9mm, Bullet Setback, Pressure

CBA Member

lotech posted this 12 October 2025

What is bullet setback? Is that when the bullet moves under recoil?

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CBA Member

Aaron posted this 12 October 2025

You may wish to rephrase the question.

With rifle in hand, I confidently go forth into the darkness.

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CBA Member

Larry Gibson posted this 13 October 2025

I have not yet done a pressure test of various seating depths in the 9mm. Such variation in bullet seated depth can occur when the bullet hits the feed ramp during feeding and is pushed back into the case. However, I have conducted a seating depth pressure variation test in the 357 Magnum cartridge.

I used the TL358-158-SWC over 5 gr of Alliant Green Dot. With a cartridge OAL of 1.632" the psi ran 24,500. I pressure tested with the seating depth variation of .050" to the shortest oal of 1.432". the psi of that oal ran 35,700. Thus we see in the 357 magnum cartridge with that load a variation 11,000 psi from just a .200 change in oal.

How much variation of pressure in the 9mm will, of course, depend on the variation in oal with a given load.

LMG

Concealment is not cover.........

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Aaron posted this 13 October 2025

Larry,

I would argue that any semi-auto bullet getting rammed back into the case upon interfacing with the feed ramp is an improperly loaded cartridge and any such ammunition would play havoc with velocity, standard deviation, and more importantly, chamber pressure. Bullets should NOT be allowed to be rammed back into the case when interfacing with ramps. Correct crimp pressure and in some cases, chemical bonding, prevent this defect.

It may interest all readers to know that years ago, I read of a seating depth study in 'high intensity cartridges' like the 9mm, 10mm, 40SW, 38 Super and others where a .10" change in seating depth in a 9mm cartridge could DOUBLE the chamber pressure due to the fast propellants used in these cartridges. Handloaders are advised to closely follow the listed bullet and O.A.L. suggestions in the loading manuals to prevent pressure excursions.

Additionally, bullets getting rammed back into the case during the feed phase will act as a 'shock absorber' and affect the forward motion and force of the slide in an adverse manner resulting in an out-of-battery slide or worse yet, a complete failure to feed.

Proper taper crimping of these cartridges will prevent bullets being forced into the case during the feed cycle.

With rifle in hand, I confidently go forth into the darkness.

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Standard Member

Keep Trying posted this 13 October 2025

Thanks Larry.

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CBA Member

lotech posted this 13 October 2025

Larry,

I would argue that any semi-auto bullet getting rammed back into the case upon interfacing with the feed ramp is an improperly loaded cartridge and any such ammunition would play havoc with velocity, standard deviation, and more importantly, chamber pressure. Bullets should NOT be allowed to be rammed back into the case when interfacing with ramps. Correct crimp pressure and in some cases, chemical bonding, prevent this defect.

It may interest all readers to know that years ago, I read of a seating depth study in 'high intensity cartridges' like the 9mm, 10mm, 40SW, 38 Super and others where a .10" change in seating depth in a 9mm cartridge could DOUBLE the chamber pressure due to the fast propellants used in these cartridges. Handloaders are advised to closely follow the listed bullet and O.A.L. suggestions in the loading manuals to prevent pressure excursions.

Additionally, bullets getting rammed back into the case during the feed phase will act as a 'shock absorber' and affect the forward motion and force of the slide in an adverse manner resulting in an out-of-battery slide or worse yet, a complete failure to feed.

Proper taper crimping of these cartridges will prevent bullets being forced into the case during the feed cycle.

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CBA Member

lotech posted this 13 October 2025

Good post, but Incredibly basic first grade level handloading procedure. Hard to believe any handloader would not be aware of this.

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CBA Regional Director

MarkinEllensburg posted this 13 October 2025

Aaron,

First, setback occurs in the best commercially produced defensive ammo. After multiple feeds into chamber from a magazine OAL gets shorter. In my daily carry pistol I check OAL after a round has been cycled twice. Short ones are lengthened back using an inertia puller and shot during the next range visit.

