6.5 PRC vs. .280AI - nearly twins?

[wombat13]

I prefer flat shooting rifles. My two hunting rifles are a .25-06 and a .300WM (in part because they both use the same powders for reloading). I have been thinking about looking for a hunting rifle in-between my .25-06 and .300WM that offers lower recoil than my .300WM, is better suited for deer and bigger game than my .25-06, and still uses the same powders (since components are so hard to come by these days).

I've been intrigued by the .280AI for a few years and the 6.5 PRC seems to be cool new kid on the block, so I decided to compare them. I assumed the 6.5 would offer lower recoil and better ballistics (less drop and drift) while the .280AI would offer more energy and a bigger hole. The data agree, but the difference between the two was much smaller than I expected. They are close enough that factors beyond the ballistics would have to drive one's decision.

Here follows my comparison approach and results. I decided begin by selecting similarly constructed bullets with similar sectional densities and BCs to try to make this as close to apples/apples as possible. I settled on the 140 gr. Accubond for the 6.5 (SD = 0.287; BC = 0.589) and the 160 gr Accubond for the .280AI (SD = 0.283; BC = 0.531). I then used the average of the highest three velocities for that weight bullet from Hodgdon's online reloading data (2,970 fps for the 6.5 and 2882 for the .280AI) and ran the ballistics in Hornady's online ballistics calculator. I also plugged the relevant data (including the previously mentioned average velocity and average charge weights for those powders) into the recoil calculator at shooterscalculator.com for an 8lb rifle. Here are the results:

Velocity fps (Muzzle/500 yards): 6.5 PRC (2,970/2,113) // .280ai (2,882/2,073)
Energy ft-lbs (Muzzle/500 yards): 6.5 PRC (2,742/1,389) // .280ai (2,951/1,527)
Drop inches @ 500 yards (200 yard zero): 6.5 PRC -38.4 // .280ai -40.5
10 mph/90 degree Drift inches @ 500 yards: 6.5 PRC 17 // .280ai 16

Recoil ft-lbs: 6.5 PRC 21.06 // .280ai 22.82
Recoil fps: 6.5 PRC 13.01 // .280ai 13.55

So, my expectations were correct, but the differences are so small that they are meaningless in the real world. Here is a summary of the advantages for each metric:

Energy ft-lbs (Muzzle/500 yards): +209/+138 advantage for .280ai
Drop inches @ 500 yards: +2.1 advantage for 6.5 PRC
Drift inches @ 500 yards: +1 for .280ai (although it may be closer as the Hornady calculator rounds).
Recoil: -1.8 ft-lbs and -0.5 fps advantage for 6.5 PRC

I don't think any animal and the majority of shooters in real world situations would be able to tell the difference between these two. I was most surprised that the trajectory and wind drift were so close. I expected the 6.5 to be significantly better, but it's basically a tie. I also expected the 6.5 to offer a greater reduction in recoil. Again, it's basically a tie.

The old .280ai stands up to the cool new kid pretty darn well!

 

[BreechFace]

I’ve had my 280ai for some time now, and when the 6.5 PRC came out I came to the same conclusion you did.

But yes it’s nice to see the efficiency of the 280ai stand up to new bullet tech. I always knew the 280ai was a highly efficient cartridge.

And just for your information a 280ai with the right throating and barrel length and a 160gr Nosler Accubond/Partition chasing the lands can hit around 3,000fps with RL25. The 280ai is an elk killing machine of a cartridge.

 

[MCMXI]

I started a thread about this very thing more than three years ago. I have a couple of rifles chambered for 6.5 PRC, one is a custom Kimber that I did most of the work on, and the other a Sako S20. For hunting I would definitely pick the .280 AI over the 6.5 PRC. For hitting small targets a long way out I'd pick the 6.5 PRC. That's what I use mine for and it's surprisingly easy to hit stuff with the PRC.

https://www.thehighroad.org/index.php?threads/your-thoughts-on-the-6-5-prc-for-hunting.836607

The .280 AI fits nicely in a relatively svelte receiver package such as the Kimber 84L but the PRC needs the 8400 receiver which is larger. Sako uses one receiver for everything so the exterior packaging argument doesn't work there but it's certainly something to think about in a lightweight mountain rifle.

 

[MCMXI]

I also plugged the relevant data (including the previously mentioned average velocity and average charge weights for those powders) into the recoil calculator at shooterscalculator.com for an 8lb rifle.

