Author: britrifles
Subject: Case Neck Concentricity
Posted: June 25 2023 at 6:07pm
Not quite ready to put the concentricity gauge away yet. I’m going to run one further test. This time with my .308/7.62 loads for my DCRA No. 4 7.62 conversion. The rifle is a Faz 1956 No. 4 Mk2 with a Long Branch made and installed 7.62 NATO barrel. It’s a very good shooter, the most accurate No. 4 I have. It has approx 1500 - 2000 rounds thru it.
Subject: Case Neck Concentricity
Posted: June 25 2023 at 6:07pm
Not quite ready to put the concentricity gauge away yet. I’m going to run one further test. This time with my .308/7.62 loads for my DCRA No. 4 7.62 conversion. The rifle is a Faz 1956 No. 4 Mk2 with a Long Branch made and installed 7.62 NATO barrel. It’s a very good shooter, the most accurate No. 4 I have. It has approx 1500 - 2000 rounds thru it.
The reloads I’m particularly interested in are loads I worked up for long range shooting, 800 and 1000 yards. These are long pointy bullets, and seated longer than the 2.80 inch magazine length so that they are within .020 to .030 inches from the lands of the rifling (175 and 168 TMK).
Had some time to kill yesterday, so I measured the bullet runout on each of the 50 rounds I had loaded for three different long range test loads:
Load 1: Lapua cases neck sized in Lee Collet Neck Sizer Die, 155 Palma MK seated to 2.81 OAL. Average bullet runout 0.0033 inches.
Load 2: Lapua cases partial length sized in Lee Full Length Die, 175 Tipped MK seated to 2.935 OAL. Average bullet runout 0.0072 inches
Load 3: Lapua cases neck sized in Lee Collet Neck Sizer Die, 168 gr Tipped MK seated to 2.950 OAL. Average bullet runout 0.0033 inches.
Similar to the .303 British loads, the lowest runout values were obtained with the Lee Collet Neck Sizer die. Load 1 and 3 had the same average runout, with a minimum of 0.000 inches and maximum of 0.006 inches. Out of 100 rounds, only three had a run out of .006 inches.
All three of these loads use Varget powder, with charge weights set according to the bullet weight. They are .308 Win published mid range loads, the maximum I’m comfortable with shooting in my No. 4 and strictly for the purposes of long range target shooting.
The Lee FL sizer again gave the largest bullet runout, with a minimum of .002 inches and maximum of 0.011 inches out of 50 rounds loaded; 10 rounds have a runout of 0.009 or larger.
I’ve recorded the runout on each round and I’ll be able to determine if it is a variable in individual shot accuracy, and accuracy of the load in general.
I plan to go test these loads in the next week or two, and will shoot them at 600, 800 and 1000 yards along with a few sighters at the shorter ranges (100 and 300 yds).
I have a Wilson .308 Bushing Type Full Length sizing die and a .308 Wilson In-Line Seater Die but have not tried them yet. That will be the next test.
I’m expecting the accuracy edge on the three above loads to go to the 168 TMKs with cases that were neck sized in the Lee Collet die. But what comes in second place, I don’t know…