New Build - Too many questions, not enough answers!

[BoltBandit]

Need some input here as I'm finally doing a new build! In 2015 or 16, I bought my first precision rifle. In its current form, I have a MPA BA chassis with internal forend weights, the original Kelbly Atlas Tactical action (I run my bolt fast and hard, no issues with the ejector some have had in the past btw), with a ZCO 527 mounted in a Sphur. The barrel is a 26" Krieger with a Dn5 brake for PRS, and a KGM suppressor for p-dog hunting, etc. I'm shooting 140gn bergers @2850fps using 42.6gn of H4350 if that matters to anyone. Up until now, I almost exclusively shot Guardian Team matches, and really never got too much into PRS for various reasons until recently. One of the huge differences in team matches versus PRS is having that team mate spot and call corrections for you. Unfortunately my shot calling skills are severely lacking, lol.

So while I continue to hone my shooting fundamentals, which I know is 99% of my issue here, I might as well pick ya'lls brain on how I can buy myself a few points at the next match I shoot, haha!

For my next build I'm leaning toward the MPA Matrix Pro-II, with a Kelbly Prometheus action (have really loved my Atlas, but I'm open to suggestions). I really like the adjustable butt stock bag rider on the MPA, so that's a huge feature for me. I'm not sure how much I'll use it in PRS, but that will be money prairie dog hunting, which I do annually with my dad. Again, open to suggestions.

Admittedly, I'm stuck on a caliber. Yes, the top shooters are winning with 6.5CM's with 153's and 156's. See above on fundamentals. Plus I already have a 6.5CM, I don't want two. The 25x47 Lapua seems like an awesome choice. Its super accurate, but not light like a dasher, and still, to my knowledge is a significant enough reduction in recoil over my 6.5CM to be noticeable. My two hang ups are only Peterson and Alpha make brass, which is expensive and hard to get, and I already have a Short Action Custom sizing die for my 6.5CM. I could resize brass, but..... meh.... Handloading takes up enough time as is.

I spoke to a high level shooter who works for a particular company who was really fond of the 25CM. Great! Buy a bushing for my SAC die and call it a day. Well, did some reading on the hide here, and the consensus seems its recoil is the same if not more than my 6.5CM. Is slowing down a 25CM to 25x47 Lapua speeds realistic? Can it maintain accuracy with a reduced load? I get conflicting information on this. But it would be cool to have one die that rules them all!!!

Ok, maybe jump on the Dasher bandwagon, or a GT. Same issue as the 25x47. New dies, but also new magazines. Can't modify existing mags bc those are for my Creedmoor. Plus there's a tradeoff IMO. Dasher, less recoil, but more wind correction. 25x47 is the opposite. Figured managing recoil is an easier fix than my wind reading skills.

6CM, high speed, good wind ballistics, but a barrel burner. Not remotely interested. This sport is expensive enough.

So there you have it ladies and gents, lay those opinions and words of wisdom on me.

 

[Emerson0311]

Worrying about having 2 different 6.5CM rifles is like worrying about having 2 different gasoline powered vehicles. Pretty soon a guy will be choosing based on color. 6.5CM works and you are set up for it already. Ignore my advice if you have too much $$$ and are just trying to spend some.

 

[Hennig]

If I’m shooting custom rifles with a ZCO, I wouldn’t be too stressed about buying some brass and dies, just personally.

 

[BoltBandit]

Worrying about having 2 different 6.5CM rifles is like worrying about having 2 different gasoline powered vehicles. Pretty soon a guy will be choosing based on color. 6.5CM works and you are set up for it already. Ignore my advice if you have too much $$$ and are just trying to spend some.

Lol, fair statement, but just wanted to try something different.

 

[BoltBandit]

If I’m shooting custom rifles with a ZCO, I wouldn’t be too stressed about buying some brass and dies, just personally.

You’re not wrong, lol. But damn those SAC dies are expensive, but soooooo good. And so many other things I could spend that money on! Like maybe an over priced bipod, or a fancy chrono, or annealer.

 

[kthomas]

If the goal is to place higher up in comps, that money is MUCH better spent on training.

If you just want a new rifle (and nothing wrong with that), then go ahead and build one. Make it different than your first one. Nothing wrong with a Prometheus action. You already have a 6.5 CM, why not something different like a 6BRA or other cartridge? Perhaps try a different chassis or a stock like a Foundation. Mix it up.

