257 Roberts/AI

[BLJ]

Considering doing something with one of these.

Currently have a 257 Roberts on a Mauser 98 action.
Shoots well but it is twisted very slow. 1/14 measured with a cleaning rod.
Always shot 87 Hornadys well, but I’m wanting to try something heavier.

Couple questions.
The 134 ELDM will be heaviest bullet I want to shoot. The other bullet I’m considering is a 120 Partition.
Would a 1/7.5 twist 20” barrel be sufficient for these bullets at 257 Roberts velocity?
What’s lightest bullet that would work with the 7.5 twist? Or do I need to go faster for the heavier bullet?

Right now the Mauser 98 has room for 5 in the mag.
Will I be able to still get 5 in the mag with a 257 Roberts AI?
It seems like there will still be enough room, it haven’t been able to find out for sure.
I’d prefer to go AI to gain the velocity but I would also prefer to keep 5 in the mag.

Any experience with any 257 Roberts stuff welcome.

Thanks.

ETA.

Does a SAAMI spec chamber work with the longer 134’s?

 

[Chris in TN]

I'd comment on this even without this question, because this is right up my alley of cool things to watch, but...

Why does magazine capacity matter? I've shot 3 deer with 3 and 4 shots when we had places to hunt with lots of deer, but that was rare, and most times I'm pretty content with 1-2 rounds in the magazine, especially hunting near home. I've never fired more than 4x in a day of big game hunting.

So a 4 round magazine wouldn't be an issue to me, in any way.
YMMV.

(My 98 Mauser sporter used to be a slow twist .257, but that was ages ago)

 

[Q_Sertorius]

I have not personally tried it yet, but I foresee no difficulties with 134-grain ELDM’s in my 1:8” twist .25-06 (based on reports from others who have already done it). I’d expect no issues with a 1:8 twist with the light bullets at .257 Roberts velocities.

I never measured the twist rate on my .257 Roberts, but it shoots the 117-grain loads very well.

I do like the idea of a 1:7.5” or 1:8” twist Roberts pushing out 134-138 grain bullets. That almost turns it into a 7x57 with a higher BC.

On the other hand, if I went for 1:7.5” or 1:8” twist, I would also plan to not waste powder and barrel life shooting lighter bullets. I did that for years when I was a poor teenager and couldn’t afford another rifle, firing many, many 70-grain .257 bullets. Never again. If I want to shoot 69-88 grain bullets, I have a .223 and a 1:8” twist 22-250.

Edit - I also don’t like AI cartridges or think they are worth the trouble.

 

[Chris in TN]

Edit - I also don’t like AI cartridges or think they are worth the trouble.

So - just a FWIW.....

I generally think of new brass as needing to be 'fireformed' for any rifle. So there's no real difference to me between an AI case and a standard case. Grab new brass, load up something near maximum seated long, shoot, now you have 'new' 1xfired brass. Same process as any standard chambering.

I built my .280ai before AI brass for it became common. I fireformed Nosler .280R brass then bought a bunch of Geco 165(?) grain .280R ammo and burned it up at the range for brass. That stuff had an almost round-nosed bullet but still shot great out to 600 yards.

But I'll freely admit that I was happy when Peterson started selling .280ai brass.

 

[Wrench]

Mag capacity is the same. 1:8 is enough.....and unless you are sitting on a pile of brass, I'd go right to a 25-06 or 08. Bob brass is hard to source and harder to source quality brass.

 

[BLJ]

The difference between 4 and 5 doesn’t sound as bad when someone else says it.
I’d just prefer to not give up what I have. If possible.

120 grain Partitions will be as light as I go.
I have 243/22ARC/223 for smaller.

I know brass is an issue. I have about 250 pieces of older Remington, with 100 of that being new from the 90’s.
I think that will suffice for my needs from this rifle.
And I’m not opposed to resizing other cartridges to get what I need. The correct head stamp isn’t an issue for me.

And I’m pretty set in cartridge. It was given to me as a 257 and unless something unexpected happens, it will stay that way.

Any info on the difference in velocity between standard chamber and AI?

Thanks.

 

[jfk69]

Agree on the 4 vs 5 not mattering to me. I’ve never shot that much hunting. 1:8 twist will stabilize the 133-134 bullets just fine. My 1:10 twist .257AI shoots everything up to 120 grains flawlessly. The AI will get you 100fps more with any weight bullet for ~5% more powder. The 257AI has a coolness factor that vanilla calibers don’t have lol. I love mine, built on a 1910 Mexican small ring M98.

 

[Chris in TN]

man, 2025 me sure would like to go back and explain to 1988 me how awesome a 20” .257R would be. I still have enough ammo to get started:

 

[West2East]

I love AI cartridges, they look sexy. There's something about a 300 Norma AI cartridge sitting on the table.... do it!

 

[BLJ]

Anyone have any numbers for a 257 AI from a 20” barrel? Preferably with something 120 grains or heavier for an idea.

 

[TaperPin]

257 Roberts brass is still available new in Nosler or Remington.

 

[BLJ]

Wonder how 90’s era Remington brass compares to today?

 

[jfk69]

Don’t know how they compare, but I’m still shooting Remington and Winchester brass from the late 90’s in mine. Some of it has 12+ firings on it. Primer pockets still good. I only FL size it when it gets tight, every 6-7 firings. Otherwise neck size with a Lee collet neck die. Love never needing to trim it.