Consistent shoulder bumping

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khaines0625

New member
I'm really struggling with keeping my shoulder bumps consistent. I've often heard the goal is to bump the shoulder back .002 from a fired piece of brass. I aim for that but struggle mightily to reach that bump for it to stay consistent across a batch.

I have the hornady headspace comparator kit. I use that to measure a piece of brass before resizing and then after. I aim for there to be a .002 reduction after. Dialing the lee full length resizing die is cumbersome but I usual can get there by starting with it backed off a ways and very slowly screwing it down, running the brass through, measuring it, and repeating the process if it hasn't bumped.

Once I have the die fit, I then lock the nut down well and run through as bunch of brass. Once I'm done I go back and measure the length using the headspace tool and am seeing lengths varying from 2.048 - 2.041. Before the resizing die they usually are at around 2.050. I want the comparator tool to show them all being the same, right? I seem to never be able to do that. I also have the problem that by the time I have the die dialed in, I have inevitably over-bumped several pieces. All in all, my shoulder bumps seem to be all over the map and I don't seem to be able to stop it.

I don't think there is any way to un-bump a piece of brass unless I fire it which makes me feel like when this happens i have basically wasted the brass. I'm also concerned about over-bumping causing excess headspace.

Can anyone relate to this frustration? Am I making this out to be a bigger deal than it is? How much of an error is this over-bumping?
 
Can anyone relate to this frustration?
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I cant.


Am I making this out to be a bigger deal than it is?
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Yes.

How much of an error is this over-bumping?
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Zero, to me.

Consider this, if you "overbump" as much as you possibly can, what have you done?? Have you "wasted" a case? ABSOLUTELY NOT! What you have done is simply FULL LENGTH RESIZED IT.

I'm also concerned about over-bumping causing excess headspace.
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And, just how, exactly do you think that could happen??

You can't size a case any smaller than the die is cut to do. Bumping the shoulder is only PARTIAL sizing. Unless there is something out of spec with your die AND your rifle(s) FL resizing does not create excess headspace.

Does your rifle show a measurable, consistent difference in accuracy with shoulder bumped ammo? IF SO, does it make any practical difference, for you?
 
OP. What press do you have? Do you clean the brass before sizing? What lube do you use? Do you lube inside the neck and with what? Do you anneal and how often? Do you sort your brass?

Others may not agree, the way you bump shoulder is full-length resizing. You just try to control the amount the brass is resized, instead of "screw it all the way down and add 1/4 turn". Nothing wrong except the end result has more tolerance than desired. You just want to tighten the tolerance. The questions I asked above are relevant to that.

-TL

Sent from my SM-N960U using Tapatalk
 
Thank you all for your responses. It may seem silly to you experienced guys at times but hearing these responses lets me know that I was thinking of the whole thing wrong. It is good to know that this is all good.

I had thought that the more shoulder bump that occurs, the looser the headspace. I had also thought that it was possible to set a full length resizing die so far down that the headspace would reach a problematic state. It appears I was wrong and I thank you all for clarifying that for me.
 
Your die does the same thing over and over, what is different is the brass. Lubrication of each case needs to be the same, and the really hard one is consistent hardness in the brass. This changes by manufacture, lot number, and number of times being fired. You need to learn to keep brass together in lots, box number or whatever. I call this case management and I can't do. To eliminate the inconsistent length you are seeing I now separate by head stamp, separate by case weight, and anneal after every firing. That's time consuming and I expect every case to be sizied to within .0005". An old gentlemen who used to be on this site advised me to know what my dies are doing and that turned out to be the best advise I have received.
 
Don't forget calipers carry their own tolerance. Not everyone can do better than+/-0.001", and it can easily go double of that.

-TL

Sent from my SM-N960U using Tapatalk
 
Nope you all are mistaken, its all about press deflection. Yes lube can cause very small variance , yes, calipers can cause small variances , yes, brass can have different springback abilities, causing variances But I have found that these do not stack at least not consistently . The only thing that I found that was consistent and the reason for my inconsistent sized brass press deflection/flex .

Unfortunately, I really don’t wanna get into the very long explanation so I’m going to try to find a very old thread where I explained it and hopefully I can find it and post a link
 
Metal god said:
Nope you all are mistaken, its all about press deflection. Yes lube can cause very small variance , yes, calipers can cause small variances , yes, brass can have different springback abilities, causing variances But I have found that these do not stack at least not consistently . The only thing that I found that was consistent and the reason for my inconsistent sized brass press deflection/flex .

