Why can't I measure shoulder bump?

[257Roberts]

Years ago I used to adjust my FL dies down just enough that my brass would chamber in the rifle. I may have to go back to this...
I apologize upfront for beating the dead horse, but frankly, I am baffled at the moment.

I've been working on my 6.5 Creedmoor & 6.5x284 brass for my NRA match rifles. Both have brand new barrels installed by one of the best in the game. My brass is now all once fired from last season. So I dug out my Hornady shoulder bump set once and thought I would try and bump down a quantifiable amount, .001-.002 inches.

I started out by measuring my fired brass, and right off the bat I suspected a problem. I am measuring up to .002 variability in fired cases to the datum line. Hornady digital caliper, Hornady bump gauges, different size gauge for each cartridge of course. Same variability across the board, regardless of cartridge.

I then went thru the process of backing the FL bushing die back from the shell holder one full turn, then working down in 1/8-1/4 turn increments and trying to measure a difference. Even with my FL die all the way down on the shell holder, I can maybe [and I emphasize MAYBE] measure .001 difference from a fired case. In my investigative readings, a die screwed full down should maybe bump the shoulder .004-.007 inches, is that a fair statement?

So I have to ask, what the heck am I doing wrong?

I use Lee shell holders, and Redding Bushing Dies, I realize that's kind of like pairing a Cadillac and a Nissan. Only set of shell holders I've ever owned. I ALWAYS use the same specific shell holder for each specific cartridge. But now I am questioning the specs of the Lee shell holders?

• Maybe they are "tall" and limiting shoulder bump [limiting die adjustment too far down]? Maybe the .001 I see if right...
• Or is the Hornady aluminum shoulder gauge set junk? Maybe I just can't measure what's happening?

Either way, I can, and maybe should go back to the old way of just sizing enough so the brass chambers, but it sure would be nice to quantify that and record it. In these new times of components scarcity, its prudent to reevaluate ones process to optimize usage life.

Thanks for all the assistance. The one good thing COVID has done is give me more time to work on my shooting, rifles, reloading and dig deep back into long range shooting.

 

[tobnpr]

Even with my FL die all the way down on the shell holder, I can maybe [and I emphasize MAYBE] measure .001 difference from a fired case.

I use a Hornady progressive press, and single-load with it.
Screwing the die down until it contacts the shellplate does not provide the maximum achievable "bump".
More often than not, I need to go well past "contact"- so that all of the slack is taken out of the linkages, and this causes the press to cam over "hard". Easily gets several thousandths more bump on a case.

Keep in mind, that dies are manufactured with liability in mind- if it were possible to oversize brass with them, resulting in failures- they'd have big problems. In rare circumstances, it may be necessary to grind the bottom of the die, but I've never had to do that.

You didn't specify what press you're using- but give it a try- screw the die in until it contacts, lower the shellplate, screw the die in an additional 1/2 turn. Then size and measure- you'll see a difference.

 

[bugman]

You never mention if the fired brass will prevent a bolt (sans FP assembly and ejector)from falling . IOW, you never mention that you confirmed that this fireformed brass was sufficiently blown out to even register a shoulder bump. Many times a too-weak fireform charge will also give the inconsistent headspace dimensions you mentioned. If the brass is significantly not blown out, all the sizing in the world won't change the headspace dimension until you get to camming the press on the shell holder. Check the deprimed fired brass in your rifle with a bare bolt.

 

[JFrank]

Once fired brass from last season may not be fully fire formed yet. Perhaps still growing in length and not consistent.
I don't do the 1/4 turn beyond touch thing to adjust the die I measure in thousandths down to contact then transfer to measure cam over if necessary.
Too much cam over IMO can stress the press linkage, I have one die with .022 cam over that is ear marked for milling when I get around to it.

 

[CharlieNC]

Your description of this problem is common one, and something I contemplated when I started loading ten years ago. Trying to uniformly bump a set of brass which exhibits a variable HS, and not knowing how it actually relates to the chamber did not make sense. Upon researching this I read a simple answer. Do not resize a fired brass, remove the primer, and partially install a new primer. Chamber this and close the bolt to finish seating the primer. Remove and measure with your comparator as the "zero" headspace dimension; then set your FL die to size .002 ( or as desired ) shorter than this. This two minute exercise will provide the proper information to save you a lot of grief.

