Tag Archives: Inside case neck reaming

RELOADERS CORNER: Inside Reaming Vs. Outside Turning


Some confuse these operations. Don’t! Here’s what each is, and isn’t…

Glen Zediker

I get a lot of questions. I always answer each one, and in doing so that experience reminds me of the wide span of topic knowledge needed to be a successful, and safe, handloader. I make an effort not to assume any level or depth of anyone’s understanding of any topic I might address. At the risk of “offending” all the experts out there by wasting their time with fundamental starts to technical pieces, I’d dang sho rather bore them than shortchange a newcomer out of elemental information.

I told folks in my last book that “grains” refers to a propellant weight, not a kernel-count. Right. But I’ve fielded that question more than once. That’s not, in my mind, a “stupid” question. Truth: The only stupid question is one that’s not asked, when there’s a need to know.

So, that was leading into this: Here’s a question I got just yesterday that sourced via someone who wasn’t even a little bit uneducated in the need for finer points of case prep. This fellow was confused about the relationship between inside case neck reaming and outside case neck turning. Here’s a longer version of the answer I returned to him —

First, there is no relationship between inside neck reaming and outside neck turning, and by that I mean they are not a combined process. As a matter of fact, these should not be combined!

They can be confused because they both ultimately accomplish the same thing, the same basic thing: each process removes material from a cartridge case neck cylinder, and that makes the case neck wall thinner. These two ops, however, are done for two different reasons.

neck reamer
Inside neck reaming is a treatment to thin excessively thickened case necks after several firings. If the neck walls get too thick, the outside diameter of the case neck might not have adequate room in the chamber to expand to release the bullet. Excess pressure! Shown is a Forster-brand accessory for its case trimmer.
IMPORTANT: “Standard” case neck reamers are for use only on fired but not resized cases! Exceptions are custom-size reamers, and I own a few of those that get use from time to time, but, as was said for tight-necked rifles, if you know about that then you already know about this…

An inside case neck reamer is intended to relieve excess material from case necks that have thickened excessively through use and reuse. Brass flows, and it flows forward.

Important! Most “standard” case neck reamers are intended to be used on fired, but not yet resized, cases! In other words: Use the reamer on the fired cases as-are. Do not use one on a case that’s had its neck resized because that will cut away way too much brass.

Another application where inside reaming is frequently recommended is in forming operations that require a reduction in case neck diameter. When a case is “necked down,” which means run through a sizing op that creates a .243 caliber from a previously .308 caliber, for instance, the neck walls thicken. An appropriately-sized reamer makes the shortest work of this tedious but necessary job. Most forming die packages either include or make mention of the specific-size reamer to use.

Outside case neck turning is done to improve the consistency of case neck wall thickness around the cylinder. It’s a step taken to improve accuracy. Outside case neck turning should be done only on brand new (unfired) brass. It’s more precisely effective and easier because that’s when the alloy is at its softest.

turned case neck
Outside neck turning is a “precision” case prep step that improves consistency of the case neck wall thicknesses. It can be done a little bit to clean up “high spots” and make the cases better, or full-area to make them nearly perfect. That, of course, also makes them universally thinner so your sizing apparatus might need to be dimensioned differently to maintain desired case neck inside diameter to retain adequate grip on the bullet.

There are specific, custom combinations that require a smaller than standard case neck outside diameter. The “tight-necked” rifle, which is just about exclusively encountered in Benchrest competition, has to have its brass modified to chamber in the rifle. The neck area of the rifle chamber is cut extra-small to provide a means to attain a “perfect” fit and minimal case neck expansion. If you’re into this, then you already knew that…

So, the primary role and use of an inside neck reamer is as a safety precaution; its secondary use is as a prep step in case forming. The primary role and use of an outside neck turner is to improve the consistency, quality, of a case neck cylinder. The idea is that more consistent wall thickness leads to a more centered case neck. And it does. Reaming does zero to improve consistency. Reaming just makes a bigger hole of the hole that’s already there; it doesn’t relocate its center.

drop test
The way (or one way) to tell if your cases need a ream is to take a fired case and see if a bullet will freely drop through the neck. If it won’t, they’re too thick. Thrown them away or refurbish them with a reamer. Resizing won’t change a thing.

Combining these ops might create a safety issue because the necks might get too thin, and that could mean there wouldn’t be enough grip on the bullet. Point is, ultimately, that reaming and turning are not equivalent even though they might seem to be doing the same thing. One is not a substitute for the other. It certainly would be possible to remove metal from the outside of the neck cylinder to overcome the effects of thickened necks, if (and only if) the neck is sized again using the usual die apparatus. When that’s the goal, though, a reamer is lower effort, faster, and less expensive to buy into.

Very important! Always (always) culminate either operation by running the cases a trip through the sizing die you normally use.

Check out a few tools at Midsouth HERE