mancat 2,368 Posted November 6, 2014 Report Share Posted November 6, 2014 I was shooting my M77 today, and between a shifting scope mount, and problems with both the factory mag and the one modded M14 mag I brought, I was getting frustrated. I couldn't keep a solid grouping, and though most of it was because of the scope mount that wouldn't stop shifting around, when I got home and pulled it out of the case to clean it, I noticed this - which somehow I never noticed at all the entire time I was shooting at the range. I can't figure out how this happened? No strike marks on the inside of the FH. Best I can think is that the milling went too deep at the front end of the cage, and there wasn't enough material there to really handle the shock of .308. I was also shooting some XM80 MG food, which may have been loaded pretty hot. Quote Link to post Share on other sites
SmilinEd 364 Posted November 6, 2014 Report Share Posted November 6, 2014 Mancat, You think the one side sprung that far out after breaking..? Wow Quote Link to post Share on other sites
mancat 2,368 Posted November 6, 2014 Author Report Share Posted November 6, 2014 No idea when it happened. I shot about 45rd of .308, so if it broke early on, it probably kept getting a nice blast. It's a CNC Warrior AIMR FH. I'll see if they might replace it with another or a cheaper one, but I have no expectations of it. Quote Link to post Share on other sites
SmilinEd 364 Posted November 6, 2014 Report Share Posted November 6, 2014 Must have been under a great deal of stress to spring that far out.. Quote Link to post Share on other sites
mancat 2,368 Posted November 6, 2014 Author Report Share Posted November 6, 2014 (edited) I just remembered that this FH has always made a bit of a "ting" noise when tapped in a certain way, almost like a tuning fork. I wonder if it was somehow improperly heat treated in a way that induced stress in the metal? Edited November 6, 2014 by mancat Quote Link to post Share on other sites
gunfun 3,931 Posted November 6, 2014 Report Share Posted November 6, 2014 Interesting. Good thing it was an easily swapped out part. Quote Link to post Share on other sites
Sim_Player 1,939 Posted November 6, 2014 Report Share Posted November 6, 2014 (edited) Bad design, stress points (heat-treating), bad machining... all possible. No damage to the rifle... equals a good day at the range. Lot's of pressure at the muzzle. It likely expanded the metal. Edited November 6, 2014 by Sim_Player 3 Quote Link to post Share on other sites
JESS1344 508 Posted November 6, 2014 Report Share Posted November 6, 2014 MANCAT, HERE'S YOUR OPPORTUNITY TO TRY OUT ONE OF THOSE OTHER FLASH HIDERS/MUZZLE BRAKES. JUS' SAYIN'......... JESS1344 Quote Link to post Share on other sites
XD45 7,124 Posted November 6, 2014 Report Share Posted November 6, 2014 I'm betting CNCW will make it good. Quote Link to post Share on other sites
thebuns1 4,323 Posted November 6, 2014 Report Share Posted November 6, 2014 Damn. Had to be poor metallurgy, if no strike marks are present. Quote Link to post Share on other sites
SGL 530 Posted November 6, 2014 Report Share Posted November 6, 2014 Oh man... that sucks about your FH, but I was expecting a lot worse. I was really glad to click here see that you weren't hurt and didn't damage the rifle. Quote Link to post Share on other sites
mancat 2,368 Posted November 6, 2014 Author Report Share Posted November 6, 2014 CNC Warrior already replied to my E-mail and shipped out a replacement. They also said that the AIMR FH design was changed to increase the wall thickness, so I'm guessing that this has happened once before, and I have the older model. 5 Quote Link to post Share on other sites
thebuns1 4,323 Posted November 6, 2014 Report Share Posted November 6, 2014 Cool. They did you right. Quote Link to post Share on other sites
mancat 2,368 Posted November 6, 2014 Author Report Share Posted November 6, 2014 I took a closer look at the FH, and found hairline cracks in the forward sections of the cage, starting at the recess milling. I then pulled out my WASR, which also has an AIMR FH installed. I noticed that it has the same hairline cracks beginning. So if you have a CNC Warrior AIMR FH on an AK, take a closer look at it. 1 Quote Link to post Share on other sites
thebuns1 4,323 Posted November 6, 2014 Report Share Posted November 6, 2014 Seems like a design flaw. Good info. 1 Quote Link to post Share on other sites
HB of CJ 1,263 Posted November 6, 2014 Report Share Posted November 6, 2014 Years ago some middle aged man, (no names please) tried to remove the long flash hider from his Belgum FN LAR by putting a screw driver between the prongs and turning it counter clock wise to remove it. Seems he did not understand that the FN flash hider had reverse threads and he was trying to tighten it rather than loosen it. Cracked the prong almost like shown in the picture. $Ouch$ HB of CJ (old coot) 1 Quote Link to post Share on other sites
