7mm RUM headspace same as 300 rum and 338 edge?

[schemi]

I currently have a savage 7mm RUM and am building a 338 edge. Can i use a fired 7mm case to headspace the edge? I am not even sure if the 7mm has the correct headspace. With factory rounds the bolt will close easily with two layers of tape one the case head.

[efm77]

I think they're the same but I would play it safe and use a headspace gauge to make sure you have it correct. I'm pretty sure the Edge can be headspaced with a 300 UM gauge but someone else will have to tell you for sure as I am not 100%.

[PEI Rob]

Yes, its the 338 RUM that is shorter. Here's the best part, since you are reloading, you somewhat control the amount of sizing that your brass goes through. If your sizing die is a good match to your chamber, the brass is worked only a little when sized. Measure the diameter as well as length of fired brass and sized brass, if a die sizes the brass body diameter too much then the shoulder moves forwards and you must push it back. Factory rounds are made so they will fit into any rifle within spec, expect the 2 pieces of tape you noticed. I would use your fired 7mmRUM brass as a headspace gauge.

[schemi]

how can I tell if my 7mm is correct?