Shoulder bump, how much is too much ?

[K22]

Here's what I do. (Bolt rifles only)

Using virgin cases after once fired, I do not bump the shoulders. I set the F/L die to zero bump (without extruding the case) for the case with the longest case headspace assuming this case chambers without issue and those always do with my rifles. Eventually after a few firings all the cases develop a relatively uniform case head space.

Often, I can go several cycles before I have to bump the shoulders. I believe the reason is that the F/L die also sizes the radial dimension of the case and often that is all that is necessary for several cycles. Bumping is a corrective procedure to restore, if needed, chambering.

Using a quality bump gauge and caliper you can easily monitor case head space, and it will tell you when you need to bump the shoulder along with a quick check in the rifle chamber.

As someone else mentioned, measuring cases with a bump gauge requires some experience and technique to obtain consistent results. Have you tested your technique by repeated measurement of some sample cases?

I have seen errors with the Hornaday tool because if you don't match up the insert with the gauge holder and caliper the same every time, you can obtain inconsistent results, granted only a few thousands but that is still undesirable. For this reason, I used the Whidden single piece, caliber group specific bump gauge permanently mounted on a dedicated caliber. This significantly increased consistency of my measurements.

 

[Old Navy]

Using my Hornady headspace tool to measure 5.56 Starline shows a number of 1.4500” to the datum line. Same number on a .223 Go gauge.

1x fired in a .223 FTR chambered barrel shows 1.4520” so a fairly tight chamber.

Brass annealed and sized with target of 1.4510”. Most are coming out 1.4500”-1.4520” range.

But for some reason I have yet to figure out, I have been getting some that are sized down shorter in the batch. These are 1.4400-1.4440”. 6-10 thou under sized from the min spec.

These are getting light primer strikes and “Click no boom” ftf.

I presume this is because it is only 1x fired in this chamber and different softness is having less spring back from the die.

I am going to go through the bolt and change the striker spring and check firing pin protrusion and try the rounds in another rifle but wanted to ask before I go down that rabbit hole….

How much below the 1.450” is too short ?

Are you adjusting your die for a cam over?

 

[jelenko]

Jeff - Just to confirm, have you measured a good sample [say 25] of the once fired cases? As Webster mentioned, I'm wondering if some of the new cases were shorter than others and didn't fully expand in the first firing.

 

[Jeff Porter]

Jeff - Just to confirm, have you measured a good sample [say 25] of the once fired cases? As Webster mentioned, I'm wondering if some of the new cases were shorter than others and didn't fully expand in the first firing.

Yes. I actually measured a bunch with the Hornady tool and a new PMA digital bump gauge. I got more consistent results with the caliper. I’ll post the spreadsheet later.

 

[Jeff Porter]

Are you adjusting your die for a cam over?

Yes. Cam over and a 5 count of dwell held down.

 

[Bill Norris]

Yes. Cam over and a 5 count of dwell held down.

Consistently pushing the press handle down smoothly and bottoming out the stroke without hard bumps and allowing dwell time really was the answer for good even shoulder bump for all of my different cases. It does help to keep the sizing wax off the shoulders as well. Almost in every case with new brass the die adjustment will need to be tweaked once the cases have been fired two or more times.

 

[Old Navy]

This is just my opinion. I think the 330 bushing sucks. Mine measures too far down on the shoulder body junction to get a repeatable measurement. If I were reloading for a precision bolt gun I would buy a 240 and have my son bore it out.

 

[Chilly807]

This is just my opinion. I think the 330 bushing sucks. Mine measures too far down on the shoulder body junction to get a repeatable measurement. If I were reloading for a precision bolt gun I would buy a 240 and have my son bore it out.

You're not wrong about the 330 bushing being on the big side of ideal for a 223. I was thinking the same thing a few days ago, measuring some Lake City brass with somewhat rounded shoulders.

I seem to recall Hornady saying that if your cartridge isn't one of the ones they have a recommended bushing for, to subtract the neck diameter from the body diameter (measured close to the shoulder/body junction on a tapered case), divide by 2, then add the result to the neck diameter. Use the closest bushing to that size for best results.

So for a 223 case, the body measures .356", and the neck measures .255", subtract and you get .101". Divide that by 2 gives you .0505". Add that to .255" and you have .3055", which is exactly halfway up the shoulder between the neck and the body. Makes sense. Call it .306".

