which ar-15 cartridge?

[rain164845]

6mm-6.8 spc or 6.8 spc. I don't mind necking down the brass and already have the die. That won't be a factor in the equation. It will be for shooting at the range and for less than 200 lb deer with an 18 inch barrel. The 6mm gets more speed and should be great with 85 and 90 grain bullets and the regular 6.8 seems to run slower with the 100- 130 gr bullets. Which one and why?

 

[AR Shooter]

Depends on where you hunt. Short range through foliage, etc., you will want the slower, heavier bullet. For open shots at somewhat longer distances you will want the 6mm bullet. Was an article in one of the hunting mags a couple of years back on the most effective cartridge for whitetail. Based on one guide's collected data over more than ten (10) years, the dear shot with a 6mm cartridge (6mm Rem or .243 Win) traveled the least distance after being hit with a lethal shot. Something like 8yd. The next most effective was the 6.5 & 7mm, with an average of about twice that distance. 30cal & larger were the least effective. Was based on several hundred deer over the period.

 

[GSPV]

Neither.

30 Major.

Why? Great bullets. Great brass necking up, not down. Can get tired 30 BR or HBR barrels cheap. Makes big holes.

 

[rain164845]

I will be limiting range to 275.

Let's discuss the 30 major. I understand that pressure will be a big convent in the at, so the major won't do what it does in a bolt gun. What can I expect from it oin the at 15?

 

[gunsandgunsmithing]

I will be limiting range to 275.

Let's discuss the 30 major. I understand that pressure will be a big convent in the at, so the major won't do what it does in a bolt gun. What can I expect from it oin the at 15?

Expect about 2650fps with 125 grain bullets. It works well in an AR15. The AR15 platform is the limiting factor vs. a bolt gun, not the cartridge.
I designed it...ask away. I'll help if I can.--Mike Ezell

 

[GSPV]

I'm looking forward to verifying how the 125 Nosler BT works on deer out of it. 8)

 

[5spd]

6x6.8 is what I am building right now because I like 6mms.
This will be for antelope & coyote.
Ease of simply necking down, brass is available.
Tons of 6mm to pick from.

 

[rcw3]

6AR Turbo 40 - - Antelopes in Wyoming - - Berger 95 Classic Hybrids

 

[pdq5oh]

Have you looked at the 6.5 Grendel? Better performance than the 6.8 and extremely accurate. Lots of good choices in high BC bullets. Lots of good factory ammo, as well.

 

[infantrytrophy]

You might also think about the 6HAGAR. It's derived from the 30 Remington/6.8 SPC case. Excellent factory brass from Hornady, so there would be no necking down the 6.8 SPC case. Factory dies available from Hornady and Redding. You might want to check on this, but I think that the 6HAGAR would have more case capacity than the 6.8 SPC necked down because the shoulder is a little farther forward. There are a number of competition shooters who shoot the 6HAGAR, so there is a fair amount of load data available.

Links:
http://www.creedmoorsports.com/shop/6mm-HAGAR/

http://6mmar.com/6mm_HAGAR.php

http://www.6mmhagar.com/default.asp

http://www.keystoneaccuracy.com/6mmhagarorders.html

 

[mattri]

Any reason the 6x45 isn't in the mix? Seems like it would fit your parameters well and be the simplest to form.

 

[GSPV]

I forgot to mention:

Because I get it to do this in my bolt gun without trying hard. Not shabby for a cartridge conceived for 3 gun fun.

Remember, that is 300 FPS faster than is safe in an AR.

 

[wwbrown]

Given the great choice of bullets in 6.5 why not neck the 6.8 SPC down to 6.5 mm? Use a bushing die for a 6.8 with bushings for the 6.5 mm and buy a reamer.

Just another option.

 

[rain164845]

Any reason the 6x45 isn't in the mix? Seems like it would fit your parameters well and be the simplest to form.

It just isn't trendy enough. Just kidding. Seems like I can get a few more FPS out of the deal with the 6-6.8SPC with the same amount of work. Brass is harder to find for the SPC though.


GSPV, it is hard to argue with those results. I just don't think I want a round that goes that slow... Sort of the same reason that I am leaning away from the base 6.8 SPC.

Keep the ideas coming though, I'm happy to hear them!

 

[ar15topgun]

6mm Fat Rat. Necked down 6.5 Grendel.

 

[GSPV]

My idea is energy on target. I get both with the 30 Major. Plus a supply of almost free barrels. Almost free brass, and the convenience of the same components that I use in my bolt guns.

 

[Tim Singleton]

Have you looked at the 7.62x40wt ?

My Wilson barrel came in last week. Working on gathering the rest of what I need to finish the upper.

I have a 300 blackout but wanted a little more velocity for deer hunting.
Keeping the blackout upper to load subsonic and build the 40wt for supersonic hunting
Both use 5.56 brass

 

[rain164845]

Is the Fat Rat a straight neck down, or does the shoulder angle or body taper change? Who chambers that one?

 

[Mr. Ten-X]

6mm-6.8 spc or 6.8 spc. I don't mind necking down the brass and already have the die. That won't be a factor in the equation. It will be for shooting at the range and for less than 200 lb deer with an 18 inch barrel. The 6mm gets more speed and should be great with 85 and 90 grain bullets and the regular 6.8 seems to run slower with the 100- 130 gr bullets. Which one and why?

As a 200yd deer cartridge, the basic 6.8SPC will deliver just over 1000 ft/lbs at 200 yds and there are bullets/loadings intended to properly expand on deer at those velocities. Not sure that you will find bullets in 6mm that will reliably expand/penetrate on deer at the velocities attainable for the 6.8 parent case.

My 16" M4 in the 6.8SPC has a verified trajectory of 2" high at 100yds and 2" low at 200yds using a Aero Precision mount (as a point of reference for angle of departure). This is not a bad arc for the effective range of the cartridge on deer.

 

[Tim Singleton]

Have you looked at the 7.62x40wt ?

My Wilson barrel came in last week. Working on gathering the rest of what I need to finish the upper.

I have a 300 blackout but wanted a little more velocity for deer hunting.
Keeping the blackout upper to load subsonic and build the 40wt for supersonic hunting
Both use 5.56 brass

16" upper 125gr bullet
2.5" high at 100 for 200 zero.
1600 ft lb at muzzle
1300 ft lb at 200