Making Major in an AR15

[Garrett]

I read Guy Neil's article in Front Sight a couple of months ago about possibly making Rifle Major with the new 6.8 SPC. It looks like this might just be on the edge of major, but do-able. There may be another option available.

I have a T/C Contender with a 10.5" barrel chambered in .300 Whisper. I think it may be possible to (safely) hot-rod the Whisper to make Rifle Major.

The .300 Whisper from SSK was designed specifically to be fired from an AR15/M16 platform. It was designed with sound suppressors in mind. To effectively suppress a firearm, you need to keep the bullet velocity under the speed of sound to avoid a loud sonic crack. Limited to a maximum of about 1100 fps., it is necessary to use a heavier bullet to put more energy on the target. Smaller diameter bullets tend to exhibit better aerodynamics. So a 200 gr. .30 would shoot better than a 200 gr. .45. The Whisper features a relatively heavy .30 caliber bullet in a short case. OAL is similar to a loaded .223 Rem (so it will fit in an unaltered M16 mag). The .300 is based on a necked-up .221 Fireball (which is a cut down .223). It will work with a factory .223 bolt. The only major change is the barrel.

I received some loading data with my T/C barrel from SSK Industries. Keep in mind, most of this data was developed around the idea of keeping a heavy bullet subsonic. The supersonic loads were with lighter bullets, and probably done with hunting in mind. Most all loads used some type of pistol powder. I think with proper powder selection, it would be possible to make major with this.

What I have been able to do so far is this:

Sierra 220 gr. RNSP @ 986 fps. = 217 PF. This was loaded with a really fast pistol powder (AA#2). The bullet fills up most of the case. Cartridge OAL is 1.195". I could seat it out around 1.250" or so and still be able to fit it in an AR15 mag. I need an extra 600 fps to make major with this bullet. Changing powders might help, but that's still a bit of a stretch. Keep in mind though, these numbers are from a 10.5" barrel. Using a barrel in the 18-20" range should help out. The primers don't show any excessive pressure signs. They still have rounded edges, and do not show any primer flow. This load was tailored to keep a heavy bullet under 1100 fps., and is likely not anywhere near maximum pressures. Still might be a stretch to make major with this bullet.

Sierra 150 gr. JFP @ 1936 fps. which gives 290 PF. This was loaded with a relatively slow pistol powder (H110). I need 2133 to make 320 PF. That's (about) an extra 200 fps. This load showed some primer flattening. It probably couldn't be pushed much faster with this powder. But there is more room in the case for a slower powder. This seems very do-able, especially when combined with a longer barrel. I'll try loading the bullet out a bit longer to give a little more internal capacity. I'll also have to see what I have lying around for fast-burning rifle powders.

Maybe I'll see how fast I can push this in the next week or so. Might be interesting.

Here's a picture for reference.

Left to right: .223 55 gr. BT, .30 150 gr. Sierra JSP, .30 200 gr. Nos BT, CorBon factory 220 gr. FMJ, .223 w/55 gr. FMJ.

[Carlos]

THis has been discussed here before:

1)Bear 11-something (aka Eric) has tried out a whisper upper; I believe in Open. He used a .223 this year at Nationals so the whisper may still be in development. It ain't an "outta the box" solution. Yet.

2)We have also talked of the 7mm T/CU (necked up .223 to 7mm) and OAL seems to be the sticking point on this.

3) It may be that the new factory Wolf brand russian 150 grain ammo in 7.62x39mm may just squeek by lower major out of a 20" barrel.

4) the 6.8 is out. (see # 2 above).

The trouble with these 4 solutions is that they have trajectories unlike the .223; perhaps they can be adapted. Seems like .223 ruled the day at this years nationals though we have no official survey to confirm this. Next year? we will see! Keep up the good work! Regards, D.

[Zak Smith]

4) the 6.8 is out. (see # 2 above).

What, OAL? I assure you that 6.8SPC has the same OAL as 5.56. That was the whole point, to fit in a M4.

The trouble with these 4 solutions is that they have trajectories unlike the .223;

6.8SPC has a MV and BC similar to 75-77gr 5.56.

You might also consider the 6.5 Grendel, which has more internal volume (for powder) than 6.8SPC.

-z

[Mickster]

Regarding Carlos's point number 3. I chronoed the Wolfsky 154 soft point out of my Colt 16" CAR-15 with the following:

2147 fps

2157 fps

2140 fps

2157 fps

2125 fps

Avg Vel = 2145 fps

Power factor = 330

This is out of a Colt barrel. AK's may be a completely different story.

[MasterLefty]

2)We have also talked of the 7mm T/CU (necked up .223 to 7mm) and OAL seems to be the sticking point on this.

Another option to the 7 TCU may be the 7x40.

Kenny

[Carlos]

As to number 3, errrr . . . chalk that one up to late-night mis-communication on my part (and a beer or two) RE: the new 6.8;

What I meant to say is:

"The new 6.8 is now available for sale to the public"

As to whether the new 6.8 will meet major & be effective in 3gun, my guese is: yes & yes. This may just be the better mousetrap & it would not surprise me in the least to see it place well (if not win) in next year's nationals. Of the options above, it would seem to be the best. Sorry for the confusion. D.

PS: Mickster: THANKS! I appreciate the data & thank you for doing the chrono work.

[uscbigdawg]

Zak,

If all goes well, I should be getting my 6.8 SPC upper in September. Do some fall/winter testing and evaluate it for SMM3G '05. With the rifle power factor down to 320, it shouldn't be a problem. I'm thinking the Sierra 120-ish grain Match King's will do it just fine.

What's the good word on the load development?

6.8 SPC is probably going to be the ticket in 3-gun as you only lose 5 rounds in mag capacity over .223, it easily makes major and once the calcs are done and various twist rates are figured, I'm sure will be a tack driver.

Rich

[Bear1142]

Garrett,

I played with the 300 whisper quite extensively last year. I was able to make major (340 PF) with ONE load, and that was by the skin of my teeth. Now that the PF is 320, making major should be no problem. The real problem is the cartridge. This round was designed for 200 yards. Proper loading will let us push it to 300, but thats about all. Even then, you'll have quite a rainbow trajectory. My recommendation is to go with the 6.8 SPC. Complete uppers and ammo are already available and if the AWB goes away, mags will be readily available. It should have not trouble making major and a good supply of components (read brass) will be easy to find. If you decide to stick with the 300 whisper, drop the 220gr. bullets and go with the 168's. They are cheaper, more accurate, and have a flatter trajectory. Good luck.

Erik

[Garrett]

Thanks Bear,

What type of powders were you using?