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How to check bolt gap...

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  • King Lou
    started a topic How to check bolt gap...

    How to check bolt gap...

    With the popularity of CETME and HK 91 type rifles, it might be useful if we make a sticky post concerning how to check bolt gap.

    Instead of checking headspace like you would on most rifles, CETME/91 type rifles have a bolt gap check. The process is simple, and requires one tool: a set of feeler gauges.

    Feeler gauges are cheap and available at any hardware store. They are basically a collection of shims of varying thicknesses.

    You also must know what a bolt head is. If you remove your entire carrier assembly, the rectangular "block" at the front of this assembly that includes the extractor is the BOLT HEAD or BH.

    Now, with an unloaded rifle, pull the charging handle back and hold it in the notch. Point the rifle at the ground and do an "HK SLAP", letting the charging handle come down, full force. While still pointing the rifle at the ground, pull the trigger, dry firing the weapon.

    Now, rest the rifle on it's top so you're looking through the mag well. If you want an inexpensive rifle rest, grab a large box, like an empty paper box from Staples, and cut a U-shaped notch in both ends. The rifle will sit in the notches. This box also makes a decent cleaning rest.

    Anyway, while looking through the mag well, you will see the BH again. Where the BH ends and the carrier begins is the gap you are going to measure. Use your feeler gauges to determine the width of this gap. You are good to go if you have a gap of .005" - .020"

    Some notes:

    On PTRs - JLD makes their rifle to a spec that is in the middle of the gap tolerance, .010" - .012" . This is a mistake in my opinion, as you should start with a gap closer to .02" on a brand new rifle. Perhaps they made their new rifle like this because they were afraid they might go over the .02" high-end tolerance? Who knows, it's not a big deal really, as a gap of .010" ensures you'll have many thousands of rounds of use out of this rifle, and besides, you can always increase your bolt gap by purchasing oversized rollers (see +4 rollers below).

    On CIA - Any rifle made by Century is suspect of shady manufacturing practices. CIA made their CETMEs and 91s with out of spec, worn out parts, particularly the CETMEs, which is too bad because CETMEs are rare and excellent rifles when in good condition.

    What CIA did was abhorrent. When they realized their rifles were "gapping" well below the minimum tolerances, the removed the bolt heads and ground the backside of them down. Putting the BH back into the rifle and checking the gap gives you a false reading. To determine if you have a ground bolt head, simply look at the back of your BH and look for grind marks and a sharp finish line. An original BH has a slight chamfer around the edges of the BH aft surface, while a ground one has a sharp corner because the chamfer has been ground off. If you have a ground BH, my recommendation is to return the rifle. If that's not possible, try to get CIA to fix the problem. Lastly, install oversized rollers to try to give you true in-spec gap size (see +4 rollers below). Replacing the locking piece (triangular shaped head, the firing pin runs through it) can also give you a tiny bit of bolt gap if the LP is heavily worn. Unfortunately, LPs are very hard to come by for the CETME, as they are different from HK LPs.

    On +4 rollers. Everyone can see the BH has two rollers on either side. Replacing standard rollers with oversized ones increases bolt gap and the longevity of your rifle. Side effects include easier charging, less recoil, and smoother operation. After you replace std rollers with +4s, double check your bolt gap to ensure you're not over the upper tolerance.

    +4 rollers are the same for CETME and all 91 models and can be found here: www.robertrtg.com among other places. Here's a pic: http://www.robertrtg.com/g3rollerext.jpg

    Thanks Robert!!!

  • longhunter
    replied
    Originally posted by StinkyCheeze View Post
    It may be useful to some to reveal the bolt gap specs in the "original" format:

    0.1mm to 0.5mm


    This is the range given in HK literature. Metric feelers are easily available in auto supply stores as well.
    I find these metric specs easier to remember also.
    0.1MM-0.5MM translates to .0039-.0196 inches, so a gap of .005-.006 is near the bottom range of acceptable.

    Leave a comment:


  • Jericho
    replied
    RTG is excellent. Nice on the phone, quick to ship, A+ company.

