What Is Radial Standard Deviation and How Does ELEY Use It to Grade Ammunition?
Radial Standard Deviation (RSD) measures the distance from each shot hole to the group’s centre point, the mean point of impact. The lower the RSD, the closer the group and the more consistent the performance. ELEY uses it as the grading standard for its ammunition: 200 rounds are fired from every batch across four different firearm brands, RSD is calculated from that proof group, and the published maximum RSD for each product is a standard every batch has already met.
It is a more demanding measure than the one most shooters quote, and that is exactly why ELEY uses it.
RSD Versus Extreme Spread
Extreme spread, the edge-to-edge measurement across a group, considers only the two furthest shots. Every other shot is thrown away.
RSD evaluates every shot fired.
The difference is not academic. Consider two 200-shot groups with an identical extreme spread. In the first, the shots are packed tightly around the centre with two outliers at the edges. In the second, the shots are spread evenly right out to the same edges. Extreme spread reports them as equal. RSD does not, because it accounts for where all 200 shots actually landed.
That makes RSD far harder to flatter with a lucky target and far harder to spoil with a single bad shot. For a manufacturer grading production lots, it is the only measure that answers the real question: how consistently does this batch place shots around its centre?
ELEY still uses group size where statistical precision is not required, and marks those figures accordingly.
The Published RSD Standard for the ELEY Range
| Product | Profile | Maximum RSD |
|---|---|---|
| ELEY tenex | Flat nose | 3.75 mm |
| ELEY ultra extreme long range | Round nose | 4.00 mm |
| ELEY tenex pistol | Round nose | 4.40 mm |
| ELEY tenex biathlon | Flat nose | 4.50 mm |
| ELEY match | Flat nose | 4.74 mm |
| ELEY semi-auto benchrest precision | Round nose | 4.90 mm |
| ELEY team | Flat nose | 5.50 mm |
| ELEY club | Round nose | 5.50 mm |
| ELEY biathlon club | Round nose | 5.50 mm |
| ELEY sport / target | Round nose | 7.00 mm |
| ELEY force | Round nose | 7.00 mm |
| ELEY contact | Round nose | 7.00 mm |
| ELEY semi-auto benchrest outlaw | Round nose | 7.00 mm |
| ELEY bullseye pistol x | Round nose | 7.00 mm |
Three products in the range are specified on group size rather than RSD, because statistical precision is not the governing requirement for their intended use:
| Product | Accuracy specification |
|---|---|
| ELEY tenex rapid fire pistol | 27 mm group* |
| ELEY high velocity hollow | 30 mm group* |
| ELEY subsonic hollow | 43 mm group* |
*Group size is used when statistical precision is not required.
How Grading Follows Testing
The sequence matters, and it runs in this order: manufacture, then test, then grade.
Cartridges are produced under the same controls: the patented flat-nose profile on the premium flat-nose family, case mouths trimmed flat, exacting crimping standards, propellant measured electronically for each individual cartridge, priming in ELEY’s air-conditioned facility, temperature-controlled lubrication, Six Sigma methodology and high-speed electronic visual inspection.
Then every batch is proof tested: 200 rounds across four different firearm brands, and RSD calculated from the result. Testing across four brands rather than one prevents a batch being validated by a single flattering barrel.
The published maximum RSD for a product is therefore not a target or an aspiration. It is a threshold the batch in your hand has already demonstrated it meets. When you buy ELEY tenex, you are buying a batch that has been measured at 3.75 mm RSD or better across four firearms.
What RSD Means for Your Buying Decision
RSD ranks products. It does not rank batches within a product against your barrel.
Every barrel has its own unique dimensions and harmonic characteristics, and each batch of ammunition performs slightly differently. What performs flawlessly in one barrel may not deliver the same results in another. Two batches of tenex that both meet the 3.75 mm standard can still perform differently through your rifle. That is why ELEY publishes the proof data for every batch rather than only the grade.
You can see that data yourself. The free Lot Analyser at eleyxshot.com opens the full 200-shot proof group for all lots of ELEY tenex, tenex pistol, tenex biathlon, tenex rapid fire pistol, match, semi-auto .22LR benchrest precision, ultra and club, including X windage and Y elevation coordinates for every shot and the radial dispersion across four barrel types.
And you can measure the combination directly. At an ELEY test range, RSD is one of the figures reported back to you for each batch tested through your own barrel, alongside the 40-shot group size, the consolidating score out of a maximum 436 on an ISSF target at 50 m, an Expected Score and a percentile ranking against every batch and barrel combination in ELEY’s database.
The Bottom Line
Radial Standard Deviation is the average distance of every shot from the group’s mean point of impact, and it is a stricter, more honest measure than extreme spread because it counts every shot rather than only the two worst. ELEY grades its entire range on it, verified by 200 proof rounds from every batch across four firearm brands.
Use the published RSD figures to choose the right product for your discipline, then use eleyxshot.com and batch testing at eley.co.uk/vip to find the individual lot that performs best in your barrel.