Rifled Shotshells

[303Guy]

Is anybody using these? I am thinking of making a set of rifled cases for my 410 and casting slugs and glue wads for it.

[Retumbo]

I have no idea what you are talking about.

[centershot]

Rifled Shotshells ???

[Hogtamer]

If you mean brass cases there have been so e threads here about that and 000 buck I believe.

[303Guy]

Yes, rifled brass cases. I know it has been done in the past. I'll do a search for past threads, thanks.

[longbow]

Sorry but you won't convince me that a "rifled" cartridge will spin a slug effectively if it is bore size.

Any spin imparted as the slug left the "rifled" cartridge would be lost to bore friction.

Now if you are talking a rifled insert like 20 ga. in a 12 ga. barrel I'm with you. I made a short 9mm insert for my 12 ga. and that works well but any diameter smaller than the original bore would work because the slug/boolit would be spun by rifling just like in a handgun or rifle then carry on without touching the rest of the shotgun bore.

Or am I not understanding what you are asking/proposing?

[303Guy]

You understand me correctly, longbow.

I have my doubts too, having wondered about the spin being lost to bore friction but then consider that if the slug enters the bore spinning, the bore friction would be in the direction of the spin, that is, in a forward spiral. So I hypothesize that once spinning, the slug will stay spinning. Of course, there is only one way to find out. And I need an excuse to rifle something. I also need to make cases for the gun anyway.

Another consideration is that once the slug has rifling impressed in it, the impressions might just assist in maintaining the spin. Or not.

The idea of the rifled case is not new. It has been done before but I have no idea of the effectiveness.

My plan is to use a slug configuration that would work in a smooth bore with the added benefit of spin. Much like an air gun pellet fired in a smooth bore. Add spin and it becomes more accurate. I started out life with a smooth bore airgun and I know for a fact that the pellets did not travel in a straight line but they did follow a path around the line of sight. I could sometimes see the pellet travelling in a wobbly path! It's amazing how those pellets would still hit a distant target!

Just another point in favor of it working - the case will be quite long so the slug should be almost up to speed by the time it exits the case so it would be spinning quite fast. Remember that the chamber is some 3.25 inches long before the taper. So the slug would have some 2 inches of travel in the case itself. Or at least, that's the thinking.

[longbow]

I've got to ask why not go with a rifled choke tube. That will ensure the slug is spinning as it leaves the muzzle. Mind you, in my opinion anyway, modern rifled choke tubes are not made correctly with their shallow fast twist rifling. I think they should mimic the Paradox guns in that they should compress the slug and I also believe they should have deep slow twist rifling... at least for round balls and full bore slugs. Sabot slugs are a different story.

I think you will find that unless the slug is smaller than bore size it will not maintain spin due to bore friction. If it was say a thou or two under bore diameter and didn't obturate then maybe.

I recall Ross Seyfreid writing about his Paradox gun and all the troubles he had getting it to shoot until he purchased an antique regulator (sizer) that swaged the slug to about 1 thou under bore diameter so it was a slip fit. That did it. He said recoil was reduced noticeably and that accuracy suddenly improved to what H&H claimed for Paradox guns. Those solid slugs were supposed to be slip fit, then the rifling at the muzzle swaged them down considerably as it spun them.

But I digress.

With the idea of a rifled cartridge you would certainly get the slug spinning as it left the cartridge but to maintain the spin I believe you will need a clearance fit to bore. Then there is the wad that is pushing the slug which will have friction between wad and slug base.

Again, something that will work for sure is a sub bore chamber insert so maybe 16 or 20 ga. rifled insert in a 12 ga. barrel. It only needs to have 6" or so long rifled section to be quite effective though longer would be better.

Whichever way you go I'll be interested in your results.

Longbow

[303Guy]

I'll try that slip fit.

[victorfox]

not wanting to rain on your parade, search "b b pelletier Tom Gaylord smoothbore airgun pellet". due to the shape of the airgun pellets available today, most of them shoot quite well from a smoothbore, like an old Diana... Closest thing I can remember is the Lyman 525 pellet slug.

[JBinMN]

Maybe this website might provide some help/inspiration?
http://www.gunadapters.com/rifled-adapters/

G'Luck!

[BAGTIC]

not wanting to rain on your parade, search "b b pelletier Tom Gaylord smoothbore airgun pellet". due to the shape of the airgun pellets available today, most of them shoot quite well from a smoothbore, like an old Diana... Closest thing I can remember is the Lyman 525 pellet slug.

I read this article and I believe the author confuses the gyroscopic stability imposed by spin with the directional stability created by low rates of spin in drag stabilized projectiles. Arrows, darts, armor piercing fin stabilized projectiles all depend on low rates of spin to prevent the projectile from veering off the original line of flight. This has nothing to do with gyroscopic stability. No projectile is perfectly contoured of balanced and will left to its own veer to one side or another. The longer it is in flight the more the deviation accumulates. Example, if it deviates to the right it will continue to deviate to the right throughout its flight with the resultant displacement being cumulative. If a slow rate of roll is imposed the initial right hand drift will sequentially be imposed in a downward, then sinistral, then upward direction. This limits the amount of drift in any single direction thereby cancelling out some of the effect. The purpose of gyroscopic stability is the attempt to prevent the projectile from yawing in the first place. The purpose of spin in a drag stabilized projectile is to cancel out the yawing tendencies of the projectile as they occur.

[Cap'n Morgan]

The purpose of spin in a drag stabilized projectile is to cancel out the yawing tendencies of the projectile as they occur.

