Hello,
I thought I would document my journey of developing a supersonic to 1k+ load for my B14 HMR. A key consideration was the limited barrel length of 20". Limiting at least in the context of meeting my goal with some of the lower BC bullets I had on hand. I initially started target shooting about 4 years ago. My first target rifle was a savage 10T-SR with a 24x DBT I barely shot it. I then got a fantastic deal on a B14 HMR in 308. which in the past year I have really enjoyed.
My initial shooting was with a batch of 100x Hornady 178GR BTHP match factory ammo. It was around 1.5 MOA (5 shot groups unless noted otherwise).
I loaded some 168 GR A-max's after that which were accurate at 0.6MOA at 2628 FPS on 43.7GR of Varget. However the commonality between most of the 308 factory ammo and bullets I found was they were not supersonic out to 1k. So I began load development based on the 168gr TMK. I have shot the 77gr TMK before in my 223 bolt gun and was pleasantly surprised. Further to this the BC's were very high.
Rifle: Bergara B14 HMR in 308 20"
Optic: 24x DBT
I was not feeling particularly stable. Below were my initial results.
0.75 MOA is good enough for me. My goal is to hit a 10inch gong at 1k yards. So that gets me in the ballpark. My velocity goal was 2600 and was hoping for near single digit SD's. So both of those goals were met. SD of 7 is great by my standards.
I have started doing larger increments with my initial load development than in the past and it has become a preference. I also do not believe there is much reason to go below 0.2GR increments with the sample size of 5 shot groups. I would expect a 10 shot group minimum to yield repeatable results.
With a ballpark figure of 44.2 GR and COAL of 2.870 feel I have a great starting point. I am beyond fortunate having access to a farm to shoot on 50% of the year when the corn isn't too high, I probably shoot 20 weekends per year, or more. hopefully within a couple weeks I can get out and do this load dev. Below is my next loading table.
I usually am unable to hit the rifling using the standard magazine since I primarily reload 223 and 308 for AR length mags. However in the case of this bullet at 2.887 I am still a long way from the rifling. I like fabricating unnecessary problems for myself, and worrying about things that don't actually matter. so the change in COAL is probably not needed. They will fit in a steel MDT magazine, but not a standard plastic magazine. but that was the primary change this time around. seating the bullets out 0.015 longer.
Within my next update I intend to include; testing results of the second table, a measured distance of jump, And hopefully a final selection on what to load for my 1000 yards goal. Also note I am using nickel plated brass because it makes me feel fancy.
