OAL (OverAll length) Gauge

Reloading is a huge subject in it’s own right and covered by countless books, articles, web sites and forums, put 5 shooters in a room and get onto the suject of shooting and you will come across 5 separate opinions.

Take the subject of OAL, COAL, OverAll Length (All the same thing in principle) This the maximum length of loaded round in a chamber, it is the length of round that when the bolt is closed just touches the lands. This may or may not be a meaningful number to you, if you are shooting .308 and your magazine will only feed 2.800″ OAL rounds what is the point in building to the extremities of the chamber at say 2.900″ if it means you have to hand feed.

In fact why bother determining the OAL? Well some rifle/bullet combinations shoot more accurately when they have a shorter jump (Distance the bullet has to travel) to the lands, some actually work better when jammed (The bullet is physically engaged into the lands when chambered, such as the Berger VLD’s

Now I could go into the merits of jam versus jump, pressure characteristics and so on but that is not the point of this article, probably because it is called OAL (OverAll length) Gauge. So back on track for a moment. How do you measure the OAL for your rifle assuming you want to? Well the old favourite was a couple of length-ways slits with a hacksaw in a case, stick a bullet in and chamber it, in theory it will slip in the neck because of the slits and give you your maximum OAL, actually it will give a longer OAL because the soft jacket of the bullet will deform slightly when pressed into the lands so you could end up .020″ over length (20 thousandths of an inch) “Woahhh! Twenty thousandths of an inch? That is slightly less than not a lot.” Yes but we are talking about accurate reloading here and that plus twenty could bump your chamber pressure up to an unacceptable/dangerous level. If you are going to laod your own better to know the exact distance.

Next way to measure OAL was a piece of pipe soldered to the end of the case, a bit of stiff wire inside and hey presto an improvised OAL gauge. I still have mine somewhere…

Stony Point/Hornady make an excellent OAL gauge however it is a bit short for my liking and apparently the ends snaps off if you are clumsy.So I make my own OAL gauges and here is one I made earlier.

This one utilises a 6mm aluminium inner and a robust outer tube. The construction is all aluminium apart from the stainless threaded lock screw, the thread on the nose that the case screws into is M8Fine because that is what I had available and the whole thing works rather well if I say so myself. I have made a few of these for mates in the past so this does mean they need to see me if they have a new case that needs tapping. I usually say cover the return postage and pop a couple of quid in the next H4H collection point or similar.

 

The Bearing Surface Comparator

This was as much a test of posting pictures as anything, it is a BSC (bearing Surface Comparator) I built recently for a friend. It is designed to measure the bearing surface of .308″ bullets for an F Class shooter. The bearing surface is the parallel section of a bullet that is gripped by the case neck, precision shooters have noted that when measured this distance can vary from bullet to bullet and can have an impact on bullet accuracy so they measure, sort and batch the bullets by bearing surface length. They are not easy things to make as the accuracy of the device is based upon how closely you can get to the bearing surface, I aim to bore the comparators to .304” this means a two thou undersize variance, any closer than this to the parent bullet diameter leads to problems.
This particular gauge has interchangeable tooling so it can also be used to measure the OAL (overall Length) of a loaded bullet versus a reference piece. My preference is analogue measuring devices with such a gauge but the end user asked for digital.
I have built these for other people in the past but am yet to put one together for myself however I have a couple of idea for improving the device so I had best build one to prove my ideas work…