Custom build: which cartridge for maximum accuracy if only shooting factory ammunition

[SDHNTR]

This is like asking a doctor which are the best donuts to eat.

 

[Truck24hr]

All those guys that said 6.5CM, i'm with them for right now.

So much great factory hunting ammo available, and shootability, leaves no better choice right now.

That may change in a few years though.

 

[jjcausey22]

6.5 Creedmoor or 6.5 PRC, depending on barrel length and max kill range.

Rifle will be between 7.5 and 8 pounds without an optic or suppressor. I really want a 20-22 inch barrel and I’ll shoot it suppressed at all times. Would like the capability to shoot game at 500-600. That could possibly increase if I get better at reading and calling wind. I will probably shoot eld-m’s in factory ammunition because I want the most margin of error with wind out to those distances.

 

[elkguide]

For accuracy with factory ammo, I would look at .300 Win Mag - .308 - 6.5 PRC as my first 3.

 

[nm.otter]

Rifle will be between 7.5 and 8 pounds without and optic or suppressor. I really want a 20-22 inch barrel and I’ll shoot it suppressed at all times.

Adding an optic and suppressor to that should make 6.5 CM a viable choice.

My suppressed 20" 6.5 CM (7 pounds 15 ounces all in) is on the hairy edge of workable spotting shots from 140-147gr slugs. 120s are noticeably easier, so I'm giving serious thought to 6mm GT.

 

[hereinaz]

Rifle will be between 7.5 and 8 pounds without an optic or suppressor. I really want a 20-22 inch barrel and I’ll shoot it suppressed at all times. Would like the capability to shoot game at 500-600. That could possibly increase if I get better at reading and calling wind. I will probably shoot eld-m’s in factory ammunition because I want the most margin of error with wind out to those distances.

IMO, 20” 6.5 PRC for 600.
22” 6.5 creed can get you there, but less margin of error for wind.

Just know you will need to focus more to manage recoil. But, either are doable suppressed.

 

[hereinaz]

Adding an optic and suppressor to that should make 6.5 CM a viable choice.

My suppressed 20" 6.5 CM (7 pounds 15 ounces all in) is on the hairy edge of workable spotting shots from 140-147gr slugs. 120s are noticeably easier, so I'm giving serious thought to 6mm GT.

Such a nice cartridge the 6 GT.

 

[bojangles808]

6.5cm. my 20in is a 600 yd gun at mountain DAs with eldms

 

[Sled]

Of your listed cartridges, I'm with the 6.5cm crowd. If you need more, you find hot factory ammo or step up to the PRC. I've had great luck with my CM shooting berger classic hunters and rarely pull out the PRC anymore. Since eagle eye ammo has had QC issues, I'll be looking into Form's recommendation of federal loads.

This might be only my opinion but I believe the Hornady chamberings are well thought out and inherently lead to less errors from tolerance stacking. In my limited experience I've had more precise rifles, factory or custom, from those Hornady chamberings. Maybe somebody with more knowledge or experience can say why or refute that.

I'll add that even though I like the creedmoor, I am not a millennial, do not wear a flat brim hat, nor do I have a man bun.

Good luck with your decision.

 

[jjcausey22]

@nm.otter has a chart with bore to capacity ratio of many popular chambering. It’s been interesting to see how some cartridges that are commonly cited to be “accurate” or “shootable” will group closely with each other on that chart.

If only shooting factory ammo, I would second what @Formidilosus listed above. 6mm Creedmoor as my number 1 pick. And stock up on federal gold medal match ammo.

Where is that chart

 

[TaperPin]

I’ll be the odd man out and go with a 7 mag and no turn neck (.315”). Its minimal dimension neck still allows factory loads, but has to be kept clean. Typically these also have minimal dimensions in the throat. 7 Rem mag has a wide variety of quality bullet choices and while certain factory loads in other cartridges are often used in competition, not much is left on the table with the 7 mag or many other common cartridges. The same could be said for a good quality 300 wm.

Not every custom barrel is the same - get the best one you can from an accuracy minded gunsmith and I’d put that against 99.9% of the custom guns out there.

 

[nm.otter]

Where is that chart

N

Post in thread 'Spotting your shot, most import factors.'

Friday at 8:56 PM

Good powders are good in the case dimensions they excel at. H4350 in a Creedmoor case at creedmoor pressures is a good example. Very repeatable and reliable. But try and fit it into a larger or smaller case, and funny things can happen.

Case capacity to bore area ratio rears its head once again. Here's a table of some common cartridges sorted by this Ratio -- dividing the usable case capacity (to bottom of neck) by the square of the bore diameter. It's a dimensionless number which can be derived either from inches or from mm/ml:

Charge efficiency, barrel life...

