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357 Mag PRIMER Question

3111 Views 19 Replies 11 Participants Last post by  zoar
Which primers should I get for loading 357 Magnum?

There are ----

Winchester #7's
CCI #300
CCI Magnum #350
Federal 150
Federal Magnum 155?

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Sounds like you got a bad batch or one stored in direct sun or near other heat source. When a round fires the primer cup acts like a little piston, pushing itself out of the primer pocket and the brass forward until the headspace determinant stops it. It is reseated when pressure from the powder pushes the head back against the breech, but that primer piston push back starts even before the firing pin retracts, so it flows the cup over the pin by the added amount of any extra headspace in the gun. That's why the fired ones are always marked a little deeper than a struck primer that didn't ignite.

Since your other brands all work, I doubt you are having the most common problem that causes this, which is the primer not seated all the way in. More likely its the result of bad storage or a defect. I'd call Winchester about it. They might be willing to test and replace. They are not hard primers and my Goldcup ran through a case of 5,000 one year when I couldn't get my usual Federals. It did so with no faults, and that gun's strike is lighter than my Redhawk's. Winchester made some primer changes since then (did for small rifle, anyway), but toward the more sensitive side, not less so.


I would stick with magnum primers for 296/H110 as recommended above. This is for a safety reason. That powder is normally run on the ragged edge of its ability to sustain burning, which is why they warn you not to drop the published loads by more than 3%. In a revolver, when the bullet base jumps the barrel/cylinder gap some gas vents, and the pressure drops a little. This is known to extinguish light loads of that powder and leave a bullet stuck in the barrel waiting for the next round to fire properly and blow the gun up. If you don't use both a magnum primer and a heavy crimp with that powder, you increase the likelihood of that happening. It will be made worse as temperature goes down.

Other powders can also behave that way, according to Hodgdon's tech, but none of the other pistol powders I've run into do it. I've also not heard of it happening with H110/296 in guns other than revolvers, but why take the chance?
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. . .Winchester SMALL PISTOL PRIMER with H110... And others on that thread said Small Pistol was the way to go.

I'm not trying to start a disagreement here at all. But I am getting very different advice on primer size under 110 and 296. . .
Two things are specific to Marshall's experience that affect the primer choice. First, I'll repeat what I said in my last post: AFAIK, the squib-out issue with H110/296 is just observed in revolvers and is due to the barrel/cylinder gap. Marshall was not using a revolver or any other chamber that bleeds a portion of the pressure off during pressure build.

Second, note that Marshall was using a heavier-than-standard weight bullet. Most often such a bullet is longer and seats deeper into the case than a standard weight bullet (say, a 110, 125, or 158 grain bullet for .357). Plus, the greater bullet mass offers more of Newton's equal and opposite reaction force for the powder to build pressure against. In effect, it is better confinement of the burning charge. The purpose of a magnum primer is to increase the start pressure inside the case at firing. That smaller powder space lessens the amount of primer gas needed to achieve adequate start pressure and the better confinement lets the initial pressure build faster.

Too much primer pressure can unseat a bullet, especially a lubricated lead bullet, part way, and that can make for erratic performance. That is why pistol primers have less priming compound that their rifle counterparts; they fire into smaller case capacities. So you do need to check what a specific primer does to your load's consistency.

A good primer on primers is this article.

This interesting set of images
indicates just how little standardization there is in primer performance among different brands. It is why changing brands can make a bigger difference in performance than just switching between standard and magnum primers within one brand.
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