December 8, 2022. Do you know what the inside (and throat) of a rifle chamber looks like? Do you know what headspace is and why it’s so important? Brownells GunTech article Gauging success – Minimum headspace and Maximum col. This article will explain the basics of headspace as well as how to measure headspace (and length-to-lands) in your barrels accurately. This article explains how to adjust your full length sizing dies to “bump up the shoulder” when necessary. The article explains that proper C.O.L. and headspace control are important. Handloading is safer and more affordable. Excessive headspace can lead to case head separation and gas ejections from the rifle’s chamber of more than 60,000 PSI. Too much headspace can cause a chamber forced bullet crack and a bullet that is more obstruction than a properly secured projectile. Excessive C.O.L. Excessive C.O.L. can lead to a rifling bound bullet, which could cause spikes in excessive pressure. [Editor’s Note: Competitive benchrest shooters often place bullets in the rifling. You can safely do this if your loads are reduced accordingly. We often get the best accuracy with some bullets. You can also get as far as the lands. This can create more pressure than a bullet seated at.010. Keep away from the initial lands contact. Like all reloading, you should start low and build up slowly. How is headspace defined? Most cartridges used in the United States are defined by ANSI/SAAMI Z299.3-4. Brownells explains that the.243 Winchester has pressure specifications, cartridge drawings, and chamber drawings. Each manufacturer who produces a firearm for.243 Winchester has a chamber drawing. This allows them to know the correct standard dimension to cut chambers or set headspace. You will notice that there are two reference dimensions for the headspace of the chamber. The upper is the area in the chamber where the shoulder is.400 The “datum” (or “basic”) line is the diameter. The lower is 1.630?1.640 Minimum – Maximum dimension between the breech (bolt face), and the point in the chamber measuring.400?. “The actual headspace for any firearm is the distance between the breech face and the point in the chamber that is intended prevent forward motion of the cartridge.
You can quickly determine the cartridge base-to ogive length by using a comparator and a set of calipers. This is the distance from the base of a case to the forward-most section of the bullet. It is commonly called the ogive. The ogive in this picture is 0.243. The next step is to use a modified (threaded), case with a Hornady OAL instrument to determine the Length-to Lands (LTL), in your rifle’s chamber. The modified case with a bullet in the neck is then inserted into the chamber. Take your time, slow down. These 5 tips will help you get reliable and repeatable LTL measurements. Make sure you have a clean chamber.
2. The modified case should be securely screwed down and placed on the OAL Gauge. Sometimes it can come loose during repeated measurements.
3. Place the modified case slowly, but gently, into the chamber.
4. Push the gray plastic rod VERY CAREFULLY. It is not uncommon for the bullet to be slightly tilted. Before you apply pressure, let the bullet center in your throat. Tap a few times until you feel resistance. Do not push too hard, as this will cause the bullet to jam in the lands.
5. You should repeat the measurement at least three more times. Follow our instructions and you should usually get a repeatable measurement within 0.0015? 3 out of 4 times.
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