The RIO .410s and Number Twelve Shot.

By Marshall Williams

I recently obtained some Spanish-made RIO shotshells loaded with #12 shot, a size with which I have no experience.  Shot sizes smaller than number 9s are all but unknown to American shooters, but standard U. S. sizes actually go down to a number 12.  

The American scheme of shot sizing comes from the one used at the beginning of the 20th. Century by Tatham Brothers of New York. This is one of many sizing systems in use over the years.   W. W. Greener’s book, “The Gun and Its Development,” lists not less than 17 different sizing systems in use in the late 19th. Century.

The American sizing system is eccentric but simple. A fine shot’s diameter in inches is found by subtracting the shot size number, 6, 7 ˝, 8, etc. from the number 17.  The result number is the pellet’s diameter in hundredths of an inch.  Under this system, to determine the diameter of a number seven, we subtract 7 from 17 and get 10. (17 - 7 = 10)  A number six shot is .10 inch in diameter.

While the diameter of shot forms an orderly procession, 6, 7 ˝, 8, etc., the number of shot in an ounce is not so simple.  An ounce of 7 1/2s contains 345 pellets, an ounce of 8s contains 410, and an ounce of 9s contains 585.  The number of shot in an ounce increases at a disproportionate rate.

To place this matter in a clay target shooter’s perspective, common shot sizes have the diameters and number per ounce as follows:



number in an ounce

7 1/2s

.095 inches 



.09 inches


8 1/2s















 No shot smaller than 9s has been loaded in American shotgun shells since before World War One.  The only smaller size used significantly is #12 which is used in the little .22 rimfire “rat shot” cartridge which contains about 1/15 ounce of shot, or about 150 of the tiny pellets.  The small cartridge is intended for killing rats and mice at very short ranges, perhaps up to 15 feet.

The RIO .410s loaded with ˝ ounce/14 grams of #12s provided me a rare opportunity to see whether these tiny shot have any use in clay target shooting.  Clearly patterns will be very dense and theoretically should spread more, so why isn’t smaller shot used for clay targets?

The simple answer to this question is easy.  Most clay targets, for instance American Skeet, allows only shot sizes as small as 9s/2mm.  But that does not answer the question of whether smaller shot would have any advantages?

To find out, I obtained a few boxes of both 12 gauge and .410 bore RIO brand shells loaded with number 12 shot.  The 12 gauge load was a 3-1-12, and the .410 load was a MAX-1/2-12.  I have shot RIO shells extensively in recent years and find them to be a quality product.

My first experiment with the .410 was to shoot selected Skeet targets. I chose stations five through eight. Results were satisfactory until I got station 7.  I got a perfectly normal break on the high house, the incomer, at about 15 to 18 yards, but then I missed the easiest shot in Skeet, the low house.  This is a straightaway and broken at perhaps 17-18 yards.  I missed it again on doubles!  Then, to make sure it was not simply poor shooting, I missed four more.  Six misses on the easiest shot in the game?  Oh, dear.

I then also shot a round using the 12 gauge RIO shells.  My breaks were satisfactory except at station four, the longest shot and longest lead in Skeet, but still taken at about 21 yards. At station four my leas on the high house looked right, but my shot knocked off only the tiniest chip.  I then I shot a low house with exactly the same result, the shot looked perfect but only produced a tiny chip. The rest of the round was satisfactory, and I got normal breaks on both station 7 low house targets.

Further investigations seemed to be in order.  First I shot patterns at 20 yards, or half the usual distance, but compatible with Skeet.  I shot the .410 shells in a Beretta 687 EL Gold Pigeon with a Skeet choke tube giving only .002 inches of constriction, and for comparison patterned both the RIO 12s and some Federal brand shells loaded with 7 1/2s..  I repeated the process in 12 gauge with cylinder choke using RIOs with one ounce of 12s and, for comparison, a Remington trap load with 1 1/8 ounces of 7 ˝s.  trap load.  Both comparisons showed a huge difference in density.

20 yard patterns, .410 with Skeet choke tube, 1/2 oz. of American 7 1/2s on left,
1/2 oz. of Spanish 12s (American 11s) on right.  My Beretta 687 EL Gold in between.

