Why can't I measure shoulder bump?

[Murray Brook]

Thanks Boyd. No questions I understand your procedure. I generally use the Hornady Comparator the standard way, but this way seems fool proof.

 

[Coyotefurharvester]

Or partially seat a spent primer in a fired case( measure oal) and chamber closing the bolt completely. Measure case again, subtract difference. Add what you want for hs. Divide your die( one full turn) adjustment height by the remainder from your case measurements. Examples: .005(final case measurements) .071(amount of vertical die movement in one full turn) . Mark your press in 12 equal segments(each will equal 0.00591inches in vertical die movement). Turn die in to correct mark. Size brass test fit or measure.

 

[Dave Marshall]

Apparently I have no social life, or meaningful things to do. Most folks spend their weekends at BBQs or home maintenance or ball games, I spend my day pondering brass and taking measurements and trying to figure out what it all means. Fascinates the hell out of me. Anyways, I took 30 pieces of 3X fired Lapua 308 brass and did a little data collection. I spent some serious time with my Hornady bump gauge tool and figuring out how to use it consistently and then playing with my Redding FL bushing die to size in various increments.

Of the 30 pics, fired late last fall in my Palma gun, all of which gave .30-.40" groups off the bench, the fired length from head to shoulder datum ranged from 1.625-1.628", with the mean value being 1.626". The listed SAAMI chamber spec is 1.630-1.640", my 3X fired brass is still shorter than SAAMI.

I then used 2 different presses, a basic Lee challenger single stage and Redding T-7 turret, using the same Lee universal shell holder [mine measured .124] and screwed the Redding FL bushing die until it firmly contacted a raised ram. Both presses gave the exact same result. All 30 sized pieces of brass GREW in shoulder length by exactly .002".

Using the same two presses and shell holder, it took an additional "1/16th to 1/8th" [very very slight] die turn [past initial contact] to bump the shoulders back down the .002", to the original fired shoulder lengths. [Just as a side note, in all cases, the OAL length of the brass grew by .004-.005"].

Another interesting point, annealing made no difference in the numbers. I annealed half the batch just to compare, and the exact same .002" growth, and then .002" set back were observed. The OAL growth was also the same at .004".

I then realized thru numbers, at least for this batch, that I didn't need to be bumping shoulders at all, because even when the shoulders grew by .002", the worst case was 1.630" and that brass still easily chambered in my gun. So then I wanted to know what the chamber of my gun actually was, so I went on the hunt in my stash of brass for something long and obnoxious, and found some old once fired LC72 match in the 1.645" range. Backing the die out and running down in micro increments, I found that a 1.631" shoulder will not chamber in my gun, no way no how, but a 1.630" will chamber just fine.

What's interesting to note, the die position for achieving 1.630" with the LC72 Match was past initial shell holder contact, or slightly more "cam over" than with my Lapua brass. This makes sense to me as the brass was bigger to start with and likely took more camming force to cause the same amount of brass engagement into the die body.

All this raises more questions though, and I am anxious to discover more details.

• Is all brass created shorter than SAAMI initially?
• Is there a better way to measure chamber dimensions outside of chamber casting or incremental sizing of brass?
• At what rate does brass spring back or shrink happen?
• There are many different reamers/brands for the same cartridges, how different are the dimensions?

I am anxious to try some of this process again with freshly fired brass or a different cartridge & gun to see if the incremental measurements are similar.

My initial conclusion is this, the overall process is extremely repeatable, and even my cheap tools can give very consistent results. I made some very poor "universal" numerical assumptions that I proved wrong thru a little data collection. [Just because brass is fired in your gun, don't assume that's your chamber dimension]. I think the takeaway here is that obviously every gun, brass, press, die, shell holder is NOT the same, and everybody's process by default must be a little different to achieve the same [or proper] result. Each individuals process is likely different for each cartridge they load for as well. If a person takes the time to do some measuring of what is actually happening with their tools and what works in the specific firearm, I think the whole process can be very precise and repeatable. I demounted and remounted all my tools into multiple presses, even removed and remounted my Hornady bump gauge, and I was able to repeat every measurement I took. This activity sure helped ease some of my questions & concerns, but also taught me that I need to pay a little closer attention to initial measurements, die setting and record keeping.