.330" is 24 thou bigger than ideal, which on a sharply angled shoulder is quite a bit. I just checked my 30 cal bushing, it measures about .298" inside, which is on the other side of ideal.

I have a "27" bushing that I'm unlikely to ever use, and a lathe I have the use of.
I think that tomorrow, one of two things is going to happen. I'll either build a new bushing from scratch if I have the time, or I'll bore the "27" bushing out to .306" and try that. It'll definitely be better than the .330" I'm using now.

 

[Dave M.]

Using my Hornady headspace tool to measure 5.56 Starline shows a number of 1.4500” to the datum line. Same number on a .223 Go gauge.

1x fired in a .223 FTR chambered barrel shows 1.4520” so a fairly tight chamber.

Brass annealed and sized with target of 1.4510”. Most are coming out 1.4500”-1.4520” range.

But for some reason I have yet to figure out, I have been getting some that are sized down shorter in the batch. These are 1.4400-1.4440”. 6-10 thou under sized from the min spec.

These are getting light primer strikes and “Click no boom” ftf.

I presume this is because it is only 1x fired in this chamber and different softness is having less spring back from the die.

I am going to go through the bolt and change the striker spring and check firing pin protrusion and try the rounds in another rifle but wanted to ask before I go down that rabbit hole….

How much below the 1.450” is too short ?

Often times new .284 brass will measure .008-.010” shorter than after I fire it 2-3 times; and honestly I’ve shot some ridiculous matches using only new brass. It can be super accurate and very competitive.
Dave

 

[Webster]

Using my Hornady headspace tool to measure 5.56 Starline shows a number of 1.4500” to the datum line. Same number on a .223 Go gauge.

1x fired in a .223 FTR chambered barrel shows 1.4520” so a fairly tight chamber.

Brass annealed and sized with target of 1.4510”. Most are coming out 1.4500”-1.4520” range.

But for some reason I have yet to figure out, I have been getting some that are sized down shorter in the batch. These are 1.4400-1.4440”. 6-10 thou under sized from the min spec.

These are getting light primer strikes and “Click no boom” ftf.

I presume this is because it is only 1x fired in this chamber and different softness is having less spring back from the die.

I am going to go through the bolt and change the striker spring and check firing pin protrusion and try the rounds in another rifle but wanted to ask before I go down that rabbit hole….

How much below the 1.450” is too short ?

The bolt FP, spring and protrusion have nothing to do with your problem.

 

[Webster]

That is what I am asking too. How can the same die setting give 0.010” different bumps. Current suspects are lube on the shoulder and different metallurgical properties of the Starline 5.56. The batch is all 1x fired in the same gun but was from two different purchases of the brass. ( different manufacturing lots ).

I notes that to get the 0.0015 set back I was needing to count to 5 (dwell time with press ram down) and would get consistent results. My theory is some of the brass was softer and didn’t spring back after being compressed.

Interesting that holding in the die for 5 seconds seems to fix the problem. This should eliminate thinking the FP, spring or protrusion is a problem. Don't waste money on the bolt. You have a problem no-one else has ever had so it’s hard to resolve. Cannot believe you have 10 thou springback.

I think you mentioned using a different bump gauge you got different results. Is it possible your measurements are all bogus? I use a simple Aluminum gauge from John Whidden attached to a digital caliper. Very simple. Always gives good numbers. The diameter in the hole in the bump gauge will determine the actual reading. They are supposed to be made with a datum point half way up the shoulder. It isn't a requirement. In any case your looking for the difference as fired and sized regardless of what the number is.

I tried to find engineering data on springback. All I could find was springback on forming aluminum sheet metal. If you made a 45 degree bend on Al in a metal brake press it takes about 2 minutes to get measurable spring back.

You must be doing something we don’t know about? If holding 5 seconds in the die solves the problem keep doing it. The problem has nothing to do with primers. Seat them to the bottom of the pocket.

 

[Straightshooter1]

Using my Hornady headspace tool to measure 5.56 Starline shows a number of 1.4500” to the datum line. Same number on a .223 Go gauge.

1x fired in a .223 FTR chambered barrel shows 1.4520” so a fairly tight chamber.

