257 Roberts Seating depth

[MooseHunter]

Building 257 Roberts on Browning Safari Sako. Wondering if I can seat bullets out farther that 2.800 inches. I will modify mag box if it will work. Thinking copper bullets. Hammers etc

 

[SeabeeKen]

I depends on how your barrel is throated. You'll have to measure to find out. I have loaded to 2.9" in my 257AI Mauser action with 90 gr Hammers

 

[LCazador]

Building 257 Roberts on Browning Safari Sako. Wondering if I can seat bullets out farther that 2.800 inches. I will modify mag box if it will work. Thinking copper bullets. Hammers etc

Seat a bullet so the boattail is about even with the neck/shoulder junction then see how it fits magazine and how much you will have to alter mag. Keep in mind monolith bullets can be much longer so rifle barrel twist must be able to stabilize that longer length.

 

[MooseHunter]

I am working with Sako basically a 579. The 90 gr Hammer was on my list. Barrel I am using is 9 twist. According to hammer 10T will work. Wondering how much I should mess with mag box. The gunsmith will figure this out as he will have the reamer and the box in hand. I may send him some dummies seated long and he can adjust COAl/box to reamer.
Does anyone run 62,000 PSI in .257 Roberts these days? Dont see how it would be a problem in modern action but figgered I would ask.

 

[JEFFPPC]

If your trying to get the most out of that case why not go .257 AI?

 

[MooseHunter]

If both cartridge's are run at 62,000 what is the velocity gain of the AI?

 

[358WCF]

If both cartridge's are run at 62,000 what is the velocity gain of the AI?

Good question. I've no pressure test equipment. Haven't worked with a standard Roberts for a few years, but about 7-10% seems about right. With my latest 257 Ackley; long action 700, 9 twist, OAL pushing 3", I'm knocking on factory listed 25-06 speeds with 100s & 115s from a 24" barrel. Brass life is good, primer edges are round, & bolt lift is normal. Re: copper... So far it seems to like the Barnes 80s & 100 TTSX pushed hard, but more testing is needed.

Case life is quite often better with improved cases, but am thinking it depends on brass, chamber, & die dimensions jiving happily. My 06 Ackley doesn't seem to agree with Lapua 06 brass as it's a bit larger at the .200 line than 90s era WW brass. Between my chamber & the Forster FL die, the WW brass goes many firings w/o trimming, the Lapua needs trim every other firing. Correlation isn't necessarily causation but is how I'm seeing this situation until proven otherwise.