The 25 Creedmoor is a standardized, modern quarter-bore centerfire rifle cartridge developed by necking down the popular 6-5 Creedmoor to accept 257-thousandths-inch bullets! Officially accepted by SAAMI in January 2025, it was engineered to bridge the gap between lightweight 6mm match cartridges and heavier 6-5mm multi-purpose rounds. By capitalizing on high-Ballistic Coefficient heavy-for-caliber bullets and an efficient short-action case architecture, the 25 Creedmoor delivers exceptional external ballistics, manageable recoil, and a flat trajectory!
25 Creedmoor Case Dimensions Overview
| Dimension Property | Specification (Imperial) | Specification (Metric) |
| Parent Case | 6-5 Creedmoor | 6-5 Creedmoor |
| Bullet Diameter | 257 thousandths in | 6 mm and 53 hundredths mm |
| Case Length | 1 in and 920 thousandths | 48 mm and 77 hundredths |
| Case Trim Length | 1 in and 910 thousandths | 48 mm and 51 hundredths |
| Overall Length (COAL) | 2 in and 825 thousandths (Max) | 71 mm and 76 hundredths |
| Rim Diameter | 473 thousandths in | 12 mm and 1 hundredth |
| Rim Thickness | 54 thousandths in | 1 mm and 37 hundredths |
| Base Diameter | 4703 ten-thousandths in | 11 mm and 95 hundredths |
| Shoulder Diameter | 462 thousandths in | 11 mm and 73 hundredths |
| Neck Diameter | 288 thousandths in | 7 mm and 32 hundredths |
| Shoulder Angle | 30 degrees | 30 degrees |
| Case Capacity | Approx 52 grains water | 3 cubic cm and 38 hundredths |
| Maximum Average Pressure | 62-thousand psi | 427-5 megapascals |
Understanding the 25 Creedmoor Case Dimensions
- Parentage: Derived directly from the 6-5 Creedmoor, retaining its body taper, small rifle or large rifle primer pockets, and efficient powder column design;
- Shoulder Geometry: Features a sharp 30-degree shoulder angle that promotes clean headspacing, uniform powder ignition, and minimized brass stretching during firing cycles;
- Short-Action Compatibility: Designed to respect standard short-action magazine parameters with a maximum overall length of 2 in and 825 thousandths, allowing seamless integration into AICS-compatible platforms;
- Quarter-Bore Optimization: Standardizes the bore and groove dimensions specifically around low-drag, high-BC 257-inch projectiles, paired with a recommended fast 1 to 7-and-a-half twist rate;
25 Creedmoor Case Dimensions in Inches and Millimeters
| Measurement Point | Max (Inches) | Min (Inches) | Max (Millimeters) | Min (Millimeters) |
| Case Length | 1 and 920 thousandths | 1 and 900 thousandths | 48 and 77 hundredths | 48 and 26 hundredths |
| Trim-To Length | 1 and 910 thousandths | None | 48 and 51 hundredths | None |
| Rim Diameter | 473 thousandths | 463 thousandths | 12 and 1 hundredth | 11 and 76 hundredths |
| Base Diameter | 4703 ten-thousandths | 4663 ten-thousandths | 11 and 95 hundredths | 11 and 84 hundredths |
| Shoulder Diameter | 462 thousandths | 457 thousandths | 11 and 73 hundredths | 11 and 61 hundredths |
| Neck Diameter | 288 thousandths | 283 thousandths | 7 and 32 hundredths | 7 and 19 hundredths |
| Bullet Diameter | 257 thousandths | 255 thousandths | 6 and 53 hundredths | 6 and 48 hundredths |
| Overall Length (COAL) | 2 and 825 thousandths | 2 and 600 thousandths | 71 and 76 hundredths | 66 and 4 hundredths |
25 Creedmoor Case Length
The maximum case length of the 25 Creedmoor is 1 in and 920 thousandths (48 mm and 77 hundredths), with a recommended trim-to length of 1 in and 910 thousandths (48 mm and 51 hundredths)! Because of the 30-degree shoulder angle, brass flow under high pressures up to 62-thousand psi is relatively controlled. However, handloaders pushing heavy match bullets should monitor case elongation after multiple firings and trim consistently to prevent neck-to-chamber interference in tight match chambers!
25 Creedmoor Base and Rim Dimensions
The 25 Creedmoor utilizes a standard beltless rimless architecture inherited from the 30 Thompson Center via the 6-5 Creedmoor!
- Rim Diameter: 473 thousandths in (12 mm and 1 hundredth)
- Base Diameter: 4703 ten-thousandths in (11 mm and 95 hundredths)
- Rim Thickness: 54 thousandths in (1 mm and 37 hundredths)
This exact geometry ensures that standard bolt faces designed for the 308 Winchester family, 6mm Creedmoor, and 6-5 Creedmoor will lock up and extract flawlessly without any custom bolt face modifications!
25 Creedmoor Shoulder and Neck Dimensions
- Shoulder Angle: 30 degrees provides an optimal balance between reliable feeding and sharp headspace definition;
- Shoulder Diameter: Measures 462 thousandths in at the junction;
- Neck Length & Diameter: The neck diameter is 288 thousandths in, engineered to maintain uniform neck tension on 257-inch projectiles! Premium brass manufacturers offer consistent neck wall thicknesses, minimizing the need for extensive neck turning in factory chambers!
25 Creedmoor Case Capacity
The internal case capacity of the 25 Creedmoor averages roughly 52 to 52-and-a-half grains of water, depending heavily on the brand of brass used! Because it shares the powder volume profile of the 6-5 Creedmoor, it functions best with medium-burn-rate rifle powders like Hodgdon H4350, Alliant RL-16, and Vihtavuori N555, achieving ideal fill ratios and consistent muzzle velocities!
25 Creedmoor Dimensions vs Similar Cartridges
| Cartridge | Bullet Diameter | Case Length | COAL | Max Pressure |
| 25 Creedmoor | 257 thousandths | 1 and 920 thousandths | 2 and 825 thousandths | 62-thousand psi |
| 6-5 Creedmoor | 264 thousandths | 1 and 920 thousandths | 2 and 825 thousandths | 62-thousand psi |
| 6mm Creedmoor | 243 thousandths | 1 and 920 thousandths | 2 and 800 thousandths | 62-thousand psi |
| 25-06 Remington | 257 thousandths | 2 and 630 thousandths | 3 and 250 thousandths | 63-thousand psi |
| 257 Roberts | 257 thousandths | 2 and 235 thousandths | 2 and 775 thousandths | 54-thousand psi |
Chamber and Case Dimensions
SAAMI-compliant 25 Creedmoor chambers feature throat dimensions optimized specifically for long, high-BC quarter-bore projectiles! The freebore is tailored so that bullets like the 134-grain ELD Match can be seated out near the lands without exceeding standard magazine length limits! Proper headspace gauge control ensures safe and repeatable case sizing for handloaders!
Common Questions
- Can I form 25 Creedmoor brass from 6-5 Creedmoor brass?Yes! Because they share the identical base, body taper, and shoulder angle, running quality 6-5 Creedmoor brass through a 25 Creedmoor full-length sizing die with proper neck bushing adjustments easily and accurately forms functional brass!
- Does the 25 Creedmoor fit in standard short-action rifles?Yes! Its maximum overall length allows it to fit seamlessly into standard short-action magazines without modification!
- What twist rate is required for 25 Creedmoor dimensions?SAAMI specifications and modern manufacturers recommend a 1 to 7-and-a-half twist rate to properly stabilize heavy, ultra-long-range 257 bullets at standard velocities!