Difference in performance with mixed brass

[gmerkt]

Saturday, I was able to do some range shooting. Including my Winchester Model 70 FW in 7mm Mauser. My handloads all used RP brass cases save three that were Graf and Sons. The Graf cases were made in Europe to CIP specs, not SAAMI. The Graf cases have a slightly larger rim and won't fit in the usual shell holder for 7mm Mauser, I have to get out my shell holder for .30-30 to work the three cases. But I'm reluctant to throw them away because of this difference.

Having loaded all of these rounds using the same components, the three rounds loaded in the Graf cases printed six inches lower to point of aim than the rest loaded in RP cases.

Here was empirical evidence that mixed brass can open up groups.

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[RX-79G]

6 inches at 100 yards? That seems like more than a velocity variation.

 

[DizzyJ]

Saturday, I was able to do some range shooting. Including my Winchester Model 70 FW in 7mm Mauser. My handloads all used RP brass cases save three that were Graf and Sons. The Graf cases were made in Europe to CIP specs, not SAAMI. The Graf cases have a slightly larger rim and won't fit in the usual shell holder for 7mm Mauser, I have to get out my shell holder for .30-30 to work the three cases. But I'm reluctant to throw them away because of this difference.

Having loaded all of these rounds using the same components, the three rounds loaded in the Graf cases printed six inches lower to point of aim than the rest loaded in RP cases.

Here was empirical evidence that mixed brass can open up groups.

That's more than I would expect from mixed brass. Remington (.223 anyway) is know to have more case capacity, but that seems extreme for 100yds.

I did a test of my own using mixed range pick up brass for the .223. Commercial, military, etc.

I was still able to work up a load that consistently shot 3/4" and under @ 100yds

 

[Cerberus Group]

Here's High Desert Cartridge 223/5.56...we use mixed headstamp brass...no where near the variation you're seeing with the Mauser.

 

[thorborg]

I've never been a steady shot so have learned to squeege on the sweep of the heart neat. as pathetic as that sounds it works just fine for hunting but surly wont wine me the turkey in the target shoot out competition.

 

[thorborg]

Something clicked and posted too soon but my point was mixed brass works for big game under 300 yards for me, but almost everything else even remotely critical, not so good. My past testing showed the major issue for me was unable to control extreme spread. My preference being no more than 10 to 15 FPS. While that's fairly easy to do with most any brass, the same load in different brass can be 100 plus or minus fps different. That's a POI change ready to happen right there when grabbing from a mixed pouch of cartridges. Better to sort.

 

[Cerberus Group]

One thing that tightened up the velocity spread was going to a scale that shows hundredths of grain measurement vs tenths.



Also, different case makers obviously have different volumes which affect velocity.

Here Kyle is using our 77gr out to 800 yards, I don't recall the groups, but he's hitting steel with a stiff cross wind (wind sock)...again various head stamps being used.

 

[Certaindeaf]

One thing that tightened up the velocity spread was going to a scale that shows hundredths of grain measurement vs tenths.

View attachment 1429404

Also, different case makers obviously have different volumes which affect velocity.

Here Kyle is using our 77gr out to 800 yards, I don't recall the groups, but he's hitting steel with a stiff cross wind (wind sock)...again various head stamps being used.

View attachment 1429405

I think having cases that directly contribute to perhaps a difference of 10,000 psi difference in a worst case scenario is of much greater concern than 1/100 grain charge weight discrepancies.

 

[Member 34319]

Posted this in, I want to say @Koda thread a bit ago. I've never seen much deviation with mixed brass when it comes to 223. Then again it could be case capacity that is the key factor at play?!?

 

[Cerberus Group]

I think having cases that directly contribute to perhaps a difference of 10,000 psi difference in a worst case scenario is of much greater concern than 1/100 grain charge weight discrepancies.

Now wondering what caliber(s) and what cases are giving that kind of pressure spread.

 

[Cerberus Group]

Posted this in, I want to say @Koda thread a bit ago. I've never seen much deviation with mixed brass when it comes to 223. Then again it could be case capacity that is the key factor at play?!?

View attachment 1429435

Yes, case capacity/volume will affect velocity and pressure...which in turn affects accuracy...apparently some cases more than others, just not seeing as much with 223.

 

[Koda]

Posted this in, I want to say @Koda thread a bit ago. I've never seen much deviation with mixed brass when it comes to 223. Then again it could be case capacity that is the key factor at play?!?

View attachment 1429435

I dont recall but Id be thrilled if I could pull that off with just non-mixed brass in my AR15.


As for the subject, I dont think a 6in difference in POI between brass in larger calibers unusual. I think there might be a scale factor with case size, comparing with 223,.... those are small cases, a change in case volume is slight compared to a larger case.

 

[Certaindeaf]

Now wondering what caliber(s) and what cases are giving that kind of pressure spread.

30-06 capacity is all over the place.

 

[Koda]

30-06 capacity is all over the place.

I recently compared volume difference between two brands with my 280AI. The difference was about 3% which worked out to about 2.2grains more room for powder in one case.

My guess is if the 7mm Mauser cases were loaded exactly the same otherwise the case itself, one could have much less (or much more) pressure, a 6in shift in POI wouldn't be unreasonable.

Just my guess.

 

[Certaindeaf]

I recently compared volume difference between two brands with my 280AI. The difference was about 3% which worked out to about 2.2grains more room for powder in one case.

My guess is if the 7mm Mauser cases were loaded exactly the same otherwise the case itself, one could have much less (or much more) pressure, a 6in shift in POI wouldn't be unreasonable.

Just my guess.

Indeed. There are a lot of capacity tables for 30-06, to include military and commercial brass over the years.

 

[Cerberus Group]

30-06 capacity is all over the place.

Ya got me there...I think 30-06 over the many years has had probably the most makers of that round vs any other

 

[Certaindeaf]

The old scheutzen shooters would use one piece of brass.. they got fine accuracy.

 

[Hashh]

Whoa, that's some range action you had with your Winchester Model 70 FW in 7mm Mauser! So, those Graf and Sons brass cases gave you a little trouble, huh? They have a bigger rim and don't fit the usual shell holder. But hey, don't throw 'em away just yet. Here's the kicker: those three rounds in the Graf cases shot six inches lower than the rest. Mixed brass can really mess with your groupings, man. It's a good thing you noticed that. Time to decide if you wanna stick with the reliable RP brass or give those Graf cases another shot.

 

[bcp]

What is the case weight difference?

Bruyce