Metallic Reloading 101 - Part 3: Case trimming, propellant and primer selectionBy Craig Maylam
- 11th May, 2020 May 11, 2020, 3:20 PM
- 1 Comment
If you’ve been following the series you should have some good brass that is correctly resized and will fit in the chamber of your rifle. If you have resized used cases then the overall length will require checking (it is actually worth checking all cases, new or used).
The overall length must be within the industry standards. Cases that are too long will increase chamber pressures because there’s little or no space left for the neck of the cartridge to expand and release the projectile. Thus when you fire a pressure spike occurs.
Checking the length is simple, just measure the case between the jaws of a Vernier caliper. The tolerance for case length it is published in loading manuals and will look something like this: 270 Winchester - max length 2.540 inches - trim length 2.530 inches.
I suggest setting up your calipers like a snap gauge by locking the jaws at the max case length. Set aside for trimming any cases that do not easily pass between the jaws. This save individually measuring each case which is tedious to say the least.
Cases should be discarded prior to the 5th trim as by now the brass will be thinning. Trimming can be done in many ways; here’s three of the most common.
FILE TYPE DIE
This is a reloading die that fits in your press the same way as your sizing dies. The case is run up into the die without lube and the excess case sticking out the top is filed off. No measuring, it’s that simple! However the file type die will only do one specific cartridge so you need a die for each of the different cartridges you intend to load.
LEE CASE LENGTH GAUGE, CUTTER AND LOCK STUD
This is an innovative tool manufactured by Lee Precision. The trimming can be done by hand or with the help of a battery drill. The trimmer comes in four parts and you need a shell holder and a centre shaft for each calibre. The rest of the set can be used for other calibres.
This system is very cost effective and accurate, however if you are loading a high volume of ammunition then it is probably not for you as it is quite a slow process.
ROTARY CASE TRIMMER
These are made by all the bigger manufacturers of reloading equipment. They can be used to trim any calibre and are quick and easy. For each calibre you need a pilot bushing and for each base size you need a plate to grip the case.
Some trimmers are fitted with a chuck or collet arrangement so you won’t need a plate for each calibre, but you will always need a calibre specific pilot bushing. Trimming is done by turning the crank handle until the cutter shaft bottoms out on the pre-set collar.
“If you have resized used cases then the overall length will require checking (it is actually worth checking all cases, new or used).”
These trimmers are a great investment and some models can also do neck turning. Some manufacturers offer a three in one cutter which trims and inside/outside deburrs the mouth of the case at the same time.
After the cases are trimmed to length they will require deburring (unless you use the 3 in 1), failing that good handtools are available for the job. You are simply looking to remove the sharp or rough edges from the case mouth.
Many years ago I purchased the entire contents of a loading room from an elderly gent from the West Coast. Among the treasures were several thousand shotgun primers. I used 400 of these for in some trap loads I made for my weekly range session.
When I had my first misfire I didn’t think too much about it, however after the 5th misfire in the space of 25 rounds I realised I had a problem. I had to take the whole batch of cartridges apart and salvage the components.
Lesson #1, keep your primers dry! Old army ammunition boxes are ideal for storing primers. Take out enough for each loading session and return any that are left.
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Primers come in two sizes, small and large for both pistol and rifle. The strength of a primer is called its “brisance”. Primers are available in Match, Standard, and Magnum grades.
If you are using large rifle primers then a good rule is that standard or match primers will properly ignite powder charges up to 62 grains (of stick or flake powder).
For my .270 loads I use CCI #200 large rifle primers because the maximum charge is 60.8 grains. If your charge is over 62 grains use a Magnum primer. Most modern reloading manuals will tell you which primer to use, so stick with what they specify and stay out of trouble.
An exception to this rule is with ball powders in cases with large primers - for these I always use a Magnum primer. Experience has taught me that ball powders are harder to ignite so a Magnum primer is good insurance.
However if a cartridge case is made to accept small primers then you should have no problem igniting ball powder with a standard small rifle primer.
Changing the brand of primer can make a big difference to the pressure of a load and affect its accuracy. If you develop a good load with a certain brand and type of primer then use the same primer the next time you load that recipe.
Primers must be seated two to three thousands of an inch below the base of the cartridge. Correct primer seating guarantees the primer has the best chance to do its job properly - it needs to be sensitive to the impact from the firing pin.
