25 SAW Cartridge Development

An Idea is Born

            Several years back, Miles Johnson and I met at Precision Rifle Series match in Navasota, Texas. The 7mm SAW was still in its early stages, and that Lone Survivor Foundation fundraiser was actually the first 2 day match I had shot the cartridge in. I shot well for my skill level at the time, and the 7mm SAW performed exactly as intended. Since then, it has grown to become a very popular chambering for our shop and many others. At the same time, Miles was working on a prototype .25 caliber bullet for competition that would take advantage of a ballistic sweet spot. He designed a bullet that retained the high BC abilities of the 6.5mm family (and actually exceeds many 6.5mm designs), while producing less recoil due to the bullet’s lighter weight because of the smaller .257 bore diameter. This hit the market as the Blackjack Bullets 131gr ACE projectile, to say it has made a splash would be an understatement. Blackjack currently offers not only the ACE projectile, but also a large selection of fast twist barrel blanks and chamber reamers for a myriad of different .25 caliber wildcat cartridges to take advantage of their bullet’s performance.

            We were, like many others in the precision rifle world, very excited to test out the capabilities of the ACE projectile. Given that our factory 7mm SAW brass came into full production this year, the timing was now perfect for one wildcat to give birth to another. We ordered up a pile of bullets, and with some sound advice from the Blackjack crew set designing a reamer for the .25 SAW. Dave Manson delivered the new reamer ahead of schedule, and before long we were off to shooting!

The Test Rifle

            The test rifle for the new cartridge is one of our new standard builds, called the Red River package. This build package is purposely designed for serious match shooting, and makes use of components designed and built by some of the most highly skilled precision rifle competitors in the sport.

• Impact 737 right hand action
• WTO SwitchLug
• Rock Creek .257 cal 1-7.25” 5R SS M40 contour barrel blank
• 26” barrel length, chambered for 25 SAW, .292” Neck/.112” Freebore
• Foundation Stocks MG1 Genesis stock
• TriggerTech Diamond curved shoe trigger, 1.0lb pull weight
• Hawkins Precision DBM
• MDT Extended OAL AICS style magazine
• Kahles K624i scope with SKMR3 reticle
• Hawkins Precision Heavy Tactical rings

Chamber Notes

            All testing was done using the prototype reamer, which was designed with a .292” Neck diameter of a .112” Freebore length. The neck yields a clearance of .002” per side on our 7mm SAW brass without neck turning.

We developed the following measurements for seating depth and cartridge length using the Wheeler seating depth method (learn more here), a Mitutoyo 6” digital caliber, and a Forster Datum Dial measurement tool:

Bullet Measurements

OAL: 1.436” -.005”
BTO: 0.749”
OTN: .687”

Unfired chamber measurements
Test bullet: 1.432”OAL/.746”BTO
Max COAL: 2.935”
Max BTO: 2.249”

A few other .257 cal bullets were measured, and the results are below for those interested:

110 Accubond: 2.250” BTO/2.760” OAL, bearing surface right at neck/shoulder
115 Berger Hunting VLD: 2.250” BTO/2.835” OAL, bearing surface well above neck/shoulder. Optimum seated.
110 Hornady ELD-X: 2.250” BTO/2.808” OAL, optimum seated.

Load Development

Break in load: 41.5gr RL16, CCI450, 2.230”BTO. Brass sized by one pass through 6.5CM die/.289” bushing, then final pass in Whidden 7mm SAW die with .281 bushing and .250 expander.
2893/13.4SD, .5” at conclusion of break in. Easy bolt lift and primer looks fine, but shows ejector mark on case head.
Same data as above but 42.0grs H4350: 2888/6.0, .55” group, easy lift, same case marks

Reloder 26 powder test, one shot per charge weight
2.229” BTO, CCI450, new formed brass as above.
44.0: 2800FPS, very mild start load
45.0: 2870FPS
45.5: 2904FPS
46.0: 2947FPS
46.5: 2990FPS
47.0: 3034, easy lift, no signs on Case head, primer beginning to flatten but not crater
47.5: 3074, easy lift, flowback on primer indent, max Case capacity. Established max for this powder

100 yard OCW test
46.4: 2984/19
46.8: 3027/14
47.1: 3038/33
All three charges shot the first three shots in sub .4”, then the fourth shot of every charge weight was a wide flyer. 33 rounds down, cleaned before continuing test

46.4: 2 foulers Fired on clean barrel, then 3 shots for group. .131” group, 2980/4.6SD for 3 shots. Combined numbers from OCW makes 2982/8.6 over 7 shots
Loaded the 46.4 load on 1x Brass, sized to 1.625” at .375 datum. Whidden sizer with .250” expander produced 2994FPS, equivalent accuracy.
Hornady die with .281 bushing and no expander produced 2981FPS, higher SD but same accuracy.

