AR15.Com Archives
 .257 Roberts
chadjetlag  [Team Member]
6/18/2011 8:16:00 PM
Has anyone ever chambered an AR in .257 roberts or ackley improved? It seems like it would be the ideal cartridge, pushing a 100 grain at 3000...it would give the extra ummmph that the 5.56 is lacking. What would be involved in building one? obviously barrel and magazine. Overall length 2.97"
wombat25  [Team Member]
6/18/2011 10:01:43 PM
Not even close. Any cartridge which is going to be chambered in an AR-15 must be no longer (overall length) than 2.26" That's the primary limitation to chambering standard hunting cartridges in the AR-15, and why most variants (6.8SPC, 6.5 Grendel, .50 Beowulf, .458 SOCOM, .450 Bushmaster, etc.) are developed specifically with the AR platform in mind. Gotta get short enough to fit in the magazine.

That 2.26" limitation is a bugger.

Altair  [Team Member]
6/18/2011 10:21:46 PM
Even in the 308 platforms I believe the overall length restriction is 2.8" so no go there either.
6mmAR15  [Member]
6/18/2011 10:44:19 PM
Roberts is a long action cartridge........even the ar 10 uses short action cartridges...........
oldschool63  [Team Member]
6/19/2011 1:06:40 AM
The 257 Roberts is a short action cartridge with a Max OAL of 2.780 Per SAAMI specs.

So it would probably work very well in the AR 10 platform. It uses the .473 bolt face so most likely all you would need is a new barrel and mag.



turboscott  [Team Member]
6/19/2011 2:20:59 AM
Originally Posted By oldschool63:
The 257 Roberts is a short action cartridge with a Max OAL of 2.780 Per SAAMI specs.

So it would probably work very well in the AR 10 platform. It uses the .473 bolt face so most likely all you would need is a new barrel and mag.





That would be sweet in a AR. 257 roberts was my first deer rifle, and I loved it.

8654  [Member]
6/19/2011 8:44:01 AM
Would they stack in the mag correctly? Looks like a bit too much taper.

8654
capitolP  [Member]
6/21/2011 2:27:03 PM
You could do a 250-3000/250 Savage in an AR-10 platform.

How about a 6.8/.257, that would be very cool.

P
Quarterbore  [Life Member]
6/21/2011 2:48:45 PM
257 Roberts is a bit too long for even the AR-10 unless you really push the bullet back into the case. A better round is the 25 Souper (25/308 wildcat). This is a shorter case that would work better with the AR-10 size rifles.

I have never done it as the 308 ammo is more available and I can kill anything with a 308 that I could kill with the 257 or a 25 wildcat so why bother... And I am a big quarter-bore fan at that and I call myself Quarterbore because of a deep affinity of the 257 Roberts and 25/06.
wombat25  [Team Member]
6/21/2011 7:02:04 PM
I too am a huge .25 fan, with both a .25-06 and a .25-223 in the safe.

I've thought about a 6.8-based .257 wildcat myself, but I pretty quickly realized there wasn't much advantage here - expensive parent brass, proprietary bolts and magazines, custom dies and barrel, and performance of the cartridge would likely suffer with .257 vs. .277 bullets.

Here's a nice article with some equations to use in estimating velocity for wildcat cartridges:

http://www.reloadingroom.com/index_files/25-308.htm
precisionpredators  [Member]
6/21/2011 8:21:53 PM
Originally Posted By capitolP:
You could do a 250-3000/250 Savage in an AR-10 platform.

How about a 6.8/.257, that would be very cool.

P

Waiting for reamers presently a variant like this 25 PPC
DeutschLuger61  [Member]
6/21/2011 11:33:48 PM
Just get a 25 WSSM from Olympia Arms. Load it for what lever of performance you want. Will beat the 257.
6mmAR15  [Member]
6/22/2011 11:58:20 AM
Originally Posted By oldschool63:
The 257 Roberts is a short action cartridge with a Max OAL of 2.780 Per SAAMI specs.

So it would probably work very well in the AR 10 platform. It uses the .473 bolt face so most likely all you would need is a new barrel and mag.






The 257 Roberts is not a 'short action' cartridge. It's case is 2.233" long, based on the 7x57 case. Anyone that chambers it will do so in their std 'long action'... It is a 'tweener in cartridge length. Too long for the short action for 308 Win cases (2.015" long), but great for seating heavy bullets out long in long actions.
oldschool63  [Team Member]
6/22/2011 9:15:31 PM
Originally Posted By 6mmAR15:
Originally Posted By oldschool63:
The 257 Roberts is a short action cartridge with a Max OAL of 2.780 Per SAAMI specs.

So it would probably work very well in the AR 10 platform. It uses the .473 bolt face so most likely all you would need is a new barrel and mag.






The 257 Roberts is not a 'short action' cartridge. It's case is 2.233" long, based on the 7x57 case. Anyone that chambers it will do so in their std 'long action'... It is a 'tweener in cartridge length. Too long for the short action for 308 Win cases (2.015" long), but great for seating heavy bullets out long in long actions.

My Remington 700 in 257 Roberts is a short action.



DeutschLuger61  [Member]
6/23/2011 12:08:17 AM
Remington gets away with that by seating the bullets deep in the case. That can't be loaded out to utilize the whole capacity of the case. They do the same thing with the 6mm Remington which is on the same case. All that doesn't make what Remington does putting them on a short action right.
Quarterbore  [Life Member]
6/23/2011 9:09:23 AM

Originally Posted By DeutschLuger61:
Remington gets away with that by seating the bullets deep in the case. That can't be loaded out to utilize the whole capacity of the case. They do the same thing with the 6mm Remington which is on the same case. All that doesn't make what Remington does putting them on a short action right.

+1 and it is the reason I would NEVER buy a Remington in 257 Roberts! Ruger you will note makes the 257 Roberts on a long action that allows the bullets to be seated out far enough to make the 257 Roberts a better round. The older Remington 722s in 257 Roberts were built on a long action.
pomofo  [Member]
6/24/2011 10:32:40 AM
257 Roberts barrel for DPMS-pattern 308 ARs.

http://shop.si-defense.com/SI_Defense_257_Roberts_Barrel_Chrome_Moly_18_p/si%20ar-b-257r-18.htm