The 6mm Creedmoor is a short action centerfire rifle cartridge featuring a maximum case length of 1.920 inches (48.77 mm) and a maximum overall cartridge length of 2.825 inches (71.76 mm). Based on official SAAMI standards, the case features a 0.473 inch rim diameter, a 0.470 inch base diameter, a 0.462 inch shoulder diameter, and a maximum neck diameter of 0.276 inches. A fully formed neck spans approximately 0.294 inches in length, providing ample tension for long projectiles. Published specifications can vary slightly depending on whether they represent maximum material conditions, nominal dimensions, or specific manufacturer tolerances across different standardization bodies.
6mm Creedmoor Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 1.920 | 48.77 | Maximum | SAAMI | Standard trim to length is 1.910 in. |
| Rim Diameter | 0.473 | 12.01 | Maximum | SAAMI | Standard short action bolt face. |
| Rim Thickness | 0.054 | 1.37 | Maximum | SAAMI | Controls extractor engagement. |
| Base Diameter | 0.470 | 11.94 | Maximum | SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | 0.462 | 11.73 | Maximum | SAAMI | Body to shoulder intersection. |
| Neck Diameter | 0.276 | 7.01 | Maximum | SAAMI | Outside case neck diameter. |
| Neck Length | 0.294 | 7.47 | Derived Nominal | SAAMI | Calculated from case length minus shoulder datum. |
| Shoulder Angle | 30° | N/A | Half Angle | SAAMI | Standard Creedmoor family shoulder geometry. |
| Overall Length | 2.825 | 71.76 | Maximum | SAAMI | Designed to fit standard AICS short action magazines. |
| Case Capacity | ~51.5 | 3.34 cm³ | Nominal (H2O) | Industry Std. | Varies by brass manufacturer and wall thickness. |
| Maximum Pressure | 62,000 | 427.47 MPa | Max Average | SAAMI (Piezo) | Identical pressure limit to the 6.5 Creedmoor. |
Understanding The 6mm Creedmoor Case Dimensions
To understand how the 6mm Creedmoor interacts with a rifle chamber, bolt, and magazine, you must analyze its discrete geometric components. Each dimension serves a specific engineering purpose to balance powder capacity with bullet seating depth.
- Case Length: Measured from the base of the rim to the case mouth, case length determines how far the brass extends into the chamber before contacting the end of the neck clearance.
- Rim Diameter and Thickness: The rim provides the gripping surface for the rifle extractor. The diameter ensures the cartridge centers on a standard short action bolt face, while the thickness affects how securely the extractor engages the brass.
- Base Diameter: This is the widest part of the main cartridge body, situated just ahead of the extractor groove. It governs how the cartridge seats into the rear of the chamber.
- Shoulder Diameter and Geometry: The shoulder acts as the physical stop that prevents the cartridge from pushing too far into the barrel. Its diameter and 30 degree angle dictate chamber fit and headspacing.
- Neck Diameter and Length: The neck holds the bullet. The outside diameter must clear the chamber walls to allow the brass to expand and release the projectile safely upon firing. The long neck length ensures proper alignment and tension for heavy, high ballistic coefficient bullets.
- Overall Cartridge Length (OAL): The measurement from the case base to the tip of the seated bullet. It dictates magazine fit and whether the bullet will prematurely engage the rifling lands.
- Case Capacity: The internal volume of the case, generally expressed in grains of water (gr H2O). This dictates the maximum powder charge the cartridge can safely hold.
6mm Creedmoor Case Dimensions In Inches And Millimeters
Official standardization utilizes inches, but metric parameters are frequently referenced by international precision shooters and brass manufacturers.
| Dimension | Measurement (Inches) | Measurement (Millimeters) |
| Maximum Case Length | 1.920 in | 48.77 mm |
| Maximum Rim Diameter | 0.473 in | 12.01 mm |
| Maximum Base Diameter | 0.470 in | 11.94 mm |
| Maximum Shoulder Diameter | 0.462 in | 11.73 mm |
| Maximum Neck Diameter | 0.276 in | 7.01 mm |
| Maximum Overall Length | 2.825 in | 71.76 mm |
6mm Creedmoor Case Length
The published maximum case length for the 6mm Creedmoor is 1.920 inches (48.77 mm). This matches the case length of its parent cartridge, the 6.5 Creedmoor.
Because brass flows forward under the extreme pressures of firing and resizing, a fired and full length resized case will frequently measure longer than a factory new case. Operating at the absolute maximum length can cause the case mouth to pinch inside the chamber throat, resulting in dangerous pressure spikes. Therefore, handloaders universally utilize a trim length of 1.910 inches. This nominal case length provides a 0.010 inch buffer to ensure consistent chamber fit and safe bullet release.