 

[Taylorbok]

Shouldn't have a problem running a 25 Creed at 2700fps ish.

Could try shooting a lighter bullet it in your 6.5 and slow it down just to make sure that's the answer you're looking for.

I'm building a PRS rifle and no way you could talk me out of a Dasher.

 

[BoltBandit]

If the goal is to place higher up in comps, that money is MUCH better spent on training.

If you just want a new rifle (and nothing wrong with that), then go ahead and build one. Make it different than your first one. Nothing wrong with a Prometheus action. You already have a 6.5 CM, why not something different like a 6BRA or other cartridge? Perhaps try a different chassis or a stock like a Foundation. Mix it up.

Definitely agree on that, and more importantly, putting in the work dry firing more than anything. But I am building a new rifle regardless.

So yeah, just looking for opinions on any and all. If you’re a fan of 6BRA, why? Same for Foundation, MDT, KRG, or whatever else comes to mind? Actions too. There’s a ton of info out there, but I’m looking for real world opinions, not a sponsored pro, or YouTuber. Thanks for the reply!

 

[BoltBandit]

Shouldn't have a problem running a 25 Creed at 2700fps ish.

Could try shooting a lighter bullet it in your 6.5 and slow it down just to make sure that's the answer you're looking for.

I'm building a PRS rifle and no way you could talk me out of a Dasher.

What do you love about the Dasher so much? It’s obviously #1 on what the pros use for a reason. Any drawbacks in your mind using such a relatively lighter bullet?

 

[BoltBandit]

Shouldn't have a problem running a 25 Creed at 2700fps ish.

Could try shooting a lighter bullet it in your 6.5 and slow it down just to make sure that's the answer you're looking for.

I'm building a PRS rifle and no way you could talk me out of a Dasher.

I’ve thought about slowing down the CM, and even going lighter as well. I read an article about detuning a round too much led to inaccuracy bc the case was not at or near capacity. I’m sure testing could sort that out when I find the time.

 

[shoots100]

Is a new rifle in whatever caliber going to help you call your shots ?
You have a rig you're familiar with suited for shooting PRS right now.
Training with someone who can show you how to call your shots would be a better expenditure of your money.
SJC

 

[kthomas]

Definitely agree on that, and more importantly, putting in the work dry firing more than anything. But I am building a new rifle regardless.

So yeah, just looking for opinions on any and all. If you’re a fan of 6BRA, why? Same for Foundation, MDT, KRG, or whatever else comes to mind? Actions too. There’s a ton of info out there, but I’m looking for real world opinions, not a sponsored pro, or YouTuber. Thanks for the reply!

I love 6BRA.

Fireforming is really simple, and the fireform rounds are just as accurate as 6BRA. It's an incredibly easy cartridge to shoot and load for. Stupid accurate. Decent barrel life.

I don't have any strong opinions about Foundation, MDT, KRG, etc. My rifles have JAE chassis's, and my TacOps has a McM A5. Every chassis and stock has its benefits and tradeoffs, and it's up to the individual to determine what works best for them.

Personally, if I was to purchase a chassis today I would strongly consider the Spuhr SICS. It has features that really intrigues me. That said, component choice is a very personal thing, it's very subjective. There's a lot of "right" answers here on paper, but what matters is what works for you.

 

[BoltBandit]

Is a new rifle in whatever caliber going to help you call your shots ?
You have a rig you're familiar with suited for shooting PRS right now.
Training with someone who can show you how to call your shots would be a better expenditure of your money.
SJC I’m sure there’s a reason the dasher is so popular.

Honestly I don’t know? Even though the 6.5 seems to making a comeback, I’m guessing there’s a reason the Dasher became so popular, and the 25’s are climbing that ladder pretty rapidly as well.

But I hear you, and believe me when I say that I know a new rig is not going to be some magic pill that will suddenly take me from being an average shooter to a great shooter. Self diagnosing, my biggest barrier to better performance is I need to put in the work. Consistently dry firing and consistently going to the range. I’ve had some training, I’m sure I can always use more. Between having two teenagers and running a business I have all kinds of excuses not to practice, lol.

