So, I’m loading some test groups for my 7-08 AR with Sierra bullets and have found substantial differences between Sierra’s 6th edition manual, and Hodgdon’s data for the 130 grain Matchking. Sierra’s max load is 50.3 grains of 760/H414, while Hodgdon has a max of 47. I can’t even fit 50 grains in the case and have enough room to fit the bullet. Neither are my starting charge, but I don’t understand where Sierra got that number.

Lawyers are more involved now days. New data publishes lower charges.

Not a hard rule, but very common.

I'm sure Sierra's load data is for a bolt gun not a gas gun.

The total case capacity is still the same. 760/414 is a ball powder so there wouldn’t really be any compression possible. 49 grains filled up the case and the neck. I don’t see how someone could seat a bullet.

because you forgot to read the introduction

They list based on the variables at hand

and the numbers are only safe suggestions
to begin with.

take a number below max and work your way
up.. measure along the way. That's your
variables

I understand how to safely reload. What I’m asking is how could they suggest a load that completely fills a case and leaves no room to seat a bullet.

I’ve also noticed guns react differently to the same charge. The 7-08 AR I gave my brother handles H4895 just fine, including the max. Mine gets pressure signs before getting within a grain of max. Interesting things.

All i can say is not all brass has the same capacity.

I have never tried to, but I have never thought or read you couldn't compress ball powder.

I’ve certainly heard of different capacities for brass, but didn’t think it could be that much. I don’t think there’s the gaps with ball powder as opposed to stick that you could crunch down. This particular weapon is very sensitive to 760/414 and H4895 so I’m not about to push the envelope by compressing.

Ball powders can be compressed some, look at Hodgdons precautions about H110 that many manuals do not seem to have read about reduced loads. Some of the variation between sources is the chambers used in the riles used for testing, some use a minimum dimension chamber, lands and grooves and in such a barrel you will max out at less powder than in almost all factory chambers or especially a max size chamber and barrel. Brass can make a big difference as well, some brass is heavier than others and capacity varies brass lot to brass lot and even more between manufactures. Compare LC brass to Winchester brass sometime for your 308/7.62X51 to see some difference. Then there is the lawyer factor.

Todays pressure measuring equipment is a lot different than what was used in the past and probably more accurate. '

Just a few reasons that they differ, I have seen some loads for the 308 for M1A and LC Brass that like the example are several grains different.

When I started loading for the 7mm-08 with 140gr bullets I had data that max was listed at 48gr of IMR 4350, Now that is 46 in most manuals. 38 was a compressed load even after settling the powder holding it against the vibrator tumbler.

I have an old Speer Manual that's very liberal on their Max. loads. Up to 4 grains.

when i use to load for the 7-08 nosler list 51gr max in win 760 for a 120 gr bullet> i loaded them at 50.5 gr and is considered a compressed load. it shot very well with that load

I guess it really is one manufacturer playing it more safe than the other. Tried both maxes for Sierra and Hodgdon with only the tiniest ejector swipe on one max combo. I did resign myself to that fact this AR-10 is only a .5 moa rifle with my hand loads. Was hoping to get 1/4 moa at least. Still not bad though.

This is why I laugh and shake my head when the reloading Nazis scream to always use the manual.

I usually load up till I see small signs of pressure then back off a grain or two.

Variation is the reason for the variation... wait what????

All chambers, barrels, rifles are different, all brass is different, all primers are different, powder even of the same brand and type from lot to lot is different. Loads are developed with different environmental conditions etc. and change goes on.

Tenyearsgone, get a piece of Lapua, Norma, and Winchester brass. Weigh each and record. Fill each with powder. Tap on it some to settle the powder and fill it on up. Weigh each again. You will see quite a difference in case capacity. Some max loads are compressed loads. Nosler lists % case fill in their manual. I took a quick look at their 7-08 data. Some max published charges are listed @ 110%. So a drop tube, and some type of mechanical vibration to settle the powder to shoehorn it all in the case would be required. Seating a bullet would result in a heavily compressed powder charge. I have read on this site where some may advise against a compressed charge. Conventional wisdom is case fill to the bottom of the neck is ideal. Sometimes heavily compressed loads, requiring a crimp to maintain consistent COAL shoot quite well though.

Edit to add: wide disparity between manuals is common place. Many handloaders, myself included, recommend cross referencing multiple data sets before starting a new work up, especially with new components. Hence the advice to always start low and work up.

Thanks for taking time to explain it in detail. I found a bunch of new brass for this rifle so inconsistent filling won't be an issue. I'm starting to compare my velocity numbers with different manuals to see if it's too much for my rifle. My 160 grain load set at Hodgdon's max of 40.3 CFE 223 is already faster than their test done in a barrel 4 inches longer than mine. I also got some minor uneven primer cratering so the Sierra max of about 2 grains higher won't be used.