mancat 2,368 Posted November 6, 2014 Author Report Share Posted November 6, 2014 I did use a screwdriver to rotate the FH installed on the M77, but not in reverse. Doesn't seem to be the cause of the other one cracking, as the FH on the WASR was always screwed on by hand. Either way, will not do it again. Quote Link to post Share on other sites
burntpowder 23 Posted November 6, 2014 Report Share Posted November 6, 2014 CNC Warrior already replied to my E-mail and shipped out a replacement. They also said that the AIMR FH design was changed to increase the wall thickness, so I'm guessing that this has happened once before, and I have the older model. Ugh I put the same exact FH on my M77 too. I only have about a box through mine so far but I will definitely be looking it over now. When did you purchase yours? -bp Quote Link to post Share on other sites
mancat 2,368 Posted November 6, 2014 Author Report Share Posted November 6, 2014 Over a year ago. When I get the replacement I can measure the wall thickness. Quote Link to post Share on other sites
XD45 7,124 Posted November 6, 2014 Report Share Posted November 6, 2014 CNCW is a stand up guy. I'm a customer for life. Quote Link to post Share on other sites
Long Shot 1,287 Posted November 6, 2014 Report Share Posted November 6, 2014 Wow, that's ugly. Glad to see it was a nice boring failure. One more case where boring is so much better than exciting. 1 Quote Link to post Share on other sites
VR762Shooter 838 Posted November 7, 2014 Report Share Posted November 7, 2014 Glad it was a good kaboom (no injury) than a very bad one. Sounds like they are doing you right with the replacement. Keep us up to date on the thickness of the newly shipped I'm interested to see how much variation between the old and new design they have. Quote Link to post Share on other sites
G O B 3,516 Posted November 7, 2014 Report Share Posted November 7, 2014 Harmonic stress cracks, most likely due to the FH resonating with the barrel, and the design that has built in stress sensitive areas at the sharp ends of the slots. Sharp edges concentrate vibrations at the sharp edge - this magnifies the force by funneling it in a very small point propagating stress cracking. I have seen 3" shafts snap off because they had a sharp inside corner where the shaft is reduced in diameter 1/16" to press the gear on. The replacement was identical with the exception of having a smoothly radiused champher where the diameter changed. The original shaft looked like it was cut off cleanly there, the replacements were still good 25 years later when the escalators were replaced. 1 Quote Link to post Share on other sites
U.S. Pratorean 1,234 Posted November 7, 2014 Report Share Posted November 7, 2014 This has happened before and it was a CNC FH and IIRC, this model. It was a metallurgy defect and Tyler @ CNC will definitely make it right. It's good there were no injuries. Quote Link to post Share on other sites
bcmsaiga 8 Posted November 7, 2014 Report Share Posted November 7, 2014 Oh that didnt happen you are lieing man cat..oh thats fake i dont see how that could of happened your a liar you must have used pliers to bend it, BAAHH!! I just dont believe that.. Sorry mancat just trying to be like a few other people here at the forum that question every god damn thing.. Quote Link to post Share on other sites
storm6490 2,768 Posted November 7, 2014 Report Share Posted November 7, 2014 damn. glad you have all your parts. Quote Link to post Share on other sites
evlblkwpnz 3,418 Posted November 7, 2014 Report Share Posted November 7, 2014 Krebs 4 Prong Flash Hider. Shorter and works great. I recommend that route if no replacement is given. Quote Link to post Share on other sites
mancat 2,368 Posted November 9, 2014 Author Report Share Posted November 9, 2014 I got the replacement AIMR FH. It's definitely thicker, and I would measure with my caliper, but I just found that the cell battery is dead. In this photo you can see where the cracks are beginning on the older FH model on the right. Each one of the relief cuts has a similar crack at the front of the FH. Will see how the new one holds up. Quote Link to post Share on other sites
BigChongus 765 Posted November 9, 2014 Report Share Posted November 9, 2014 Hard to tell from the pics, but it looks like the radius at the ends of the cuts may be larger too. Quote Link to post Share on other sites
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