November 12th, 2017

Primer Pocket Gauge — Cool Tool Checks for Loose Pockets

Repeated firings at stout pressures can cause primer pockets to grow in diameter. This can create an unsafe condition if your primers are not seating properly. Are your primer pockets “good to go”, or have they been pushed to the point of no return? Do you really know? Many guys try to gauge primer pocket tightness by “feel”, as they seat the primer. But that method isn’t precise. Now there’s a better way…

Primer depth diameter gauge brass cartridgeThe folks at Ballistictools.com have created a handy set of precision-machined gauges that let you quickly and accurately check your primer pockets. These gauges are offered in two sizes — for large and small primer pockets. A two-piece set of both large and small gauges costs just $19.99. These gauges let you quickly measure the depth of a primer pocket, and check if the crimp has been removed properly. Most importantly, the gauge tells you if the primer pocket has opened up too much. One side of the gauge has an enlarged diameter plug. If that “No-Go” side fits in the primer pocket, you should ditch the case — it’s toast.

Primer depth diameter gauge brass cartridge
CLICK HERE to order Primer Pocket Gauge Set from Ballistictools.com.

Precision ground from O-1 tool steel, these primer pocket gauges serve multiple functions. The inventor of these tools explains:

I created the prototype of this tool for my own use in brass processing. I needed a way to quickly and easily measure primer pockets that was reliable and did not require wasting a primer. This tool has been indispensable for me and I would never go back to the old method of uncertainty and guessing.

One side of this gauge is the “go” side which quickly tells you the depth of a primer pocket, whether any crimp is properly removed, and whether the primer pocket is loose. If it feels loose on the “go” side, use the other end of the tool, the “no go” side, to test to see if the primer pocket is too loose to hold a primer. If the no-go slides into the pocket, then you know to junk that brass.

Product tip from Boyd Allen. We welcome reader submissions.
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February 12th, 2017

Understanding Headspace — What You Need to Know

Ultimate Reloader Brownells headspacing go gage gauge barrel gunsmithing
This illustration shows headspace measurement for the popular .308 Winchester cartridge, which headspaces on the shoulder. Image copyright 2015 Ultimate Reloader.

In this Brownells Tech Tip, Brownells gun tech Steve Ostrem explains what headspace is and why it’s one of the most critical measurements for nearly all firearms. Even if you’re an experienced rifle shooter, it’s worth watching this video to refresh your understanding of headspace measurements, and the correct use of “GO” and “NO-GO” gauges.

Headspace Definition
In firearms, headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge (the datum reference) to the face of the bolt. Used as a verb, headspace refers to the interference created between this part of the chamber and the feature of the cartridge that achieves the correct positioning. Different cartridges have their datum lines in different positions in relation to the cartridge. For example, 5.56x45mm NATO ammunition headspaces off the shoulder of the cartridge, whereas .303 British headspaces off the forward rim of the cartridge.

If the headspace is too short, ammunition that is in specification may not chamber correctly. If headspace is too large, the ammunition may not fit as intended or designed and the cartridge case may rupture, possibly damaging the firearm and injuring the shooter. (Source: Wikipedia)

Forster Headspace diagram belted magnum rimfire

Go gauge gage NOGO no-go field gaugesHeadspace Gauges
Headspace is measured with a set of two headspace gauges: a “Go” gauge, and a “No-Go” gauge. Headspace gauges resemble the cartridges for the chambers they are designed to headspace, and are typically made of heat-treated tool steel. Both a “Go” and a “No-Go” gauge are required for a gunsmith to headspace a firearm properly. A third gauge, the “Field” gauge, is used (as the name implies) in the field to indicate the absolute maximum safe headspace. This gauge is used because, over time, the bolt and receiver will wear, the bolt and lugs compress, and the receiver may stretch, all causing the headspace to gradually increase from the “factory specs” measured by the “Go” and “No-Go” gauges. A bolt that closes on “No-Go” but not on “Field” is close to being unsafe to fire, and may malfunction on cartridges that are slightly out of spec. (Source: Wikipedia)

To learn more, read Brownell’s longer article Headspace Gauges and How to Use Them. Among other things, this explains the relative lengths of “Go”, “No-Go”, and “Field” gauges. The “Field” is actually the longest: “The GO gauge corresponds to the SAAMI (Sporting Arms & Ammunition Manufacturer’s Institute) minimum chamber length, while the FIELD gauge usually matches the maximum chamber depth, or slightly less. NO-GO gauges are an intermediate length between minimum and maximum, that, technically, is a voluntary dimension. A firearm that closes on a NO-GO gauge and does not close on a FIELD gauge may not give good accuracy and may have very short cartridge case life from the ammunition re-loader’s standpoint.”

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