Additional Powder Testing

The following charge weights were formulated based on a predicted 52000 PSI chamber pressure. As powders and actual pressures can vary significantly from predictions, we loaded the predicted charge weights and recorded the actual results we found. The charge weight and predicted velocity for each are listed, followed by the actual fired data and group size if a group was fired.

• Reloder 23: 45.7/2861, 3018 actual, max pressure, 1 shot only.
• Reloder 16: 40.8/2849, 2866/3.7SD actual, .6”, safe pressure.
• IMR7828SSC: 46.0/2874, 2951/8.4SD actual. .35”, max pressure. Slight heavy lift at top of stroke
• H1000: 48.9(110% predicted Case fill)/2845, shot 47.5, 2927/4.0SD, .5”, max fill
• H4350: 41.6/2767, 2879/5.1 actual. .75”, safe pressure but near max.

Field testing and BC confirmation

            With an established accurate load running 46.4 grains of Reloder 26, it was time to move out to longer distances and start putting lead on steel. Blackjack recommends a .330 G7 BC for the 131 ACE, so we used that as our start point. The test barrel now had 80 rounds on it which was enough to check for a speed up, so before shooting at distance we re-checked velocity on the load. As expected, a slight velocity increase had occurred. The 46.4 grain load was now running just a touch over 3000FPS, and still shooting a bughole at 100 yards. Our first plate was 400 yards, and the projected trajectory would require 1.6 mils of elevation. At this distance the bullet shot slightly flatter than predicted, only requiring 1.5 mils for a center hit. The first 400 yard group came in under 2”(less than .5MOA at that distance), so we were comfident in the load to go further out. At 600 yards, the actual drop lined perfectly with the prediction on 3.0 mils. With a slightly switching wind in effect we printed a 3 ¾” group at 600, with only 2.5” of vertical dispersion. The group size didn’t set any records, but from experience this level of accuracy is more than adequate for a competition or long-range hunting rifle. Based on the solid data gathered, we moved on to 1090 yards. I have a 1 MOA round plate and a 2 MOA square at this distance, so I decided to burn the first shot on the 1 MOA plate. If I hit it on the first round I’d have my self-esteem boost for the day, and if not the area around the plate would give me excellent feedback for a correction. I dialed the predicted 7.6 mils of elevation and sent the bullet through warm west Texas air. It sailed just left of the target, and from the dirt impact it appeared to have been just slightly high of my aiming point. Armed now with humility and a good wind call, I dialed down a tenth and moved to the 2 MOA square. The first shot on the plate touched my center aiming point! I ran the bolt and dropped another one into the orange paint, seemingly on top of the first impact. A third shot made a nice group, falling just slightly slow of the first two hits. The group measured at 4 ¾”, roughly .41 MOA at that distance. After adjusting the BC numbers based on the data, we found a .335 G7 to match almost perfectly. 

            There were still a few loaded rounds left, so I decided to throw on a Dead Air Armament Nomad-30 suppressor to get a feel for the cartridge’s recoil impulse in field shooting. I’ve been running that suppressor and my 6.5 Creedmoor trainer barrel on my personal match gun, so this would give me a good impression of felt recoil versus another popular cartridge. I checked for POI shift at 100(there was none), and then got on my 1 MOA plate at 400 yards. Armed with the knowledge that 1.5 mils would hit it there and a nice constant breeze, I made an easy first round hit on the small steel. The succeeding shots just made the impact of the first bullet darker, so I knew it must be a decent group. After inspecting the plate, I found that it was my personal best group to date at that distance. Those three shots measured just under 11/16” center to center, roughly .65”. That works out to .16 MOA!

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Summary and Lessons Learned

1. This cartridge/bullet combination is crazy accurate! We’ve always loved how consistent the 7mm SAW is, and the 25 SAW is more of the same. It didn’t require a bunch of tuning on seating depth or loading gymnastics. Load it .020” off the lands, give it the powder it likes, and get to shooting tiny groups.
2. Future reamers will probably run a slightly longer freebore. The .112” Freebore put the bullet around 2.935” max OAL, and the extended MDT or A/W magazines can accommodate 2.960” with ease. We will probably end up lengthening the freebore to .142”, so that a loaded round .020” off lands is at 2.945”. This would still mag feed very well, but give just a shade more case volume (and maybe a little extra speed)
3. We will probably have Redding make 25 SAW custom FL sizer dies. We think this would be the most straightforward case forming method, and save time over a two-step process using different size neck bushings.
4. The 7mm seating stems in our Whidden, Redding, and Hornady 7mm SAW die sets all reliably seated the 131 ACE without issue. The Redding stem left a slight contact ring, but did not cut the jacket or contact the bullet nose.