What is the right amount of setback?

[gregjc9]

I've done a lot of research here and on other boards on the proper amount of setback, and seems like I'm more confused the more I read and test. I've heard of, and regularly perform, the bench press test, and my reloads pass that test just fine. My concern here is I know I get some setback with my reloads when chambering, but I dont know how much is "acceptable".

Disclaimer: I've been reloading for less than a year, but have loaded a few thousand rounds of 380, 9mm and 45 on my Lee Classic Turret. I'm using the Lee 4 die set, which includes the FCD. The reload in question here is 9mm.

Before testing, I adjusted the expander die to minimal flare. The bullets used were Powerbond jacketed FMJ RN.

To test the amount of setback, I first noted the OAL of the reload. I then chamber the round, ejected it and measured the OAL. I repeated this process 4 times and noted the results.

I then tightened the crimp on the FCD a little at a time, then repeated the same process above with dummy rounds.

I made a dummy round for each subsequent test. I found I got a total of .0235" of setback when chambering one of my older reloads a total of 4 times. I also found that if I really cranked down on the crimp on the FCD die, I got more setback than if I used a lighter crimp. This confirms what I've read here and elsewhere that too much crimp can have a negative impact on neck tension.

With a lighter crimp on the FCD, I could get a total of .0080" total setback after 4 chamberings of a dummy round. I know the main way to get optimum neck tension is by adjusting the sizing die, but I dont believe there is any way to adjust the Lee sizing die.

I also did the same tests with factory rounds from Blazer and Remington, they had significantly more setback than my reloads.

Ideally, I suppose one would have zero setback, but is that really possible? (I'm probably over analyzing this.)

I can send anyone that's interested a spreadsheet of the data, if anyone needs help sleeping.

[gregjc9]

Just ran across a very interesting article. Sums up just what I tried to post above.

[Unclenick]

It's the expander die that affects neck tension if it's expanding too far, and the resizing die that does it if the neck it too thin (like Remington brass often seems to be; at least, it is in .45 ACP). Getting the resizing die tighter requires ordering a custom die, as the carbide ring has to be smaller.

Overcrimping springs the case away from the sides of the bullet and it can't be pressed back 100%. You just have to not overcrimp. It's the only reason I know for trimming semi-auto cases: getting the crimps consistent.

OK. Ignore the below. The last post I was reading was for a .308 and my brain got stuck there and wrote the below response before I figured that out and wrote the above. But I'll leave this for those noting the problem in rifles:

Haven't seen the article, but unless you marked your bullets the chances are you are seeing shoulder setback and not bullet setback. Hatcher notes that rapid work on a bolt can set a .30-06 shoulder back something like 0.006 (IIRC) in a chamber that didn't jam the case at all.

You can test this. Even if you don't have a case comparator to check the shoulder datum distance from the head (instead of to the bullet tip), you can look for the case getting slightly fatter. It is expanding into the extra width in the chamber above maximum case diameter spec that makes this possible and common.

[PA-Joe]

For pistol rounds most people do not worry about setbacks. The magazine and proper feeding are more important factors. I thought you were talking about setback from the lands? Are the bullets setting back into the case as you reload them?

[Unclenick]

I don't think you need to worry much with jacketed bullets in thick enough brass, but I've seen lubricated lead bullets pushed all the way back into the case when a thin case neck couldn't grip it hard enough. In that case you do need to worry about it. That can create damaging pressure. Raising the bullet base pressure on a cast or swaged lead bullet also increases leading and spoils accuracy.

[SL1]

First, the set-back in your handloads may be more than you think. Hand-cycling the action to feed a round does not necessarily create the same amount of set-back as the auto-cycle caused by firing a round. So, when I test for setback, I put the dummy in a magazine under a live round and fire the round to auto-load the dummy, then eject and measure the dummy. For me, that has ALWAYS produced more set-back.