Anyway, I’ve been shooting the same rifle for 10 years, and quite frankly ready to try something different. It also allows me to have a backup gun as well as a rifle for my son to shoot when we go prairie dog hunting next year, and hopefully he’ll want to shoot some comps with me as too. That spoiled ass kid is in for a rude awakening if he thinks my ZCO is staying on my old rifle

 

[BoltBandit]

I love 6BRA.

Fireforming is really simple, and the fireform rounds are just as accurate as 6BRA. It's an incredibly easy cartridge to shoot and load for. Stupid accurate. Decent barrel life.

I don't have any strong opinions about Foundation, MDT, KRG, etc. My rifles have JAE chassis's, and my TacOps has a McM A5. Every chassis and stock has its benefits and tradeoffs, and it's up to the individual to determine what works best for them.

Personally, if I was to purchase a chassis today I would strongly consider the Spuhr SICS. It has features that really intrigues me. That said, component choice is a very personal thing, it's very subjective. There's a lot of "right" answers here on paper, but what matters is what works for you.

I’ve heard that about the 6BRA. Do you feel it’s limiting in longer distances or higher winds?

Oh yeah, I forgot they even made a chassis. I’ll check them out for sure. I’m guessing they’re expensive as hell given the price of their mounts, lol

 

[diggler1833]

If @BoltBandit likes the 6.5 Creedmoor... make another. Yes, one rifle will get left in the safe more... but it would anyway if you got another cartridge.

I've got (3) 6.5 Creedmoors, (2) 6.5x47L, and (1) .260 Rem (and a partridge in a pear tree...). Just make sure one differs from another just enough to make it a tad unique, and you'll appreciate both.

I also don't think you'll notice the drop in recoil until you get down to the 6mms. I don't notice the difference between my 6 and 6.5 Creeds unless I shoot them together... and I don't do that often (yes, there is a small difference).

 

[BoltBandit]

If @BoltBandit likes the 6.5 Creedmoor... make another. Yes, one rifle will get left in the safe more... but it would anyway if you got another cartridge.

I've got (3) 6.5 Creedmoors, (2) 6.5x47L, and (1) .260 Rem (and a partridge in a pear tree...). Just make sure one differs from another just enough to make it a tad unique, and you'll appreciate both.

I also don't think you'll notice the drop in recoil until you get down to the 6mms. I don't notice the difference between my 6 and 6.5 Creeds unless I shoot them together... and I don't do that often (yes, there is a small difference).

See, I want to be like you, variety is the spice of life!

But thank you, you're actually getting to the meat of my question. I can look at ballistic data till the cows come home, and there are differences for sure, but how does that translate in the real world?

My good friend was telling me that if I was looking for a caliber that was a bit easier to spot, that the there really wasn't much point in a 25x47L, it's too close to a 6.5CM. He agrees with you and is strongly suggesting a Dasher or GT if I want any meaningful difference.

 

[Jamesl0822]

Could you train to manage your recoil so that you see your misses better? Sure
But, that’s not really what you’re asking. You have $ for a new build set aside and you want the group’s opinion on which route to go on your build if your goal is to see your misses better?

Caliber: 25 cm or 25x47 both great choices both very similar in performance to what you already have… dies and brass for 25x47, just brass for 25cm and a bushing
6 Dasher GT or BR these are the easy button and yes it is following the crowd but there’s a damn good reason. You’re in Ga and the wind is rarely that big of a deal
Action: Kelbly Prometheus, BAT Hammerhead, Borden Rimrock if you want a Ferrari
Lone Peak Fusion, impact 737 if you want the dependable family car
With your goals in mind, I’d go 6mm bc the 25x47 is so close to a 6.5 creedmoor that I put them in the same category. Unless you’re a collector, I just don’t see the need for a 25 and a 6.5. Plus you can always put a 25 barrel on your atlas action?

Good luck keep us posted

 

[diggler1833]

See, I want to be like you, variety is the spice of life!

But thank you, you're actually getting to the meat of my question. I can look at ballistic data till the cows come home, and there are differences for sure, but how does that translate in the real world?

My good friend was telling me that if I was looking for a caliber that was a bit easier to spot, that the there really wasn't much point in a 25x47L, it's too close to a 6.5CM. He agrees with you and is strongly suggesting a Dasher or GT if I want any meaningful difference.

