Primer Substitutions

By Mitchel Demand

I do not need to tell any of you about the shortages we have in ammunition and reloading supplies. We can all see it every time we walk into a sporting goods store or gun shop. Because primers are so hard to find we have been getting quite a few questions about substituting primers in the loading process. Here is a chart of primer dimensions just to get us started. This chart came right off the SAMMI website.

Let us start with Large Rifle Primers (LRP) vs Large Pistol Primers (LPP). Both are roughly the same diameter. This is where the similarity ends. The LRP is at least .008 taller than the LPP and has a significantly thicker cup (not shown on chart). This means a LRP will not seat flush or below the face of the case head in a pistol cartridge, thus creating a dangerous situation; However, the LPP will fit and seat in a LRP primer pocket, but it will seat too deep. Just because it fits does not mean it will work. The thinner cup of the LPP can be pierced by the firing pin of a rifle and harm the gun and its user. Also due to the slower burning powders in a rifle ammunition the charge from the LPP is insufficient for reliable use. In summary, do not substitute LPP for LRP at all, period.

Here is where math and physics can get you hurt. Small Pistol Primers (SPP) and Small Rifle Primers (SRP) are virtually identical in size as are the primer pockets of their respective cases. This does not mean that they can be substituted for each other. The SRP still has a much thicker cup and hotter ignition. There is no verifiable data for the difference in fire rate between the primers. Ask any of the primer manufacturers and they will not tell you. Been there done that. Here again a SPP should never be substituted for an SRP. I do realize there are times that one can use a SRP in place of a Small Pistol Magnum Primer. My issue with this, where is the data? How do we know it is safe? People say they have done it with no issues and good for them. In a revolver I can see giving it a try if one can find verifiable data. I certainly would not risk it with an unsupported chamber in a semi-auto pistol.

To sum it all up, do not substitute SPP for SRP or LPP for LRP at all, period. It is possible to substitute LRP for Small Pistol Magnum Primers in certain situations if the certified loading data supports it.

Have fun and stay safe
Mitchell