Primers: Round and Flat

[MikeS]

Hi All.

In the past I've seen cartridges where the primer seems to be rounded, not flat like most cartridges, and I just assumed the primers were made that way. Well, tonight I'm loading some 45ACP rounds, and while most of them were small primer, and I've been priming them with a Lee handheld priming tool, 10 of the cases were actually large primer, and so rather than swapping over the hand priming tool I decided to use the on press priming setup. I have an old Lyman All American press, and it uses priming stems that are removable, and normally I leave them off the press. Well, I have 4 of these stems, 2 for large primer, 2 for small. Well, I stick one of the large primer stems on the press, and start priming the cases. When I primed the first case, I checked it, and the primer was rounded, like the cartridges I'd seen years ago. I checked my primers (I'm using Tula primers), and they're flat like all the primers I've ever used are. So I prime a second one, and it too is rounded. I pulled out the priming stem, and sure enough, the base of it (the part that pushes in the primer) isn't flat, but rather is rounded! I grabbed my other stems, and I have 2 rounded ones, and 2 flat ones, one each for large & small primers.

What is the purpose of having a priming stem that rounds out the primers? Which am I better off using, the flat one, or the rounded one? One advantage I could think of with using rounded primers would be to make it easier to see if the primers are getting flattened out by too much pressure. But I'm curious, in the past did they sell primers that were rounded, which these stems are designed to work with? If so, would using the rounded primer punches hurt modern flat primers? Thanks for any insight to this.

[beagle]

This goes a long ways back in loading history. When I started loading in the 50s, primers came in both rounded and flat. I don't remember if the same company made both or it was a company thing. Some of the old Lyman loaders came with both style punches....round face and flat.

As well as I recall, the rounded primer was a mind thing in the mind of the old timers. They figured that a rounded primer ignited more reliably than did a flat primer. Years of use has proven this a fallacy and we only have flat primers now. Many of the military primers were loaded like that as well and I've seen .45 ACP, old .30 (WWI vintage) and .30 Carbine loaded with rounded primers.

Properly seated, a round primer looks nice but it still goes bang just like a flat one./beagle

[stubshaft]

I remember using rounded primers way back when but always used a flat seating stem to seat them.

[kmag]

Never understood why rounded primers were used, but back in the 50's I was at a range that was used by the security personnel at a federal reserve. They had a Star loader set up ( first progressive I ever saw and was amazed at the press and the price) and it used rounded primers. Shot a lot of rounded primers but never loaded any. Knew a few folks that had a good supply and used them up and them went to flat ones. I never saw any of the rounded ones for sale but remember seeing rounded primer stems for sale.

[BOOM BOOM]

HI,
Had the same set up to start with , both round & flat punches & a Lyman press around 1968-69. Never noticed a difference in result, but I was not really looking for a difference.:Fire::Fire:

[MikeS]

Ok, so I guess the next question is, did I ruin the flat primer by seating it with the round punch? I mean the primer now looks just like the old rounded ones, and considering that the way primers are made they're supposed to be put under pressure by the loading process, so does the fact that the cup of the primer is now a different shape than it was originally supposed to be mean that it's not properly pressured (or stressed, or whatever the term is for when the anvil presses against the priming compound)? Should I take one or two of the primed cases and stick them in a gun and see if they go bang?

[stubshaft]

I doubt it. The primer cup will/does act like a minie ball skirt and expands to seal when pressure is applied.

[olafhardt]

Why not try a couple of primed cases? I once got a primer side ways, so I tried it, it popped, thus I got some research data. Since I feel that one form of personel wealth is having lots of stories to tell, this one lowly primer increased my personal assets and was not wasted. If you try a few and tell us we will be richer!

[cajun shooter]

The firing of primed cases without anything in the case will cause the primer to back out and jam many revolvers. It's not a good thing to do with this type of firearm.

[3006guns]

Primer used to come in the rounded or domed shape years ago. Priming stems were made in a convex shape to accomodate them, but in truth will seat either style of primer. Pressing the rounded primers flat won't hurt them...they still go "bang".

I just finished using up a box of RWS (German) large rifle primers that were rounded and dated from the late seventies. 250 primers to a box/10 boxes in the sleeve for a total of 2500. The price? $6.95!

[1Shirt]

Times past back in the early 60's, I bought a few thousand mil surplus (corrosive) LR primers from Hogden in Shawnee Mission,Ka. for (if memory serves me right) about $5.00 a thousand. Can't remember for sure, but think they may have been rounded. At any rate they shot, even thou cleaning right after shooting was a big priority.
1Shirt!::D

[Rocky Raab]

What the guys above said is right. Primers came either domed or flat, and presses came with four seater stems to accommodate both shapes and both sizes.

I have most of a thousand Western 1½ small pistol primers, domed, on my shelf. They seat just fine with flat punches - and are the most accurate primer I've found yet in my Hornet rifle. I'm very thrifty with them because I'll never find another brick.

[beagle]

You didn't ruin them. I've done thousands like that. Rounded primers are hard to seat straight for some reason and even with a rounded punch, I don't think I have ever seated a full box of cases that were flawless.

Just had a partial box of roundeds last year that I got from somewhere. I even had a rounded punch for my 310 tool as they made them as well and tried to load a flawless box of Hornets but I still messed them up.

As well as I recall, Lyman made some of the older punches on 310 tools and some of the priming rams for the Trueline Jr. that could be switched from round to flat by driving out a pin and swithching ends./beagle

[MikeS]

Ok, several folks have said that you can seat the rounded primers just fine with a flat punch, but does it work the other way around as well? Can I seat flat primers with a rounded punch (which makes the primers come out rounded) without harming the primer?

[Char-Gar]

Like some of the others, my reloading goes back to the 50's where there both round and flat primers on the market and presses came with large and small primings arms for both types.

Being rather lazy, I seated some round primers with the flat stem and nothing bad happened so I continued to do so through thousands of primers. Doing so did not change the shape of the primer.

I have never tried to seat flat primers with a round stem. Have you tried it and are the primers being changed to round by the effort? Or are you just wondering?

If they do indeed come out round, I would not think that would be a good thing. Anytime you break that hard cake of compound in the primer, erratic ignition can be the result.

[beagle]

Seems like I tried that and the primers were a bit domed for my tastes. Kinda gave the appearance of not being seated below the primer pocket lip. It may have been an optical illusion and it's be a few years back. I probably shot 'em anyway at that stage of my reloading. Seems like that's when I turned all my "roundy" punches flat.

I do know that I have one old Lachmiller seating stem for small primers left that's for roundies.../beagle

[MikeS]

Have you tried it and are the primers being changed to round by the effort? Or are you just wondering?

If they do indeed come out round, I would not think that would be a good thing. Anytime you break that hard cake of compound in the primer, erratic ignition can be the result.

Yes, I seated some primers, and they came out round! I was thinking the same thing that it could be breaking the priming compound, and that might not be a good idea. I already loaded a few cases that were primed like this, so I guess I'll try them, and see what happens.

[runfiverun]

i'd think that the doming would cushion the firing pin blow.
i wouldn't use them for anything i needed to fire fer sure.