My "collection" is purely out of retardation. But I do have some pretty unique firearms in the chamberings that I mentioned... so I find quite a bit of enjoyment in shooting all of them.

I also have a 6GT and a couple 6CMs (some are just barrels for other rifles that I swap back and forth). It is really difficult to find fault with the 6GT, and they are very, very close to a warm 6.5CM/.260 Rem out to most PRS distances. The 6CM is a flat-shooting titan, the downside to that cartridge is definitely the barrel life. Since I'm a good ol' boy who just plinks and kills a few things, I'm not really concerned with barrel life as much as the next guy.

I don't pretend to be into PRS, never tried it, never will. I certainly appreciate all of the innovation into precision rifles, optics, and components that the explosion of PRS has created within the past 15 years however.

Best of luck man.

 

[Taylorbok]

What do you love about the Dasher so much? It’s obviously #1 on what the pros use for a reason. Any drawbacks in your mind using such a relatively lighter bullet?

For me why deviate from what is working so well for so many others?
I'm just thinking about getting into the sport so it's easiest to just follow what works. I shoot ELR currently
Plus I like how the little chubby case looks.

For sure you are giving up some wind but it's not the total wind hold you need to look at it, it's the difference between the cartridges when there is a wind switch or when you're wind call is off that really makes the difference.

Say @ 1000 Yards, 9-10mph wind
6 Dasher is 1.95-2.14 mil = dif .19 mil
6.5 Creed is 1.46-1.60 mil= dif .14 mil

.14-.19= .05 mil, that's how much wind you actually gain or lose (per mph of error). The idea is with the lighter recoiling cartridge you'll be better off to see where you miss and make those small correction vs trying to fight the heavier recoil for a slight edge in the wind. Obviously these numbers can be altered a fair bit depending on what speed and bullet you are using.

 

[BoltBandit]

For me why deviate from what is working so well for so many others?
I'm just thinking about getting into the sport so it's easiest to just follow what works. I shoot ELR currently
Plus I like how the little chubby case looks.

For sure you are giving up some wind but it's not the total wind hold you need to look at it, it's the difference between the cartridges when there is a wind switch or when you're wind call is off that really makes the difference.

Say @ 1000 Yards, 9-10mph wind
6 Dasher is 1.95-2.14 mil = dif .19 mil
6.5 Creed is 1.46-1.60 mil= dif .14 mil

.14-.19= .05 mil, that's how much wind you actually gain or lose (per mph of error). The idea is with the lighter recoiling cartridge you'll be better off to see where you miss and make those small correction vs trying to fight the heavier recoil for a slight edge in the wind. Obviously these numbers can be altered a fair bit depending on what speed and bullet you are using.

LOL, that's a good question, and partly my tendency to go against the grain. Personal problem for sure!

But you bring up a really good point on the difference in a wind call. Never thought to look at the math that way. Much appreciated!

 

[carbonbased]

https://precisionrifleblog.com/2025/09/19/best-rifle-cartridge/

More reading material

 

[BoltBandit]

https://precisionrifleblog.com/2025/09/19/best-rifle-cartridge/

More reading material

Yeah, I’ve scoured that up and down, lol.

 

[WeR0206]

Yeah, I’ve scoured that up and down, lol.

If you really want to mix it up and make it as easy as possible to self spot your misses, etc. what about a 6 ARC bolt action (24+ inch barrel)? I don't think most top PRS shooters are maxing out the speed that's possible with the dashers anyway for this very reason. Something to think about. You'd shoot the same bullets that are dominating PRS (Berger 105 and 109 hybrids, etc.) but with less powder/recoil. The only caveat is the bolt face for 6 arc is the less common "small" PPC size (0.455") which aren't available for all actions in the market.

 

[mark5pt56]

I just had a 6ARC bolt gun built, 26" barrel. Initial firing last week, box each of Hornady factory 105/108, avg 2741/42. I hope to shoot again this week and possible see some increase as the barrel breaks in.
Just to give you some numbers for the caliber if it helps make a decision.
ATX chassis, long fore end, comp contour barrel, no weights and an Area 419 HFM brake-very mild. Zero issues feeding with MDT 6ARC magazines.
Origin action with the ARC bolt face.

