6.5 PRC vs. .280AI - nearly twins?

[MCMXI]

ASSUMING the same bullet construction, bullets of similar SD give similar penetration if they impact at similar speeds.

Yes, we can agree to disagree, but that's quite a few assumptions there. Even bullets from the same family can vary significantly in their construction. Jacket thickness, jacket taper, jacket material, lead chemistry, tooling pressure during manufacturing seating the core, work hardening of the jacket and so on.

The example you mention isn't compelling and would need to be expanded since gel is a poor indicator of real world performance. Unfortunately ballistic gelatin is all we have to make us warm and fuzzy about perceived bullet performance, but in the world of bullet and ammunition development it's pretty much despised. It's one of those things that sales and marketing get all excited about because it's something that consumers get all excited about. It's main use at Remington was to tell us if the cup and core would separate upon penetration, to give some idea as to expansion, and to give some indication of mass loss but not much more than that. When you've shot thousands of bullets into gel you start to lose respect for the validity of the test medium. The FBI test is far more extensive and still gives erroneous results.

Most cup and core bullets will lose mass after impact which changes SD. Bullets in the real world exist in an infinite number of states as they start and finally complete expansion. This is complex and if you were to test numerous bullets with similar construction and SDs the results would be all over the map.

The ELD-X bullets you mention, what's the maximum expanded diameter of each (not the final expanded diameter) and what's the duration of that maximum diameter +/- 5%?

 

[wombat13]

Just ran the numbers with Barnes LRX bullets and used Barnes load data. Results at 500 yards are below. The bottom line is that these two are almost ballistically identical with similar bullets. The 280ai gives you a wider wound channel and about 14% more energy (+181 ft-lbs) at the expense of 18% more recoil (+3.3 ft-lbs). As of now, it looks like appropriate hunting bullets are more readily available for 7mm, but that may change.

Bullets: Barnes 6.5mm 127 gr LRX (only one they offer) vs. 7mm 145 gr LRX

Below data are always listed with 6.5mm first and 7mm second.

Sectional density: 0.260 vs 0.257
BC: 0.468 vs. 0.486
Muzzle Velocity: 3,129 vs 3,083
Muzzle energy: 2,761 vs 3,060

500 yards:
Velocity: 2,174 vs. 2,169
Energy: 1,333 vs 1,514
Drop (in): -35.1 vs. -35.9
Drift (in): 17 vs. 17

Barnes makes the LRX in two other weights for 7mm, 139 gr and 168 gr. Stepping down from 145 to 139, the 280ai cuts the drop down to -33.8 in but the wind drift increases to 20 in. Step up to the 168 gr and the drop increases to -41.8 in but the wind drift decreases to 16 in. Recoil is about the same for all of the .280ai loads.

 

[MCMXI]

Step up to the 168 gr and the drop increases to -41.8 in but the wind drift decreases to 16 in. Recoil is about the same for all of the .280ai loads.

This is what I would shoot from a .280 AI ... the heavy for caliber 168gr LRX since bullet drop is basically irrelevant with range finders. From a .264 it would be the 127gr LRX so this is the only comparison I would make. Next up would be looking at the actual rifle, optic, suppressor model and/or end cap, muzzle brake if QD with a brake, taking into consideration barrel length, total weight, magazine capacity and so on. There aren't that many .280 AI and 6.5 PRC factory rifle options out there. What two rifles would you compare?

Suppressors, end caps and brakes can add another level of complexity when choosing between the two. I'll have to check if anyone makes .284 suppressors or end caps. Of course you can run a .30 cal suppressor worst case.

 

[LoonWulf]

I think savage and ruger offer both, but I'm not sure if they are available in the same model rifle......
Christensen offers both in the same rifles, not positive if the PRC is long or short tho.

If I were to build a custom rifle for either, I'm pretty sure the specs would be identical.....or well close.....
There are some "medium" length custom options out there and I'd probably use that version if available.

 

[MCMXI]

I think savage and ruger offer both, but I'm not sure if they are available in the same model rifle......
Christensen offers both in the same rifles, not positive if the PRC is long or short tho.

If I were to build a custom rifle for either, I'm pretty sure the specs would be identical.....or well close.....
There are some "medium" length custom options out there and I'd probably use that version if available.

Yes, action length is another consideration. The Sako S20 I bought is on the heavy side so I'd look at something lighter if I were planning on using it for hunting. Neither Sako nor Tikka offer .280 AI rifles ... too bad really because I'd be interested in a Tikka.

 

[WisBorn]

I find it interesting that the 6.5 prc and 280 ai are very close in ballistics.

I find it really interesting that wildcatters and manufacturers are building more and more efficient cartridges.
A good example is the 300 wsm compaired to the 300 wm. Same ballistics with the standard weight hunting bullets like 180 Accubonds, the heaviest high BC bullets need the extra powder capacity to shine.

