If you`re loading for accuracy, it`s important to uniform the

If you’re loading for accuracy, it’s important to uniform the flash holes and primer pockets. All
the boxer primed flash holes I know of are punched, which can leave burrs and irregularities in
size or shape. Lapua used to be drilled, but isn’t anymore. In testing the best of the commercial
brass available, it helps to uniform both the primer pockets and flash holes if you want to keep
your handloads to the highest standards you can. You only need to uniform the flash holes once,
check the primer pocket from time to time.
Image X-X: The Forster Primer Primer (pun by author), courtesy Forster Products.
Photo X-X: Lake City ball and LC match brass that was uniformed before tumbling, simply to show why
you want to do this. Note the relieved areas, including a burr on the M118 case (middle case - top row).
The M118 match cases were the best of military production 7.62x51 brass.
Note the variations below. Shiny areas were cut with a uniformer.
New Lapua .308 brass. The case on the left is untouched, right uniformed.
Photo X-X: New Norma brass. The case on the left is untouched, right uniformed.
Photo X-X; Fred Sinclair’s original primer pocket uniformer.
Photo X-X: Current Sinclair Uniformer kit, for both large and small primer pocket. P/N 749-011-518.
The Sinclair 8000 series uniformers can be used with power drills or drill presses. P/N 749-003-711
Photo X-X; The K&M uniformer with the handle I use. K&M P/N# CARLRPCT
Fred Sinclair’s original uniformer is the best I’ve known of or used as far as handling and the
ability to mount it into a drill press to use under power. The K&M and current Sinclair
uniformers is more accurate in the dimensions of the primer pocket, but with ball cases the K&M
does tend to get stuck from time to time when using it by hand.
When doing ball brass you want to swage the primer pocket first and then take a simple inside
the case neck reamer to remove any dimpling around the primer pocket. This helps because
swaging primer pockets with a tool can leave a dimple on the edge around the primer pocket. If
you leave these it can cause malfunctions in a close tolerance rifles. While I normally uniform
the flash hole after swaging, if you find you flash hole uniformer getting stuck, do the flash hole
before. This happens because some swaging tools can fold burrs over making them tougher to
clear after.
Something you do NOT want to see this after uniforming a primer pocket
Photo X-X: The rippling you see is called chattering. This means you’re not getting a uniform
surface in the bottom of the primer pocket because the cutting edges of the uniformer are not
cutting properly or you may be doing something wrong. You will not get consistent primer
seating with this kind of primer pocket.
If you hear that someone says they found a burr in the flash hole, the answer is simple. In the
example below, while Lapua flash holes used to be drilled; as noted all current boxer primed
cases are punched. Even the production facilities that properly maintain their production
equipment to the high standards we expect, you can and do find occasional inconsistences.
That’s why you uniform the primer pockets and flash holes. Case in Point, the best commercial
manufactured brass is Lapua, you may find issues like below:
Photo X-X, Sample of an obvious burr in the flash hole, courtesy of K&M Precision Shooting Products.
Photo X-X: Sample of small burrs in the flash hole,
Cross section courtesy of K&M Precision Shooting products.
It’s an important issue when loading accurate ammo to uniform the flash hole for proper ignition.
Second issue is this: When tumbling the brass after lubing and sizing them, if you use Corn cob
media (I do), you’ll find fragments of the media in flash holes as seen later.
The best flash holes uniformers I’ve used or tested:
Photo X-X; The Sinclair Flash Hole Uniformer, for both large and small primer pockets. P/N 749-008-617.
The Sinclair tool is very quick and easy to use. It’s simple to change from small to large flash
holes by changing the indexing part of the tool (switching ends). Only trick to this one is be sure
to locktite the set screw that holds the reamer in place.
The K&M which is exceptionally good and more precise since it indexes off the case mouth and
dresses the inside of the case around the flash hole; but slightly slower for production runs. It
relieves the flash hole to .080 where the Sinclair tool is .081. I find these products exceptional,
but not the only ones currently offered.
Photo X-X: The K&M Flash hole uniformer that indexes off the case mouth. K&M P/N UPSTD080.
Photo X-X: The Sinclair Flash Uniformer that indexes off the case mouth. P/N 749-003-822.
As noted above, Corn cob and occasionally stainless steel pellets seem to loveto stick in uniformed flash
holes. It’s good to check them after tumbling.
Photo X-X: The never ending love story; corn cob media and flash holes.
Photo X-X: Stainless Steel media (see appendix).