giving the case time to release it's grip on the walls of the chamber. 2) Another solution is to use a gas tube that is flared to allow the pressure to drop to a sufficient level to slow the gas' entering the carrier key which gives the case time to shrink and extract properly under the force of the extractor. 3) The third solution which causes me some concern and seems to frequently be combined with solution 1 is to add a strong extractor spring and O-ring thereby increasing the grip the extractor has on the rim of the case eliminating the slipping of the extractor. Solution 3 by itself does not solve the problem of too much pressure acting on the carrier and essentially rips the expanded casing from the chamber. Not only would this seem to damage the cases if you're into reloading but also would seem to cause excessive wear on the chamber and possibly break the extractor after a sufficient amount of rounds have been ripped from the chamber in this fashion. Correct me if I'm wrong please. So this leaves solution 1 and 2. From your experience with carbines, which seems to be the most effective? Also, has anybody used the PRI Fat Boy gas tube which has the flared chamber and if you have had problems with this tube, can you suggest another that may work? Thanks! |
| Sometimes a FTE is just a tight or rough chamber. I have shot a number of 16" carbines, and never had trouble with extraction or ripping/deforming rims. If your chamber is good, just get a heavier extractor spring and be done with it. It's cheap and it works. Brass extraction is a violent process, no matter how you do it. |
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Polish the chamber.
Keep it free of CLP Keep you ammo free of CLP Do not use coated ammo (it expands when heated and causes sticky) Check to see if your extractor is 'clipping' brass off each round, these flects can foul the chamber, as well. This will have to be solved with a grind (pro) Clean, dry, polished, with good ammo...and maybe a dremel |
| Thanks to everybody for their responses. It seems I should go with the extractor spring uprgade and H3 buffer for a cheap upgrade. However, I'm compelled to look at an adjustable gas block as reducing the gas pressure in the tube would seem to increase muzzle velocities, always a plus on a carbine. Hmmmmm. |
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