Fired case neck dimension
- Thread starter COLT45SA
- Start date
Most of the time it will show @ .001 less than actual chamber dimension.
COLT45SA
Silver $$ Contributor
Thank you~!
Yes, that's a good rule of thumb but I find it's actually a little closer than that with full power loads. Gotta hit it pretty hard just to get it really formed in the neck on one firing and then...how much did the bbl swell vs how much did the brass spring back kinda thing. Just some variables that are tough to quantify that affect the end number to a fair degree. But...if calipers are the tool being used to measure with...Well....just forget I even commented.
Sometimes a person can see the differences in the way brass expands and contracts, in a ladder load from mild to hot rounds, you do need a micrometer though. Get a lot of 100 brass, they probably won't all expand and contract the same on the first couple of shots. You'd think 50-60K or more in pressure would do the job, but brass is made in a liquid form and poured into sheets, cut into a disc, then stamped into shape, so it has variances in it. It'll harden at different rates, annealing may help, but, the makeup of the brass will still govern that, to some extent. The fired dim's are pretty close, but, not perfect.
I think there is only one normal neck chamber diameter for a no turn neck? Check a few SAAMI chamber blueprints. The manufacturer may not be legally held to that dimension. But my guess is they do.
For 6mm. I thought a no turn neck was always .272".
No, not always sir. Even right now, newer Lapua brass is thicker than it was within same cartridge even. A .272 is pretty tight or maybe even too tight with some of it. I've added a thou to my newest reamers because of this.
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The .276" unsized neck area has expanded to the necks chamber. After over 20 loadings, it no longer expands or springs back. No annealing, for the most part.
The unsized area makes it slightly harder to chamber rounds. Light drag.
Firing a 68 gr Berger with IMR 4350 will not expand necks fully with starting loads. Even at maximum pressure, spring back happens a lot on first 3 firing.
The unsized area makes it slightly harder to chamber rounds. Light drag.
Firing a 68 gr Berger with IMR 4350 will not expand necks fully with starting loads. Even at maximum pressure, spring back happens a lot on first 3 firing.
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4350 in a ppc or even a BR with 68's? How in the world did you get anywhere near a "max pressure?"
"A cross sectioned .222 chamber with a gazillion rounds down the barrel. Normal cleaning and nothing more. Bushing die..You can clearly see where the neck bushing stopped sizing the neck of the brass. "
http://forum.accurateshooter.com/threads/erosion-from-blowback-on-necks.3938810/page-2
From post #24. Photo by gunsandgunsmithing.
http://forum.accurateshooter.com/threads/erosion-from-blowback-on-necks.3938810/page-2
From post #24. Photo by gunsandgunsmithing.
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243 winchester.
Lol! That's my picture! Pretty interesting though, isn't it. The guy only neck sized most of the time and being a 222, the bbl lasted a really long time but I just don't remember what he told me for a round count on it. You can clearly see the step where over time, the dirty(probably), unsized portion of the neck is in the chamber. Not sure it really matters but it's an eye opener either way.
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Oh, ok. That makes sense now. Thanks!
I'll add...while the pic looks like clear rifling left..boy, it was almost totally gone for at least a couple or three inches. Like I said, a bazillion rounds down that pipe. He never shot fast or for long at a time and really kept his stuff clean. He never got it what I'd call hot or even close to it. This sucker was just worn out. IIRC, it still shot way better than one should expect it to though when it finally gave up the ghost on him.
Sure is. Not sure if good or bad. But my 40x factory barrel likes it that way. Thank you for posting your photo. Food for thought.
Shooter13
Gold $$ Contributor
Not really, I have a 6PPC with a .274 neck, brass comes out .273
No turn dimension is what ever the buyer told the reamer maker. Now .272 is about as close to standard as you can get today. Tomorrow somebody may come up with a different dimension that works better!
Frank
Frank
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