 

[Dave Marshall]

How close to zero are your chambers cut? If they are cut close to zero, you may need to modify your dies or shell holder in order to size your brass a little shorter.
Sizing dies meant to resize brass fired in generous factory chambers may not be the right tool for what you have. If your dies, when screwed down to the shell holder, size to zero and you’re already at zero with your fired case, then they aren’t going to do much sizing at all. I suspect your chambers are cut closer to zero than you think.

I would also fully expect several thousandths variance in headspace for brass that has not been annealed and to account for measuring error with less than precision tools. Calipers are not precision measuring tools.

 

[MagnumManiac]

Here are the facts. Camming over is the ONLY way to get consistent shoulder bump...and no, it doesn’t ‘stress’ the linkage, it’s designed to do this.
When Partial FL sizing, aka shoulder bumping, with the brass all the way up in the die, if there is a gap between the bottom of the die and shell holder, then FL sizing is NOT happening.
Just because the die touches the shell holder without the brass present means diddly squat. The brass resists the sizing and without cam over the linkage WILL NOT overcome this due to the linkage slack.
If you have a press that doesn’t cam over, like a Lee, then you need to use a feeler gauge under the case head in the shell holder. A .010” normally overcomes most issues.
With a cam over press, once touching, screw the die IN 1/12 turn, size a case, measure and repeat until you get the desired bump.

Cheers.

 

[fatelvis]

I started out by measuring my fired brass, and right off the bat I suspected a problem. I am measuring up to .002 variability in fired cases to the datum line. Hornady digital caliper, Hornady bump gauges, different size gauge for each cartridge of course. Same variability across the board, regardless of cartridge

Varying by about .002" between fired cases is totally normal until they are fired a couple to a few times. They have not fully expanded to conform to your chamber's dimensions.

I then went thru the process of backing the FL bushing die back from the shell holder one full turn, then working down in 1/8-1/4 turn increments and trying to measure a difference. Even with my FL die all the way down on the shell holder, I can maybe [and I emphasize MAYBE] measure .001 difference from a fired case. In my investigative readings, a die screwed full down should maybe bump the shoulder .004-.007 inches, is that a fair statement?

Sometimes you need to grind some steel off THE TOP of the shellholder, so the sizing die can overbump a shoulder, if not careful. This allows you to adjust your die down, and bump the shoulder between the desired .001"-.003" amount.

Forum Boss: This is correct, but you can also try different brands of shell holders and you may not have to grind. I have Redding, Lee, RCBS.

 

[358WCF]

Here are the facts. Camming over is the ONLY way to get consistent shoulder bump...and no, it doesn’t ‘stress’ the linkage, it’s designed to do this.
When Partial FL sizing, aka shoulder bumping, with the brass all the way up in the die, if there is a gap between the bottom of the die and shell holder, then FL sizing is NOT happening.
Just because the die touches the shell holder without the brass present means diddly squat. The brass resists the sizing and without cam over the linkage WILL NOT overcome this due to the linkage slack.
If you have a press that doesn’t cam over, like a Lee, then you need to use a feeler gauge under the case head in the shell holder. A .010” normally overcomes most issues.
With a cam over press, once touching, screw the die IN 1/12 turn, size a case, measure and repeat until you get the desired bump.

Cheers.

I'm unsure how you can be so absolute about your statement. Dies & chambers differ. Think about a minimum die/Maximum chamber scenario... or the other way around. Back when I had the shop, a buddy who was starting to shoot a 308 in NRA hi-power matches stopped by looking for a set of dies to better fit his chamber. We checked every 308 FL die in the shop & my personal sets as well. If memory is right it was 6 or 7 different dies from 3 manufacturers. Not one measured the same.

When I was still using a threaded press, if the die didn't need to touch the shellholder something/anything was used on top of the ram to raise the die snugly into the threads while tightening the lock ring. This really seemed to help with sizing induced runout on the few cases that were checked.

