Pressure with Neck-Sized Brass but not Full Length Sized Brass?

[TOM H]

Ok, here is a pic of a case head. The mark is on the ACK, and this is one of the worst ones. As far as measurements of the FL and NS cases go, they were trimmed to the same length, prepped the same, same bushing, the only difference is the FL cases have had the shoulder bumped back 0.002". NS cases measure 2.140, FL cases 2.138, and new cases 2.137 measured with a hornady headspace gauge. I went back and chambered some of the NS brass and it is pretty tight, hard to close the bolt. Of course, the new and FL cases chamber with no resistance. My theory is that with the NS cases that are a tight fit in the chamber combined with a near max load has nowhere to expand to, so it flows into the ejector hole? What do y'all think?

Also, it's harder than I thought it would be to take a pic of an ejector mark!

Got a question. working up loads did you FL size or neck size also after firing new case do you NS and how many before NS get hard to chamber. Reason I ask is I've got 280AI and I've use Nosler brass and I can run pretty hot loads after firing new case I can get maybe 3/4 NS firing before FL and I use bushing dies

Have you tried rechambering a round after firing new or FL before NS? there is something missing beside just being hot load. I think if you read Backwood83 last post were kind of thinking same thing and Mike mention something isn't right. You might want to tell us what load are you using?

 

[MSLRHunter]

Got a question. working up loads did you FL size or neck size also after firing new case do you NS and how many before NS get hard to chamber. Reason I ask is I've got 280AI and I've use Nosler brass and I can run pretty hot loads after firing new case I can get maybe 3/4 NS firing before FL and I use bushing dies

Have you tried rechambering a round after firing new or FL before NS? there is something missing beside just being hot load. I think if you read Backwood83 last post were kind of thinking same thing and Mike mention something isn't right. You might want to tell us what load are you using?

After firing my new brass I FL sized some and NS some to see which my rifle prefers. My load is 58.2gr H4831sc, nosler brass, federal 210m, Berger 168 vld. I worked up to this load with new brass and no pressure signs. After the first firing , the FL brass still showed no pressure, but the NS brass had the ejector marks.

 

[backwoods83]

Its merely because of the tight fit, if 58.2 is where you topped out at fl sizing, then about 58.5 is what it would take to match it by just neck sizing. Try using a softer load on new brass before neck sizing next time.