Michael,
I just emailed you a photo of Mike's latest AR-15 with with the 26" Shilen XX 222 bull barrel. He just started shooting this one this week end. It is a tight neck chamber. Necks are turned down to a 0.0085 wall thickness. This is a heavy rifle. Over the 13.5# weight class. Barrel was hand lapped before the first shot. Scope is a 36X
Mike started with new Laupa 222 brass. Turned the necks and then fired them in the chamber with 50 Gr V Max bullets to fit the cases to the chamber. While he was fire forming the brass to better fit the chamber the groups were down to about 1/4".
In the photo you will see the rifle forearm is fitted with a flat plate. There was some wobble between this plate and the forearm that opened the group. An the trigger in this receiver was about 4 pounds, singe stage. Next weekend I am sure Mike with have these two issues corrected. One of his other lowers has a single stage trigger that is very crisp and set to 8 oz. This makes a big difference.
An issue with most AR rifles is how the barrel fits into the upper receiver. Too Loose. This one is very tight and set with a stud tight compound.
With a little more work and shooting better quality match bullets I expect this rifle to shoot aggs down to 0.150 and maybe better @ 100 yards when wind is not bad. The 222s are very accurate when set up right. But they are not equal to a 6 PPC when the winds blow and the distance is increased.
The 222 barrel life is helped a lot by the case design. Look at the 222 case along side a 223 case. The 222 has a much longer neck. Because of this there is much less hot gas in the chamber throat area. A 223 with the same powder charge will burn the throat faster.
Mikes 222 is a hand pull bolt. It has no gas tube. The thin wall tight fitting BR neck cases do not work in a semi auto. We tried to make them work. Mike got them to work in the 6.5 BR but the semi auto would bend the thin wall necks. And the tight necks do not feed trouble free.
If you want a very accurate rifle in the AR 15 frame the tight neck 222 is a very good choice. But you have to go all the way.
If you want to have a semi auto there is no advantage to the 222 over the 223.
Most of my 223 AR-15 rifles with a fresh barrel would shoot a true agg of about 1/2" using Laupa brass, match bullets and a BR quality scope. This is shooting from a concrete BR table top with quality BR table equipment and four wind flags. All of my AR rifles have had single stage triggers with a very light crisp pull. As light a pull as safe. My Stoner M-4 would shoot five shots into a 1/2" circle in under 10 seconds when the barrel was fresh. Now the barrel has 1,700+ rounds down the tube and 3/4+ groups are the best it will do. It held tight till about 1,200 rounds. I had a 223 26" bull barrel that went over 2,000 round before it started to show signs of age.
I have seen 222 barrels with 5,000+ rounds that would still shoot under 1/4". Capt Bob must have over 15,000 rounds down his 222 barrel and it is still quite good. When it was at 10,000 or so it would shoot with our PPC match rifles on a calm day at 100 yards.
Bottom Line!
How close where the groups from one to anothe,r in the two calibers is my biggest question.
For many years the small group record was a 222. In an AR 15 without the gas tube using a tight neck you can expect 0.015 and likely better. But only if you go all the way.
In a semi auto AR-15 you can expect 1/2" if you use premium barrel, match bullets, Laupa brass, BR quality scope and shoot from a concrete table with BR table gear and use at least four wind flags. The gunsmith who puts the rifle together has to have experience with the precision issues for the AR. Or you can buy a complete precision AR form one of the custom shops. I scoped and set up a "Wilson" for a shooter. It shot 1/2" out of the box with a 6.5X20X50 30 mm tube Leupold scope.
Remember! The scope, the table equipment and the wind flags are as important as the rifle if you want to agg small groups.
Jon
