FPS/grains used. If you have a standard cartridge that gets 3000 fps/60 grs, you get a factor of 50. If you improve the case and now get 3200/62, your efficiency factor is 51.6.

Charlie, what cartridges and bullet weights did you use in the above post? The lighter for caliber bullets used the more I would expect the example to holdup. Heavy for caliber bullets not as much.

I can get into why later, or at least my beliefs on why and there are several things at play

I also tried multiple brands and calibers for fire forming. Here’s what I have pics of

Norma 338-06 A2 Virgin vs fire formed



Hornady 270 Nickel Plated before and after fire forming



Full formed and loaded 338 Sherm

Here's the 338-06 AI. Notice how much longer the neck is versus the Sherman?

^^Great example^^

And yes, you can often determine how many fps one grain of powder makes. I did this with my .223 A.I. Each grain of powder makes more velocity in the better case geometry brass. That's what I meant by "fuel mileage", also know as case geometry efficiency.

The math certainly works out. However, no cartridge names are supplied in the example. Review of the Sierra reloading manual edition 5 reveals mixed results on the few AI cartridges referenced; i.e. 22-250, 250 savage, 257 Roberts, 25-06, 280 and 30-06. All AI versions produce greater max velocity than the standard version - with heavier powder charges - though the mixed results are revealed when comparing the powder charges with the same velocity between the 2 cartridges; some are higher, some are lower. Regardless, the 338 Sherman is an interesting cartridge. Particularly since the shoulder is moved so much further north, using some of the long neck of the parent .270WIN case to increase case capacity. It's seems so simple it's a wonder it was not done before.

RDub270 if you improve a case and use the exact powder and charge as the unimproved it will yield a lower velocity every time I would think due to less pressure. The benefit of improved cases is being able to run the same pressure with more powder.

A more efficient case can obtain the same velocity with less of the same powder. Ie Creed vs .260

Having an improved shoulder and having an efficient case is not always the same thing. Efficiency is about the powder column geometry. Improved simply increases volume.

I pulled all that out of my rear so take it for what it s worth.

It has been done in various forms. Most similar is the 270-338 HGT in 1981 by Troester. Good article on it in Handloader magazine issue 92. — https://www.yumpu.com/en/document/view/25770631/number-92-wolfe-publishing-company

wp75169 - Agreed, and I appreciate your last line...I really needed the laugh today. Thank you, sir.

Thank you for the link. I noticed the reference to a 270-338 HGT a page or 2 earlier and could find nothing on it.

You didn't ask for an example, you asked how to calculate it. I provided your answer. Now take the books you were reading and plug their math into the formula and see what result you get.

From FJG's example of the 7-08 vs AI, he increased 120fps on 1.8 grs. A typical 7-08 load is ~43-44 grs. Let's say 44. 2700/44=61.36 , 2820/45.8 = 61.57. In this case the AI shows to have increased efficiency.

Here’s some interesting hypothetical QL numbers I just ran...

For the 338 Sherman vs 338 Win Mag shooting the Barnes 210 gr TTSX in a 24 barrel with same 99.8% burn rate of Varget...

To attain the same velocity of 2780 FPS, the Sherm would need 57.87 gr Varget vs 61.60 gr for the 338 win mag. That’s almost 4 gr difference to attain the same velocity.

Incidentally, QL shows the Sherman as mine is configured using my brass with a PMax of 65k would push the 210 gr Barnes TTSX:
Varget — 2825 FPS
RL-16 — 2933 FPS
RL-17 — 2963 FPS

Both are loaded with 180 ELD-M to 3000fps. This is the absolute maximum I can get out of the 7 Rem Mag, but I have more headroom in the 7 SAUM and have pushed the same bullet to 3200.

On a side note Red, how does the nickel case appear to be holding up to the forming change?

I use nickel on my Ruger Only 45 Colt loads so they never accidentally get loaded into a lesser chamber. Easy to tell them apart. I’ve always heard it’s brittle, but i use a heavy factory crimp and never had any issues.

I love the nickel brass. This is brass I got from pulling the 270 bullets from Hornady Outfitter ammo. It seems much more consistent in weight from case to case than Win or federal. Seems to hold up better to firing them other nickel cases I have used in past for other calibers — no loose primer pockets after 3-4 firings. Haven’t had any problems with flaking with firing and resizing.

Only issue I had was that when necking up with a tapered expander button (even with 2 steps 30 cal then .338) in the sizing die, I did split 1 out of 5 of the necks. Once I switched to the Sinclair expander mandrel i didn’t have that prob. What’s also nice about the mandrel sis they are sized 0.002” smaller than caliber so they create very uniform neck tension. I first FL size with a bushing to give > .003 tension then run them back over the mandrel to give the 0.002 neck tension. I don’t neck turn, so this really helps push the ununiform neck thickness to the outside and rather than the inside that occurs with the bushings. Once I started doing this I saw my groups go for 1/2 moa to 1/4-1/8.

Impressive. I had trouble with the 338-06 until I found a good supply of once fired 35 whelen. I totally trashed an expander on a 30-06 case when I started. Had I been more patient I could have saved it. Fortunately it’s a 3 die set so I pulled the expander out of the neck die.

I think a 338 win mag is a handy rifle to have in the arsenal. I would look for a good used Tikka m695 or any other brand you like. It’s minimum and would perform well with 225 grain Barnes TSX

My primary elk gun is a .338 win Mag. I've killed several elk with it and no tracking is necessary. It's a Ruger M77 tang safety I purchased new in 1984 I upgraded to a B&C fiber stock, put a good pad on it, trigger job and break. Shoots very accurate for a big bore gun and pleasant to shoot. Best bullet I've found is a Nosler Accubond .225 gr8.
Good Luck