An Easy and Accurate Ackley Type 6.5 mm Cartridge but with the Proven 30˚ Accuracy Shoulder
The 260 Imp 30˚ is a 6.5 mm wildcat cartridge with a powder capacity larger than the 260 Remington 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 260 Imp 30˚, in addition to being a great long range 6.5 mm cartridge, is also a viable cartridge for magazine feed applications from a short action magazine (highpower competition, tactical matches, etc.) especially where the use of the 139-142 gr. can provide superior long range performance, all with minimal wind drift on windy days.
The 260 Imp 30˚ Cartridge
The 260 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 260 Rem. brass or ammo for fire forming with no modification. Load up 260 Remington brass or take 260 Remington factory ammo, stick it in your gun and shoot it – – – DONE!
– No initial neck turning or trimming required.
– Works well with existing Lapua and Remington 260 brass.
– Sizing dies and die sets are available and in stock.
– Adequate case capacity for top velocities without being a “barrel burner.”
– 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 – Contact http://www.6mmar.com/ To Order
Reloading dies are readily available for the 260 Imp 30˚. At the time of the writing of this, factory 260 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 260 Imp 30˚ At this point, I have two barrels chambered up in the 260 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 H4350, IMR 4350, Reloader 17, VihtaVuori N150, N550, and N160, and H4831SC. I have worked a fair amount with H4350 and Reloader 17, and both have no problem getting the 139-142 gr. 6.5mm match bullets runing well up in the 2900+ fps range.
Some Initial Chrono Results:
With 30″ barrel with chamber throated long for the 142 Sierras:
42 gr. H4350 with Sierra 142 = 2685 fps
43 gr. H4350 with Sierra 142 = 2760 fps
44 gr. H4350 with Sierra 142 = 2833 fps
45 gr. H4350 with Sierra 142 = 2903 fps
With 26″ Barrel with the shorter throated reamer below. Brass used was fireformed
Lapua 260 Rem brass, primers used were CCI BR-2 primers. Bullets were
loaded at 2.870″ OAL and magazine fed from an Accuracy International
magazine (AICS short action magazine). The 140 gr Hybrid bullet hits the
lands at around 2.905″ OAL in this chamber, a Sierra 142 hits the lands at
around 2.845″ OAL in this chamber and a Berger 140 gr VLD hits the lands
around 2.873″ OAL in this chamber.
42 gr. H4350, Berger 140 gr. Hybrid bullet = 2686 fps
43 gr. H4350, Berger 140 gr. Hybrid bullet = 2759 fps
44 gr. H4350, Berger 140 gr. Hybrid bullet = 2820 fps
45 gr. H4350, Berger 140 gr. Hybrid bullet = 2888 fps – Light Compression
46 gr. H4350, Berger 140 gr. Hybrid bullet = 2915 fps – Compressed Load
42 gr. RL17, Berger 140 gr. Hybrid bullet = 2769 fps
43 gr. RL17, Berger 140 gr. Hybrid bullet = 2841 fps
44 gr. RL17, Berger 140 gr. Hybrid bullet = 2919 fps
45 gr. RL17, Berger 140 gr. Hybrid bullet = 2997 fps
39 gr. N150, Berger 140 gr. Hybrid bullet = 2794 fps
40 gr. N150, Berger 140 gr. Hybrid bullet = 2832 fps
41 gr. N150, Berger 140 gr. Hybrid bullet = 2889 fps – Some pressure
42 gr. N150, Berger 140 gr. Hybrid bullet = 2955 fps – Too much pressure
Reamer Prints Below (two different prints)
The 260 Imp 30˚ reamer just below is throated and was set up for magazine fed rounds out of a short action while keeping bullets close to the rifling at a magazine length OAL
The 260 Imp 30˚LR reamer below is throated long and is ideal for loads keeping the full bearing surface of 139-142 gr. bullets forward of the neck/shoulder junction of the case.
Max Case and Trim Length for 260 Imp 30˚ Brass Cases
There is no formal established max case or trim lengths for the 260 Imp 30˚ brass. The author suggests the following for guidelines:
Max Case Length: 2.035″
Trim Length: 2.025″
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.