Greetings to all! I visited Gerard's site last night and read about how to test if your rifle has an over size chamber neck area. Anyway I did the test on my latest 7x57 which was manufactured in 2005. It is a CZ 550 LUX.
I taped the neck of a factory loaded round and a dummy round as detailed on the site and when I chambered both, the tape was NOT touched at all! Imeasuerd the outside diameter of both rounds with tape removed and I get 7.9mm. A once fired factory case unsized measured 8.2mm outside diameter at the neck.

Is this too much clearance and do I rebarrel or rechamber? Anybody else have the same 'problem' with their CZ 550 7x57?
Thanks in advance
Lal

I can't find SAAMI specs for the 7x57 chamber, but for the similar .280 Rem chamber SAAMI shows a neck diameter of .3156" (8.016mm) plus or minus .002" (.05MM).

At 8.2mm (.323") your chamber's neck would be only .0054" (.134mm) oversized. So your chamber's neck sounds somewhat "generous" to me, but not unsafe.

In order to minimize tooling costs manufacturers start with chamber reamers which sometimes fudge over the maximum specification. That way they can get more chambers out of the reamer before it has worn to less than minimum specs.

If your rifle's accuracy is satisfactory, then the only negative impact of an oversized chamber neck is that the brass is worked more when reloaded and will, all things being equal, crack from work hardening earlier than would brass fired in a tighter chamber.

One way to compensate for an overly large chamber neck is to use brass necked down from a larger caliber. For instance, if you necked down .30-06 brass and trimmed it to length you would end up with a thicker case neck that more closely matched your chamber. Such a case would probably not enter the chamber with the tape wrap. Whether this would appreciably improve your accuracy is another question.

Thanks Stonecreek. I have reloaded all my cases ten times and then toss them without any necks splitting thus far. Accuracy is excellent with Impala 110gr mono factory loads but have yet to find a homebrew that can equal them. Will keep trying.
Regards

http://www.saami.org/PubResour...fle/7mm%20Mauser.pdf

http://www.saami.org/PubResour...%207mm%20Express.pdf

I have had friends ream a 7mm57 chamber to 280 Remington, it worked except the 280 reamer will not clean up the 7mm57 chamber because of the difference in neck diameter. 280 cases fired in the new chamber will have two different neck diameters, same problem when reaming a 308 W chamber to 30/06, the 30/06 reamer will not clean up the 308 W chamber.

There could be .005” difference in the diameter between the two neck diameters. A builder of bench rester type rifles was informed the neck of his 308 W chambers were loose, I thought it unusual, his rifles shoot one hole groups. Anyhow he asked me to help with tightening up the necks so I boxed up a few tools and went for a visit. He had no shortage of once fired and new 30/06 cases. I formed 30/06 to 308 W. I formed the 308 W cases to match the length of his fired cases from the shoulder to the head of the case, I increased the neck diameter of the formed cases to .341” from .335”, the diameter of the fired case necks was .345”.

And again, not sure, he wanted to tighten up the necks to reduce case neck expansion when fired, his rifles have no problem shooting better than the shooter. I explained to him reducing the neck expansion would increase case life, I explained to him I had little interest in increasing case life when it came to accuracy, a very boring conversation for me goes something like, “My rifle shoots one hole groups and I get 20 firings before I have to etc., etc.. the cases.”.

Forming dies, there are not many I do not have. If I had one it would be the 308 W, if I had two the second would be the 243 W.

F. Guffey

F.Guffey thanks for that. Cant view the sites for some reason.....

http://www.saami.org/specifica...nformation/index.cfm

forgive, I tried the two links, both work on this end. I access the sight through the link above.

F. Guffey

Thanks Guffey I found that very interesting. Still a little confused though!

"Still a little confused though!"

I accept that, about what part?

F. Guffey

Forget about how big your chamber is and shoot it. If it shoots like you like it, good. Taping the neck is not a precise method; the SAAMI neck diameter for the 7x57 chamber is 8.263mm or .3253+.002 where the shoulder joins the neck. For ammo, it is 8.237mm or .3243 -008, So you can see that, with a max chamber and min ammo, you can have a lot of clearance. I measured some 3M masking tape; .0035. I hope you aren't going to spend hundreds of dollars based on a piece of tape. Your measurements are within specification.

dpcd you answered my question. Many thanks to everyone for your help. The diagrams were useful and I have them saved F. Guffey.
Many thanks again.
Regards
Lal

Centering the round in the chamber is the key when chamber necks are on the large side. Control how much the shoulder is pushed back on sizing. Sizing Link