At what point is G3/Cetme bolt gap dangerous?


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Monkeyleg
March 13, 2005, 01:20 AM
On some forum, THR or another, a poster mentioned that a bolt gap at or under .004" was dangerous.

The poster didn't say why, but I would assume that it's because the bolt gap affects timing, and too small a bolt gap could lead to the rifle firing before reaching full battery and lockup.

Can anyone 'splain this in more detail to me?

Thanks for any replies.

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itgoesboom
March 13, 2005, 03:09 AM
Monkey,

I would run a search over at cetmerifles.com or gunboards in the cetme section. Perro had a few times discussed the reason why it was so dangerous, and I believe it did have something to do with the timing, but also unsafe pressures and such.

Is your rifle at a lowbolt gap right now? If so there are ways to fix it.

My century CETME came to me with a bolt gap of about .007-.008, and right now it is right at the upper limit, .019-.020.

All I did was put in +4 rollers, and replace the extractor spring (that actually had the most difference). Nobody can explain why the extractor spring made such a difference, but I can see that the extractor sticks out just a hair past the bolt head, so it sort of makes sense.

I.G.B.

Feanaro
March 13, 2005, 04:22 AM
The maximum headspace is .5mm, more than that and the action unlocks early. Less than .25mm and the rifle will probably have trouble with extraction/ejection. In inches that would be about .019 and .009. Larger is better here, as headspace actually becomes smaller with time due the the locking system.

http://www.hot51.com/headspace.htm

Monkeyleg
March 13, 2005, 07:36 PM
Thanks for the replies. I had the rifle out at the range today for the first time since giving it a thorough cleaning. I had expected it to perform better.

Wrong. It was essentially a single-shot rifle today.

After each shot, it would chamber the next round, but the bolt head protruded far enough out of the bolt carrier that the firing pin wouldn't strike the primer. Then it started jamming to the point where I couldn't pull the bolt back using the charging handle. I had to whack the charging handle with my staple gun to open the action. And none of the rounds would eject without tilting the rifle back and smacking the side of the receiver.

I thought I'd be able to get this thing working properly myself. After all, there aren't that many parts, and I don't see how the bolt assembly can be put back together wrong.

After shooting just nine rounds, I took it back to the gun shop, and they're going to send it back to Century. The owner wrote them a short letter saying pretty emphatically that Century had better fix it 100% or replace it with a rifle that works, or his days of selling their guns are over.

He also had a lightly-used Cetme that he said he'd give me if Century didn't follow through.

Unreal.

itgoesboom
March 14, 2005, 01:38 AM
Might be better off just getting a refund, Century is pretty much out of the CETME rifles (yeah, they say this everyyear, but apparantly its actually true this year.).

Hope it works out.

I.G.B.

Feanaro
March 14, 2005, 05:26 AM
I thought I'd be able to get this thing working properly myself.

It sounds like your headspace was too small. So you could probably have fixed it with over-sized rollers. http://www.robertrtg.com/g3.html

But that sort of headspace in a new rifle is unacceptable. Hope the next one Century sends you works out better.

Monkeyleg
April 22, 2005, 11:59 PM
An update on my problem:

After many weeks at the factory, my G3 finally came back to the local shop. The first thing I did was check the bolt gap. Previously it was just shy of .005". Now it's about .008". Not a huge jump, but better. I suspect they plopped in a different bolt carrier group.

I won't be able to take it to the range until tomorrow or Sunday. But I did notice one thing right off the bat.

If I pull back the charging handle and let it slam forward, the bolt head is once again sticking out from the bolt carrier about 1/8" or so, same as before. If I pull back the charging handle, put it in the locking slot, put the safety on, then release the charging handle--even letting it ride forward gently--the bolt head doesn't stick out from the bolt carrier.

I have no idea what engaging the safety has to do with this, but it apparently does, at least on the first charging of the bolt. What happens with subsequent rounds from the magazine I won't know until a trip to the range.

The internals on this rifle look so simple that I'm amazed that there could be problems.

Any input much appreciated.

itgoesboom
April 23, 2005, 12:20 AM
Monkey,

Be very, very cautious.

