Precision Hand Loading For Long Range-Chapter One: Brass Sort & Prep
Primer pocket uniforming cuts all the primer pockets to exactly the same depth, in the name of consistent and uniform ignition. Here are the tools, a cleaned and uniformed pocket and the bulk of the material that was removed:
Deburr the Flash Holes
The flash hole is the hole in the head of the case that the sparks pass through to ignite the powder. In the manufacturing process this hole is not drilled. It is punched and that generally leaves a burr on the inside, or the whole "flap" of metal that was punched out. This can shield a portion of the powder from the sparks and lead to inconsistent ignition case to case. A deburring tool does just that. It cleans up the powder side of the flash hole for consistent ignition. The particular tool depicted here has the depth preset so the cutter (a common center drill) can only cut so deep into the flash hole:
All the mail order companies and most local shops carry these simple tools. A primer pocket uniformer can be used after each firing to clean the carbon out of the pocket. But you should revisit the primer pockets of your cases at least every three firings or so depending how hot your load is, as the brass flows with each shot, and they will eventually no longer be uniformed.
Trim to Length
Upon firing of the loaded round the case greatly softens and inflates like a balloon to fill the chamber of the weapon. This seals the chamber and prevents gas leaks, etc. But with the brass nearing a liquid ("plastic") state, it flows with the pressure of the propellant gas. Hence, as stated before, our primer pocket is not staying uniform. The overall length of the case grows and the mouth of the case typically thins at the very edge, as well as a “donut” eventually developing at the juncture of the shoulder and neck. Your reloading manual will give you the nominal "trim to length" measurement of a given cartridge case. So place said case in your case trimmer and trim it back to this specification. Correct? No.
NO!!! We are precision shooters for crying out loud. I have a friend that mows every case he gets his hands on back to minimum length, and it gripes me to no end.
Historically and generally speaking, the classic ultra accurate cartridges of the bench rest environment have longer than normal case necks. The typical case neck for a given cartridge is one caliber wide. Example: a 308 Winchester's bullet is a diameter of .308" so therefore the rule of thumb is that the mouth of the case should be "about" .308" long minimum. This allows good bullet tension and support so our carefully assembled loaded round's bullet is sitting dead in line with the case’s centerline, which is in line with the centerline of the bore. All this leads to good shooting and smiles. The more we hack back the case mouth, the less neck we have to make sure our bullet is held inline. And the benchrest cartridges I mentioned have caliber plus neck lengths for this reason.
So what do we do? If the case gets too long, it will engage the rifling at the same time the bullet tries, giving us a wild and very dangerous pressure spike. If we hack it back to bare minimum we may have given room for some small loss of accuracy, especially with rough handling of ammo in the field. But we HAVE TO maintain consistency from case to case for shot to shot.
The answer is to measure the chamber length in your individual rifle and stay trimmed back from that actual number. Small chamber plugs to get that measurement are sold by Sinclair and others. Here is one I whipped out on the lathe yesterday for 30 cal:
To use a gauge like this:
1. Thoroughly clean your weapons chamber.
2. Take a scrap case and trim it WAY back with your case trimmer, say .050" SHORTER than book spec.
3. Seat your plug gauge into the case - long.
4. Ease this round into your weapon and fully close and lock the bolt.
5. Remove the case gently without bumping the gauge. It has hit the end of the chamber and be pushed back into the case by the action of locking the bolt.
Measure the overall length of the case, head of the case to end of the plug, and note that measurement somewhere obvious and permanent in regards to loading for this particular rifle. It would probably be a good idea to repeat this measurement three times and average all three readings.
Now until this dimension changes (barrel removal, etc.), trim your brass just short of this measurement instead of “book trim to” specs.
Once we have our cases all trimmed to a uniform length for our specific rifle we now need to deburr the mouth of the case.
I'm sure anybody that is reloading knows what a deburring tool looks like for hand loading. Others: just do a Google search. Deburr the outside of the case just enough to remove the burr and put the slightest bevel on the edge of the case, the most minimal possible. As far as deburring the inside, gently cut a bevel on the inside of the case until it goes almost full diameter,that is the inside bevel almost cuts to the outside edge of the case mouth when looking from the end.
It is next to impossible to photograph, but you can see this inside chamfer is cut almost, but not all the way, to the outside edge of the case:
This is so that when we seat our precious bullet the opening of the mouth of the case does not cut, mar or peel back small portions of the soft bullet jacket.
And last but not least we need to prime our case. Practically every company that handles reloading components sells priming tools. For the wealthier individuals, I'd point you towards Sinclair International and those type suppliers. But a good job of priming can be done with lesser priced tools.
The main thing is that the tool have as much "feel" of the process as possible. You want to be able to clearly feel the primer bottom out in the primer pocket of the case, so you can keep the primers seated consistently case to case to case. This pre-loads the anvil of the primer the same for each round giving more uniform ignition shot to shot.
In the next chapter we will discuss how to inspect, sort and prep our bullets for a long journey.
Tres MonCeret is a career machinist, gunsmith, competitive shooter, writer and instructor of many modern & primitive outdoor topics. He is currently looking for work in one of these venues in any geographically "cool place" to live. Resumes available.
Join the discussion of this article HERE at the Article Discussion Forum.