Load data for .257 Ackley Improved + .258 | 85gr | Rim Rock RNFP Cowboy
Recommended Powder(s): ReloadSwiss RS 60, Somchem S365
Load Specifications
(Use the Personalized Load Calculator below to adjust )
Bullet: | .258 | 85gr | Rim Rock RNFP Cowboy |
Manufacturer SKU: | #001 |
Bullet Weight: | 85gr | 5.5g |
Bullet Diameter: | 0.258" | 6.55mm |
Bullet Length: | <<locked>> |
Caliber: | .257 Ackley Improved load data |
Case Length (l3): | 2.333" | 59.3mm |
Cartridge Length (C.O.L.): | <<locked>> |
Seated Depth: | <<locked>> |
Shank Seated Depth: | <<locked>> |
Case Capacity: | 63.0 Grains of Water | 4.09 cm³ |
Primer Size: | Large Rifle (LR) |
Max. allowed Pressure: | 48200 psi | 3323 bar |
LID: | LID_B10489_C102 |
Last updated: | 2026-06-09 |
Load data for 94 loads in caliber .257 Ackley Improved with .258 | 85gr | Rim Rock RNFP Cowboy bullet and 47 powders such as ReloadSwiss RS 60, Somchem S365. The key underlying parameters are shown in the table above.
Important Notice: DO NOT go below Minimum Charge or above Maximum Charge unless there are reasons. Since xxlreloading.com has no control over the equipment and components used by the customer and the data used in connection with the website, any responsibility and liability for the results achieved is rejected. Also see our Terms of Service.
Questions regarding the load data: Please read the information in the next tab "Explanations".
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A load must fulfill certain criteria to be listed in the default view below - see "powder criteria to fulfill to be listed".
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Our load data might deviate from other sources - see the "most common reasons for deviations".
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All loads are based on the bullet and case dimensions shown under "Load Specifications" - see "reloading suggestions" if you deviate.
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You can set your specifications in the "Personalized Load Calculator".
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Use the Personalized Load Calculator to customize loads to your own specific requirements. Find more details in the help section.
Our default view only displays powders/loads that fulfill certain criteria: Max pressure of a load <=90% of Max. Standardized Pressure. Fill Rate (Min FR): >80% and <100% for rife loads, >60% and <100% for pistol loads. Min. Propellant Combustion (Min z): >90% for rifle loads , >80% for pistol/revolver loads. Relax these criteria at your own risk to potentially get more powders shown in the load tables.
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Click on the desired row in the tables below to add a specific load / powder to your Diary and manage there.
Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
ADI AR 2208 | <<locked>> | 84% | 42801 | 89% | **00 | 97% |
Accurate 4064 | <<locked>> | 84% | 42772 | 89% | **17 | 100% |
Accurate 4350 | <<locked>> | 92% | 42714 | 89% | **69 | 96% |
Alliant Reloder- TS 15.5 | <<locked>> | 85% | 43091 | 89% | **40 | 98% |
Alliant Reloder-16 | <<locked>> | 93% | 42699 | 89% | **89 | 96% |
Alliant Reloder-17 | <<locked>> | 89% | 43366 | 90% | **41 | 98% |
Alliant Reloder-23 | <<locked>> | 97% | 34113 | 71% | **79 | 95% |
