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We need something new to argue about. Tapered necks?

So I have an early (08/2017) pre SAAMI approval print from JGS released by Joe Thielen at Hornady for the 6.5 PRC that has a .299"-.299" parallel neck???

The popular 6.5 PRC AW2 reamers have .0008" taper.
 
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I have reamers which are made both ways, to drawings I made. If I am building a tight necked rifle and intend to neck turn, I like a straight neck. If it is to be a no-turn, I prefer a tapered neck. I like the tapered neck because it will always ream clean. A straight neck may have an occasional scratch. When it comes to accuracy, I can't honestly say I see a difference; as long as the chamber is straight and concentric, it usually works out. WH
 
Section a case lengthwise, and look at the side wall thickness going from head to case mouth. It is a continuous taper. In order for the clearance of the neck of a loaded round in the chamber to be constant going up the neck from shoulder to mouth, the chamber neck has to be tapered, to correspond to neck's taper. SAAMI chambers are for unturned necks. If you seat a bullet into the neck of an unturned case, so that the entire neck contains the full diameter section of the bullet, and measure the diameter of the neck at various points along its length, you will find that it is tapered in a manner similar to the taper in a SAAMI chamber.
 
You guys start threads like this and I get 15 phone calls asking about it...

I don't know the rationale for including (or not including) the taper in the standardized chambers. I tend to think it has to do with the fact the virgin brass walls taper, resulting in the neck root of a loaded round being slightly larger diameter than the neck mouth, with the chamber then being designed to give an equal amount of clearances along the neck length. Of course, the counter to that line of thought are prints like the Creedmoor's posted above, one showing no taper in either chamber and cartridge and the other showing taper only in the chamber.

From a theoretical machinist/tool performance point of view, you should see a better finish from a tapered cutter. It cuts along the entire length, rather than just the leading edge. But then anyone who has used a chucking reamer may have cause to disagree with that.

I'm relatively certain reamer makers generally spec wildcat reamers (that they are only making one of) with no taper because it is cheaper to set up and grind with a template. At least here, the shoulder and neck are ground in the same operation/setup, with a single template. It is cost effective to have a template with a given shoulder angle and a straight neck, not so much to have a bunch of templates for a given shoulder angle and various neck tapers. Templates are quite time consuming to make. For reamers that we make in volume on the CNC, a tapered neck is just as easy as a straight one.

I do not see a downside to either version with unturned brass. I do think a straight chamber neck is more appropriate for neck turned brass.

I have not noticed any difference in accuracy/precision between the two, but I don't neck turn.
 
WSnyder said:
Wait a minute. Both SAAMI Creedmoor’s are a tapered neck. .001” difference from back to front.

Edit: The 6CM is not but the 6.5 is so now what???
Click to expand...
Yes...weird stuff, for sure.

I have an early SAMMI sheet for the 6.5 Creedmoor showing the neck being .2970 for the entire length. The only reason I have it is because one of my pals that I call 'G3' (Gas Gun Guy) ;) was going to have one done for another AR platform and had some concerns about the straight neck and cycling. He'd had some issues with straight necks in a couple other AR barrels (223 and 20 Practical) and a chamber redo to tapered necks in both made the issues go away according to him.

I know slightly less than zilch about gas guns but did see the issues before and the results after.

Good shootin' -Al
 
Ray Gross said:
You guys start threads like this and I get 15 phone calls asking about it...

I don't know the rationale for including (or not including) the taper in the standardized chambers. I tend to think it has to do with the fact the virgin brass walls taper, resulting in the neck root of a loaded round being slightly larger diameter than the neck mouth, with the chamber then being designed to give an equal amount of clearances along the neck length. Of course, the counter to that line of thought are prints like the Creedmoor's posted above, one showing no taper in either chamber and cartridge and the other showing taper only in the chamber.

From a theoretical machinist/tool performance point of view, you should see a better finish from a tapered cutter. It cuts along the entire length, rather than just the leading edge. But then anyone who has used a chucking reamer may have cause to disagree with that.

I'm relatively certain reamer makers generally spec wildcat reamers (that they are only making one of) with no taper because it is cheaper to set up and grind with a template. At least here, the shoulder and neck are ground in the same operation/setup, with a single template. It is cost effective to have a template with a given shoulder angle and a straight neck, not so much to have a bunch of templates for a given shoulder angle and various neck tapers. Templates are quite time consuming to make. For reamers that we make in volume on the CNC, a tapered neck is just as easy as a straight one.

I do not see a downside to either version with unturned brass. I do think a straight chamber neck is more appropriate for neck turned brass.

I have not noticed any difference in accuracy/precision between the two, but I don't neck turn.
Click to expand...

Sorry Ray! - Defer them to me, I'm happy to take the call.
 
LVLAaron said:
In my case, I did. Other than extraction... is there a reason to use a tapered neck?
Click to expand...

When you chamber a tapered neck you can clean up a chip scratch. With a straight neck you would have to run the reamer in the entire length of the neck clean up a chip scratch.

I have zero opinion on tapered necks. That was just something that I noticed.
 
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