05 October 2004, 07:17
JustCRe: 6.5X55 Improved
Batman,..The velocity can be safely increased by using the slower powders which work so much better with a 40degree shoulder than they ever would have in the parent cartridge.
I am getting 7mm mag velocities with 4831sc and RL22 in a 280AI. I am getting 3200fps with no pressure signs yet in a 6.5-06AI with 140gr a-max pills and RL22. I have also successfully used H1000 in that case to get over 3000fps. I will be trying RL25 next for near 100% loads and fast MV.
The problem with the AI is that folks try to stick to the same old powders from the parent caliber and with the faster burn rates,...are flirting with disaster trying to get the "supposed" velocity gains. Even Parker himself was working with powders that are far faster and unsuited compared to the modern propellants. Just my observations.
05 October 2004, 10:58
BatmanJustC
You're on dangerous ground! Your 3200 fps is easily exceeding what should be expected from a 264 WinMag. I hope you dont think that your 6.5 AI has more case capacity than the .264? Also, as to the slower powders, you'll need to gain a lot more case capacity than just a couple of grains with the AI to see vast improvements with slower powders.
Trust me, you're WAY above the 46,000 psi of the parent cartridge. You're even above the 51,000 psi of what's recommended for modern actions. I would venture you're even exceeding the 64,000 psi of the .264 Winchester Magnum as you have less case capacity than the .264 and you're comfortably above what should be safely loaded in the .264.
This is exactly why I say the AI crowd is dangerous. You just cant accept that you're only increasing the case capacity a minute amount so you push it and push it until you see some "pressure signs."
So, some words on the pressure signs you're looking for...They dont exist for the most part in an AI chamber. Under the best circumstances, the long used pressure signs are way off safety wise. By the time you see your standard pressure signs, you're 70k or above in your AI gun...This should scare you!
You may have noticed that over the past 10 years, reloading manuals have toned it down quite a bit. That's because we now know a lot more about pressure than we did even 10 years ago. Most all modern manuals are published with Pizeo-electric (strain gauge) testing, giving much more accurate pressures than ever before.
You haven't ran into problems yet because yo're probably not doing anything extreme as far as temperature goes, but I would never shoot your loads on a hot day or out of a hot barrel.
I'm not trying to pick on you, I'm just hoping to clear the air on AI cartridges...They simply cant turn a standard cartridge into a magnum unless you're willing to push the pressure way too high.
AI's were touted as a magic way to increase the performance of your rifle in an age where everyone was guessing about pressure. Often times, there weren't any problems, but now and again, guns went KB.
So, for those of us that don't have a strain guage to test pressure, we educate ourselves well and make a scientific guess, which is what my first suggestion was. Go back and read what I wrote and think about the logic there...It works and it's safe. Your methood of working up your loads and watch for pressure signs is what we've all been doing for decades, but we now know it's not safe.
With a poorly cut chamber, the old method of lookgin for case head expansion, bolt lift etc. worked pretty well. However, with a hand reamed chamber like the AI which tends to be on the tight side and a little more concentric, this just doesn't work. In these nice chambers the brass doesn't get worked, which is what we're lookging for with traditional methods. If your brass is not allowed to get worked then there's nothing to measure until the extremely good steels of your rifle start stretching, which means you're already at the danger poing.
AI fans, stop talking about blistering velocities and magnum performacne, it's just not true. The AI's are a great idea by giving top of the books performance with an added safety level, more concentric chambers, which means your gun will shoot better, and long case life.
That is the attraction to the AI, not velocity.
