Reamer design

[Blindman54]

I'm thinking of a new build but I would like to know if changing the angle the shoulder will make a cartridge more accurate or more efficient? I understand that a 40 degree shoulder slows the brass from getting longer for less trimming. But I'm more interested in the 30 or 35 degree shoulder. All advice is welcome

 

[adam32+P]

What cartridge are you thinking?

 

[FEENIX]

I'm thinking of a new build but I would like to know if changing the angle the shoulder will make a cartridge more accurate or more efficient? I understand that a 40 degree shoulder slows the brass from getting longer for less trimming. But I'm more interested in the 30 or 35 degree shoulder. All advice is welcome

That is very subjective. As @adam32+P noted, which cartridge are you trying to improve? For instance, if it is a .30-06 parent case, and you prefer the 35-degree shoulder, then the .30 Gibbs is your easy button.

 

[Blindman54]

What cartridge are you thinking?

I'm thinking about either the 223 Rem or 308 Win

 

[adam32+P]

I'm thinking about either the 223 Rem or 308 Win

.223 Ackley is the easy button, 40°.

.308 Win leave it as it is.

 

[MagnumManiac]

The real answer lies in HOW the sharper shoulder angle changes the burning characteristics of the powder and how it makes using a slower powder for more velocity possible.
Two things change, the powder is more efficiently burnt and held in the case protecting the throat, and it also changes the burn rate of the powder so you can step up one grade slower in the burn rate effectively.
If you change the shoulder angle, it is also wise to reduce the case taper, so this needs planning too.

Cheers.

 

[Nitrogrrl]

Remember once fire-formed, you ideally want the neck to be at least as long as your caliber projectile. This from Dave Kiff at PT&G. Also would recommend picking up the set of books by Ackley, "Handbook For Shooters and Reloaders Vol. 1 and 2", and if you can afford them, "Small Arms Design Vol. 1" and "Small Arms Ballistics Vol. 2", by Whelen (try to find them with the inserts, expect to pay through the nose but worth the expense. I believe both are necessary because Whelen goes into great detail, during the '20's and '30's when everything was SO much more challenging to accomplish, which show you more about How and Why. Ackley picks up from there, not as technical so both sets of books will get you on the track.

 

[MagnumManiac]

Remember once fire-formed, you ideally want the neck to be at least as long as your caliber projectile

This is simply not a necessary factor, neither is having an extra long neck.
Many cartridges out there function perfectly with less than calibre long necks, the reasons are too many to list here, but one is mechanical restrictions, being the shoulder has been moved forward to optimise powder space at the expense of neck length. Necks have one function, to hold the bullet from falling out, nothing more…

Cheers.