Unfortunately, I really don’t wanna get into the very long explanation so I’m going to try to find a very old thread where I explained it and hopefully I can find it and post a link
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That's why I asked for the kind of press the op was using. It is indeed one of the major factors.

-TL

Sent from my SM-N960U using Tapatalk
 
The goal of minium shoulder bump is to not stress the brass at the base any more than you need to for that gun (it may or may not work in another gun depending on where the shoulder is in the other gun, less and it won't more and it will)

I have seen the endless debates on sizing, it has to be loose, tight is better. Shrug.

I had the same thing occurr in regards to bump of the shoulder (measur4e before and after). Not quite as bad but what I wound up doing was going for at least .003.

It wanders from that to .005. As not one agrees on anything, that is good enough for me.

I can't say I have lost any brass since I refined it to that. Neck cracks yes and the cure to that was an Annie annealer. I make no claims for accuracy or neck tension, just that it stops the cracks in their tracks. If I forget to do it and get a crack, I can anneal and no more cracks.

Now if you are going to try to shoot 1/4 inch groups, some of that might make a difference. Me? I am happy with 1/2 inch groups and get an occasional 1/4.
 
The main thing i have found with getting a constant sizing is that i need to keep the brass in the die for about a full one to 2 seconds or so. If i just run the brass in and out of the die quickly i get much less constant measurements from the base to the shoulder.
 
Khaines0625,

When you push a shoulder back too far on a case that headspaces on the shoulder, you are increasing what is called Head Clearance and not Headspace. Many people, including some professionals (Brownells' two video gun experts, for example), confuse the two. Clarification may be had by going to SAAMI's website and looking them up under "H' in the online glossary of terms they maintain.

There are different factors you can control to reduce the spread of head-to-shoulder lengths in your resizing efforts. As Metal god says, press stretch is a big one. If you set up a sizing die by turning it down to just kiss the shell holder when the press ram is all the way up, then insert a lubricated case and press it up to maximum ram height, when you look sideways at the shell holder and put a light behind it, you see a crack of light between its deck and the die mouth on either side of the case. The exact size of that crack varies from case to case, causing that variation in the finished sizing job you see. In full-length resizing, you prevent this by adding an extra quarter turn to the sizing die beyond where it kisses the deck of the raised shell holder (more for lighter aluminum presses). This is done so the ram intentionally stretches the press via the shell holder and stretches it more than the force of sizing the case can do. This ensures the case goes as far into the die as the shell holder allows, regardless of variation in case hardness. Well, Redding figured out that if they made shell holders that were taller than standard, the shooter could also set them up like a standard shell holder but prevent the case from going as far into the die as a standard shell holder does, yet still get consistent press stretch. These shell holders are called their Competition Shell Holders and are available in sets of five with 0.002" length increments each. You may argue that they should have made them 0.001" increments, but there will still be a little variation due to other factors mentioned so that hitting a value tighter than a 0.002" tolerance is hard.

Other factors can have some effect. Withdrawing the standard expander through a case neck on the downstroke can stretch the shoulder of the case a little or even pull it slightly off-axis. If you want to avoid that problem completely, resize the case body and shoulder using a bushing type die with a bushing chosen to provide your desired final neck diameter without having to expand it any. The only thing you lose by that method is the expander's ability to iron small dents out of case necks on their way in. Alternatively, you can resize in a Redding Body Die or else in a bushing die with the bushing removed, so you resize the case body and shoulder without sizing the neck and then size the neck separately with a Lee Collet Die. The Lee Collet Die is an inexpensive and somewhat rough-feeling tool, but it does a remarkable job of keeping the neck concentric with the case body, and it has a mandrel that will iron out small dents.

If you are shooting in a self-loader, you also want to check your cases for rims that have been slightly bent by vigorous extraction. A bent rim that sits on the case support ledge on the bottom of the slot in the shell holder can make your case go too far into the die, or it can fool your measurement of the same. If you get a lot of them, consider a gun modification to slow extraction down.

Finally, you come to the question of how much good all this does. The military marksmanship units found long ago that new brass produced better accuracy for their service rifle competition teams than reloaded brass did, so they stopped trying to collect and reload brass altogether (they could afford new brass). I suspect the problem was a combination of things like the rim bends and the fact that brass that has come out of different chambers needs slightly different degrees of resizing and may need annealing to get more uniform resizing anyway. One advantage of setting case shoulder locations close to their as-fired location as compared to full-length resizing is greater brass life. It will work the brass less. But whether it gives you greater group precision or not is something you will have to experiment with to find out.
 
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