I always expected that much. Why would Wilhelm Brenneke go through the trouble of adding helical ribs to his slug if it didn't add any advantage? My own slug experiments pretty much confirms the increased accuracy at longer distances (beyond 50 yards) of a helical design.

According to the FBI:
https://www.ncjrs.gov/pdffiles1/Digi...32229NCJRS.pdf

"The slight rotation imparted by the ribs reduces the effect of manufacturing irregularities. In tests performed by Winchester-Western, the slug rotation was confirmed, resulting in consistently smaller groups for rifled slugs than unrifled slugs…"

One of these days I'll run a test to get an idea of the number of revs pr second the slugs go through at the 50 yard mark - a couple of cardboard targets with a known distance between, and some sort of soft marking on the slug to leave an imprint on the targets. Then it's just a matter of measuring the angular difference between the two impacts and do the math. Any of you guys have a lipstick I can borrow?

[longbow]

Cap'n Morgan:

This is so far the best video I have found of riled slugs in slomo:

https://www.youtube.com/watch?v=jRPo19DWlZY

and based on this I stand corrected. I have been maintaining that the rifling would have little to no effect but the slugs do pick up some rotation. Certainly not enough to impart gyroscopic stability but as BAGTIC points out above a slow rotation while not imparting any gyroscopic stability does help keep the projectile "on track".

Wilhelm Brenneke may have sorted that out himself before the slomo camera was even a thought. And of course your own testing has confirmed superior accuracy with helical ribs.

So, again, I stand corrected. I have to say that I would not have believed it if I hadn't seen it. The rotation is slow but it is certainly there.

Longbow

[Cap'n Morgan]

Interesting video. Thanks. I would've loved to see them test it at a longer range to see if the rotation increases (air induced rotation) or remain the same (barrel induced rotation). Since I don't have a 8000 fps camera I'm still looking for some sort of grease pencil to mark my slugs with.

From what I read the rotation of foster slugs could be anywhere between one turn in 24 feet to more than 100 feet depending on the choke - not much, but still enough for 3 to 12 full revolutions at a 100 yards. I do believe the Brenneke rotation is partly air-induced as the nose design, unlike the Foster slug, has a small shoulder which makes the fins more protruded. If my hair-brained idea works it should be possible to measure the rotation at different distances.

[Ballistics in Scotland]

Aha, I found them! Those early cartridges were probably Courtier's, from General Journée's "Tir des fusils de chasse".



The bullet, resembling a Minié ball, was pregrooved to fit three ridges in the brass case, on a sort of internal sleeve. I don't see why they couldn't simply be pressed into the case from the outside, for cannelures don't get completely squashed out at such pressures, and they wouldn't get squashed until the bullet has passed on to expose them.

The twist looks considerably greater than would be required in a rifle with such a bullet, so maybe the spin was reduced by bore friction. General Journée says, as some have suggested here, that the rotation was conserved if the bullet wasn't of an excessive calibre which causes undue forcement in the bore. But with the hollow base I don't think it could have remained a smooth sliding fit.

There are snags, apart from the likely cost. He says the accuracy reduced as velocity increased, and he obtained the best accuracy at 50 metres with only 160 metres per second, i.e. about 500ft./sec. The figures in his table mean an average deviation of 6.6cm. at 100 yards and a total group size of 30cm. But a velocity of 287m./sec. increased the average deviation to 14cm. With over 200m./sec. the cases stuck firmly in the chamber, and had to be removed with a cleaning rod or cartridge extractor. Compared with the best smoothbore cases, you don't get much for all that complexity.

As to bore friction, the bullet accelerates in the bore, and there can be only one point, if any, at which the rifling engraving is in line with the lead-to-steel movement. But I don't think that, with the right diameter, would matter too much. Bullets experience a great deal of air friction in their flight, and rotational velocity declines more slowly than forward motion. At 1000 yards the bullet has elbowed aside several times its weight in air, and sand scratches on its surface show that it is actually spinning in a tighter helix than it did at the muzzle. With that fast twist in the Courtier case, I think it would have plenty of spin left.

Arrows were indeed given a twisting flight by the feather fletchings. They might be helically glued on, but I think feathers from the same wing of the bird, probably the wing they didn't sell for quill pens that wouldn't poke the writer in the eye, would be enough. This probably inspired the first rifling in wheel-lock firearms. But no arrow was gyroscopically stabilised, or strictly with speaking stabilised at all.

There are more modern tools for judging the rifling twist a bullet requires, but we don't go far wrong with Greenhill's formula, that bullet diameter multiplied by length, woboth expressed in calibres, should equal 150 or less, but 200 will sometimes work. A 1.2 in. long .30 diameter bullet should have a 37½ calibre, or 11.25in. twist. It will give a 3000ft./sec. bullet a rotation of about 186,000rpm., and some faster-rotating bullets can disintegrate in the air through centrifugal force. An arrow 100 calibres in length would require a 1.5 to 2 calibre twist, impossible to impart by feathers, but which would produce guaranteed disintegration if we did.

What spinning an arrow did was to take the deflection caused by irregularities of construction and by its complicated little wiggle around the bow, and convert them into a corkscrew path which with luck would never be larger than the vitals of deer or Frenchman. People used rifled firearms successfully for a long, long time before they realised that something different was happening.

Nikita Krushchev asked President Nixon what the fins on a 1950s American car were for, and Nixon didn't think to point out that Krushchev's jacket had lapels. I suspect that Brenneke's ribs worked on a similar principle. It has been known for a long time that they didn't impart gyroscopic stability, but it certainly seems possible that as with the arrow, they distribute the deflection caused by irregularities of construction. Against that, though, is that a smooth slug, made by modern extrusion or die-casting, might be less likely to have any.