Old Navy
Gold $$ Contributor
Are you adjusting your die for a cam over?
Shoulder bump, how much is too much ?
- Thread starter Jeff Porter
- Start date
Jeff Porter
Gold $$ Contributor
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
Gold $$ Contributor
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.
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.
Last edited:
Dave M.
F-Open Class shooter (284 win, 6dasher, 6.5-7PRCW)
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
The bolt FP, spring and protrusion have nothing to do with your problem.
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.
Last edited:
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.
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.
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.
"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.
Jeff Porter
Gold $$ Contributor
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.
2x fired – Click and Bang recent outing- 5 pieces.
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
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.
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.
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
Site $$ Sponsor
Most likely it's your annealing doing that.
6 thou excess is enough to cause ftf.
I would stop annealing for the time being. Even though I'll get roasted for saying this, it's overrated. It's just another variable that can be wrong very easily.
urbanrifleman
Site $$ Sponsor
Just jam the bullet 30 thou into the lands and shoot them.
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
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
Gold $$ Contributor
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.
If 6 thou sloop was enough to cause fail to fire wouldn't all factory loaded ammo fail. Of course it doesn't. I never measured an unfired factory case and compared to a fired case with a bump gauge. Whatever the dimensions are factory ammo is a very loose fit in the chamber. None of this is complicated why all the post and replies. Don't see why you need to compare with a no/go gauge. A fired case is your standard to compare to.
I understand. However, my f-class fireform load will shoot within a few points of my normal match loads, so I will fireform at a club match. The biggest difference is that the velocity is around 100 fps lower. Nothing is 'wasted'.
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.