That's a fantastic explanation!

And the RB weakness explanation supports my belief that only black powder should be used in the rolling blocks.

It has been a very long time since I closed my gunshop--back in the late 80's.  I thought I wanted to be an RB expert. I let it be known I was working with these guns.

I had one gun come into the shop that had opened-partially.  A 7mm Mauser.

I used to have the broken breech block from the incident. It's long gone or stuffed in a storage box some where. The gun had a ruptured case-front half still in chamber.  The back of the case was  gone.  The firing pin also gone.  The back part of the breech block, the part that rolls back and  bears on the hammer as it rolls under the  breech block to lock, was broke off.

The cartridge was smokeless. I was assured it was a factory round, but doubt it.   The owner never brought any other ammo in for me to check, kept forgetting. 

I had several people come in with the 7mm's that had problems with case stretching and head separations.   

My own 7mm Mauser RB was also stretching brass.  It was not a uniform lateral stretch,rather an angular stretch.  The stretch was greater at the top of the case, than at the bottom.   

It was pretty obvious there was some sort of flex or movement in the breech block going on.  Or perhap the block face wasn't truly square to the back of the  barrel. I never determined for sure which.

I never saw any indication of this flexing stretching in the rimmed cartridge guns . I have fired a lot of rounds through my 45/70 RB and not seen any indication of case stretching.

I am pretty sure Frank deHaas wrote a bit on this.

The only rimless RB's I saw were 7 mmMauser.  There were stories that there were some RB's in 30 Govt.  Was that 30-40 or 30-06?  Never saw one or talked to any who had actually seen one or knew for sure which cartridge was used.

I found unless you possessed deep skill and knowledge that Gunsmithing was not a good way to eat regular.  I had neither so I moved on.  I did some custom work after that, but haven't touch an RB since the 90's.

It's my understanding that the 7mm rolling blocks have generous or oversized chambers as compared to more modern rifles chambered in 7mm Mauser. Is this not correct?

My military r/b had a very heavy trigger, bought piano springs from RBKen here many moons ago, it is a very crisp sub 3LB one now .Just swapped out the trigger spring. Mal in au.

Many of the 7MM that I have seen the breach block is not square to the barrel face I have squared up a few over the years, some by machining the face and one by building up with weld. Recently had a Savage 99 come in that the bolt is not square and causing the brass to crack.

There's a difference between the SAAMI 7x57 and the RB 7x57. Not much, but enough to sometimes cause issues when shooting/reloading the 7mm RBs. BTDT.

DoubleD wrote on May 20^th, 2025 at 7:19am:


Anecdotally I deal with the egregiously oversize chamber of my 7mm (overly long by about 1/32" - breechblock square and tight to barrel tenon) by starting with fresh brass and enlarging the neck to 8mm then necking down to 7mm incrementally until the breechblock closes on it. The resulting micro shoulder is sufficient to guarantee headspace and not allow the head/body to stretch in an ungodly manner upon initial firing. Neck size only from there on out.

They, the 7mm's, are a law onto themselves.