Century had a bad habit of grinding the boltheads to increase bolt gap, although that only gave a false reading and didn't do anything to fix the actual problem. Go to CETMErifles.com, and look in the member primer about this, it will show you how to check it out.

The other thing Century was doing was putting in oversize rollers, and I am not talking the +2 or +4 rollers, but +6 or +8. If that isn't bad enough, apparently, nobody taught the monkeys how to use a lathe properly, and they are uneven and just shoddy.

If I was you, I would (1) take your rifle apart, and remove the bolt head and make sure that the back of the bolt head isn't ground, (2) use a micrometer to check the diameter of the rollers and (3) make sure all the surfaces of the rollers are even.

I.G.B.

itgoesboom
April 23, 2005, 12:28 AM
If I pull back the charging handle and let it slam forward, the bolt head is once again sticking out from the bolt carrier about 1/8" or so, same as before. If I pull back the charging handle, put it in the locking slot, put the safety on, then release the charging handle--even letting it ride forward gently--the bolt head doesn't stick out from the bolt carrier.


Monkey,

The proper way to check bolt gap is to cock the rifle, put it in the locking slot, keep the safety off, do the "hk slap" by slapping the cocking handle, letting it fly forward, and pull the trigger after wards, and then check the bolt gap.

Ofcourse, before you do this, make sure the rifle is unloaded ;)

I.G.B.

Dave R
April 23, 2005, 01:44 AM
Another possibility--Century parkerizes the bolts. That puts a pretty rough surface on them. Lots of friction. But after the bolt reciprocates a few hundred times, the finish smooths out and the bolt moves more freely.

Back when I bought my CETME, a lot of folks on CETMERIFLES reported that they would work the action a few hundred times while watching TV before taking them to the range. Smoothed the action out pretty well.

itgoesboom
April 23, 2005, 02:07 AM
Dave,

These rifles definatly do better with use, and need to wear in a bit.

I am finally getting that *&#$ stock assembly to come off without too much effort. Only took the last 8 months.

I.G.B.

Dave R
April 23, 2005, 11:42 AM
LOL. Yup, another example of Century's build quality. Some rifles also have a problem with the trigger group being tight.

When Cruffler.com (a website devoted to C&R & surplus rifles) did their review of the CETME, they couldn't get their buttstock off, either. They also had the problem with "not enough windage." Returned it to Century. Century sent them a good rifle. I had my dealer fix my "not enough windage" problem.

Now I love my CETME.

Feanaro
April 23, 2005, 03:20 PM
I am finally getting that *&#$ stock assembly to come off without too much effort.

Hehehe, I had similar problems with the G3 stock I added to my CETME. The first time I took it off I had to enlist another person(both of us weighing in at 200ish pounds without [much :D] fat) and a c-clamp. And it took about ten minutes. After around two, threes months I can get it off with two hands and a foot. ;) I push as gently as I can on the PG with the foot, pull on the stock with right hand and use the left to keep the rifle from hitting the walls. :evil:

I consider CETMEs project rifles. They need a little TLC to work properly, as well as about 200 rounds to get the parts mated together. I like tinkering but I'd probably recommend the PTR line to someone not up for the work.

Monkeyleg
April 23, 2005, 06:40 PM
Ok. After spending a lot of time over on cetmerifles.com, I understand better how all this works.

Using the "HK slap," everything moves into position normally. Why the safety would affect this when not using the "HK slap," I don't know.

Next step is to take it to the range.

itgoesboom
April 25, 2005, 01:32 AM
Hehehe, I had similar problems with the G3 stock I added to my CETME. The first time I took it off I had to enlist another person(both of us weighing in at 200ish pounds without [much ] fat) and a c-clamp. And it took about ten minutes. After around two, threes months I can get it off with two hands and a foot. I push as gently as I can on the PG with the foot, pull on the stock with right hand and use the left to keep the rifle from hitting the walls.


I just always used a series of hand slaps to the top and bottom of the stock that I have on, hitting towards the back of the buttstock, and that gets it off fairly fast. Even quicker if I pull back the charging handle (watch that stock fly :what: ). Doesn't matter if I have the crappy CAI stock or the HK stock that I have now, they are both so tight.

I.G.B.

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