.257 Roberts AI - interesting info from Barsness

Guy Miner

Master Loader
Apr 6, 2006
Over on 24 Hour Campfire, I happened upon this reply of John's to a question about AI cartridges, and velocity gains. Very interesting reading:

"Here's what I do when working with an "improved" case where there's no pressure-tested loading data:

First, I measure the case capacity of the standard round. This is most accurately and easily done with a fired but unsized case. Weight the case empty, then fill it full of water and insert a bullet in the neck, causing the excess water to overflow. A cannelured bullet is easiest, because you simply insert it to the cannelure.

After removing the bullet, wipe any water off the outside of the case and re-weigh it. (The water has enough tension to stay in the case, if you don't try to knock it out.) The difference between the empty case and the water-filled case is the "functional" case capacity with that bullet.

Next, divide the capacity of the improved case by the capacity of the standard case. Let's use the .257 Ackley as an example, since you already mentioned it. Usually the capacity of the improved case with a 100-grain bullet will be around 57 grains, and the capacity of the standard case around 52. Divide 57 by 52 and we get 1.096.

Now we us the 4-to-1 Formula for calculating the potential extra velocity. Dividing .096 by 4 results in .024, which means the improved case will get approximately 2.4% more velocity when loaded TO THE SAME PRESSURE.

If we look at +P data for the .257 (not the old-fashioned low-pressure wimp data, since nobody has any idea why it's still used, or ever was), we find the top velocity loads for 100-grain bullets get around 3100-3200 fps. This means our Ackley Improved rifle is capable of around 3175-3275 fps AT THE SAME PRESSURE.

Now we can start loading ammo. Maximum loads for the standard cartridge will be perfectly safe, since the larger improved chamber reduces pressures. We start with one of these, using one of the powder producing the highest velocity in the standard case, and note the average velocity.

Hornady's latest manual, for instance, lists 49.7 grains if Superformance powder as producing 3200 fps with the 100-grain Interlock Spire Point in the .257. This is from a 22" barrel.

When we fire this load in our .257 Ackley Improved rifle (let's say it also has a 22" barrel) it won't get that much velocity, because of the larger chamber. Let's say it gets 3100 fps.

So we add more powder, a half-grain at a time, watching the chronograph to check the velocity. Eventually the chronograph will probably read around 3275 WITHOUT ANY "PRESSURE SIGNS"." I know this from using this technique with several rifles chambered for improved cartridges.

Now, we probably could continue to add powder without seeing any pressure signs, but that doesn't mean pressure isn't really high, since often they don't show up until 70,000 PSI or even more. And 3275 is plenty of velocity with a 100-grain bullet anyway.

Or, if you do have a .257 Ackley Improved and don't want to go to all this trouble, you could look up the data in any of several current sources that include pressure-tested .257 Ackley data. But the technique does work for improved rounds.

But somebody already commented that the big jump in velocities with improved rounds is due to more pressure. This is true, since most handloaders using improved rounds work up loads using "pressure signs." Since most factory cartridges are limited to 60-65,000 PSI, adding another 5,000-10,000 PSI results in considerably higher velocity.

If the factory cartridge has an even lower pressure limit (and many do) the difference between the velocity of the standard round and Improved ammo loaded with "pressure signs" is even greater. This is exactly why the .250 Savage AI gets so much more velocity than the factory ammo, since the SAAMI pressure limit is very low, and even +P .257 Roberts data is only 58,000 PSI.

But the biggie is that you can start with maximum powder charges for the standard round without any worries.
Thanks Guy,
I shoot 3 different Ackleys and that is the method I've always used.... minus the math. Start with max standard loads and using the chrono instead of pressure signs to know you've reached pressure. I love my Ackleys, not for the extra speed but for the reduction in brass prep and the longer brass life. I shoot the 22-250,257 and the 280 Ackleys.

Thanks Guy! Still working on a load for my 257 Ackley. Using IMR 4350 and 100gr BT. I went away from the 110gr AB since they are so scarce.
My first "wildcat" was a rechambered Mod 700 Classic in .257 Roberts to the AI. I seated the bullets way out and used a bunch of IMR 4350/120 Hornady HP. I have no idea how fast it was going but it was pure death on crows and whitetail deer!
Thanks Guy. I did something similar to this working up loads recently for my 250 Savage AI, along with some help from the good folks on here.

I get speeds very close to that of the 257 Roberts +P with the improved 250 AI case which in my chamber has a capacity of 51.5g. While this is about 4.5g less capacity that the Roberts, the 25 inch barrel more than makes up for that difference.
Guy, that is he best approach I've seen yet. Some folks get scary with the Ackleys when they post loads. Pressure is pressure and if a similarily equipped 7mm mag can't do it or would struggle I know a 280 Ackley has to be flogging it to get there.
It's kind of funny, I've never loaded for an AI cartridge, but have been fascinated by them for years.

Guess when I wanted more, I just went with a "magnum" cartridge.

I kind of feel like Elmer Keith..."Efficiency be da---, its results I'm after!" ha I like all I can get from a cartridge design, safely of course. I think some folks are crazy with pressure, sure, but I feel too many folks are skittish about it. I also do not feel that just because a hot load won't give 10 reloadings per case that it is useless, ha. I feel 3 reloadings is acceptable with a hot load, but I don't shoot them that much anyhow, so that goes a long way. The best use I have for any Ackley design is that I can get safe loads, with moderate to semi high pressure that only a standard case would get with way too much pressure. Case in point, my 35 Whelen AI gets 2950 with the 200 TTSX or the older 200X gets 2970. I get this with a 22" bbl and bullets seated out for the Remington long throat. I'd have to push a standard Whelen a bit in a 22" bbl to get there. I have been using some Whelen AI cases since '95! Anything more calls for a bigger case for me too.
Before we got chronographs, I reckon most of us were contentedly loading to about 50k PSI and about 150fps less than max. We were happy!

Then we started speed testing our loads, and it was never enough!

These days I'm generally back to loading 50 to 150fps less than max. The pigs and deer have never minded.
bobnob said:
Before we got chronographs, I reckon most of us were contentedly loading to about 50k PSI and about 150fps less than max. We were happy!

Then we started speed testing our loads, and it was never enough!

Yep! I've had a chrono mess up some good loads for me too! lol More power! (y)