Secondly, find and post the source for the "years ago" article claiming double pressure from setback in "high" pressure cartridges. I would believe substantial increases in pressure but double tips my skepticism balance.

Larry's test shows a moderate .357 load to an over max load (per current SAAMI limits) from a .2" change in seating depth. I think we all agree that seating depth does matter and does have an impact on pressure.

@Keep Trying, doing a test such as you want would be interesting but of limited usefulness in my opinion. There is no way to know how much each cartridge shrinks upon normal chambering and I would not be surprised if it is not uniform. There are a number of variables that could effect this. The safest thing to do is first, as Aaron points out is to properly crimp all loads, and secondly only cycle once. Understanding that the second part might not be practical if ne has to clear a pistol between firing.

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CBA Member

Larry Gibson posted this 13 October 2025

Aaron

I'm a bit bewildered as to why that post was addressed to me?

What I addressed was in answer to the OPs question. It may astound you but in my considerable experience with the 9mm and the 45 ACP cartridges od commercial, military and handloaded varieties fired in many different semi auto and full auto firearms. I've seen numerous instances of bullets set back due to hitting and stopping/jamming on feed ramps. I've also seen such bullet setback caused when a fail to extract occurred and the feeding round jammed into the case in the chamber.

Assuming the OPs question was in relation to such cartridges with the bullets slightly set back having higher pressures than normal and, if so, how much. The subject of properly loading 9mm cartridges with appropriate neck tension on the bullet is another matter. Yes, proper neck tension can most often prevent bullet set back as such. However, under some circumstances bullet set back can occur even with the most fastidiously assembled handloads. The OPs question thus remains; is the pressure higher and if so, how much and, I'm assuming, do we want to actually shoot those cartridges?

LMG

Concealment is not cover.........

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Aaron posted this 13 October 2025

Well Larry, you stated that bullet setback occurs when interfacing with the feed ramp. I disagree with your position. That's why it was directed to you. I too have extensive experience in munitions and firearms but an appeal to authority, yours or mine, is a waste of time. Repeated banging of the same round getting chambered 12 times may set a bullet back due to the ignorant use of the same bullet over and over again. But that is not a standard practice when old duffers like us were in military or law enforcement.

Simply put, I disagree with you for the reasons I stated. No big deal. Someone disagrees with your statement. That initiates great debate.

I can't quote the source of that article I mentioned. I read it somewhere decades ago and filed it away in my brain housing group. To call me out because I can't produce the source today is a feeble attempt to negate my statement. I read it years ago probably in a industry slick. I'll bet you can't supply source code for all your positions either. It's in the collective collage of your experience. That's what experience is.

Stick to your guns with collapsing bullets, and I'll stick to my guns with bullets that don't get smashed into the case. I'll bet Remington, Winchester, and all the major ammunition manufacturers will state their bullets will not 'set back' when chambered properly. Your experiences as well as mine, with my extensive experience, shows bullet failure when abnormal conditions are at play. Improperly modified feed ramps with dremel tools, handloads for range practice ammo, and other such 'non-factory' ammo and/or conditions.

Under normal conditions, with unmodified guns, with factory ammo or properly loaded handloads, bullets should not set back when chambered.

You have a good evening Larry. I'm going out to the shed to load up some non-shortening 38 Super ammo! Bowling pins beware!

Be astounded!!

With rifle in hand, I confidently go forth into the darkness.

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CBA Member

Aaron posted this 13 October 2025

Secondly, find and post the source for the "years ago" article claiming double pressure from setback in "high" pressure cartridges. I would believe substantial increases in pressure but double tips my skepticism balance.