 

[BoltBandit]

Thanks guys, never considered the 6 Arc. Although I’m not a fan of the smaller bolt face. I’ll have to see if the Prometheus is interchangeable if I go that route.

 

[Taylorbok]

Personally I wouldn't do an ARC. You would but running at or near max pressure to keep up with tuned down Dasher speeds.

 

[WeR0206]

Personally I wouldn't do an ARC. You would but running at or near max pressure to keep up with tuned down Dasher speeds.

True but id be more worried about that if it was a gas gun. Running a 6 arc bolt gun at or near max pressure should result in higher case fill % and higher % powder burned which should result in lower ES and SD’s in speed.

You could still find a powder whose burn rate results in high % case fill etc for a lower speed dasher load but it might be harder to zero in on it.

It is def nice that dashers etc use the same bolt face as 308. Like all things each approach has its pros and cons and the OP needs to weight each for his use case

 

[CStroud]

Thanks guys, never considered the 6 Arc. Although I’m not a fan of the smaller bolt face. I’ll have to see if the Prometheus is interchangeable if I go that route.

Kelbly makes a ppc bolt for the arc cartridges.

 

[flogxal]

Another vote for sticking with 6.5 Creedmoor. You mentioned handloading taking up enough time as it is. You want to tackle a new set of dies and new cartridge despite that? I get the urge for something different. But I think mastering the thing you're already using is a wiser path. Unless it's just a hobby-level interest, just shooting for fun, enjoying different firearms. Then build / buy at random for the variety.

In gas gun world I have spent a fair amount of time working on 6.5 Grendel loads. I have a 6 ARC upper that I've ignored because I don't want to start handloading another new cartridge. Hell I'm ignoring the AR 6.5 Grendel almost all year this year from my focus on 6.5 Creedmoor bolt gun. I would not be looking at a different cartridge for my PRS/long range bolt gun uses. In fact I bought a 2d barrel for my 6.5 Creedmoor, ready to stick with the cartridge.

But I'm not trying to win or place highly in PRS.

 

[Taylorbok]

True but id be more worried about that if it was a gas gun. Running a 6 arc bolt gun at or near max pressure should result in higher case fill % and higher % powder burned which should result in lower ES and SD’s in speed.

You could still find a powder whose burn rate results in high % case fill etc for a lower speed dasher load but it might be harder to zero in on it.

It is def nice that dashers etc use the same bolt face as 308. Like all things each approach has its pros and cons and the OP needs to weight each for his use case

I haven't seen anything that adequately correlates low SD's to higher case fill. IMO that is mostly a myth, until you get way down in fill.

also
to the same point as @flogxal before I had a family and way more time I had no problem tinkering with several different cartridges and having a different one for every occasion. Now I'm looking to condense cartridges so I can be more efficient with my time reloading and shooting

 

[WeR0206]

I haven't seen anything that adequately correlates low SD's to higher case fill. IMO that is mostly a myth, until you get way down in fill.

also
to the same point as @flogxal before I had a family and way more time I had no problem tinkering with several different cartridges and having a different one for every occasion. Now I'm looking to condense cartridges so I can be more efficient with my time reloading and shooting

I've seen it in my own testing (as charge weights/case fill % goes up SD and ES go down)...it's also physics (higher case fill % means higher % powder burned which gives more consistent output) but as you said the threshold seems to be around 90% case fill but this could vary wildly with different types of cases (223 rem vs. 6 arc, etc.). Once you dip below that your SD's and ES's will jump up....like all things YMMV

 

[BoltBandit]

I haven't seen anything that adequately correlates low SD's to higher case fill. IMO that is mostly a myth, until you get way down in fill.

also
to the same point as @flogxal before I had a family and way more time I had no problem tinkering with several different cartridges and having a different one for every occasion. Now I'm looking to condense cartridges so I can be more efficient with my time reloading and shooting

There was a good article that I saw somewhere discussing how cartridges work better when powder charges are closer to full capacity of the case in terms of accuracy. For instance, detuning a 30-06 to a .308 would result in poor accuracy. I'm sure there's a break even point like anything in this world.

 

[BoltBandit]

Hey guys, first I want to thank everyone for all their input, it's been very helpful in my decision making process. But I've made a decision..... drum roll please, lol.