Not much different than what auto manufacturers are doing with turbocharged 4 cylinder motors. Just bought a Equinox with a 1.5T can't believe the acceleration. Wouldn't want to pull a bass boat with it but you need to respect the technology.

 

[LoonWulf]

Yes, action length is another consideration. The Sako S20 I bought is on the heavy side so I'd look at something lighter if I were planning on using it for hunting. Neither Sako nor Tikka offer .280 AI rifles ... too bad really because I'd be interested in a Tikka.

When my ffl buddy could get the T3xs for 500ish I considered using one as the basis for a Pseudo custom build with a Pre-fit barrel in .280AI. I also considered doing an American, but then the Christensen fell in my lap.....
After having the M18 Id rather have one build on THAT or the Sauer, but those barrels arnt easy swaps from what I understand...........EEEEEENNNYYYYY way......6 or 1/2 dozen.....

I find it interesting that the 6.5 prc and 280 ai are very close in ballistics.

I find it really interesting that wildcatters and manufacturers are building more and more efficient cartridges.
A good example is the 300 wsm compaired to the 300 wm. Same ballistics with the standard weight hunting bullets like 180 Accubonds, the heaviest high BC bullets need the extra powder capacity to shine.

Not much different than what auto manufacturers are doing with turbocharged 4 cylinder motors. Just bought a Equinox with a 1.5T can't believe the acceleration. Wouldn't want to pull a bass boat with it but you need to respect the technology.

Ill argue that the efficiency of case design isn't as noticeable as the performance increase in newer ICEs. There's certainly something to it tho, but it has to be taken as a whole to really have meaning to the shooter.
(We've also got alot better powders than they did in the heyday of big cases and the magnum craze.....this advantage goes across the board, so looking at OLDER reference data isnt as consistent)

A lot of the value really comes down to specifics I think.......

Heres a QL comparison with all the rifle spec, and bullet set to the same. The only difference being the cartridges chosen

300WM
ReloadSwiss RS 76 *C 108.2 85.6 5.55 3179 100.0 62000 13981 1.135 ! Near Maximum !
Alliant Reloder-26 *C 99.7 78.8 5.11 3125 100.0 62000 12985 1.158 ! Near Maximum !
ReloadSwiss RS 80 *C 110.0 87.8 5.69 3112 97.7 59829 14231 1.165 ! Near Maximum !
Alliant Reloder-25 *C 108.6 79.5 5.15 3107 100.0 62000 12640 1.143 ! Near Maximum


300WSM
Alliant Reloder-26 *C 104.8 72.8 4.72 3097 100.0 62000 11796 1.148 ! Near Maximum !
Norma MRP *C 105.5 71.1 4.61 3066 99.7 62000 11908 1.149 ! Near Maximum !
Vihtavuori N560 *C 107.2 70.8 4.58 3052 97.5 62000 12111 1.147 ! Near Maximum !
PB Clermont PCL 517 109.7 75.7 4.90 3042 98.2 62000 11884 1.139 ! Near Maximum

In this example on the extremes your using about 13gr more powder to get 82fps more velocity.....will 13gr more ejectus really matter in terms of recoil? will a 1" longer bolt throw (if considering a 2.8" action to a 3.7" action) matter, will the extra round most belted mag rifles hold matter?......really depends on what the user wants.

That brings me back to my love for the 7RM, theres faster and slower, theres shorter, thinner, longer, fatter etc......In a specific setting, I might choose any of them over the 7RM, but its mostly fitting the cartridge to the specifics of the rifle and usage.

 

[wombat13]

Above, MCMXI said to pick the one with the least wind drift, so I looked at them again focusing only on wind drift. There just isn't that much difference in wind drift between these two to make much of a difference. I admit, my longest shot at a target or an animal so far is 200 yards, so I'm not even a newbie at long-range shooting. Someone with more experience can chime in here. I'm not trying to prove I'm right; just trying to look at this in different ways and every way I look at it, there seems to be virtually no difference between these two ballistically.

Here are two ways that I compared these chamberings and bullets. The first is wind drift at 10, 20, and 30 mph. The second is how much error in wind estimation would cause you to miss the vitals on an elk (which I'm assuming is 16" wide, so you can miss by up to 8").

So here is the wind drift at 500 yards for 6.5 prc with 127 gr lrx, and .280ai with 139 gr, 145 gr, and 168 gr lrx bullets (in that order):

10mph: 17.0", 16.5", 16.6", 16.3"
20mph: 34", 33.1", 33.2", 32.6"
30mph: 51", 49.6", 49.8", 48.9"

So at 500 yards, even with a 30mph wind, there is only a max difference of 2.1" of wind drift with lrx bullets!

The other way of looking at this is, what if you think there is a 10mph wind but you're wrong. How wrong can you be and have the wind drift be within 8" of your estimate at 500 yards, allowing your shot to remain in the kill zone of an elk?