Well simply put, I can't. It was probably decades ago too. That does not mean I didn't read it however and it certainly doesn't mean it's not true. BTW, .1" in a 9mm is a heck of a lot of setback. The purpose of the article was bullet seating depth anyway but that can change with setback if allowed. That article on the 9mm loading always made me conscious of my taper crimps on semi-auto cartridges. The reference to higher chamber pressure was for "intense" cartridges like the 9mm, 10mm, 40S&W, and now the 357 SIG and such. Fast powders, short barrels, fast pressure/time curve.

Regardless, believe what you will based on your experience and reading. I try to remember that I don't know it all, nor will I ever. But bullet setback as a normal course of action? No way.

We were taught for duty ammo "ride the ramp one time" then into the 'shoot em later can' if not fired after chambering. For range ammo just chamber away!

With rifle in hand, I confidently go forth into the darkness.

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CBA Member

Larry Gibson posted this 14 October 2025

Aaron

The OP simply asked "Does anyone know of a test of various powders and the effect on pressure in the 9mm Luger during bullet setback?"

Apparently you're not able to answer the question with any degree of certainty.

Perhaps you should consider why you were taught "We were taught for duty ammo "ride the ramp one time"....... before taking my position to task. Seems what you were taught agrees with what I've said can happen.

LMG

Concealment is not cover.........

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Aaron posted this 14 October 2025

There is no test data available since bullets are not supposed to “setback” during feeding. If that were the case, ammunition manufactures could not publish consistent performance data nor meet Milspec standards. Enough of this banter. We can agree to disagree can’t we?

With rifle in hand, I confidently go forth into the darkness.

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Standard Member

Keep Trying posted this 14 October 2025

In the Speer Reloading Manual, Number Ten, page 349 there is a pressure test of 9mm seating depth and pressure.

The powder used is not stated and I wonder how much it matters.

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lotech posted this 14 October 2025

I'll assume that's the same chart Speer published in multiple manuals. According to the chart, it matters a great deal and their explanation is a simple one, easy to understand. How could anyone interpret it differently? The powder used is not the main point. Seating depth is.

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CBA Regional Director

MarkinEllensburg posted this 14 October 2025

Aaron,

I did not say you did not read it but often the case is things read "years ago" are remembered not exactly as the original was written. it is the claim of "double" pressure that would surprise me. Your contention about

ammunition manufactures could not publish consistent performance data nor meet Milspec standards

seems to assume that they are testing feeding from a magazine up a feed ramp. I don't claim to have ever seen a universal receiver but I would doubt they have a feed ramp and are anything other than single loaded.

Found in another thread on a different forum a quote:

Speer #10 - page 349 - paragraph #6

"Loads that produced 28,000 cup went to 62,000 cup when bullets were purposely seated .030" deeper"

Perhaps someone with a copy of Speer #10 can confirm.

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CBA Member

Larry Gibson posted this 14 October 2025

Page 349 in Speer's #10 manual does not show a chart. It states in the explanation of the 9mm Parabellum cartridge before the data;

"There is considerable variation in case mouth thickness between brands and lots of cases. All must be sized to hold bullets very tightly and the expander ball should not exceed .354" in diameter. Because this case headspaces on the case mouth, very little crimp can be used. Test case neck tension by pushing the bullet of loaded rounds against the loading bench. If the bullet is easily moved deeper into the case, malfunctions may occur. But more important, loads that produced 28,000 cup went to 62,000 cup when bullets were purposely seated .030" deeper! Thus, it is of the utmost importance that bullet do not become deeper seated in the feeding cycle."

Concealment is not cover.........

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delmarskid posted this 15 October 2025

.030” is 1/32” , that’s a little less than the thickness of a pencil’s lead.

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Online CBA Member

Ed Harris posted this 16 October 2025

When I was at Ruger working on development of the P85 pistol we wanted to buy an extra quantity of NATO proof loads to run an accelerated endurance test. My contact at WCC told me to just reseat M882 Ball 0.05 deeper and we'd get the same result. Tested some and indeed we did. Do not recall the exact pressure, but it was over 70kpsi

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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