Something you might not know about setback...

[EddieCoyle]

I cross posted this at www.vintagepistols.com

I recently picked up a Walther PPS as a new carry gun. I selected Federal Hydra-Shok PD Low Recoil 135gr ammo for carry (mainly because this is what my local place had).

Like many people that carry autos with a round in the pipe, I've been careful to unload and reload my mags regularly to avoid chambering and rechambering the same round to prevent bullet setback.

For those of you that aren't familiar with the term, "setback" describes the tendency of a bullet to seat itself deeper in the case each time you chamber it, either due to inertia, or the bullet contacting the rifling. If the bullet sets back enough, it decreases the available volume inside the case, and can result in a dangerous over-pressure condition when you fire the round. For this reason, many of us fully unload the magazine each time we unload the gun, and place the most recently chambered round in the bottom of the mag.

When I was looking at my ammo, I noticed a secondary "crimp" (it looks like a cannelure) on the outside of the case, near where the bottom of the bullet ends up after seating. You can see it in the photo of my ammo below:

I've seen the same "crimp" on revolver brass that I reload.

I was curious what it was for, so I called one of my customers who is a manufacturing engineer at an ammo plant. He told me that the crimp is there to minimize or eliminate bullet setback.

OK. I had to know. Did it work? I decided to do an experiment.

I measured a random Hydra-Shok round - 1.002", then chambered it ten times in my PPS, and ten times in my Glock 17. I "slingshotted" the slide five times, and used the slide lock lever five times each, then re-measured the round. The new measurement was... 1.002".

I guess it works.

 

[Mil-Dot]

Great post!
Thanks, M-l-Dot

 

[eisenhow]

Nice writeup. Did he mentioned which ammo lines they did this on or when they started? I just opened a box of Federal HST (9mm 124gr +P )and don't see a secondary crimp.

 

[packingungal]

Interesting...thanks EC.

 

[dixidawg]

That's interesting. I too was nervous about this in my Kahr. I have two rounds that were in my rotation that ended up roughly .025" shorter OAL than new ones out of the box.

They are the same Federal 135gn low recoil Hydra Shok JHP that you show in your picture.

Odd thing is my OAL from the factory is 1.100". The 2 shorter ones are 1.075" I have no idea if this is enough to make a material difference in pressure, so I had marked them and pulled them out of my rotation. I am now careful to monitor how many times I chamber and I measure them often.

 

[mikem317]

I measured a random Hydra-Shok round - 1.002", then chambered it ten times in my PPS, and ten times in my Glock 17. I "slingshotted" the slide five times, and used the slide lock lever five times each, then re-measured the round. The new measurement was... 1.002".

I wonder what data you would collect after 10, 100 and 1000 repetitions.

 

[appraiser]

Setback is SUPER CRITICAL in the Glock 40's and many people believe it is the cause of the infamous Glock 40 KaBooms .

In my .40 I never chamber the same round more than twice.

 

[EddieCoyle]

I wonder what data you would collect after 10, 100 and 1000 repetitions.

Who the f*** rechambers the same round 1000 times? Seriously. Come over, I'll give you the shit, and you can try it.

Setback is SUPER CRITICAL in the Glock 40's and many people believe it is the cause of the infamous Glock 40 KaBooms .

In my .40 I never chamber the same round more than twice.

Have you ever measured it?

 

[wolf223]

wow, thanks.

question: i fired some really "hot" .40's last year that my brother had laying around. he's one of the guys who likes to unload and reload his firearms when he gets home.

-is this the reason why they were so "hot"???

i don't reload and don't really know much about it. but the loads were freakin HOT! they were Federal JHP's, 165gr.

after shooting his 25 rounds, the rest of the ammo seemed like .22LR.

 

[Lucas McCain]

Thanks Jim, I always wondered what that "crimp" was for.

 

[atilla]

i carry federal hydra-shok .38 spl rounds in my 442 and they also have this extra crimping--this must be the standard for the ammunition as i don't think there would be as much of an issue with this in a revolver as in an automatic.

 

[EddieCoyle]

wow, thanks.

question: i fired some really "hot" .40's last year that my brother had laying around. he's one of the guys who likes to unload and reload his firearms when he gets home.

-is this the reason why they were so "hot"???

i don't reload and don't really know much about it. but the loads were freakin HOT! they were Federal JHP's, 165gr.

after shooting his 25 rounds, the rest of the ammo seemed like .22LR.

.40's are tough, like Glockaholic said. That could very well be the reason that you felt what you did. Although it's unlikey that all of those rounds were rechambered. Is the guy that reloaded them (assuming they were reloaded) related to me?

 

[EddieCoyle]

i carry federal hydra-shok .38 spl rounds in my 442 and they also have this extra crimping--this must be the standard for the ammunition as i don't think there would be as much of an issue with this in a revolver as in an automatic.

Recoil (especially in a light gun like yours) can cause the bullets in the other chambers to pull out of the case. The extra crimp at the bottom of the bullet won't prevent pull-out, but it will prevent inertial setback.

I load some 700 grain rounds for my .500 that I crimp the ever-livin' crap out of, that still pull to the point where I have to single load them.

 

[atilla]

wow, really? i never though that would be such a problem with something as light as (well, compared to that .500!) as my 442.

should i be concerned about loading and unloading this thing with the carry rounds? i only have five rounds left since i shot all the rest to get a feel for them. if i should swap the rounds i keep in there i'd like to hear what you've got to say about that. i just bought a box of .38s so maybe i will go shoot this again next weekend.

 

[appraiser]

Who the f*** rechambers the same round 1000 times? Seriously. Come over, I'll give you the shit, and you can try it.



Have you ever measured it?