This is where the comparison falls down a bit. I think you'll see more of a weight difference in the real world. Not only is the barrel going to be heavier for the PRC, but the action will be in some comparisons. The Kimber 84L shooting the .280 AI is still a relative pussy cat and would be my choice for mountain hunting.

You picked a heavy for caliber .284 cal bullet and a medium weight .264 cal bullet which helped the ballistics for the .280 too but I do agree that the .280 AI is a great cartridge and in terms of hunting it would be my choice, particularly since I only hunt with solid copper bullets and the options for the .264 are very limited. The .284 has 139gr, 145gr and 168gr LRX bullets from Barnes but only a 127gr LRX in .264.

 

[LoonWulf]

Comparing the bcs of what i shoot, I needed 20gr+/- of bullet weight to match the 6.5 with a 7mm.

The m18 mauser in 6.5PRC would launch 140/143 grain hornady bullets at 3050 from its 24" barrel with full value handloads.

My Christensen Ridgeline will launch 162amax/eldms at 3050 from its 26" barrel.

Comparatively my 6.5CMs will get 2800, my 6.5-284 would get 2990 (24" barrel), and my .264WM will reach 3200 (26" barrel).

My 7-08 should break 2800 with 162s (been running 120-140s so far), my 7mags would break 3050/3150 depending on the gun, and the large cased STW/Noslers break 3200......


They all offer similar performance, but the 7s recoil a bit more because of that extra 20gr of bullet.....they also HAVE the extra 20gr of bullet.

 

[MCMXI]

Comparing the bcs of what i shoot, I needed 20gr+/- of bullet weight to match the 6.5 with a 7mm.

The m18 mauser in 6.5PRC would launch 140/143 grain hornady bullets at 3050 from its 24" barrel with full value handloads.

My Christensen Ridgeline will launch 162amax/eldms at 3050 from its 26" barrel.

Comparatively my 6.5CMs will get 2800, my 6.5-284 would get 2990 (24" barrel), and my .264WM will reach 3200 (26" barrel).

My 7-08 should break 2800 with 162s (been running 120-140s so far), my 7mags would break 3050/3150 depending on the gun, and the large cased STW/Noslers break 3200......


They all offer similar performance, but the 7ss recoil a bit more to do so because of that extra 20gr of bullet.....they also HAVE the extra 20gr of bullet.

Good information there. Another thing to think about when comparing the 6.5 PRC to the .280 AI for hunting applications is magazine capacity which is usually less for the PRC. Not a big deal to many but it's one more consideration, along with rifle weight, size, etc. I've never owned a .280 AI but if the right one comes along I would probably jump in with both feet.

 

[WisBorn]

I was going to recommend the 7mm rem mag. 2900 fps at the muzzle & 2086 at 500
Federal factory load 160 Accubond.

That is why the 280 AI is cool. Ballistic twins with the 7rm.

 

[troy fairweather]

Have/had both really like both, I would wait on a 6.5 prc brass and ammo are very hard to get right now unless you have the money.

 

[wombat13]

This is where the comparison falls down a bit. I think you'll see more of a weight difference in the real world. Not only is the barrel going to be heavier for the PRC, but the action will be in some comparisons. The Kimber 84L shooting the .280 AI is still a relative pussy cat and would be my choice for mountain hunting.

You picked a heavy for caliber .284 cal bullet and a medium weight .264 cal bullet which helped the ballistics for the .280 too but I do agree that the .280 AI is a great cartridge and in terms of hunting it would be my choice, particularly since I only hunt with solid copper bullets and the options for the .264 are very limited. The .284 has 139gr, 145gr and 168gr LRX bullets from Barnes but only a 127gr LRX in .264.

Since this is a hunting comparison, I started by trying to find bullets that have similar construction and similar sectional densities so that penetration and terminal performance should be similar. Isn't that the usual approach? Figure out what bullet is required and then determine what chambering is required to deliver it the necessary distance?

 

[wombat13]

Comparing the bcs of what i shoot, I needed 20gr+/- of bullet weight to match the 6.5 with a 7mm.

That matches the data published by Nosler. The SDs and BCs for the 140 6.5mm and 160 7mm are very similar, which is why I chose those to compare.

 

[twarr1]

So, my expectations were correct, but the differences are so small that they are meaningless in the real world.

For every caliber there has to be a metric equivalent and vice-versa.
We like to think, and manufacturers like us to think, every new cartridge is different. Marketing.

