When is a chamber too large?

S

SuperBruce

Private
Minuteman
Dec 27, 2020
52
15
Utah
#1
I have a barrel problem. I bought a prefit barrel in 308 win to put on an action I have laying around. I put it on and shoot ~100 rounds through the thing. It was an ok shooter, considering the profile. However, when I went to size the brass it was very difficult, to the extent that it stripped the threads on the Lee spline drive die bushing (aluminum). I checked the Lapua brass (which has been fired about 8 times through a different rifle) at the .200 line and it's measuring 0.4740" with calipers that claim to have 0.0005" accuracy. I fired some cheaper Winchester factory ammo and they come out measuring 0.4735" at the 0.200 line.

So it appears the chamber is wallowed, but only ever so slightly, perhaps 0.001 to maybe 0.002 depending on the spring-back of the brass. One one hand, it's oversized and I have to find another way to size the brass. On the other, it's not that bad. Where do people draw the line on sending it back to the smith? And will this degree of wallowing compromise the brass?

Thanks in advance for your advice.
 
#2
When is a chamber too large?

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#4
if its .001 to .002 over the reamer size thats not enough to affect accuracy. Shouldnt be enough to cause the sizing issues youre experiencing. Most guys with manual lathes have their tailstock off the spindle axis (high, low, left,right, whatever) and getting a chamber .001 or more over the reamer is not remotely uncommon. Pushing a reamer with a tailstock not perfectly on the spindle centerline will cause this. Look at the chamfer on your die and make sure youre lubing a new die with some sizing wax before yuo get to sizing a bunch of cases
 
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#5
Bugholes said:
if its .001 to .002 over the reamer size thats not enough to affect accuracy.
Click to expand...
Thank you for the reply. The rifle seems to shoot reasonably well. My concern is mostly about trouble sizing and perhaps excessively working the brass (although I suspect it's fine).
In the case of 308 Win, what would the SAAMI reamer diameter be? From the published diagram here I believe that is .4714" and the spec allows the chamber to be 0.002" larger for tolerance. So when you say 0.001 to 0.002 over reamer size, are you suggesting an upper limit of 0.4734", 0.4754", or something else? Also, I'm not measuring the chamber directly but going off the diameter of fired brass. I presume there is some spring-back after firing, but I can't imagine it's more than 0.001, so I'd guess my chamber is essentially 0.475", or 0.0015" larger than the upper limit of SAAMI tolerance. It's entirely possible I'm reading the diagrams incorrectly, or my assumption on spring-back is wrong, so any corrections on that are appreciated.

As for the die: this is not a new one. It's a Hornady match grade die I've used it for a few years now without issue loading the same brass for a different rifle. For lube I typically use a healthy dose of Hornady One shot spray on lube which has worked well for me for about 5 different cartridges so far.
 
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#8
I've sized brass that was fired in rifles with chambers on the large side and the imperial sizing die wax made the job go a lot better in my experience.
 
#9
I wouldn't think that would be to large to safely fire but the brass would probably have issues in another chamber. Also I wouldn't trust any caliper to .0005. If u need that precise of a measurement you need a micrometer.
 
#10
SuperBruce said:
I have a barrel problem. I bought a prefit barrel in 308 win to put on an action I have laying around. I put it on and shoot ~100 rounds through the thing. It was an ok shooter, considering the profile. However, when I went to size the brass it was very difficult, to the extent that it stripped the threads on the Lee spline drive die bushing (aluminum). I checked the Lapua brass (which has been fired about 8 times through a different rifle) at the .200 line and it's measuring 0.4740" with calipers that claim to have 0.0005" accuracy. I fired some cheaper Winchester factory ammo and they come out measuring 0.4735" at the 0.200 line.

So it appears the chamber is wallowed, but only ever so slightly, perhaps 0.001 to maybe 0.002 depending on the spring-back of the brass. One one hand, it's oversized and I have to find another way to size the brass. On the other, it's not that bad. Where do people draw the line on sending it back to the smith? And will this degree of wallowing compromise the brass?

Thanks in advance for your advice.
Click to expand...

Bugholes said:
If your die used to size 308 cases correctly with normal effort, and it’s struggling to resize cases from this new chamber in question, and your using similar/same brass, you should probably contact the gunsmith
Click to expand...
He can definitely contact the gunsmith. Another option would be to send 3 pieces of brass that were fired in the chamber in question to Whidden (or whoever else makes custom full length sizing dies) and get a custom full length sizing die made. It will cost $212+ but it'll probably be faster than going back and forth with the smith. With this type of die you could even specify the neck OD you want and not need to use bushings to set your neck tension. Or you can squeeze it down a few thou past target neck tension in the custom die then expand it back out with a mandrel to your target neck tension to have more flexibility.

Whidden Custom Non Bushing Full Length Sizing Die ($212)
 
#11
I had a Remington VLS 308 that had a huge chamber. If I only ever shot store bought ammo, it would have never been noticed.

I just neck sized a set of brass for that rifle. It eventually became a Remage with a properly sized chamber.
 
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