We have recently been exploring cartridges that would greatly benefit from the +P throating modifications we do. We have just built a 300 PRC for a rental rifle on our LRKM platform to use in our long range shooting classes. https://www.defensiveedge.net/index.php/classes
I choose the 300 PRC for one of several reasons:
• soft shooting (compared to a 338 Terminator)
• low powder consumption
• ability to run a 215 Berger @ 3000 fps
• 2000 yards target capability
• ability to shoot some rounds through it in a day and not have students get beat up
• the case has no belt
• case design is modern and efficient
• has been adopted by military units that we work with
• can feed out of a detachable box mag (although the LRKM doesn’t have one)
These were the key features that drew us to the 300 PRC. Is it a 300 Terminator? Of course not, it isn’t ever going to shoot a 215 gr. bullet @ 3400 fps. Let’s talk about what the 300 PRC is then. The 300 PRC is a 300 Winchester Mag length cartridge that has been improved with a 30 degree shoulder and less case body taper all good things to a point. There is no belt (not that these cases ever needed one) this greatly aids in feeding, especially from a detachable box magazine. It doesn’t require a 4.00” mag box even with VLD/ ULD bullets. The SAMMI spec chamber will put the max OAL with a 215 Berger at roughly 3.735”. The case has an H2O capacity of 99.0 gr. and that is a 7 grain advantage over the 300 Winchester Magnum (this becomes important later).
So with the LRKM spun up and ready to roll it was time to start load development. I started with the following base information and QuickLoad predicitions:
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Case: Hornady 300 PRC
Max Case Length: 2.585”
Case Trim Length: 2.575”
Primer: CCI 250
Powder: H 1000
Bullet: 215 gr. Berger Hybrid Target
OAL Max: 3.735” raw 2.902” w / Reloading Comp
Barrel: Hart, .308”, 1-9 twist, 26” finished length, Sendero Contour DE fluted
QuickLOAD Prediction: Max load 87.0 gr. H 1000, 103.4% case capacity, 3001 fps, 100% barrel burn, 4288 ft/lbs, muzzle pressure 12639 psi
Now with this info I started a pressure series to establish max pressure.
OAL: -.000” (2.902” W / Reloading Comp)
Charge Velocity Notes
82.0 gr 3080 fps Faint click a top
83.0 gr 3081 fps Faint Ejector mark
84.0 gr 3126 fps Ejector Mark
85.0 gr DNS
86.0 gr DNS
87.0 gr DNS Just starting to make OAL longer from compression .002”
As you can see this is why no matter what your source you always start 10% lower than max and work up. 87.0 grains would have blown the primer right out. Now starting with an 82.0 grain max pressure I shot a couple of groups at -.000” and -.005”.
Shooting 82.0 gr @ -.000”
3058, 3044, 3065 fps .75 moa
Shooting 82.0 gr @ -.005”
3058, 3064, 3069 fps .25 moa
Now while the load at -.005” was great after inspecting the case and bolt lift (faint but detectable) I decided that I wanted to run a little less pressure.
Shooting 81.0 gr. @ -.005” 2+1 .5 moa
Shooting 81.0 gr. @ -.010” 2+1 .4 moa
After shooting these groups I decided to drop one more grain and go with -.010”. After enough years of doing this you sort of get a feel for it.
Shooting 80.0 gr. @ -.010” .216” ES 9 fps Average Velocity 2996 fps
So at this point normally you whistle to yourself and think about all the great long range shots you are going to make with this kind of performance. Unfortunately my mind doesn’t always work that way. My first thoughts were, “Hey, I am 7 grains of H1000 under max case compression capacity. I wonder how much velocity I would gain it I +P modified the throat?” Well there is only one way to find out.
So the +P modification is simple to work with as it doesn’t require anything different in terms of dies, brass etc. Starting at the final load of the non +P round of 80.0 grains resulted in a velocity drop of almost 100 fps from the pressure reduction of the +P throat.
Charge Velocity Notes
80.0 gr. 2909 fps Max load from non +P chamber
81.0 gr. 2952 fps
82.0 gr. 2998 fps Equal to 80.0 gr load in standard chamber
83.0 gr. 3037 fps
84.0 gr. 3081 fps
85.0 gr. 3130 fps Faint bolt lift similar to 81.0 gr. in standard chamber
84.5 gr. 3106 fps no ejector mark, no bolt lift
Shot 84.5 grains @ -.005” , -.010” and -.015”
Jump Group ES
-.005” .473” 19
-.010” .258” 9
-.015” .184” 23
So clearly we will be running the -.010” load with the lower ES even though the -.015” load shot slightly tighter. The higher ES of the -.015” load makes it less of a choice at distance. This is pretty standard + P improvement if case capacity allows. The thing I like the best here is the combination. The 215 Berger at 3100 fps is serious hunting medicine. The use of H1000 will ensure that it will always do the same thing day in and day out. Only using 84.5 grains of powder will allow for decent barrel life. It uses a standard magnum bolt face. It doesn’t rule any category in terms of accuracy, velocity, efficiency or match component availability but it is a great combination for certain applications.