[Alliant Reloder-26]* | <<locked>> | 97% | 38319 | 80% | **46 | 94% |
Bofors RP3 | <<locked>> | 85% | 42772 | 89% | **43 | 98% |
[Bofors RP7]* | <<locked>> | 88% | 43033 | 89% | **77 | 92% |
Hodgdon H380 | <<locked>> | 84% | 43004 | 89% | **30 | 96% |
[Hodgdon H414]* | <<locked>> | 90% | 42917 | 89% | **73 | 93% |
Hodgdon Hybrid 100V | <<locked>> | 96% | 43279 | 90% | **59 | 98% |
[Hodgdon Superperformance]* | <<locked>> | 90% | 43004 | 89% | **69 | 92% |
Hodgdon TrailBoss | <<locked>> | 96% | 33083 | 69% | **93 | 100% |
IMR 4064 | <<locked>> | 83% | 43207 | 90% | **00 | 97% |
[IMR 4350]* | <<locked>> | 92% | 42728 | 89% | **87 | 92% |
[IMR 4451 Enduron]* | <<locked>> | 87% | 42714 | 89% | **74 | 93% |
IMR 4831 | <<locked>> | 94% | 42844 | 89% | **50 | 96% |
Lovex S062 | <<locked>> | 83% | 42902 | 89% | **10 | 99% |
Lovex S065 | <<locked>> | 90% | 43047 | 89% | **91 | 95% |
[Lovex S070]* | <<locked>> | 91% | 42931 | 89% | **04 | 93% |
Norma 203B | <<locked>> | 83% | 43221 | 90% | **46 | 98% |
Norma URP | <<locked>> | 92% | 42757 | 89% | **66 | 96% |
Ramshot Big Game | <<locked>> | 83% | 42946 | 89% | **59 | 97% |
[Ramshot Hunter]* | <<locked>> | 93% | 43105 | 89% | **76 | 94% |
ReloadSwiss RS 14 | <<locked>> | 96% | 33257 | 69% | **33 | 100% |
[ReloadSwiss RS 50]* | <<locked>> | 84% | 42569 | 88% | **87 | 94% |
ReloadSwiss RS 60 👍 | <<locked>> | 87% | 42931 | 89% | **38 | 100% |
ReloadSwiss RS 62 | <<locked>> | 92% | 42670 | 89% | **92 | 96% |
ReloadSwiss RS 70 | <<locked>> | 92% | 42598 | 88% | **92 | 95% |
Rottweil R 903 | <<locked>> | 87% | 43062 | 89% | **33 | 98% |
[Rottweil R 907]* | <<locked>> | 88% | 43033 | 89% | **77 | 92% |
SNPE Vectan SP 11 | <<locked>> | 86% | 43236 | 90% | **63 | 97% |
SNPE Vectan Tubal 5000 | <<locked>> | 85% | 43236 | 90% | **35 | 100% |
[SNPE Vectan Tubal 7000]* | <<locked>> | 90% | 43265 | 90% | **48 | 93% |
Shooters World Long Rifle | <<locked>> | 90% | 43047 | 89% | **91 | 95% |
Shooters World Precision | <<locked>> | 83% | 42902 | 89% | **10 | 99% |
Somchem S355 | <<locked>> | 87% | 43178 | 90% | **33 | 98% |
Somchem S365 👍 | <<locked>> | 96% | 42975 | 89% | **22 | 99% |
Vihtavuori N135 | <<locked>> | 84% | 43004 | 89% | **84 | 100% |
Vihtavuori N150 | <<locked>> | 88% | 42917 | 89% | **84 | 99% |
Vihtavuori N160 | <<locked>> | 91% | 42467 | 88% | **23 | 96% |
Vihtavuori N550 | <<locked>> | 92% | 43033 | 89% | **43 | 96% |
Vihtavuori N555 | <<locked>> | 97% | 37072 | 77% | **64 | 95% |
Winchester 6.5 StaBALL | <<locked>> | 91% | 43221 | 90% | **10 | 98% |
[Winchester 760]* | <<locked>> | 90% | 42917 | 89% | **73 | 93% |
Max Load - Barrel Length: 23.60''
Powder | Charge | FR | MaxP | % | V(0) | z |
|---|---|---|---|---|---|---|
ADI AR 2208 | <<locked>> | 81% | 38072 | 79% | **79 | 95% |
Accurate 4064 | <<locked>> | 81% | 37782 | 78% | **09 | 99% |
[Accurate 4350]* | <<locked>> | 83% | 29588 | 61% | **15 | 90% |
Alliant Reloder- TS 15.5 | <<locked>> | 81% | 37579 | 78% | **09 | 97% |
[Alliant Reloder-16]* | <<locked>> | 83% | 30661 | 64% | **48 | 90% |
[Alliant Reloder-17]* | <<locked>> | 81% | 32343 | 67% | **27 | 94% |
[Alliant Reloder-23]* | <<locked>> | 90% | 27528 | 57% | **46 | 90% |
[Alliant Reloder-26]* | <<locked>> | 93% | 32648 | 68% | **69 | 90% |
Bofors RP3 | <<locked>> | 81% | 37130 | 77% | **05 | 97% |
[Bofors RP7]* | <<locked>> | 85% | 38232 | 79% | **69 | 90% |
