With a 26" tube what are the velocity gains? any real word experience? Thanx in advance!

I don't have one but have looked into it a bit. From what I found, somewhere about 125fps faster than the plain ol' 25-06. This was from actual shooters of the AI version.

Pop, do this for your own interest.

Look at a 25-06 and a 257 Weatherby side by side.

Look up all the reloading data about the two and get a feel for the real difference between them. Use 25'/sec per inch to equate the different barrel lengths.

Now after all this ask yourself.....how much am I going to gain by the increased amout of chamber volume of improving the 25-06.

Don't have a 25-06AI but do have a 25 Gibbs. Loaded to the same pressure and OAL you will gain 1% velocity for each 4% of powder.

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you will gain 1% velocity for each 4% of powder.

This has been a very good rule of thumb...an excellent way of approximating the velocity gains of a new case.

i believe ther term is called overbore - that is to say its more powder than can really be handled by the bore size, not as in over and under

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This has been a very good rule of thumb...an excellent way of approximating the velocity gains of a new case

I spent a lot of time, powder, bullets using a pressure barrel and strain guages on several conversions. Taking the standard to AI to Improved to very improved. The results will vary a little but the 1 for 4 will get you as close as anything.

The comparison of the 25-06 to 257Wby is a good way to look at it. When I was building my first wildcat 280 I plotted the velocity vs capacity of all the 7mm cases I could find data on. From the 7-08 up through the 280 almost to the 7x61 you get a nice slopping line. My testing of a 280-280AI-280JRS to my 280PDK(Gibbs + 2 grs)followed this line. Once you cross the 7-61 the line starts to flatten and as you get past the STW you are pretty much flat.

The 1-4 rule of thumb is an average that depends on the relative volume of the case to the bore, ie., as a case gets larger in relation to the bore, the potential percentage gain in velocity falls, providing ever smaller velocity gains.

The lion's share of the velocity gains with improved cartridges is mostly a result of the owner's willingness to increase pressures in order to achieve a preconceived notion of what the velocity gain should be.

Exceptions might be cartridges in which the standard version has significant body taper and/or shoulder slope like the .257 AI or the .22 K-Hornet. Cartridges based on the .30-06 case just don't have enough room to increase case capacity to make a signficant difference.

With all that said, I just obtained my first .25-06 a few weeks ago. I have been handloading for 41 years, have owned a chronograph for 34 or those years, and have a lot of experience with large capacity cases and slow powders. I was surprised by just how slow a powder was demanded by the .25-06, with old standby H4831 being a bit fast with the heavier bullets, and even IMR 7828 failing to fill the case with maximum loads using a 115 grain bullet. This tells me that there is VERY little to be gained from increasing the case capacity in this caliber. I would not expect to gain even 50 fps at the same pressures.

"Improving" the .25-06 is not a worthwhile endeavor, in my opinion.

I have a 25-06 AI - it's clearly over bore with very little to be gained over the standard 25-06, which I believe is already over bore. I don't recommend it; PO Ackley didn't recommend it. Also, it's hard on barrels.

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The 1-4 rule of thumb is an average that depends on the relative volume of the case to the bore, ie., as a case gets larger in relation to the bore, the potential percentage gain in velocity falls, providing ever smaller velocity gains.

I agree 100%. Some of the smaller cases are a little higher. Some of the way overbore are almost no gain. For the 06 bases cases it is pretty much righ on.

Heck of a deal to spend as much time as I did to come up with that info. Only to find it numerous places after the internet got popular.