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Bullet Setback Effect on Velocity, etc.

2295 Views 4 Replies 3 Participants Last post by  zeke
With some lower cost ammo the bullets are not crimped tightly in the cartridge case. During firing the recoil impulses could (and do) cause such ammo to result in bullet setback into the case.
Do you know of any data showing how much setback would be a concern? Or what is your opinion on setback?
Will setback cause a velocity increase enough to be a concern, since this means higher chamber pressure as well.
Or do you think chamber pressure and velocity are mainly controlled by the powder loading and setback shouldn't be a concern.

After all, in a muzzle loader the bullet is rammed tightly against the powder to achieve maximum velocity. So why aren't regular cartidges made with the case full of powder so no setback can occur?

I don't have a chronograph so I lack any data to contribute. But I do see setback with some lower cost stuff like what comes in ValuPacs.

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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.

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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.
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I've noticed it alot with my dept's guys ammo, when they reload the same round in the pipe over & over.

I suggest to them to rotate the round they use to load with after a few times.

I've seen this happen with all types & quality ammo.
When first started loading the 45 acp , and was trying for max velocity 185 jhp loads, noticed 2 rounds recording much too high a velocity (thankfully was using a chrono). Traced the problem to bullet setback. Not as much a problem with light loads. Since then, load up a dummy round of new combinations of brass and bullets to be tried. Just the bullet and brass, no powder or primer.
Insert the dummy round in mag, lock back slide then release and recheck the COL. Even most factory loads exibit some setback, some significantly worse than others. Have started to appreciate the differences in brass quality (manufacturer, times fired etc), Lee undersize dies, Lee FC, turned down expander plugs and heavier bullets when nessary.
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