AR upper

[Shemp]

I've got a nice DDC Geissele Mk4 rail that I got for el cheap and am going to build an upper...but I'm torn. I have a Mk18 upper and like the size, but am also a bit amazed at the velocity loss compared to a 12.5 barrel. Should I build another 10.5ish super or go with a 12.5? Or 11.5? Using 75-77gr pills, is there enough of a performance difference between a 12.5 and a 10.3 to even think about?

 

[BangBang]

@The Mechanic (Greg Vess)

 

[The Mechanic]

At the end of the barrel the muzzle velocity is maybe 125 fps. and energy is going to minimal. At 100 it's only 150 per sec difference on a 55 gr. pill so I don't think it's going to make a huge difference at the yardages that barrel would be intended for.

 

[chance]

9.5” rail? 10.3 fits it perfect. But there is a jump in velocity to a 12.5. Are you going to use it to kill stuff? If not planning on it then 10.3 would be my choice

 

[Shemp]

9.5” rail? 10.3 fits it perfect. But there is a jump in velocity to a 12.5. Are you going to use it to kill stuff? If not planning on it then 10.3 would be my choice

Not planning on that per se...but it will be one of my general purpose go-to guns.

 

[Radar363]

@The Mechanic (Greg Vess)

 

[Mr. Goodbar]

If i already had a 10.5" then I'd do a 12.5". 12.5" scoped upper will be hunting upper

 

[cmshoot]

Not planning on that per se...but it will be one of my general purpose go-to guns.

When USMC Force Recon looked at going to something shorter than the 14.5” M4, they looked at a bunch of different lengths and in the end went with the 12.5”.

 

[Radar363]

I have a couple of Bravo Company KINO uppers, they have the 11.5 inch barrel with carbine gas but the FSB is out at mid-length.
I have kinda long arms and this setup gives me a little more real estate to hang on to.

Disclaimer: I am not an AR expert or an Operator of any kind and have done no ballistics testing to determine if this barrel length is optimal for anything.

 

[The Mechanic]

If you are going to be hunting with it I would think you want all you could get. Another idea is do a 10.5 in a 6.8 and barrel,DD bolt and mag and get some real stopping power. You can get a 85 grain pill out to 3,000 and more with a hot load in a ARP barrel. There chambers are designed for hot loads. There is lot less velocity diff. with that caliber on shorter barrels. It's what the cartridge was designed for.
You can practice with shelf ammo and I can work you up some of my special loads 100 at a time in a neat little plastic holder. Use those for SD mags and hunting.. This is the difference between shelf Hornady Match Ammo and Hand loaded the same Hornady V-Max pill. You see the difference in the middle the accuracy and in the four corners sub MOA accuracy.
The top target was shelf ammo in the middle and hand loads in the corners. The second target was all hand loads. I want to compare the difference with a mag off each.

 

[The Mechanic]

You buy a bolt for 68 bucks from Daniel defense and use the same carrier, get your barrel ARP. Wilson likes hand loads a lot but ARP are chrome moly vanadium and nitrided for prolonged use. Then you get comparable ballistics of a 6.5 grendel all the way out to 400 yards. You will out the door for 268 plus a couple of mags. Then for hunting you can go all the way up to 115 pills and pack a wallop.

 

[The Mechanic]

Food for thought....

 

[Shemp]

That ammo is just so expensive...maybe as a secondary rifle. I like 6.8 alot... but ammo is prohibitively expensive

 

[BangBang]

Another idea is do a 10.5 in a 6.8

 

[Radar363]

View attachment 44206

 

[dial1911]

That ammo is just so expensive...maybe as a secondary rifle. I like 6.8 alot... but ammo is prohibitively expensive

This is where I'm at with 6.8 and .458... like the idea, would like a .50 Beowulf too- but just can't justify a dollar a shot.