NOE 279-124-FN GC in 6.8 SPC?

[Elric]

Folks, I have toyed with the 280468(s) in a 6.8 SPC Contender rifle. The design sorta expects seating it so deep that the gas check is only partly in the neck, or nose sizing to reduce the _nose_ below .270-.271 so it will fit farther into the bore (I don't mean the .277 groove, I mean the .271 bore). I expect that both the long and short 280468 work wonderfully in a 270 Winchester, which most likely has a longer neck and throat...

http://noebulletmolds.com/NV/produc...ucts_id=983&osCsid=572dobntml4skhpam3c3au8475

Has anyone tried the NOE 279-124-FN GC in a 6.8mm SPC chambered Thompson / Center Contender?

http://ps-2.kev009.com/ohlandl/Cast_Bullet/7-30_Experience/7-30_Waters_Experience.html
I would love getting the 285448 design in a 280448, without the Kephart band. Perchance the front driving band could be extended to end at the front edge of the Kephart band, or the entire bullet could be shortened to make up for the removal of the Kephardt band. To me, the KB only holds on to the bullet when casting, and removing it would make a good mould even better.

I love the smaller case capacity of the 6.8 SPC round, but the throat fails (IMHO) to accept many cast bullet designs....

I like the 104gr bullet size (easy on lead), the bullet shape (nice little pill), potential accuracy (if this GC and neck thing is sordid out), and the best thing would be a rimmed 6.8 SPC cartridge.... If I had bucks, I could get a reamer made up for a 7mm Hornet or a 7mm SPC, get a Contender rifle barrel made up, and use the 285448. But the reamers would run @300 delivered (roughing and finish). Barrel @315 or so delivered (Ed's T/Cs).

OTOH, a $80 or so mould beats @600+++ every time.

Or... perhaps using a 6.8mm SPC II chamber reamer to extend things another .100 or so in the throat...

 

[Brad]

What is a Kephardt band? Not familiar with that at all.

 

[Elric]

A Kephart band (or scraper) was a 1900 era attempt to design a bullet that could scrape black powder fouling upon each shot. It came in two forms that I am aware of, the one on a 285448 is a small, thin band separate from the forward (top) drive band with a groove in front of it, and the other form was a drive band with a groove in front of it for the residum or whatever they called the fouling in those days.

The first was a 308206

http://castboolits.gunloads.com/showthread.php?217687-Horace-Kephart-The-Kephart-Band-308206

 

[Brad]

Ah, a scraper band. I don't like em. I want a smooth transition from nose to full band diameter.

 

[Elric]

Transition of the nose directly to a full band diameter may prove problematic in a short throat... I like the bore diameter nose and the space to the driving band. Sorta like the illegitimate love child of a Loverin design and an RCBS bore rider. He's got the nose diameter of RCBS, but the body of a Loverin....

 

[fiver]

here's what your dealing with.
a 1.3* taper in front of a .15 ish ball seat area.
the jacketed bullets they make are actually a good fit for this throat.
I'd copy the length from the base of the neck into that area right in front of the case for your drive bands [.36 to base of G/C] then follow that taper for the nose shape [.15] step it down to .270 for a short bore ride section and just round it off to a flat point.

http://www.saami.org/PubResources/CC_Drawings/Rifle/6_8mm Remington SPC.pdf

 

[RBHarter]

Elrick.
I'm going to bet that your TC has a SAAMI chamber vs the SPCII with a longer leade/throat area.
The 279-124 NOE was designed specifically for the SPCII chamber. In my "how cheap can I build a hunting accuracy AR" I am able to get accuracy and velocities that match the 130 gr jacketed counterpart .

The major difference between the 6.8 SPCII and SAAMI is the leade / throat dimensions that allow higher velocities and reduced pressures in a Weatherby like fashion. With a jump or extended seating length .

There is a forum dedicated to the 6.8 cartridge and while it is populated by AR drivers there are very many bolt and Contender shooters also .
http://68forums.com/forums/search.php?searchid=1148815

There are a handful of cast threads there and dozens maybe 100s about the chambers and the nuances from the various bbl makers and reamer providers .

 

[Josh]

I have a few moulds designed just for the 6.8 SPC, give me til the morning and I will get you a pic. Fiver has the big brother (300 blk middleweight) if he has a pic handy.

 

[Elric]

Elrick.
I'm going to bet that your TC has a SAAMI chamber vs the SPCII with a longer leade/throat area.
There are a handful of cast threads there and dozens maybe 100s about the chambers and the nuances from the various bbl makers and reamer providers .

"Or... perhaps using a 6.8mm SPC II chamber reamer to extend things another .100 or so in the throat..."

The part of the myriad versions of SPC chambers is spot on, which is why I asked about a SPC II reamer. Yes the G2 is the original SPC spec. Works well with jacketed bullets. Yes I have dived into the 6.8 forum, which is where I get some caution..

 

[RBHarter]

Elrick
Here's my whole work up from a point of about 80 rounds of jackets from 40 of factory FC FMJ and 10 rounds of Hornady factory 120SST.
The remedial basics of casting you can probably pass over . The platform is a Blackthorne products A2 with a CHEAP low pro gas block and CHEAPER free float fore stock it currently with the loads listed will hold slightly under 2" at 100 yd for 10 shots fired in a field condition with a good rest . I have sent a few bullets for folks to try and all have had good results.
My load is probably in the 42-45 kpsi range maybe higher .
http://68forums.com/forums/showthre...uot-free-quot-bullets-or-casting-on-the-cheap

I don't know if my documented run will help or not .
For what it is worth I also have a 7x6.8 mildcat Carcano that has about 10 jackets through it and lots of patches . It also will not shoot top loads but can reach 2300 fps with a 27-130 fp that weighs 145 gr. ..... lesson there weigh bullets from the new mould don't take for granted that the quality name brand will drop what the tag says it does..... the Carcano handles gas quite well. 8t was cut with a 7-30 Waters neck out , that was the plan , who knew that the 6.8 SPCII would have a fatter neck than a 7-30 .

The biggest pit fall I've had is that the 270 sister bullets are intended for the long neck of the 270 and need to be seated deep to chamber (also magazine length in the AR) which cuts in the case capacity. I adjusted the seating depth to 2.275 with the last trial with 279-124 through a .280 push through sizer mostly it just set the gas check . My standard length at .278 was 2.3. The AR bbl is 16" crown to the extension face, chamber/bbl length is closer to 15 with a mid length gas. All of this is important to my data . The twist is 1-11 at .269x.277 . I reached 2130 fps with H322 and the described groups . My alloy is 2-5 yo WW and 1-20 derived from tamper seals 75-25 . It expands well in practical tests is of about 18 bhn when water dropped and rested 14 days. It remains ridged enough at the successful load to leave 31 cal holes in 1/4 plate steel at 100 yd. Slowed to 1900 it craters and leaves flat gas checks. There may be pearls in the above thread as most entries immediately after shooting.

 

[Josh]

Here is the 6.8 mould I have, it is a 117 gr design.

 

[fiver]

I do have it's big brother.
the wife smacked down a couple of ground squirrels and a rock chuck with it today from her 300.

 

[Josh]

I need to run mine in the 300 BLK too, so much stuff to do, not enough time.

 

[fiver]

oh- yeah...
i've been home for over a month and I think I am further behind now.