Many many years ago I picked up a Rem 700 in 7mm Rem Mag from a guy getting a divorce.  I absolutely fell in love with the rifle.  He gave me the recipe he worked up for the rifle and some the components he used.  The brass was nickel plated (yeah, yeah, I know.  I've read all the negatives to nickel plated brass (and agree with them), but I went many years not knowing the issues and was so happy with my rifle and the load).  

I went to order some more brass and it's no longer made.  I really don't want to mess with the load as it is so good, but I'd like to load a bunch of ammo up for it.  What do I do?  Is there any way to figure out a way to use different brass with same results?  Obviously there is, but how do I go about it without it taking forever and driving me nuts?  Is it as simple as picking another quality brass and using a chrono to match the speed of my original load?

I suppose what I'm really asking is with the same bullet, does changing the brass affect accuracy if you can match the speed of original load?

Who made the nickel plated brass?

Does the same company make it in non-plated?

That would be the easiest point to start with.

I can't recall off the top of my head but I think Remington made it.  I may be dreaming that up though.  I'll have to look.

Just switch to Remington Brass brass then.   You’ll just have less neck splits.

You can compare brass batches by

1. weight of empty casing

2. weight of a fired in the chamber case filled to the neck with water and compare the weight of the water minus the weight of the case.

This will help you estimate how close the internal volume is.

Neat idea

That's what I'd do.  

You might have to put some numbers on how great the load really is, but if you're talking about a hunting type rifle at non extreme ranges, it seems like it would be pretty easy to switch brass, tweak the charge if needed to match velocity, and be really close.

https://www.grafs.com/retail/catalog/product/productId/72653

Start here buy some brass load the same bullet and powder charge with the same COAL and test them for accuracy.

I have a similar problem with 7mm WSM.

Best solution.

Just rework the load in brass you can find.  And, that is going to be the problem!  Remington brass not found like in the old days.
Using the nickel plated brass load as a benchmark for velocity and accuracy.

This.

I wouldn't worry about comparing water capacity at all. Find a good quantity of new brass, back off your old load data by about 3%, workup as normal, and stop when you get the same chrono velocity. Accuracy should be on par if you're using bullets, primers, and powder from your old load.

Peterson Cartridge makes 7mm Rem Mag brass, too.

OP, just pick up high quality brass, Lapua, ADG or Norma, get enough of the same lot to last you.. Then reduce your load by 7% and work up to matching velocity..You will love using high quality brass and you will be right where you started I not even better....Take care of your brass and you will be set....

Here is ADG brass, out of stock but you can search around in case someone has it in stock.......

https://atlasdg.com/product/7rm/

Pertersons quality seems to be lacking lately, my buddy bought some and was very disappointed..ADG/Lapua/Norma have all been excellent brass for us...

Let's see now, 7 mm Mag is hard to find, but 300 Win Mag is common.  I predict a barrel change in your future.  I went from 338 Win Mag to 300 Win mag for component availability.

Paladin

ETA:
https://www.midsouthshooterssupply.com/item/0005840045r/7mm-remington-magnum-unprimed-rifle-brass-box-of-50

https://www.powdervalley.com/product/prvi-7mm-rem-mag-50/

I was also very disappointed.  So much so, I just bought some NORMA brass, instead of Peterson, and put it in storage.

I was able to remedy the problem by neck turning every case.  I don't recall how much I took off but it was a lot (several mils).  The necks were so thick, after bullet seating they would not chamber.  IIRC, there was even a seating die issue.  Other than that, the brass was very nice.  Even the necks were uniform, just too thick.

Still, when your sources of supply become limited, it's good to know who can provide something to at least get you and keep you shooting.