Shoulder Bump

[Spartan-117]

I have 20 fireformed cases of 6.5 CM Lapua brass. The SAAMI drawing uses a Ø0.400" datum and allows 1.537" to 1.544" (rounded to the nearest thousandth).
If all twenty cases are within 1.537" - 1.544" do I still need to bump the shoulder back?

 

[rwj]

Can you close the bolt without resistance on a fired empty (primer removed) case?

If yes, there is no need to move the shoulder, perhaps not even resize the body.

If no, first try resizing just the body then check in the chamber again.

If it still doesn’t chamber, then begin adjusting the die to move the shoulder.

This assumes the case is not too long and the neck end face is not contacting the chamber.

 

[NZ_Fclass]

^^^ This.
I never have to bump my 6mmBR cases, but always bump 308 and 6.5's. I like them to feed like whipped cream.

 

[Straightshooter1]

I have 20 fireformed cases of 6.5 CM Lapua brass. The SAAMI drawing uses a Ø0.400" datum and allows 1.537" to 1.544" (rounded to the nearest thousandth).
If all twenty cases are within 1.537" - 1.544" do I still need to bump the shoulder back?

What matters is how those cases fit in your particular chamber. After fireforming, the cases may or may not need bumping. After only the 1st firing, if the cases will still fit easily into the chamber, I wouldn't bump the shoulders. Very likely, after the second firing, you'll likely have to bump the shoulders then.

 

[Dkk37058]

To check bolt closer on fired cases don’t forget to remove the firing pin spring assembly and ejector spring to keep from getting a false feel on bolt closing

 

[Coyotefurharvester]

If the cases are fully formed, usually the datum lengths are very similar(primers removed).

 

[jxb]

You might want to compare base to datum and OAL to your new/factory cases, they may not have moved at all. My 6.5 CM didn't move shoulder until I got up near max powder load.

 

[NorCalMikie]

Put the fired case back in the chamber. Close the bolt. Any resistance? NO? Neck size and reload. Forget about pulling the primer to check for resistance. The firing pin (when bolt is cocked) is BELOW the bolt face surface.
As far as OAL of the case, check YOUR chamber length BEFOR thinking about trimming. Chamber/reamer cut length is usually about .020 LONGER than MAX trim length.
Neck size and shoulder size. Body size if you feel resistance. YMMV.

 

[K22]

Your rifle chamber and bump gauge are your guide here. Lots of good advice in the previous posts.

Bumping the shoulder should not be done out of hand without a measurement basis (reason) to do it. This assumes a group of cases are dedicated to a specific rifle and you are rotating the use of the cases.

I am not a fan of neck sizing, but you can accomplish the same result with a full-size die by adjusting the die to give you zero bump. I do this all the time with virgin cases. The reason I like a full-size (F/L) die even though I am not bumping the shoulder is that it sizes the radial dimension of the case which is often the culprit in difficult chambering of a reloaded case. In fact, I have gone as high as 6 reloads on some brand of case and rifles without having to bump the shoulder using a F/L die as I described.

Another possible added benefit, although I have never proven it by testing, but intuitively, it seems reasonable that this provide a better uniform neck / case body alignment.

 

[Spartan-117]

This is a wealth of information. Thanks to all that responded.

 

[jds holler]

Dang, I miss F Guffy when we get one of these threads. jd

 

[powderbrake]

View the video on sizing brass
wheeler videos

 

[gambleone]

Dang, I miss F Guffy when we get one of these threads. jd

Likewise, It was fun trying to decipher his remarks. I miss
the Guffster.

 

[209jones]

Most of the time, you will find, that 1st firing will give some shorter and some longer cases. I usually only bump the longest case, about .001-.0015, enough to stop the shorter ones from growing any longer than the longest one when sizing them. Then on second firing, find the longest case again and set the die to bump to about .002, usually leave the die set there after that. Being as I have neck dies, I often use those on 1st shot for some guns, depending on purpose of the load and gun, I may use a neck die til 4th or 5th shot, then set up an FLS die for it and bump to about .002, go back to the neck die again for a few more shots. I usually only FLS for a round that I'd consider for comps/target or big game hunting.

 

[jxb]

View the video on sizing brass
wheeler videos

View all of his videos, lots of goodness to be had there.

 

[DaveTooley]

This may go against the grain but I like to FL size from the start. The reason is the brass will work harden as it gets tighter in the chamber. Then FL sizing is trickier usually requiring more bump to achieve a free running bolt. Here's why it works for me. FL sizing starts on the body with the shoulder coming into play at the very end of the stroke. As the die sizes the body the shoulder is pushed forward. That's why backing off a FL die doesn't work for neck sizing. With the case being longer at this point you can adjust the shoulder bump using nothing but a striped bolt. I like the bolt to drag ever so slightly. All this prior to work hardening. YMMV

 

[K22]

This may go against the grain but I like to FL size from the start. The reason is the brass will work harden as it gets tighter in the chamber. Then FL sizing is trickier usually requiring more bump to achieve a free running bolt. Here's why it works for me. FL sizing starts on the body with the shoulder coming into play at the very end of the stroke. As the die sizes the body the shoulder is pushed forward. That's why backing off a FL die doesn't work for neck sizing. With the case being longer at this point you can adjust the shoulder bump using nothing but a striped bolt. I like the bolt to drag ever so slightly. All this prior to work hardening. YMMV

What I think you are referring to by trying to use a F/L die for only neck sizing is what is termed, "partial sizing" which is described in the 5th Edition of the Nosler Manual. In my opinion, this is the worst of all the sizing procedures since it produces the effect, I think you are describing. I was quite surprised to see it a reloading manual.

German Salazar in his blog on sizing also trashed this "partial sizing" procedure.

I used the F/L die on virgin cases, but I set it (quite easier with Skip Shims), so the die contacts the case shoulder on the longest fire formed virgin cases. This produces zero to a slight bump of .001. Shorter cases extrude when the shoulder contacts the die. Thus, I obtain all cases sized to the approximate same head space. I just completed this for a new lot of cases for one of my 223 Rem bolt rifles. I found over the years that this work very well in terms of producing cases that chamber reliably without unnecessarily overworking the case.

 

[Chris Edmondson]

I body size every time; some cases are longer to start with, some shorter, they all end up the same when I'm done. Unless I measure all the pieces in advance, I have no way to know if there are long ones that may resist chambering, easier to just size 'em and be done with it.

 

[243winxb]

The crush fit, when closing the bolt, tells me all i need to know.