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Posted: 1/17/2010 12:13:21 PM EDT
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Hey guys. Looking for a bit of help please.
I want to load some Sierra 168 grain HPBT Match King loads for my DPMS LR-308. I would like to use Varget powder. I consulted three loading manuals (Sierra, Lee, and Nosler) and the Hodgdon web site. I noticed a large difference between recommended loads. For example, Sierra has 38.7 to 43.5 grains; the Hodgdon web site has 42.0 to 46.0C. I am in the load development stage, and am wondering what extremes to use. Should I stick with Sierra to start, since they use less powder, or should I use what Hodgdon recommends? Thanks for any insight. Brad |
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Calculate the average maximum from all the sources you have.
Start 10% below that. Use 0.5 to 1 grain increments as you work back up to the effective maximum you calculated (the average). Look at the range of maximum loads from the manuals as the range of possibilities. That means the maximum load your gun will tolerate might be at the low end, it might be the largest maximum load you find, or somewhere in between. |
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Time out, the biggest basis of varying load charge weight variance is the cases used to develop the data. Interpolation of reloading data is foolish! Very Foolish! Look at Hodgdon data it was deveoloped with WW brass. Sierra with Federal brass. So, your best bet is to use data that is based on the BRASS you are going to load with reduction of 10 percent and work up.. As a side note In the 308 Federal brass sucks! Crappy case life as it is soft brass. Whereas, WW will give you much better case life.
But, if you are loading for a gas gun then your case life will be minimized due to the working of the brass with FL sizing. You may consider getting an Instant Indicator or RCBS precision Mic to set up your FL die to bump the shoulder just enough to allow reliable chambering of your brass. This will help increase case life. |
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Semi-auto rifles run better on mid-range load data. Virtually every manual uses bolt actions for their load development. Until recently (Sierra for .223 and Hornady .223 & .308) semi-auto shooters were left on their own to develop their loads. Hornady's Service Rifle data for .308 and their 168 grain bullet lists 42.7 grains of Varget as a maximum load. This was fired in a M1-A having a 22" barrel.Velocity was the fastest listed in their data @ 2600 fps. They used Hornady brass which I have no experience with. OAL was 2.80"
You didn't say how long your barrel is or if you own a chronograph. Reduce maximum velocity by at least 25 fps for every inch less in barrel length. 20" barrel would be 2550 fps. If your using military brass reduce this maximum by at least 1.0 full grain of powder, perhaps 1.5 grains. I use 41.0 grains of IMR-4064 in Lake City brass and 168 Sierras, or 40.5 grains of IMR-4895 with this bullet. My loads when placed in Sierras manual would line up with approximately 41.0 grains of Varget. I would try 39.5, 40.0, 40.5, 41.0 and 41.5* as the maximum from a semi-auto. Watch for pressure signs, shoot for the best grouping load. Sierra lists 43.5 grains of Varget and 2700 fps as their maximum from 26" bolt action rifle. *using military brass, Lake City or IMI. |
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Different bullet = different construction. Jacket thickness varies, as does core hardness. Obviously, a harder bullet is going to generate more pressure because it's more difficult to deform(in this case, being engraved by the rifling). A bullet with more bearing surface is going to generate more pressure because there is more surface area and thus more friction.