I hope this post was helpful. Not meant to stir the pot, just sharing my findings.

Are you using an expander ball on your decapping stem when you resize your brass?

At one time, I decided I wanted to try using expanders to fine tune neck tension. The brass I was sizing (6xc) had been fired a few times and had developed donuts in the neck/shoulder junction. As the case was withdrawn from the neck bushing on the press downstroke, the expander ball produced enough drag to stretch the shoulders slightly and take a few degrees out of the shoulder angle. I figured this out after I had sized about 1500 cases, lol. I felt like quite the dummy. I gave up on the expander idea as I absolutely refuse to neck turn that much brass. I removed the expander and bumped the shoulders again. Most of the cases feed and fire just fine.

One thing I will mention is that Lapua brass seems to be a bit harder to anneal than other makers. It takes a little more time in the flame to get a consistent result. I would bet after three firings your .308 brass is pretty hard and would expect more spring back after sizing. I also wouldn’t bother using the Lee press for the kind of precision you’re trying to achieve.

 

[fatelvis]

Not to hijack the thread, but I thought this might be of interest and importance to those here.
In regards to cam over, I had a discussion with the engineer from Redding (he was that week’s guest) on The handloader podcast. He flat out told me that the T-7 press was designed expressively for cam over use. That put my mind to ease, because I always felt I was damaging the press by camming over.

 

[searcher]

My dies don’t touch my shell holder. I get EXTREMELY repeatable bump, and runout numbers less than .001”, to the point I stopped checking. I don’t measure bump with a comparator on a caliper either (good for +/-.002”). I use a fixture with a dial indicator.

Maybe the dial indicator on your setup is stuck in one position? (Just kidding). I have multiple presses, including some really nice gear like the Bruno D press. I will do runs of hundreds to thousands of pieces at a time in various calibers. I do not use dies that require camming over to set shoulders where needed. I have never once gone through a run of brass and ended up with variation of under .001" on the run. I'm pretty amazed your brass has no memory and your press no runout. I'm envious.

 

[Tokay444]

Maybe the dial indicator on your setup is stuck in one position? (Just kidding). I have multiple presses, including some really nice gear like the Bruno D press. I will do runs of hundreds to thousands of pieces at a time in various calibers. I do not use dies that require camming over to set shoulders where needed. I have never once gone through a run of brass and ended up with variation of under .001" on the run. I'm pretty amazed your brass has no memory and your press no runout. I'm envious.

I generally process my brass 100 pcs at a time. Sometimes less, but not more, and I follow the exact same method every time.
Deprime.
Anneal.
Wet tumble. (With or without pins. Lately without)
Chamfer.
Lube.
Body size/shoulder bump.
Neck size.
Dry tumble to clean lube.
Mandrel.
Prime.
Charge.
Seat.
This has been my regiment over 15 firings so far of Lapua 6.5 Creedmoor SRP brass, and 20 firings of Alpha 6.5 Creedmoor SRP brass before that, and 10 firings of Alpha 6.5 Creedmoor LRP brass before that. I made and learned from my mistakes in charge weights and speed chasing in the LRP Alpha brass.
You’ll notice I don’t trim either. I don’t need to. My brass never grows. It did when I thought I could save some time switching to a Mighty Armory Gold Match die, but having to trim ended up cancelling out the time savings of eliminating three press operations, and that die caused me to have shoulder sooting issues I could never get to the bottom of, so I’ve switched back to the above method.
I’m waiting on a 6BR barrel and I have about 350 pcs of brass lined up for it, so my batch sizes are slated to increase. I hope to observe the same consistency.

 

[divingin]

One thing that I feel contributes greatly to inconsistency in sizing is press stretch. Or rather press stretch and case lube.

As you stuff a case into the sizing die, the force causes the press frame to stretch (this is why the manufacturers say to screw the die in to touch the shellplate, lower the ram, and screw in a bit more. This assures contact at the top of the ram stroke, which we've already determined can be a bad idea depending on your setup.) If you are trying to size to specific amount of setback (rather than the max amount possible, as would happen with full contact between die and shellplate), and your cases exhibit differing resistance to sizing (I'll use inconsistent lube as the cause, as you can't do much about cases that are blown out differently), the amount of stretch the press exhibits will change, and so will your results.

