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Thread: Be an informed consumer!

  1. #151
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    Quote Originally Posted by LRRPF52 View Post
    Here are some pics of the nitrided extension that chipped like glass with the mere touch of a rubber Cratex polishing bit. You can see it on the right feed lip. I've done scores of feed lip jobs where the lips don't match the extended M4 ramps, even with M4 extensions, because the industry is all over the map when it comes to matching these parts up. For those of us who shoot a lot of 68-77gr BTHP's, we like to have a smooth transition there, with no possibility of the meplat catching on the edge of the feed ramps of the extension.

    There has been a learning curve for some manufacturers on QPQ/ferritic nitrocarburizing, which is why I think I got this barrel at such a low price. $170 for a fluted, CMV, .223 Wylde chamber seemed about 1/3 of what I should have been paying, but I rolled the dice. I had it in a rifle upper without ramps before, and was planning on moving it to an M4 upper. The index pin was also sharply cut of with grinder marks on it, with no consideration for clearing the female threads of a barrel nut, so I radiused it and made it so that it would perform as expected.

    After having a mechanical engineer look at it, he said it appeared to be through hardened, and kept asking me if I had dropped it on a hard surface. There is also some galling on the bottom of the 3 o'clock tooth of the extension, which looks like it could have come from installation with the barrel extension tool. The barrel is quite accurate though.





    Tragic. Dented spot looks kind of dirty where the rest really shines.
    So let me ask you. If carburizing called for by the mil spec hardens the extension 20 times, 20 times deeper than Melonite which would likely cause through hardening?
    On a related topic what are those shiny extensions made from and why are they shiny? Can't possibly be stainless so are they untreated 8620? Why are Armalite extensions parkerized?
    LRRPF52 is the Super Moderator of the Grendel Forum, number 1 Grendel and Alexander Arms promoter. I promote the 6.8SPC. He travels the internet to bad mouth the 6.8, the 264LBC and any company that competes with Alexander Arms.
    Last edited by constructor; 05-21-15 at 22:34.

  2. #152
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    I was able to salvage the barrel in question by continuing the depth of the polish with a Cratex bit. It was improperly nitrided to the extent that the edge of the feed ramps were embrittled.

    LRRPF52 is the number 1 Grendel and Alexander Arms promoter. I promote the 6.8SPC. He travels the internet to bad mouth the 6.8, the 264LBC and any company that competes with Alexander Arms.
    These statements are total BS, and have zero to do with the thread. I have .264 LBC barrels in my inventory right now. Notice the personal attacks everyone.

  3. #153
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    Just a heads up: I had recently had a friend I helped with his AR15 after he got into a "deal" he couldn't pass up, even after I told him to wait until I got back from being out of State.

    It had some garbage aluminum gas block canted way out of position, some sub $100 barrel, unknown BCG, 2.9oz carbine buffer with 16" CLGS, UTG handguard, cheap plastic garbage stock, etc.

    I replaced as many bad parts as possible, trouble-shot the gas system while installing a new steel gas block with correct alignment, gas tube aligned perfectly, H2 buffer, etc. The barrel actually shot really well at 100yds, cartridges drop in and out with gravity, springs looked ok. Got the thing running and it was accurate.

    He saw all these "deals" with nitrided BCG's, NiB, accessories, etc., couldn't hold back. I told him to buy ammo and get some quality trigger time, don't get sucked into all the ancillary crap that will do nothing for you. He got the nitrided BCG anyway, and started having FTFire malf's regularly. I took a look at everything, and noticed there was marring to the firing pin around the sides of the tip.

    Placing the firing pin inside the bolt showed that there was about .020-.030" of resistance in the final travel of the firing pin. I tested the pin on several other bolts, no problems. Then I checked that bolt with other firing pins, and the same problem was encountered. There were burrs inside the firing pin aperture behind the bolt face. That's the first I've seen that happen.

    The vendor took care of it, sent a call tag, and replaced it with another BCG. Added another thing to inspect in my laundry list of QC checks, and reinforces what I've seen: Just because something is nitrided doesn't mean it's a quality part, or "better than Mil-spec".

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