Home Forums Hunting & Shooting Ask The Gunwriters Cases capacity 6.5 PRC v RPM

I am considering leaping into the present and getting a 6.5.

Does anyone know the case capacities of the PRC vs Wby RPM? I need numbers that use the same method of measurement for each.

Thanks.

The RPM has a water capacity of 81.5 grains

I'm seeing 68.8 for the PRC..."Nov 9, 2018 — Shooting Times magazine's look at the PRC gives its case 68.8gn water"


A comparison of case capacities is a good starting point for finding out. When filled to the brim, gross water capacity of the 6.5 PRC averaged 67.6 grains. Moving down to smaller capacities, we have 6.5 Creedmoor and 6.5-284 cases made by Hornady at 53.4 grains and 64.3 grains respectively. Moving up to a couple with bigger capacities, we have the 6.5 Remington Magnum at 70.2 grains and the .264 Winchester Magnum at 84.1 grains. Capacities for the 26 Nosler and 6.5-300 Weatherby Magnum are 98.2 and 96.7 grains respectively.

Despite their similarities, the 6.5 PRC and 6.5 RPM are opposites in some regards. The PRC requires a magnum bolt face but fits in a short action whereas the RPM utilizes a standard-diameter bolt but demands a long action.

Manufacturer-supplied velocity figures show the RPM is slightly faster than the PRC, but not by much. With factory loads the RPM will push a 140-grain InterLock bullet out the pipe at 2,975 fps, and it makes 3,075 fps with a 140-grain AccuBond. That beats the figures for the Hornady bullets in the PRC slightly, but the PRC is firing slightly heavier bullets with higher ballistic coefficients.

The RPM’s case capacity is greater than the PRC, but the PRC’s neck design allows bullets to be seated farther out, and the PRC’s throat design already has a reputation for gilt-edge accuracy. Higher-BC PRC bullets carry energy better, too. At 200 yards all of the RPM loads beat the PRC’s energy figures. At 400 yards the PRC takes the lead, though, and at 500 yards the PRC retains 100 ft.-lbs. more energy than any of the RPM loads.


https://www.rifleshootermag.com/editorial/65-prc-vs-65-rpm-what-you-need-to-know/377415

From a chart on backfire tv that shows cubic inches.
"The following chart shows the usable case volume of all popular rifle cartridges, measured in square inches. By “usable case volume,” I mean the internal area of the body of the case and shoulder, but none of the neck. This would be the space occupied by powder in the case of a flat-based bullet that doesn’t protrude into the powder column....I am showing the case capacity of all popular rifle cartridges by actually doing the math from the published drawings of the case to determine the precise internal volume of each cartridge. "

6.5 PRC- 0.6464 ci (I am assuming cubic inches was meant, not "square inches" for volume as stated in the article.)
6.5 RPM- 0.7759 ci

257
Thanks for your epistle regard 6.5’s BUT it doesn’t answer the question.

rcam
Did the source you quote have the case capacities for both measuring to the same point on the case?

Redrab
Bingo. Thanks for your answer.

Rick,

The 6.5 PRC is basically a short-action 6.5-06, which ain't a bad thing.

It could also be compared to a .270 Winchester with higher-BC bullets.

Have used mine (a custom by Charlie Sisk) to take more game over the past few years than the rest of my rifles combined.

John
Thanks for your informative reply.

I have been accumulating the parts to create a 6.5-06. I have a new Henriksen reamer and set of RCBS dies and a AnTi action and a barrel. But I am a velocity junkie and am considering getting the 6.5 RPM thereby “wasting” the reamer and dies and committing myself to expensive and hard to acquire brass cases. Silly!

That said I realize another 125 fps isn’t going to make a big difference in this age of laser rangefinders and advanced optical systems and high BC bullets. I should spend my dollars on a high end Swarovski or Nightforce. Even then, given that my self imposed limit is around a quarter of a mile, there isn’t much real difference except inside my noggin. It is in that space where the problem resides.

Please don’t remind me that my 1-9 twisted 270 is pretty much the same thing.

Of course I am clearly neither a gun nut nor a rifle looney (loony). Which spelling do you prefer?

Rick,

Obvious what you "need" is a collection of rifles chambered for all the 6.5mm rounds. The middle-range would include not just the 6.5 PRC and 6.5-06, but a 6.5-284...especially the Norma version, which has an overall length like the .270--so bullets can be seated out a little further and gain all the muzzle velocity possible, perhaps even 50 fps.