Brass annealed and sized with target of 1.4510”. Most are coming out 1.4500”-1.4520” range.

But for some reason I have yet to figure out, I have been getting some that are sized down shorter in the batch. These are 1.4400-1.4440”. 6-10 thou under sized from the min spec.

These are getting light primer strikes and “Click no boom” ftf.

I presume this is because it is only 1x fired in this chamber and different softness is having less spring back from the die.

I am going to go through the bolt and change the striker spring and check firing pin protrusion and try the rounds in another rifle but wanted to ask before I go down that rabbit hole….

How much below the 1.450” is too short ?

IMHO. . . your fired brass coming out at 1.452" or a little less, I think sizing anything less than 1.448 is too much, as that can easily cause premature failure when repeated . . . depending of the particular brass you're using. I'm certain those cases that are .006 - .010" "under sized", continually, will fail in a short time. And those short of a case will produce hangfires, light primer strikes and FTF's.

If you're seeing some being sized to 1.450 and others to 1.440. . . something just isn't right, for sure. I think it'll take some hands on investigation to figure it out. .010 variation just doesn't seem possible with equipment being used and/or working properly.

 

[Ringostar]

I’m surprised that nobody has asked this yet. Do your once fired brass still chamber before sizing? If so, then they probably aren’t fully fire formed and shouldn’t be bumped back at all. I haven’t had new brass fully formed in just one firing. You can’t just use the measurement of a go gauge.

 

[searcher]

As many have noted, a .002" bump (assuming brass IS fully blown out) is what most accuracy-minded folks would recommend, many go tighter than that - to the point where you can feel a slight case crush when the bolt is almost closed on a chambered cartridge and is considered by more than a few as "ideal". The more you bump, the more slop you are introducing to your load and that never contributes to repeatability and consistency. The more you bump - the worse it will likely get.

"How far can you go?" deserves two answers. For accuracy, the more you bump, the more consistency you lose and still have rounds consistently ignite AND uniformly ignite, I'd think if you had more than a few thousands bump - you risk not getting as consistent primer strikes as you might want - along with greater potential misalignment of bullet to center of bore axis. Go beyond .008" and you are getting into complete misfire realm.

 

[JFrank]

IMH hillbilly O the trick to setting a case back is freely cycling before and ‘after’ ignition. Just picking a number like .0015 or .002 may or may not be correct for one’s particular application.
Don’t be afraid to go an extra .001

 

[Jeff Porter]

556 sizing update…

Not sure how or where the short sized brass occurred but it is 0.010” under what I thought it was. I had sized and fired about 100 rounds for SWN in February with no issues.

Upon returning, I had changed tools to measure headspace/case dimensions and added a new lock ring to my die set. This meant re setting the die in my Forster Co-Ax press. Somewhere in that stacking of tolerances I got out of the correct die setting that worked in January. Unless someone wants to go into the full FMEA and 6M Root cause analysis, suffice to say that between man, machine, measurement and method I had made enough small mistakes to add up to this FTF end result.



Test format – To determine if I can salvage any of these cases as good, I wanted to see I f could use the tools I have to get a number that will have the highest probability of going bang when I pull the trigger.

I have the Hornady tool with the previously determined best worst option 0.330” insert and I have a new PMA digital case checker with .223 case holder.

Since my measuring technique and instrument precision was questioned, I used a 223 Go Gauge as a standard. Measuring the Go Gauge 5 times with each tool.

For the caliper and head space gauge, I would seat the case spin it a few times to seat it and apply gentle pressure to the caliper ( to hold it while I wrote the value). This gave 5 consecutive measurements of 1.4540”



The PMA tool uses case family specific holders and the value is not representative of a real number, only a reference. The tool head with the indicator sits on top of the case holder, the indicator is zeroed to origin on the empty case holder. The case seats on the chamber cut into the holder and extends proud of the case holder some distance and that is measured by the indicator. To use the tool, I put the case in the holder and gently apply some pressure to overcome the spring force if the indicator against the case head and seat the tool on the top of the holder. I find this most repeatable. This gave 5 measurements of 0.5120.





Using these tools and these techniques and the base line of the Go Gauge numbers, I made some measurements of the 5.56 Starline brass. This was brass from the same 1x fired lot I was sizing.