6mm Creedmoor Base And Rim Dimensions
The 6mm Creedmoor features a rimless, bottleneck design. Its base diameter measures 0.470 inches, while the rim diameter is slightly wider at 0.473 inches.
This 0.473 inch rim diameter is a foundational standard shared by the .308 Winchester family. It dictates that the cartridge fits perfectly on a standard short action bolt face. The rim thickness of 0.054 inches determines how well the bolt extractor claw can grip the cartridge during the violent rearward motion of cycling the action.
6mm Creedmoor Shoulder And Neck Dimensions
Above the straight taper of the body, the case steps down to grip a 6mm (0.243 caliber) bullet. The shoulder diameter at the intersection of the case body is 0.462 inches. From there, the brass angles inward at a steep 30 degree half angle to meet the neck.
The neck diameter reaches a maximum allowable SAAMI specification of 0.276 inches. To safely release a 0.243 inch bullet, the chamber neck must be slightly wider than the cartridge neck. A loaded cartridge typically measures around 0.272 to 0.274 inches at the neck depending on the brass wall thickness. The 30 degree shoulder combined with minimal body taper promotes highly efficient powder ignition and limits brass stretching during firing.
6mm Creedmoor Case Capacity
Case capacity heavily influences internal ballistics, powder selection, and pressure generation. The nominal, industry accepted capacity for the 6mm Creedmoor is approximately 51.5 grains of water, or roughly 3.34 cubic centimeters.
This capacity makes the 6mm Creedmoor highly efficient, capable of pushing heavy 105 grain to 115 grain bullets at competitive velocities without burning excessive amounts of powder. Case capacity is not a static specification. It fluctuates between brass manufacturers. Premium brass manufacturers like Lapua or Alpha Munitions often utilize thicker web structures near the case head for durability, which slightly reduces the internal volume compared to standard Hornady brass.
6mm Creedmoor Case Dimensions vs 6.5 Creedmoor
The 6mm Creedmoor is a direct descendant of the 6.5 Creedmoor, and their dimensions reflect this close relationship.
| Dimension | 6mm Creedmoor | 6.5 Creedmoor | Source |
| Case Length | 1.920 in | 1.920 in | SAAMI |
| Rim Diameter | 0.473 in | 0.473 in | SAAMI |
| Base Diameter | 0.470 in | 0.470 in | SAAMI |
| Shoulder Diameter | 0.462 in | 0.462 in | SAAMI |
| Neck Diameter | 0.276 in | 0.295 in | SAAMI |
| Overall Length | 2.825 in | 2.825 in | SAAMI |
| Case Capacity | ~51.5 gr H2O | ~52.5 gr H2O | Standard Data |
6mm Creedmoor Case Dimensions vs Similar Cartridges
The 6mm Creedmoor competes in a crowded field of highly accurate 6mm centerfire cartridges designed for precision rifle shooting.
| Cartridge | Case Length | Base Diameter | Shoulder Angle | Neck Diameter | Overall Length |
| 6mm Creedmoor | 1.920 in | 0.470 in | 30° | 0.276 in | 2.825 in |
| .243 Winchester | 2.045 in | 0.471 in | 20° | 0.276 in | 2.710 in |
| 6mm Dasher | 1.555 in | 0.470 in | 40° | 0.268 in | 2.390 in |
| 6mm ARC | 1.490 in | 0.441 in | 30° | 0.276 in | 2.260 in |
| 6×47 Lapua | 1.850 in | 0.470 in | 30° | 0.273 in | 2.795 in |
6mm Creedmoor vs 6.5 Creedmoor Case Dimensions
The 6mm Creedmoor shares identical case lengths (1.920 inches), base diameters (0.470 inches), rim diameters (0.473 inches), and the signature 30 degree shoulder angle as the 6.5 Creedmoor.
The only dimensional difference resides in the neck. The 6mm Creedmoor features a neck diameter reduced to 0.276 inches to hold a smaller 0.243 caliber bullet, whereas the 6.5 Creedmoor features a wider 0.295 inch neck diameter for a 0.264 caliber bullet. Because the case bodies are identical, 6mm Creedmoor and 6.5 Creedmoor cartridges feed interchangeably from the exact same short action magazines.
6mm Creedmoor vs .243 Winchester Case Dimensions
For decades, the .243 Winchester was the standard 6mm short action cartridge. The 6mm Creedmoor was designed specifically to fix the geometric shortcomings of the .243 Winchester for modern long range shooting.
