Rifle Blowup - credit Starline Brass

Secondary Explosion Effect A Reality

Rifle Blowup - credit Starline Brass
Rifle Blowup – credit Starline Brass

Q: What can you tell me about a mysterious phenomenon that affects handloads with reduced charges of slow burning powders, and blows up guns? It doesn’t make any sense to me that less powder can produce more pressure?
Jeff Wilkins

A: Alas, while it may not make sense, it does happen. In fact it may have happened to me once with my .25 WSM, but although the bolt lugs were set back, the rifle held together and I couldn’t prove anything. Nils Kvale of Norma and P.O Ackley both confirmed this “pressure excursion” does happen, but said they were unable to duplicate the phenomenon in their ballistic laboratories. However, in more recent times S.E.E has been reproduced at will in at least one ballistic laboratory. It is the main reason why some ultra-slow burning powders have never been sold in canisters to reloaders. If not used precisely right, there is a very real chance, slim though it may be, for a pressure excursion. There have been several different theories advanced about what happens to cause a pressure excursion, but they’re academic, for now. We know that S.E.E occurs when reduced charges of very slow burning powders are loaded and only in large capacity cartridges that have a relatively small bore size. The danger can exist in any of the magnum cases from .257 up through about .300 and in many non-magnum cases of the sort usually described as being “over bore” capacity. Theoretically, it could happen just as easily with a .25-06 case that has too much air space behind the bullet. Case shape may play a role, but this has not been confirmed. The best way to avoid S.E.E is to strictly avoid loading reduced charges of slow burning powders that are 10 percent or more below the recommended maximums in any small bore cartridge which has a large case.




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Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.


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