In a recent post, I responded to a setback comment rather cavalierly. ( http://smith-wessonforum.com/141177931-post27.html)

However, when I got to thinking about my response, I thought it best to do a little experiment. I found the results a bit surprising.


We've read about setback, and about certain cases of extreme setback, e.g., a person that cycled his ammo for months. Usually when unloading and reloading I "shuffle" my ammo in my mag so as to minimize setback on one round.

However, I was curious how quickly setback can happen, and how severe. So I took my Defender 9mm and reloaded a Hornady 147 Gr XTP 20 times. Sometimes I slingshot the slide, and sometimes I released the slide stop (I always slingshot, by the way). The results were very interesting.

At the start, both of the rounds below, out of the box, measured 28.08 mm. After cycling the round on the left as described above, it measured 26.98 mm. That's about a 4% decrease on overall length. I'm not sure if that will cause over pressure, but to be safe I'm going to disassemble the round instead of firing it.

I typically carry Golden Sabers, and I have not performed this experiment on that particular bullet. But the results below are enough to make me a believer that setback can occur in a surprisingly few number of cycles. Fortunately my Defender can "walk in" a round from the magazine, and I can use that technique to minimize setback.

Thanks, very interesting and informative.

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John. SWCA #1586

I have a Sub 2000 with Glock magazines. It shoots round-nosed ammo no problem. I tried flat nose 147 grain FMJ. Numerous fail to feed with severe bullet setback. Dangerous it was; those 147s are already taking up much space in the 9mm case. I discontinued further testing and threw away the set-back rounds.

Bullet setback depends upon a number of variables. Case neck tension, bullet profile, and the path from the magazine to the chamber. Weak case neck tension will result in setback, even with the first chambering. A flat nosed bullet is more likely to bang into the feed ramp and suffer setback than a round nosed bullet. Some pistols have fewer bumps in the road from the magazine to the chamber than others. Things to keep in mind when that slide slams forward, chambering that round. I'm not a fan of repeatedly chambering the same round.

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VCDL, GOA, NRA

Individual situations are different, but unless you need to repeatedly load and unload a magazine, don't do it. I never encountered any problems with reliability, feeding, or firing when leaving magazines alone for six months at a time with a Beretta 9mm. Again, a person's needs are different and my suggestion won't work for everyone, but it will work well for most.

I will change out a magazine to use target ammo and then reload SD ammo for the weapon when finished, but that ammo is never racked into the barrel, until needed.

I have three dogs that give me plenty of notice when anything comes onto my property.

I worked for a company that required that your gun be unloaded and turned in every night. You kept the magazine and one extra round in your locker till the next day. They were deeply afraid that an employee would do something illegal with their gun. They got to the point that you could not even take your gun out for practice. Daily carry and requalifications were the only times your gun was allowed to be removed from its rack.

This caused the ammunition to have setback rather quickly. Employees were told to put their setback ammo further down in the magazines. Furthermore they were instructed to change magazines every few months. I replaced any ammo that was setback too far.

We used M&P 40's at the time. They now issue FN 509's. They retired me over a year ago so I don't know their policies now.

There are quite a few LEO agencies and departments that specify quarterly rotation of all duty ammo with fresh ammo. This is done in part, because of concerns with bullet set back, especially with the almost total change to semi-auto firearms in the last 40 or so years.

I don't know of any reliable metric that will accurately chart pressure increases based on the amount of bullet set back, too many variables, but any amount will result in some increase.

Larry

You can tell by chronographing loads. If there is a pressure increase due to the bullet being deeper in the case, velocity will increase. Depending on the cartridge, powder, and increased depth of the bullet in the case, velocity difference could be significant and even potentially dangerous. If the difference was minimal, say 50 fps, I wouldn't be concerned as long as the bullet was not loose in the case.

However, to get meaningful results using this method, you'll need to chrongraph more than one round that has the bullet setback and compare velocities with several rounds with bullet seated to normal depth. Few would go to the trouble to do this.

The problem may not even exist with some ammo.

