CZ 550 Bolt Will Not Close On Go Gauge

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BigBore585

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So Im going to be converting my CZ 550 American Safari in 458 Win Mag to the 458 Lott. I stripped the rifle and bolt down to a bare bolt (no extractor or firing pin assembly) and I decided to try out the head space gauges I ordered from Pacific Tool and Gauge. Now when I insert the No Go Gauge the bolt will not close at all, which is good. I inserted the Go Gauge and the bolt closes half way and stops. I can insert an unfired round and the bolt closes fully, with no force really needed. So Im kinda at a loss right now. I think that the gauge is machined wrong. I do not want to start reaming the chamber out and not have good gauges. Im going to be using a PTG 458 Lott pull-thru finishing reamer to cut the chamber. Im wondering if anyone has run into the same problem, and what did they do to correct it? Any help Or ideas would be great! I am trying to get it done before sunday so I can load up some rounds and try it out.
Thanks!
 
BigBore585 said:
So Im going to be converting my CZ 550 American Safari in 458 Win Mag to the 458 Lott. I stripped the rifle and bolt down to a bare bolt (no extractor or firing pin assembly) and I decided to try out the head space gauges I ordered from Pacific Tool and Gauge. Now when I insert the No Go Gauge the bolt will not close at all, which is good. I inserted the Go Gauge and the bolt closes half way and stops. I can insert an unfired round and the bolt closes fully, with no force really needed. So Im kinda at a loss right now. I think that the gauge is machined wrong. I do not want to start reaming the chamber out and not have good gauges. Im going to be using a PTG 458 Lott pull-thru finishing reamer to cut the chamber. Im wondering if anyone has run into the same problem, and what did they do to correct it? Any help Or ideas would be great! I am trying to get it done before sunday so I can load up some rounds and try it out.
Thanks!
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Sounds like your chamber is .0005 or so short. I would question the chamber before the gauge. Does the .0005 matter?
NormB
 
When rechambering belted mags, you stop the reamer just as it contacts the existing chamber "belt". Put some "magic marker" on the front surface of the belt, and when it shows the first sign of scuffing - stop. No need for gauges if you're careful, for rechambering belted or rimmed cartridges.
 
Pacific Tool and Gauge? Machined wrong? I don't know about their go gauges, but I do know that they can't grind a match reamer to spec.
 
The go gauge is supposed to be exactly .220" from the front of the belt to the rear of the gauge... fairly easy to measure and manufacture. All brass however is made to a smaller dimension so being tight on a belted go gauge actually is good.

Re chambering a belted magnum chamber to another belted magnum chamber is very tricky... how do you fully ream the old chamber and not increase the headspace? Stopping exactly as the belted portion of the reamer meets the belted portion of the chamber requires very precise methods.
 
When rechambering belted mags, you stop the reamer just as it contacts the existing chamber "belt". Put some "magic marker" on the front surface of the belt, and when it shows the first sign of scuffing - stop. No need for gauges if you're careful, for rechambering belted or rimmed cartridges.
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Thats what I was kinda planning on doing.
 
The Africans often use a rechambering reamer instead of a normal chambering reamer. It can't cut the belt recess deeper because it is made with no cutting structure in that area. It just bottoms out and that's it. They are often used with a extension and driven by hand. Its hard to find a .458 CZ that hasn't been converted to a Lott.

Most of my custom chambered magnums won't close on a go-gauge.
 
I thought about using a reamer that would not cut belt any deaper, but I figured if Im really careful, I should be fine. I also did some searching around on the interweb, and found some info stating CZ cuts tight chamber for accuracy, and many will not close on a go gauge.
 
Andy said:
When rechambering belted mags, you stop the reamer just as it contacts the existing chamber "belt". Put some "magic marker" on the front surface of the belt, and when it shows the first sign of scuffing - stop. No need for gauges if you're careful, for rechambering belted or rimmed cartridges.
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The first signs of scuffing could be as little as a thousands of an inch but with inexperience could easily be a few thou..
 
The first signs of scuffing could be as little as a thousands of an inch but with inexperience could easily be a few thou..
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I agree. Its my first time doing this kind of stuff with a rifle, but not my first go playing with precision machining of metal. Im not a machinist, but going through school to become a mechanic, I have learned a thing or two.
 
I have done many, patience is the key and I use black flat spray paint on the existing belted chamber. Then I can cut up until I see the paint start to cut but not the steel at the belt........it works slick, then usually another .002 and all is clean and properly headspaced.
 
I also did some searching around on the interweb, and found some info stating CZ cuts tight chamber for accuracy, and many will not close on a go gauge.
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I don't know about that, at least with the 550 Magnums. The chambers on mine were friggen huge, and resizing the cases is like trying to shove a water balloon down a gopher hole. That is deliberate, practically the only thing that matters on the big guns is that they work everytime, no matter what. They do seem to shoot very well in spite of this.
 
c-fbmi said:
I have done many, patience is the key and I use black flat spray paint on the existing belted chamber. Then I can cut up until I see the paint start to cut but not the steel at the belt........it works slick, then usually another .002 and all is clean and properly headspaced.
Click to expand...

I like the paint idea. Quite a bit thicker and gives a bit more room before cutting any metal away. Going to do this next time.
 
I inserted the Go Gauge and the bolt closes half way and stops. I can insert an unfired round and the bolt closes fully, with no force really needed.
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you have no problem .. unless you wish to create one. Incidentally it is very instructive to "mike" a good sample of your brass belts and different manufacturers ... my experience is they vary ... ymmv too :)
 
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