 

[BreechFace]

I was going to recommend the 7mm rem mag. 2900 fps at the muzzle & 2086 at 500
Federal factory load 160 Accubond.

That is why the 280 AI is cool. Ballistic twins with the 7rm.

Until one wants to launch heavies then the 7RM takes over because the longer heavy bullet profiles eat into too much of the 280ai case capacity.

But if one is happy with the performance of 160-165gr bullets I see no reason for the 7RM.

 

[troy fairweather]

There's a few guys with long action prc guns a few I've talked to have 24" barrels, some guys are hitting 3000 the the 156 Berger. There using the long throat reamers tho.

 

[WisBorn]

Until one wants to launch heavies then the 7RM takes over because the longer heavy bullet profiles eat into too much of the 280ai case capacity.

But if one is happy with the performance of 160-165gr bullets I see no reason for the 7RM.

Sure there is a reason for the 7rm - I like it

 

[MCMXI]

Since this is a hunting comparison, I started by trying to find bullets that have similar construction and similar sectional densities so that penetration and terminal performance should be similar. Isn't that the usual approach? Figure out what bullet is required and then determine what chambering is required to deliver it the necessary distance?

It's a good on paper exercise, but sectional density doesn't say anything about penetration because it doesn't account for one of the major aspects of terminal ballistics which is expansion which greatly affects penetration and the size of the wound channel. It's a good comparison though and most will come to the same conclusion i.e. the .280 AI and 6.5 PRC are ballistically similar on paper, but in the real world the differences might be more significant and in favor of the .280 AI.

When I'm trying to pick a rifle/cartridge combination for hunting, I look at the bullets I'd want to shoot for the cartridges under consideration rather than comparing bullets that I wouldn't use. So again, on paper it might appear that the .280 AI and 6.5 PRC are very close, but in reality the differences can be significantly greater. For you the comparison of Accubond bullets might be valid, but for me it wouldn't help me that much unless the comparison were made for LRX or TTSX bullets. I'd also want to figure out which rifles I'd be comparing, which optics, rings etc., so that a recoil comparison would be more meaningful.

 

[jmr40]

I have felt for a long time the 280 is probably the best all around cartridge for general big game hunting. The AI version may be better. I've had a couple of 280's over the years but I've been married to the 30's most of my life. I tried 280 and concede that it is better than 30-06, 7-08 is better than 308. Just not enough better for me to sell my old faithful rifles nor enough better to justify having both. I let my 280's go, but if starting over, or advising a younger shooter just starting would push them toward the 7mm's.

I have tried the 6.5CM and like it well enough. I feel 26 caliber is enough different than 30 to justify both. But for me the fast 6.5's have just never appealed to me. Between these 2 I like the 280 better. And part of it is an extra round or 2 in the magazine.

 

[BreechFace]

Sure there is a reason for the 7rm - I like it

Me too.

 

[MCMXI]

I have tried the 6.5CM and like it well enough. I feel 26 caliber is enough different than 30 to justify both. But for me the fast 6.5's have just never appealed to me. Between these 2 I like the 280 better. And part of it is an extra round or 2 in the magazine.

I have a 6.5 Creedmoor, 6.5x47mm Lapua, and two 6.5 PRCs and I'm not really a fan of the .264 caliber ... go figure. I have all the parts to build a couple of 7mm-08 AI rifles which should really be something. I just need to do it. I had a Savage Weather Warrior in 7mm-08 Rem but it was such a pile of junk that I sold it. It soured me a little to the whole 7mm-08 Rem experience but I'm sure it'll be a distant memory soon.

I guess I can think of the 7mm-08 AI as the smaller sibling to the .280 AI. I'll be hunting with a .308 Win this year though ... still my all time favorite cartridge.

 

[troy fairweather]

Here are some 6.5 prc test loads I did today, these are with the new nosler brass and some more eldm 147s using h4831sc. They are about 25tho off the lands and max mag length is about 3.00" so it works out. Some guns I've seen have the longer throat and don't have the mag to make use of it, so kills some velocity. The factory ammo seem pretty mild from what I've seen, some rifles are in the middle 2800s.

 

[LoonWulf]

Sure there is a reason for the 7rm - I like it

Ive had larger, Ive had smaller, but Ive never had a 7mm Ive liked better.......Ive also owned more 7mm Remington Magnums than any other chambering besides 6.5CM......and that I think is a tie.