0X fired – 3 pieces. – Obviously – I should have my brass no shorter than this, but here we are. I presume these are minimum SAAMI spec as to fit in any rifle. These chamber and fire with zero issues. Single digit SD, Teens ES and 0.2 groups.

0x fired 556
PMA	Hornady
0.5125​	1.454​
0.5125​	1.454​
0.5125​	1.455​

2x fired – Click and Bang recent outing- 5 pieces.

2x fired 556- Click/boom
0.5120​	1.451​
0.5130​	1.451​
0.5120​	1.452​
0.5125​	1.452​
0.5130​	1.452​

So it would seem that 0.512/1.451” after firing brass works, Presuming it was longer and shrunk during firing. Looking at 0x data, likely 0.003” shrink upon firing. Still single digit SD, Teens ES and 0.2 groups. Brass was not fully formed to the chamber.

Let’s look at the ones that did not fire.

Set of short FTF bullets

Click no boom
0.5020​	1.4400​
0.5035​	1.4430​
0.5045​	1.4410​
0.5045​	1.4420​
0.5050​	1.4410​
0.5030​	1.4450​

Pretty clear the 0.010” shorter headspace will cause an ignition problem.



I have 300 loaded and 200 primed brass that was all sized at the same time, lets look at some loaded rounds and see if I will need to pull these bullets.

Loaded 90 JLK
PMA	H​
0.5115​	1.4540​
0.5085​	1.4480​
0.5105​	1.4510​
0.5110​	1.4510​
0.5085​	1.4490​
0.5100​	1.4520​
0.5105​	1.4510​
0.5085​	1.4480​
0.5105​	1.4500​
0.5090​	1.4500​
0.5140​	1.4560​

I took these ten to the range to see where the FTF occurs with brass sized. I had hoped that the 1.451” brass that is -0.003” under 0x fired size would still ignite. But only the first and last case that were the same as the 0x dimension fired.

I tried some that failed to fire in a different rifle and some of them fired, some did not, but second primer strike is not a good measure.

I have ordered another 500pc of new brass. This is a $150 lesson to check your ammo in the rifle after making changes to your system.

I had considered measuring these and looking for cases that measured 0.512/1.154 or longer but will likely just pull it all, save the bullets, powder, primers and scrap the brass.

If someone wants a batch of 500 once fired 5.56 Starline brass for necking up to 6mm or making 300 BO I think this would still work for that.

 

[urbanrifleman]

Using my Hornady headspace tool to measure 5.56 Starline shows a number of 1.4500” to the datum line. Same number on a .223 Go gauge.

1x fired in a .223 FTR chambered barrel shows 1.4520” so a fairly tight chamber.

Brass annealed and sized with target of 1.4510”. Most are coming out 1.4500”-1.4520” range.

But for some reason I have yet to figure out, I have been getting some that are sized down shorter in the batch. These are 1.4400-1.4440”. 6-10 thou under sized from the min spec.

These are getting light primer strikes and “Click no boom” ftf.

I presume this is because it is only 1x fired in this chamber and different softness is having less spring back from the die.

I am going to go through the bolt and change the striker spring and check firing pin protrusion and try the rounds in another rifle but wanted to ask before I go down that rabbit hole….

How much below the 1.450” is too short ?

Most likely it's your annealing doing that.

6 thou excess is enough to cause ftf.

I would stop annealing for the time being. Even though I'll get roasted for saying this, it's overrated. It's just another variable that can be wrong very easily.

 

[urbanrifleman]

556 sizing update…

Not sure how or where the short sized brass occurred but it is 0.010” under what I thought it was. I had sized and fired about 100 rounds for SWN in February with no issues.

Upon returning, I had changed tools to measure headspace/case dimensions and added a new lock ring to my die set. This meant re setting the die in my Forster Co-Ax press. Somewhere in that stacking of tolerances I got out of the correct die setting that worked in January. Unless someone wants to go into the full FMEA and 6M Root cause analysis, suffice to say that between man, machine, measurement and method I had made enough small mistakes to add up to this FTF end result.



Test format – To determine if I can salvage any of these cases as good, I wanted to see I f could use the tools I have to get a number that will have the highest probability of going bang when I pull the trigger.

