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KLR
06-03-2016, 10:10 PM
So what is the reason for the difference in neck dimensions? A 30-30 has a .003" taper, a 30-40 Krag has about .001", a 30-06 is straight. Why? Is one better?
Thanks.
country gent
06-03-2016, 10:12 PM
SOme of this is due to the extraction exerted by the action they were chambered in. The camming of bolt actions did much better than single shots or lever guns at Pulling the fired cartridge out.
williamwaco
06-03-2016, 10:22 PM
Are you looking at a cartridge drawing or a chamber drawing?
JWT
06-03-2016, 10:35 PM
Are you looking at a cartridge drawing or a chamber drawing?

Looks like both for 30-30 and 30-40. 30-06 cartridge is straight but the chamber is tapered according to SAAMI.

169541
169540
169539
KLR
06-03-2016, 10:43 PM
Looks like both for 30-30 and 30-40. 30-06 cartridge is straight but the chamber is tapered according to SAAMI.

169541
169540
169539


Thanks. I was looking at chamber specs but must have looked at cartridge specs for the 30-06. So is it necessary to have a slight taper?
JWT
06-03-2016, 11:29 PM
Sammi spec for the 30-06 chamber shows a .0021 taper.
runfiverun
06-04-2016, 12:14 AM
dies are cut straight the chambers are cut tapered.
the chambers are tapered to draft angles so you can get the brass in and back out of them easier.

if I had the choice I wouldn't have a rifles neck cut with a taper.
I tried to get the XCB rifles reamer cut without the neck taper.
EDG
06-12-2016, 01:49 PM
The chamber necks are specified to be tapered because there is some tolerance required when manufacturing anything.

The taper of the neck is equal to the tolerance permitted for the neck diameter. This is just ordinary engineering practice.

If the case mouth goes to maximum size and the base of the neck goes to minimum size you will have a straight chamber neck.
Without this convention you could wind up with the chamber mouth larger than the base of the neck and a fired cartridge will lock itself into the chamber when it expands.

Reloading dies do not have that taper most of the time.

However you can find old BPCR dies that faithfully reproduce the neck taper of some of the old rounds. However when you expand the case and seat a bullet you effectively make the neck straight.

What we choose can often be different from mass production manufacturing.
Sure we can use a straight neck but it might not be such a good idea for a half million rifles that will be used in combat.