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.

 

[jotrot]

heavy brass usually means less capacity so you will run into pressure sooner with less powder, you should start load development over

 

[The Oregonian]

If you want to test it just do a quick pressure test…start at starting load and keep going by .5gr or so til you see pressure signs. Then you know where your limits are and you can test safely below that.

 

[QuietTexan]

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?

Even if you measure the case capacity difference, you'll still have to shoot (at least part of) the ladder with the new brass to work up. That's the only way to know the answer to your question. You don't have to go all the way to the bottom, but at least drop 10% from max and work back up to the top.

And if you're trying to find max pressure, you have to do that in fired brass - new brass will behave differently the first time it expands and pressure signs will change on the next firing. Tuning wise you can adjust the load a couple tenths and stay in the node going from new to reloaded, but if you max out something in new brass be careful the second time out.

 

[giannid]

I actually filled up both primed cases with powder this evening. The Hornady holds 1.6 grains more powder than the Starline. I don't plan on finding max pressure. It's a gas gun and I'm content with 3000 FPS.

 

[waveslayer]

You need to measure the H2O capacity. Heavier doesn't mean more volume, it could be thicker brass and have keys volume, the case head could be thick like ADG brass and have less volume. You will want to true QL get your actual powder burn rate, then measure your old brass versus new brass and use QL based on that powders burn rate.

I do this all the time. New Lapua brass uses 43.7 grains of Varget, Winchester 44 grains, Hornady 43.5... Winchester weighs more... go figure

 

[Mikecr]

I think you have a good plan. Just following the golden rule: work up with any change

 

[QuietTexan]

I don't plan on finding max pressure. It's a gas gun and I'm content with 3000 FPS.

Yeah no reason to do a bunch of work then. Drop 10%, ladder back up to 3k FPS, run it. Probably will only take you 5 rounds.

 

[PddPdd]

I would try to find the same velocity node you used with the Hornady brass and see if you're getting the same accuracy. If you're happy with that, no need to find a higher pressure node or pressure signs.

 

[Pa Grizz]

Found out the hard why about changing brass Worked up a load with Remington brass for a 243 A friend gave me some federal brass Loaded up same load Was not a max load Locked my rifle so tight I liked to never got it open Found to late Federal brass is thicker meaning less space more pressure

 

[WYOHTF]

I ran into this issue with Lake City 7.62x51 brass,
I changed to a magnum match primer, velocities showed back up and es and as got a lot lower.
I was running IMR4064 and Varget back then.

This was for a .308 win running 165sst

 

[waveslayer]

why don't you give me your measurements and I will do the leg work for you with QL, you should be within .1 grains.

 

[Mikecr]

QL can't estimate H20 capacity.
Thicker brass springs back differently than thinner.
And it has to be measured-after fully fire formed to stable.

 

[waveslayer]

QL can't estimate H20 capacity.
Thicker brass springs back differently than thinner.
And it has to be measured-after fully fire formed to stable.

correct, but if you have the h2O data, then your velocity I can get a pretty good prediction of what charge you need to accommodate the less or more case volume. And it should be measured after using your die because you can alter the h2O capacity if you resize it from fire formed... unless you are smart enough to set your dies to just bump the shoulders and neck enough