I have the Hornady tool with the previously determined best worst option 0.330” insert and I have a new PMA digital case checker with .223 case holder.

Since my measuring technique and instrument precision was questioned, I used a 223 Go Gauge as a standard. Measuring the Go Gauge 5 times with each tool.

For the caliper and head space gauge, I would seat the case spin it a few times to seat it and apply gentle pressure to the caliper ( to hold it while I wrote the value). This gave 5 consecutive measurements of 1.4540”

View attachment 1641881

The PMA tool uses case family specific holders and the value is not representative of a real number, only a reference. The tool head with the indicator sits on top of the case holder, the indicator is zeroed to origin on the empty case holder. The case seats on the chamber cut into the holder and extends proud of the case holder some distance and that is measured by the indicator. To use the tool, I put the case in the holder and gently apply some pressure to overcome the spring force if the indicator against the case head and seat the tool on the top of the holder. I find this most repeatable. This gave 5 measurements of 0.5120.

View attachment 1641883

View attachment 1641882

Using these tools and these techniques and the base line of the Go Gauge numbers, I made some measurements of the 5.56 Starline brass. This was brass from the same 1x fired lot I was sizing.

0X fired – 3 pieces. – Obviously – I should have my brass no shorter than this, but here we are. I presume these are minimum SAAMI spec as to fit in any rifle. These chamber and fire with zero issues. Single digit SD, Teens ES and 0.2 groups.

0x fired 556
PMA	Hornady
0.5125​	1.454​
0.5125​	1.454​
0.5125​	1.455​

2x fired – Click and Bang recent outing- 5 pieces.

2x fired 556- Click/boom
0.5120​	1.451​
0.5130​	1.451​
0.5120​	1.452​
0.5125​	1.452​
0.5130​	1.452​

So it would seem that 0.512/1.451” after firing brass works, Presuming it was longer and shrunk during firing. Looking at 0x data, likely 0.003” shrink upon firing. Still single digit SD, Teens ES and 0.2 groups. Brass was not fully formed to the chamber.

Let’s look at the ones that did not fire.

Set of short FTF bullets

Click no boom
0.5020​	1.4400​
0.5035​	1.4430​
0.5045​	1.4410​
0.5045​	1.4420​
0.5050​	1.4410​
0.5030​	1.4450​

Pretty clear the 0.010” shorter headspace will cause an ignition problem.



I have 300 loaded and 200 primed brass that was all sized at the same time, lets look at some loaded rounds and see if I will need to pull these bullets.

Loaded 90 JLK
PMA	H​
0.5115​	1.4540​
0.5085​	1.4480​
0.5105​	1.4510​
0.5110​	1.4510​
0.5085​	1.4490​
0.5100​	1.4520​
0.5105​	1.4510​
0.5085​	1.4480​
0.5105​	1.4500​
0.5090​	1.4500​
0.5140​	1.4560​

I took these ten to the range to see where the FTF occurs with brass sized. I had hoped that the 1.451” brass that is -0.003” under 0x fired size would still ignite. But only the first and last case that were the same as the 0x dimension fired.

I tried some that failed to fire in a different rifle and some of them fired, some did not, but second primer strike is not a good measure.

I have ordered another 500pc of new brass. This is a $150 lesson to check your ammo in the rifle after making changes to your system.

I had considered measuring these and looking for cases that measured 0.512/1.154 or longer but will likely just pull it all, save the bullets, powder, primers and scrap the brass.

If someone wants a batch of 500 once fired 5.56 Starline brass for necking up to 6mm or making 300 BO I think this would still work for that.

Just jam the bullet 30 thou into the lands and shoot them.

 

[Codyway]

Take a piece of brass that will chamber and add layers of scotch tape until the bolt will just snugly close. Measure it. It's pretty close to your headspace dimension.
Take a few pieces of brass and, with a slightly reduced charge, fire with the bullets seated into the lands 0.040-0.050. Knock out the spent primers and measure. Should be pretty close to what you measured with the tape. If not increase powder till it does. Now fireform the rest of your brass this way. Now set your sizing die to bump a few thou. Should be good to go

 

[Jeff Porter]

It’s not worth the primer powder and bullet to save the brass by jamming and fire forming. Those components are more valuable in new brass. Not to mention my time has some value.