I was leaning toward the MPA Matrix Pro-II anyway and found a great deal on a 100% certificate here, so that was a no brainer. Now to decide on a color, but that's easy enough.

I've decided to run a Kelbly Prometheus action. I absolutely love my Atlas, and this is pretty much the same thing but with an integral rail and recoil lug. Plus the bolts are interchangeable, giving me a backup firing pin if the issue were to ever arrise.

I've settled on the 6x47 Lapua. Comments above and elsewhere in the PRS world is that the 6x47 is a barrel burner. Although true, those guys are also running speeds north of 3,100 fps. By slowing down to the 2,900fps range, I can get barrel life similar to a 6.5CM with ballistics similar to the dasher, albeit a slight disadvantage in recoil. Two pros who I highly respect run their 6x47's this way with great barrel life, which was my main concern with the 6x47 Lapua. Although minor in the grand scheme of things, I appreciate the modularity of being able to spin up a 25x47 L and simply change the bushing in the die. All three rounds 6x47, 25x47, and 6.5CM perform exceptionally using H4350.

Again, thanks for all the feed back guys, and shoot 'em straight!

 

[Taylorbok]

There was a good article that I saw somewhere discussing how cartridges work better when powder charges are closer to full capacity of the case in terms of accuracy. For instance, detuning a 30-06 to a .308 would result in poor accuracy. I'm sure there's a break even point like anything in this world.

a 30-06 can run at 308 speeds pretty easily but I'm guessing that was just a poor example. Think 300 RUM at 308 speeds.
Anyways I do agree when you are trying to drop powder to unreasonable levels it would likely become an issue. I've even heard of it being dangerous as the primer can light all the powder at once and cause an explosion vs a controlled burn.

But I was speaking more in the realm of reasonable as @WeR0206 initially was saying a max load (or over max) will be more precise which there's no real data to back that up from what I've seen and read 80% + case fill is totally reasonable to produce good results.

also there's no physics law that says more powder burned give a more consistent output. Yes variance in a larger charge is a smaller percent change which will produce more consistent results but the difference between a 39 and 40gr charge is negligible, if you are talking 40gr vs 100gr that is different.

 

[BoltBandit]

a 30-06 can run at 308 speeds pretty easily but I'm guessing that was just a poor example. Think 300 RUM at 308 speeds.
Anyways I do agree when you are trying to drop powder to unreasonable levels it would likely become an issue. I've even heard of it being dangerous as the primer can light all the powder at once and cause an explosion vs a controlled burn.

But I was speaking more in the realm of reasonable as @WeR0206 initially was saying a max load (or over max) will be more precise which there's no real data to back that up from what I've seen and read 80% + case fill is totally reasonable to produce good results.

also there's no physics law that says more powder burned give a more consistent output. Yes variance in a larger charge is a smaller percent change which will produce more consistent results but the difference between a 39 and 40gr charge is negligible, if you are talking 40gr vs 100gr that is different.

Probably was a poor example, lol, but yeah, I agree with your point and example as well. I need to find that article. By my own dumb logic, pushing anything to its max causes instability and weakness in any given system.

 

[WeR0206]

a 30-06 can run at 308 speeds pretty easily but I'm guessing that was just a poor example. Think 300 RUM at 308 speeds.
Anyways I do agree when you are trying to drop powder to unreasonable levels it would likely become an issue. I've even heard of it being dangerous as the primer can light all the powder at once and cause an explosion vs a controlled burn.

But I was speaking more in the realm of reasonable as @WeR0206 initially was saying a max load (or over max) will be more precise which there's no real data to back that up from what I've seen and read 80% + case fill is totally reasonable to produce good results.

also there's no physics law that says more powder burned give a more consistent output. Yes variance in a larger charge is a smaller percent change which will produce more consistent results but the difference between a 39 and 40gr charge is negligible, if you are talking 40gr vs 100gr that is different.

I largely agree with you. My point re: physics and high case fill %'s still stands (note, Max load doesn't always mean high case fill %). Higher case fill % will cause the % powder burned to go up, this concept revolves around the fundamental principles of propellant combustion dynamics, pressure-volume relationships, and flame propagation in a confined space. Do some research on these topics if you don't believe me. If I had to choose between a load that was 80% case fill vs. 90% id take the 90% every single time. Same with 90 vs 95, I'd take 95. I'd take the highest possible case fill % I can get b/c I know via physics it's more likely to result in a more consistent output.

