Bore size versus performance
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- All started here
- Bottom line
- By the way
If you are a regular reader of this blog you know that I am exploring the reloading of .22 rimfire cartridges. Researching that endeavor has opened my eyes to a world of reloading that I didn’t know existed. Not only are people reloading .22 rimfire cartridges, they are doing it for most other rimfire calibers. Today will be an airgun-related discussion about bore size that started as research for reloading the .41 rimfire short case.
All started here
It all began when I posted the photo of the Remington double derringer in Part 1 of the reloading series. That image caught my attention and started me on a journey to see where this goes.
When I first posted this picture I said your grandfather’s .41-rimfire derringer is a good reason to reload rimfire.
As I did my research I discovered two new books that seemed to offer a lot of valuable information. The first is titled The 41 Short Rim-Fire and subtitled Deadliest Round in the West. It’s by Brendan Michael Murphy and was self-published in 2017. My topic today came from this book.
After ordering that book I realized that people were not just reloading .41 rimfire shorts, they had to be shooting them! And, of all the guns that shoot them, none is more universally recognized than the Remington double derringer! Was there a book about that gun, I wondered? Yes, there was. In 2008 Graphic Publishers put out Dr. William H. Elliot’s Remington Double Deringer. This book has four authors — Douglas S. Drummond, Rudolph H. Johnson, MD, Elias J. Williams, Jr. and James W. Barnard. I ordered that one, too.
Incidentally, the spelling of Deringer is correct for the man, Henry Deringer, as well as for the guns he created. The spelling derringer is the colloquial term that has entered the English language for a short pistol. Either spelling is correct.
I was bitten! Not only did I want to know what it was like to shoot a .41 rimfire short — I wanted to know what it was like to shoot one in a Remington double derringer! But before I took the plunge, I read both books and gained a lot of knowledge about the firearm and about the cartridge. Therein lies my introduction to today’s report.
The first book was written by an author who just wanted to set the record straight. I can identify with that. For years writers have written that the .41 rimfire short is a weak and inaccurate round. It propels a 135-grain lead bullet out the spout at 375 to 450 f.p.s. — hardly a good defense weapon. Or so the writers said. But author Murphy wanted to know more. He wanted to know why the round was so weak, when his research told him it should have been far more powerful.
In his collection of Remington derringers Murphy discovered that the earliest ones (their entire production was from about 1867-1935 and the early ones were made 1868-1888) were obviously made for black powder because that was all that was around. Remington continued making the gun more or less in the same way for those black powder cartridges, right up to the end of the 19th century (1898, or so). By that time semi-smokeless gunpowder had been invented and by the start of the 20th century smokeless powder was on the market. Black powder cartridges were still on the market and would be for several more decades but smokeless powder was the wave of the future.
That caused a problem for Remington. Smokeless powder creates more pressure than black powder when both are loaded correctly. Yes, black powder can blow up a gun, but that’s when it is not loaded properly. Remington wanted to continue making their double derringer, but they knew that cartridge makers would soon be loading them with smokeless powder. How do you keep from blowing up the older guns that have been around for almost 40 years when smokeless cartridges are used?
Brendan Murphy discovered that Remington did it by making the bore of the newer derringers smaller — 0.399-inches as compared to 0.405 to 0.407-inches for the older pistols. He slugged the bores of examples of Remington double derringers in his own collection to prove that. He also measured the bullets in both old black powder cartridges and in newer smokeless rounds. Sure enough, they followed suit. Shoot a smokeless round in an older derringer and there is so much space around the smaller bullet that the pressure never builds. Shoot a black powder round in a newer derringer and — well, the pure lead bullet gets mangled on the sides but the pressure doesn’t rise above where it normally should. Either way the shooter is protected.
And that is why writers have said all that they did about this old cartridge. So Brendan started experimenting. He pulled a bullet from a recent rimfire cartridge and it measured 0.401-inches in diameter. That will hardly work in a bore of 0.405 to 0.407-inches! But it’s perfect for a more modern 0.399-inch bore.
I’ll cut to the chase to get us to where we need to be. Using the more modern undersized bullets in an older (circa 1868 to 1888) derringer, Murphy got velocities of 365 to 453 f.p.s. — about what the gun writers have claimed. At an average velocity of 421 f.p.s. the 130-grain bullet produces 51.18 foot-pounds of energy (less weight for the bullet comes from the smaller diameter). That’s less energy than a .22 short!
