09-27-2013, 04:29 PM
So as a follow up to a previous post I asked bob for some more info so here it is.
I got the powder load from the Alexander Arms Website which suggested 30.9 grains of A2520 with the 123 grain bullet. I backed off 0.9 grains and use the 30 grain load for this bullet weight exclusively. It should be noted that this powder is sensitive to the chamber temperature, based on my experience, after firing the 3 round in a 5 round series. The 5th round will result in an slightly expanded primer pocket and will no longer hold a new primer. I shoot sets of 3 rounds and then cool down.
I use the Remington 7-1/2 Bench Rest Small Primer which results in a velocity of 2550 fps. The two bullets used are the 123 grain Match king (BC@0.51) and the 123 Lapua Scenar (BC@0.547). I do need to re-run the chronograph effort in the near future.
This primer has been adapted exclusively based on some early work at Freedom Arms that I had the privilege to be a part of during the load development for the 454 Casull.
I use the Nightforce and Sierra Infinity Ballistics Programs for the base chart development as a function of Altitude and Outside Air Temperature. Site specific settings are adjusted using the Gunwerks HP PDA Ballistics Program calculator. The two primary locations are Idaho Falls @ 4700 feet and Boise, Idaho @ 2830 feet. Humidity is dry, normally runs in the 25 to 30 % range. So as density altitude works in you favor, increasing Outside Air Temperature, ranges can be extended significantly. Remember that an increasing Density Altitude is bad for aircraft but good for bullets, less drag..
This rifles is sighted in at 4880 feet and must be adjusted 2.0 MOA-UP when a bench is setup in Boise for the same ZERO; and then adjusted for temperature.
My Grendel is ZEROED at 700 yards at a range with an altitude of 4880 feet here in the Snake River Plane - North of Idaho Falls... When shooting suppressed, I loose 2.0 MOA which also must be taken in to the site specific location also.
I always us my temperature specific calculator for determining sonic velocity regardless of location during the planning phase. Sonic Velocity changes with altitude because the temperature drops 7-1/2 degrees per 1000 feet... At the bench, it is a function of the surrounding outside air temperature. It is a complicated formula but it can be found doing a Web search.
Depending on bullet selection (ie. Ballistics Coefficient) and temperature/humidity, the transition to transonic occurs in the 1200 to 1350 yard range for the 123 grain bullet. This is base on my calculations using the mentioned programs, not actually measured.
It is encouraging to see that someone asked about the milk jugs.. When you fill a milk jug with water, let the rays of the sun pass through it, they refract and light the jug up like a light bulb. I can see it at 1760 yards easily...!! I don't think anyone can hit something they can't see.. I like to be able to see what I'm shooting at. I think someone asked once why I was shooting at JUNK.. I didn't explain it then but now you know.
By the way, the limit on my Grendel setup is 1425 yards, I have 5 rounds in a jug at this distance with the 123 grain Lapua Scenar bullet and 80 degrees on the OAT and low humidity at Boise, Idaho. That photograph was posted a year ago and everyone seemed to be in dis-belief.... That is 20 MOA in the base, 40.5 MOA on the dial up, and the lowest hold-over bar in the Leupold TMR Scope (Plus 4 X 3.6 = MOA)...
Wind is another day....
I got the powder load from the Alexander Arms Website which suggested 30.9 grains of A2520 with the 123 grain bullet. I backed off 0.9 grains and use the 30 grain load for this bullet weight exclusively. It should be noted that this powder is sensitive to the chamber temperature, based on my experience, after firing the 3 round in a 5 round series. The 5th round will result in an slightly expanded primer pocket and will no longer hold a new primer. I shoot sets of 3 rounds and then cool down.
I use the Remington 7-1/2 Bench Rest Small Primer which results in a velocity of 2550 fps. The two bullets used are the 123 grain Match king (BC@0.51) and the 123 Lapua Scenar (BC@0.547). I do need to re-run the chronograph effort in the near future.
This primer has been adapted exclusively based on some early work at Freedom Arms that I had the privilege to be a part of during the load development for the 454 Casull.
I use the Nightforce and Sierra Infinity Ballistics Programs for the base chart development as a function of Altitude and Outside Air Temperature. Site specific settings are adjusted using the Gunwerks HP PDA Ballistics Program calculator. The two primary locations are Idaho Falls @ 4700 feet and Boise, Idaho @ 2830 feet. Humidity is dry, normally runs in the 25 to 30 % range. So as density altitude works in you favor, increasing Outside Air Temperature, ranges can be extended significantly. Remember that an increasing Density Altitude is bad for aircraft but good for bullets, less drag..
This rifles is sighted in at 4880 feet and must be adjusted 2.0 MOA-UP when a bench is setup in Boise for the same ZERO; and then adjusted for temperature.
My Grendel is ZEROED at 700 yards at a range with an altitude of 4880 feet here in the Snake River Plane - North of Idaho Falls... When shooting suppressed, I loose 2.0 MOA which also must be taken in to the site specific location also.
I always us my temperature specific calculator for determining sonic velocity regardless of location during the planning phase. Sonic Velocity changes with altitude because the temperature drops 7-1/2 degrees per 1000 feet... At the bench, it is a function of the surrounding outside air temperature. It is a complicated formula but it can be found doing a Web search.
Depending on bullet selection (ie. Ballistics Coefficient) and temperature/humidity, the transition to transonic occurs in the 1200 to 1350 yard range for the 123 grain bullet. This is base on my calculations using the mentioned programs, not actually measured.
It is encouraging to see that someone asked about the milk jugs.. When you fill a milk jug with water, let the rays of the sun pass through it, they refract and light the jug up like a light bulb. I can see it at 1760 yards easily...!! I don't think anyone can hit something they can't see.. I like to be able to see what I'm shooting at. I think someone asked once why I was shooting at JUNK.. I didn't explain it then but now you know.
By the way, the limit on my Grendel setup is 1425 yards, I have 5 rounds in a jug at this distance with the 123 grain Lapua Scenar bullet and 80 degrees on the OAT and low humidity at Boise, Idaho. That photograph was posted a year ago and everyone seemed to be in dis-belief.... That is 20 MOA in the base, 40.5 MOA on the dial up, and the lowest hold-over bar in the Leupold TMR Scope (Plus 4 X 3.6 = MOA)...
Wind is another day....