Better accuracy with Virgin Brass?

[MTLIVIN]

I noticed with my semi-custom 7mm Rem Mag I get better accuracy and velocity spreads with virgin Norma brass. I shot my best groups ever with new brass, 180 hybrids, 215M, and H1000 that were under 0.2" @ 100 yards. With sized brass I get 0.5"-0.6".

I've been very slightly bumping the shoulder back 0.001 using RCBS gold medal FL dies with a 0.003 undersized neck bushing and RCBS Gold Medal seating die. Everything I know tells me I should get better groups, not worst with sized brass. My 5-shot ES is 12fps w virgin brass, 40 with re-sized brass. Average velocity is 15 fps higher with sized brass.

Gonna try a size smaller neck bushing, and maybe bumping back more and less, but without a gauge to measure run out I'm not sure what else to try, any suggestions?

 

[rcoody]

I noticed with my semi-custom 7mm Rem Mag I get better accuracy and velocity spreads with virgin Norma brass. I shot my best groups ever with new brass, 180 hybrids, 215M, and H1000 that were under 0.2" @ 100 yards. With sized brass I get 0.5"-0.6".

I've been very slightly bumping the shoulder back 0.001 using RCBS gold medal FL dies with a 0.003 undersized neck bushing and RCBS Gold Medal seating die. Everything I know tells me I should get better groups, not worst with sized brass. My 5-shot ES is 12fps w virgin brass, 40 with re-sized brass. Average velocity is 15 fps higher with sized brass.

Gonna try a size smaller neck bushing, and maybe bumping back more and less, but without a gauge to measure run out I'm not sure what else to try, any suggestions?

with the differences you have I would certainly measure runout.

sounds like neck tension needs work too.

Did you resize the new brass before loading it?

how many times fired is your resized brass?

Have all the ones you are shooting all been fired the same number of times?

how does the bullet seating effort compare between virgin brass and your fired brass?

annealing works!

 

[918v]

Anneal the necks to factory spec.

 

[MTLIVIN]

The sized brass is all second fire Norma brass, I do not mix brass, it all stays together and gets shot the same # of times. I started with 2 - 100 count boxed of Norma brass. I did run the new brass through my FL sizing die but only the neck collet touched and barely at that, it was incredibly uniform right out of the box.

As this is only the second fire, I cant see how annealing is already needed, especially as Im only sizing down with a bushing and no expander ball.

 

[rcoody]

The sized brass is all second fire Norma brass, I do not mix brass, it all stays together and gets shot the same # of times. I started with 2 - 100 count boxed of Norma brass. I did run the new brass through my FL sizing die but only the neck collet touched and barely at that, it was incredibly uniform right out of the box.

As this is only the second fire, I cant see how annealing is already needed, especially as Im only sizing down with a bushing and no expander ball.

what about bullet seating effort between the virgin brass and the fired brass?

 

[Laelkhunter]

Anneal the necks to factory spec.

What exactly is the "factory specs" for annealing?

 

[Timber338]

I've been very slightly bumping the shoulder back 0.001 using RCBS gold medal FL dies with a 0.003 undersized neck bushing and RCBS Gold Medal seating die. Everything I know tells me I should get better groups, not worst with sized brass. My 5-shot ES is 12fps w virgin brass, 40 with re-sized brass. Average velocity is 15 fps higher with sized brass.

I'm assuming you're bumping your shoulder back .001 smaller than the size of your chamber (or the size of the fired brass) ... I"m not sure of the exact process you are using for controlling the shoulder bump, but virgin brass will always have the shoulder bumped back quite a bit back from the shoulder. The lower velocity of virgin brass is expected as it takes some energy to expand the virgin brass to fit your chamber. Is it possible that you are not bumping the shoulder far enough during your resize operation? If the brass is too long the shoulder will interfere in the chamber and the bolt will close harder than normal.

One thing you can do is disassemble the firing pin from your bolt so that there is no spring tension when you close the bolt. Closing the bolt with a correctly sized brass should feel almost identical to closing the bolt with no brass at all... which is basically no added force.

If you are doing it right, this won't be the issue, but either way, check out Redding's Competition Shellholders. They make setting your shoulder bump very simple and accurate.

