March 2nd, 2020

Case Prep 101 — Primer Pockets and Flash Holes

USAMU Handloading hump day flash hole primer pocket uniforming case prep RCBS Lyman
Case Prep Xpress photo courtesy Lyman Products.

Each Wednesday, the U.S. Army Marksmanship Unit publishes a reloading “how-to” article on the USAMU Facebook page. One “Handloading Hump Day” article covered two basic case prep chores — uniforming primer pockets and deburring flash-holes. Visit the USAMU Facebook page for other tips.

USAMU Handloading hump day reloading tips

Primer Pocket & Flash-Hole Conditioning

This week, we’ll address a question that frequently arises: “Do you uniform primer pockets and deburr flash-holes?” As we tailor our handloading methods to the specific needs of each instance, the answer, not surprisingly, is “Sometimes!” However, don’t flip that dial just yet, as what determines our approach may be helpful in deciding how to address one’s own techniques. Moreover, we have a buried “Easter Egg” morsel that may bring a chuckle, as well as useful safety information!

Generally, the USAMU Handloading Shop does not uniform primer pockets (PP) or deburr flash holes (FH) of our rifle brass. We’re certainly not against it… Rather, this reflects the very high volume of ammunition we load, the fact that very few cases are ever re-loaded for a second firing, and the types of brass we use. However, as a need is perceived, we DO deburr flash holes. Of interest, we have fired many very small, 1000-yard test groups and aggregates using weight-selected, domestic brass that had not had PPs uniformed or FHs deburred.

USAMU Handloading hump day flash hole primer pocket uniforming case prep RCBS Lyman

Before and After — On the left is a fired, deprimed 7.62×51 case with primer residue intact. On the right the primer pocket has been uniformed to SAAMI specs. Note the shiny finish at the bottom of the pocket — evidence of the the removal of metal when uniforming the primer pocket.

As to the type cases we use, many thousands of our long-range 5.56mm cases come to us from the arsenal with the primer of our choice pre-installed and staked-in, per usual practice. Obviously, we cannot uniform either FHs or PPs on this live, primed brass. However, after careful sorting, inspection and preparation, we do obtain match-winning results with it.

Shooters who reload their brass several times may decide to uniform PPs and deburr FHs, especially on their “300-yard and beyond” brass. Here, they will use the cases many times, while the uniforming is performed only once. Also, most handloaders only process moderate amounts of brass, compared to our multi-thousand round lots.

Having high quality Long Range (LR) brass helps. Many of the better brass manufacturers [make] their flash holes so that no burrs are created. Still, it does pay to inspect even THESE manufacturer’s products, as occasional slips are inevitable. Very rarely, some of the best makers will have a significant burr in, say, 1 per 1000 or 2000 cases, and it’s worth catching those.

Exceptions can always be found. Recently, we began processing a large lot of match brass from a premier manufacturer. We were startled to find that every case had a significant burr in the FH — something we’d never before seen from this maker. We then broke out the FH deburring tools and went to work.

Some observers have noted that it can be difficult to truly verify the contribution to accuracy of these procedures — particularly when firing from the shoulder, in conditions. Members of this staff, as individual rifle competitors, do often perform these operations on their privately-owned LR rifle brass. One could ascribe this to the old High Power Rifle maxim that “if you think it helps, then it helps.”

However, a World Champion and Olympic Gold/Silver medalist here commented on his own handloading (for International competition, which demands VERY fine accuracy). He noted that he did seem to see a decline in accuracy whenever he did not uniform FHs, deburr FHs and clean primer pockets before each reloading. (One might be tempted to counter that only a truly World Class shooter could reliably detect the difference.) However, with the wisdom of decades experience, our Champion also remarked that “It could have been that I just wasn’t shooting as well that day.”

For those who do opt for these procedures, note that various tool models may have adjustable depth-stops; pay attention to the instructions. Some FH-deburring tools (which enter the case mouth, not the primer pocket) are dependent upon uniform case length for best results.

USAMU Handloading hump day flash hole primer pocket uniforming case prep RCBS Lyman

Above is a flash-hole deburring tool on an RCBS powered case-prep unit. These case prep machines can save a lot of pain and misery, helping one perform various functions quickly and efficiently.

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