308 case expansion in win brass

[300 RUM]

I was doing some load development this week and noticed some bad signs. I loaded up 20 win 308's and 20 Lapua 308's with the exact same charge (41gr H4898). The lapua brass which is what I have been using for some time looked just fine after firing and then FL sizing. BUT! the Win brass loaded with the same (41grs H4898)looked fine after firing but after FL sizing (cleaned case)the Win brass measured .463 just after the extractor grove and tapers up to .468 is this a pressure sign?

 

[Keith Glasscock]

Nope, it is a sign that the breach end of your chamber is larger than the case head, and the resizing die is a standard die. I have the same problem...

If you want to measure case heads for pressure, you'll need a blade micrometer and measure the inside of the extracor groove. A dial caliper can be used to diagnose way-too-high pressure, but doesn't have the sensitivity to see the .0002-.0003" inches that indicate a max load.

Just remember that new, fireforming brass will move more than older brass will for the same pressure.

I've found that win brass makes wonderful, shiny extractor marks when I get it too hot. It does this at the same point that significant cratering and flattening of the primer occurs. In theory, Win brass, with its greater internal volume, will produce less pressure than Lapua for an identical powder charge.

Hope this helps,
Keith

 

[300 RUM]

Heres a photo of the case BUS

 

[300 RUM]

So how does that happen, is it bad machining, does it effect accuracy, will it hurt anything?

 

[243winxb]

Photo looks normal. May be the difference in brass wall thickness & the diameter of the new brass when it was made. See drawings for +/- measurements. The thicker web does not expand like the rest of the body. http://www.saami.org/PubResources/CC_Drawings/Rifle/308%20Winchester.pdf

 

[amlevin]

All my Winchester brass (.308) looks just like that. Been using most cases for over three years with numerous loadings. Don't have any separation problems or does it seem to affect accuracy. I load 175's with 43gr Varget +/- .5 gr and load 168's with same powder at 44.4 gr. I have similar "marks" on my Lapua brass, just not as pronounced. Lapua is a little thicker in the case walls thus has less capacity but neither Win or Lap cases seem to have any issues with this little "bulge". It would appear to me that the only way to prevent this would be to have a custom chamber cut with less tolerance. Closer to original case dimensions. But then your sizing die would have to be smaller too.

 

[300 RUM]

I've not seen this before and jumped the gun on becoming alarmed. All the dimensions are well with in the specs, i guess i'm used too Lapua brass. I have had a lot of people tell me Win brass creates a better "case to chamber" seal and will actually give more consistent neck tensions then Lapua. I'm aware of most pros and cons of both manufacturers, it is just time to start replacing brass and I figured I would try the Win brass out.

Thanks every one, big help. I'm glad it was just an oversight on my part.

 

[SmokinJoe]

Measure some unfired cases in both brands. You will probably find that the Lapua is a little bigger at the case head end than the W-W. That is pretty typical of Lapua brass in my experience.

 

[300 RUM]

New W-W brass measures .463 and new Lapua brass measures .469. That right there explains everything, my chamber is a Bisley 308.Not to mention the new W-W cases also shrunk .003. Another note the fired Lapua brass has some expansion also it measures only .001!

 

[bigedp51]

Did you forget "WHY" you bought Lapua brass in the first place. :

 

[300 RUM]

Did you forget "WHY" you bought Lapua brass in the first place. :

I'm beginning to thinks so!

 

[K22]

I've experienced the same thing with 223 Winchester and Remington brass in seven different rifles (3 Remingtons, 2 Brownings, 1 Weatherby, 1 Custom Douglass). Only about 5 to 8% of the brass in each 100 round lot was affected with this "bulging". I initially detected the condition while checking headspace in my Wilson Case Gage. Some of the cases wouldn't seat into the gage and upon further examination I noticed the bulge at the base of the case.

Being no expert, I wasn't sure what was going on so I segregated the affected cases. I didn't suspect the load because it was well under maximum and it's a load I've used for many years. In addition, I found no classic signs of pressure. I'm still not sure what's the root cause but it seems to be due to some indivivual case imperfection since only a few are affected. But then again maybe it's being caused by the reloading die since that's the one constant to all reloads.

I've resized the bulged cases and reloaded them and had no signs of head separation. The very badly bulged ones I discared. Interesting I've found no such issue with my 243, 22 250 or 308 reloads so maybe it's the die but why would only a few cases be affected???

Would like to hear from others on this issue who are more knowlegable.

 

[bigedp51]

It is nothing more than the base diameter of the cases.

Below two .303 British cartridges fired in the same Enfield rifle, the HXP case had the smallest diameter and expanded further to meet the chamber walls. The Prvi Partizan case had the largest base diameter and the case walls were .010 thicker in the base web area.

(the Prvi cases are the Enfield rifles Lapua cases)