The 257 RAPTOR is a .257 caliber / 6.35mm cartridge designed as a medium game hunting cartridge out to 300 yards.  

The cartridge and chamber design are optimized for AR-15 using the AR-15 native 5.56 bolt and magazines.  That’s right, the 257 RAPTOR does not require a non-standard bolt or magazines or any modification to the upper receiver to enlarge the ejection port. Of course, if you want to, we have designed in the capability to ASC Stainless Steel Magazines that extend the seating depth to 2.29 inches for increased powder capacity and performance.

Most importantly, the 257 RAPTOR can load all 257 caliber bullets from 70 grains to 120 grains grains and function at AR-15 magazine length.

The 257 RAPTOR cartridge case is easily made from 223 Remington, 222 Remington or 5.56 NATO brass with only resizing and trimming the neck to the final length – No fire forming is required.

What was our goal to achieve? We sought to have multiple hunting bullet options that deliver 1,000 foot pounds of terminal energy at 200 yards while still achieving a minimum of 1800 fps at 300 yards in a light weight hunting rifle configuration. We are talking bullets like the Nosler Partition or Tip, not a match bullet unsuitable for hunting. To put this in perspective, the 45 RAPTOR with a 225 grain Hornady FTX at 2465 fps achieves just over 1,000 foot pounds of terminal energy at 200 yards. Before you think this rifle is a heavy weight, a 257 caliber rifle, with an 18 inch barrel, can weigh as little as 4.25 pounds. which depending on optics, will weigh under 6 pounds with a scope and under 5 pounds with a red / green dot optic such as the Trijicon MRO.

A common question is “What is different between the 25-45 Sharps and the 257 RAPTOR?”

The 25-45 Sharps is a 223 Remington necked up to .257 caliber, not unlike the 6×45 is a 223 Remington necked up to .243 caliber or 6mm.   While simple a case to form, the maximum bullet exposure of either the 25-45 Sharps or the 6×45 cartridge is .478 inches when restricting the overall length of either cartridge to 2.25 inches or .518 inches when using an ASC Stainless Magazine that can seat to 2.29 inches. Unfortunately, many .257 caliber hunting bullets heavier than 90 grains have an ogive longer that .478 or .518 inches can’t be seated in the 25-45 Sharps.

In contrast, the 257 RAPTOR allows a maximum bullet exposure of .675 inches permitting the use of the full range of .257 bullets from 70 grains up to 120 grains while keeping within a 2.25 inch magazine length restriction of the AR-15.  In addition, when seating bullets to a maximum cartridge length of 2.25 inches, the 257 RAPTOR will have .959″of bullet length forward of the main powder column allowing for an efficient powder density with minimal bullet intrusion into the main body of the case.   When using the ASC Stainless Steel Magazine, when seated to 2.29 inches, the amount of bullet forward of the powder column is increased to .999 inches. This is an important consideration when looking at different .257 bullets and the overall length of each bullet:

  • Nosler 85 grain Ballistic Tip: 1.00″
  • Nosler 100 grain Ballistic Tip: 1.115″
  • Nosler 100 grain E-Tip: 1.195″
  • Nosler 100 grain Partition: 1.035″
  • Nosler 110 grain Accubond: 1.195″
  • Nosler 115 grain Ballistic Tip: 1.207″
  • Nosler 115 grain Partition: 1.145″
  • Nosler 120 grain Partition: 1.175″
  • Sierra 70 grain Blitz King: .878″
  • Sierra 87 grain Varminter: .860″
  • Sierra 90 grain Game King: .890″
  • Sierra 90 grain Blitz King: 1.071″
  • Sierra 100 grain Match King: 1.086″
  • Sierra 117 grain Pro Hunter: 1.080″
  • Sierra 117 grain Game King: 1.116″
  • Sierra 120 grain Game King: 1.170″
  • Speer 87 grain SP: .820″
  • Speer 87 grain TNT: .920″
  • Speer 100 grain BTSP: .995″
  • Speer 100 grain SP: 1.019″
  • Speer 120 grain BTSP: 1.140″
  • Speer 120 grain SP: .995″

For example, the Nosler 110 grain Accubond has an overall length of 1.195″ so subtracting .999 means that only .196″ is below the neck / shoulder intersection when using the ASC Stainless Magazine. As another example, the Nosler 100 grain Partition has an overall length of 1.035″ so again subtracting .999″ means that only .036″ of the bullet is below the neck / shoulder intersection when using the ASC magazine.

Now, with the popularity of the 300 AAC Blackout, what does the 257 RAPTOR do that the 300 AAC Blackout doesn’t?

Compared to the 257 RAPTOR, the 300 AAC Blackout is a shorter cartridge and has less powder capacity to drive bullets at supersonic velocities.  In addition, for equal weight bullets, 257 caliber bullets have a much higher ballistic coefficient allowing them to retain velocity and energy to greater ranges.   Therefore, if you take a 110 or 115 grain bullet in either caliber, the 257 RAPTOR will not only drive the bullet faster due to higher powder capacity, the ballistic design of the bullet will let you use that performance out to a longer distance.

Another question that has been asked. Given my history with the 6.5 Grendel, why not neck the Grendel case down to .257 caliber?  Well going back to 1997 and 1998 when the original work that led to the Grendel was occurring, the .257 caliber was actually the preferred caliber except for one thing that gave the 6.5mm an advantage – the availability of match bullets.  As a pure hunting cartridge, the 257 was the clear winner with the abundance of hunting bullet offerings between 100 and 120 grains. However, my original work was to build high-power competition cartridge in the AR-15 with hunting being a secondary priority. Fast forward to the present, a 257 Grendel would be superior as a hunting cartridge to the 6.5 Grendel.   However, another aspect of my RAPTOR designs is to eliminate non-standard parts like bolts and magazines.  While the 45 RAPTOR ended up requiring special magazines, the 375 RAPTOR, 7 RAPTOR and 257 RAPTOR have all eliminated proprietary components to the benefit of the end user while obtaining the performance I set-out to achieve.

While we are finalizing our load data and performance data, we can tell you that both the 257 RAPTOR and 375 RAPTOR use the same powders further reducing the complexity if you want both a medium bore and large bore for your AR-15 and AR-10 respectively.

2021 Update

We have finalized the chamber design to use both standard magazines and ASC stainless steel magazines to allow either 2.26 or 2.29 overall length loadings. We will be performing load pressure tests in March 2020 and when complete, we will order a production run of die sets that will be available here as well as releasing the reamer to x-caliber barrels who has asked to add the 257 Raptor to their chambering offerings.

If you have a question, please email arne@northamericansportsman.com