July 21st, 2021

A Worthwhile Wildcat — the 6mm-223 for XTC Competition

6mm 223 sinclair

Intro: Ron Dague wanted a new gun that was similar to his trusty .223 Rem rifle, but which fired 6mm bullets. There is a superb choice of bullets in this caliber, and Ron found that the 95gr Berger VLD could be driven to a healthy 2604 FPS by the small .223 Rem case. This 6mm wildcat based on the common .223 Remington offers excellent accuracy and very low recoil — something very important in the cross-the-course discipline. In addition, Ron’s 95gr load with Alliant Reloder 15 delivered an ES of just 4 fps over ten shots. That exceptionally low ES helps achieve minimal vertical dispersion at 600 yards.

6mm 223 Across the course McMilland stock Ron Dague Sinclair InternationalBy Ron Dague, Sinclair Reloading Tech
From Sinclair’s GunTech Articles Archive

I have watched a change in thinking for NRA High Power across the course in match rifles and calibers. There are several [popular chamberings]: 6mm AR, 6.5 Grendel, 6XC, and 6.5 Creedmoor. I have seen these rifles perform and all have done very well.

When I started this project I was looking for a cartridge that shoots and feeds well from a magazine[.] I had shot the .223 Rem in my 722 Remington and knew it had fed well so I chose the .223 Remington necked up to 6mm.

The 6mm-223 gives me what I have in the standard .223 only with a better selection of bullets. I wanted a better 600-yard bullet with a higher BC than provided by the 80 and 82 grain bullets. I also wanted a 600-yard line bullet with a .500 or better B.C. for those shots that should be 10 ring or better but seem to find the 9 ring no matter how well I held and broke the shot.

6mm 223 sinclairPutting the 6mm-233 Project Together
My project started with ordering a 6mm barrel from Bartlein with a 1-8″ twist. I called Pacific Tool and ordered the 6mm-223 reamer. I found a used Remington 700 action at a local gun shop and already had a Remington 40X stock. I then started putting the gun together.

I already had a .223 Remington match rifle, and I wanted the 6mm-223 to be as close to the same as I could make it. I installed the barreled action in a wood 40X stock to work up load data and work out any magazine feeding issues. While I was working on that, I looked for a McMillan Baker Special stock and finally found one to finish this project. I bedded the action and stock, then took the rifle to the range to check zeros on the sights and scope. I was surprised that I didn’t have to change anything on the sights. I thought changing the stock would cause sight changes. The thought went through my head, “Maybe the 40X stock isn’t all that bad”.

Here’s line-up of 6mm bullets. The Berger 95gr VLD is in the middle.
berger 6mm bullet hornady sierra line up 6mm 233

I took the new rifle to the first match of the year, a National Match Course match, and my off-hand score was 83, rapid sitting 95, rapid prone 95, and slow fire prone 197 — for total aggregate 470. This may not be my best work, but on match day the wind was blowing about 15 mph and the temp was around 40° F, with rain threatening. This was a reduced course of fire — we shot at 200 and 300 yards on reduced targets.

I used 70gr Berger bullets for this match, loaded in Remington brass with 25 grains of VihtaVuori N540 and Federal 205M primers. When I worked up loads for this rifle, N540 gave the best accuracy with the best extreme spread — 2,950 fps with an extreme spread of 20 fps on a 10-shot string. The load for 600 yards was with a 95gr Berger VLD bullet, with 23.0 grains of Reloder 15, Lapua cases, and the same Federal 205M primers. This load is 2,604 fps, with an extreme spread of 4 fps over a 10-shot string. I’ve shot this load at several 3×600 yard matches, and the accuracy has proven to be very good. At the last 3×600 match, my scores were as follows: 199-10x and 198-11X with scope, and 193-10X with iron sights. Best 600-yard score so far with iron sights was 198-12X.

6mm-223 Rem Rifle Specifications: 700 BDL action and floor plate, Bartlein 6mm 1:8″ twist, McMillan Baker Special stock in Desert Camo, Centra front and rear sights, Ken Farrell bases with stripper clip guide, Sinclair hand stop, and Jewell trigger. Gunsmith Neil Keller helped me with the metal work and instructed me on the action work and rebarreling.

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