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Question on Different Powder Loads

P*per2000 said: I recently got a RCBS reloading kit as a gift, and it game with a Speer reloading manual. In the Speer reloading manual, it says that the minimum load for a .308 win using 180gr bullets and IMR 4320 powder is 40grains, and the maximum is 44grains. But I also have a Sierra reloading manual, and it gives the minimum load for the same setup as 37.5grains, and the maximum as 42.5grains. It's the exact same case, same powder, and virtually identical bullets (both 180grain boat-tails), yet quite different loads. Why the big difference? Does the manufacturer of the bullet really make that big of a change?

Sc*r270 said: In some cases I believe it can, I know Barnes seems to be able to push their bullets faster then standard bullets. Also depends on the individual pressure gun each company had when doing the data, which lot of powder, which lot of primers etc. There are so many variables, that is why load manuals tell you to start at the min and work up, because a max load in their pressure gun may be over max in your individual gun, they also say to do the same thing when getting a new lot of powder.

Sc*tt_N said: You're being wise to cross reference your data for safety reasons. A 3rd manual, or comparing to published data on the Internet would not be a bad idea at all.

P*per2000 said: You're being wise to cross reference your data for safety reasons. A 3rd manual, or comparing to published data on the Internet would not be a bad idea at all. Ironically, it's this very site that led me to buy a second manual. I've read a couple of times people saying to purchase multiple manuals.

t-st*r said: and my old speer 11 says a top end of 43 grains- so go figure- bottom line is that you HAVE to build up until you see pressure sgns

G*nderite said: Pressure varies dramatically between guns. Remingtons, for example, have chambers designed by their liability lawyers. Very deep throats reduce pressure. The reverse is true. Some rifles have tighter necks, shorter throats and build pressure faster. The Max in the book does not mean you can load that much powder. It means what THEY could load. Your rifle might have a max of 5 grains more or less. I recall a Start load in a 6.5x55 that had to have the bolt pounded open in one rifle, but was slick as snot in another. When the book says start low and work up, it means it. What I do with a new powder or rifle is load 3 or 5 of each in .5 gr increments and go to the rnage and shoot them for group, knowing that I may have to stop before I shoot them all and bring the over-loaded ones home. Then I have a good idea where to do some load development.

gps said: You're being wise to cross reference your data for safety reasons. Agreed. When confronted with the choice between taking a chance and simply dropping $20-$30 on a manual to know for sure, the choice is clear and it's cheap insurance. Lots of interesting reading too... In emailing a couple of bullet manufacturers for data and info, I found them to be very helpful and quick to respond.

g*nlaker said: It's the exact same case, same powder, and virtually identical bullets (both 180grain boat-tails), yet quite different loads. Why the big difference? Does the manufacturer of the bullet really make that big of a change? The differences can come from differences in test equipment and procedures used in each case. But there can definitely be a difference in pressures from bullets that appear very similar to the eye and have the same weight. These differences are due to bearing surface area of the bullet, slight differences in nose profile, jacket material, and possibly more. Also there is a variation between lots of powder, just to make the situation more tricky. Pretty much like everyone says: start from the bottom and work up slowly. :D Chris.

L*fty Dick said: Go read the part in the Speer manual about "why ballisticians get grey hair" So many variables enter into the equation that any one or 6 things could effect the outcome. And on IMR4320, IMR lost the original recipie a while back, so the burn rate has changed in the newer lots, more so than is normal than say lot to lot in other powders.

s*nior said: There's also the fact that for legality's sake with newer manuals, the less close to Max the companys are willing to publish.

CR*WCA said: Max speed does not necessarily mean most accurate!!!!!

gps said: There's also the fact that for legality's sake with newer manuals, the less close to Max the companys are willing to publish. Interestingly, the Lyman 49th edition specifically addresses this AND denies it. They claim the max data to be the real deal. They also make it clear, in less-than-politically-correct terms that if you're not the sort to follow instructions exactly, then reloading is not for you. LOL!

s*nray said: "...the less close to Max the companys are willing to publish..." Nope. Like gunlaker says, it has to do with test conditions on the day of the test. Follow your manual religiously. Barnes bullets are solid copper. They need Barnes data. They can be driven a bit faster because there's nothing to separate or break up. No jacket to come off at excess speeds. Pressures are far more important than velocity anyway.

d*wnwindtracker2 said: I don't buy the lawyerproofing,until the strain gauges,all the bullet companies had were the inexact CUP pressure barrels and if they didn't have them for those rifle looney cartridges,they did by the seat of the pants,like you and me.Now anyone can glue a strain gauge on a rifle and be your own more accurate ballistics lab.The new data reflects the new accuracy. 180 cup and core bullets like Speer and Sierra are fairly interchangeable in a 30-06,even the Partion,which surprised me,but not copper clad like Swifts , solid like Barnes ,or semi-solid like Trophy-Bonded.They all will increase pressures. I got this from a ballistian testing with his Ohler 43. Of course if your're walking on the edge,any misstep and you are over. Burn rates vary with Lot#. Rifles also vary,sometimes even in common as dirt 308s.

22t*45 said: Once I got confident with my chrony, I trust the manuals less. I almost never get advertised velocity from a load. I am too cheap to work at max pressure, and wreck all my brass, so I load up until I see pressure signs, then back off 150 fps or so. This seems to be enough to reduce the pressure enough to make the brass last, and some times it exceeds the manual predicted velocity, and sometimes it is less. I shoot my 7 rem mag at 3000 fps with 175 grain Speer Mag Tips,(with a 22 inch barrel) and my 300 win mag at 2900 with 200 grain Speer Grand Slams. I have other rifles that the velocities do not impress.. But, as almost every reloading writer has said, 200 fps extra or less was not the difference between sucess and failure.