If a primer is seated too deep (ie; crushed) then the insides may be damaged and chances are you will end up with misfires. Case lube inside a primer will ruin it also, so make sure you clean your hands before you start handling the primers.
PRESS-MOUNTED PRIMING ARMS
Most presses come with primer seating arms. The seating is usually done on the down stroke of the ram. Seating primers on the down stroke for me is a bit clumsy and lacks the sensitivity I feel I need to do a proper job. The upside with this system however is that if you have the correct shell holder you can prime as you go; there is no need to buy any extra components.
HAND-HELD PRIMING TOOLS
I have used a Lee priming tool for years. It does the job without me touching the primers and it also has some “feel” to it. I can “feel” the primer going into the bottom of the pocket and I know I’m not crushing it too much.
If you are reloading cases that have already seen a few loads then you will be able to easily detect an enlarged primer pocket. Cases with enlarged pockets should have their necks flattened with pliers and be discarded immediately so they cannot be used again.
The Lee and other hand-held units also have the advantage that they can be used away from the loading bench, in winter I do most of my priming inside the house where it’s a bit warmer!
Propellants (ie; powders) are designated according to their burning rate. The fastest burning rates are used to load rimfire, shotshell and pistol cartridges, the slowest burning rates are used for big cartridges like the massive magnum cartridges.
Burning rate charts are of some use in selecting a powder that will work in a given calibre but they cannot be used to determine the actual charge weight you should load. It is wise to use new powders in sealed tins sourced from a reputable supplier.
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The problem with part tins of propellant from unknown sources is that you have no idea how they have been stored, so you may not be able to reproduce a load when you get a fresh batch. There are several concerns with part tins obtained from private sources.
First, the propellant may be stored in the wrong tin. You could blow your rifle up because you have the wrong burn rate for your calibre.
Second, the propellant may have been stored poorly (ie; it’s damp) and not be performing correctly. When you get your new batch your loads could run over pressure because the propellant is now performing the way it’s supposed to.
Lastly, you unwittingly develop a load with an obsolete powder and discover the grade you no longer available when you need more, so you have to begin load development all over again.
ADI, IMR, Alliant and Winchester propellants have a great history of continuity of supply so you can feel safe that you will always be able to purchase more of them when you need it. To select a suitable powder consult a loading manual. They cost a few dollars but are worth their weight in gold.
I shy away from loads sourced from the internet as there is often no known reference and some of the loads I’ve seen are just plain dangerous.
“To select a suitable powder consult a loading manual... I shy away from loads sourced from the internet as there is often no known reference and some loads I’ve seen are just plain dangerous.”
If the loading density (the depth to which the powder fills the case) is listed, try for around 90% with your starting load, good accuracy usually starts around 90-95%. You will notice that for any given calibre there will be several powder grades given, I usually pick a slower burn rate because it is likely to fill the case up more.
You don’t often find one powder that will do multiple calibres. There will be a perfect powder for your load and I doubt it will be perfect in any other load, so resign yourself to the fact you will need a can of powder for each load/rifle.
For the .270 load I am developing I have another problem in that the projectile weight I intend to use is not listed. In this case I will use load data for a slightly heavier projectile.
To safely do this the projectiles must be similary constructed, by this I mean that you cannot use data for solid monolithic copper bullets if you’re shooting bullets of lead core construction. I am loading Hornady 145 grain ELD-X projectiles with IMR 7977 powder, so I am using data listed for a 150 grain projectile. (See table below)
|The load is listed as follows:|
|Start||56.6gr, 2717 fps, 50,600PSI|
|Maximum||60.8gr C, 2940 fps, 61,300PSI|
From this I know that the starting load is 56.5 grains and it should give 2717 feet per second velocity. The maximum load is 60.8 grains for a velocity of 2940fps. In the data I used, IMR 7977 was the second slowest powder listed and the letter C after the max load means it is a compressed load.
A compressed load means the powder fills the case completely so as it is seated the bullet will compress it, which is what I was looking for. We are also given a COL (cartridge overall length). If we seat the bullets to achieve this precise length then we know they’ll fit a standard chamber perfectly.
New propellants are being developed all the time, and some may make your rifle group better or shoot a flatter trajectory than it has before. Don’t be afraid to test these latest propellants - just changing powders can make a noticeable difference.
Next issue I will deal with measuring powders.
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