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Thread: Loading for AI cartridges

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    Moderator LuJon's Avatar
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    Default Loading for AI cartridges

    For those of you loading for AI cartridges do you just use the parent cartridge recipies then work up looking for pressure signs if there isn't an AI specific load in a particular pouwder? I would expect powders that worked good in the parent to also work well in the converted chamber just with a slightly larger charge. Is this correct?

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    I have used the max for the parent case and then went up 3 or 4 grains depending on what I see for pressure signs. I started using accubonds so I just use there data. I really like mine, but fire forming all the brass was a PIA. I hope that barnes comes out with some 280 ai data. A 150 or 160 barnes would be a killing machine.

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    Quote Originally Posted by LuJon View Post
    For those of you loading for AI cartridges do you just use the parent cartridge recipies then work up looking for pressure signs if there isn't an AI specific load in a particular pouwder? I would expect powders that worked good in the parent to also work well in the converted chamber just with a slightly larger charge. Is this correct?
    Lots of ways to skin a cat, but I trust the chronograph for AI development work. While every chambering/barrel/bullet combination is a law unto itself, there is an expected velocity threshold and when it is reached I'm done regardless of pressure signs. Of course if I encounter pressure signs along the way I'll stop my development, restart with another powder/bullet/primer combo and try again. IME, parent case maximum charges are a good starting place in most instances.

    As to what powders work best in an AI chamber, I'd say you're on the money with what works well in the parent case is going to be a good selection in the offspring.
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    What has me intrigued is R17 in a 280 AI behind a 160 Accubond fired by a Fed 210. R17 is supposed to have a similar burn rate to 4350 but higher load density. The big interest I have in it is that it is reported to have great velocity with minimal fluctuations at different temps when compared to R22 which seems to be the "standard" for the 280AI. The Alliant website lists 51.5 grains of R17 behind a Speer 160 gr BTSP for 2825fps in the standard 280. I wonder how that would transfer over to the 160 in the AI. Anyone have one of those magic software programs that can break it down?

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    The AI version only holds 1.5 to 2 grains more powder than the standard .280 Remington. The problem is that SAAMI pressure limit for the Remington is only 60,000 PSI, while the AI is 65,000 PSI. So if the load data does not list pressures, then you don't know to what limit they went. If the 2825 fps with RL-17 was at only 60,000 PSI, then you could probably add 3 or more grains of powder and get another 100+ fps in the AI. But if the 2825 in the standard .280 was at 62,000 PSI (still completely safe) or more, then only 1-2 grains more of powder could be loaded safely, and only 50 fps more velocity should be expected.

    In either case, RL-17 should be a good powder, although IMR-7828 and RL-22 seem to give the absolute top velocities for most people.

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    Interesting note is Nosler #6 shows IMR4350 @ 55.5 grains (max load) behind a 160 accubond @ 3002fps to be the most accurate for that powder. If R17 is in fact very close to it then it should be a good selection. I am not really looking to push the limits, just would like to see 3K and good accuracy in something that will handle our conditions. Interesting note, in their test barrel R22 and 7828 both showed the min listed load to be the most accurate and only ~ 2850 each.

    Oh well not much I can do till I get a 280 AI and associated materials to play with. Hopefully it won't be too much longer!

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    why not use a proven recipe, call or message Sterling at ARCTIC AMMO
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    Another reason for the R17 interest is that there are already 2 WSM cartridges in the stable that I am hoping to use it for. Both of them have tons of positive reports from guys using it.

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    In my 338/06 ack imp I used just a grain or two under the max 338/06 A square published load for fireforming, then went to several internet sites for some refrences to compare to standard published data. Reloadersnest.com is full of good info on a ton of calibers. The load I settled on was around 3 grains over standard max the issue I had was with case capacity I couldnt get enough H4350 in it with out heavily compressing the charge, so I went with H414 and am able to get a 250 TSX out the 23 inch pipe at 2650. Go with the Standard go to powdersfor your caliber you arent changing the powder charge/expansion ratio enough to warrant a major slow down in burn rates.
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    Here is some data I had on my 7mm Gibbs. I no longer have it. I had it rebarreld to something else. Side note I posted this in accurate reloading when I had the 7mm Gibbs. Forgot to add someone ran my load for the 160 through QL and that load was at 64,000 PSI. The load with 175 according to QL was 2755 @ 55,125 psi.

    Well been going to the range alot to test loads for this rifle. Here are some good starting points for anyone that has a 7mm Gibbs. Some notes apparantley this barrel does not like boattails it will not shoot them and it does not like the Nosler/winchest combined technology bullets either. It shows the most potential with the flat base bullet especially with Speer flat base bullets. I tried some Hornady 175 and it shot them pretty good I got up to 56.0 grs of H-4831 with that bullet and stopped it was not showing any pressure with that load. So I feel I could of got up to an easy 58-59gr with that bullet. But stopped and started messing with 160gr bullets.
    I just recently got a chrono so the only load I have chrono are these loads:
    160gr Speer 61.5gr of H-4831 CCI 250 26 inch barrel. Velocity with a 5 shot string 3023 F.P.S was the avg. No signs of pressure.. I have tried H-4350, RL-22 and H-1000 but groups were not good at all. I have been tempted to get some IMR 7828 and some IMR 4831 to try out in it. But I guess for now I will stick with H-4831 it seems to be working pretty good.

