Thread: Chamber Reamers: Straight Neck or Tapered Neck

A question for the technically inclined here please.

What are the perceived trade-offs of having the above; a chamber where the neck is cut perfectly cylindrically versus one that tapers down in diameter from the shoulder neck junction out to the case mouth by say 0.0005" - 0.0015" (as this appears to be the common level of narrowing)?

Given how the straight wall design appears to predominate, and the springiness of brass, I can't see the taper being just a design choice around ease of extraction.
Surely the designers have other benefits in mind?
Maybe the idea is that sizing a slightly conical neck results in improved centering - particularly in a bushing die situation where the case walls may not necessarily be contacted - with better resulting concentricity in the sized neck?

Tapered necks stem from militiary design. The tapered neck allows some gas to flow around the outside of the case after the main pressure spike and aids extraction.This was developed during the early age of BP cartridges. It doesn't aid centering. The barrel throat and shoulders of the case do the centering

Thanks Walker, interesting. I am particularly interested the reason for continuing to retain some taper in modern designs. The standard CIP design for the 6.5x47 Lapua has 0.0012" taper for example. This is specifically an accuracy round where I can't see the designers being particularly concerned about extraction. Could there be any other factors at play relating to accuracy please ?

6 ten thousands of an inch isn't much of a taper but as it's a high pressure case it will be to stop possible seperation of neck to shoulder junction by allowing body thickness brass to protrude into the neck.

Probably helped A LOT when dropping the cartridges into the chambers when facing that charging Rhino/ lion / elephant with trembling hand.

Post this in all the relevant categories, someone will have exact answers I'm picking. You could also e-mail a barrel-maker, as they often advertise this service, as able to be customised to your need (havent seen them explain it further)

If you draw an exaggerated picture of the projectile, in the case, after detonation, the projectile would theoretically be held tighter, by the end of the case-neck (rather than being held,by the complete length,that it was seated),as the case expanded, from the shoulder forward. This could theoretically help alignment, or projectile speed(less resistance from the neck as tension decreases,from case-expansion into taper). The mechanics of what happens, might help solve the "Why"it is done, but I guess the "Proving" might be a bit trickier ? Perhaps the resultant lower pressure might allow more of a particular powder, in a long barrel ? People swear-by the most interesting of things, Good Luck!