I also have a 6.5-.284, but bought it more for sentimental reasons than anything else. It belonged to the late Tom McIntyre, and is also an Ultra Light Arms rifle. It's a sort of compromise between the Norma version and the "short" version of the cartridge, where bullets are seated to a max 2.85" like the .284 itself. The ULA Model 20 action, of course, has a magazine allowing cartridges up to 3.0" in overall length.

I suspect, due to using a bunch of 6.5s to kill big game, that it will work despite that "handicap."

6.5 mm chamberings are the rage and perform well.

If you’re building/buying a hunting rig and want to cut to the chase, a 7mm offering is what you want. Shooting fast .264 bullets side by side against 7mm chamberings is eye-opening at ELR


7mm bullets trump 6.5mm bullets in BC and can be driven at velocities that make them shine

If you don’t require LR shooting, they also cover everything short.

Present? 6.8 is the new present day .270. Being a 270 fan I always enjoy your 270 africa reports:) Need a 6.8W with 155 Barnes LRX if want to be up to date. 6.5 is old now:)

Lou

rcam
You are, of course, correct. My only issue is that I am becoming less interested in recoil. A 7 PRC is a wonderful cartridge. Actually it is what most fans of the 280AI really want. In the 7 pound rifles I am willing to pack it is too much for me.

I can shoot precisely with my 8# 375 H&H but I would rather not. Remember Quigley’s famous line.

Thanks again for your learned input.

Rick

Lou 270

I continue to search about for a reason to get something besides a 270W but there really isn’t anything to be gained, as you must already know.

Best to you
Rick

Sounds like you would like a 6.5, which is enough reason to get one, regardless of whether it has significant real advantages over a .270. Since you like light rifles but not too much recoil, I'd say the PRC might be the better choice.

However, I have no actual experience with either of the cartridges you list, so this is merely my theoretical two cents worth. However, I've enjoyed my 6.5 CM and have considered a 6.5 PRC, so I can see where you're coming from.

It's nice to have choices.

Rick,

Just curious: How many of the 6.5s and 7mms have you used in the field?

John

Never shot a 6.5 PRC but have an RPM in their lightest offering, weighs just under 7 lbs scoped. Using the supplied muzzle brake the recoil feels about like a 243. Also have a 7 pound 7mm Mashburn, also with brake. It also is extremely mild to shoot, even with 175gr loads that are running nearly 3100 fps. To me it’s about the same as my 270. Given that, I’d not be afraid of the 7 PRC and would pick it over the 6.5 offerings.

bowman

Having choices isn’t necessarily a good thing. It can be but not always.

I started hunting and shooting at age 13 in Southeast Idaho, an area which was producing monster mule deer. Big 4 points and non-typicals were common. My first deer scored around 180 B&C. My second at age 14 was bigger. Most if not all of the hunters had exactly one “high-powered” rifle many of which were “sporterized” military rifles. In those days that area allowed two over the counter tags per hunter. There were also “extra tags” available. The season was about 60 days.

Nobody even considered having more than one hunting rifle. A 270W was quite rare.

My dad’s buddy with whom we hunted had a pickup with a positraction rear differential which was pretty exotic.

Rick,

I understand what you're saying about choices. They don't necessarily make you happier.

I started hunting in NE Oregon near the Idaho border at age 12 in circumstances similar in many ways to what you describe, except that the mule deer bucks were not as large as those in SE Idaho. And I started with a "sporterized" military rifle.

I was hunting with my extended family and those were some of the most memorable hunting experiences of my life.

I doubt that having more rifles to choose from would have mattered.

Still, I think it's fun to have choices in hunting rifles, even if we don't always choose to exercise them.

Shot deer and elk with the 6.5 Swede and the 140 grain Partition for quite a while. Then moved on to the 6.5 CM and the 140 grain NPT and NAB on elk until those bullets disappeared. Then switched to the 143 grain ELD-X for a few seasons until other bonded bullets made a comeback.

Used a buddy's 6.5 PRC with the 143 grain ELD-X factory load at the last minute on an elk out past 460+ yards just for that little extra velocity insurance over the 6.5 CM I was carrying. The PRC is a very nice cartridge, but since the circumstances on that one shot were rather unique for me, I see no reason for me to get one other than I'm simply bored to tears and need something else to play with.