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    Here's my technique for loading AI cartridges, and I've loaded for all AI's and some that are Ackleys that never were. Take the parent case and fill with water and weigh it. Then take the same brand (WW, R-P, etc) brass that has been fire formed, fill with water and weigh it. Take 75% of the weight difference of the water filled cases and add no more than that to the parent case max load.

    Here's my reasoning. AI'd cartridges often don't show normal pressure signs the way the more tapered parent case will show. AI's may not show the normal max pressure signs until the primer pocket expands so much it won't hold a primer. That is mucho too much pressure. Most AI shooters load above the parent pressure limit because they don't have the normal signs of max pressure at parent case max so they add powder until they see the signs. I am just saying that we shouldn't rely on the normal signs.

    It will take a lengthy explanation for this but if you trust my thousands of AI cartridge pressure testing experience, try this.

    It isn't true that an AI cartridge only holds 2.2 grains more or 5 grains more or even 5% more than the parent. There is no flat amount unless you speak of one particular cartridge. Obviously the extreme case taper of the 250-3000 Savage when AI'd holds a greater % more powder than does the 243 AI vs. the parent 243 because the 243 Win has less taper. The AI'd cartridge increase in powder capacity comes from less body taper and the steeper shoulder angle.


    The 280 AI holds about 5% more than the parent 280 Rem and will give about 3% greater velocity at the same pressure. This is quite typical of any improved cartridge. It takes 5% more powder to give 3% velocity and that is a generous estimate. This is still keeping the parent cartridge pressure limit.

    One poster points out the 280 is SAAMi spec'd at 60,000 psi, I believe it is actually 56,000 psi but I do think that 60,000 psi is a good limit for all the AI's in strong bolt guns. Generally we use the parent pressure spec for the AI'd version of same cartridge. Obviously the same case is found in the 270 and 30-06 and the 270 is spec'd at 60K, but if you don't have a piezo crystal pressure transduce equipped barrel this is a moot point.

    Remember, the one big advantage of a true Ackley Improved cartridge is that we can safely and efficiently fire factory parent case ammunition in the AI chamber. If the AI is properly chambered there will be felt shoulder contact when closing the bolt on an AI chamber with factory (correct headspace) ammo. Of course many of the AI's never had a parent case. Such as the 6.5-06,the 375-06, the or the 30-280 AI. (The 280 rem case necked up to 30 caliber then AI'd) The 280 has greater case capacity than the 30-06 and makes a super 30 when compared to the standard 30-06. I've used this case extensively for several bullet diameters, including the 338 Rag Horn.....just a name.
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    Quote Originally Posted by LuJon View Post
    For those of you loading for AI cartridges do you just use the parent cartridge recipies then work up looking for pressure signs if there isn't an AI specific load in a particular pouwder? I would expect powders that worked good in the parent to also work well in the converted chamber just with a slightly larger charge. Is this correct?

    Not necessarilly. I have a 338-06 and a 338-06 AI. The AI seems to love the 4350 powder but the std 338 -06 works better with 4895. There are many other examples but to answer your question they can use the same powders but optimum performance may not be there for both. The general direction to go is as case capacity increases and bore size remains the same we need to go to slightly slower powder to maintain the same efficiency and consequently the same edge in performance. I have the advantage of seeing pressure equipment used with many of these AI's and I do have lots of data but I think the real joy of a wildcat is the experiment in load development. If you have a popular parent case its easy to extrapolate or even to make scientific guesses about the charge weight. Before there was load data for the 6.5-06, we had the 25-06 and the 270. It is exactly in between and when we AI the 6.5 we add excitement to the quest. Common sense must prevail and powder of appropriate burn weight must be used. If we neck down, use slower powder, if we neck up we can use faster powder. We also want to fill the case...but of course we may have to go to a slower burn powder when we increase the powder capacity such as with the AI or other improved cartridge patterns. It's all part of the fun.
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    Interesting thread.

    My 6.5-06AI likes 4831SC best....by maybe a full 1" at 100 yds. You really need to try a variety of powders and see what bullet and load your barrels likes.

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    Murphy, I'm just about to start a new load development for the 35 Whelen AI with Alliant Power Pro 2000-MR powder. Burn rate is supposed to be the same or slightly slower than RL-15, but it's much denser, so better case fill. I have 200, 225, 250 and 275 grain bullets to play with. Stay tuned . . . .

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