Bumping the shoulder back.

[Jerry45]

I’ve been reading about reloading rifle cartridges for long range shooting. The author wrights about bumping the shoulder back. I’ve always be under the impression that once a case has been fired, fire-formed, in a chamber it is intended to be used in all that should be done is neck sizing. Yah yah I know and trimming, cleaning checking for stress etc. But what I don’t understand is why would one want to bump the shoulder back or how it could be accomplished if one isn’t full-length sizing. I don’t believe full-length sizing is the best thing when it comes to seeking better accuracy from bolt guns either.

[Ideal Tool]

Hello, Jerry45. While it is true, a fire-formed case should match up to chamber dimensions..the brass has a tendency to "grow" at each shot..there will come a point where the bolt begins to become stiff in closing..the brass has flowed into neck/shoulder area. This is where a bump die comes in..not sizing body, but pushing shoulder back a few .001"' takes care of this. I have noticed this brass flow at the other end also...I use a solid carbide pocket uniformer to clean pockets..this has a built-in non-adj. stop. Even though the pockets were uniformed before loading & tool no longer cut..There is usually a few chips coming out at each firing. Best of luck!

[a7mmnut]

By the time you have to do this, chances are the neck needs turning also. It's always a good idea to check wall thickness at the neck after the first firing or two.

-7-

[Jim243]

I don’t believe full-length sizing is the best thing when it comes to seeking better accuracy from bolt guns either.

"Bolt guns either?????" What type of guns are we talking about?

Jim

[Jerry45]

Thanks for the replies guys. I knew the neck grew but thought that that was because the bullet was pulling on it while the case was is a state of flow. I didn’t realize the entire case would grow. I also remember reading somewhere that it’s a good idea to full-length size after several firings. Looks like more reading and questions are in my future and probably more sizing equipment. I’ve had a case trimmer for years and just purchased a couple of Lee neck sizing dies.

Jim, I am talking about bolt guns. 30/06 Remington action and a Savage in .223. Using “either” was a pore choice of wording on my part. What I meant was it is my understanding that full-length sizing isn’t necessary (will shorten case life) in bolt guns and can affect consistency.

[Jim243]

Jerry

Fire forming the cases and use of the Lee neck sizing dies will not require you to bump the sholder of the case. As you use the case over and over a little streach will occure and you will need to full length resize the case after about 3 to 5 uses. You then will bump the shoulder. Depending on how hot your loads are you may need to full length resize more often.

Another problem of neck sizing only is that the case (the brass) get hardened with each use and you should "anneal" the case neck at least after 3 uses, some do it after each use to keep the neck soft and workable without cracking.

Also some will check to make sure the width (thickness) of the brass at the neck is uniform and will turn the necks to make sure it is. In addition some will always check the concentric properties of the case to insure it is perfectly even all around.

The quest for accuracy is a never ending battle between the reloader and what he can do to get that extra 0.001 MOA out of his reloads.

Jim

[wncchester]

"I knew the neck grew but thought that that was because the bullet was pulling on it while the case was is a state of flow."

Case necks grow from sizing. A bullet has virtually no pulling power. Brass can be streched but never never get in a state of flow or get extruded at our normal pressures while supported by the chamber, they are much to solid for that..

[wncchester]

"I knew the neck grew but thought that that was because the bullet was pulling on it while the case was is a state of flow."

Case necks grow from sizing, not firing. Squeezing a cylinder down in diameter always makes it longer.

A bullet has insufficent pulling power to affect a case neck. We can easily seat and pull bullets as we want but the neck length won't be affected.

Brass can be streched but will never never get in a state of flow or be extruded at our normal pressures while it's supported by the chamber, it's much to solid for that. Massive over charges can extrude a case head around the bolt but won't change a neck so long as the barrel doesn't get blown apart, even then the neck will get shredded sideways but not longer.

[Jerry45]

Jim, I keep telling myself I need to anneal but can't bring myself to put the torch to the brass. I’m sure I'll get over it shortly.

