Too much shoulder bump...

[TBass]

I have a 6.5 SAUM's that I am reloading for. I am shooting a 140 gr Berger bullet with 61 grains of H1000. I noticed that on half of my loaded brass I accidently bumped the shoulder back .007 too much.

Should I expect to see any real differences in velocities?
Does this have the real possiblity of dramatically effecting accuracy out to 500 yards?

 

[m1match]

You probably won't see any noticeable difference in velocity or accuracy, but you will probably see shortened case life. On future loadings, I'd check the inside of the cases forward of the case head with a bent paperclip for incipient head separations.

 

[nn8734]

I have a 6.5 SAUM's that I am reloading for. I am shooting a 140 gr Berger bullet with 61 grains of H1000. I noticed that on half of my loaded brass I accidently bumped the shoulder back .007 too much.

Should I expect to see any real differences in velocities?
Does this have the real possiblity of dramatically effecting accuracy out to 500 yards?

Agree with m1match you prob won’t see any difference in meaningful difference in velocity but to confirm I’d run a small sample of rounds w/the over sized brass over your chrono to be sure and definitely keep them all separate from your other brass for that rifle.

 

[TBass]

thestoicmarcusaurelius - I track what you are saying... that being said. The O-give lenght on the properly bumped cases versus the over bumped cases is exacatly the same.

 

[spife7980]

I'm certainly no expert so take this with a grain of salt.

Whether you will see a detriment to accuracy, imo, will be mostly dependent on sensitivity to seating depth of the load that you developed.

A change in shoulder bump changes seating depth so if your shoulder bump is inconsistent then your seating depth will be inconsistent.

Whether that inconsistency shows up on target or not depends on how sensitive your load is to seating depth changes.

It also matters what your definition of accuracy is for this application as far as whether you are likely to notice a difference or not.

No, a change is seating depth is a change in seating depth.
Where the sizing die puts the shoulder doesn't change where the seating die puts a bullet.

The way I understand it is that bumping the shoulder and extra 7 thousandths would be roughly equivalent to seating the bullets longer by 7 thousandths

Yeah, relative to the case and the bullet. But that has squat to do with the chamber and no real bearing on anything.

 

[BLKWLFK9]

If it is an isolated incident and doesn't continue to be sized back .007, you shouldn't have a problem from the 1 time. If you continued to size it back .007, you are going to over work your brass and have future issues or at best case, shortened brass life. Just be sure youre bumping it .003 or less and you should be fine.

 

[TBass]

Spife7980 - I think I follow what you are saying and agree with you.

Essentially the O-give to the lands will be no different between the properly bumped shoulder and the overly bumbed shoulder.

The only thing that I might see which "m1Match" brought up is some excessive wear on my brass.

 

[TBass]

Bingo - I just watched the video... and that makes total sense.

It's this type of knowledge and discussions that take place on the Hide that makes it such an invaluable tool!

Well I will shoot the oversized cases and see if accuracy is greatly impacted.

 

[spife7980]

I think what spife may not be taking into account is that when the firing pin hits the primer, it drives the case forward until it hits the shoulder

Seating depth to me is measured from the bolt face. In that sense where the case is, or the empty space that might exist behind it, has no bearing on the measurement.

What you/cortina are discussing is the excessive headspace clearance so this is where terminology places a part and Im as lacking in my vocabulary and as much to blame for when I said "has no bearing" as anyone. So yes, the distance from the lands can change by the amount of excess headspace clearance but I wouldnt call that seating depth. Id call that the distance from the lands.

 

[m1match]

To illustrate how oversizing shortens case life, I had a batch of LC94Match cases shot in my bolt gun that normally goes more than 10 loadings before the cases start showing neck cracks or incipient head separations. I let my sizing die get out of adjustment and I was bumping the shoulders about 10 thousandths (.010 instead of .002 to .003). After 3 loadings I got a partial head separation on one case and the rest of the batch was in similarly sorry shape ready for the recycling bin.

 

[Barelstroker]

I agree that your terminology is better. And, it would have been better to say that shoulder bump inconsistency would result in inconsistency in distance to the lands (unless seating depth was adjusted by a corresponding amount).

That's how I think about seating depth is setting the optimum distance to the lands with the seating die assuming consistent shoulder bump (but I can see your point that that's technically incorrect and not what "seating depth" is) and the seating die is working the same way regardless.

You are correct thestoicmarcusaurelius.
It all starts where the firing pin pushes the case datum to the chamber datum. If the case datum is further away from the chamber datum, the Ogive is pushed closer to the lands.
There is a way to nullify the shoulder bump differences if you seat with a Wilson seating die by, placing a thin washer in the bottom of the seater cup, to raise the case up into the seater body so that the seater body rests on the case datum. This way, the datum to ogive length is always the same regardless of base to datum length.
I have a machined seater cup specifically for this purpose.

 

[PinesAndProjectiles]

I can’t answer the accuracy issue, but my guess is it won’t suffer much, if at all.

As for the excessive shoulder bump, you may see ejector marks in your head stamps.

I bumped some 6.5x47 brass too much and even though the load was perfectly safe, I would get ejector marks in every piece of brass.

Primers were never flat and there was never heavy bolt lift, just those damn ejector marks.

 

[TBass]

End result - I did not notice any difference between the normal rounds and the rounds with the shoulders bumped too much. In fact I was able to use the same dope to hit an 8” piece of steel at 600 yards four out of four times (two were the oversized brass and two were the normally sized brass). So I am going to call that good enough for this deer season.

Thank you for everyone’s feedback

 

[Holliday]

To illustrate how oversizing shortens case life, I had a batch of LC94Match cases shot in my bolt gun that normally goes more than 10 loadings before the cases start showing neck cracks or incipient head separations. I let my sizing die get out of adjustment and I was bumping the shoulders about 10 thousandths (.010 instead of .002 to .003). After 3 loadings I got a partial head separation on one case and the rest of the batch was in similarly sorry shape ready for the recycling bin.

I just did the exact same thing. I was getting definite pre-seperation on the 5th firing. Checked and I was sizing .009” instead of .002” ....Pissed me off for making such a rookie mistake and toasting about $200 brass prematurely in today market.

 

[Barelstroker]

I just did the exact same thing. I was getting definite pre-seperation on the 5th firing. Checked and I was sizing .009” instead of .002” ....Pissed me off for making such a rookie mistake and toasting about $200 brass prematurely in today market.

Yeah, that is shit. I feel for you man. At least you got onto it in time with no further damage.
We all make mistakes & your booboo seems like something I may have done myself a time or two. LOL.