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)
Headspace 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.”
Forum member Rich DeSimone uses a handy “Stub Gauge” for setting shoulder “bump” and seating depth. The gauge is made from a section of barrel lopped off when the muzzle is crowned. The chambering reamer is run in about 1/4 of the way, enough to capture the neck and shoulder area of the case. Rich then uses his full-length die to “bump” a master case with the ideal amount of headspace for easy feeding and extraction. He takes that case and sets it in this Stub Gauge, and measures from the front of the gauge to the rim. He can then quickly compare any fired case to a his “master” case with optimal headspace. Since the gauge measures off the shoulder datum, this tells him how much to bump his fired brass.
In addition, the Stub Gauge can be used to set bullet seating-depth. Rich has a channel cut transversely on one side of the gauge, exposing the throat area. Since the interior of the gauge is identical to the chamber in his gun, this lets him see where a seated bullet engages the rifling. He can tinker with bullet seating length until he gets just the right amount of land contact on the bullet, confirmed visually. Then he measures the case OAL and sets his seating dies accordingly. This is much handier than using a Stoney Point Tool to measure distance to the lands. As your barrel’s throat wears, you may seat your bullets out further to “chase the lands”, but the gauge provides a constant land engagement point, in the barrel’s “as new” condition. By measuring the difference between the land contact point on the gauge and the actual contact point on your barrel, you can determine throat “migration”.
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Need a new barrel for your Remington-actioned hunting or tactical rifle? McRee’s Precision has you covered. McRee’s is now offering complete, no-gunsmithing re-barreling kits for Remington and Rem-clone actions. These feature a high-quality, pre-chambered “PRE-FIT” stainless barrel from Criterion, a Savage-style barrel nut, a recoil lug, and a special barrel-nut wrench. With this system you can easily re-barrel your favorite Remington rifle yourself in less than an hour. You don’t need to pay gunsmithing fees, or wait weeks (or months) for a busy smith to do the job.
Right now McRee’s Precision is offering Rem-action Pre-Fit barrel packages (complete with barrel nut, recoil lug, and wrench) starting at just $412.50 (On Sale). Choose from four chamberings: .243 Win, .260 Rem, .308 Win, and .300 Win Mag. These Pre-Fit barrel kits are “100% complete and ready-to-install”. All you need to do is remove your current barrel, place the recoil lug, spin on the new tube, follow the instructions for setting head-space, then torque the barrel nut against the lug. NOTE: You may require a barrel vise and action wrench to remove the original barrel. Minor inletting changes may be needed forward of the action.
The folks at McRee’s Precision say their Pre-Fit system offers many advantages: “Remington Pre-Fitted Barrel Kits have become popular over the years. If Savage can do it, why not for our Remingtons? Our [Criterion-supplied] barrels are spec’d to the McRee standard of performance. We require a minimum of 0.5 MOA with good factory ammo and 0.2 MOA with quality handloads. There are several places to get the tools required to remove your factory barrel correctly. Once you have your barrel removed all you have to do is follow the normal Savage procedure to install your new barrel. We recommend that you contact your local gunsmith for the install. Feel free to call us with any questions.”
Product Tip from Ed LongRange. We welcome readers’ submissions.
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On German Salazar’s Rifleman’s Journal website, you’ll find an excellent 5-Part Series on barrel chambering. The Series, entitled The Voyeur’s Guide to Barrel Chambering, is not intended to be a “how-to” instructional treatise for gunsmiths. Instead, German’s 5-Part Guide is aimed at the end user — the shooter. German explains: “This Series isn’t intended for anyone who owns a lathe; instead it is for those of us who send an action off to get a new barrel installed. Those who have the equipment know what to do and how to do it and I have nothing to teach them. On the other hand, if you’ve ever wondered just what goes into barrel fitting, this is it.” PART I | PART II | PART III | PART IV | PART V
With well-written text and dozens of very high-quality images, German takes you through the chambering, threading, shoulder-fitting, and crowning processes from start to finish. The idea is to give the “barrel consumer” a clear idea of the processes involved when a barrel blank is converted into functional form, complete with chamber, threaded tenon, fitted breech, and crown.
We highly recommend German’s 5-Part Voyeur’s Guide to Barrel Chambering. German, with the aid of John Lowther (who ran the machines), did a great job. The series has already drawn much attention from our Forum members, along with praise. After reading the articles, John C. from Australia wrote: “Your Chambering articles… really are excellent [and] informative for those of us too scared to watch our gunsmith chamber one of our barrels lest we distract him at a crucial moment!”
