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el bromisto
01-20-2014, 11:17 AM
I had a disappointing weekend. I've had a parts kit and a barreled Century receiver that I finally tested. The first case failed to eject and the bolt was stuck very tight. I took off the lower and had to hammer the bolt back using the cocking lever. I didn't try another round because I'm concerned there's something very wrong.

The bolt gap was right at 0.020" and the CT gap was about .040". It took -8 rollers and some machining of the cocking handle to get it there. I also had to tweak the ejector to ride in the bolt properly.

Any ideas on what's wrong? I have a new cocking tube and surplus barrel/trunnion. I'm thinking about fully demilling the receiver and starting from scratch, but if there are adjustments I can make to the assembled parts I'd rather do that.

Arkane
01-20-2014, 03:23 PM
Will it hand cycle dummy rounds without a problem?

el bromisto
01-20-2014, 10:27 PM
It cycles them with a vengeance. I only have two dummy rounds but they eject across the garage and load from the magazine just like I hoped a live round would.

automick
01-21-2014, 11:15 AM
What ammo did you use.!
Are the Flutes clean.!

holescreek
01-21-2014, 11:34 AM
What did the case look like when you finally got it out? Specifically, were there heavy ridges left in it from the chamber flutes?

rustypirate
01-21-2014, 06:55 PM
The fact that you had to use -8 rollers and machining of the charging handle to get the gaps right tells me that you started with something that was VERY out of spec.

I would suspect that re-pressing the barrel would be in order to get everything right, and while you are at it, swap out that charging handle with one that has not been messed with.

When you are levering out the charging handle to the open position, do you feel any resistance?

el bromisto
01-21-2014, 07:19 PM
I was shooting brass cased ammo. I'll look up the headstamp and get some pictures later on tonight. I don't know what to say about feeling resistance when operating the cocking lever. I've never shot any others so I don't know how they feel, but for what it's worth it didn't feel like any resistance beyond unlocking the bolt.
I agree that something was way out of spec. I guess my question really comes down to whether or not the spec's can be fixed by rollers or if I should take more drastic action. Rusty seems to have cast a vote in the "more drastic action" category.

holescreek
01-21-2014, 07:53 PM
If you fired a round and the cartridge stuck in the chamber and locked the action closed it was likely that the brass you were shooting was commercial and probably thin-walled. If the brass was NATO and stuck in the chamber it could indicate that the chamber flutes were A) dirty/clogged b)too shallow c)too deep. A photo of the cartridge fired from the rifle could tell the story.

el bromisto
01-21-2014, 11:01 PM
The cartridge was Cavim '91. I did a little reading and it looks like a lot of people have problems with it. Do these pictures show anything useful?
4174141740

holescreek
01-21-2014, 11:30 PM
The cartridge was Cavim '91. I did a little reading and it looks like a lot of people have problems with it. Do these pictures show anything useful?
4174141740

Yes. The photo shows a couple of things. It shows that the cartridge didn't come out because the brass expanded into the grooves. It also makes me suspicious about the chamber fluting on the shoulder area of the chamber. The black lines in the right photo should have extended down the shoulder to the side of the case.

Clean your flutes really well before you shoot it next time (I use an M16 chamber brush and shove the steel bristles into the flutes) and shoot some NATO brass. You shouldn't have any trouble at all with steel cased ammo.

rustypirate
01-22-2014, 01:40 AM
If your charging handle unlocked the bolt head, then that would be the resistance I was inquiring about.

I also agree with holescreek, the flutes up in the neck area of the chamber look to be clogged up which would prevent the gasses escaping through them, and caused pressure to expand the brass into the flutes, jamming up everything.

The flutes need to be clean, clean, cleanin order the proper cycling.

el bromisto
01-22-2014, 02:23 PM
Thanks guys! I will give the flutes a good douching and see if it works better. While I'm at it, how do you all check for the flutes being in spec? I thought I read somewhere they should be 0.035" deep but that seems like a lot to me.

holescreek
01-22-2014, 03:44 PM
I cut my flutes .020" deep and .020 wide back in the old days. The big thing is that they need to run continuously from the case mouth down the shoulder and into the side. Any break in the groove will stop gas flow and ruin your day.

el bromisto
02-17-2014, 05:47 PM
I finally got her back out over the weekend. Cleaned the heck out of the flutes and ran this ammo. (http://www.sportsmansguide.com/net/cb/20rd-308-win-168gr-fmjbt-ammo.aspx?a=1326075) It skyrocketed to about 60% reliability! Obviously that's unacceptable. What's the likelihood of the chamber flutes being out of spec, as opposed to any of the other problems that cause poor cycling? Is a chamber casting the only way to know for sure?