260 to 6.5-284 - is it worth it???

[Trickymissfit]

taking a line or two from Parker Ackley himself. The .308 case family is somewhat of an improved case from the outset, so velocity gains will be minimal at best. Perhaps 2800fps with a 140 grain bullet in a very stiff load in the Ackley version, and still be safe. On the otherhand the 6.5/284 will do an honest and honest 2850fps and maybe slightly more while still being safe. The .257AI necked upto 6.5 is known to hit the 2900fps mark and still be safe (some are getting 2950fps which must have some serious pressure). Even the 6.5x55 can approach these velocities without going into over pressure in a modern action. Looks to me like a 6.5x55AI might just be the near perfect round for the 6.5 and yet not toast a barrel a couple times a year. It should do the 2900fps mark easily. But the 6.5/.257AI is easier. And with that case the barrel is going to last a lot longer that the .260AI or the 6.5-284
gary

 

[stomp442]

Having built a number of 260 Ackleys for myself as well as a few friends I will say that 2950 fps from a 26" tube is quite easily done with 140 grain bullets. I currently have a safe full of 6.5s of one type or another and the 260 Ackley is by far my favorite. I also have a 6.5-284 with a 26" tube that I have tested just about every bullet and powder combination I can find and have yet to see where it will provide any increase in performance over the Ackley when barrel lengths are the same. It will however require quite a bit more powder to push the same 140gr bullet at the same velocity. I have had both cartridges up and over 3000fps and both cartridges show signs of pressure and decreased accuracy at that point. When backed off to the sweet spot right around the 2900-2950 mark the only difference is that the Ackley is using 42-44gr of powder while the 6.5-284 is using 56-58gr of powder. I love 6.5s and have used them to take game at some pretty extreme ranges and couldn't be happier with their performance.

 

[elkaholic]

taking a line or two from Parker Ackley himself. The .308 case family is somewhat of an improved case from the outset, so velocity gains will be minimal at best. Perhaps 2800fps with a 140 grain bullet in a very stiff load in the Ackley version, and still be safe. On the otherhand the 6.5/284 will do an honest and honest 2850fps and maybe slightly more while still being safe. The .257AI necked upto 6.5 is known to hit the 2900fps mark and still be safe (some are getting 2950fps which must have some serious pressure). Even the 6.5x55 can approach these velocities without going into over pressure in a modern action. Looks to me like a 6.5x55AI might just be the near perfect round for the 6.5 and yet not toast a barrel a couple times a year. It should do the 2900fps mark easily. But the 6.5/.257AI is easier. And with that case the barrel is going to last a lot longer that the .260AI or the 6.5-284
gary

I know a couple of guys that shoot A.I. Swedes, and they are indeed a pretty sweet cartridge.....Rich

 

[Trickymissfit]

I know a couple of guys that shoot A.I. Swedes, and they are indeed a pretty sweet cartridge.....Rich

when you look at the 6.5x55 improved, and just seems to be a good fit for a .264 bore. Kinda tells you just how much powder the bore can handle efficiently. A lot of guys claim to be getting a little over 3000fps with the 6.5-284, but nobody really knows the actual chamber pressure when quoting those velocities. I've even heard talk of 3100fps with a 140 grain bullet from time to time. Gotta be getting close to 65K psi or more. I do know that the 2900fps out of the 57mm improved case is for real and the chamber pressure is OK. Another one that has always caught me eye is the 6.5x250 improved case, but that should be pretty close to the 6.5x47.
gary

 

[benchracer]

Lapua brass fired in my 6.5x55 (modern, commercial action) averages a case capacity of 58.5 grains of water. Prvi 7x57 brass fired in my Ruger #1 averages about 61.8 grains. That, at least, gives one a starting point to figure out what either case capacity would look like after being given the Ackley treatment.

My best accuracy load for 6.5x55 uses 48.2 grains of H4831 with a 140 Berger VLD. I have never shot it across a chrono (I need to, though, and I will now that I own one.), but QL says it should be doing 2900ish from my rifle.