Sierra bullet = Sierra data. |
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Quoted:
Time out, the biggest basis of varying load charge weight variance is the cases used to develop the data. . Sorry, I do not agree with this statement. There are way to many variables to call any one component the culprit when it comes to variations in load data. Depending on the powder, lot to lot variation can be the largest factor, as can the type of rifle or test barrel used, the bearing surface of the bullets used, the list goes on. Lyman 48 lists, 168gr Sierra HPBT, Varget––41.0gr 2491fps 42200psi Max 45.7gr 2766fps 61100psi Sierra #5 lists, 168gr Sierra HPBT, Varget––38.7gr 2400fps Max 43.5gr 2700fps Hodgdon list, 168gr Sierra HPBT, Varget––42.0gr 2520fps 41200CUP Max 46gr 2731fps 50600CUP Different bullet. Speer #13 168gr Match HP Varget Start 42gr 2539fps Max 46gr 2751fps Nosler #6 168gr Bullets, Varget Start 42gr 2662fps Max 46gr 2820fps Putting all this together looks like Sierra is the odd man here. Looks to me as if a good Starting point would be 41gr and work up to 46gr. |
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Steve,
Now, if your assertion was aimed at the 223, I might agree. But. any rifle case bigger then the 223 family the reloader should pay attention to what the data source used to generate the data. Believe what you want but simply put case capacity with the bullet mentioned by the OP IS in effect the single most important factor. Why because that is what the reloader can control. Since the bullet is common place. The powder is named. Primers can be had. Now. a lot reloaders do not have a chrono. So, when the day is done KISS METHOD is something that is best applied to reloading. I would not want to try 46 gr of Varget in a Federal Case or LC brass topped off with a 168gr SMK. And, for that matter needing a trip to the gunsmith for the gun and a trip to the ER with the reloader. Then compounding it by the OP using it in a gas gun, well think what you want. But, it is best to keep things simple. Heck if I plucked the 46gr in my custom chambered 308 with WW brass I get all kinds of pressure. A friend of mine attended a shooting school last fall, a fellow student must have been a poor reloader.....cause his loads we locking up his gun. By his own admission he said he loaded them hot. Can you imagine having to pull 700 rds of 308, then compound it by messing up the class with his totally preventable problems? |
| Bottom line, it's your face. Be safe and start low, work up loads watching for pressure signs along the way. If you want to take chances with 50-60 K worth of pressure near your face then by all means, let me know so I can move away. Most of the time, my most accurate loads are middle of the road and don't reach anywhere near max. Start low and work up. |
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Sierra puts it this way and says it very well:
...reloading manuals are not carved in stone. Think of a reloading manual as a REPORT, and you'll be in a much better position to understand this. In essence, a reloading manual says, "We tried this particular component combination, and these are the results we obtained." When you duplicate the load shown in a manual, you're using a different rifle (even if it is the same make, model, and caliber), a different lot of powder (even if it is the same brand and type), a different lot of cases (even if they are from the same manufacturer, etc.), a different lot of, well... you get the idea. There is an amazing number of variables that effect any load combination. With the difference in the manuals, you're just seeing first hand examples. Again, start low and work your load up.
The averaging method that AeroE suggests is the best way to go for load development, and the way I do it as well. It has never put me in trouble yet. |
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Quoted:
Sierra puts it this way and says it very well: ...reloading manuals are not carved in stone. Think of a reloading manual as a REPORT, and you'll be in a much better position to understand this. In essence, a reloading manual says, "We tried this particular component combination, and these are the results we obtained." When you duplicate the load shown in a manual, you're using a different rifle (even if it is the same make, model, and caliber), a different lot of powder (even if it is the same brand and type), a different lot of cases (even if they are from the same manufacturer, etc.), a different lot of, well... you get the idea. There is an amazing number of variables that effect any load combination. With the difference in the manuals, you're just seeing first hand examples. Again, start low and work your load up.
The averaging method that AeroE suggests is the best way to go for load development, and the way I do it as well. It has never put me in trouble yet. That's the method you taught us. Before that, I generally used the largest load I found and then tip toed my way there. The problem with that is finding a start load with confidence. Averaging gives us a good place to start (the 10% down load) that is lower than every maximum load that I have checked, so that gives us some confidence that the start load will be safe. I think this provides a good balance of risk. +P loads present an additional complication. Try to find one in the Sierra data for .38 Special; standard pressure loads lap well over into the +P loads published by every other source. This entire thread comes down to this - we have to pay attention to the details, and then to the results. Maximum published loads may not cause a rifle to blow up, but they can wreck brass, pierce primers, and bind bolts in some rifles or environmental conditions. I'm tight, so I want to avoid the possibility of wrecking a rifle, I'm short of patience so I want to avoid other unnecessary aggravation, and I'm interested in accuracy first. |
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Thank you guys. I appreciate the help.
