Range Report 8.75 twist .260? and 6x45mmAI (6-.223AI)

[mm509]

My gunsmith has an Obermeyer 5r barrel in 8.75 twist, that he ordered for a customer and they never showed again. He said he would make a SWEET deal on it. I was curious if this is too slow to spin 140gr class of bullets in the 6.5mm? As that is all I am planning on shooting. I want to take this round as far as I can, but before I commit to the barrel I want to make sure it is going to work for what I intend.

Also, I am contemplating a rebarrel for my 223. I was hell bent for election to go with an 8 twist 22 cal barrel and Ackley Improve the chamber. But upon further research I found the 6x45mm and it really caught my attention. It is very similar to shooting heavy 22's in an 8 twist, but I could only shoot the lighter 6mm bullets. I didn't see any information on a 6x45mmAI, which got me thinking I might be able to sling a little heavier bullet? I would be happy with around 2800-3000fps when shooting 105's, is this possible? Muzzle length would be around 24", but is not set in stone. My whole reasoning behind this is....shooting 6mm bullet at decent velocities with minimal amount of powder charge.

 

[bohem]

Re: 8.75 twist .260? and 6x45mmAI (6-.223AI)

The 8.75tw barrel will stabilize the 140 class bullets usually, it depends on your AO (local altitude, temp, general DA in the region). I've seen them work from a 10tw up high and be unstable from an 8.5tw on a cold, high pressure day down low.

The 6-223 AI is called the "6mm TCU" or 6TCU. Look at that for better info.

I built a 6-223 last year to play around and did it on an 8tw barrel. I've shot up to the 105 Amax's with it and only managed about 2650 or so from a 28" tube and a crammed full case of powder showing pressure signs. You might be able to go faster depending on barrel, powder, etc etc...

 

[MTETM]

Re: 8.75 twist .260? and 6x45mmAI (6-.223AI)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mmedearis509</div><div class="ubbcode-body">

Also, I am contemplating a rebarrel for my 223. I was hell bent for election to go with an 8 twist 22 cal barrel and Ackley Improve the chamber. But upon further research I found the 6x45mm and it really caught my attention. It is very similar to shooting heavy 22's in an 8 twist, but I could only shoot the lighter 6mm bullets. I didn't see any information on a 6x45mmAI, which got me thinking I might be able to sling a little heavier bullet? I would be happy with around 2800-3000fps when shooting 105's, is this possible? Muzzle length would be around 24", but is not set in stone. My whole reasoning behind this is....shooting 6mm bullet at decent velocities with minimal amount of powder charge. </div></div>

I would suggest sticking with the 223ai and shoot either 75 or 80's in it. You will get good velocities, good BC's and easy on the powder with no recoil.

My experience says you will need to go to a standard bolt face and a 6xc or similar for the velocities you are looking for with the 105's in a 6mm.

 

[ChadTRG42]

Re: 8.75 twist .260? and 6x45mmAI (6-.223AI)

Per Berger, a 1:9" twist will stabilze the 140 VLD's. But they list 1:8". I run a 1:8.5" twist in a 260 Rem, and it works fine for the 140 VLD's. At a minimum, Greenhill shows a twist of 1:8.8" will stabilize a 140 VLD (1.420" long bullet) at 2650 fps . If you stay above this velocity, you should be fine. Most 140's run about 2800 fps. I'd say go for it if the deal is sweet and it's what you want.

 

[darrenk75b]

Re: 8.75 twist .260? and 6x45mmAI (6-.223AI)

The 6x45 is nice at limited ranges. At distance, the higher BC of the .224 bullets will show their advantage.

 

[selfbowhunter]

Re: 8.75 twist .260? and 6x45mmAI (6-.223AI)

i built myself a 6tcu for a truck gun. it originally had a 10twist pac-nor and would push the 85's to 3000fps in a 22" tube. it now wears a 26" brougton 14twist which i find useless for what i really want to do though it will push the 60's to 3600fps with incredible accuracy. i love the round ALMOST as much as the .223AI. if you are wanting to hunt larger game with it i would go for the horsepower of the TCU and push the hell out of it. if you are hunting varmints, steel, and the occasional deer or hog, i would go with the .223AI and the 75 or 80 a-max and push the hell out of it!

chuck