Bullet Setback Effect on Velocity, etc.

Hello, oldgrandpa. I think that the pressure range the cartridge is in plays a strong part in how much setback can affect it being dangerous or not. In other words I suspect that high-pressure, low-case-capacity cartridges such as 9 x 19mm, .40 S&W, and maybe .357 SIG could be more prone to problems than lower pressure rounds such as the .45 ACP. Much would have to do with the particular gun's chamber support, ie: a fully supported chamber would probably tolerate more setback (if approaching case bursting pressures) than a less fully supported one.

I guess that one could get the actual case capacity volumn present when a bullet is seated normally and then measure how much is lost when setback occurs and determine the increase in pressure using the SAAMI figures for standard or +P in a given caliber assuming that you don't have pressure measuring equipment; I know that I don't.

It is my understanding that the .40 S&W, being a modern round that began life loaded to near max pressures/velocities with modern powders, is reported to have blown a few magazines out of pistols when cases gave way to excessive pressures attributed to setback. How much of this is true I cannot say.

Speaking only for myself, I would be concerned with it more in high-pressure rounds than in lower pressure rounds and wouldn't use any high-end +P ammo exhibiting setback or anything in .40 showing signs of it...a round or two of ammo is much cheaper than my only set of eyes or an injured hand.

Best.

Set back is likely caused by it hitting the feed ramp not by recoil pretty good discussion here previously. Unlike most rifle rounds handgun brass size generally has little to do with volume needed. For example .357 magnum brass is longer so it wont fit in a chamber made for a .38 not because more space is needed. But you are on to something. I have found that generally the fuller you can get the case the more consistent the round. You can figure that be finding out how many grains (weight) per cc (Volume) various powders of apropriate burn rate are. I would assume manufacturers could develop a powder that would do like you said but that would involve a different powder for each round and bullet weight. Not a very cost effective way of making ammo. I am sure they do what most reloaders end up doing and selecting a powder while ideal for none is suitable for a wide variety of the calibers they load.