As for feeding the round multiple times, it seems that set-back doesn't always get added in proportion to the numbr of feeds the cartridge endures. There may be nearly zero set-back on the first feed, with ever-increasing amounts on subsequent feeds. So, my first endeavor is to set-up my dies so that there is as little set-back as possible on the FIRST feed. Then, I will see how many feeds those rounds can endure before the NEXT feed will give me more set-back than I consider safe.

What amount of set-back is considered safe? Well, it depends on the load and gun. In small cases like the 9mm with heavy bullets, there is precious-little space for the powder, and just a little setback can make a big percentage change in available powder space and cause a case to blow if it is a hot load to start with. In the 9mm section of Speer Manual #10 (on page 349), it says with respect to set-back, "... loads that produced 28,000 CUP went to 62,000 CUP when bullets were purposely seated 0.030" deeper!" I have never been able to make QuickLOAD produce a situation with THAT big of a pressure difference from 0.03" of set-back, but I sure wouldn't want to use a computer simulation to argue with a major company's pressure test data. So, I try to keep my handload set-back to no more than a few thousandths of an inch on the first auto-feed. I limit the number of feeds I will allow with the same cartidge based on how many feeds I can get before the NEXT one gives me a total of 0.005". As a matter of practice, I try to not let a cartridge (handload or factory) see more than 2 auto-feeds. But, I am shooting hot cartridges (.40 S&W and .357 Sig) and am concerned about setback more than I would probably be with a .45 ACP.

The article that you provided a link to has a useful idea that I have already incorporated in loading my straight-walled pistol cases: put a cannelure in the case wall to support the base of the bullet. I sort-of do that by sizing my brass with a carbide die that makes the inside diameter significantly smaller than the bullet, then use an expander plug to expand only down as far as where the base of the bullet will be when seated. This leaves a little shelf that helps support the base of the bullet against set-back. To do that and flare the case mouth, too, I needed to make some special expander plugs that have the right distance between the flare section and the end of the expander section. I have either turned-down the excess expander section of factory plugs or made my own from full-thread bolts. It is a pain to make those, but I think it helps with the potential for some thin-walled cases getting into my mixed brass and giving me less neck tension than was provided by the brass that I used for my dummy round set-back tests. If making the special expander plug is not feasible for you, you can expand and flare in 2 separate steps, using a cut-off expander plug to do the flaring. That way, you only need to make one special plug that will flare for all bullet lengths.

SL1

[gregjc9]

Awesome feedback guys, much appreciated. I will have to reread a few times to digest it all.

SL1, I recall reading that section in the Speer manual #14 IIRC. Since my loads are for range sessions and mostly plated bullets, the loads are at the middle of the range using Power Pistol for 9mm and W231 for 45. I will go back and reread that section as it applies to the powder and loads I'm using.

I knew I would get the best info here.

[gregjc9]

SL1:

So, I try to keep my handload set-back to no more than a few thousandths of an inch on the first auto-feed.

I made a few more dummy rounds and took a few measurements:

Bullet OD: .3550
Case OD: .3710 (after resizing)
Case ID: .3510 (after resizing) This leaves a case wall thickness of approx .0100"
OD of cartridge after FCD: .3750 (Max is .380)

I chambered a few dummy rounds, and the lowest setback I could get was approx .0035", which I think at this point is pretty acceptable, and tracks with what you stated.

I will try and remember to take my caliper with me to the range next time I go, and measure the setback as you suggested.

It just strikes me as being very ironic, that there is a LOT of concern about trying to find the perfect COAL, yet there seems to be very little information on the need to determine the setback on auto-feed. (I'm not talking about extreme setback where pressure is increased dangerously high.) It seems like the correct COAL when a round is made, would be the auto-feed setback + the best COAL per barrel gauge test. (I hope that makes sense.)

Thanks again for the info!!

[SL1]

Regarding trying to load to a COL that accounts for set-back: I don't think that makes any sense. From an auto-loading pistol perspective, the "best" COL is the one that feeds reliably. Even a bullet that sets-back a lot can feed OK (unfortunately), apparently because the bullet is set-back AFTER it encounters the feed ramp enough to make its trajectory into the chamber sucessful. So seating the bullet it to be already "set-back" isn't useful. And, acceptable levels of set-back aren't really large enough to be the "make-or-break" factor in successful feeding.

