Depends on what you mean by "almost". Apart from chamber dimensions, brass thickness/weight, bullet weight, primer sensitivity and pressure levels, they are almost identical. Sometimes bullet diameters are significantly different, as well.
"Hungry" here on the board has a standing offer. Send him 5 fired cases, and he will measure them, and let you know what the exact situation is with your rifle. Sometimes it might be better not to know.
Fortunately, most commercial ammunition is of very high quality, and a failure of non handloaded ammuntion is extemely rare. Handloading cases fired in a rifle with generous headspace is a different situation.