Riddle me this... New vs. Fired Brass

[CB11WYO]

I've recently found a good load for my new 7mm Rem. Mag (using once-or-more-fired brass) and have now begun breaking in some new Winchester brass.

My pet load with the once-or-more-fired brass which I used during development was giving me under 1 MOA accuracy, usually about .75 .

Using the same load with my brand new brass I'm really drilling 'em... usually .5 MOA and sometimes better...

Now this seems to be exactly opposite of what my prior experience/thinking has been. Seems that the broke-in brass usually perform better than brand-new out-of-the-bag brass.

Any of you experience this or have possible explanations??

Or is this just another thing to add to my gun's "personality" profile and another testament that nothing is a given in precision shooting?? lightbulb

 

[MudRunner2005]

Could be brass fatigue, and your neck tensions on your "broke in" brass aren't holding the bullet consistantly, therefore your chamber pressure is different per load...

That's just a possibility, not saying that's what it is. I just figured I'd throw that out there as a potential thing to look for.

 

[g0rd0]

the old brass just might need annealing

 

[Nimrodmar10]

Are both lots of brass from the same manufacturer? If not, that could make a difference.

 

[CB11WYO]

Mud- Brass Fatigue/Neck Tension sounds like it probably is a contributing factor...

g0rd0- Annealing might be the answer then, considering Mud's idea as well. I've read up recently on annealing and such, never attempted it though. I think I at least understand the benefits etc...

Nimrod- yes both lots of brass were same manufacturer

 

[varmintH8R]

Do you neck size your fired brass? Sometimes a touch of headspace can change accuracy...

 

[Mikecr]

That new brass(lower capacity) happened to shoot better means your current fired brass(higher capacity) tune isn't best.
I'd pay attention to your new brass muzzle velocity and go after it.

 

[MNbogboy]

I agree with Mikecr....Velocities with new brass as a rule tend to be lower with new brass (sometimes as much as 25 to 50 fps in calibers from 222 up to 30-06)....This seems to break the capacity/pressure/velocity rule but other factors including forces exhausted during case expansion and possibly the reflectivity of the new brass seem to change burning characteristics somewhat (powder residue in new brass adheres inside the case walls different than in multiple fired cases).....I do not have experience with the larger magnums however and my head may be up my rear on this one.....

If you use a chrono, you should compare velocities and work your "fired" brass load to the more accurate velocity as Mike said.

You are probably already aware that the type of dies a person uses may be a contributing factor....The expander nipple on a lot of common 2 piece die sets may cause a concentricity issue because of uneven forces placed on the brass when withdrawing it through the expander...In essence new brass may be "straighter" right out of the box...If you are using this style die there are a few techniques including cleaning powder residue from the necks before sizing and also slightly lubing the inside of the necks and/or expander....Allowing your expander rod to float (loosen the locknut) will also help....Multiple passes through the die rotating the cartridge with each stroke may and should help keep your necks true if the die truly is causing a problem....Also as others have said your brass may be "aging/hardening" to the point where bullet seating pressure is different or possibly so much that you may again be deforming the brass enough to distort bullet/bore alignment....

Good luck,
Randy

 

[CB11WYO]

Varmint- I full-length size all my fired brass, to the extent of bumping the shoulder .002". The head-space issue is partly why I don't understand that new brass could be more accurate... my fired and sized brass has got to have better/more correct head-spacing than the brand new stuff... I dunno

mikecr/MNbogboy- Thanks and I think I'll look more into the difference in my new brass vs fired brass veloctiy. If I remember right they really aren't that much different, more like the 25-30 fps range... have to check my records

 

[CB11WYO]

Thanks guys for all your help!

I've got some good ideas and leads now

Thanks to reloading I'm becoming frustratingly more and more OCD all the time

 

[g0rd0]

annealing is easy
I use a set of spark plug plyers to hold the brass at the base, I then heat the neck and shoulder with a butaine, crème brule torch (your wife will know where to find one around $15.00) lay them on a cement floor in the garage then fl size after they cool. I do this every 5th load.
My 7mm rm brass is federal and on the 12th loading going stong

 

[CB11WYO]

annealing is easy
I use a set of spark plug plyers to hold the brass at the base, I then heat the neck and shoulder with a butaine, crème brule torch (your wife will know where to find one around $15.00) lay them on a cement floor in the garage then fl size after they cool. I do this every 5th load.
My 7mm rm brass is federal and on the 12th loading going stong

And that just keeps them from work hardening/becoming too rigid right?
What's your technique for knowing how hot to get them? if you don't mind me asking...

 

[Bart B]

Many folks get excellent accuracy with new brass.

For example, good commercial .308 Win. match ammo's produced sub 2/3 MOA accuracy at 600 yards in properly rebuilt M1 and M14 service rifles. A bit better in bolt action match rifles. That ammo's got new brass, metered powder charges with a 3/10th grain spread, bullet runout up to 4/1000ths inch and a 3-grain spread in case weight. All in MIL SPEC or SAAMI spec chambers. The US Palma Team's loaded several thousand rounds of new .308 cases with the same component variables that's shot 1/2 MOA at 600 yards in all sorts of rifle barrels from around the world. I've shot sub 1/2 MOA 15-shot groups at 1000 yards with new, unprepped .30-.338 mag cases.

New brass headspacing on its shoulders that's made well centers perfectly in the chamber up front as its shoulder mates perfectly with the chamber shoulder from firing pin impact before it fires. Doesn't matter how much space there is around the case body to the chamber wall; the back end's pressed against the chamber wall by the extractor in most instances.

For years since the first belted case was used to win the big 1000 yard match at the 1935 Nationals, folks got best accuracy with new belted cases compared to any method of resizing fired ones. Only when a "body" die was made to size just the case body all the way completely back to the belt eliminating that pressure ridge that usually showed up a few thousandths in front of it that interferred with repeatable case positioning at its back end in the chamber.

 

[g0rd0]

that is what brings the brass back to "softer" state. Takes the brittleness out of them, if you will.
How I know how hot it is, while holding the brass I heat with direct flame the neck and shoulder (top 1/3rd of the case), with majority of the flame around the base of the neck keep the brass moveing around for 3 seconds. If you first do this in a dimly light space you can see the brass change colour. Once the cherry red spreads below the shoulder stop. For me it takes 3 seconds (I timed it).
After the brass has cooled you must fl size. Some say to drop in oil but, if you quench your brass you may take out the softening that you just put back in.
There are products out there that you rub on your cases before that show the colour change to the novice but, I feel that it is an added expense and something more to clean up.
here is a short video of a commercial machine there a few different makes out there and are around $400.00
[ame=http://www.youtube.com/watch?v=iy6OwiuWV7A]Cartridge Annealing Machine - YouTube[/ame]