Factory-formed or cylinder brass?

nvshooter

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Have been thinking about creating another mildcat round. It will be an elongated 6.5mm Creedmoor that I call as of this moment, the 6.5mm Croodmeer. It will utilize the .30-06 Springsteen case and be 2.100 inches long-- the same as a 300WSM to make sure it's a short-action round. Neck length will be 1X the bullet diameter. Shoulder angle will be 23 degrees--the same as a .223Rem case. The angle was chosen because there is a neck-turning tool available that has the blade already cut to that angle. I expect I will have to turn the necks because the brass will most likely be kind o' thick right where we find the bottom of the neck on an '06 case. My question is, Should I use cheap & plentiful factory-formed brass? Or should I procure cylinder brass at $0.78 apiece?





23-degree shoulder angle.JPG
 
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I don't remember what the OAL is of a '06 natively, but necking down even a .308 will cause it to grow. I'm fairly sure changing the body taper will also cause it to grow. Whether it does this predictably or consistently is another matter. However you're probably looking at minimum two annealing steps and I don't think you have any good taper and plug dies (if you want I could in theory design them for you), which leads me to tell you just start with .30-06 brass and go from there.
 
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nvshooter

nvshooter

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I don't remember what the OAL is of a '06 natively, but necking down even a .308 will cause it to grow. I'm fairly sure changing the body taper will also cause it to grow. Whether it does this predictably or consistently is another matter. However you're probably looking at minimum two annealing steps and I don't think you have any good taper and plug dies, which leads me to tell you just start with .30-06 brass and go from there.
An '06 case is 2.494 inches long; the Lee Precision case-trimming mandrel trims 'em down to 2.487 inches. The Peterson "wildcat tubes" are 0.075 inches longer than my design length, so they'll work. The Peterson tubes' wall thickness is 0.009 inches down to about where the shoulder is on a 6.5mm Creedmoor. Good thinking on their part.

The dies will be custom-designed by Ben Syring at Hornady; Hornady will make the three forming dies and the two-die reloading set-- just as they did for my two previous mildcats. I'll have Ben design for a neck bushing in the resizer, something I did not have done the first time around. The neck tension was too little on the .358-caliber example, and I had to have Lee make a set of neck-only dies. Took a year; I've forgotten the cost.

Dave Manson will make the floating-pilot reamer and headspace gauges-- just as he did for my first two. Lee Precision will make the Factory Crimp Die-- just as they did for my first two. I had a rough cost estimate written-up for these hard parts, but I've lost it. I sort o' remember the dies, reamer and gauges were around $750 or so. Then we will need to buy a rifle with a heavy barrel; I'm thinkin' a barreled Howa M1500 in 6.5 Creed for around $500 and some. Aluminum chassis; another $500-some. Cut the mildcat chamber in the Howa barrel; another $350-some. Muzzle brake and install it; $270-some. It adds up...
 
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nvshooter

nvshooter

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Did a calculation of the case capacities of the Creedmoor versus the Croodmeer. If I did it right, the Croodmeer has a 29.9% greater case capacity to the bottom of the neck. I'm pretty sure my calculations are correct. I did them twice-- and slowly-- to make sure I made no careless errors in a blind haste. If a 6.5mm Creed will throw a bullet a mile at a waiting milk jug, a shell with dam-ned near 30% more powder space will also certainly do it. It can even be said that the Croodmeer is the "magnum version" of the Creedmoor...
 
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nvshooter

nvshooter

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Did a calculation of the case capacities of the Creedmoor versus the Croodmeer. If I did it right, the Croodmeer has a 29.9% greater case capacity to the bottom of the neck.
I had to have made a mistake. I just now calculated the volume to the shoulder point of each. I averaged the head diameters-- 0.473" for the Creed and 0.468" for the Crood: 0.4705 inches average). The shoulders are .462" for the Creed and .450" for the Crood; average is .46325 inches. The difference is in the distance from the head to the shoulder point. The Creed has it at 1.490 inches; the Crood has it at 1.6527 inches. The Creed calculates-out to having a volume of 0.25114 cubic inches to its shoulder. The Crood calculates-out to having a case volume of 0.27856 cubic inches to its shoulder, for an increased capacity of 10.9 percent. That's huge! Will figger-out the grains-of-water capacities at a later time.

I have yet to calculate the volume in the conical portion of the case; I'm happy with the Croodmeer being almost 11% greater in capacity. I did not involve myself with calculating the volume lost to the rim and interior webbing; knowing I'm over 10% greater in volume that the Creed is satisfaction enough.

The Crood has a 23-degree shoulder angle. I am now thinking I may go to a 30-degree angle to find an even greater case capacity with a more-similar look between the two cases. I imagine Hornady Custom Manufacturing can tell me if I can cold-form a 30-degree angle on a thin-wall case. Might take four forming dies instead of three, plus a resizing die to finish the case to a near-exact shape that can be chambered.
 
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nvshooter

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Calculated anew the case volume of the Croodmeer from the base datum (0.200" above the head); found the volume to be pretty much spot-on at 70 grains (4.567cc) of water to the mouth. That's a ton! This round will either still be running supersonic at 1600 yards or will be wildly inaccurate because the Case Volume : Powder Charge ratio is bad. Will cost about $5000 to find out.

I see the case volume of the Creed listed at 3.40cc, which is about 52 grains o' water. My mildcat is 34% greater in volume. That's encroaching on super-magnum territory. Like necking a .17-caliber bullet into a 300RUM case. Wondering now which powders would do well in such a shell...

Dimenshunned 6.5mm Croodmeer.JPG
 

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