case mouth flaring – The ExhaustNotes Blog

By Joe Berk

One of my favorite rifles is the Enfield No. 4 Mark 2, a bolt action rifle just dripping with history and charisma. The No. 4 Mark 2 was the last in the Enfield rifle series, with a run of 59,000 produced by Britain’s Fazakerly armory for Ireland in the 1950s. It was the last Enfield in a long line of continuously improved rifle designs, and it includes a much-improved trigger design. Most of these Irish rifles were never issued and many were sold in their unfired, cosmoline-laden condition. Mine comes from that group. It’s the one in which I tested the reloaded ammo featured in this blog series.

Once-fired .303 British cartridge cases. They almost look like scaled-down .375 H&H cases.

A close-up view of the .303 British case after firing. These cartridge cases are ready for the reloading process.

The headstamp. These are Winchester cases. Note the spent and indented primer, which will be removed in the case resizing process.

I have a stash of once-fired .303 British brass acquired from generous friends over the years. I will reload them with 200-grain cast bullets made by good buddy Roy Hursman, sized to 0.313 inches, which I also use in my Modelo 1909 Argentine Mauser and Mosin-Nagant rifle. I thought they might work well in the Enfield (and they did; I’ll tell you a bit about that here and provide much more detail in Part 3 of this series).

The cast lead bullets I load in my .303 British ammo. These weigh 200 grains. They have been lubed (the red grease in the lube grooves), gas checked (the copper cap on the base), and swaged down to 0.313 inches. They work great in the 7.65 Belgian Mauser, 7.62x54R Russian, and .303 British cartridges.

What I didn’t have in my shop was a set of dies in .303 British. I naturally turned to Lee Precision. I believe in Lee reloading equipment. I have their dies for the .22 Hornet, .22 250, .243 Winchester, 6.5 Creedmoor, .30 Carbine, .30 40 Krag, .300 H&H, .300 Weatherby, .38 Special/.357 Magnum, .44 Special/.44 Magnum, .45 ACP, .45 Colt, and probably a few others I can’t remember as I type this blog. I also use other Lee reloading equipment. I think their Classic Turret Press is the best reloading press of its type for loading handgun cartridges. The bottom line here is that I’ve never been disappointed with Lee products, and I say that as a guy who has been using Lee gear for 50 years.

I ordered Lee’s Ultimate 4-die set, and what I received surprised me. I received the four dies (which I expected) and a micrometer bullet seating attachment (which I did not). Each Lee die set also includes a little packet of case lube for the resizing operation (it’s not shown in the photos below). It’s a nice touch; Lee basically gives you everything but the reloading press and the components (bullets, brass, primers, and powder) to load a specific cartridge with each of their die sets.

The Lee ULee Ultimate 4-Die set includes four dies normally included in a single box. My set included a micrometer bullet seating attachment not evaluated in this blog series (although I will evaluate it in a future blog). The fourth die (the collet die) was provided in a separate container (see below). In the photo above, we have the full-length resizing die (top), the bullet seating die (bottom), the factory crimp die (right), the micrometer bullet seating feature, the shell holder, and a measuring cup (not used by me). Lee also provides a small pack of case lube (not shown here).

The Lee collet neck sizing die, used in lieu of the full-length resizing die to neck size the brass case.

I won’t get into the micrometer bullet seater in this three-part .303 British Lee die set review (that review will occur down the road a bit).

The Lee Ultimate 4-die set includes two resizing dies (a full-length resizing die, and a collet die for neck sizing only), a bullet seating die (that also includes a roll crimping feature), and a separate crimping die for applying what Lee calls a factory crimp. The die set also includes a shell holder (a nice touch, as other manufacturer’s die sets do not) and a powder scoop. I’ve never used the powder scoop; I use a more precise powder dispenser.

The once-fired brass I had on had was good stuff. It was in the original factory boxes and it was in good shape. Because the rifles it had been fired in previously were not my Enfield, I knew I would have to full length resize the brass first to return each case to factory dimensions. To do that, I mounted the Lee shellholder in my press, ran the press all the way up, and then installed the full-length resizing die, screwing it down in the press until it contacted the shell holder. I then retracted the press ram, turned the die another 1/8 of a turn into the press, and locked the die in place with its locking ring.

The Lee .303 British shell holder installed in my reloading press. It snaps into place. Dies and shell holders are typically interchangeable between reloading press and die manufacturers. I use a single-stage RCBS Rockchucker reloading press; Lee dies and shell holders fit it perfectly.

Lee’s full-length resizing die installed in the press. This die simultaneously resizes a fired case to factory specification and punches out the spent primer. Note the locking ring on the die body.

The business end of the Lee full-length resizing die after resizing a bunch of cases. This photo shows the decapping pin, which removes the old primer.

I lubed each case with the lube Lee provided and ran it through the full-length resizing die, which simultaneously brought the cases back to factory dimensions and removed each case’s spent primer. The full-length resizing dies does both steps in one operation.

I intended using cast bullets in the .303 Enfield, so for me the reloading process included an additional step: Flaring the case mouth. Case mouth flaring allows cast bullets to enter the cartridge case without the case shaving any lead from the bullet. To flare the case mouths, I use a Lee universal flaring tool I purchased decades ago. It’s a clever die set that uses a cone to impart a slight bellmouth to the case.