Good info thanks for the help. I’m working up a load now so we’ll see how hot or not it needs to be. Since I “will” have to full-length size sooner or later the information I read about adjusting “the die” is valid and now makes sense.

Winchester: "Brass cab be streched but never never get in a state of flow or get extruded at our normal pressures while supported by the chamber.

There are people, so called “experts”, that will argue about that with you. No, I’m NO expert and I’m not arguing, don’t know enough about it. Hence my quest for truth and knowledge.

[wncchester]

"There are people, so called “experts”, that will argue about (flow) with you."

Yeah. We can get arguments from self-appointed web experts on most anything. I'm no expert either but I know some of them; they are clearly wrong on this issue at a common sense level.

The only way brass can "flow" is when it's molten or massively press extruded, as in case forming; neither condition applies to ammunition at normal pressures. In fact, what establishes the maximum safe "normal" rifle chamber pressure limit for modern cartridges is that level which is dependably too low to extrude the metal, if that weren't true we would be having blown cartridges on a regular basis.

[Jerry45]

^ That makes sense to me.

[Walkalong]

Then explain how brass gets longer when fired and then re-sized in the same die as before.

[Jerry45]

The same why a steal garbage can expands when you set off an M80 in it then is reshaped using a hammer. It would take way too long to explain the technical theory and metallurgy dynamics involved. If I had a clue what they were.

[F. Guffey]

"There are people, so called “experts”, that will argue about (flow) with you."

Finally it has been talked to death, it would not be so bad except it sounds like there are some that are just making it up. Again, I ask " Is it case stretch, or flow or is it stretch and flow?

F. Guffey

[F. Guffey]

Bumping? Bumping sounds like an accident , I place the shoulder on my cases exactly where I want them, I have presses that bump, once on the way up and again on the way down because I have a few presses that cam over, in fact I have more cam over presses than I do presses that jam, wedge and or lock up before caming over, How do I determine if a press cams over?? I use the companion tool to the press the feeler gage, my cam over presses are not bump presses, they are bump-bump presses but that would take forever to explain. Again, I use the versatile die, the full length sizer die, is full length sizes, partial body sizes with neck sizing, neck sizing with out case body sizing with the aid of the feeler gage, when preventing the die from full length sizing I adjust the die gap with the feeler gage to prevent the die from sizing by adjusting the die off the shell holder, no accident, no bump unless I use a cam over press, then I get a pump on the way up and a bump on the way down, and if I adjust the die down beyond the amount of bump I stretch the press, on the way up and on the way down without a bump.

Forming is different, when I form cases I erase the shoulder and formed it where I want it , the old neck does not move, it is still where it was before I started forming.

For those that believe the case stretches, first locate the skid mark then post pictures, and what ever it is that happens to the neck when sized,, expanded and fired just avoid trying to explain, it might be too complicated for a few on this forum.

F. Guffey

[Jerry45]

Bumping refers to moving the shoulder back a set amount; say .001 to .003, rather than letting the die (set to touch the shell holder) decide the amount to set it back. This I know because there is a tool made “specificity” for measuring it. I can’t give specifics because I haven’t learned enough about it yet. I’m researching, researching, researching. Who knows, in a couple a days I may be and “expert”. LOL!!!!!!!!!!!

[F. Guffey]

A good start would be to learn to say feeler gage, standard and transfer, the die can be adjusted with a feeler gage or a depth micrometer (dial caliper) the length of the case from the head of the case to it's shoulder can be measured with junk and a Dial caliber or 'datums' when I started posting on this form there was a 'datum line' to me it was/is a round hole, when measuring from the hole called datum the amount of money spent depends on how well the user understands Datums.

F. Guffey

[Doodlebugger45]

Heh

Yeah, F. Guffey knows what you're referring to. And then some. He has a rather unique way of expressing himself.

What he is getting at is that there is a very easy way to bump the shoulder back to an exact and repeatable amount using the full size die.

