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H 4198/IMR 4198

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BillyHill View Drop Down
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    Posted: December 20 2016 at 8:07pm
I'm starting to work up a cast load for my 303 with a 185 grn gas checked bullet cast from wheel weights. I found data for IMR 4198 with a start load of 21 grains at 1500 fps and a max load of 28 grains at 1950 fps.  I don't have IMR 4198 but I do have H4198.  I was going to start at 22 grains and work my way up.  In the load data that I have seen where 4198 powder is listed, the charge weight is almost identical for  both Hogdon and IMR powder using the same bullet/weight.  Has anyone tried H4198 for cast loads.  I think if I start at the low end and carefully work my way up I should be OK.  The data I have is from the Lyman Manual. 
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Stanforth View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stanforth Quote  Post ReplyReply Direct Link To This Post Posted: February 23 2017 at 9:12am
I treat them as the same.
Life.. a sexually transmitted condition that is invariably fatal.
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Personally I would use a starting load of 16gr of Alliant 2400
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pogson Quote  Post ReplyReply Direct Link To This Post Posted: July 14 2018 at 4:28am
Originally posted by Stanforth Stanforth wrote:

I treat them as the same.


They are very similar but definitely not the same. Hodgdon, for instance, gives these data for 222 Rem:
IMR
IMR 4198 .224" 2.130" 16.5 2,722 35,900 PSI 18.7 3,017 47,700 PSI
Hodgdon
H4198 .224" 2.130" 17.5 2,733 33,400 CUP 19.5 3,017 45,300 CUP
In this case, one grain more H4198 powder gives about the same velocity as a charge of IMR4198. That's about 5% difference in charge for the same effect. I would work up carefully to see what works in your situation. It's best to do that with any change of components or even lot of components of the same brand. One can expect that deviations will tend to cancel with such a complex process as reloading and firing but in the worst case the deviations will all be in the same direction and at least could give unsatisfactory results and in the worst case someone gets hurt. Change of brass, bullet, rifle, primer can all cause similar effects. Stick with what works but find it carefully changing just one thing at a time.

The velocity of the bullet at the muzzle is a result of the average pressure in the barrel as the bullet travels its length. A change in powder can easily have the same average pressure but with a different peak pressure, where bad things can happen affecting the integrity of the case or rifle.

Playing with the powder is like playing with fire. It can work for you or against you. Don't do what I once did when I first started reloading, thinking that if 10% below max was safer, 20% would be even safer! It wasn't. I got amazing muzzle flashes and reports. Others have had detonations. Powders are designed to work at reasonable pressures. Too low can cause very erratic burning and even pressure spikes just as too high almost certainly will. When in doubt, I choose a middling load and work up and down in small steps to see what works best.
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