Bolt Gap - How To

[M1 Tanker]

Right out of the manuals.

.1-.5mm or .004 to .02 inches. Use feeler gages available from any auto part store.

159

160

[submarinedriver]

M1 Tanker,

Thanks for the fantastic diagram.

Jeff

[Seattlefungus]

Hey tanker, I have that manual too, it talks about a cocking tube straightening tool, to straighten and remove dents in the cocking tube. Know where I can get one? I have the German Armorer tools for the receiver mandrels to remove dents, but not the cocking tube...

[drhall762]

Very good to know, especially on my first build.

Thanks,
Dave:)

[M1 Tanker]

Robertrtg.com has some german tool sets....big money though.

[SteelCore]

Man, I always thought on a CETME when you got below .008 or above .016 there could be problems....I musta pulled those #s outta my arse or something.

Thanks.

[wulf50guy]

Man, I always thought on a CETME when you got below .008 or above .016 there could be problems....I musta pulled those #s outta my arse or something.

Thanks.

No it isn't just you. I seem to recall those numbers as well.

[Seattlefungus]

Tank, I have the RTG kit, (his last one). none of the tools is the right diameter to enter a cocking tube. From the H&K manual, I got the impression it's something similar to a plumbers ruptured nipple extractor.

[texlurch]

.008 - .016 is where they seem to run the best.
.004-.020 is the min/max, if you will.
Mine did not like .004 and would not cycle consistently; .008 and it runs fine.

[Perro]

nope, there is a specific tool in there to straighten cocking tubes
i have it in my kit - it is not like a plumbers broken nipple extractor, but a long tube threaded in back and tapered in front that is driven into the cocking tube. One of the cleaning rods is threaded into the back of it to pull it back out.


and youre missing part of the equation from HK
you also need to show the page explaining OPTIMUM bolt gap being from .010 - .018

[SteelCore]

Ah, I think that is what I remember. I know that when mine dropped to .010, the felt recoil increased, and the plus 4s moved it up to .012, and made it run really nice.

Thanks, Perro!

[Perro]

this is the page youre missing

[texlurch]

Excellent.. I am adding that to my bolt gap/ground bolt doc....

[Karl E. Hungus]

ok new question, given that a gun has a slightly less than nominal bolt gap of about .007, could replacing the locking piece with a brandy new one also serve to expand the bolt gap? or is it pretty much regulated by just roller size?

[M1 Tanker]

Trunnion, bolt, roller and locking piece all wear and shrink gap. A new locking piece usually gives you .001 to .003 more gap.

[Lon Moer]

So, you can alter the bolt gap by changing around;
- different locking piece
- different rollers
- different size rollers
- different bolt head, with the same rollers
- different bolt head, with the same size rollers
- different bolt head, with different size rollers


are there any other steps between those and the extreme end of repressing the barrel?:confused:

[jfowl31]

if you replace all those parts, and still are below spec, unfortunately, no there is no other way of doing it.

It takes thousands and thousands of rounds for the rifle to wear down that much, so a full rebuild of the rifle is not out of the question... It sounds like a whole lot of work if you think of a Century rifle as a new rifle, but really the century rifles are decades old, and have been shot a TON.

[Perro]

the parts that wear on your gun shrinking bolt gap

rollers - diameter shrinks

locking piece - on the ramps where the rollers ride

trunnion - where the rollers mate for locking

barrels face - look inside with a flash light, youll see an outline of your bolt head on the barrels face - this isnt present on a new barrel - this comes from the bolt crashing into it, and it does shrink gap

bolt head - the face from smashing into the barrel shrinks, and the windows that the rollers sit in enlarge both reducing bolt gap


the bolt locking lever also wears out as does the mating surface of the bolts shoulder. with the bolt closed and the locking lever locked over the top of the bolts shoulder, it should not have any free play there. Take a screw driver and lightly pry the bolt head away from the carrier, but not enough to raise the locking lever any - if you have alot of play there, replace your locking lever with a new one.