 

[BoydAllen]

Here are the facts. Camming over is the ONLY way to get consistent shoulder bump...and no, it doesn’t ‘stress’ the linkage, it’s designed to do this.
When Partial FL sizing, aka shoulder bumping, with the brass all the way up in the die, if there is a gap between the bottom of the die and shell holder, then FL sizing is NOT happening.
Just because the die touches the shell holder without the brass present means diddly squat. The brass resists the sizing and without cam over the linkage WILL NOT overcome this due to the linkage slack.
If you have a press that doesn’t cam over, like a Lee, then you need to use a feeler gauge under the case head in the shell holder. A .010” normally overcomes most issues.
With a cam over press, once touching, screw the die IN 1/12 turn, size a case, measure and repeat until you get the desired bump.

Cheers.

I disagree with so much of this that it would be hard to know where to start. Instead I will relate a relevant experience. A friend was experiencing inconsistent shoulder bump using good dies and a Forster press. We were able to adjust a two torch rotary annealer to produce brass that bumped to a total variance of .001 (plus or minus half that) while retaining enough neck hardness for magazine feeding rounds loaded with heavy bullets. The calibers were .338 Lapua and 7mm WSM. For my PPC I am able to get very consistent shoulder bump without camming over, as well as for my .222 Rem. bench and varmint rifles.

On of the problems that I have see is fellows trying to bump cases that have not grown (shoulder to head) long enough to need it. I have been able to come up with a way to make an accurate die bump adjustment based on once fired brass.

 

[Uncle Ed]

My guess is your die and chamber are a very close match and full length resizing is not squeezing the case body and moving the shoulder upward. Look at the image below, the more the die reduces the case body diameter the more the case shoulder is squeezed upward in the die.

How much does sizing the case reduce its body diameter? How much longer is the case OAL after sizing?

1. Take one of your sized cases and measure it from the case mouth to its base and write it down.

2. Take a fired spent primer and just using finger pressure start the primer into the primer pocket.

3. Now chamber the case and let the bolt face seat the primer and eject the case.

4. now measure the case again from the base of the primer to the case mouth and write it down.

5. Now subtract the first measurement from the second and this is your head clearance or how much shorter the case is from chamber headspace.

 

[257Roberts]

Lots of feedback here, I appreciate it. I use a T-7 turret press, and I agree that there is tool head flex when sizing. However in this case, I did have the die screwed much further down to ensure solid 0 gap shell holder contact and the brass fully inserted in the die, and that is really the source of my question. This brass is once fired, Lapua and Gunwerks [ADG]. They are not weak loads by any means [2775fps 147gr Creedmoor and 2950fps 150gr 6.5x284], but I agree that maybe the brass hasn't stretched enough to matter yet. The barrels where all chambered by Whidden Gunworks, Johns reputation needs no explanation. I assume they are very tight close to zero dimension chambers.

I have 308 left to do. This is an older used barrel. This is maybe 3 times fired Lapua brass, and I will anneal it first. I am anxious to try the process again, and I will use my Lee single stage. I am very curious to see if I can get bump before contact with the shell holder.

I will report my findings on this thread.

 

[FIREPHOTO798]

I agree with fatelvis (forum boss comment) about different shell holders. I had the same problem with a 280 Rem. I needed another couple of thousandths on the shoulder bump. Started measuring shell holder depth on several brands between the rim face and the top face of the holder. Found +/- .004 variation, even on the same brand. Picked one that was the thinnest and the problem was solved. I gained about .003 on the shoulder bump.

 

[Coyotefurharvester]

One of the biggest brass sizing problems I ever had, when I got my 7saum in early 2000's. Needed a die set, found a Redding, had a RCBS shell holder. From the start I had I couldn't move the shoulder, happen to stop at a store and saw the correct Redding sh. No issues since, always able to size enough so field stripped bolt falls closed on brass for hunting.