 

[MTLIVIN]

I'm assuming you're bumping your shoulder back .001 smaller than the size of your chamber (or the size of the fired brass) ... I"m not sure of the exact process you are using for controlling the shoulder bump, but virgin brass will always have the shoulder bumped back quite a bit back from the shoulder. The lower velocity of virgin brass is expected as it takes some energy to expand the virgin brass to fit your chamber. Is it possible that you are not bumping the shoulder far enough during your resize operation? If the brass is too long the shoulder will interfere in the chamber and the bolt will close harder than normal.

One thing you can do is disassemble the firing pin from your bolt so that there is no spring tension when you close the bolt. Closing the bolt with a correctly sized brass should feel almost identical to closing the bolt with no brass at all... which is basically no added force.

If you are doing it right, this won't be the issue, but either way, check out Redding's Competition Shellholders. They make setting your shoulder bump very simple and accurate.

I am using a Hornady guage to control the amount of shoulder bump, haven't had any issue doing this on any other rifle. But under sizing the brass is really just neck sizing so I don't see this as an issue either. Im planning on testing FL size, partial FL size, and neck size only loads on my next outing and see if I get any better results.

I just got this rifle back right before rifle season and after firing my first 100 rounds of new brass had to order another 100 brass to reproduce my results as I didn't have time to dig into the issue then.

Additional Info: Bechmark 26" 1:9 twist throated long, Manners EH3 stock, Savage/Stevens action w the barel nut (and it is headspaced correctly, tight tolerance there)

 

[Timber338]

It sure sounds like you are doing everything right.

The only thing I can think of is that the higher pressure that is being generated with the 2nd fired brass is pushing you out of your accuracy node. Maybe drop .3 to .5 grains and it will drop that initial pressure impulse back down to where it is with the virgin brass?

 

[MTLIVIN]

It sure sounds like you are doing everything right.

The only thing I can think of is that the higher pressure that is being generated with the 2nd fired brass is pushing you out of your accuracy node. Maybe drop .3 to .5 grains and it will drop that initial pressure impulse back down to where it is with the virgin brass?

I will give this a shot too, might be the case as the node did seem awfully small.

I tried a few different primers over the magnetospeed too and 215M was still the best ES. Surprisingly Remington 9.5M was 40 fps faster and WLRM were very close but a touch faster than 215M's. Ran out of time but have CCI 250's and 210M's to try also, but hesitant to use 210M's with the sub zero temps I sometimes hunt in.

 

[Mikecr]

The new brass is absorbing some energy in all that expansion, and it's higher in load density (which is good), and your barrel happens to like it. That's an abstract one direction or another in going from new to fire formed brass. It could have easily shot much worse.
But,, you're not going to be shooting only new brass, right?
This is why powder development with new brass is usually a waste of time.

I would not back off same powder to leave lower load density with stable fire formed brass. I would develop with a slightly slower powder that well fills the formed cases at your best seating.
You fully tested to determine best seating, right?

 

[doverpack12]

Try cleaning the inside of the necks with an alcohol wipe about 1.5" x 1.5" on a .22 brass slotted jag. This should reproduce the same surface on the inside of the neck as new brass and has given good results to myself and a few others I picked up the trick from. They were having the same issue you describe.

 

[bigedp51]

I collected milsurp rifles with long fat chamber that tortured thinner commercial brass. I had your same problem magnified and got very good groups with new brass but the same case reloaded would shoot shotgun patterns.

The problem was the large diameter military chambers and cases with unequal case wall thicknesses. This caused the cases to warp excessively and become banana shaped when fired, this warping causes the base of the case to tilt and no longer be 90 degrees to the axis of the bore. Meaning if you set the case on its base it looks like the "Leaning Tower of Pisa".

The case will expand more on the thin side of the case and the spring back action of the brass causes the case to warp. When you full length resize the case it causes the case to tilt even more at the base increasing the warping. The smaller the diameter of the new case in relation to the diameter of the chamber increases the warping effect.

You may have a bad batch of brass with unequal case wall thickness, a off center chamber, defective dies, a expander pulling the necks off center or all of the above.

You will need a good gauge to find and check for these problems.

If you really want to truly experience warped banana shaped cases then just collect British Enfield rifles and shoot Winchester brass. Now think about what is happening in front of the belt when the cartridge is fired.

 

[918v]

What exactly is the "factory specs" for annealing?

105Hv