SL1

[WESHOOT2]

I found methods that eliminate any potential setback; I use those.

I recommend Power Pistol in 9x19 and W231 in 45 ACP, but I do not recommend thinking that any setback is acceptable.

[drail]

Any amount of setback is unacceptable. The manufacturers are not concerned because they don't intend for the consumer to rechamber the same round over and over. It only has to hold OAL for one or maybe two chamberings in their opinion. Unfortunately today we now have many people unloading and rechambering the same round repeatedly. These people will argue that they have no choice and must do it. No matter how you justify it it's a bad idea. Ammunition CAN be made to not setback. Experienced reloaders have done it for years.

[gregjc9]

Great information guys. I agree with the concept of zero setback, but what do you do to attain that? Shave down the expander die? I have read taking the expander die down .003" to .005" below bullet diameter generally seems to do the trick. I'm using the Lee powder through die, so there is no expander die I can trim down.

I have read as much as I can about neck tension, it's all done at the sizing die, minimal flare, minimal crimp, etc (caveat, for straight walled pistol rounds). I'm using a LEE 4 die carbide set, which includes the FCD - which is set to relieve the flare, and maybe just a touch more (this setting seems to provide the least amount of setback).

I did find my sizing die was a little loose, and had backed out a little. Probably due to resetting the decaping pin a couple of times. After adjusting it again, setting the powder drop to minimal flare, and testing more dummy rounds, I got about .0030" setback. Not much, but still some.

I'm not being OCD about this (really, I'm not), I just find the concept interesting - a mental challange. And if I can learn more, and maybe produce some better ammo as a result, it will be worth it.

[gregjc9]

Any amount of setback is unacceptable. The manufacturers are not concerned because they don't intend for the consumer to rechamber the same round over and over. It only has to hold OAL for one or maybe two chamberings in their opinion. Unfortunately today we now have many people unloading and rechambering the same round repeatedly. These people will argue that they have no choice and must do it. No matter how you justify it it's a bad idea. Ammunition CAN be made to not setback. Experienced reloaders have done it for years.

I tested a few Blazer and Remington UMC rounds, and they showed significantly more setback from one auto-feed, than my reloads did.

[SL1]

As you found, factroy ammo DOES have some set-back in MANY instances. So, the idea that ONLY ZERO set-back is acceptable for handloads really doesn't make sense. In many cartridges (particularly those that head-space on the case mouth), it can only be minimized, not eliminated with the tools normally available to handloaders.

Considering YOUR die set, one thing to check is your FCD. It has a carbide ring in its base that is intended to size any over-SAAMI-spec outside dimension down so that it will be SURE to chamber. My experience with those dies is that some of those carbide rings are a little tight, and that means that they will slightly swage the BULLET as it is withdrawn from the die. (It has nothing to do with die ADJUSTMENT, it is a manufacturing issue.) IF you have on of those tight carbide rings and it compresses the brass around the bullet as the cartridge is withdrawn from the die, it REDUCES case neck tension on the bullet, which can increase set-back. The reason is that the brass case is spingier that the lead in the bullet, so, after being compressed by the die, it effectively has less "interference fit". (That is, the bullet is slighly smaller, and doesn't have to hold the brass case out to the same diameter as before, while the case has sprung back more towards its original diameter.) You can usually feel if your cartridges are dragging on the carbide ring when the bullet section is being pulled out of the die. IF so, then you can use an FCD body from a larger sized cartridge with the internals from your 9mm FCD to make sure that doesn't happen. (The internals of all the straight-walled FCDs fit in all the die bodies for that type of FCD.) Or, you could just use a different brand of taper crimp die, because only Lee uses a carbide ring in the crimp die.

You can reduce the expander plug diameter to maybe 0.005" below bullet diameter, but, at that point or a little before, you get the brass stretching plastically and/or the brass actually reducing the bullet's diameter plastically, so that the final neck tension can only be increased to a certain limit before the inelastic deformations prevent further gains.

SL1