We know you’ll learn something from reading through German’s 5-Part Series. And if you see a photo on German’s website that intrigues you, simply click on it to see a larger, higher-resolution version. All the images in the Voyeur Series on RiflemansJournal.com can be zoomed to larger formats.
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Dan Lilja of Lilja Barrels has announced that, starting this month (June), his company will offer a pre-threading option for in-stock and made-to-order Lilja barrels. The price for the threading option is $30 per barrel. The first offerings will be for Rem 700 actions, and Lilja will, later on, offer pre-chambered barrels as well. Dan tells us: “To begin with we are threading for the Remington 700 actions. Other action types will be added in the future. And we are also planning to offer chambering along with the threading for a limited number of cartridges in the near future.”
Details of Pre-Threaded Barrels — Gunsmithing Still Required
Pre-Threading will only be offered, initially, on 28″ or 30″ blanks (length prior to threading). The barrel will NOT be finish-crowned, and Lilja does not offer muzzle threading except for drop-in AR-type barrels. Dan points out that his pre-threaded barrels are not ready to install: “The barrels will still require a gunsmith, experienced at fitting barrels to actions, to make the final fitting and headspacing adjustments on a lathe and using headspace gauges. Lilja will turn these threads for the nominal dimensions for the action type. But action makers have tolerances and other operations such as truing an action face or bolt or lapping bolt lugs can change dimensions enough that headspace or thread shank length may need to be modified.”
Story lead from EdLongrange. We welcome reader submissions.
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Lothar Walther has some new “pre-fit” barrel offerings that should interest Garand and AR shooters. Garand Match competitors and vintage military rifle shooters will be pleased that LW is now offering “finished” Garand barrels, pre-chambered in your choice of six (6) different chamberings: .270 Win, 7×64, .308 Win,.30-06, 8x57IS and 9.3×62. These are all four-groove barrels with 24″ length. Twist rates along with land/groove diameters are listed on the Lothar Walther website. NOTE: Though these barrels come pre-chambered, you’ll still need a competent gunsmith for final fitting and headspacing.
Finished M1 Garand Barrel
AR15 Barrels — Multiple Contour Options
For AR15 shooters, Lothar Walther now offers a wide variety of pre-chambered AR15 barrels, set up for either .222 Rem and .223 Rem. With the .223 Rem barrels you have a choice of either standard .223 Rem OR .223 Wylde chambers. You can select either stainless steel or what LW calls “special rifle steel”. For most of these contours, other calibers/chamberings (.204 Ruger, .17 Rem., .30/.221 Fireball, 6.5 CSS, 6.8 SPC) are available on request. Extra charges may apply. Gunsmith required for attachment of barrel extension, drilling of gas port, and attachment of gas block, and (optional) front sight.
Contour 6000:16
Contour 6100:20
Contour 6100:24
Contour 6200:24
Contour 6200:26
Contour 6300-1675-MU
North American customers can order these “finished” Garand and AR15 barrels by contacting:
Robert Whitley of AR-X Enterprises visited the JGS booth to review the Oregon-based tool-maker’s offerings for 2012. In the video below, Cary Pugh of JGS Precision Mfg., spotlights some popular JGS products including chamber reamers, headspace gauges, core drills, counter-bores, and more….
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Headspace Gauges
Forum member Rich DeSimone uses a handy “Stub Gauge” for setting shoulder “bump” and seating depth. The gauge is made from a section of barrel lopped off when the muzzle is crowned. The chambering reamer is run in about 1/4 of the way, enough to capture the neck and shoulder area of the case. Rich then uses his full-length die to “bump” a master case with the ideal amount of headspace for easy feeding and extraction. He takes that case and sets it in this Stub Gauge, and measures from the front of the gauge to the rim. He can then quickly compare any fired case to a his “master” case with optimal headspace. Since the gauge measures off the shoulder datum, this tells him how much to bump his fired brass.
On German Salazar’s 
Dan Lilja of 
Lothar Walther has some new “pre-fit” barrel offerings that should interest Garand and AR shooters. Garand Match competitors and vintage military rifle shooters will be pleased that LW is now offering “finished” Garand barrels, pre-chambered in your choice of six (6) different chamberings: .270 Win, 7×64, .308 Win,.30-06, 8x57IS and 9.3×62. These are all four-groove barrels with 24″ length. Twist rates along with land/groove diameters are listed on the 
