Sierra Load Data -- What gives?

1. Different bullets can have different profiles, which can lead to different amounts of case being used or left free.

2. Check the OAL - Sierra (or their bullet profile) may have their OAL different.

3. Different test equipment or methods can produce different results.

4. Except for certain powders that are hard to ignite or otherwise sensitive to light loads, most listed "start loads" are just their measured max, minus 10%... not necessarily a true minimum.

That's what they came up with for data with that powder and THEIR BULLET. I've been in the ballistics lab at Sierra Bullets, and if that's what they say is the minimum and maximum for their bullet, then that's what I would pretty much stick to, since they extensively test with pressure barrels.

The bearing surface of the individual bullet has a huge impact on friction, which in turn has a huge impact on pressure, which dictates the powder charge. If in doubt, you can always call the techs at Sierra.

Hope this helps.

Fred

Don't really know why, but with all the many variables involved in the process I do understand it is there.
Having all those books is good. You were able to cross reference and see a discrepancy . What I usually do is average them out, take all the minimum charges add them up and use the average, do the same with maximum .
Then I take an average of minimum and maximum and start in the middle range of the loads.
May not be scientific , but you have to start somewhere and being in the middle is a good place to start.
Gary

Each has there own data. Their powder, their gun, etc. Hornady book has a very low range for their 178 bthp with varget. This is why we start low and test. We make ladder loads and chrono them. With my gun. my powder, my primer, I found Hornady to be way off. Hodgdon to be better load than what Hornady loads state. So as I said before, look at more than one book, check other people you know and their load data, then START LOW AND WORK YOUR WAY UP!

Maybe it's because I'm new to reloading and take a cautious and conservative approach, but if I'm using Sierra bullets I'm using their book and their load data. Same/same with the other bullet brands

If I run into a situation in which 3 or 4 different sources are all vastly different regarding start and max, I then average the min and max, thus developing a table of sorts to work with.

OTOH, and in your particular case, you've found that all but one source has the same table, with the only exception being the bullet manufacturer. In this case, I would be inclined to use the bullet manufacturer's start charge, then work up while assessing pressures as you go up.

In actuality, this is nothing unusual in the world of reloading, and it only reinforces the proper approach to load development, that being to start with a safe practical charge, then work up. Nothing is particularly perplexing about this circumstance, it's quite common.

I generally start my bottle neck developments at mid table, or just under mid table anyway, so I see no real risk in using any of those tables.

GS

I don't think Sierra has ever used SAAMI spec pressure/velocity barrels to develop reloading data. All I've seen in their published data are firearms. Sometimes commercial ones and occasionally custom ones. Their current .308 load data lists a Savage 12VSS rifle with a 26" barrel and 1:10 twist. I've an older manual that lists a Winchester 70 match rifle with a 26" barrel with a 1:12 twist. Their first manual with .308 Win. data used a Winchester 70 sporting rifle with a 22" barrel; if memory serves me right talking with their ballistics man who did it working there back in the '60's.

They've traditionally used rail guns testing for accuracy to eliminate all the rifle and human variables for quality control. People touring their plant often mistake them for pressure test barrels. The loads for each bullet listed as most accurate is proved so across several rifles.

Sierra has typically been conservative in their load data. They use the same thing most other data's derived from. Visual inspection of cartridge cases and primers and their opinion of what it shows. Here's their data from the 5th edition of their manual:

http://www.6mmbr.citymaker.com/f/Sierra308Win.pdf

It lists 43 grains of Varget as max under their 165. "Starting" load is 38.5. Current Sierra Infinity software lists that same rifle with 43 grains of Varget as max for their 165. Same software lists their 168-gr. HPMK maxed out with 43.5 grains of Varget and their 175 HPMK and all their 180's with 41.7 grains of Varget.

A given load will easily produce a 100 fps spread in average muzzle velocity across several barrels. That means its peak pressure is also not the same across all of them. And visual inspections of what shows excessive pressure varies across several humans. I've shot 7.62 NATO arsenal proof loads in military rifles whose fired cases and primers looked "a little warm but still OK" to several people. Go figure that out as they were spec'd at 67,500 cup and normal service load max spec was 50,000 cup.

But all that's someone's maximum load. Some use standards and others a wild guess. There are no standards for establishing a starting load. What some actually starts with may well be lower than what they publish as a starting load. Oft times, a 10% reduction of what the maximum load is used.

With all the .308 barrels having different internal dimensions plus the variables across all lots of powder and primers, it's only normal to see a wide range of starting and maximum load data.

46 gr of Varget and 165/168 gr bullets from Sierra, Nosler, Berger, and Hornady have all given me good results with no pressure signs. The velocity according to my chronograph has been right where I expected it to be. Speer bullets have a reputation for more pressure so I didn't try max loads when using those bullets. Federal brass has the same reputation so I never tried max loads when using Federal brass.

I'd start low and see what happens. I'm betting you can safely use 46 gr, or very close to it. But you never know with individual rifles. It has never been an issue in any of mine.

The Lee book states a starting load of 42 gr. and maximum of 46 gr. for jacketed 165 gr. bullets.

Click to expand...

First, Lee doesn't do their own load testing; all Lee's loads come from other's published load data. Second, in the case of of the 46.0gr load of Varget, if you go to the original source, you will find that the load was developed with Winchester brass. Winchester brass is the lightest and has the most case capacity of commonly available .308 brass. Using this maximum load with other brass is asking for trouble. There is a wide variance in case capacity with .308/7.62x51 brass, moreso than any other cartridge that I know of, so attention must be paid to that fact.

Don

Delete

"...That's what they came up with for data with that powder and THEIR BULLET..." Yep And using the firearm/universal receiver THEY used in their testing.
You do not need data that is manufacturer specific.
"...you will find that the load was developed with..." And a 24" barrel with 1 in 12 rifling.

As said it's about the brass used and other components. Cases vary by each manufacturer so pay attention to which case was used in the load.

I've also found Varget to have some big differences lot to lot. My current lot needs almost 2.0 gr more powder to produce velocities the same as the last lot that I used.

Start low and work up in your rifle. Different brass, bullets chambers all affect pressure limits. Be safe.

When in doubt, start with the lowest starting load. No down side, no problems. If this load doesn't do it for you, add a bit more powder. I sincerely doubt if any game can tell the difference a few hundred fps makes as long as the load is accurate.

I agree that reloading manuals don't match exactly for many reasons (toss the Lee ), mainly because they don't use the exact same components and/or equipment.

It is generally the best to use data developed by the bullet manufacturer as the design of the bullet has a significant impact on the pressure developed. Even using the Lee or other data that lists a heavier powder charge as maximum you would start at a safe level that fits the Sierra data IF you use normal and prudent load development procedures reducing the max load by 10% and working up. Likely you would find pressure signs or loss in accuracy would appear as you approach the maximum load listed by Sierra.