What's the effect of using heavier brass?

[giannid]

So I've got a new 6 mm creedmoor gasser that I developed a load for during the brass shortage. I ended up resizing some old Hornady 6.5 creedmoor brass down to 6mm. Using 100 grain Hornady interlock, the hornady manual gives me a starting 35.6 and a max charge of 43.9 with H4350. I usually test in half grain increments so I shot 17 different loads, which had 3 different nodes. I ended up settling on 41.5 grains as it seemed to give me the best sd numbers and I was right at 3000 fps and shot a 3/4 inch group at 100 yards.

So I finally scored scored some Starline brass and want to start over load development with the new brass. I'd like to do it with saving as much components as I can. The old Hornady brass ranged from 149 grain to 155 grain per piece. The starline brass is definitely more consistent at 160 to 162 grains per piece. I haven't measured case capacity between the two but I imagine it's less with the starline because of the weight of the brass.

My question is, is it possible to get in the same node with the new brass? Really would like to stay in that 3000 fps mark as long as I get the accuracy and good SD numbers. I'm hoping to not have to go out and shoot 17 different loads for my ladder test. I know the barrel shoots good. Just trying to do load development using the least amount of components.

 

[nn8734]

Just back off your charge weight by a grain or so and re-shoot test groups in .3 or .2 grain increments. Slightly heavier brass usually means slightly lighter charge weights to achieve the same velocity.

But you won’t know for sure of the particulars (new poi, target vs actual MV, MV consistency, pressure threshold, if applicable) until you test.

 

[John Glidewell]

The better comparison would be internal case capacity. Less case capacity will have higher pressures at lower charge weights. If you want to be on safe side back off .5 grains and work your way back up. But in my experience Starline is very close to Hornady on internal case capacity and hardness. Brass from Peterson, Lapua or Alpha are much thicker with lower case capacity.

 

[GrumpyOleFart]

☝
Reduce your load and test.

 

[giannid]

I actually filled up both primed cases with powder this evening. The Hornady holds 1.6 grains more powder than the Starline.

 

[John Glidewell]

That is not how you check capacity. You use water filled level to case mouth.

 

[FN15]

Op, I have been through similar situation.
I hated it at the time I could not find Winchester brass for my 2 wildcats based off of 284 brass. I swithched to Laupa brass and will never go back even f I find the other. Better brass yields better accuracy,

 

[Rocketvapor]

The 35.6gn is 19 percent off the max load of 43.9gn. That's a pretty large range. Was the max indicated as a compressed load?
Your 41.5gn is about 5% off the listed max.
The Hodgdon online data lists a similar 100gr bullet as
100 GR. HDY BTSP

Hodgdon

H4350

38.8

2,879

48,200 PSI

42.7

3,113

59,800 PSI

Your range of case weights, 149-155, and 160-162 gives you a difference of 5gn to 13gn between the two brands.
Pick something close to the average weight of each brand giving you a difference of maybe 8 or 9 grains.

While water capacity is the preferred capacity method, cases with the same geometry can be compared with powder almost as accurately.
For differences less than a grain, use water capacity but with 1.6 grains of powder difference you can get pretty darn close.
Looks like the brass to powder ratio is between 6 and 9 to 1.
Which case weights did you use and what were the powder weights you had to get 1.6 grains?

If you want to try the water method, add one drop of dish soap to about 1/2 cup of water. Mix and set aside for a while.
Take an average case with a reversed spent primer (record case weights used) from each brand carefully fill each case with an eye dropper to a positive (convex) meniscus and touch the meniscus with a tiny piece of tissue paper to level it to the top of the case. The tissue will wick a little water off.
I bet you come up darn close to the powder method.

I don't think you need to repeat the entire 17 load test with the new brass.
As I stated in the other forum, Try 1/4 grain increments a couple percent below and up close to the 41.5gn.
40.5, 40.75, 41.0, 41.25gn. Obviously STOP if things look higher than your previous velocities.
You will likely end up with an increased percent of fill. Watch that you don't get close to 100% with the heavier cases as that will change pressures.

 

[Rocketvapor]

I had a similar situation with 22 Nosler brass and 6mm Hagar brass converted to 22 Nosgar.
The Nosler is the stuff with the rebated rim and the Hagar has a 6.8 sized rim and is much heavier, both in the case head and body.
I started 1 grain less than my 'Special' load and lost 75 fps. A whole grain (about -3%) for this case was too much.
Load was NOT 35 grains.

 

[Milo 2.5]

I actually filled up both primed cases with powder this evening. The Hornady holds 1.6 grains more powder than the Starline.

There is actually a formula for this exact same thing, damned if i can recall it. I know I was in the same boat with 6 SLR and Win brass, switched to Rem brand, and not remembering, tried my own method of figuring what pct of case cap was used for the first brass and transferring that number to the new brass. Say you are using 87% of Hornady, use that with Starline.
It got me real close.

 

[9/11]

Just back off your charge weight by a grain or so and re-shoot test groups in .3 or .2 grain increments. Slightly heavier brass usually means slightly lighter charge weights to achieve the same velocity.

But you won’t know for sure of the particulars (new poi, target vs actual MV, MV consistency, pressure threshold, if applicable) until you test.

I'm doing 308 brass down to 243 by annealing and resizing to 6.5 first brass is thicker!

 

[918v]

Just back off your charge weight by a grain or so and re-shoot test groups in .3 or .2 grain increments. Slightly heavier brass usually means slightly lighter charge weights to achieve the same velocity.

But you won’t know for sure of the particulars (new poi, target vs actual MV, MV consistency, pressure threshold, if applicable) until you test.

This

 

[smoothy8500]

Wouldn’t using powder be completely unreliable since powder can “settle “?

 

[918v]

Powder settling depends on the drop tube length

 

[supercorndogs]

I'm doing 308 brass down to 243 by annealing and resizing to 6.5 first brass is thicker!

My dad did some 308 down to 243, he had to neck turn it.

 

[Doom]

Measuring case capacity is fairly reliable when using fine grained spherical or ball powder. Extruded powders not so much.

 

[9/11]

My dad did some 308 down to 243, he had to neck turn it.

6.5 needs neck turned down .090 to be in spec

 

[supercorndogs]

What spec?

 

[918v]

What spec?

You know… spec!

 

[spife7980]

What spec?

Its an abbreviation of specification.

 

[9/11]

What spec?

1.920 case length for 6.5 and 2.030 for 243

 

[supercorndogs]

Its an abbreviation of specification.

Since you missed it, what is the specification for neck thickness? Although I can clearly see now that 9/11 thinks neck turing is trimming.

I would like to see a someone try to turn .09 off a neck it dan thick or getting damn thin anyway.

 

[9/11]

Necking it down is just the same for any wildcat cartridge the hat trick is trimming case to length in the case the metal thickness in the neck is a few thousands larger say .004 ,trimming to length first is the best strategy as to ease forming and lessen resistance to drawing the die down on the brass not forgetting annealing and much case lube! Being cautious with the forming as you get the feel! I'm a machinist not a terminology guy

 

[Mike Casselton]

Its an abbreviation of specification.

 

[r.tenorio671]

...I suggest you do a volume capacity test on the heavier brass and compare it to your old brass. A change in case volume capacity could affect powder capacity and the resultant change in peak pressure attained.

 

[9/11]

George! Did and came out far above my highest capacity loads 47 gr with clear neck just off a sample of varget so I'm not that concerned with limitation capacity of brass but yes need ladder redone considering the new material!