Honestly, if you have the magazine length getting the 280AI to 7mag spec with bullets upto 160gr/class takes about 2" of the barrel and running the highest velocity powders you can.
My guns using 62gr of RL-23 to equal my "average" 7 mags using 73gr of Retumbo behind the same bullets. (this actually beats the RAM in 7mag I had by about 60fps)
Ive got some 190A-tips loaded at 3.5ish coal that I still need to shoot...doubt my 1-9 will handle them but it should be interesting anyway.

with 180+ and a long throat, the added capacity of the Magnums comes into their own.
My X-bolt in 28 Nosler was cranking 190s down range at 3100. Im launching 185s at 3150 from my Christensen.
I think a long throat the 7mag would probably be in the 2900-3000 range.

 

[wombat13]

It's a good on paper exercise, but sectional density doesn't say anything about penetration because it doesn't account for one of the major aspects of terminal ballistics which is expansion which greatly affects penetration and the size of the wound channel. It's a good comparison though and most will come to the same conclusion i.e. the .280 AI and 6.5 PRC are ballistically similar on paper, but in the real world the differences might be more significant and in favor of the .280 AI.

I really don't understand the first sentence in this comment. I compared the two Accubond bullets with similar construction and with similar sectional density specifically because they should create as close to a similar wound channel as can be expected. Are you saying that it is not a meaningful comparison because one Accubond bullet will expand better than the other Accubond bullet? If the problem is the difference between initial bullet diameters, then how could one ever compare chamberings in two different calibers? A .375 will always be bigger than a .338. If initial bullet diameter invalidates any ballistic comparison then all we need to know is .375>.338>.308>.284>.264>.257>.243.

Ultimately, I think we agree, but you keep posting these comments to say that the comparison is not that meaningful, yet how would one do it differently? Skip the paper comparison, buy two rifles, and shoot a bunch of game, then figure out which to keep?

I think the takeaway from this comparison is that these two chamberings are so close that factors other than the ballistics would have to drive the decision (which is what I wrote in my initial post). They both can reach out a long ways with bullets capable of taking most NA game. So, one could make the decision based on any number of factors, such as which powders they use, which rifles are available, which bullets and weights are available, etc.

In any case, for your purposes, I guess the .280AI has a big advantage. Barnes makes TTSX in two weights for 6.5 and four weights for 7mm and makes LRX in one weight for 6.5 but 3 weights for 7mm.

 

[WisBorn]

@wombat13 I want to apologize for my 7mm rem mag comment. I didn't want to hijack your thread.
I remember reading and wanting a 280 rem
for years. The 280 always seamed like the best compromise of the 270, 280, 30-06.

With the factory offering of the 280AI it just kicked up the cool factor.

 

[jmr40]

sectional density doesn't say anything about penetration because it doesn't account for one of the major aspects of terminal ballistics which is expansion which greatly affects penetration

We're just gonna have to agree to disagree. ASSUMING the same bullet construction, bullets of similar SD give similar penetration if they impact at similar speeds. Impact speed plays a part too. If the bullets impact faster than they were designed then you also get over expansion and limited penetration. It's not unusual to see the same bullet fired from a 308 penetrate deeper than when fired from a 300 WM. Particularly at close range.

Now if you compare something like a Barnes solid copper bullet with a similar SD as a bullet known for rapid expansion such as the Hornady SST then forget SD, it is meaningless because the bullets are so dissimilar. But if you're comparing the same or similar bullets in different calibers then SD is a pretty accurate indicator of penetration.

And this isn't just theory. I've seen real world tests showing 143 gr Hornady ELD-X 6.5 mm bullets fired into gel giving exactly the same penetration as Hornady's 178 gr ELD-X 308 bullets.

 

[wombat13]

@wombat13 I want to apologize for my 7mm rem mag comment. I didn't want to hijack your thread.
I remember reading and wanting a 280 rem
for years. The 280 always seamed like the best compromise of the 270, 280, 30-06.

With the factory offering of the 280AI it just kicked up the cool factor.

That wasn't a hijack at all. .280AI is close enough 7mm Rem mag that I'd be surprised if it didn't get discussed.

 

[MCMXI]

Ultimately, I think we agree, but you keep posting these comments to say that the comparison is not that meaningful.

That's not my intention if that's how it's coming across. Your comparison is a good starting place but a real world comparison will typically be a lot more nuanced. That's all.