Some additional information: I have a 20" barrel on my LR-308. I will be using once fired Lake City Brass that has been full length sized and trimmed, and Winchester WLR primers. Tonight I will average out the max load from the four sources I have and reduce that by 10%. Since I am using military brass, do you think I should then subtract 1 grain to compensate for the thicker case? I do have a chronograph, so I will use that when I test fire my reloads this spring. Brad |
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I wouldn't reduce the 10% down load for the GI cases; the point of the "start low" exercise is to give us some head room to accommodate the differences in our components from those used in the load data. I also wouldn't load more than 5 at each of the load increments, or no more than you want to break down.
If any of the data has pressures listed, take a look at that, too, to get an idea of the approximate range your start load will fall. If it's low enough that a 6 or 8 thousand psi spike in pressure is still less than the maximum, I think that is a low risk start. If you're real spooky about pulling the trigger on your first reloads, load one or two or three 10% down from the lowest of the maximum charges to shoot first for confidence building. These will also serve to foul the barrel. Then go to the computed start load. We could start at the minimum charge weight listed in manuals, but an awful large lot of components are burned up before getting to the high speed loads we usually want. But there's nothing wrong with loading minimum charge weights to save on gunpowder or reduce recoil if it suits you. I loaded a bunch of .30-06 cartridges with 110 grain bullets and light charges in late December to make low recoil coyote loads. I may run them across a chronograph later, but I'm confident they are running around 3100 fps, and that will do. If my guess is off 100 or 150 fps, it just won't matter and they're a heck of a lot more pleasant to shoot than a full house load fer deer killin'. |
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Since you have a chronograph you are ahead of the game. This takes a lot of the guesstimation out of working up your load. Simply chronograph some factory .308 loads similar to what you want to load (like the Fed 168-gr GM) in your rifle and use that velocity as a benchmark.
As long as you are using a powder that is one that has a burning rate (not too fast) that makes it one of the popular 7.62/.308 powders - and Varget fits that category - and a bullet of same or close weight (listed together in the same section of the reloading manual) and somewhat similar construction - you can then shoot your workups over the chronograph and when you get within factory velocity specs, + or - 50 fps or so, then you can rest assured that your load is safe in your rifle. So using Varget + 168-gr Sierra MatchKing bullets would be a good start to matching Federal Gold Match ammo. So using your chronograph to establish a "benchmark" for velocity, in conjunction with sticking with load data in the various manuals, and good observation during the work-up process will allow you to find a safe factory pressure load for your rifle. 7.62 NATO is nice because it is not extra hot like 5.56 military ammo. This works because: "...next to real pressure equipment, a chronograph is the best guide to excessive pressure for the home handloader. There are no “magic barrels” that allow another 100 to 200 fps!" - Handloader, June 2004, “More Pressure Experiments” (Reading Chamber Pressure), John Barsness. "The best predictor of pressure is a chronograph. If you're getting muzzle velocities noticeably higher than is common for that cartridge, powder and bullet, then your pressures are higher than they should be. It's that simple. If you work up loads using that rule, then you don't need to look at fired cases, because the pressure will never get high enough to form ejector-hole marks on the case heads or blow primers." John Barsness - Ask the Gunwriters forum - www.24hourcampfire.com "Muzzle velocity for a selected load is a function of the mean effective pressure and the barrel length." - Lloyd E. Brownell, Ph.D. - Firearms Pressure Factors, Wolfe Publishing Co. "Think of the firearm as a single-stroke internal combustion engine with an expendable piston, the bullet. Everything else being equal, a certain average pressure will always produce the same velocity. This means that, everything else being equal, if the velocity changes so did the pressure..." - Handloader Magazine editor Dave Scovill. |
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