Differences between loading manuals data. for .308 Win

Jleote · January 8, 2013, 08:21 PM

My search turned up nothing so I'm probably asking a n00b question.

I've looked at several different guides for reloading (powder) specs and get different answers.

Im using my own once shot brass.
IMR 4320 Powder
Hornady A-Max 168gr Bullets.

Closest I can find in the Lyman book is 168gr HPBT they say 42.0 start to 45gr max

Sierra book for a 168gr HPBT says 39.6 - 43.1gr.

I called Hornady today and they are saying 33.9 - 42.2gr

I've been loading to 42.2gr for the last 300 rounds.

I should be listening to hornady right? They would know best for their rounds I would assume.

I've recently had a FTE because of a sheared extractor lip on my LR-308. I wonder if its due to the fact I'm at the high limit of the load according to hornady.

SMH.

Jerry45 · January 8, 2013, 08:58 PM

You should listen to your rifle. Start low and increase powder charge until you find what gives you the best groups OR you start seeing signs of overpressure. If you've been loading 42.2 and there are no sines of overpressure than drop down and work up to at least to that. If your groups don't tighten up to your liking start loading up in increments of 0.2 gr. until they tighten up or you see signs of pressure.

My 308 likes a couple of grans below max. My .223 likes 0.5 under recommended max. It showed no signs of over pressure at max but I couldn't fit any more powder in the case.

Jleote · January 8, 2013, 11:07 PM

Grouping with my loads is actually really good. Dont see much of a difference between them and factory 168gr ammo at 100 yards actually.

No signs of over pressure at all either.

I'm waiting for my replacement Extractor to come from DPMS then ill head back with some less hot loads and see I guess.

Bart B. · January 9, 2013, 06:53 AM

Visible pressure signs are not a good way to judge pressure. Softer brass will show "visible" signs long before hard brass does for a given amount of peak pressure.

And starting low then working up a few tenths of a grain at a time may not show any improvement in accuracy. Especially at ranges of 300 yards and less. I've worn out several .308 Win. barrels and they all shot the same level of accuracy through 300 yards with 41 through 44 grains of IMR4064 across 3 or 4 different case makes using 168 grain bullets.

IMR4320 is probably a bit slow for best performance with 168's in a .308 case. Varget and IMR4064 have an excellent track record as does IMR4895 in 7.62 NATO match ammo.

The main reason there's a spread in charge weights for a given cartridge and bullet weight is different places use different test standards and have different objectives in developing a load. Few, if any, of them state these conditions in their load data. And your barrel as well as the powder, primer and cases is not exactly the same as what they use. Therefore, it's very normal to see a few grains difference in starting and maximum charge weights. Expect your load that matches one of theirs to have a different performance level than they loading data folks got. They may well have different ways of testing for accuracy than you use, too.

Jleote · January 9, 2013, 09:49 AM

Ty for all of that info. I really appreciate it.

January 8, 2013, 08:21 PM	#1
Jleote Junior Member Join Date: January 7, 2013 Posts: 5	Differences between loading manuals data. for .308 Win My search turned up nothing so I'm probably asking a n00b question. I've looked at several different guides for reloading (powder) specs and get different answers. Im using my own once shot brass. IMR 4320 Powder Hornady A-Max 168gr Bullets. Closest I can find in the Lyman book is 168gr HPBT they say 42.0 start to 45gr max Sierra book for a 168gr HPBT says 39.6 - 43.1gr. I called Hornady today and they are saying 33.9 - 42.2gr I've been loading to 42.2gr for the last 300 rounds. I should be listening to hornady right? They would know best for their rounds I would assume. I've recently had a FTE because of a sheared extractor lip on my LR-308. I wonder if its due to the fact I'm at the high limit of the load according to hornady. SMH.

January 8, 2013, 08:58 PM	#2
Jerry45 Senior Member Join Date: April 18, 2000 Location: Metairie, Louisiana Posts: 890	You should listen to your rifle. Start low and increase powder charge until you find what gives you the best groups OR you start seeing signs of overpressure. If you've been loading 42.2 and there are no sines of overpressure than drop down and work up to at least to that. If your groups don't tighten up to your liking start loading up in increments of 0.2 gr. until they tighten up or you see signs of pressure. My 308 likes a couple of grans below max. My .223 likes 0.5 under recommended max. It showed no signs of over pressure at max but I couldn't fit any more powder in the case. __________________ Guns are not dangerous! People are! RKBA! Last edited by Jerry45; January 8, 2013 at 11:51 PM.

January 9, 2013, 06:53 AM	#4
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Visible pressure signs are not a good way to judge pressure. Softer brass will show "visible" signs long before hard brass does for a given amount of peak pressure. And starting low then working up a few tenths of a grain at a time may not show any improvement in accuracy. Especially at ranges of 300 yards and less. I've worn out several .308 Win. barrels and they all shot the same level of accuracy through 300 yards with 41 through 44 grains of IMR4064 across 3 or 4 different case makes using 168 grain bullets. IMR4320 is probably a bit slow for best performance with 168's in a .308 case. Varget and IMR4064 have an excellent track record as does IMR4895 in 7.62 NATO match ammo. The main reason there's a spread in charge weights for a given cartridge and bullet weight is different places use different test standards and have different objectives in developing a load. Few, if any, of them state these conditions in their load data. And your barrel as well as the powder, primer and cases is not exactly the same as what they use. Therefore, it's very normal to see a few grains difference in starting and maximum charge weights. Expect your load that matches one of theirs to have a different performance level than they loading data folks got. They may well have different ways of testing for accuracy than you use, too. Last edited by Bart B.; January 9, 2013 at 07:40 AM.

January 8, 2013, 11:07 PM	#3
Jleote Junior Member Join Date: January 7, 2013 Posts: 5	Grouping with my loads is actually really good. Dont see much of a difference between them and factory 168gr ammo at 100 yards actually. No signs of over pressure at all either. I'm waiting for my replacement Extractor to come from DPMS then ill head back with some less hot loads and see I guess.

January 9, 2013, 09:49 AM	#5
Jleote Junior Member Join Date: January 7, 2013 Posts: 5	Ty for all of that info. I really appreciate it.