700 receiver mag vs ultra mag , feed rails , mag box differences

[tdean]

I am trying to wrap my mind around the differences between the mag and ultra mag 700 receivers.

1. 700 mag receiver has wider feed rails than the ultra mag receiver
2. 700 ultra mag box is not as tapered as magnum box and the feedlips are shorter than the ultramag box

i tried putting an ultra mag box in the magnum action and the 26 nosler cases would just pop out. Because there were no lips or rails to hold them back.


Is it safe to say that on the ultras the actions feed rails hold the rounds in and on the mags the mag boxes feed lips hold the rounds in. ?

Will try and post some pics

Just trying to understand what's the best way to build a ultra mag based cartridge on a mag action

 

[tdean]

Pics

Ultra is .563 wide

Mag is .747

 

[Edd]

If I was faced with your issue, I would use a Wyatt center feed magazine box.

 

[tdean]

I agree just wanting some gunsmith advise on what they have done and if they agree with my synopsis

 

[MudRunner2005]

All of that sounds backwards to me... The RUM should be wider.

 

[Deleted member 46119]

You have it all right.

On the RUM the feed is controlled with the "lips" on the action.

Converting the 300 RUM to 28-Nosler, it just worked. The 270 that the 277-Nosler was made from "lips" that are to narrow. I am slowly widening them until it feeds correct.

Based on the RUM/28Nosler, this will be when the feed lips are .560. Started out much narrower.

 

[tdean]

Thank you!!

 

[Edd]

If you have a standard belted mag action that measures .747" between the feed rails, I think someone has modified them.

 

[Danny1788]

If you have a standard belted mag action that measures .747" between the feed rails, I think someone has modified them.

I agree 100% most of the time they are pretty close to the .550" of the ultramag case head, I have done a 6.5saum, and a few 28 noslers on mag actions. Sometimes the fatter case fits just fine other times it only needs to be filed/stones to let the case pass through the feed rails.

The biggest change to make it work is upfront by the feed ramp into the barrel. On the mag actions the feed rail tapers into the feed ramp on a ultra mag action its wider to let the fatter case pass through.

 

[tdean]

I think you guys are right. I'm sorry the mag action was made to take a aics mag and dbm. Other smith must have had to open it up.