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Old 09-21-2016, 08:22 AM   #1
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Substituting primers

Fwiw, some recent discussion on primers made me think of some experimenting I did a few years ago on the subject of primer substitution; so I thought I’d dig it up and share it here.

For a long time, a lot of pistol shooters have used small rifle primers in cartridges that normally use small pistol primers; typically when pushing or hot-rodding their calibers. In calibers like .38 super, 9x23, etc, where competitive shooters are trying to milk all the performance they can get, the harder rifle primers are handy because they can withstand higher pressures than pistol primers. The main thing to watch is that since the primer body on rifle primers is harder than on pistol primers (to withstand the higher pressures of rifle cartridges), some pistols supposedly won’t ignite the harder rifle primer. I can see how that could be a concern, but personally I’ve never had a problem with it in any of my guns. I've used small rifle primers even in striker-fired glock and M&P pistols and haven’t had that problem, but it could certainly be a valid issue to watch for.

When I first began checking into the practice and trying it out for myself, I chrono’ed some loads to see if there was a difference performance-wise when using small rifle vs small pistol primers, all other factors in the equation being the same. The difference between small pistol and small rifle was negligible, which surprised me. I’d read some places that the rifle primers were inherently ‘hotter’, and that seemed logical. But it wasn’t borne out in testing. Frankly, the difference between rifle and pistol primer use was less than the variation of the results using the same loads out of another, almost identical, gun. I started with a 4” L-frame 681, to give some safety-cushion with the .38spl loads I was experimenting with. I used small pistol magnum primers, small rifle, and small rifle magnum. Load was a 158-grain LSWC over 4.0 grains of bullseye, in .38 spl cases. Chrono averages, thru the 4” smith 681:

SP Magnum primer — 906 fps
SR Standard primer — 922 fps (1.7% faster than small pistol magnum primer)
SR Magnum primer — 921 fps (pretty much same as SR standard primer)

Don’t know why the magnum rifle didn’t exceed the standard rifle velocity-wise (I really expected it to), but that’s what they did.

Since experimenting with them, chronographing them, function-testing them in my own guns, and seeing the results for myself, I’ve mostly settled on small rifle primers for my small-pistol caliber applications. The 9mm and .38spl get regular, and the .357 gets magnum, and they all do fine. I do still use small pistol, but not primarily. Small rifle just gives more flexibility, since they’ll work for anything from .38 and 9mm, up to .223, 30carbine, and .300 blackout as well.

All that said, this whole conversation is about SMALL rifle primers and SMALL pistol primers only. They are the same dimensionally. Large rifle and large pistol primers are NOT the same dimensionally; their diameter is the same, but their height is not. The primer pocket depth is 0.008" deeper for rifle than for pistol. This means that using a large rifle primer in a large pistol case will tend to make the primer stand proud (over-long) about eight one-thousandths. IE, instead of being .003" or so recessed below the case-head, it will actually stand .005" or so out PAST the surface of the case-head. I do know of some folks that have done this and gotten away with it fine, but the potential for slamfires is too great for me personally, unless the primer is over-borne (basically semi-crushed) deeper than it’s intended to be by the maker.

Going the other direction — using a pistol primer in a small rifle case — doesn't have this particular problem, but in addition to potential over-seating-depth issues causing light firing-pin strikes, being softer metal it also would run the risk of piercing at the firing pin strike unless the round was loaded way down pressure-wise.

Anyway, just something I came across years back, checked more into and during one of the recent primer-shortage droughts & adopted personally, and thought I'd pass along.
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Old 09-21-2016, 08:42 AM   #2
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the makers probably offer different primers for a reason, folks. The rifle primer's flame burns longer and hotter (supposedly) so as to properly ignite larger charges of slower burning powder. This seems a bit of a joke to me, since the ignited powder near the primer surely would ignite the rest of the charge, but hey, i have no proof of things in either direction. IF the rifle primer's flame IS hotter, that might turn a safe/hot load (in the pistol) into an overload. Softer primers, however, DO tend to "flow" back out around your firing pin in handguns using hot loads. Alcan primers were so soft that they did so with a very mild load in .45 ACP.
Old 09-22-2016, 03:30 PM   #3
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Originally Posted by justme View Post
the makers probably offer different primers for a reason, folks.
From the guy that suggested trying to remove and then dissect a primer from a loaded shotgun shell, to try and use part of the primer in a pistol..? Really?

Originally Posted by justme View Post
The rifle primer's flame burns longer and hotter (supposedly) so as to properly ignite larger charges of slower burning powder.
I’d read that before, and was a factor in my starting out with a bunch of safety space — using .38 loads in an L-Frame .357 revolver to start with. Didn’t see much evidence of it though. While the rifle primers gave very-slightly higher velocities, it was less of a difference than the same load just put thru a different gun with the same barrel length. Not what I expected, but that's why we test...

Originally Posted by justme View Post
…Softer primers, however, DO tend to "flow" back out around your firing pin in handguns using hot loads.
Happens even more in carbine-length barrels, and as much as I like handgun-caliber carbines, it may be an issue for me more than most. I don’t recall the load data for my 125- and 140-grain carbine-oriented loads for .357, but when fired thru either of the carbines the primer flattens noticeably more than out of a handgun. Longer barrel means longer acceleration time, which means increased amount of time that the primer has that backpressure on it, compared to the handgun barrel.

Basically, it’s the same reason we get more velocity from the longer barrel — more time under pressure, with that pressure pushing with equal force on the bullet at one end and on the case & primer on the other.
Old 10-11-2016, 08:31 AM   #4
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All primer and powder column heights behave differently. The primer and column height, as opposed to its constituents, are the most relevant variables for load developers in this regard.

IME Remington typically yields the most velocity whereas load consistency will be much more tailored. I prefer CCI and Federal primers for rifle cartridges, in that order, unless it's a long magnum where I (and most manufacturing bodies) have found the Federal Match primers to yield better results.

CCI in pistols all day.
Old 10-11-2016, 08:40 AM   #5
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Originally Posted by ethereal View Post
...CCI in pistols all day.
My favorite as well, followed by remington. CCI's also my favorite for 22LR ammo.

For non-precise stuff (ie, most pistol stuff), I'm not personally all that finicky though and will buy whichever of the main brands is cheapest. Most of the time I'm shooting pistol it's at shorter ranges, and the differences are almost imperceptible; to me at least.

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