doublegunshop.com - home Forums General Discussion Double Rifles, Paradox Guns & Gauge Rifles @ doublegunshop.com 8 bore pinfire rifle has arrived

received the French 8 bore pinfire rifle today. Nice and big. Weight is close to 11 pounds. Groove diameter of .873, chamber cast base in front of the rim is .937 same all the way to the end, no taper. Length is 3.65". I haven't slugged the bore yet. I have to find a hunk of lead large enough. Sights = 25 meter standing and 50, 100, and 150 folding

Wow!

Photos of all the marks, I haven't found the crown over DV yet

Crown over the DV is Devisme's trademark.

What is an average twist rate for an 8 bore rifle? Mine seems really fast. 1 in 12" Bore slugged and the diameter is right at .840".

Cool gun. I have a Blissett 8 bore pinfire shotgun. It came with about 40 modern brass cases. Haven't shot it yet, but look forward to doing so. Have a couple of pinfire double rifles, but cannot remember the twist rate at the moment. Not sure if they were for balls or conical bullets.

The barrel looks to be in incredible condition for it's age. I suspect that has a lot to do with the fact that the possibility of using an 8 bore rifle in France would seem to have always beem very limited. Maybe ordered by someone was expecting Hannibel to come back through!

I havea coup;e of 8 gauges and after reading this, I was struck byt he dimensions. The chamber seems normal except for the non-taper. The groove diameter is what threw me. I have a combination gun by Sauer which is chamberedfor a 16 ga in the shot barrel and a 20 ga bore cartridge in the rifle barrel. That barrel was made from a 20 gauge barrel rifled to a groove diameter of a 16 gage and chambered for a short 20 ga brass case. A case ID sized ball is used in the 20 gauge load and expands to the 16 gauge sized groove size.

A normal bore sized 8 gauge bullet for a smooth bore would be around .835". (I shoot that size round ball in my Scott single barrel).With the case being .937 straight, I suspect the case ID may be larger than the
normal groove diameter you would get with a noral tapered case. It may take some detective work to find the proper diameter that will obdurate into the bore and be a tight fit in the cartridge. The round balls I shoot fit snugly in a new tapered brass case. You might also have a mold made for a heeled bullet that could be crimped into a tapered case to avoid a paradox type crimp.

If your gun is made for a straight brass case of groove size interior case size, you may need to have some custom cases turned or anneal new cases and fireform them before loading. I presume custom cases would be needed anyway for a pinfire. Never tried to deal with one. I have seen references as to new ones custom made or conversion or standard cases.

Made some 8 bore pinfire cases for my rifle. Waiting on a custom mold then I can get it firing again.

Mike

How did you measure the twist? In looking at the photos down the barrel it is hard to judge distance but If you look at the track of an individual land it seems they turnslightly more than 1/2 revolution in the distance that is visible. I have a couple of cape guns with bore gauge barrels and they are a much more moderate twist. A 12" twist is right up there with modern big bore rifles shooting jacketed bullets. I would be afraid of slippage with lead bullets of that size.

I have a Scott single 8 bore shotgun of an era just a little older than your gun. It is cylinder bore and I developed some 8 gauge ball loads for it with .835 bore size round balls (2 oz). My gun weighs a few oz. less than yours. The recoil of these relatively mild loads at shotgun velocities were not bad but firm. I know that later bore rifles operated at substantially higher velocities and used projectiles of considerably higher weight. I imagine recoil would have been pretty significant especially a light gun ( 2 to 3 pounds lighter than a double). I don't really have any idea what the loading would have been for the pinfire as to weight and velocity. I don't know if the design was for a bullet form or a ball. Many of the later German cartridges I suspect were based on ball loads and had slow twist rates to match.

marked a cleaning rod, shoved it in with a tight fitting swab, rifling measure 24 1/4", Did two turns.

Hearing that this 8 bore Pinfire rifle had a 1 in 12" rifling twist really got my attention. I would have expected to see something more like a 1 in 36" twist rate found in many 12 gauge slug barrels.

I became interested in rifling twist rates at a very young age. The first deer rifle I used was my Dad's .244 Remington, which fell out of favor compared to the .243 Winchester, due to its' 1 in 12" twist that supposedly wouldn't stabilize 100 gr. bullets. My Dad found that it would stabilize 100 gr. Nosler Partitions to around 1 MOA, because the Noslers were more blunt than most 100 gr. .243 spitzers. That was plenty good for deer, but the same rifle would shoot tiny one-hole clusters with 75 gr. Sierra hollow points.

But then, I'd also heard about the problems of over-stabilizing some bullets such as .17 caliber bullets with thin jackets at very high velocity. Upon doing a little research, it seems that a 1 in 12" twist in an 8 bore rifle will most likely work just fine. There are several handy online rifling twist rate calculators such as this one where you can crunch some numbers:

https://bergerbullets.com/twist-rate-calculator/

I played around with this calculator using some wild guesses as to bullet weight, bullet length, and ballistic coefficient of some imaginary lead round nosed .840" diameter bullet at roughly 1000 feet per second. I used very low ballistic coefficient numbers including some low B.C.'s similar to what you'd find with a lead round ball, and ended up with several different stabilization factors ranging from 40 to 55, which the calculator says will be stable. That is quite a bit higher than what are considered more optimum mimimum numbers like 1.5 to 1.7. But from what I read, over-stabilization isn't near as much a problem as under-stabilization. A very extreme high bullet rpm will cause more yaw or drift at extreme ranges, but that sure won't be a problem in an 8 bore. It could create more instability if there are casting voids that produce an unbalanced bullet, but that can happen even with a normal twist rate.

One other thing I wonder about concerns what I've read in the past about naked lead round balls or bullets "stripping" the rifling and leading the bore at higher lead bullet velocities. If that is actually true, it might create the need to use a slightly harder bullet alloy, a different bullet lube, or even paper patching. But it isn't likely that a very old 8 bore Pinfire is going to be pushed to any magnum velocities. BTW, this is a cool gun in amazing condition. It will be interesting to see results of actual shooting.