Adjusting for case volume

[1stmar]

Curious how you guys adjust for case volume differences between brass manufacturers. I have a load that works well in x brand brass and would like to try y brand brass. Y brand brass has 5% more volume. Do you guys add 5% more powder and keep everything else the same? Assuming still below max charge

[RC20]

I just do 3/10 above and below the load to see if there is any difference.

Usually a tray of 50, 15 below, 15 above and 20 with the standard.

[mikld]

The old saw for reloading is; "with any component change, reduce loads and work back up". Normally I won't go quite that far, but my loads rarely go near max. so I will normally drop a load 1 grain or so and work back up. My math sucks so I rarely try any formula or percentage, but I will closely observe and record results of any change...

Normally when I work up a load I will be as consistent with the components as I can; same headstamp, same primer, same powder lot, same bullet, just changing the powder charge. When a load looks like it has potential, I'll tweek charges buy .3 grain up or down. If I want more from a load, I may change one component then work up again.

I like reloading so all this research/testing/shooting/recording/analyzing is fun for me. Quicker methods like the ladder test, and OCW are faster, but I have no real need for "faster"...

[NoSecondBest]

Shoot them and see what the difference is. Why fix it if it isn't broke?

[Dufus]

I will give my example.

Most of my 30-06 brass is WW and REM or R-P (same stuff).

The internal volume of the REM/R-P brass is less than the WW.

In order to get the same workable loads and velocity, I have to reduce the powder charge by 3.0 gr. with the REM/R-P brass.

If I load both the same powder charge, the REM/R-P brass quickly creates over max charges for my rifles.

This brass is from mostly the 1970s. I have a lot of both.

[jmorris]

I don’t load “full tilt” rounds much these days, if I need more power I just get out a more powerful gun.

I do cull brass that has enough internal volume difference my powder check dies can tell the difference.

https://www.youtube.com/watch?v=6EU9deSKm48

[1stmar]

Thanks for the responses. I dont load to max charges either. Max accuracy and if that gets to max accuracy thats ok but it rarely has. Ive decided to try more expensive brass to see if it makes a difference. I know case volume is a key attribute in quickload so i assumed there was a formula you could use to get equivalent barrel time/velocity to replicate the same performance.

[Unclenick]

CAUTION: The following post includes loading data or advice beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.


If this is a high power rifle cartridge there are a couple of strategies out there. An old one based on a Wm. C. Davis, Jr. article from long ago is to use 0.533 grains of powder for each additional grain of water capacity under the bullet. This based on using a powder similar to IMR4895 or 4064. This is meant to work over a narrow range, but should be OK with yours.

But before you do any of that, you need to be sure the volume difference is real. Don't depend on brass weight or resized cases to tell you anything certain. Run one of each headstamp of average weight through your FL sizing die. Trim both to the same length. Put the old load in both and fire both. Take the fired cases straight to your scale and weigh them. Fill each one with water level to the mouth (no meniscus) with tap water (tapping them on the way to dislodge any air bubbles), and weigh them again and then subtract their dry weights from their wet weights to get the weight of the water they hold. For each grain more water, Davis suggests that 0.53-grain charge difference. Depending on the powder it will be a little bit more or less.

Another strategy that is safe when going from smaller to larger cases using the same type of powder only and the type of primers only, but which would raise pressure going the other way, is to take a chronograph and increase the charge in small steps until you get an average velocity match with the new brass.

[1stmar]

Thanks unclenick. I was close, only gap was tapping the cases to remove any air bubbles. Will check again. Thank you.

[RC20]

And the 3/10 above on my work would only be if there was space to do so, clearly not with a load that was showing any pressure signs and only cautiously if it was at maximum but now pressure signs there.

I don't push max, I look for accurate loads below that so I have some play room when testing.

I never assume max is max either, if I get any pressure sign up in the higher ends but below max, I stop.

[RC20]

I know my method is somewhat heretical, but the times I wanted to compare case capacity, I just used W748, filled it up and then scraped off the excess with a flat edge.

You could do a tap when its full as well.

I think my test with 06 came up with a ratio of 5 grain case weight difference to 1 grain powder difference.

I will re-run my test and log it, should always do that but get sidetracked.

[1stmar]

Rc20 that makes sense. Any ball powder should work, ie 231

[F. Guffey]

Adjusting for case volume

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Curious how you guys adjust for case volume differences between brass manufacturers. I have a load that works well in x brand brass and would like to try y brand brass. Y brand brass has 5% more volume. Do you guys add 5% more powder and keep everything else the same? Assuming still below max charge

Not me: Again: I have one 30/06 chamber that is .011" longer from the shoulder to the bolt face than a normal, everyday, common old go-gage length chamber.

