Curious about the bore size on the 7mm Remington Rolling Blocks

[brstevns]

I am curious as to what others are finding about bore size on their Rem RB in 7mm. Mine is .288 and I find a bullet of .292 works the best for me. It seems like the old saying ( fill the throat ) on this one.

[sass2924]

Are you using regular 7x57 brass. I’ve seen others report it does not always fit the chambers of the RB’s, not sure though.

[Lostinidaho]

What other brass would you use?

[brstevns]

I have also sized down 8x57 testing as I go, to get a tight fit. I have also expanded up 6mm Rem and 257 Roberts to 30 cal and sized back down for a tight fit. I am only shooting a 10 Unique load for the my first firing.

[marlinman93]

What other brass would you use?

You wouldn't normally use anything but 7x57 brass. But often chambers are a bit "loose" so it's a good idea to fire form factory 7x57 brass, and then don't full length size it. Simply neck size it after forming, and it will fit your particular gun's chamber a lot better, and brass will last longer.
I haven't owned a 7mm Roller in a very long time, but had several in the past. I loaded cast lead bullets in those I shot, and my mold drops a .288" bullet that worked well in my guns. The old Ideal mold I have is for a gas checked bullet, and I loaded to around 1400 fps in mine.

[Reverend Al]

At the time these rifles were manufactured the 7x57 military cartridges of the day weren't necessarily produced to today's specs. They were usually longer in overall case length and the shoulder length is often further forward than today's brass. Don't expect it to match today's SAAMI specs for 7x57 Mauser because it won't! Many people who shoot these old 7x57 Rollers use .30-06 or .270 cases, and form them by pushing the shoulder back slowly until the action will just close ensuring correct headspace. (In my case I already had a bunch of 7x57 brass on hand so I neck expanded the cases up to about .30 calibre with a tapered mandrel and then sized them back down until the "false" shoulder I formed headspaced properly in my rifle.) Making a cerrosafe chamber casting would give you the exact chamber length of your rifle so that you can trim cases to the proper length to match your chamber as well. Mine has a fairly "fat" chamber and is a bit hard on brass since even with low pressure loads it tends to expand cases generously at the base. Just some of the joys of shooting these old guns ... but the good news is that suitable brass can be formed easily and cheaply and simply replaced after a couple of firings if necessary. Enjoy shooting your old Roller ...

[brstevns]

No one as yet said what their bore size is.

[curator]

My 1902 Remington rolling block 7mm mikes at .288 in the grooves but has a looooong .290+ throat. Nobody mentioned that the breech blocks on these rollers are not always perpendicular to the bore. I have to mark the head-stamp area so I can reorient each case the same as it was initially fireformed or I have trouble closing the breech block. Not all have this issue, but it is something to be aware of when reloading for them.

[brstevns]

My 1902 Remington rolling block 7mm mikes at .288 in the grooves but has a looooong .290+ throat. Nobody mentioned that the breech blocks on these rollers are not always perpendicular to the bore. I have to mark the head-stamp area so I can reorient each case the same as it was initially fireformed or I have trouble closing the breech block. Not all have this issue, but it is something to be aware of when reloading for them.

I use a permanent marker on the case, mark a line before I ever start loading. I know to put this mark up.

[marlinman93]

No one as yet said what their bore size is.

Guess I didn't say the exact bore size when I said mine shot good with a .288" bullet. Mine was a .287" bore.

[high standard 40]

I don't have a 7MM Mag per se, but I have an XP100 that has a cut and re-chambered barrel from a Remington 700 7MM Mag. My barrel has a .284" bore with a .277" groove. For best accuracy I do have to size to .287" because my chamber has a large throat diameter.

[Reverend Al]

I guess I'll have to slug mine and find out what size it measures ... I've only shot it so far with .284" 175 grain J words ...