Case prep new brass

[Viperdoc]

From previous thread on high SD with Varget in my 223 AR, it was suggested that bullet tension might be the big variable (new Lapua brass). They were FL resized using a standard Redding die, then neck chamfered with a Giraud (great power tool). Case tension is around 0.002.

I did notice when running many of the new cases through the Giraud trimmer that the neck chamfer was uneven, more bevel on one side compared to the other. Is this possibly a sign that there is excessive runout?

So, since yesterday I ordered a precision mike, concentricity gauge, a mandrel, and an outside neck trimmer. (Thanks guys)

With new brass should the steps be then: 1. FL resize 2. run mandrel (what size?) 3. turn outside neck 4. chamfer and size to length

Should there be another resize after turning the necks, especially if the mandrel enlarges the neck, in order to maintain the 0.002 tension or better?

Would like to see consistent sub 0.5MOA groups or better- am I an AR shooter trying to get bench rest results? Is this a reasonable goal? (Krieger barrel varmint rifle and also a service rifle).

 

[jr600yd]

There are two sizes of mandrels you want. The first is .001 smaller than bullet diameter. This is used in conjction with a die to open the neck and force any irregularities from the inside of the neck to the outside. The second manderal is .002 smaller than bullet diameter. This is used in conjunction with your neck turing tool for neck turning. You can get both these from Sinclair. Seeing one side of the neck thicker than the other is not unusual. Most new cases will look something like a bannana.

I always FL resize my new brass before the first firing. Headspace is critical for ultimate accuracy. In my gass guns I like a little more shoulder setback than with my bolt guns. The gas gun bolt doesn't have the camming force of the bolt gun and I want the thing to work everytime so I set the shoulder back .003-.004. As you mentioned neck tension aids accuracy. You may want to try a bushing die so you can adjust for .002-.004 tension depending what your rifle likes. Also bullet jump. This will depend on what bullet your shooting. Off the lands or forced .010-.020

I would first FL size my new brass, Trim to length and deburr and campher. Next I would turn the necks just enough to knock off any high spot. You may find neck turning for an AR a waist of time.

Good shooting, Jim

 

[broncman]

Viper Doc, I also have a 26" Krieger Barreled AR in 1 in 9. It loves Varget AND 77 SMK's ! The 69 grainers are 5/8 to 3/4 but the 77's are consistent 10 shot 1/2 inch groups. I spent a WHOLE summer chasing that rabbit!

Here is what I did. Winchester brass or Hornady's Frontier(the best in my gun). Sort by weight, fl size, chamfer inside and out and check flash hole.

Then I weighed the bullets and sorted them. Then sorted weights using a bullet comparator for base to ogive length. It appeared my lot was made on 2 machines as I had 2 distinct lots after sorted.

I found Federal Gold Medal Match primers to be the best for groups. 24.3 grains of Varget and seated to 1.855 using the Hornady Comparator.

SD was 24 fps.

My AR has a carrier weight similar to Tubbs setup.


OH YEA!! I sorted all loaded bullets to less than .001 bullet runout after loaded. I use a Hornady New Dimension Micrometer seater.

Runout had the greatest effect on accuracy in my AR. It made the difference between 3/4" groups and 1/2" groups. I shot all groups at least 5 shots. I have a BUNCH of one hole .2-.3"s three shot groups.

8)