However, when he reloaded a couple cases with a modern compressed load of 13 grains of a mixture of FFFG and FFFFG black powder and a bullet that measured 0.406-inches in diameter, the velocity was 586 to 611 f.p.s — for the same cartridge in the same pistol! At an average 601 f.p.s. for the 135-grain bullet (heavier because of a larger diameter) 108 foot-pounds were produced. That’s about equivalent to a standard speed .22 long rifle cartridge.
What has any of this to do with airguns? A couple things, actually, and you need to know your airguns to understand. First of all — airguns are still shooting black powder. What I mean by that is airguns still use air. We breathe the same air that Jesus, Charlemagne and Abraham Lincoln breathed. And, since our guns run on that air, nothing has changed in the power department. More air means more velocity for a given projectile — just as it does for black powder. A longer barrel means more velocity for pneumatic airguns (multi-pump and precharged) just as it does for black powder firearms.
And bullet size matters. Only we don’t shoot bullets, except for big bores and those smallbore guns that shoot solid slugs. We shoot diabolo pellets. What’s different about them is their flared skirt that conforms to the bore of an airgun when the shot is fired. It does so at pressures that are far below those of black powder cartridges — even little ones like the .41-caliber short. A precharged pneumatic might present air pressure of just 800-1,000 psi to the base of a pellet, while a .41 rimfire short might present 8,000-10,000 psi to the base of its bullet. I know I’m just guessing at those black powder numbers, but I do know that black powder pressure peaks around 12,000 and 15,000 psi in rifles with very long barrels. At that pressure level it would really be stated as copper units of pressure or CUP, due to the test device used to obtain them.
The point is, the base of a pellet has to flare easily, where the base of a lead bullet has more pressure to squash it out to fill the bore. And this is why, as black powder shooters, we know the importance of softer lead bullets. But I digress.
As airgunners, we understand the importance of pellet skirts, but what about pellet heads? Remember those gun writers who said the .41 rimfire short was underpowered? They also said it was inaccurate — for the same reason — because the bullet didn’t fit the bore. Not that any of them bothered to check — or even to understand!
But the readers of this blog do understand and they understand quite well. We even have a reader, Jerry Cupples, who makes the PelletGage that allows us to accurately measure the size of our pellet heads. And I have a very special PelletGage that Jerry once made. It goes to the thousandth of a millimeter instead of the hundredth. I don’t care whether the holes are exactly the sizes that are marked. All I want is pellets with heads of a certain diameter that I can relate to a general size range like, “Larger than 4.51 mm.”
This is the PelletGage I used.
I sorted .177-caliber JSB Exact Heavy pellets for a test in Cloud9’s new RAW field target rifle. I wanted them all to be the same size and according to the PelletGage they have heads larger than 4.510 mm and smaller than 4.515 mm.
Out of 36 pellets gaged, 20 were of a uniform size of 4.515mm and 16 had heads of a different size. Of those 16, 14 were smaller than the 20 I accepted and 2 were larger. This tells us that JSB pellets are very uniform in size and after we shoot them we will know how they relate to the RAW rifle, in the accuracy department.
By the way
Oh, and by the way, I did get a Remington double derringer to use in the fuiture of the rimfire reloading report. It was originally shipped from Remington in November of 1923, so it had to have been made earlier than that — but not much. From the two books I mentioned earlier I know it has a 0.399- to 0.401-inch bore, and I can concentrate on getting a mold for a bullet that size, once I slug the barrels to confirm it.
My new/old Remington double derringer.
My new/old Remington derringer was re-blued at some point, so a lot of collector value was taken away. But it’s solid, it locks up well and it hasn’t got any of the fatal flaws of this firearm, such as cracked barrel hinges.
This pistol was either not shot very much or it was well taken care of. Finding crisp bores like this is not common.
Some people pay no attention to what’s going on. That’s why Remington had to downsize the bores on their derringers — to keep people safe when the ammunition changed. With the information gathered in the two books mentioned above I’m going to leapfrog ahead of the pack in my quest to reload for the .41 rimfire cartridge.