[Hodgdon H380]* | <<locked>> | 81% | 38130 | 79% | **05 | 94% |
[Hodgdon H414]* | <<locked>> | 86% | 36666 | 76% | **09 | 90% |
[Hodgdon Hybrid 100V]* | <<locked>> | 81% | 26121 | 54% | **71 | 90% |
[Hodgdon Superperformance]* | <<locked>> | 88% | 39015 | 81% | **71 | 90% |
Hodgdon TrailBoss | <<locked>> | 81% | 26208 | 54% | **19 | 100% |
IMR 4064 | <<locked>> | 81% | 39987 | 83% | **22 | 96% |
[IMR 4350]* | <<locked>> | 88% | 38029 | 79% | **82 | 90% |
[IMR 4451 Enduron]* | <<locked>> | 83% | 37289 | 77% | **36 | 90% |
[IMR 4831]* | <<locked>> | 83% | 29631 | 61% | **99 | 90% |
Lovex S062 | <<locked>> | 81% | 39668 | 82% | **28 | 98% |
[Lovex S065]* | <<locked>> | 81% | 32822 | 68% | **25 | 90% |
[Lovex S070]* | <<locked>> | 86% | 36114 | 75% | **33 | 90% |
Norma 203B | <<locked>> | 81% | 39943 | 83% | **64 | 97% |
[Norma URP]* | <<locked>> | 83% | 30226 | 63% | **28 | 90% |
Ramshot Big Game | <<locked>> | 81% | 39769 | 83% | **74 | 96% |
[Ramshot Hunter]* | <<locked>> | 87% | 34867 | 72% | **56 | 90% |
ReloadSwiss RS 14 | <<locked>> | 81% | 26484 | 55% | **65 | 100% |
[ReloadSwiss RS 50]* | <<locked>> | 81% | 38653 | 80% | **92 | 92% |
ReloadSwiss RS 60 | <<locked>> | 81% | 34490 | 72% | **25 | 98% |
[ReloadSwiss RS 62]* | <<locked>> | 84% | 30821 | 64% | **71 | 90% |
[ReloadSwiss RS 70]* | <<locked>> | 86% | 33794 | 70% | **46 | 90% |
Rottweil R 903 | <<locked>> | 81% | 34301 | 71% | **20 | 96% |
[Rottweil R 907]* | <<locked>> | 85% | 38232 | 79% | **69 | 90% |
SNPE Vectan SP 11 | <<locked>> | 81% | 36143 | 75% | **89 | 95% |
SNPE Vectan Tubal 5000 | <<locked>> | 81% | 37565 | 78% | **13 | 100% |
[SNPE Vectan Tubal 7000]* | <<locked>> | 85% | 36158 | 75% | **74 | 90% |
[Shooters World Long Rifle]* | <<locked>> | 81% | 32822 | 68% | **25 | 90% |
Shooters World Precision | <<locked>> | 81% | 39668 | 82% | **28 | 98% |
Somchem S355 | <<locked>> | 81% | 35389 | 73% | **33 | 96% |
[Somchem S365]* | <<locked>> | 81% | 25382 | 53% | **97 | 91% |
Vihtavuori N135 | <<locked>> | 81% | 38798 | 80% | **99 | 100% |
Vihtavuori N150 | <<locked>> | 81% | 33750 | 70% | **71 | 97% |
[Vihtavuori N160]* | <<locked>> | 81% | 30182 | 63% | **89 | 90% |
[Vihtavuori N550]* | <<locked>> | 82% | 30124 | 62% | **05 | 90% |
[Vihtavuori N555]* | <<locked>> | 89% | 28282 | 59% | **08 | 90% |
[Winchester 6.5 StaBALL]* | <<locked>> | 81% | 30168 | 63% | **59 | 93% |
[Winchester 760]* | <<locked>> | 86% | 36666 | 76% | **09 | 90% |
Start Load - Barrel Length: 23.60''
Any powder missing? Then click here.
FR ... fill rate of the cartridge in percent
MaxP ... max. pressure of load in psi or bar
% ... max. pressure of load in percent of the maximum allowed pressure for this caliber
V(0) ... muzzle velocity in feet per second (fps) or meters per second (m/s)
z ... powder burnt in percent
[...] *... not dangerous but load has suboptimal powder burnt with possible characteristics such as extensive muzzle flash or inaccurate loads.
[...] ²... fill rate low - you might want to consider using a filler to ensure proper ignition.
[...] ᴾ... possible press load - work up slowly to this load while watching for signs of excessive pressure.
👍 ... recommended powder/load for this caliber and bullet combination based on its ballistic performance.
<<locked>>... you need to buy an access license to unlock the data