I believe you are referring to a tool such as the Hornady cartridge headspace gauge. It works fine, or you can fashion your own gauge with the proper bushing or something. Anyway, you take one of your fired cases and use that gauge along with your own calipers and get a measurement. This gives you some number that measures from the case head to a specific point on the case shoulder. Write that number down. It tells you how long the case is to the datum point on the shoulder just as it comes out of the rifle. Now, run the same case through your full-length sizing die when the die is adjusted all the way down so it touches the shell holder. Make the same measurement again with the gauge and your calipers. The difference between those numbers tells you how much sizing would be done normally using the FL sizer. But, you don't really want to size it all the way down to SAMMI specs, right? You just want to move the shoulder back by maybe 0.002" or so. Let's say for example that after FL sizing, the shoulder was bumped back by 0.013" compared to what came out of your rifle. But you only want to bump it back 0.002". So FL sizing is pushing it back 0.011" MORE than you desire. Instead of using trial and error, simply take out the 0.011" feeler gauge, put the feeler gauge on top of the shell holder, and then screw the FL sizer die down until it hits the feeler gauge and loock the ring down on thhe die. That will make a 0.011" gap between the die and the shell holder. Now run a different fired case through with FL sizer die and measure it. Presto! The shoulder will be pushed back or bumped by just 0.002".

[a7mmnut]

Guffey:

If it wasn't flow and stretch, you wouldn't get a bright ring of very thin brass left just above you belt (head spacing location) on the magnums, would you?

-7-

[Jerry45]

I was being facetious, hence the “expert” comment and the LOL! I’m quite familiar with the use of a feeler-gauge and micrometer. I understand the mechanics behind resizing however, there’s soooooo many different “opinions” of what is good and bad in terms of what affects and does not affect accuracy that I question everything. Some things are straightforward and others are oblique. For instance, I was under the impression that full-length sizing was no longer necessary once I purchased a neck-sizing die. Through the information gathered in this thread I see that it is whne and why.

Please don’t confuse my kidding around with folks as being a smart-ass I really do appreciated the responses. Some things I already know and some I don’t. It’s all good!

[Toddco]

So the question still has not been answered. if brass does not "flow" while in a rifle, how do the necks become thicker and the flash holes become smaller, etc. The thing that comes to mind is: if the brass comes out of a rifle cleanly, then why would we want to change anything except the size of the neck so it will hold a bullet again?

[amamnn]

If you are loading for a semi auto rifle then bumping (only) will not be an option; the only thing that you might be able to do like that is to buy a Redding body bump die, but I don't see any real benefit in that here except in Redding's bottom line. If you know what you are doing and your chamber is fairly tight you will set up your FL sizer for only the required amount of sizing--less is more. A Wilson case gage is a handy tool to have to guide you in setting up your die using fired cases.

But for bolt guns.............

I use a lot of Redding dies, but the best die IMHO for bushing style neck sizing which you can set to bump back your shoulder--if it needs it--is far and away the Forster. It does in one die what Redding cannot do with two. It's almost like having a custom built die for your cartridge--as long as your chamber is not something akin to Colossal Cave. Once you use the Redding body bump--you have actually done a full length sizing sans neck.

[Jim243]

if the brass comes out of a rifle cleanly, then why would we want to change anything except the size of the neck so it will hold a bullet again

The bad guy is headspace. In a perfect world your chamber would be completely sealed. Don't blame me, but it isn't, it has this big big hole at the end of it that is filled by your bolt. Well bolts are not made out of Kryptonite so live with it, but after getting pounded hundreds and hundreds of times with 30,000 lbs per square inch of preasure they tend to wear. This produces headspace out of spec, and guess where your cartrage flows (yes Virginia there is a Santa Clause and cases get hot enough to soften).

When you bump a shoulder on a case, you are adjusting it only a thousandth of an inch to bring it back into the correct demension. That's why it's called a bump and not a squeeze.

Jim