Loading .308 with 748. Books vs Quickload

[DRNewcomb]

I'm looking through my available powders for one that will safely push a Sierra 169 at 2750 fps out of a .308. Looking at my old Sierra manual (2nd ed) it shows a max load of 48.6 gn of 748 yielding a MV of 2800 fps with a 168 gn MK. Looking at a similar vintage Winchester manual and interpolating between listed bullet weights, I get a charge of ~ 47.5 gn

When I plug the same loads into Quickload, it shows peak pressures of 73 kpsi, (11 kpsi over max) and 68.3 kpsi (6.3 kpsi over max)!

This seems like a considerable discrepancy and more than I've seen with other powders. At least when I compare the Sierra manaul with QL using IMR powders, I don't see any dangerous overpressure conditions.

My can of 748 is probably 1990s vintage (The price tag says $13.75), So, the powder reasonably matches the date of the manual.

Is 748 different today? Does QL do better with some powders than others?

 

[6bra1k]

its why it is called LOAD DEVELOPMENT.
neither are bibles..they are tools, only as good as the user
start low and work up..nothing has changed
take notes..then the next time you will have a closer starting point

 

[Hoot]

Though is is not vast, my experience with QL has been that it tends to overestimate pressure and velocity for Winchester powders. Don't ask me why and no I haven't used every Winchester powder that it supports. That having been said, don't do anything foolish. Always start low and work up.

Hoot

 

[CJ6]

You'll like 748...Just work it up.

 

[GLO123]

Just picked up a pound of 748 last week for $36.00. Looking forward to working up a load for Nosler 125gr ballistic tips in my .308. My advice is to start low on your Sierra book load specs and work up.

 

[Straightshooter1]

I'm looking through my available powders for one that will safely push a Sierra 169 at 2750 fps out of a .308. Looking at my old Sierra manual (2nd ed) it shows a max load of 48.6 gn of 748 yielding a MV of 2800 fps with a 168 gn MK. Looking at a similar vintage Winchester manual and interpolating between listed bullet weights, I get a charge of ~ 47.5 gn

When I plug the same loads into Quickload, it shows peak pressures of 73 kpsi, (11 kpsi over max) and 68.3 kpsi (6.3 kpsi over max)!

This seems like a considerable discrepancy and more than I've seen with other powders. At least when I compare the Sierra manaul with QL using IMR powders, I don't see any dangerous overpressure conditions.

My can of 748 is probably 1990s vintage (The price tag says $13.75), So, the powder reasonably matches the date of the manual.

Is 748 different today? Does QL do better with some powders than others?

The formula for 749 is probably not much different today than it was, if at all. But, I wouldn't be surprised in the least if you found the moisture content of that old batch to be a lot less than the current ones. A powder's burn rate can dramatically increase when when it looses a lot of its moisture content or the burn rate can slow down a lot if the powder absorbs a lot of moisture.

 

[ScottMcc]

My particular rem 700/308/5R rifle produces max load velocities with book starting loads. Quickload has been consistently way off, both in predicting much lower velocities and in saying the velocities I am getting are crazy-overpressure loads. With cfe-223, I break 3,000 fps easily on my Labradar with 150gr hornady fmj bullets and 47.5 grains cfe223 in lake city 2014 nato brass. Quickload says that load should only go 2,700. Yet 47.5 gr is less than anyone's starting load, plus I have no hard bolt lift or flattened primers.

 

[Ned Ludd]

I'd suggest starting with the more conservative of the two published starting loads. Load a few rounds, get an average velocity, then plug all the pertinent inputs back into QL and adjust burn rate (Ba) until predicted velocity exactly matches measured velocity. That will safely tell you exactly where you are with your specific reloading components, Anything else will be at least partly, if not totally, a guess.

 

[Jager]

Sierra's current manual (6th Ed) lists 45.9/W748 as their max load, at 2780 fps. If you plug that into QuickLoad, using QL defaults, you'll find that load just a bit under SAAMI max.

Berger, for their 168gr .308 bullet, lists 43.5/W748, making 2744 fps, as their max.

So the three modern sources line up pretty well with each other with respect to a 168gr bullet, using W748, in a .308. I'd suggest that it's the Sierra 2nd Ed data that is the outlier.

No, W748 hasn't changed, beyond the usual lot-to-lot variation that we've always seen. But ballistics labs have much better tools and procedures today and ought be viewed as a more definitive source than their earlier counterparts.

I would do exactly what @Ned Ludd suggests... load up three rounds using a very conservative load (Sierra 6th Ed lists 40.0/W748 as their starting load, and I'd just go with that). Put those three rounds in front of a good chronograph. Take their average, plug that into QuickLoad, along with the average of the actual measured water capacity of those three pieces of brass. Adjust the burn rate in QL to match the velocity you saw. That's your first baseline and should put you very close to the actual pressure your rifle is making.

QuickLoad is a linear model, so as you move from there to an increasingly heavy load you'll begin to see QL's numbers deviate. The more steps in your ladder, the more deviation. I usually recommend adjusting Ba one more time as, or after, you've dialed into whatever maximum load you settle on (I'm much more concerned with what pressures I'm running at max than what my starting load is).

Let us know how that 169gr bullet shoots.

 

[DRNewcomb]

Thanks to everyone who replied. I do approach load development fairly conservatively. My major concern was with the difference between QL and my loading manuals when using 748 vs the agreement I saw with IMR powders. When one source says 45 grains is a safe starting load and another says it's nearing maximum, I get a little concerned.

 

[SKWERLZ]

Thanks to everyone who replied. I do approach load development fairly conservatively. My major concern was with the difference between QL and my loading manuals when using 748 vs the agreement I saw with IMR powders. When one source says 45 grains is a safe starting load and another says it's nearing maximum, I get a little concerned.

Different barrels and brass factor in loading manual differences as well.

W748 is a pretty decent powder, love it for pew pew 223 loads and launching 69SMK’s

 

[littlebuddybr]

Just picked up a pound of 748 last week for $36.00. Looking forward to working up a load for Nosler 125gr ballistic tips in my .308. My advice is to start low on your Sierra book load specs and work up.

I used to shoot 748 with 125 gr ballistic tips. It would shoot extremely well.

The 125gr s.m.k. shot very good also.

 

[r bose]

QL uses lots of different parameters to give outcomes. Seating depth and case capacity measured in H20 will give the biggest differences in overall pressure developed in a load. 308 brass can be all over the place. Win brass MUCH lighter/more capacity than militaryIMI/Lapua. Measure carefully. BTW primers will make a difference too!! Almost impossible to get "the load" out of a manual. It's just a guide, like others said work up.

 

[Catfur]

Every barrel is different, every chamber is different, primers can differ quite a bit, case capacity as well, and powder can vary dramatically from lot to lot.

Oh, and all the tiny details of every different bullet matter too, there is no such thing in reality as a generic 169gr bullet.

 

[Zero333]

I use lots of w-748 for 308win and 223rem. I say today's lots of w-748 are pretty close to Quickload. No idea about w-748 from the 90's.

I use a mild load for a M1A with 168 amax., 42.5 gr w748, FC brass. 2.770" from 18.5" barrel, I get right arund 2,550 fps in the hot humid summer and 2,467 in the freezing winter from a 18.5" barrel. QL estimates my load to move at 2,501 fps and 51,872 psi