Nerdy Necks Redux

[wookie76]

I was intrigued by the earlier post about neck lengths, and started playing around with dimensions in Excel.

A few notes:
Dimensions are from ammoguide.com.
Short action chamberings only and nothing belted.
I arbitrarily dismissed all chamberings smaller than .204 and bigger than .308.
These are of the bench rest type.  Since the premium bullet choices are limited, I also arbitrarily dismissed the .257 and .277 offerings.

Old school manual machinists talk about inch taper per foot.  My brain can't handle that due to my cnc background, so I trig-ed out the body taper in degrees.

You can't have it all.  I would rather have a calculated neck length and 30º shoulder that intersects the body taper, than a calculated shoulder height.

The most "Ackley-ish" factory offering appears to be the 30 T/C, but this chambering looks like it's going nowhere.
https://spreadsheets.google.com/pub?key=0AsWmkhaqiUW5dHFWcXU0emR6cEQ0YmN4VjZpWU9Gc3c&hl=en&single=true&gid=0&output=html

[briannmilewis]

What are your conclusions?

[wookie76]

I just have hunches.

I don't think the shoulder height should be set, I think it should be derived from the 30º neck angle intersection with a .25º body taper.  I don't think a neck angle greater than 30º is any great advantage.

I think a neck shorter than the given norm of caliber length would be fine, to a point.  I don't think it would be a problem to go down a standard caliber length.  Such as a .308 bore down to a .280 neck, or 6.5 bore to a .240 neck.

But some combo's just work, like the 6.5-284 and 6mm Dasher.

http://en.wikipedia.org/wiki/Texas_sharpshooter_fallacy

[briannmilewis]

I agree that the 30 deg shoulder is the best angle for any cartridge.

I agree with you that the shoulder height is of no consequence.

I believe where the shoulder starts on the case body is critical if we are to get the most accuracy and reliability out of any cartridge. The 40 deg shoulders of Ackley and others, get more powder in the case, but I believe 40 deg shoulders do not make the round as accurate as is possible.

The four things the BR cases and the PPC cases have in common regardless of case diameter: 30 Degree shoulder angle, 1.52" or there abouts case length, and a shoulder that starts approx at case length x .7072. The tapers are .010 or .011. Shoulder length varies, neck length varies.

I think anyone can improve most cartridges of 2" case length or less by applying the "BR" specs.
The formula results in very long necks with cases over 2". The WSSMs are a good case of close enough is good enough as they are almost BR specd. The 30-30 shoulder starts at the BR length for the cartridge, 1.440", the place where the case length x 0.7072 would place it. Did the designer of the 30-30 know something that no one else did at that time?

I believe that if we put a 30 deg shoulder on the 30-30 exactly where the current shallow shoulder starts, and reduce the taper to.010 or .012, it is currently .021, you would have a great shooter with a long neck close to .500.

The 17 Ackley Hornet is almost a perfect BR case and shoots extremely accurately. Ackley put a 30 deg shoulder on a case he tapered .011 and the shoulder starts at 1.109" from base. If he used the formula case length x 0.7072 the shoulder would start at 0.99" from the base.

A 30 deg Hornet where the shoulder starts at 0.99" from the base, I believe, would be a better cartridge than any of the current Hornet variants. I should make that a project and see if i am proved wrong.

All I can say is there are a lot of projects we could do without spending a fortune if we stick to Savage Axis (Edge) bolts and Handis.

 

[briannmilewis]

Shane and I have been kicking around modifying the 221 FB and 223 Rem cases to BR specs after the 223 Short is done.

I just suggested to Shane that we do a Bench Rest makeover of the 223 Rem, cheap brass and easy case forming.

If we trim the case to 1.52" like the 22BR/22PPC, change the shoulder angle from 25^o to 30^o like the BR/PPC, and change the place where the shoulder begins (1.075 from base) like BR/PPC, the result is a neck length of .270 by chance, which can be considered a medium neck length for the caliber. We also do not care about the shoulder height, it is about .175.

It will literally look like a small brother of the 22BR/22PPC and look very similar and be a tad smaller in diameter to the 5.45x39, but using a standard .224 bullet.

OK now I am done.

Just looking forward to the fun.