 

[BoydAllen]

Here is my standard advice/procedure for settig up a FL die when I am forced to work with once fired brass. Adjust the die so that the shoulder to head dimension is exactly the same as the once fired case (measured with primer removed) and try it in the rifle with the striker assembly removed from the bolt. If the case goes in easily, you do not need to worry about bumping shoulders. Memorize this: The only reason to bump shoulders is to create clearance WHEN WE NEED IT.
I have a fancier method is someone is interested but this should suffice for most.

 

[B2Lee]

And I'll go a different direction. The Stoney Point/Hornady comparator gauges are useless junk. Get yourself a set from Short Action Customs. With the correct shoulder angle you are measuring at the point that is important...not some arbitrary distance somewhere close. I suffered for years trying to get my neck bump back set correctly. Once I bought a SAC comparator body for my Mitutoyo's....I found happiness. I can now truly measure what I've been trying to measure with failure.

Also, I anneal EVERY TIME....my shoulders are bumped back 2thou with the occasional 2.5thou. Life is good now. Also, and I know many will argue...but I've done the experiment several times. Deviation in anneal time can create different should bump backs from the same die setting...from one piece to the very next. An AMP annealer will remedy this situation. I can flame anneal and be off just a bit...and feel while sizing whether the piece of brass will be long, short...or just right. With the AMP...they are all....just right.

 

[K22]

1. First issue: Lee shell holders & Redding Dies - unless Lee changed the design, the ones I have are not compatible with Redding or RCBC dies - they're too thin.

2. Second issue - With my cases and press, unless I have some cam over of the ram I cannot size the case even to zero case head space - the case will extrude and lengthen. Granted my press is 50 years old and has some play in it but unless the die touches the shoulder of the case, the case will lengthen most of the time.

3. Third issue - As some one else said, the only reason to size at all is so the case will chamber without force and the neck is sized to hold a bullet. There is nothing magically about a .001 to .002" shoulder bump. The rifle chamber is the ultimate gauge to access the adequacy of sizing. I have a 223 Rem with a Douglas match barrel which I need only a zero shoulder bump to obtain optimum chambering. You might say - well why not just neck size. Because FL die also sizes the case radially which improves chambering. Bottom line - While the standard .001 to .002" bump is a good target sizing standard for bolt rifles, the final criteria is rifle chamber.

4. Fourth issue - I'm sure most get good results with the Hornady tool. I don't like them because they have an interface between the insert and holder. Usage can be improved by placing match marks on the insert and holder to assure the same alignment from reloading session to reloading session if the tool is disassemble and reassembled. Also check for squareness of the holder against the caliper. I prefer the Whidden, one piece gauges, since it has no inserts and is caliber group specific.

5. Fifth issue - to obtain consistent measurements with a bump gauge and caliper you have to develop and consistent technique of pressure against the case and rotating the case to assure and seating and alignment with the gauge and jaw of the caliper before taking a reading.

 

[BoydAllen]

I have had a Stoney Point tool with bullet and shoulder inserts since they first came out, and I have had no problem getting consistent results.....but in the course of helping others I have come to the conclusion that some bright people have trouble doing things that are simple for me. (more than 20 years experience these attachments may have something to to with that.) Recently, after he struggled with the Hornady tool, I had one fellow buy the Davidson setup which has two parts that mount on a caliper, one for the bullet ogive and the other for the case head. The tool is built so that when they are mounted they align with each other. Problem solved.

 

[ronemus]

1. First issue: Lee shell holders & Redding Dies - unless Lee changed the design, the ones I have are not compatible with Redding or RCBC dies - they're too thin.

+1 There is no standard for shellholders, and each manufacturer is free to make them as they please; usually a manufacturer will be consistent over time, but even that is not guaranteed.. In order to get cases sized properly, you usually need to use the same brand of shellholder and die. You can mix and match, but as you have found, you may not get the desired result. There is a clue in the fact that manufacturers don't use the same numbering system for shellholders.

I am able to get good results with my Stoney Point/Hornady headspace gauge, but it does have its limitations. The best results can be obtained by using a barrel stub cut with the same reamer as the chamber; however, most of us don't find it necessary to do so. You need to find a method that works for you.

 

[JFrank]

All of mine are .125