2-1/2" seems to be the most common length for brass .410 shotshells. Midway has them for $23/25. RMC has full 3" brass, but the price is a bit breathtaking at $70/25.

Are there any less expensive options out there? I've read about 2-3/4 and 2-7/8 brass, but haven't located any yet.

9.3x74R rifle brass, annealed/fireformed. Hornady and Norma are available.

The only way to go where you want to go is to pay the RMC price, which is cheap really at about 3 bucks each, the cases will last indefinitely...I've paid twice that for some of my wet dream cases...look up the price for 50-140 brass!!!! Or, make your own out of 9.3x74R or an available large bore rimmed cartridge like the 40-90 Sharps straight...there are several that would work and Buffalo Arms has them...but those case prices are a bit high also. This wildcatting in ANY form is pricey!!!!

You would have to turn the case base end a few thou' and the rim a smidge depending on the actual dimensions of your 410 chamber...so unless you have a lathe, there is another cost to consider.

You also have to consider the ejector/extractor if you want to use the 9.3x74R...it might work OK, it might not, depending on the shotgun/rifle/pistol...it works somewhat with 444 M cases which has a smaller diameter rim than the 410 shotshell.

Might be better just to just use 3" plastic 410 and call it good. Much cheaper in the short run.

Luck