imr 7828 sc question

[stillquietvoice]

has anyone used 7828 for mid bullet weights in 7 mm-08. im loading for three cals and need alternate powders for all 3. my cals are 243 win,7-08, and 3006. have used h4895 blc2 and imr 4064 recently. availibity on those have been spotty at best. my sgs has 7828 sc 760 and h380 in stock. sgs has 7 lb 7828 on shelf.
i checked hogden site and only saw 1 load listed for7-08 with 168 hpbt.
my first question is has anyone used 7828 with 139-140 gr bullets. second of the 3 available witch one will work best in all three cals.

[Metal god]

I don't shoot either the calibers or use the powder but I'd say in general 7828 is slower then I'd likely try for mid weight bullets in those calibers . I'd likely try burn rates around IMR 4320 / 4350 , RL-17 & 19 , N550 somewhere in that range .

[huntinaz]

7828 is too slow for what you are doing which is why you can't find data.

[Unclenick]

Right. Too slow. A large percent will never burn and the portion that does will never reach normal peak pressure for the cartridge. QuickLOAD shows a 139 grain bullet in a case filled 100% under the bullet (not including the space taken up by the bullet) will only reach about half normal pressure and will throw almost a quarter of the powder out unburned. But that's theoretical. In practice, when powders are run this low they often experience erratic ignition and resulting velocity. Additionally, the pressure can fire the bullet forward then chase it with the plug of unburned powder which can slam into it in the bore and ring the barrel or worse. So it is at least a chance that it is actually dangerous to your gun's health.

[stillquietvoice]

thanks for the heads up i will keep looking for s suitable powder. just havent been able to locate any.

[Metal god]

U.N. that's interesting indeed . I've known of light for caliber bullets out running the slower powders and even the secondary pressure spikes

This is something you wrote a little while back in this thread
http://thefiringline.com/forums/show...ight=secondary

Originally Posted by Unclenick

My current working theory is that when the powder mass catches up with the bullet, the bullet is upset outward during the attempt at sudden momentum transfer. If that stretches the bore radially even a little it will greatly increase the apparent friction. At that point pressure will abruptly straighten and push forward on the bullet base and bore. There are a couple of kinds of elastic event you can imagine occurring from that. One would be like Al’s Mode 6 on the harmonics page linked to above. Looking at how a long barrel deflects in his rifle animation, you can imagine that something pulling the barrel straight would crack a deflecting muzzle like a whip, which would be the other form. The problem is, I would expect an elastic event like that to ring, and not just stop and be damped out, the way the spike is. Though, of course, the stock bedding may do some of that damping, as might the receiver mass. Still, I’d expect some amount of reflection and ringing.

When I read that with the rest of that thread . I have to say my mind was blown . The un-burned powder possibly slamming into the back of the bullet upsetting it is an amazing theory . I would love to see those additional test with more strain gauges through out the length of the barrel you talked about . I find this thought direction very interesting .

[T. O'Heir]

You able to find IMR4350? Been using it for eons with .243. Wide range of bullet weights in the 7mm. Not so wide in .30-06, but 150's and 168's are there.