I also chronographed the speed of each shot.  My chronograph is not designed for  shotgun shells; it is intended for individual rifle and pistol bullets, so it shows you only the velocity of the first pellet in the cloud of shot.  Nevertheless, the shot is very close together at short ranges, so while the results are not as precise as with single bullets, they show anything seriously wrong.  Velocities were what I expected. The RIO .410 load gave a velocity consistent with the expected 1200 fps muzzle velocity.  The 12 gauge load was noticeably faster, around 1350 fps, a little faster than I expected for a three dram - one ounce load.

The number 12s patterned both denser and wider than the control patterns with 7 1/2s.  The huge advantage in numbers accounts for the density and it is widely accepted that smaller shot spreads faster and gives wider patterns than larger shot.

I also shot stationary clay target using both .410 and 12 gauges shells loaded with 12s at 21 yards, the ordinary Skeet distance. I used a twig to prop up the targets with the blaze orange side facing me. Even though the .410 load hit the target with about 15 pellets, it only knocked off chips; it did not break the clay target.  The 12 hit the target with more pellets at a higher velocity and the target broke but did not crumble as one would expect a similar load of 9s to do.

Disassembling a .410 shells, I found the shot charge to weigh 210 grains quite close to a half ounce or 218.5 grains. I did not do this with a 12 gauge shell.

I measured a number of the tiny small pellets using a dial caliper accurate to 1/1000 of an inch.  This is quite difficult as fingers are too big to hold the pellet to measure it, and the effort is tedious.  Nevertheless, I measured a number of pellets to my satisfaction and found diameters as small as .005 inches and as large as .007 inches, but the majority measured around .062 inches. These are slightly larger than American 11s, not 12s.

Manufacturing tolerances in the best of shot permits some variation, usually from half a size large to half a size small.  Smaller the shot sizes make such differences appear significantly greater, but the variations I note were within my expectations.

I weighed a small number of pellets, 32, and found that they weighed 11.5 grains. From this information. I calculated that the pellets average around 1220 to the ounce.  This number is consistent with the average diameter I got, although I weighed different pellets from those I had measured with the calipers. As noted above, American 11s should run about 1342 pellets to the ounce.

One and a half rounds of casual Skeet, four patterns, two damaged targets, and one dissected shell are not conclusive evidence, but the results are suggestive.

For instance, why are RIO’s 12s comparable in size to American 11s? As noted above, there are many systems of sizing shot, and in two common European systems the number 12 is assigned to shot that run ca. 1250 to the ounce.  

Why did I miss six station 7 low house targets with the .410 but break the high house targets at the same distance? Several factors figure into this.  First, the target flies straight away from the shooter at a speed near 50 fps and this speed is subtracted from the shot velocity in order to determine impact energy. The high house is an incomer and approaches the shooter at 50 fps.  This velocity must be added to the shot velocity and increases impact energy.  That 100 fps second difference in average velocity should explain why high houses break and low houses do not when shot at nearly the same distance.  

Why did the 12 gauge shells break the station seven low house targets?  The 12 gauge shells gave a velocity that was 150 fps faster and it had twice as many pellets as the .410 load.  Therefore it hit the target more than twice the target breaking energy of the .410.

This result is reenforced by shooting the stationary clay targets at 21 yards.  The .410 merely chipped the target; the 12 gauge broke it, but did not smash it.  The .410 load has half as many pellets and a slightly lower velocity than the 12 gauge pellets, so it simply runs out of target breaking energy sooner than the 12 gauge load.  Station 7 tells me that distance is about 17-18 yards for the .410.  

Nevertheless, it appears that even the 12 gauge 12s are rapidly running out of target breaking energy at that range. The 12 gauge results on station support this.  Station 4 is the only Skeet station where the targets are never closer than 21 yards, but I usually break Skeet targets a little nearer than that on the other stations.  I got gave satisfactory breaks at the other stations, but only chipped my station four targets.  Combined with the weak break on the stationary target at 21 yards, my guess is that even the 12 gauge load of Spanish 12s/American 11s is very near its target breaking limit at 21 yards.

Based on this, these extremely small pellets offer little advantage to clay target shooters.  The smallest shot gives both a wider and denser pattern, but it lacks the energy to break the targets at ordinary shooting distances. On the closest shots, say Skeet station eight, it might help.   

In closing, I would observe that what is required to break clay targets is often different from what is required in game shooting.  The wisdom of the ages says that the smallest shot once was the mainstay of naturalists and taxidermists who wanted to kill small birds and animals with minimal damage.  The effects may be much different on animals.