View Single Post
Old January 9, 2010, 03:02 PM   #7
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 18,098
It's more that a slow powder performs better with a heavier bullet. Hard to ignite powders, like spherical propellants, burn more completely with a heavier bullet, too.

All powders need enough pressure to burn completely. A light bullet can be too easy to push down the bore, offering too little of Isaac Newton's "equal and opposite reaction" force for a slower powder to build pressure against. Using a faster powder builds pressure against that low resistance faster. In effect, the powder burn has to keep up with the bullet going down the bore faster. As the bullet goes down the bore, the total volume the powder burns in gets bigger. That's because the volume of the bore behind the bullet is being added to what was already in the chamber. That works to reduce pressure. That additional bore volume is what is meant by the term "expansion" in internal ballistics. The ratio of the volume behind the bullet in a case expanded to fill the chamber, to that same volume with the volume of the whole bore added to it at the moment the bullet is about to exit the muzzle, is called the expansion ratio of the gun.

For 150's, IMR4064 is a powder that does well, as it has enough bulk to fill the case well at reasonable charge levels. Hodgdon gives 47 grains to start and 51 grains maximum with the 150 grain Nosler in a Winchester case using Winchester WLR primer and seated to 3.250" length. The Hornady 150 grain BT FMJ seats to 3.185" COL with the cannelure lined up with the case mouth of a case trimmed to 2.484", and in Lake City cases with Federal 210 primers, I found 48.5 grains of IMR4064 to be about the best load out of my Springfield and Garand, both with that bullet at that COL. Your SST seats a little longer to 3.230" and a little deeper, according to Hornady's manual, and in QuickLOAD if you knock 0.4 grains of my load, performance should match. So 48.1 grains of IMR4064 in Lake City cases.

Hodgdon also lists BL-C(2), but 49 grains is the starting load and 54 grains is maximum. Since you are under that range, you probably don't have enough pressure to burn the powder completely. Ball powders also, in my experience, benefit from deburring case flash holes to help with ignition. They also benefit from using magnum primers to help with ignition. If you don't want to change powder, I would at least get some magnum primers to try, if you haven't done that already, and move the charge up. If I use QuickLOAD to look at the barrel times, it appears to me it will take about 51.3 grains of BL-C(2) to match the 4064 load I gave for the SST. It won't be as consistent because it fills the case about 81%, where the IMR4064 load is closer to 90%, which will reduce MV ES. If you go to the magnum primer, you may have to reduce it as much as 5% to get the performance match, but there is no way to know until you try?

But again, that is in Lake City cases. They come out of my Springfield's chamber with 69.2 grains as-fired case water capacity on average, when trimmed to 2.484" before firing. I don't know what brass you're using? Remington cases I got in the past used to match the Lake City volume pretty closely in my guns, but I haven't measured them for a number of years. The rule of thumb for rifle powders in the load density range we are using is going to be to raise the charge 0.5 grains for each additional grain of case water capacity you have available in a fired case, and vice versa.

IMR4064 will also work very well, perhaps even best, with your 165 grain bullet if you decide to get some? Match rifle and Garand shooters have favored IMR4064 with 168 grain Sierra MatchKings in the .30-06 for decades now.

Attached is Hodgdon's 150 grain bullet data.
Attached Files
File Type: pdf Hodgdon Powder Company 30-06 150 gr. only.pdf (77.3 KB, 19 views)
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle

Last edited by Unclenick; January 9, 2010 at 03:11 PM.
Unclenick is offline  
 
Page generated in 0.04409 seconds with 9 queries