Below is a longer case version of the 284 Winchester. I am still looking for info on it    

The 280 Remington was introduced in 1957 and is based on a 30-06 case necked to .284" and the shoulder moved a fraction forward. In 1979 Remington renamed the cartridge to the 7mm Express Remington, which was exactly the same cartridge with updated factory loads. It...

   The 280 RCBS is basically the Fred Huntington version of the 280 Ackley Improved, but with a 30° shoulder, whereas the 280 Ackley has a 40° shoulder.

   The 280 Dubiel was developed by John Dubiel and was formed by necking down the 300 Holland & Holland.

The 28-30-120 was designed by Charles H. Herrick for the Stevens Company around 1900 in answer to a demand for a cartridge a little more powerful than the .25-caliber cartridges, but not quite as large as the .32-40, so that it could be used satisfactorily for deer,...

   Replica made for collectors by OPM in South Africa. The originals of this are extremely rare. Dating from around 1912, it was produced by Winchester but it is uncertain if it was officially tested. It is a 30-06 necked down to .28. also known without a...

The 28 Nosler was developed as a companion to the 26 Nosler that was launched earlier and is intended to be one the most powerful 7mm loads offered commercially. It shared the same case and overall length than the 26 Nosler.   

The 277 was developed by Mad Dog Shooting Systems and is based on the 5.56 NATO case necked up to 6.8mm. Any existing AR platform can be used with just a barrel change. The 277 Wolverine is basically a hybrid cartridge between the 5.56 NATO, 6.8mm SPC, 300 Blackout...

For a time now the US Army has been searching for a Next Generation Squad Weapon System and during 2018 it supplied the specifications of what type of system they were looking for and invited the firearms industry to come up with the designs for a Squad Infantry Rifle...

   The ICL cartridges used the same minimum body taper like the Ackley Improved versions but instead of a 28 or 40 degree shoulder (Ackley) the ICL used a 45 degree shoulder.

   The 275 Hoffman is a normal 275 Holland & Holland with a proprietary headstamp.

   Karlyn Flare Colonial Ammunition Co for the New Zealand Forestry Service The two S&B variations are proof loads SOUTH AFRICAN HEADSTAMPS AND VARIATIONS    Red anodized aluminium dummy by THOR Engineering    PMP basic brass...

   Basically a newer/different version of the 270-08 wildcat from the 1950's but with slight improvement. How slight is probably up for debate. The South African 270 SABI is almost identical to this.

   The 270 Newton caliber is most probably not one of Charles Newtons inventions. It would seem that it came along much later than the original 30, 35, 40 and famous 256 (6.5-06) Newton calibers. This case is by Speer, but apparently Western also made it....

One of the Art Mashburn wildcats   

Designed by Elgin Gates and based on the 300 Savage case. It is one of the more popular of the IHMSA (International Handgun Metallic Silhouette Association) cartridges.

   Yet another attempt at a 1000 yd. match cartridge.

   Another version of the 284 Win case being necked down, this time to .270 cal.

   This is the prototype for the 264 Win Mag, but without the belt

   Les Baer Custom for an AR platform

The .260 was introduced in 1997 by Remington and has achieved a modest following. It is not nearly as successful as the 6,5 Creedmoor, despite being on par and in all probability a better cartridge. The reason maybe for not achieving a bigger following was the fact...

   The 260 AAR, or All Around Rifle was originally designed by P.O. Ackley and is essentially a 257 Roberts Ackley Improved that was necked to 6.5mm.

   Relatively new cartridge officially launched at the 2014 SHOT show. Full detail HERE