While both utilize a 0.470 inch base and a 0.473 inch rim, the .243 Winchester features a longer 2.045 inch case length and a shallower 20 degree shoulder. The critical difference lies in the overall length geometry. The 6mm Creedmoor uses a shorter 1.920 inch case paired with a longer 2.825 inch overall length. This allows shooters to seat long, aerodynamic, heavy for caliber bullets far out of the powder column while still fitting perfectly inside standard short action magazines. The .243 Winchester case is too long to easily accommodate these modern bullets without seating them deeply into the case, which sacrifices powder capacity.
6mm Creedmoor Chamber And Case Dimensions
A rifle chamber must be fractionally larger than the cartridge it accepts. The relationship between 6mm Creedmoor case dimensions and chamber dimensions centers heavily on headspacing.
Headspace for the 6mm Creedmoor is measured from the bolt face to a specific datum line on the 30 degree case shoulder. When the firing pin strikes, the case expands to seal the chamber. If the case dimensions are too small relative to the chamber, the brass will stretch aggressively to fill the void, thinning the material near the base. If the case dimensions are too large, the bolt will not close.
6mm Creedmoor Case Forming And Resizing
Because the 6mm Creedmoor is simply a necked down 6.5 Creedmoor, handloaders can easily form their own brass if factory 6mm Creedmoor cases are unavailable.
This process involves forcing high quality 6.5 Creedmoor brass through a specialized 6mm Creedmoor sizing die. Because all Creedmoor cases share the same 1.920 inch length and 30 degree shoulder, modifying 6.5 Creedmoor brass only requires a single pass through a sizing die to constrict the neck from 0.295 inches down to 0.276 inches. Neck turning is occasionally required afterward to ensure the compressed brass walls do not become too thick for the rifle chamber.
6mm Creedmoor Manufacturer Specifications vs Actual Measurements
There is a documented difference between absolute SAAMI standards and the dimensions of a physical cartridge sitting on a reloading bench.
SAAMI lists maximum material conditions. Ammunition manufacturers intentionally produce brass slightly smaller than these maximums to guarantee their cartridges will chamber in any rifle, regardless of how tightly the manufacturer cut the chamber. A fired 6mm Creedmoor case expands to the exact dimensions of the specific rifle chamber it was fired in. When a handloader runs this fired brass through a full length sizing die, the machine compresses the base, shoulder, and neck back down to factory nominal tolerances.
Common Questions
What are the 6mm Creedmoor case dimensions?
The key maximum case dimensions for the 6mm Creedmoor include a 1.920 inch case length, a 0.473 inch rim diameter, a 0.470 inch base diameter, a 0.462 inch shoulder diameter, and a 0.276 inch neck diameter.
What is the 6mm Creedmoor case length?
The maximum SAAMI case length for the 6mm Creedmoor is 1.920 inches (48.77 mm). The standard trim to length for reloading is 1.910 inches.
What is the 6mm Creedmoor rim diameter?
The 6mm Creedmoor rim diameter is 0.473 inches (12.01 mm), which fits standard short action bolt faces.
What is the 6mm Creedmoor base diameter?
The base diameter of the 6mm Creedmoor, measured just above the extractor groove, is 0.470 inches (11.94 mm).
What is the 6mm Creedmoor shoulder diameter?
The maximum shoulder diameter of the 6mm Creedmoor is 0.462 inches (11.73 mm).
What is the 6mm Creedmoor neck diameter?
The maximum outside neck diameter of the 6mm Creedmoor is 0.276 inches (7.01 mm).
What is the 6mm Creedmoor case capacity?
The nominal case capacity of the 6mm Creedmoor is approximately 51.5 grains of water (H2O), or 3.34 cubic centimeters. Actual capacity varies depending on the brass manufacturer wall thickness.
What is the 6mm Creedmoor overall length?
The maximum overall cartridge length for the 6mm Creedmoor is 2.825 inches (71.76 mm) under SAAMI specifications.
How does 6mm Creedmoor compare with 6.5 Creedmoor case dimensions?
The 6mm Creedmoor shares the exact same case length, base diameter, rim diameter, and shoulder angle as the 6.5 Creedmoor. It simply features a neck reduced to 0.276 inches to hold a smaller 0.243 caliber bullet.
How does 6mm Creedmoor compare with .243 Winchester case dimensions?
Both cartridges share a 0.470 inch base and 0.473 inch rim, but the 6mm Creedmoor features a shorter 1.920 inch case length and a steeper 30 degree shoulder. The .243 Winchester has a longer 2.045 inch case length with a 20 degree shoulder. The 6mm Creedmoor design allows longer bullets to be seated without exceeding standard magazine lengths.
What is the 6mm Creedmoor maximum pressure?
The SAAMI maximum average pressure for the 6mm Creedmoor is 62,000 psi (piezo method), matching the pressure specification of the 6.5 Creedmoor.