My best accuracy load for my 6.5-284 Norma came in at 52.5 grains of H4831 with a 140 AMAX, while showing faint ejector marks. Likewise, I never chronoed that load, but I shot it side by side with my Swede out to 600 yards. There was very little difference between the two. QL estimates 2930ish for that load, which explains a lot about why I saw very little difference.

I, personally, found the 6.5-284 to be a very underwhelming cartridge. To be fair, I never tried Retumbo in it, which might have changed things a bit.

Not long after I shot the two rifles side by side, Winchester re-introduced the Model 70 in .264 WM. I had to have one and finally succeeded in getting my hands on a Model 70 Sporter so chambered. Even shooting 140 Partitions, it easily produced 3000 fps with a lot of throttle left. On the flip side, the rifle responded well to being downloaded to Swede Military action equivalent loads. I have yet to work up loads with 140 Berger VLD's, but all indications are that Retumbo or RL-33 will deliver a good bit more speed at near full throttle loads.

I found the .264 WM to be what I was looking for when I decided to step up from the 6.5x55. Of course, heat and barrel life mean that the WM is best as a hunting round. I wouldn't use it as a target or match round. Since my 6.5-284 wears an 8 twist Krieger barrel, I decided to have it punched out to .264 WM to handle the 160 Matrix VLD class bullets (my 9 twist Winchester won't do that).

If I want to go fast and flat, I will reach for my .264's. If I want to do anything that involves a high round count (like match or varmint shooting), I will reach for my Swede.

Housed in a modern action, and loaded accordingly, I was surprised to learn that my Swede occupied the same performance level as my 6.5-284. With Lapua brass being much less expensive and more available for the Swede, ditching the 6.5-284 seemed like a pretty obvious choice. If someone wants more than the Swede, but doesn't want to go all the way to .264 WM level performance, I think going the 6.5x55AI or 6.5-257AI route makes more sense. I would take either over the 6.5-284, based on my experience with my rifles.

 

[Mikecr]

Gary, you're off in your velocity numbers in 26cal.
I shoot a 26wssm Imp, which holds right at the same H20 capacity as a 260AI. My barrel is 28".
My accuracy load is 47.4gr IMR4350, and well measured MV is ~3025fps with 139Laps/140VLDs.
I have tested this cartridge up to ~3200fps where FL sizing would just be req'd according to my blade mic.
With a decent chamber and enough barrel steel around it, I am certain a 6.5x284 can meet this and at lower pressures given it's capacity.

The real problem is ~3200fps is not very good for accuracy in ~140gr bullets.
So there is no better in bigger, and this reality is just what the 6.5x284 shooters come around to.
260AI capacity puts you right in the best known sweet spot with the most successful 26cal bullets.
~2950-3050 with ~140s
You're welcome to check it. Go to 1kyd BR sites and poll for it.

Oh, and nothing about the 308 case family is improved. They have always been improved -by us.
On velocity gains, who cares?
Accuracy, long term of it, is what matters. This is really what improving cartridges is about.

 

[elkaholic]

Gary, you're off in your velocity numbers in 26cal.
I shoot a 26wssm Imp, which holds right at the same H20 capacity as a 260AI. My barrel is 28".
My accuracy load is 47.4gr IMR4350, and well measured MV is ~3025fps with 139Laps/140VLDs.
I have tested this cartridge up to ~3200fps where FL sizing would just be req'd according to my blade mic.
With a decent chamber and enough barrel steel around it, I am certain a 6.5x284 can meet this and at lower pressures given it's capacity.

The real problem is ~3200fps is not very good for accuracy in ~140gr bullets.
So there is no better in bigger, and this reality is just what the 6.5x284 shooters come around to.
260AI capacity puts you right in the best known sweet spot with the most successful 26cal bullets.
~2950-3050 with ~140s
You're welcome to check it. Go to 1kyd BR sites and poll for it.

Oh, and nothing about the 308 case family is improved. They have always been improved -by us.
On velocity gains, who cares?
Accuracy, long term of it, is what matters. This is really what improving cartridges is about.

Mike.....what barrel length is that on your WSSM?

