Surprised @ difference between Siera & Hodgdon loads for 168 SMK
- Thread starter Linko
- Start date
The book may be right but always work up to the first signs of pressure then back off. I would call Hodgdon tomorrow, they are very helpful and yes mistakes have been made over the years in printing. When in doubt call the manufacturer.
Well, if you stack all the tolerances in diametrically opposing directions then yes it can be as written. Just a simple diference of one fast lot and one slow lot. Add one tight barrel and one loose barrel, and there you go.
Shows the rational for starting low and working up. And it could be the tolerance of changing IMR and H on the print out.
I have 6 or 8 manuals, when I see this I start cross referencing. I have called the source too for confirmation of data. They tend to be very cooperative.
Shows the rational for starting low and working up. And it could be the tolerance of changing IMR and H on the print out.
I have 6 or 8 manuals, when I see this I start cross referencing. I have called the source too for confirmation of data. They tend to be very cooperative.
I have noticed Sierra has backed off a lot on some of their loads in the 6th edition manual compared to the 5th edition, especially in .223 bolt loads.
Fast14riot
Gold $$ Contributor
The difference between Sierra and Hodgdon with the 175smk, H4350 in 30-06 is even greater. Hodgdon starting load is above Sierra's max load.
old_heli_logger
Gold $$ Contributor
I always go with the bullet manufacturers data because they know best what their own bullets have for bearing surface and friction/drag. Start low and watch for pressure signs. Be careful
muleman69
USMC -1st marine Div. RVN
Let us no the results if you can as I'm going to the same powder and bullet. Thank you
+1 on this , some powder manufacturers data is very high.... Most actual manuals are conservative , some more than others but even they can have big differences in charges... This is why you can't have too many references , I just picked up the new Sierra manual myself... I don't have as many manuals as some but I still have 7 both new and very old...
lawyers versus handloaders
Putting differences in test barrels and powder lots aside that can see such variations, there is another factor dependent on how the data compiler lists loads. That is type a) where starting and maximum charge weights are shown, or type b) Hornady, Sierra, Speer where MVs are shown in columns, usually in 100 fps steps, sometimes in 50 fps for smaller cartridges, and the appropriate charge weight is shown underneath.
Both sets of providers load, shoot and measure pressures in a relatively small range of charge weight steps, this fed directly into a laptop or PC these days. The top charge will normally be be below peak allowed pressures. A charge weight v pressure graph is then drawn with the line falling between the points scatter (at one time manually now done by the software) which allows the maximum charge to be extrapolated to the point where the graph line says it produces maximum SAAMI pressure. (Or, of course whatever pressure level the powder / bullet company sets as its maximum which may be below SAAMI to give some safety factor.)
If a Type a) presentation, that value is quoted as is. In the case of Type b) (MV columns), the software produces a set of calculated charge weights that match those MVs used in the table. Maximum charge weight = that for the highest MV available within allowable pressures. If you look at these tables, the steps are usually constant give or take small variations. So in the case of Sierra (Edition V) data for 308 with the 168 SMK/H4895, it is in 1.3gn steps = 100 fps and the maximum quoted is 39.9gn for 2,600 fps MV, the next step would likely be 41.2gn for 2,700 fps. Now it may be that 39.9 exactly produces Sierra's chosen PMax, but the odds are against that. There is an equal chance that the graph says it is 41.1gn producing an estimated 2,692 fps (each tenth of a grain variation = 7.7 fps off the graph). Sierra can't quote that value as it doesn't match the fixed speed and it can't quote the marginally higher one that does as it'll be 'over-pressure'.
In this case, that still doesn't explain fully why the Sierra load is apparently low. I find the 1.3 gn steps surprisingly low after many, many years of loading 308 Win. A full grain change usually changes MV by ~60 fps in this cartridge / bullet weight in a 30-inch barrel, likely a little less in a shorter one, that is ~ 6 fps change per 0.1gn powder. One would therefore expect 1.6-1.7gn steps to be needed to achieve a 100 fps MV change.
There is another factor too that can affect loads manual maximum charges but which doesn't apply here as both Sierra and Hogdon quote charges for the 168gn MK on its own (in Sierra's Edition V anyway). Where there are lots of bullet models in a given weight (or a small weight range), the bullet manufacturer may lump them all together. Most will likely produce very similar pressures, but there may be one or two that produce significantly higher pressures than the others. For safety, that model or those models must be used by the data-set compiler thereby depressing the allowable maximum safe loads for other models that produce less pressure. The latest (10th edition) Hornady manual has tables for 10 different bullets in some weights in 0.308 calibre for instance.
