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Discussion in 'Reloading' started by notahd, Nov 1, 2011.
Looking for a pet load for a 220 swift using 70 gr bullets and 4831 IMR powder. I have 1in9" barrel
In 1986 I built a custom 220AI using a Rem 700, Douglas 25.5 inch 1-12 twist SS barrel. I hoped to use the 68 grain Hornady and 69 grain Sierra which had just been released in Oz, however, my testing quickly showed that the 12 twist barrel would not stabilise them.
I found that with the powders I tested, IMR 4831 was the best powder for velocity, and gave good accuracy with both the 55 and 60 grain bullets.
I also found that with the powders I tested, IMR 7828 gave the best velocity with the 68 and 69 grain bullets. However, I couldn't get close to the 3,765 ps velocity achieved by my gunsmith prior to shipping, using 47.0 grains Norma 205 with the 68 grain Hornady HPBT.
My chrono data is listed below using Winchester cases, Federal 215 primer, and Sierra 69 grain HPBT.
43.0 grains IMR 4831- 3,470 fps
44.0 grains IMR 4831 -3,563 fps
44.5 grains IMR 4831 -3,593 fps (Max)
47.0 grains IMR 7828 - 3,488 fps
48.0 grains IMR 7828 - 3,596 fps
48.5 grains IMR 7828 - 3,653 fps. (Max)
Chamber dimensions of wildcat cartridges vary considerably, so I suggest you start at about 40.0 grains of IMR 4831 with the 70 grain bullet and work up from there.
The 220AI version that I used would take about 48.5 grains to fill the case to the bottom of the neck using long extruded powders (ie. IMR 4831, & IMR 7828). It would take about 50.0 grains to fill the case to the bottom of the neck with short cut extruded powders (ie. Re22, H4831sc) and about 52.0 grains to fill the case to the bottom of the neck with ball powders (ie W785, H870)
Although you will probably achieve good results using IMR 4831 with the 70 grain bullet, if I was to build another 220AI today I would first be trying slower powders such as Reloader 22, H4831sc, Vihtavouri N560, and IMR 7828sc with that bullet weight.
Hope that the above is of some help. Good luck with your 220AI. Brian
Thanks for the information. we will put it to good use.