An Easy and Accurate Ackley Type 6 mm Cartridge but with the Proven 30˚ Accuracy Shoulder
The 243 Imp 30˚ is a 6 mm wildcat cartridge with a powder capacity larger than the 243 Winchester but with a slightly longer neck and the proven 30 degree shoulder angle that is seen so often in the top performing accuracy cartridges. It was designed for rifles (bolt guns and semi-automatic rifles) that have a .308 bolt face and can handle a cartridge of that size. It is not suitable for use with an AR-15, but will work out of rifles like a short action Remington 700 and semi-auto rifles like an Armalite AR-10, a DPMS LR-308, etc.
The 243 Imp 30˚, in addition to being a great long range 6 mm cartridge, is also a viable cartridge for magazine feed applications from a short action magazine (high power competition, tactical matches, etc.) especially where the use of the 105-115 gr. can provide superior long range performance, all with minimal wind drift on windy days.
The 243 Imp 30˚ Cartridge
The 243 Imp 30˚ has some excellent attributes:
– Very easy to make! Chamber uses common and readily available 308 Win. head space gages (i.e. no special head space gages required).
– Chamber accepts factory 243 Win. brass or ammo for fire forming with no modification. Load up 243 Winchester brass or take 243 Winchester factory ammo, stick it in your gun and shoot it – – – DONE!
– No initial neck turning or trimming required.
– Works well with existing Lapua, Winchester and Remington 243 brass.
– Sizing dies and die sets are available and in stock.
– Adequate case capacity for top velocities.
– Chamber Reamer drawings are available for you to use (see below) to have your favorite reamer maker or gunsmith obtain a reamer.
Die Sets Readily Available – 6mmar.com To Order
Reloading dies are readily available for the 243 Imp 30˚. At the time of the writing of this, factory 243 Imp 30˚ dies have been made by Redding (i.e. Type S. FL Bushing die and Competition Seater) and are in stock.
Working With The 243 Imp 30˚
At this point, I have two barrels chambered up in the 243 Imp 30˚, and both of them shoot very well. The cartridge does not seem to be finicky and it seems easy to load for. In addition, there are a lot of popular powders that work very well with the cartridge, including H1000, H4831SC, H4350, Reloader 17, Reloader 19, Reloader 22, VihtaVuori N160, N560, and N165.
Some Initial Chrono Results – 30″ Krieger 6mm 1:7.5″ twist barrel:
Fire forming loading (very accurate in author’s rifle) to fire form Winchester
brand 243 Win brass:
47.5 gr. H1000, Berger 108 gr. BT bullet .015″ in the lands = 2990 fps
43.5 gr. H4831SC, Sierra 107 gr. bullet, .020″ jump to the lands = 2967 fps
Loads with fire formed brass using Winchester brands brass:
47.5 gr. H1000, Berger 108 gr. BT bullet, .015″ in the lands = 3017 fps
47.5 gr. H1000, DTAC 115 gr. bullet, .015″ in the lands = 2974 fps
47.5 gr. H1000, DTAC 115 gr. bullet, .040″ jump to the lands = 2929 fps
48.0 gr. H1000, DTAC 115 gr. bullet, .015″ in the lands = 2994 fps
48.5 gr. H1000, DTAC 115 gr. bullet, .015″ in the lands = 3029 fps
47.0 gr. H1000, Berger 105 gr. Hybrid Target bullet, .015″ in the lands = 3018 fps
48.0 gr. H1000, Berger 105 gr. Hybrid Target bullet, .015″ in the lands = 3087 fps
49.0 gr. H1000, Berger 105 gr. Hybrid Target bullet, .015″ in the lands = 3149 fps
50.0 gr. H1000, Berger 105 gr. Hybrid Target bullet, .015″ in the lands = 3204 fps
42.0 gr. H4831SC, Berger 105 gr. Hybrid Target bullet, .015″ in the lands = 2893 fps
43.0 gr. H4831SC, Berger 105 gr. Hybrid Target bullet, .015″ in the lands = 2973 fps
43.5 gr. H4831SC, Sierra 107 gr. bullet, .015″ jump to the lands = 2986 fps
43.5 gr. H4831SC, DTAC 115 gr. bullet, .015″ jump to the lands = 2999 fps
43.5 gr. H4831SC, DTAC 115 gr. bullet, .015″ in the lands = 2993 fps
44.0 gr. H4831SC, DTAC 115 gr. bullet, .015″ in the lands = 3013 fps
44.5 gr. H4831SC, DTAC 115 gr. bullet, .015″ in the lands = 3044 fps
Reamer Prints Below (three different prints)
The 243 Imp 30˚ reamer just below is shorter throated and was set up for smaller varmint bullets and/or also magazine fed rounds out of a short action while keeping bullets close to the rifling at a magazine length OAL
Mid Length Throat Reamer Below (Throated predominantly for 105-108 gr bullets)
Long Range Reamer Below (Throated long for 115 gr. bullets)
The 243 Imp 30˚LR reamer below is throated long and is ideal for loads keeping the full bearing surface of 115 gr. bullets forward of the neck/shoulder junction of the case.
Max Case and Trim Length for 243 Imp 30˚ Brass Cases
There is no formal established max case or trim lengths for the 243 Imp 30˚ brass. The author suggests the following for guidelines:
Max Case Length: 2.045″
Trim Length: 2.035″
Written by Robert Whitley for 6mmar.com, but subsequently removed, we feel this information is so helpful that we posted it for future reference and archive purposes. Contact Robert at www.6mmar.com for info and purchase enquiries.