• nm.otter

• 

 

[jimh406]

I'd lean Hornady calibers since they were designed for target shooting with tight chambers. Note: I don't own a Hornady caliber.

 

[SouthernCharm]

Ask the builder which ammo do they spec their guns too. They will tell you which factory ammo will shoot mom or better. Then ask them if a certain cartridge is more accurate.

 

[sierracharlie338]

Adding an optic and suppressor to that should make 6.5 CM a viable choice.

My suppressed 20" 6.5 CM (7 pounds 15 ounces all in) is on the hairy edge of workable spotting shots from 140-147gr slugs. 120s are noticeably easier, so I'm giving serious thought to 6mm GT.

It’s a kitten of a cartridge, you won’t regret it.

Such a nice cartridge the 6 GT.

Agreed!

 

[Dave Thomas]

I don't think many gun builders would condone you shooting mom.

 

[MuleyFever]

N

Post in thread 'Spotting your shot, most import factors.'

Friday at 8:56 PM

Good powders are good in the case dimensions they excel at. H4350 in a Creedmoor case at creedmoor pressures is a good example. Very repeatable and reliable. But try and fit it into a larger or smaller case, and funny things can happen.

Case capacity to bore area ratio rears its head once again. Here's a table of some common cartridges sorted by this Ratio -- dividing the usable case capacity (to bottom of neck) by the square of the bore diameter. It's a dimensionless number which can be derived either from inches or from mm/ml:

Charge efficiency, barrel life...

• nm.otter

• 

What am I looking at here? What does the ratio correlate to?

 

[jjcausey22]

Out of those a suppressed 300prc with a 22” benchmark sendero paired with a bat vesper action.

Do you think a 300 prc has the accuracy potential of the smaller prc’s in a hunting weight rifle. Just concerned that it won’t be as consistent due to the higher recoil.

 

[Formidilosus]

The only ones I saw were the target hybrids, which have a thicker jacket I thought.

They do. But, the 105gr and 109gr 6mm Berger Hybrids, the 130gr and 140gr 6.5mm, and the 308 185gr Berger Juggernauts generally kill well, and ai would personally rather use them with the possible downsides rather than deal with Hornady’s absolute inconsistency.

 

[jimh406]

Do you think a 300 prc has the accuracy potential of the smaller prc’s in a hunting weight rifle. Just concerned that it won’t be as consistent due to the higher recoil.

Just a Grok summary with things to consider. No idea if you can handle kick or not. I'm assuming you will use a brake or suppressor.

The 300 PRC is generally considered the most inherently accurate Hornady PRC cartridge, particularly for extreme long-range precision.

All three Hornady PRC cartridges (6.5 PRC, 7mm PRC, and 300 PRC) are engineered for excellent accuracy through modern design features like a 30° shoulder, minimal body taper, beltless cases for better headspacing, tight throat tolerances (just ~0.0005–0.0008" over bullet diameter), and optimization for long, high-BC bullets with temperature-stable powders. These traits promote superior concentricity, alignment, and consistency compared to older magnums.

However, the 300 PRC stands out as the most precision-oriented:

• It was specifically developed with input from the U.S. Department of Defense for extended long-range sniping, emphasizing "match-grade" accuracy and heavy-for-caliber bullets (e.g., 212–225gr ELD-M at ~2,800–2,950 fps).
• Hornady describes it as a "large 30 caliber match accurate cartridge" designed concurrently with its chamber for "excellent alignment and highly tuned performance."
• Real-world reports frequently highlight sub-0.5 MOA groups with factory match ammo, and it's praised for outperforming belts like the .300 Win Mag in consistency and long-range precision.

The 7mm PRC (introduced 2022) is a close second—often called a "do-it-all" with outstanding factory-load accuracy (e.g., 0.3–0.5 MOA in tests) and the best trajectory/wind performance among the three due to high-BC 7mm bullets (175–180gr ELD-X/M). It excels in hunting/precision balance with less recoil than the 300 PRC.

The 6.5 PRC is highly accurate with very low recoil, making it forgiving and repeatable for shooters, but its smaller bullets lose energy and drift more at extreme ranges compared to the larger siblings.

Inherent accuracy is ultimately rifle-, load-, and shooter-dependent, but the 300 PRC's design and military validation give it the edge for pure precision potential, especially beyond 1,000 yards. For most hunters or all-around use, the 7mm PRC's combination of accuracy, flatter trajectory, and manageable recoil often feels "most accurate" in practice.