Rifle reloading Powder Residue

[Opat63]

I have been experiencing a lot of burnt powder residue on my casing after firing. I am shooting a Japanese Aisaka 99 using Accurate 4350 174gn bullet. I load closer to the minimum load. I didn’t notice this when I used IMR 4064. Any ideas why. Thank you

[lugerstew]

The lighter the load, the less pressure to make the case swell tighter to the chamber. This allows more powder residue blowback to come back in the chamber.
I really haven't noticed this with Imr 4064 in my 223 or my 308, but when I used light loads with CFE 223 I had terrible problems with blowback, cases were black all the way back to the base.
If it were me, I would do load work ups, working up close to max, of course looking for overpressure as well.

[ernie8]

What loading data are you using ?

[mehavey]

If I look at an old Lyman Manual for the 7.7 Jap, and translate 45.7gr min load of IMR 4350 to AA 4350 for a 174gr HPBT, I get only 34,000 psi, but ~94% burn in a 26" barrel.

OUGHT not to be too bad.
I wouldn't worry about it

[44 AMP]

If I look at an old Lyman Manual for the 7.7 Jap, and translate 45.7gr min load of IMR 4350...

Which old Lyman manual are you looking at to "translate"??

I've got the 45th Edition (1970) and for the 180gr jacketed, the starting load of IMR 4350 is listed at 47gr. for a velocity just over 2,200fps.

This is a light load (some 300fps below potential) and IMR 4350 is just a tad on the slow side for best performance in the 7.7mm Jap.

IMR 4895 is a better choice, and I think both 4064 and 4320 are both better than 4350 in that case.

The lighter the load, the less pressure to make the case swell tighter to the chamber. This allows more powder residue blowback to come back in the chamber.

The lighter the load, the lower the pressure, is true, but its not a matter of how "hard" the brass is pushed in total, its how much at which point in time and which point on the case.

The soot stains are are proof that the brass has not yet sealed to the chamber when the gas gets there, as the bullet moves out of the case, but, the case does seal to the chamber right after that, otherwise you would have gas blowing out the back of the action (and you don't, right??)

Slower powders burn slower and so build up pressure slower, and even though when full pressure is reached it will be as much or even more than other, faster powders, since it gets there slightly slower, it is more prone to APPEARING to be too low pressure and leaving sooty brass.

Upping the load level or going to a faster burning powder will probably reduce or eliminate your sooting problem.

[mehavey]

Which old Lyman manual are you looking at to "translate"??

Would you believe. . . . Sierra 5th ? (p 634)
And I say "translate" since 'IMR' does not directly <=> 'AA' for '4350'
and the Accurate Powder loading data (online) did not list the 7.7JAP
(at least I didn't see it)

Be that as it may...
For that S-th / 174gr HPBT @ listed 3.150" OAL using QL with 26" barrel:

IMR 4350/45.7gr --> 35,462psi/2,389fps/89.8%
AA- 4350/45.7gr --> 32,530psi/2,407fps/93.5%

Neither powder gave enough pressure to reliably seal the brass, but then 90%+ burn wouldn't particularly worry me about unburned powder fractions.

Then again, the OP hasn't said what the actual powder weight used was, nor the load data source . . .

[jetinteriorguy]

You could try crimping the neck if your not doing so now. This might help build initial pressure enough to expand the case before the bullet is clear, thus sealing it.

[paknheat]

Go back to using the 4064.


Sent from my iPhone using Tapatalk Pro