6 dasher vs. 6 arc, you could probably find the right combo in dasher (high % case fill that produces the lower speed) but it might be harder to find. Seems like folks have already cracked the code using varget, etc. for their dasher loads.

 

[Taylorbok]

I largely agree with you. My point re: physics and high case fill %'s still stands (note, Max load doesn't always mean high case fill %). Higher case fill % will cause the % powder burned to go up, this concept revolves around the fundamental principles of propellant combustion dynamics, pressure-volume relationships, and flame propagation in a confined space. Do some research on these topics if you don't believe me. If I had to choose between a load that was 80% case fill vs. 90% id take the 90% every single time. Same with 90 vs 95, I'd take 95. I'd take the highest possible case fill % I can get b/c I know via physics it's more likely to result in a more consistent output.

6 dasher vs. 6 arc, you could probably find the right combo in dasher (high % case fill that produces the lower speed) but it might be harder to find. Seems like folks have already cracked the code using varget, etc. for their dasher loads.

My point is that choosing a load or cartridge based on case fill over how it actually shoots is stupid.
I've never seen any valuable data that suggests 90% vs 80% has a meaningful impact.

Also I've seen way more and larger velocity issues caused trying to run a case at or over max pressure than I've ever heard of from running 80% case fill

 

[WeR0206]

My point is that choosing a load or cartridge based on case fill over how it actually shoots is stupid.
I've never seen any valuable data that suggests 90% vs 80% has a meaningful impact.

Also I've seen way more and larger velocity issues caused trying to run a case at or over max pressure than I've ever heard of from running 80% case fill

Where did I say you should choose case fill % over how something actually shoots?

I agree with your point that being right at or over max chamber pressure will give you poor results, you glossed over my point that high case fill % doesn’t automatically mean you are at max chamber pressure. Step one is determine what your use case is and what velocity you need. Step two is to determine if you can obtain your target velocity with the chamber/barrel length you are considering if you can’t, then it’s not for you. For example, in 556 I will look for loads that would be between 50 and 60,000 psi (assuming max pressure is 62K psi). Then I would try to find the powder that would give me the highest possible case fill % that would not breach my pressure thresholds And still give me the speed I’m looking for. Being right up at Max chamber pressure is not a good place to be due to changes in temperature, etc. it’s risky.

 

[Junco Grande]

If you want to be different, (than 6.5 guys even though your comment) be different. Don't ask permission from everyone here, I think the answers might show that you're splitting hairs on trade offs.

 

[Kickin45]

I recently built a 6GT for something different. Already have 3 65CM’s.
The GT is the easiest easy button I’ve ever pushed.
FPS from 2750 up to 2925 is a laser beam!
I settled on 2870 so I could see my trace.
The recoil, on my setup (strike nuke and an M24 barrel) is less than my suppressed SR15.

My buddy and I went to the range the other day. It has steel set up at 400, 500 and 600 (farthest that range has)
We had 100 rounds of factory Hornady 109 ammo to waste.
We took turns and played a game of who would miss first. 4” plates all the way up to buck silhouettes with “vital” spinners all at different distances.
I know 600yds for that round isn’t anything special, but at 80 rnds, we got bored and left.
6GT is the Goldilocks cartridge.
Load it with 112’s or 115’s at 2850 and it’s hard to beat. And you can shoot it all day comfortably.

 

[BoltBandit]

If you want to be different, (than 6.5 guys even though your comment) be different. Don't ask permission from everyone here, I think the answers might show that you're splitting hairs on trade offs.

Yeah, I’m a research junky. Just can’t help myself from getting in the weeds, lol.

 

[flogxal]

a 30-06 can run at 308 speeds pretty easily but I'm guessing that was just a poor example. Think 300 RUM at 308 speeds.
Anyways I do agree when you are trying to drop powder to unreasonable levels it would likely become an issue. I've even heard of it being dangerous as the primer can light all the powder at once and cause an explosion vs a controlled burn.