    Leave a comment:


  • grassyknoll999
    replied
    Q: How to remove Rollers on G3/HK91 or Cetme?
    A: 1, Strip rifle and remove bolt assemble.
    2, Remove Bolt head from Carrier
    3, On the top of the bolt head you will see a small hole with a roll pin. Using a small punch tap out the roll pin. Retainer plate and rollers will now slide out.
    4, Shake bolt head until the roll pin falls out.
    5, Now put it back together, check your bolt gap and go shooting.

    This came from RTG's site. I'd recommend anybody with an HK91 or clone visit them. They're a great company. Every time I've dealt with them, they were very helpful.

    Leave a comment:


  • toftae
    replied
    changin rollers

    Any one know how hard it is to change the rollers? or could u just put up a set of instructions

    Leave a comment:


  • grassyknoll999
    replied
    Rtg also has an excellent parts list for essential replacement parts for the G-3. If you purchase rollers, you may also want to order an extra retaining plate and roll pin. They're cheap, and if you need them, you'll be glad you did. I have ordered many parts from them and found them to be very helpful and decent people. I'd recommend them to anybody.

    Leave a comment:


  • chauncey
    replied
    Originally posted by chauncey View Post
    interestingly, Springfield Armory advised me that by following this process and finding a gap < or = 0.005", the rifle is safe to fire! I sent them the rifle, with a pdf copy of your post, and I'm interested to see their response!
    so an update, what, 18 months later, after some griping I sent the rifle (at my expense) to SA and they adjusted the bolt gap - not sure how, the bolt head wasn't ground and from what I can tell they didn't install oversize rollers. do you think they re-pressed the barrel? don't ask me to look, I sold the rifle to an informed purchaser last fall...

    Leave a comment:


  • tonysrep
    replied
    thought I would post my gap of my springfield sar 3 (it said g3 on the box from springfield)I have shot about 2000 rounds thru this gun with no malfunctions. The gap is a snug .012 with no visible wear

    Leave a comment:


  • Crank
    replied
    My new PTR 91 came out at .015 + so I suppose I got a good one

    Leave a comment:


  • HuntersDad
    replied
    Originally posted by King Lou View Post
    Side effects include easier charging, less recoil, and smoother operation. After you replace std rollers with +4s, double check your bolt gap to ensure you're not over the upper tolerance.
    I am very facinated by these side effects. As a newbie to the G3/91 rifles, how does replacing the standard 8mm rollers with 8.04mm rollers decrease recoil?

    Be patient.. I am learning!!

    Leave a comment:


  • chauncey
    replied
    interestingly, Springfield Armory advised me that by following this process and finding a gap < or = 0.005", the rifle is safe to fire! I sent them the rifle, with a pdf copy of your post, and I'm interested to see their response!

    Leave a comment:


  • StinkyCheeze
    replied
    Metric Specs

    It may be useful to some to reveal the bolt gap specs in the "original" format:

    0.1mm to 0.5mm


    This is the range given in HK literature. Metric feelers are easily available in auto supply stores as well.
    I find these metric specs easier to remember also.

    Leave a comment:


  • The_War_Wagon
    replied
    after cleaning my friends ptr ,we checked the bolt gap it was less than .006
    Say CZ7 - how OLD is your friend's PTR, and how many rounds (roughly) has he fired through it? Inquiring minds would like to know, as I understand their mfg. tolerances of yesteryear were different, before P. Everett Weed came on-board last year.

    My PTR is spankin' new, but I'd still like to hear about these things, to be safe myself!

    Bob

    Leave a comment:


  • cz7
    replied
    bolt gap/headspace

    crap after cleaning my friends ptr ,we checked the bolt gap it was less than .006'' !opps [a bit of history hk had a time contract with the army to turn in all weapons and rebuilt them at 40% the cost of weapon in a 18 month time period ] well ,parts time again !!

    Leave a comment:


  • Love&a45
    replied
    It is my understanding that the bolt gap decreases as wear increases. When the bolt gap gets too small, the rifle is no longer safe to fire. A rifle that has a larger (but within spec.) initial bolt gap would maintain an acceptable bolt gap for a greater number of rounds.
    Last edited by Love&a45; 05-28-2007, 02:12 PM.

    Leave a comment:

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