Reloading - Attention to Detail

When reloading a cartridge, it is often the small variations to case prep that are missed and that can actually make a big difference to the overall accuracy, velocity and consistency of your reloads. Attention to detail is key to providing a really good reload that not only is repeatable but achieves the best that can be expected from the case or components within it.

One area in case prep that often gets a bit left out is the elimination of any burrs within the case around the primer flash hole, and also actually inside the primer pocket. If you think about it, this area is where all the cartridge action starts, with the initial ignition of the powder. Get this wrong and you are already on the back foot.

After cleaning the cases thoroughly, weight sorting and batching cases into regular weight and uniformity, I always deburr the flash holes and re-cut the primer pocket. Otherwise, you will be wondering later on if that dodgy flier or lacklustre velocity was anything to do with a primer issue. Eliminate it at the start to put your mind at rest. Flash hole deburring is a one-time operation and is best used on brand new cases.

Rationale

When cartridge cases are made, the primer flash hole is more often than not punched through from the end. This inevitably leaves a burr on the inside of the hole within the case. Sometimes it breaks off, but often it forms an irregular rim and this will affect the way the primer flash ignites the powder charge, causing variations to the combustion process and thus spurious results.

Quality brass like Lapua, Norma or Nosler Custom have their flash holes cut or drilled and are far less likely to have any burrs inside, but I still uniform them just to be sure.

It is a very easy process and there are a good array of tools made specifically for the job that remove the burrs and leave a slight chamfer or bevel to the inside face of the flash hole, thus allowing an unimpeded flow of primer flame to ignite the powder.

Tools

Flash hole deburrers are all loosely the same and show a cutter, depth stop and handle. It is important not to scrimp on this tool and make sure you get one with a depth stop, otherwise, you will take away too much metal around the crucial end of the case! Some flash hole cutters are calibre specific, with tapered tops to fit the varying sizes of the case mouth, whilst some primer holes are very small and need a smaller pilot spigot.

I use a K&M but others are available from RCBC, Lyman, Hornady and 21st Century. They all do basically the same job. The K&M tool is designed to be inserted through the case mouth and uses the web of the case or case mouth with attached stop fitted to locate with a small protrusion to sit into the primer hole. The tool has a hardened cutting edge and a few turns produce a small chamfer on the inside edge of the flash hole, removing any burrs made when the primer hole was made. I also have a Sinclair primer hole reamer that then uniforms the actual diameter of the primer hole itself. The belt and braces approach.

Flash hole deburring

Here’s how to use them correctly. Step one is to set the stop or centring device to the correct depth and trim cases to length if stretched. This is why this procedure is best done on virgin brass.

Next, insert the tool through the neck of the case until the cutter spigot engages the burr/flash hole. Then, apply a small amount of pressure on the tool and rotate slowly, clockwise, so you can feel the cutter actually cutting. It will then stop as it bottoms out on the floor of the case. Remove the tool and shake-free any burrs/debris and visually inspect to see a nice and bright, clean-cut flash hole.

You can order the tool in steel for about £35 or carbide for double that. The size options are 0.059 or 0.082 but primer flash holes with 0.062 flash holes, like the PPC cases, will need a specific tool to perform this operation. For small cases like some of the .17 calibre etc, some manufacturers make a smaller shaft to fit through the neck, like the Pee Wee deburrer for my .17 Wildcats.

Some people use a powered tool for this job, but to be honest, this is one case prep job that really needs a fine touch and I always deburr by hand.

Primer pocket uniforming

The next area is primer pocket uniforming. The aim is to make sure the pocket that the primer sits in is perfectly square, without rounded edges to the bottom faces, otherwise, the primer will not seat correctly at the precise depth. This can cause irregular ignition and is most noticeable when a case is stood up on a flat surface and it rocks as the primer is sticking out.

When chambered, a protruding primer will cause the head of the case to sit deeper and on ignition, the case will back out of the chamber to fill the bolt face. This stretches and thins your cases.

If you look into a primer pocket you will see that it is dish-shaped. If you then look at the bottom of the actual primer itself, it has a protruding anvil section and the sides or anvil cap have very square edges. When the primer is seated, the anvil rests on the dished primer pocket bottom and as the firing pin hits the primer cup, it is forced down, compressing the primer mixture onto the anvil section and igniting it. If the primer pocket is dished, the primer does not sit square or level and inconsistent ignition can and will occur. Not only that, but the depth is vitally important too, as variations to the depth will alter the relationship between the firing pin strike and the primer, with dire consequences of irregular pressure and velocities.

This often manifests itself as vertical shot dispersal or string on targets down range and as most firing pins protrude 0.040 to 0.060 thousandths of an inch, then only a 0.010 thou seating depth difference of the primer can cause a 20% difference to the striking force of the firing pin. Normally, small rifle primer pockets have a minimum of 0.117 depth and 0.1730 diameter, plus a maximum measurement of 0.123 and 0.1745 respectively. Large rifle primer pockets have a depth and diameter minimum of 0.125 and 0.2085 and a maximum of 0.132 and 0.2100 respectively. If the case shows the minimum specifications and your actual primer is larger than spec, then it will seat too high, tight or verse versa.

Primer pocket uniformers are widely available. I use a K&M (£35) as they are precision ground carbide tools with at least five cutting flutes, for smooth, flat uniforming of the bottom of the primer pocket. There is a shoulder or stop collar ground in the carbide tool bit that butts up against the primer pocket to manage a uniform depth to SAAMI specs. They come in various sizes for small and large rifle primers and make sure the stop collar sits square to the case at all times, don’t be tempted to rush and twist the cutter, it will make things worse!

As usual, cut clockwise and be gentle but with uniform pressure. You will only be removing very small amounts of the sidewall and bottom corners. The cutting comes to an obvious end as the cutter bottoms out, remove the tool and shake off any brass swarf. Then, reinsert and cutter again, just in case the swarf was causing an interrupted depth.

People do use power tools for this but again be very careful, as it’s easy to tilt the cutter and bugger it up! Use a slow speed of under 1000rpm and clear swarf or chips away regularly otherwise problems will occur.

Do not be discouraged if very little brass comes out, as the primer pocket may be at the high end of the SAMMI spec, whilst others may be very shallow and thus have a lot to be removed. Ultimately, what you want is a nice, square and clean primer pocket so that the primer seats level. Also, it is good practice after shooting the case and after cleaning the pocket of burnt primer residue to re-cut, as brass can flow back into the pocket after firing. If the cutter feels very loose in the primer pocket, then this is a very good indication that your loads may well be overpressure. I have this a lot with my wildcat rounds.

Conclusions

A small but very important set of tools for the accuracy conscious rifle shooter. They don’t cost a lot and will make a big difference to the way your reloads turn out. It’s just another tool to eliminate one more variable that might be causing low velocities or inaccuracies.

Contacts

Norman Clark - Reloading Supplies - www.normanclarkgunsmith.com
Hannam’s - Reloading Kit - www.hannamsreloading.com
1967 Spud - Reloading Gear - www.1967spud.com
Edgar Brothers -Hornady - www.edgarbrothers.com/shooting-sports
Highland Outdoors - Custom Brass - www.highlandoutdoors.co.uk