This may be heresy to some, but my EDC for the past 15 years or so is a well trusted Gen 3 Glock 19. I always "walk in" that first round before leaving the house. Takes a couple of seconds to load and press check. There may well be other makes and models this would be not work with, but it does work for me and old Roscoe. And yes, I've extensively tested this.

I always drop one round into the chamber, let the slide close and then put a completely loaded magazine in the pistol.
Why cheat myself out of a round. Plus the problem or worry about the above issue doesn't even exist.
Unless that one loose round hanging around when you unload the pistol really bothers you.

Is this situation with factory ammo? I have never seen that before, not good.
If handloads, they need a taper crimp. I don’t shoot factory to often but do on my Sig 365XL for concealed carry. The rest of the time, for practice and plinking at the range, shoot hand loads. They are all taper crimped to specifications. 45acp and 9mm have never done that in my pistols.

I put several setback rounds in a plastic baggy and posted it on a bulletin board. Seeing is believing.

That's factory 9mm Hornady XTP 147 GR ammo. Again, that's after about 20 cycles in a 9mm 1911 (Colt Defender). As others have noted, setback may be less of a factor in other guns.

I thought it would take many more cycles for it to happen, but the onset was relatively quick.

Can't address other manufacturers, but Glock specifically says not to do this, in order to avoid possible extractor failure.

I always carry topped off as well. The pistol is loaded administratively (full magazine placed in magazine well, slide racked, pistol holstered, magazine drawn, topped off, and reinserted.

Set back has never been an issue, but i don't unload much.

So I decided to see if "walking" the the round into the chamber (basically holding onto the slide to keep the slide at a slow speed as it strips the round and chambers) would cause any setback. On the Defender it did not. 20 cycles, no change.

Some guns cannot load properly this way, but fortunately my defender does.

I don’t have issues with set back, but then I use dies for my semi auto rounds that that over size the case, and leaves it undersized in the belling process so that the bullet has to expand the case when it is seated

It creates a wasp waist effect that some folks hate. But those are the same folks that usually have problems with set back.

Put setback rounds further down in the magazine? Whaaaaat? I guess they were hoping that if you had to use your sidearm that you would not fire enough rounds to get to the one that was most likely to go "kaboom".

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VCDL, GOA, NRA

There's a lot of semis where that procedure won't work. When I learned to shoot I was told it was an absolute no-no in any semi-auto weapon.

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Release the Kraken

I was issued 9mm and .45 for many years, and did some informal setback testing myself. I discovered some factory ammo displayed measureable setback after chambering the round just once. Twice or more, it sometimes become real noticeable to the naked eye. I make an effort to chamber a round just one time. I suspect manufacturers only envisioned their ammunition being chambered one time.......

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NRA Life, COTEP 640

When I retired in ‘97 we were carrying the Glock 23, but the new issue is a G19. I qualified for LEOSA last week and still have never heard what if any training the troops get about this set back issue. My EDC in retirement is still a J Frame but I do pocket my LCP now & then. When I unload it for maintenance I put the chambered round in a bag for the range, but it’s never been a problem.

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Old Cop
LEO (Ret.)

There were some pretty significant discussions of this on the old 10-8 forums about 2007. As a result of the experiences described by some very savvy people (10-8 was a pretty serious place, with screening before signup, etc.) I got to the point that if I chambered a round in any semi-auto platform, it was fired in order to remove it unless there was an emergency and in that case it was discarded. It can vary by platform and load, but in no way is it worth the risk.

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NHI, 10-8.

This is an interresting post..........

It just dawned on me that maybe, some of those low or high fps in my test loads, might be from a bullet moving back or forward,
when the slide goes home with my "Pistol loads" that have no cannelure?

Once you pull the trigger there is no way of checking the OAL.

Now see what you did !!
I will be dreaming of this for a week..................

Don't.

Even at a buck a round, ammo's not worth your life.

Here's the problem. Guns are made so as the slide comes forward, it strips a round off the magazine. The rim of the cartridge slides in behind the extractor. No strain on the extractor.

But if you do it your way, the extractor crashes into the rim, and then has to hop over the rim. It's not made to do this. Particularly on 1911.

Every time I re-load a gun for EDC, I throw the one that was previously in the chamber into the range stuff and shoot it.