Originally Posted by Joe King
I was referring to his findings related to barrel length only. I do not see what case capacity has to with anything beyond what MikeCR stated. Which I completely agree with
are you saying Dan Lilja never messed with 378 based chamberings? Cause he used a 338-378 for that test
when you see the suffix "AI" placed behind a certain cartridge case it means Ackley improved normally. Ackley never did anything with the .378 style case. But he did develope a .338-06 improved round. To the best of my knowledge that's the only .338 he did.
To further delve into barrel length and what you get is another story. Barrel rigidity becomes a player in this game unless unless we're looking at shotguns. Plus we also get the stress transfered into the bridge of the reciever (becomes the fulcrum point). Lilja once stated in a paper he wrote that a 21" number seven contour barrel was 2.75 times stiffer than the same thing 26" long. I pretty much confirmed this with a C/H Remington barrel (actually ended up about 2.85). This relates a lot to shot to shot consistancey.
Then there is the issue of barrel harmonics in relationship to bullet travel. But we also want to get the most out of a certain bullet, so everything ends up being a compromise.
Dan Lilja did some testing with a 34" barrel and said he was quite satisfied with the results. I can't remember the caliber, but it seems to me it was based off the .378 WBY case. Out of curiosity I took a look at three loading manuals to see what they were doing in them. Only one showed the .338/378 loadings, so you must forgive me here. The .338/378 was the fastest in velocity, but used another ten grains of powder to gain 100 feet per second with a 28" barrel. The .338 Lapua used a 24.5" barrel and was down about 200fps, but used about 15 grains less powder to get there. The Remington was down 100fps, but used slightly less powder than the Lapua in a 26" barrel. (I see a trend here already). The .340 WBY mag used even less powder and still got 2900fps with a 26" barrel. I also took a look at the .338 Win. mag for a comparison, and was stunned! They were getting 2650fps-2700fps with ten grains less powder than the .340mag and a 24" barrel. All bullets checked were 250 grain, and I'm sure that when you move upto 300 grain bullets the bigger cases will do much better. What I saw in these charts was a lot of powder being blown out the end of the barrel, and very little gain for anything past 26" in length, and the Lapua with a 24.5" barrel was probably about all that the .338 bore could handle (had it had a 28" barrel, it would probably have been just about as fast as the big case. Even more interesting was that the little .338-06 (unimproved) did 2600fps with about 50 grains of powder and a 23.5" barrel!! The .338AI will do 2750fps with a 24" barrel, and 2800fps with a 26" barrel. I couldn't find my data for the .338RCM, and perhaps somebody can add this to the list.