Case head expansion problem?

[saladin]

hi all. i have started working up some handloads for the new Ruger #1, and got some good results with 27gr of 748 driving a 39gr sierra in hornady brass. The primers don't look overly stressed, but the expansion ring on fired cases is set well back towards the head. Because it's a single shot, there is no polish-mark off the bolt-face to help with diagnosis so i decided to mike the case head. Expansion was 2 thou! now, i have been lead to believe that half a thou was around the upper limit of allowable expansion. is this true? is 2 thou manifestly excessive? has anyone else discovered that Hornady brass is unusually soft, which might explain this expansion? Certainly 27 gr of 748 is under the max loads in my reloading tables, but the expansion would suggest that it is far too hot.

anyone with experience in this area would be most helpful.

cheers, jason.

[jo191145]

Yep .002 is to much expansion. You are measuring the rim correct? It sounds as if you are so I'll assume so.
27.0 Win 748 should not be a HOT load with the 39.
Any idea where the lands are?
Maybe jammed in the lands with a fresh bore could be to hot
Ammo sitting in that hot Australian sun by chance?

Besides that I'm at a lost. Everyones complaining thier brass is to soft and I can't get my necks to expand
Good Luck.

[Ahab]

Huh? Are you talking about measuring the O.D. of the rim or the expansion of the case just forward of the rim after firing? Cases from my Savage expand .005", while those from my Contender,
.006".

[saladin]

just forward of the rim, ahab. further investigation has revealed that the starting size of the brass falls into two distinct sizes, one being .001 larger than the other size. this brings the after-firing expansion back to around .001 - still too much. I'll back the load off and see what the effect is.

[jo191145]

Anyone can feel free to correct me if I'm wrong but to measure case head expansion one must measure the rim. I have heard of some people measuring the extractor groove with the thin part of a caliper blade. Thats probably another alternative.

saladin
Measuring forward of either of these two points as you are doing is incorrect. Your basically just measuring your chamber size. Expansion on that part of the case is to be expected.

The actual amount of expansion one looks for on the rim is well below .001 per shot. But I'm not sure exactly what that measurment is.
A micrometer is needed for these measurments. Calipers are just not fine enough.
That is why when using hot loads brass can be spent after five firings. The primer holes have stretched out.

Your load is probably quite safe,enjoy