I never measured it, but I based my decision on an analysis of KB's in guns used by a federal agency, where they would put a bullet in an empty mag to use to load the gun in the morning, then put a full magazine in the gun. At night they would drop the magazine, eject the live round, putting it back in an empty magazine to use again. When they actually had to fire the gun, after many cycles of loading/unloading, there were KB's.

I forget the actual amount of setback, but since the .40's are known for the steep ramp, and KB's, it seemed reasonable enough to me not to to risk a 600 dollar gun over a 50 cent bullet.

 

[EddieCoyle]

I forget the actual amount of setback, but since the .40's are known for the steep ramp, and KB's, it seemed reasonable enough to me not to to risk a 600 dollar gun over a 50 cent bullet.

I agree, and I didn't mean to imply that you don't have to worry about setback. Glock .40s with the stock barrel are notorious for kBooms. Some people attribute this to setback (which is probably the case when factory ammo causes the kB).

I merely wanted to point out that with some ammo/gun combinations, it might not be as much of a concern as with others.

 

[01SVTvert]

Wondering how much setback would affect factory self defense ammo. I know of a department that runs Glocks and some of the people who work there, must, because of their job, load and unload at least a couple times a day. Figure even twice a day at 200 days a year and the ammo could get ratty. Doubt many know to rotate ammo or to get rid of the beat duty ammo.

I still have some old 9mm hydrashocks that must have been chambered over 100 times roughly. Cases are beat, was from years ago when I had no idea that ammo was particular to constant chambering. Sits in a box of ammo now, will prob never get shot unless I get a caliper and check it out now.

 

[Dirtypacman]

Thanks Jim, I always wondered what that "crimp" was for.

+1 to that.

I love learning something new. This board is great for just that.

 

[trophygrl]

same here-- i just noticed that all of our 38 spcl ammo is crimped--now i know why

 

[lord1234]

I did not know about setback. Thanks jim for the education!

 

[45collector]

My .45 carry rounds are Federal Hydra-shoks. They have the crimp as well. I've got a handful of rounds that have been chambered via slingshot at least a dozen times each and they are no shorter than when they came out of the box.

About twice a year though, I shoot up all remaining carry ammo, and buy a new box. I guess I just like the look of shiny copper coating.

 

[EddieCoyle]

About twice a year though, I shoot up all remaining carry ammo, and buy a new box. I guess I just like the look of shiny copper coating.

That's always a good idea.

 

[Dick]

wow, really? i never though that would be such a problem with something as light as (well, compared to that .500!) as my 442.

should i be concerned about loading and unloading this thing with the carry rounds? i only have five rounds left since i shot all the rest to get a feel for them. if i should swap the rounds i keep in there i'd like to hear what you've got to say about that. i just bought a box of .38s so maybe i will go shoot this again next weekend.

No, you're misunderstanding the situation. Bullets pulling out of the case is a totally different phenomenon from the initial topic of the thread. When the gun fires, it recoils (which, of course, you already knew). The bullets (and I mean bullets, not cartridges) in the other four cylinders, being heavy, tend to stay where they are while the gun moves back taking the cases with it (potentially), which moves the bullets out of their cases a bit. The lightness of the 442 makes it recoil faster and that increases the potential for this problem to occur.

If all you're doing is loading and unloading the revolver there's no chance of this happening - it's only when you shoot it, and quite possibly not even then.

 

[atilla]

i might have worded things a bit off but my concern was for the recoil. didn't think it would be a huge issue with only five rounds.

thanks EC and dick!

 

[Ray-500]

My .45 carry rounds are Federal Hydra-shoks. They have the crimp as well. I've got a handful of rounds that have been chambered via slingshot at least a dozen times each and they are no shorter than when they came out of the box.

About twice a year though, I shoot up all remaining carry ammo, and buy a new box. I guess I just like the look of shiny copper coating.

Good Luck to you my friend. Still have Military Match Grade going as far back as 1969 (white box, labeled Match). Calibers are in both .45 ACP and .22. Also have "Lake City" circa late sixties in 30.06. All function perfectly, and I still use the .45 in Steel Plate matches. Grin, no problem with the ammo, just my own capability.

 

[mikem317]

Who the f*** rechambers the same round 1000 times? Seriously. Come over, I'll give you the shit, and you can try it.

I have no idea. I was wondering if you expanded "n", the number of times an instance is chambered to a more meaningful number to see if there's evidence suggesting that setback increases.

Most populations or samples need to at least 30 to have some order of significance.

 

[eisenhow]

I have no idea. I was wondering if you expanded "n", the number of times an instance is chambered to a more meaningful number to see if there's evidence suggesting that setback increases.

Most populations or samples need to at least 30 to have some order of significance.

Don't feel bad, doing it more, at least until you hit an unreasonable number of iterations or you saw a measurable setback was the first thing I thought of. I guess it's the engineer in me.

 

[GSG]

Thanks for that EC, I never knew what those were for.

So am I the only one who keeps his carry guns loaded all the time, even in the safe? Methinks that makes setback less of an issue.

 

[Pomeraniac]

So am I the only one who keeps his carry guns loaded all the time, even in the safe? Methinks that makes setback less of an issue.

Nope, you're not the only one.

 

[45collector]

Good Luck to you my friend. Still have Military Match Grade going as far back as 1969 (white box, labeled Match). Calibers are in both .45 ACP and .22. Also have "Lake City" circa late sixties in 30.06. All function perfectly, and I still use the .45 in Steel Plate matches. Grin, no problem with the ammo, just my own capability.

Cool. But do you trust 40 year old ammo in a carry gun? I don't. If it were only for the range, I wouldn't care if I was shooting 100 year old ammo. If it doesn't go bang, tap and rack and try again.