Re: 7mm creedmoor
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jedi</div><div class="ubbcode-body">Hmmm me thinks you guys maybe confused
XC is Norma made to tubbs specs
it is large rifle
XC brass is rated @ 65kpsi vs 60kpsi for Cm brass </div></div>
This type of rationalization is flawed for a very basic reason:
The rating and the case head design are two different things. Since you have the 1895/6 Mauser Case head design (aka anything with a Std. head and large primer pocket) you're effectively limited to 65-66ksi. The only way that changes is if the brass has been compromised in some way.
I've done the calculations to back up what VarmintAL did with LSDyna, though I did it with Abaqus 6-8.EF1 and my results were within 3% of his across the board. For reproducing a complex computer model like that with a different code, <5% difference is very good.
I've run Norma brass and seen no indication between Norma, Win, R-P and Hornady that indicates any of them can sustain more loadings than the other at 62+ksi pressures. They all give up the ghost and pushing the caliber that hard reduces the ballistic efficiency and you cause wear at a higher than normal rate. I did the tests to prove out my computer model with a tightly chambered, custom built 30-06 and a Matlab driven DAQ card in grad school.
The rating value has little to do with the function and everything to do with the company attorneys that reviewed the spec prior to publication.
Look up 2 different specs for 308 ammo, they are the same brass, same case, same everything except the Winchester and Black Hills have published different Pmax allowables...
Strange, since WW makes BHA brass.
The extra performance that might comes from the XC case would be a big jump if you ran small primer pockets because then you can run the cases upwards of 72ksi without brass issues. However, not all receivers are ammenable to such behavior. There's no replacement for displacement and the XC holds a little more go-dust than the C case can hold.
The bottom on this, in my professional opinion as an engineer, is that if you really need to go over 2850fps with a 162gr bullet and a sub 26" barrel, pick a chambering that has at least 60gr of water capacity. Otherwise, the 7CM is not a magic caliber, some barrels are just "fast" and others are just "slow"... I seem to have a "slow" Brux on a 308 right now, it's 1.25" longer than my last 308 but it runs a full 80fps slower across the board.
RODENT sounds lucky to me that he got a speedy tube, congrats. I don't think that Melonite is the answer to the velocity question, making a bigger hole at the chamber end is the solution to that.
Jedi, I'm intrigued by your 60gr water case, sounds very similar to something that I've been tinkering with but have yet to grind a reamer for at this moment. The QuickLoad simulations appear to be positive in that I can bridge the gap between 7-08 and 284 Win while keeping it in a short action comfortably, which was my ultimate goal. I have a long action short magnum that outruns everything else in this discussion, but it's a big heavy rifle that tends to break targets and burn a lot of powder, I want something to increase barrel life, use a common bullet with my 7/300WSM, run common powder to my 30-06 or 300WSM or 308 Win, while getting at least the performance of a 6.5CM with 140's in it. The 7CM fits that bill and has the added benefit that I already own Comp Dies for the 6.5CM, have hundreds of pieces of brass that is 1 neck size step from being "done" and an action that has shown to feed the CM case like butter.
I don't think you're off base that a small bore 7mm like the 7-08 is not going to get magic properties because of melonite, for me the XC case loses on cost of brass alone. $1+ each when the Hornady brass I have already has produced stellar groups for a tactical rifle and I have to go buy new dies as well is just a no go.
