Rifle · Wildcat (no SAAMI/CIP standard)
6x45mm
A 6mm (.243) wildcat made by necking up the .223 Remington / 5.56x45mm case.
- Caliber
- 0.243″ · 6.17 mm
- Introduced
- 1965
- Case
- Rimless
- Parent
- .223 Remington
- Primary use
- Varmint, Hunting, Target
- Status
- Wildcat
- Introduced
- 1965
- Type
- Rifle
- Origin
- United States
- Standard
- Wildcat (no SAAMI/CIP standard)
- Status
- Wildcat
- Availability
- Rare
- Case capacity
- 26.9 gr H₂O
- Twist (typical)
- 1:10 (faster for bullets over 80 gr)
- Primer
- Small Rifle
- Case type
- Rimless
- Max pressure
- 52,000 psi
- Eff. range
- 400 yd
- Max range
- 3000 yd
- Recoil
- 5–8 ft·lb
Ballistics
Velocity only, no drag model: no published ballistic coefficient is on file for 6x45mm, so this is the shape gravity alone gives the advertised velocity. Drag would steepen it. The tool below solves real loads through their published G1 or G7 model.
Open in Ballistic Compare- Parent case
- .223 Remington
Representative trajectory — modeled from a single velocity input (no published BC for this cartridge yet).
Dimensionscase measurements · scale drawing · size vs familiar rounds
Case dimensions — the scale drawing at the top of the page is built from these.
Wikipedia; Sierra & Handloader load data · verified| Measure | mm | in | ✓ |
|---|---|---|---|
| Bullet ⌀ | 6.17 | 0.243 | |
| Neck ⌀ | 6.90 | 0.272 | ✓ |
| Shoulder ⌀ | 9.00 | 0.354 | ✓ |
| Shoulder angle | 23° | — | |
| Base ⌀ | 9.55 | 0.376 | ✓ |
| Rim ⌀ | 9.60 | 0.378 | ✓ |
| Belt ⌀ | — | — | |
| Rim thickness | 1.14 | 0.045 | |
| Neck length | — | — | |
| Case length | 44.70 | 1.760 | |
| Overall length | 57.40 | 2.260 |
Size vs familiar rounds
Drawn at true 1:1 — every case is accurate relative to the others. Absolute size depends on your screen's pixel density, so measuring one against a real ruler may be off. 6x45mm is highlighted below.
Reloading costestimate cost per round vs factory
Estimate your cost per round and how it compares to factory. Inputs are yours — nothing is stored.
Cost estimate only — not load data. Charge weight is your input; follow published manuals for safe charges.
Lineage
Connected reference
History
Shooters began necking the .223 Remington up to 6mm soon after the .223 reached the commercial market, and the 6x45mm dates to about 1965. No major ammunition maker adopted it, so it stayed a wildcat; Black Hills Ammunition began limited distribution in February 2010. It endures with handloaders who want more bullet weight and a better ballistic coefficient than the .223 offers without leaving the AR-15 / small-frame platform.
FAQs
- What twist rate does 6x45mm use?
- 6x45mm typically uses a 1:10 (faster for bullets over 80 gr) twist rate.
- What bullet diameter is 6x45mm?
- 6x45mm uses a 0.243″ (6.17 mm) diameter bullet.
- Is 6x45mm still in production?
- 6x45mm is wildcat; typical availability is rare.
- What is 6x45mm used for?
- 6x45mm is primarily used for varmint, hunting, target, competition.
- What is 6x45mm based on?
- 6x45mm is derived from the .223 Remington case.
Sources & provenance
Data & sources. Specs compiled from the Lindcott Armory reference; the trajectory is modeled (point-mass), not measured. See methodology. Spotted an error? Report it →