Just watched Jim’s YT video on downloading the 7PRC to 280AI velocities (nice stock BTW). My concern would be decreased load density (powder voids in the case) causing issues with consistency/precision. Did you choose a powder to consume those voids and get the load density back up to near 100%? Or maybe you don’t believe that’s an issue to worry about?
Great question
I haven’t really seen the correlation between load density and accuracy.
In this case, I was using 62.5gr of h1000 and max is 64.3 with this 175gr bullet.
That load works well for me. 62.5 gr of H1000. 175 ELDX
That seems to be about 87% load density with 13% empty space in the case. On the range, shooting prone with a bipod, it might be fine due to the consistency in ammo orientation. But in the field, it seems that this could cause pretty big swings in velocity as the orientation of the gun (and rounds) goes from vertical (up or down) to horizontal. That powder void moving from the primer area to the bullet area of the case would surely make a difference. So I like the idea of having a far more capable cartridge like the 7PRC, but loading down for 280 AI performance (velocity, recoil, etc) for certain applications. But it seems that velocity SDs would be at risk. Would be interesting to try a slower extruded powder that would give the desired velocity but fill the case more completely.
Then again, maybe I’m splitting hairs. Just trying to fully understand the pros and cons of this.
I read my response again and I guess it comes across as argumentative. Not my intention. I’m a HUGE Backfire and Jim Harmer fan boy. Been watching for years and Jim got me started on handloading/reloading and I freaking love it. So I’m looking for some education on this point.
Why my question? I know there are studies where folks “dumb down” a load to simulate 500 yd terminal performance on a short range. For instance Vortex Nation did that to test terminal performance on a range of copper bullets in ballistics gel at 50 yds. Loading down to 1900 fps muzzle velocity created wild velocity swings, so they had to be very meticulous in how they oriented the rounds as they chambered them. Otherwise the void in the case would move around from shot to shot and ruin their study. Maybe that situation was a 70% load density so the void was massive. I don’t have those figures, but of course it’s an extreme case.
So my question - what is the minimum load density we should be targeting to avoid that inconsistency? Anything above 85%? 90%? To Jim’s point, I’m sure it doesn’t matter as long as you are above a certain threshold. And maybe it has little effect as long as I stay in the published min to max powder range. Any guidance?
There was a time when cornmeal or other mostly inert organics were used to fill the case in order to maintain consistent powder burn. Mind you this was early 20th century and late 19th century. Not clue if anyone still tinkers with that idea.
I was literally coming here to ask about the lowest you could safely load an accurate 7 PRC round. I am looking for one rifle to do it all, and that is common enough and with ammo and reloading parts are common and cheap enough. I am about to buy a 6.5 PRC from Bergara, but I want to hunt elk too with a group of friends, and would love to be less limited. There is a huge chasm between 6.5 rounds and 7mm rounds. How close can you get a 7 PRC to a 6.5 PRC in terms of recoil (before considering muzzle breaks / cans, and the like)?
I’m hoping to get my first 100 rounds of 7 PRC brass loaded tomorrow and fire formed to the chamber Friday. I might record it with and without the break and see what it’s like. If the range will allow me to record with my phone I’ll post the videos to my post with the PH3 to keep Jim’s bandwidth bill down a tad.
Didn’t sound argumentative to me. It’s a good question, and I don’t know that I have the answers.
I almost always load my handloads very mild so I’m pretty used to having slightly lower case fill ratios on my loads. But I’m sure there is a lower limit. Just not sure what that would be.
I think your bullet choice and ethical hunting range are going to matter more in this scenario than the caliber. The 6.5 PRC is wildly capable with the correct bullet choice and shot distance. And this is coming from a guy that loves his Bergara in 7 PRC more than any of my other bolt guns.
On the other side, if you put a backstop recoil pad and a can on the end of anything, especially a 7 PRC, you are going to be blown away by how light the perceived felt recoil feels.
If loading the 7prc down to 280 AI, could you just use the load data for 280 AI in the 7 PRC case? I personally haven’t loaded for either one, so maybe that’s a dumb question. Or does the case of the 7 PRC have quite a bit more case capacity than the 280?
You’d want to use the 7 prc load data and just go to a powder weight to equal the velocity. If you use a different case’s load data, it could be dangerous as the different case’s shape effects pressure.
Final question for me on this topic. The 280 AI recoil seems to be a sweet spot and is the reason I want that cartridge. But Jim’s video showing a 7PRC loaded down to 280 AI velocities got me thinking about doing exactly that. So my last question - can I assume the velocity profile of that reduced 7 PRC load aligns with 280 AI recoil profile? Seems logical, just confirming. Either way, I’ll be buying the backstop pad.
For the same weight bullet going the same velocity in the same weight rifle, then the only thing that would make a difference is the powder charge. The load with the larger powder charge will have more recoil.
In this particular instance, if that’s something that you can actually notice is a completely different story however.