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Hornady Overall length Gauge

Hornady Overall length Gauge

When I purchased my Chiappa 1886, in 45-70, I made my own ammo using 405-grain GM hard cast bullets. They are top-quality and work great, but they proved expensive; so, I decided to try home cast bullets, using the Lee 405-grain flat nose bullet mould. The new bullets are the same weight as those by GM but aren’t as long and, as the bullets are shorter, the finished rounds are also shorter. With the new reloads exceeding the minimal overall length given in the reloading data, I did not anticipate any problems.

The problem

The first time I loaded a round, I hit a problem; it was difficult to chamber, with significant resistance when I closed the action. On ejecting the unfired round, the cause of the problem was immediately evident; there were deep indentations on the bullet, where the rifling had dug into it. Even though the rounds were shorter than those previously used, the new bullets were engaging into the rifling when the action was closed. On close examination, it was clear that the new, shorter bullets were fatter in the ogive, (the curve of the bullet from the tip to the full diameter straight section) so they were wider than the GM bullets at the point where the rifling starts in the barrel. The GM bullets narrowed down quicker forward of the case neck, so did not hit the rifling in the same way.

The solution

Queue the Hornady Overall Length (O.A.L) gauge! This ingenious tool is designed to allow you to control the distance that a bullet travels before it reaches the rifling in the barrel. This very small distance, called free travel, is critical and can affect accuracy; so, being able to measure and control it is a great advantage. If a bullet engages in the rifling on chambering, like my home cast stuff, then on firing, the rifling will resist the bullet’s start up the barrel. This will occur until the pressure has built sufficiently inside the case to overcome this additional resistance and, in some circumstances, this build-up of pressure could be dangerous.

The tool consists of an aluminium bar, which is threaded at one end, to take a modified case in the calibre of your rifle. Through the centre of this bar is a smaller diameter ‘bullet adjustment rod’, which can be slid back and forth inside the outer bar and locked in position with a thumb screw. There is a curved version of the tool available, for use with under lever guns, however when I used one I had to adjust it with a file to make it fit into the Chiappa without catching on the extractor. It is testament to the quality of this tool that I was able to file away a significant amount of metal without compromising its function.

Adjustable rod

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With a bullet deeply inserted into the mouth of the modified case, it is inserted into the chamber of the gun. You then push the adjustment rod in until you feel the bullet come into contact with the rifling. The adjustment rod in then locked in place with the thumb screw and the tool is removed from the chamber (if the bullet gets stuck in the rifling it may need to be pushed out from the muzzle end with a suitably sized wooden dowel and put back into the modified case). Once the tool is removed, you can measure the overall length of the cartridge with that particular bullet. Different types, designs or weights of bullet, even though they are the same calibre in the same gun, will give a different measurement. The best way to measure the OAL is to use a calliper and Hornady have very cleverly formed a cut out on the shaft of the tool, at the back of the case head, where the blade of the calliper can sit, to gain the most accurate reading.

Once you have got an accurate measurement of the overall length of the cartridge, you can then make an adjustment to introduce some free travel for your reloads. Hornady suggest free travel of somewhere between .020 and .040-inches, so I decided to go in the middle at .030-inches, or 0.762mm. The most consistent measurement I got for the 45-70 with the 405-grain bullet was 63.59mm. Deducting 0.762mm from this figure gave me an ideal cartridge Over All Length of 62.828mm; so, I adjusted my bullet seating die as close as I could to this figure and made up a batch of rounds to try. It was immediately noticeable that the new rounds chambered effortlessly, and when I ejected an unfired round there were no marks from the rifling on the bullet. Problem solved! The reloads functioned well and were still accurate and consistent.

Add-on tools

In common with many shooting accessories, there are some extras available to enhance the performance of this tool. ‘Bullet Comparators’ are available in various sizes and they sit over the bullet while the OAL is being measured, to allow you to take the measurement from the bullet’s ogive, rather from the bullet tip. I did not find them necessary to overcome the problem I was having with my home cast bullets, but they may be worth considering if you want the enhanced the measurements being taken.

Practice and repeatability

Like many aspects of reloading, you need to develop a ‘feel’ for using this tool, in order to achieve the necessary consistency in the measurements taken. When seating the modified case into the chamber, it proved beneficial to rotate it slightly in both directions, to ensure that it is seated properly and to remove any dirt or oil from the chamber that might prevent it from doing so. You then need to ensure that the amount of pressure you apply to the bullet adjustment rod is consistent; otherwise, the measurements you get will vary. You are pushing the bullet to the rifling to be able to register exactly where it is relative to the length of the cartridge, not to engage the bullet into it. Softer bullets, or those with a longer ogive, will travel into the rifling too far if you apply too much pressure. I found that the right amount of pressure, with .308 jacketed bullets, left the bullet in the gun when the tool was removed but it could then be knocked out with a cleaning rod using almost no pressure at all. With plenty of practice, you will find that the OAL measurements you are getting when you repeat the process over and over become more consistent.


Had I not had the problem with my home cast bullets, then I would never have come across this useful bit of kit. With reloading, there are numerous variables involved, which all affect the consistency and accuracy of your ammunition. The OAL gauge allows you to remove the free travel from the list of variables and keep it constant, no matter what size or shape of bullet you are using in your rifle. It also allows you to avoid making ammunition that may engage in the rifling when you chamber a round and cause excessive pressure and damage your gun. This is definitely a bit of kit that is worth adding to the reloading bench. Well-made and reasonably priced, this tool is well worth buying and something you will use over and over.


  • Name: Hornady Overall Length Gauge
  • Options: Straight for bolt action rifles, curved for lever action guns
  • Price: Straight Gauge RRP £54.50, Curved gauge RRP £62.70 Modified Cases RRP £ 7.95 to £10.40, depending on calibre
  • Contact: Edgar Brothers Ltd., edgarbrothers.com