 

[Jim in Cali]

260 Ackley before a 6.5-284 anyday and everyday should have done it yesterday!

 

[Greyfox]

I like my 260's but I find that all the available brass(ncluding Lapua) is weak when stretching the velocity, with primer pockets loosening up after a few reloads. I find that the 6,5x284 brass and case design is superior being good for over a dozen reloads even with stiff loads. iMHO.

 

[Mikecr]

Greyfox, you're not alone in your experience there. Many find the same.
The base 260's undercapacity leaves everyone pushing it, while the cartridge is in no way designed to be pushed.
There are at least several common variants to the 6.5x284 chamber with different levels of improvement. And downloaded to accuracy, it's case lasts longer than a base 260 pushed very heavily.
That's a plus for the 6.5x284 that is unfortunately negated by ~1200rnd barrel life. Plus it's difficult to make a downloaded cartridge shoot as well as another pushed to more forgiving/higher pressure curve.

So the 260 is not enough, and the 6.5x284 is too much. Neither better really, because accuracy from them isn't viable in the long term.
For ~1kyd long term accuracy, the answer is not bigger or smaller, but right in between(an improved 260).
Had Lapua 260 brass been available earlier, I would have went 260I instead of 26wssm, because it would have been way easier & less expensive.

elkaholic, my barrel's are 28" Border.

 

[Trickymissfit]

Gary, you're off in your velocity numbers in 26cal.
I shoot a 26wssm Imp, which holds right at the same H20 capacity as a 260AI. My barrel is 28".
My accuracy load is 47.4gr IMR4350, and well measured MV is ~3025fps with 139Laps/140VLDs.
I have tested this cartridge up to ~3200fps where FL sizing would just be req'd according to my blade mic.
With a decent chamber and enough barrel steel around it, I am certain a 6.5x284 can meet this and at lower pressures given it's capacity.

The real problem is ~3200fps is not very good for accuracy in ~140gr bullets.
So there is no better in bigger, and this reality is just what the 6.5x284 shooters come around to.
260AI capacity puts you right in the best known sweet spot with the most successful 26cal bullets.
~2950-3050 with ~140s
You're welcome to check it. Go to 1kyd BR sites and poll for it.

Oh, and nothing about the 308 case family is improved. They have always been improved -by us.
On velocity gains, who cares?
Accuracy, long term of it, is what matters. This is really what improving cartridges is about.

Mike, I pretty much used book numbers that I knew were fairly accurate (forget Hornaday and Sierra). Then I cross referenced for actual chamber pressures where quoted. I know a couple guys that are saying they are seeing a tick under 3100fps from the 6.5-06 with a 140 grain bullet. I don't doubt it, but also have no idea what kind of chamber pressure they are shooting at. With the .260, I think 2800fps is realistic and still safe. Yet most books call out sub 2700fps specs. Accurate does post the chamber pressure specs. Accurate says that a chamber pressure of 60K psi (considered max by SAMMI) will get you about 2740fps with 43 grains of AA4350. Now on the otherhand the 6.5x57 (necked up Roberts case) will do an honest 2730 fps (H4831 with no chamber pressure spec). Guys over on Accurate Shooter are seeing 2950fps with a .257AI case necked up to 6.5. I'd think these specs are real. There are actually two different reamers they are using from Dave Kiff, but are still very close dimensionally. I can't testify about barrel life for sure on the .260, although I'm getting ready to order in one, and possibly two. One will be rechambered to 6.5x57 improved with a 30 degree neck. Twist rate and throat are still up in there air right now. It's also quite possible that I may negate the .260 for a 6.5x47 instead.

