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Thread: New member with a c308 guestion

  1. #1
    Veteran Has Been's Avatar
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    New member with a c308 guestion

    Greetings everyone. I'm new here and have a guestion regarding my C308. I've had it for 2 years now and last night I noticed something I hadn't see before..... very slight roller dents in the rails to the rear of the reciever. They're so light you have to hold it just right to even see them. Now for a bit of history on this rifle.
    I bought it new from Adademy Sports and first thing I did when I got it home was tear it down and give it a good cleaning. It was so gritty I wondered if it had been assembled in a sand box. I also inspected all parts, which looked new to me. Found a couple burrs that needed removing and adjusted the recoil spring guide rod. Everything was in spec except for bolt gap, which was a tad wide at .023" but figured/hoped it would shrink a bit during initial break in but after nearly 1000 rounds it's still the same. I kept an eye out for developing problems, like roller dents, for the 300-400 rounds but noticed nothing out of the ordinary and quit worrying about it after that.
    When a first bought this rifle I did quite a bit of reliability/ accuracy testing with a wide variety of ammo that included surplus, Russian steel case, commercial hunting ammo and hand loads.
    Recoil was always noticeable but didnt strike me as being excessive except with the 180gr commercial hunting ammo. Last summer I swapped out the cheesy plastic navy grip and furniture for a steel grip frame and wood furniture. Buttstock assembly is HK and handguard is Cetme.
    Looks were greatly improved and I also noticed recoil was much softer, even with the 180gr stuff.
    I fired approx. 80-100 rounds of 180gr ammo during accuracy testing. It was spread out over a month or more and the heavy stuff was tested at the end after I'd quit watching for problems with this rifle and well before a swapped out the butt assembly.
    My question is this...is it possible the roller dents were caused by a combination of a worn out Cetme buffer and the 180gr ammo or is the slightly wide bolt gap the culprit?
    Last edited by Has Been; 05-29-2019 at 02:50 PM.

  2. #2
    Senior Veteran Combloc's Avatar
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    Those marks are usually due to worn out recoil spring and buffer. Hot loads will do it too. Essentially, the bolt is traveling to the rear too hard and fast.

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    holescreek's Avatar
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    The bolt gap range specification of .004"~.020" sets the proper amount of spring pressure where the bolt locking lever meets the ramp on the bolt head. When it is at the low end (.004") it's harder to unlock the bolt and when it's at the high end (.020") the bolt unlocks very easily. The leverage to overcome the spring pressure comes from the shoulder angles of the locking piece installed. Since this is a blowback system the weight of the carrier and the return spring integrity also plays an large part. If everything is in spec, the carrier won't hit the buffer while shooting the correct ammo and the rifle is a smooth shooter with minimal recoil.

    You shot ammo the rifle was not set up to shoot, with a bad (but easily correctable) bolt gap, in a rifle assembled with used parts of questionable quality (amount of wear from service life).

    The rifle needs to be tuned to shoot in specific conditions whether it be heavy ball ammo or suppressed or it will start beating itself up. Tuning is typically limited to changing roller sizes to get the proper gap, special conditions require changing the locking piece shoulder angle to delay opening too soon and sending the carrier into the buffer like a rocket.

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    Veteran Has Been's Avatar
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    Thanks for the replies. I'll measure the rollers this evening after work and post the results. BTW, what is the recoil spring specs concerning minimum length?

  5. #5
    holescreek's Avatar
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    I've never seen a length specified on recoil springs anywhere that I can remember.

  6. #6
    Veteran Has Been's Avatar
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    Rollers measure .315"

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    Quote Originally Posted by Has Been View Post
    Rollers measure .315"
    Those are standard rollers. 8mm

    Or wore out bigger ones.
    14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer

  8. #8
    Veteran Has Been's Avatar
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    Got a pair of - 6 and - 8's otw. Hopefully one or the other will get BG down to at least .020" or slightly below. I reckon I'll find out when they get here.

  9. #9
    holescreek's Avatar
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    I think -4's would put you in the sweet spot, -6 rollers might work OK too.

  10. #10
    Veteran Has Been's Avatar
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    Rollers should be here tomorrow. In the mean time the 4 u.s. made parts needed to assemble a trigger pack to get the 922r parts count back in correct proportion arrived Saturday. I managed to get all the bearing surfaces polished and the parts assembled before my hands gave out. That little bit really ticked off the arthritis and now it takes both hands to pick up my coffee cup. Getting old is for the birds....
    Last edited by Has Been; 06-03-2019 at 05:44 AM.

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