Both sets of providers load, shoot and measure pressures in a relatively small range of charge weight steps, this fed directly into a laptop or PC these days. The top charge will normally be be below peak allowed pressures. A charge weight v pressure graph is then drawn with the line falling between the points scatter (at one time manually now done by the software) which allows the maximum charge to be extrapolated to the point where the graph line says it produces maximum SAAMI pressure. (Or, of course whatever pressure level the powder / bullet company sets as its maximum which may be below SAAMI to give some safety factor.)
If a Type a) presentation, that value is quoted as is. In the case of Type b) (MV columns), the software produces a set of calculated charge weights that match those MVs used in the table. Maximum charge weight = that for the highest MV available within allowable pressures. If you look at these tables, the steps are usually constant give or take small variations. So in the case of Sierra (Edition V) data for 308 with the 168 SMK/H4895, it is in 1.3gn steps = 100 fps and the maximum quoted is 39.9gn for 2,600 fps MV, the next step would likely be 41.2gn for 2,700 fps. Now it may be that 39.9 exactly produces Sierra's chosen PMax, but the odds are against that. There is an equal chance that the graph says it is 41.1gn producing an estimated 2,692 fps (each tenth of a grain variation = 7.7 fps off the graph). Sierra can't quote that value as it doesn't match the fixed speed and it can't quote the marginally higher one that does as it'll be 'over-pressure'.
In this case, that still doesn't explain fully why the Sierra load is apparently low. I find the 1.3 gn steps surprisingly low after many, many years of loading 308 Win. A full grain change usually changes MV by ~60 fps in this cartridge / bullet weight in a 30-inch barrel, likely a little less in a shorter one, that is ~ 6 fps change per 0.1gn powder. One would therefore expect 1.6-1.7gn steps to be needed to achieve a 100 fps MV change.
There is another factor too that can affect loads manual maximum charges but which doesn't apply here as both Sierra and Hogdon quote charges for the 168gn MK on its own (in Sierra's Edition V anyway). Where there are lots of bullet models in a given weight (or a small weight range), the bullet manufacturer may lump them all together. Most will likely produce very similar pressures, but there may be one or two that produce significantly higher pressures than the others. For safety, that model or those models must be used by the data-set compiler thereby depressing the allowable maximum safe loads for other models that produce less pressure. The latest (10th edition) Hornady manual has tables for 10 different bullets in some weights in 0.308 calibre for instance.
My brother in law has some old manuals '50s '60s and they all show higher powder charges. Still nothing wrong w/ stating low although I will admit I usually start at about halfway between low and high charges. I usually find something below max recommended but sometimes I do go over. of course looking for pressure signs along the way.
My take is Lawyers and product liability is definitely at play. Gary
My take is Lawyers and product liability is definitely at play. Gary
AckleymanII
Gold $$ Contributor
These people are not indicating what is safe in your rifle, they are saying what was safe in their test barrel, with their particular lot number of powder, etc. This is meant as a guide for your situation, ONLY! You have to watch your pressure signs and adjust accordingly.
Back then the bullet companies used case-head expansion measurement (with a blade form 0.0001" micrometer) to check on pressure effects. They'd usually take some factory rounds from Winchester/Remington, shoot them in their test barrels and take the case-head readings/measured expansion from the unfired state as a ceiling for case expansion in their fired handloaded cases. (Ken Waters used a modified version of this when working his Rifle / Handloader magazines' 'Pet Loads' up. This used growth in the diameter of the 'pressure ring on the lower case body just above the solid web and he again used readings from factory cartridges fired in the same chamber as his benchmark.)
When these companies were first able to invest in copper pellet crusher pressure-barrels like the big ammunition companies, government arsenals etc did, they reportedly got nasty shocks with the pressures some of their old top loads were producing. Some previous maximum loads were rumoured to have been reduced by a couple of grains or more in 308 and 30-06 size cartridges.
I once saw data for the 308 cartridge with 5 grains difference in max. Hard to believe.
Linko, I’m going to have to eat my words. I looked up your load in both Sierra manuals, and they have increased their max load with H4895 in the new sixth edition. It’s real close to Hodgdon specs, but you will have to check for yourself.
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