If you do have cases that are fired to substantially different body diameters, it may help to approach your final measurements in one step, relube and set the final dimension in a second sizing. You'll have more consistent force on the press when trying to fine tune the brass.

 

[6MMsteve]

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 never cam over and get very good bumpin or readings on my peterson 6xc brass no more than .0002 diff actually I have never cammmmed a press...but my headspace is set tight always

 

[6MMsteve]

Never understood camming over. Doesn't make sense to me. You can only shove the case so far into the die?

never have cammed one myself..maybe I'm missin sumthin

 

[BoydAllen]

Not to hijack the thread, but I thought this might be of interest and importance to those here.
In regards to cam over, I had a discussion with the engineer from Redding (he was that week’s guest) on The handloader podcast. He flat out told me that the T-7 press was designed expressively for cam over use. That put my mind to ease, because I always felt I was damaging the press by camming over.

There is cam over, and then there is CAM OVER. I would say that the latter really gets you nothing more than the former. Back in my neanderthal years, I actually mushroomed the bottom of the sliding piece of a collet die with my rock chucker. I remind my self of those kinds of mistakes from time to time when I am helping beginners. The first thing that I teach them about setting up a FL die is to ignore any mfg. instruction that tells them to screw it down untill it touches the shell holder and then lower the ram and turn it an additional quarter turn. I have even seen this jackassery on YouTube. A little cam over will make bump more uniform if you can get there with the correct bump. If you have more than that IMO it is time to do a little work on the shell holder.

 

[skeeljc]

If you are sizing with a gap between the shell holder and the die the headspace will change depending on how much force it takes to size the case (the press deflects under load). I like setting the die so it contacts the shell holder with some force (near equal to the force required to size) and use Redding competition shell holders to vary the shoulder bump. This works with presses that cam over and those that have a stop. If the die and the shell holder remain in contact at the end of the sizing the results will be consistent.

 

[Tokay444]

Yeah, like I said above, I have extremely consistent results, without all that. Seems others do as well, so I don’t know who’s telling who what, but my experience tells me all I need to know.

 

[CA_Shooter]

What is a good shoulder bump variation? +/- .0005 (for example 1.5425 to 1.5435)? +/- .001 (for example 1.5415 to 1.5435)?

 

[Richard Coody]

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.

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...

nothing wrong with that technique. Your rifles chamber is the best chamber gauge you can have..

from what I have read on this thread your brass is not fully fireformed. If a piece of fired brass chambers easily its not fireformed. Just set your full length die up to size the neck and not touch the shoulder load and shoot. When you get a piece of fired brass that chambers tight then measure base to shoulder datum with your comparator. Then slowly thread the die in in tiny increments, you will feel resistance when you get to the shoulder, and size and measure again. It is easy to overdo it at this point. Tiny die movements make large changes in the shoulder bump. Might take 2 or 3 pieces of brass before you get that die adjusted for 1 or 2 thousandth bump. Then chamber that piece of brass. If it chambers easily then lock that die down and don't mess with it any more.

As for consistent shoulder bump as your brass work hardens from the firing/sizing cycle your bump will become more difficult to maintain consistency. My experience is annealing cures this problem. Otherwise as your brass ages you are going to be chasing that bump.

 

[ronemus]

What is a good shoulder bump variation? +/- .0005 (for example 1.5425 to 1.5435)? +/- .001 (for example 1.5415 to 1.5435)?

With the process I spelled out in an earlier post, I can get bump variation of +/-0.0005, and that's my goal. I start looking for problems if I see more variation. Note that's for one lot of brass, fired the same number of times in one rifle.

 

[Uncle Ed]

257Roberts

Pausing at the top of the ram stroke for 4 or 5 seconds will make the shoulder location more uniform.

If any sizing lube is forced/squeezed upward to the shoulder of the die the shoulder location will "NOT" be uniform.

The reloading manuals tell you after lubing the cases to wipe the shoulder and neck off.