Now back to the big fat cases. I know guys are getting well over 3200fps with the .270WSM cased necked down to 6.5, and have heard some crazy numbers from a necked up 25WSM to 6.5 case.
gary

 

[elkaholic]

Mike, I pretty much used book numbers that I knew were fairly accurate (forget Hornaday and Sierra). Then I cross referenced for actual chamber pressures where quoted. I know a couple guys that are saying they are seeing a tick under 3100fps from the 6.5-06 with a 140 grain bullet. I don't doubt it, but also have no idea what kind of chamber pressure they are shooting at. With the .260, I think 2800fps is realistic and still safe. Yet most books call out sub 2700fps specs. Accurate does post the chamber pressure specs. Accurate says that a chamber pressure of 60K psi (considered max by SAMMI) will get you about 2740fps with 43 grains of AA4350. Now on the otherhand the 6.5x57 (necked up Roberts case) will do an honest 2730 fps (H4831 with no chamber pressure spec). Guys over on Accurate Shooter are seeing 2950fps with a .257AI case necked up to 6.5. I'd think these specs are real. There are actually two different reamers they are using from Dave Kiff, but are still very close dimensionally. I can't testify about barrel life for sure on the .260, although I'm getting ready to order in one, and possibly two. One will be rechambered to 6.5x57 improved with a 30 degree neck. Twist rate and throat are still up in there air right now. It's also quite possible that I may negate the .260 for a 6.5x47 instead.

Now back to the big fat cases. I know guys are getting well over 3200fps with the .270WSM cased necked down to 6.5, and have heard some crazy numbers from a necked up 25WSM to 6.5 case.
gary

I was skeptical of velocities that were claimed with the short fast cases when they first came out, but since developing the 6.5 SS, and seeing what some others have done, I now believe. While I admit that I don't have exact pressure data, I know that I can reach 0ver 3100' with 160 grain bullets, and can load a couple more grains before I feel I am getting over according to case stretching dimensions. Some of the loads we have fired also check out on quickload. I don't have a good explanation about why they are more efficient, but they are! I also think that with the Norma case, minimal body taper, and 40 degree shoulder, pressures don't show as quickly.......Rich

 

[Mikecr]

I love Norma brass but it is softer than both Lapua and Winchester and the pockets don't last as long..
Cartridge Brass Alloys Revealed by X-Ray Spectrometers « Daily Bulletin

There is pressure and there is pressure 'problems'. Completely different, because pressure is your friend -until it isn't.

Improved cases with their low body taper and high shoulder angles remove many pressure problems.
There is also the ratio of body diameter to cal, to burn more powder INSIDE the chamber rather than adding to bullet mass further down a bore.
Then you set the right capacity for selected bullets and powder to reach a goal at a stable and rational pressure curve. A long enough barrel to burn more powder inside it, producing lower muzzle pressures.
Tight coaxial throat, and tight chamber end clearance to reduce SD. Lands you can reach and without seating bearing near donuts.
Sufficient barrel steel around the chamber area, and tight clearances to reduce brass yielding from the git-go. Bushed firing pin, tight breech clearance, beefy aftermarket action.

These are mostly overlooked by the many amateurs building guns today. They think velocity and little else.

 

[elkaholic]

I love Norma brass but it is softer than both Lapua and Winchester and the pockets don't last as long..
Cartridge Brass Alloys Revealed by X-Ray Spectrometers « Daily Bulletin

There is pressure and there is pressure 'problems'. Completely different, because pressure is your friend -until it isn't.

Improved cases with their low body taper and high shoulder angles remove many pressure problems.
There is also the ratio of body diameter to cal, to burn more powder INSIDE the chamber rather than adding to bullet mass further down a bore.
Then you set the right capacity for selected bullets and powder to reach a goal at a stable and rational pressure curve. A long enough barrel to burn more powder inside it, producing lower muzzle pressures.
Tight coaxial throat, and tight chamber end clearance to reduce SD. Lands you can reach and without seating bearing near donuts.
Sufficient barrel steel around the chamber area, and tight clearances to reduce brass yielding from the git-go. Bushed firing pin, tight breech clearance, beefy aftermarket action.
These are mostly overlooked by the many amateurs building guns today. They think velocity and little else.

Thanks Mike.......I know that Norma isn't up to Lapua toughness, but my experience in the SAUM is that it is the best there is.
I agree with the statement about "pressure vs pressure problems".
Another often overlooked fact is that the shortened case increases the useful barrel length available to burn powder. i.e. my SS case in a 26" would equal my 6.5 Sherman case with a 27 1/2".......Rich