But I was speaking more in the realm of reasonable as @WeR0206 initially was saying a max load (or over max) will be more precise which there's no real data to back that up from what I've seen and read 80% + case fill is totally reasonable to produce good results.

also there's no physics law that says more powder burned give a more consistent output. Yes variance in a larger charge is a smaller percent change which will produce more consistent results but the difference between a 39 and 40gr charge is negligible, if you are talking 40gr vs 100gr that is different.

If I'm remembering it correctly, Jeff Siewert's book talks about powder fill vs case capacity in terms of consistency of burn. The more empty space, the more inconsistency is possible -- independent of max pressure approaches, I mean. Siewert talked about trying to accurize lower-fill charges by filling the empty space with a combustion-inert substance like puffed rice cereal/dry baby food.

 

[Rocketmandb]

There was a good article that I saw somewhere discussing how cartridges work better when powder charges are closer to full capacity of the case in terms of accuracy.

This is actually true, but true with caveats. See my response to @flogxal below.

If I'm remembering it correctly, Jeff Siewert's book talks about powder fill vs case capacity in terms of consistency of burn. The more empty space, the more inconsistency is possible -- independent of max pressure approaches, I mean. Siewert talked about trying to accurize lower-fill charges by filling the empty space with a combustion-inert substance like puffed rice cereal/dry baby food.

He does talk about it in his book, and it makes sense. If there is empty space, then you can get more (or less, depending) powder stacked up against the rear (or forward) area of the case. This will change your burn rate from one case to the next. However...

My point is that choosing a load or cartridge based on case fill over how it actually shoots is stupid.

This is also true. I would certainly discount faster-burning powders that would take you into the 80s% of case fill over a slower-burning one that gets you well into the 90s - given they deliver similar velocities. However, it makes no sense to choose a caliber based on this. If you want to maximize case fill, then:

1) Choose your caliber
2) Choose a powder that gives you your desired velocity at the highest case fill

I have started to move to slower burning powders, but only in part because of the case fill component. For me, it's more that I tend to believe that an elongated pressure curve (lower peak + longer burn) delivers a longer, more manageable impulse (definitively true) coupled with a more consistent burn (my theory only).

 

[flogxal]

For sure I would hope someone is not choosing a combination only based on fill %. I see it as a powder choice among several for a given bullet. Optimum fill % doesn't automatically mean great results downrange.

 

[Rocketmandb]

For sure I would hope someone is not choosing a combination only based on fill %. I see it as a powder choice among several for a given bullet. Optimum fill % doesn't automatically mean great results downrange.

It also doesn't necessarily mean you get better consistency. If you have a lower case fill, but chamber each round in the same manner, you can get as good results as a higher case fill because the powder distribution should remain consistent.

As an example, I used to use H4895 in my 6 BRA. It worked great, and I got very consistent results, yielding ~4.x fps in standard deviations. When H4895 got tougher to find, I decided to try Varget, then N540. Both are slower powders that are very similar to each other, and both yield higher case fill. I'm getting very similar results to what I was getting with H4895.

 

[flogxal]

Thanks, I like those thoughts.

Do you think in a semi-auto, like an AR, it's a better idea to optimize the fill if you can -- given the more violent feeding etc.?

 

[Rocketmandb]

Do you think in a semi-auto, like an AR, it's a better idea to optimize the fill if you can -- given the more violent feeding etc.?

Definitely yes. But then, in a semi-auto, will it really matter?

 

[BoltBandit]

This is actually true, but true with caveats. See my response to @flogxal below.



He does talk about it in his book, and it makes sense. If there is empty space, then you can get more (or less, depending) powder stacked up against the rear (or forward) area of the case. This will change your burn rate from one case to the next. However...



This is also true. I would certainly discount faster-burning powders that would take you into the 80s% of case fill over a slower-burning one that gets you well into the 90s - given they deliver similar velocities. However, it makes no sense to choose a caliber based on this. If you want to maximize case fill, then:

1) Choose your caliber
2) Choose a powder that gives you your desired velocity at the highest case fill

I have started to move to slower burning powders, but only in part because of the case fill component. For me, it's more that I tend to believe that an elongated pressure curve (lower peak + longer burn) delivers a longer, more manageable impulse (definitively true) coupled with a more consistent burn (my theory only).

I also understand that a lower peak/slower burn wont wear out the throat as fast and distributes more wear to the middle of the barrel.