Whatever happens, do "NOT" go to another reloading forum and ask F. Guffey........
"Why can't I measure shoulder bump". (it might make you go insane)

​

Inconsistent headspace?​

• Thread starterJohn Rambo
• Start dateJan 13, 2018

https://forum.accurateshooter.com/threads/inconsistent-headspace.3942700/page-2

 

[Metal God]

Never understood camming over. Doesn't make sense to me. You can only shove the case so far into the die?

To be honest , I did not read all 5 pages hope this is still relevant .

It's not about pushing the case farther into the case , it's about taking the flex out of the press .

This is a pic of a Hornady press and the die and shell holder touching when the ram if fully up with NO case in the die . Note no gap between the die and shell holder .

This pic is of the same die setting but this time the ram is fully up while sizing a case . Note there is now a gap between the die and shell holder .

When you put a load on/into the press like what happens when sizing a case that load results in press and linkage deflection . This is often what is happening when someone says they can't bump there shoulders enough . They believe when there die and shell holder are touching on initial set up . They are also touching when they size there cases and they often are not . This results in those inconsistent shoulder bumps .

If they screwed the die down another 1/4-ish turn they would get full cam over where the die and shell holder stay in contact with one another through cam over . This will result in a much more consistently sized case ( head to datum ) . The problem with real/full cam over ( firm contact between die and shell holder ) with a "standard" shell holder ( deck height .125 ) is this often sizes the case ( bumps the shoulder back ) further then the .001 or .002 we usually want .

Press deflection is caused by several factors - how work hardened the case/shoulder is , lube used , quality/strength of press . Your cases will resist there sizing causing the press to deflect more or less depending on those factors . I believe one poster said they fixed there inconsistent sizing by annealing there cases . This is one way that can help solve the problem because the softer neck and shoulder resist sizing less resulting in less press deflection and less case spring back .

Although annealing is a method that can help solve the inconsistent sizing problem . It's a costly one ( price of the annealing machine ) that also takes up a good bit of time and energy to do so . I do anneal my cases but not after every firing ( I'm not shooting long range comp ) I don't feel the need . Rather I anneal every 4th firing or so . This causes my cases to not only get work hardened but work hardened quite inconsistently . This results in some cases resisting there sizing more then others .

Ok no problem I just screw the die down to make hard contact with the shell holder and I should be gtg right - WRONG . My issue and most of us is that we often only want to bump the shoulders a couple thousandths . The problem is having hard contact between the die and shell holder sizes the case ( head to datum ) to much . So to get the proper bump you need to back the die out a bit but when you do we reintroduce all that case resistance , press deflection and spring back again .

That's where the Redding competition shell holders come into play . There deck heights get deeper by .002 incrementally through a set of five shell holders . Meaning the Redding standard shell holders deck height is .125 the the first comp shell holder deck height is .127 the next is .129 , next .131 etc etc . This allows you to have hard/full contact between the die and shell holder while being able to size your cases longer ( head to datum ) in .002 increments . This removes all the press deflection problems and results in very consistently sized cases even after several firings .

How cool or useful are the Redding competition shell holders . With out getting into exact numbers . I reload for many multiples of rifles in the same caliber/cartridge . Many of which need the cases sized different ( head to datum ) then the others . In the 7 or so years I've been using the comp shell holders I've never needed to adjust my die to accommodate for a different rifle . I simply use the comp shell holder that gets me the bump I need . Which is much quicker with less fuss then annealing every time .

Hope that helps
MG

 

[JFrank]

In a perfect world wouldn't a die be exactly .125 shorter than your SAMMI chamber?

Aren't SAMMI chamber specs + - .004 ?

How often are chambers a perfect match to a die?

How shall I measure cam over in thousandths?

How many thousandths difference between hard cam over and a complete cycle?

Almost every press i look at has slightly different linkage, how shall I know which one is a cam over press ?

 

[cw308]

Metal
Great Post, makes perfect sense. I use the same system . Hope Things are going well.
Chris

 

[Coyotefurharvester]

MG, I learned something today, thank you. One question can the competition sh be used with other brands of dies(rcbs,Hornady) ? Oh, 2 things learned today, thanks out to Tokay also, I can see a slight change in my procedure could eliminate the occasional need to trim.