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.


Knurling woes…

Occasionally I have to put a knurl on something, you know… that sort of chequered finish on things like thumbscrews and the likes. This knurling is to give a grippy finish when you have wet hands and has to be identical on 12 units. So for the sake of repeatability I start with a given diameter, set my knurling tool to parallel to the work face, set a feed rate, wind in the first cut and kick it off, second cut back across with a few more thou and a final cut in the original direction gives me a finished result.

Hmmm… I think to myself as I look at my handy work that is bloody good, I put a chamfer cut across the ends and it goes on the bench for the next stage. Next piece in the lathe, repeat the process and I now have two identical components.This goes for the third one as well, I am on a roll now and I start the knurl on the fourth, exactly the same settings as the previous and get a totally different, much finer knurl pattern. A reverse cut does not help matters and of frustration I stick a heavy cut on and wind the speed up to maximum.

A perfect knurl!

Yeah……… go figure.

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…


Did I mention I finished with a V Bull?

OK, so a V is not particularly impressive and I saw a few hit today at 800 & 1000 yards but they were thin on the ground at 1200 yards, it was bloody windy for Barton Road and decidedly damp as well.I had swapped out the rings on the S&L so I knew it needed to be zeroed. Once my first stint of RCO duties were finished I settled down at the 800 firing point and bore sighted at a flag pole at 400, as I have Apel mounts and rings fitted I can adjust the zero through the rear mount which is a nice touch so a couple of tweaks and it ‘looked’ to be right. Time to try. I use BulletFlight to do my base calculations so I entered the distance and temperature and took the shot, saw the spash so dropped a couple of MOA off and was on the frame, up a bit and Happy days. Now I had an 800 ‘zero’ I could add just under 11MOA at the 1000 yard point. It turned out I only needed 9.125 MOA to get to the V so that was OK albeit a tad strange as BF is usually within 1MOA of the mechanical elevation.BF suggested I need another 14.6MOA for 1200 but that put the POI way high, the good news at 1200 is you can shoot and easily watch the splash, this time I had to drop 3.6MOA to get on the 5 ring. Now I know the MV as I chronoed it end of last year so either my Kahles is not giving what I know to be MOA or I am missing something, this does provoke the question, are Kahles ‘scopes graduated in true MOA or shooters MOA? Either way it does not explain the factor of 1:1.2 I had to apply to the software calculations to get my actual drops. Wind was harsh for Barton Road but not enough to do this.

Anyway, last shot at 1200 was a V finish, considering it was a skinny little 139 grain round shot from a lightweight sporter rifle with a 12X ‘scope and I had been dancing around the 5″ white V Bull for the majority of my shots so in that respect I was pleased.