A bit more on vintage spread-shot cartridges

[ccdjg]

As a follow-on from the previous thread, John Atkins kindly sent me some vintage Spanish spread-shot airgun cartridges to check out. These dated to the 1970’s and were originally in the Joe Gilbart airgun pellet collection. Not much is known about them, other than that they are .177 calibre, were purchased in 1970 in Spain, and were called “Cartuchos M.G. Neumaticos” (M.G. air cartridges).




The cartridges consist of a short clear plastic tube containing about 8-10 small lead shot, with a 1mm air inlet hole at the base and completely sealed at the other end with what appears to be wax or shellac.




As they have no flange at the base the cartridge was obviously intended to leave the barrel when fired, and presumably the idea was that compressed air entering the hole in the base would propel the shot out of the cartridge, leaving the slower moving casing behind. This would also require the shot to have enough energy to pierce the seal.

When I looked at these, I must admit I was a bit sceptical. Firstly the air inlet hole seemed very small to do the job, and secondly the seal seemed to be too strong to be easily broken. I decided to put these to the test using my .177 Millita air rifle. This had reasonable power, and I also thought that the fact that it was rifled might help, as the rifling could slow down the movement of the plastic casing and help the shot accelerate ahead.

My misgivings proved correct, as every cartridge I tried failed to separate the lead shot from the casing, and the complete cartridge hit the target and made a single large entry hole. When the fired cartridges were located and inspected, they either still contained all their shot and had an unbroken seal, or more usually showed the seal broken but still retaining some of the shot. I reckon that the shot only left the casing at the moment the cartridge struck the target, and it was the momentum of the lead shot that helped to pierce the seal. These are typical targets:



So as they stand, the shot cartridges are pretty useless!

I next thought I would try modifying them, to see if I could get them to work as they were intended to, and the first thing I looked at was the effect of the size of the air inlet hole, which had always seemed too small to me. The hole was enlarged from 1mm to 2 mm (any larger would have let the shot fall out). However, this had very little effect, and after a number of attempts only one test shot showed signs of the shot leaving the casing before impact when just three pellets penetrated the target, with the main casing making its own large penetration hole. All the other attempts showed only the single intact cartridge hole on the target.


The other variable to consider was the strength of the seal, as if this is too strong the shot would be unable to pierce it. It did seem very tough to me, and it took some scraping to remove it. I prepared a few shot cartridges with the air transport hole enlarged to 2mm, and with the seal removed. A very loose plug of tissue was inserted in place of the seal to stop the lead shot falling out. However even these doubly ‘improved’ cartridges failed to work, and none of those tested showed any sign of the shot separating from the casing before the cartridge hit the target.

So how these cartridges were ever expected to work I do not know. Perhaps they worked with high power FAC rated air guns?

In conclusion, of all the methods for producing a spread shot effect from a moderately powerful air rifle that I have tested, the chalk-imbedded cartridge is the most reliable and convenient.

This is the original 1894 patent from Lanes Brothers:

[Garvin]

Maybe when those Spanish cartridges were newer the plastic -- now yellowed/hardened/shrunken (?) -- was fresh and supple which meant (a) that the shot could move past it more easily and (b) that it wedged in the rifling, holding back the cartridge body?

Just a thought.

[ccdjg]

Like you Danny, I wondered if the fact that these were 50 years old might have been a factor in their abysmal performance.

The hardening of the seals over time no doubt has happened, as the seals are brown and very tough and brittle. However, the fact that the cartridges still did not work when the seal was removed discounts this as a contributing factor.

The lack of tightness of the cartridge in the barrel might be the main culprit, if the plastic had shrunk over time. Although the cartridges were a good tight fit in the barrel of my gun, I had a look at making them even tighter. I expanded the base of a couple with heat (they seem to be made of polythene or polypropylene so could be shaped with a bit of heat) but this still did not result in the lead shot leaving the cartridge case. Finally I deliberately splayed out the base of a couple of them, as here:



I enlarged the air entry hole to 2mm, and then broke up the seal so that the shot faced very little resistance to leaving the casing. The results with these were much better. The casing did leave the barrel but did not reach the target (range 16 ft), whereas all the lead shot hit the target with reasonable force. However the spread was very wide.

So it seems that these cartridges can be made to work if they are sufficiently tight in the barrel. However, it is difficult to see how this tightness could have been achieved with them in their original form.

[grahamrob]

Good effort, thanks for sharing.

[Jerry Cornelius]

Well, at least they look cool, even if they are useless

Tbh that’s a 50% improvement on me most days !