What does that mean? The chamber is .002" longer than a field reject length gage and .016" longer than a minimum length/full length sized case.

Back to adjusting for case volume: When sizing the case I am in control of case volume, if I choose to reduce volume I shorten the distance from the shoulder of the case to the case head. If I choose to increase volume I increase the distance from the shoulder of the case to the case head.

There are pother factors: I have cases with .200" thick case heads from the cup above the web to the case head; I also have cases that have a case head thickness of .260" Forget what the outside of the case looks like because the powder columns are different length and have a different diameter powder column.

I do not insist on using the cases with thick case heads, I do feel they are safer

F. Guffey

[1stmar]

Interesting post guffey. I never considered adjusting for volume that way. Ive always tried to keep the shoulder within .003 unless its a gas gun.

[T. O'Heir]

Smokeless powder isn't loaded by volume. It's loaded by mass. The slight differences by manufacturer aren't enough to worry about either. Far less so for hunting ammo. It might matter to a Bench Rest shooter, but nobody else.

[1stmar]

I did some measurements agaiin this morning. My 308 load is 42.5 gr of 4064 using lc brass ,168smk and cci priners. This load in my garand hovers between .9 and 1.1”. Using the formula unclenick recommended and using lapua brass, accounting for the volume difference my load should be 43.6gr. 1.1gr of difference is substantial. If i recall an unrelated thread indicated fed GMM load was 43.5 of 4064. Maybe a coincidence. When the weather breaks i will load up some and see if there is any difference in group sizes.

[cw308]

I only shoot benchrest , I shoot 3 different brands of brass one each week , HSM ADI and FC . Using the same load same bullet , everything exact except the cases . All three shoot groups just as tight , would not change your load without testing first .

[F. Guffey]

I built a rifle, it was a 270W with a VZ receiver. When finished I loaded 12 different loads using 12 different cases, different loads with different powders and as many bullets as I had.

It took me all day to avoid heating the rifle; I did not adjust the scope, I used one point of aim. The groups moved but did not open up.

When finished I found the groups moved and I did not have a flyer out of 120 rounds.

I loaded another 120 rounds of 12 different loads with 12 different cases and then I delivered the rifle with ammo to the new owner. I wanted him to take the rifle to the rang and determine what the rifle liked.

He called and said the rifle liked everything. He said he shout one round and then zeroed the scope. SO? There was no magic load.

Anyhow, I was happy.

F. Guffey

[1stmar]

I have seen both sides. In 308 i have fired ppu and lc brass in the same group and alll shots went into 1.25”. With 223 the difference between lc brass and fc is zero but Ga brass was significant. I plan to try both

[Don Fischer]

If I remember right most manuals say to start 10% below max and work up. Get into the data and most tell you the case they used. Use any case you want but start 10% below max and work up. No I don't do that but not willing to tell how far to drop. Sure as can be someone will try it, get t wrong and I'm the bad guy. Once you have learned to reload, not just read everything you can, it will get easier!

[std7mag]

T.O. apparently never heard of the Lee volume method....
Even their auto disk is measured in volume.

[Marco Califo]

The slight differences by manufacturer aren't enough to worry about either

308/7.62 as discussed here is the cartridge with the most variation between brands and military brass. That is enough to worry about.
Rather than adjust for different volumes, I would try for consistent brass. 500 prepped LC (sized, trimmed, crimp removed, like years) from Top Brass is $115 @ Midsouth.

[1stmar]

I have tried the Davis compensation on two different cartridges (22-250 and 3006). This seemed to work very well for me. I had been using win brass and 4064 for both cartridges, i tried switching to lapua. Both rifles shoot about the same (probably the limit of my capability), about .3”. With the lapua brass my groups were noticeably larger, after adjusting for case volume they are now inline or better than the win brass.

Great tip, thanks nick. Will be trying some 308 and possibly 223 as well.

[Unclenick]

Glad that worked out for you.

If you want to get more sophisticated, invest in a copy of QuickLOAD. Even if it doesn't match your load exactly, it tends to do so relatively. That is, put your standard load in, including the case volume, obviously, and then note the barrel time in ms in the output window. With the new volume, tweak the charge weight until that barrel time matches the original.

[1stmar]

Thanks Nick. Quickload is on my list. Been watching some videos to get familiar with it. Any short cuts when changing bullets, either weight or manufacturer?