Lee’s Universal Case Mouth Expander. I bought this in the 1970s and I’m still using it.

The Lee Universal Case Mouth Expander disassembled. The amount the case mouth is flared is determined by how far the die body is screwed into the reloading press, and by how far the adjuster (top item in this photo) is screwed into the die body. The cone (shown in the middle of this photo) is what flares the case mouth. Lee provides two cones; one of small-to-medium calibers (shown here), and one for larger calibers (not shown here).

When empty cartridge cases are run into the Lee Universal Case Mouth Expander) it imparts a slight flare to the case mouth. If you do it right, you can barely see the flare (as is the case for the case shown here) and the bullet enters the case with no lead shaving.

The approach to case mouth flaring is to install the Lee Universal Case Mouth Expander in the press and adjust it to impart just enough flare to allow the bullet’s base to enter the case. You don’t need much flare (less is more here; too much will work harden the brass unnecessarily). I’ll jump ahead a bit and mention here that if you can find that happy spot where you flare the case mouth just enough to allow the bullet to enter the case, you won’t have to crimp the case mouth later to eliminate the flare.

A perfectly-flared case mouth, with just enough flare to allow a bullet to start into the case without shaving any lead.

After completing the above full-length resizing and flaring, I reloaded 20 rounds (like you see in the photo at the top of this blog). Then I did what I always do: I labeled the box of reloaded ammo. After that, I fired the reloaded ammo in my Enfield.

I’m not going to cover the rest of the reloading process in Part 1 of this series, but I will in Parts 2 and 3. I’m jumping ahead here by mentioning firing the full-length resized ammo because I wanted brass that had been fired in my rifle. Ammo fired in my rifle would be perfectly formed to my rifle’s chamber, which is minutely different than other rifles’ chambers. That’s because of rifle chamber dimensioning tolerances. The once-fired brass I had was fired in other rifles, so I needed to shoot it in my rifle so the cases conformed to my chamber.

How did the full-length resized .303 ammo shoot? Very well, thank you. Take a look.

This was the first time I had fired this ammo in my rifle, so I needed to dial it in. The first three rounds went low at 50 yards (the nice tight group at about 5:30 on the outer edge of the 6-ring), so I ran the Enfield’s ladder aperture sight up. Oops, too much, which resulted in the group high in the 6-ring. I went down half the distance on the rear aperture, and the next three rounds were just above the bullseye. Down a click or two more, and the rifle was on the money. In case you were wondering, I used 21.0 grains of IMR 4227 and a Winchester large primer (but more on the load in Part 2 of this series).

Having fired my full-length resized ammo in my Enfield, the fired brass could now be neck sized instead of full-length resized. The idea behind neck sizing is that the clearance between the chamber and the brass case is greatly reduced by neck sizing (as opposed to full-length resizing), and theoretically, neck sizing should result in increased accuracy because the case won’t be rattling around in the chamber. There are a couple of another advantages to neck sizing, too. One is that it works the brass less, so it should last longer. A third advantage is that you don’t have to lube and then clean the cases. They can be neck sized without using lubricant. I’ll say more on that in a moment. Not having to lube (and then cleaning the lube from the cases) greatly speeds up the reloading process.

Now that I had brass cases that had been fired in my rifle, I installed and adjusted the Lee collet die in my press. The collet die performs two operations. It has a decapping pin that punches out the spent primer, and it has a set of four collets that compress the case neck around a spindle to bring it back to new brass factory dimensions (that’s the neck sizing operation). You can adjust the die’s depth in the press to adjust the final inside diameter of the case neck, which is a very useful feature to have. Ideally, the resized case neck inside diameter should only be 0.001 to 0.002 inch smaller than the bullet diameter. That amount of case neck inside diameter undersizing will allow the case the grip the bullet firmly so that it won’t push into or pull out of the case. You could make it tighter and still seat the bullet, but doing so would expand the case mouth more with the bullet’s insertion, and that is not desirable. It would distort the case and possibly introduce non-concentricity or angular misalignment between the bullet and the case, and that would hurt accuracy.

The Lee collet die installed in my RCBS Rockchucker press. This die will neck size the case instead of full-length resizing it.

A .303 case entering the Lee Collet Die. By adjusting the depth to which the Collet Die is screwed into the press, you can control the neck-sized-only cases’ neck diameters. I adjusted the die to provide a 0.312 neck inside diameter, which gives 0.001-inch interference between the bullet and the case neck.

After completing the die seating depth adjustment, I had the case mouth diameter exactly where I wanted it: 0.312 inches. My cast bullets were at 0.313 inches, so I was good to go.

Not the world’s best photo (mea culpa). Parallax makes the inside diameter in this photo look like 0.313 inches; it was actually reading 0.312 inches. That’s what I wanted.

Next up will be our Part 2 of the Lee .303 British Ultimate 4-Die set review. Stay tuned.

So far, I am very impressed with this set of Lee dies. I’m not surprised, though. As I mentioned earlier, I’ve been using Lee equipment for decades, and it has always pegged the needle on my quality meter. These dies are good at any price. The fact that they cost less than any of the competitors’ products is a huge plus.

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