6.5 prc with 127 lrx: 4.7 mph (i.e., if you estimate 10mph wind you will still hit in the vitals at 500 yards if the wind is up to 14.7 mph)
.280ai with 139 lrx: 4.8 mph
.280ai with 145 lrx: 4.8 mph
.280ai with 168 lrx: 4.9 mph

In other words, if you misjudge the wind by 4.5 mph you'd still hit with any of them but if you misjudge by 5 mph you'll miss with all of them. There just really is no difference, assuming Hornady's online ballistic calculator is correct.

The tradeoff really is recoil and energy/bullet diameter. Moving up from the 6.5 prc/127 lrx to the .280ai with the 145 lrx costs you 18% more recoil (+3.3 ft-lbs) but yields 14% more energy (+181 ft-lbs) and 16% more cross-sectional area (prior to expansion). If both bullets expand with the same percent increase (say to 75% greater than their initial diameter) then the .280ai still gives a 16% wider wound channel.

Seems like the 6.5 PRC is the winner for targets and the .280ai has a slight edge for hunting (if you need the bigger hole and more energy). By the way, the average of the highest 3 velocities published by Barnes for the 7mm RM and the 168 lrx is only 12 fps faster than the same average for .280ai, so it costs 10 grains more powder to get 12 fps!

 

[WVRJ]

When I wanted to build a rifle for deer hunting and long range steel ringing,these two cartridges were the ones that made it to my short list.Both are great long range rounds,and I'd have to go along with what a few guys have already said-the 6.5 PRC is the better choice for target shooting and the 280AI is better for hunting.I went with the 280AI for a few reasons.For me,the 280 is at my limit for recoil unless I put a brake on the gun.One big reason for my choice is the fact that if I'm in a bind,280 Remington ammo can be fired in the 280AI.The 7MM caliber has a little better bullet selection than the 6.5,but not as much as a few years ago.I use a detachable magazine and I can put 6 in the mag and one in the chamber,which is an impressive number of rounds to have on board.The PRC would be 1 or 2 less.I'm hunting with 168 grain Berger Classic Hunters,and they're chronographing in the mid 2900's and for 1,000 yard target shooting,160 grain Sierra Tipped Matchkings are running a little over 3,000.Both bullets do very well in the wind.The final deal breaker for me was the fact that the action I used had a 280 Rem. barrel,so I had brass and bullets galore.If I had it to do over,I'd still opt for the 280AI.

 

[WisBorn]

@wombat13 I went back and read your opening post.
I also have had some experience with 25-06 and 300 wm. As mentioned earlier I have a 7mm RM and really like the rifle. I slowly learned to love the cartridge. I traded off my 300wm A Bolt with a BOSS towards my Weatherby Mark V 7rm. I wanted a shorter overall rifle, without the soup can noise maker on the end of the barrel!

I always wanted a Weatherby and love the rifle. I would have preferred a 30-06 or better a 280 rem. But had to pick a magnum and decide to try the 7rm.

I think you will like the 280AI and its capabilities. A little less hammer effect than the 300 but much less recoil. And a good step above the 25-06. The 280 will become your all around rifle. The 300 your elk choice and your 25-06 your go to antelope rifle (I think the 25-06 is a sweet cartridge for that kind of hunting)....

 

[wombat13]

@wombat13 I went back and read your opening post.
I also have had some experience with 25-06 and 300 wm. As mentioned earlier I have a 7mm RM and really like the rifle. I slowly learned to love the cartridge. I traded off my 300wm A Bolt with a BOSS towards my Weatherby Mark V 7rm. I wanted a shorter overall rifle, without the soup can noise maker on the end of the barrel!

I always wanted a Weatherby and love the rifle. I would have preferred a 30-06 or better a 280 rem. But had to pick a magnum and decide to try the 7rm.

I think you will like the 280AI and its capabilities. A little less hammer effect than the 300 but much less recoil. And a good step above the 25-06. The 280 will become your all around rifle. The 300 your elk choice and your 25-06 your go to antelope rifle (I think the 25-06 is a sweet cartridge for that kind of hunting)....

I think I'm settling on the .280AI. I just looked at the ballistics for my .300WM. The .300WM 175 lrx very slightly outperforms the .280AI 145 lrx (35.4" vs 35.9" of drop and 15.8" vs. 16.6" of wind drift) but at the cost of 60% more recoil (34.6 ft-lbs vs 21.6 fl-lbs). So ballistically they are nearly identical but the .300WM gives 24% more energy, 18% larger cross-sectional area, hits you with 60% more recoil.

 

[BreechFace]

@wombat13 your research is the same that I did long ago on the 280ai. It is why I’m of the mind that it is nearly the perfect hunting cartridge.

And it’s a lot of fun to shoot at distance as well. With its downside for targets being the excessive recoil as it compares to shooting slippery 6mm’s.

It’s efficiency is hard to surpass.