I just chrono'ed a .556 load using 27.6 grains of win 748 behind a 55 gr fmj. I averaged 2994 fps with a sd of 27. Accuracy was good and I'm overall happy with the load. It was around 10 degrees Fahrenheit out. I know that win 748 is temp sensitive. My question is how much more velocity should i expect during summer in say 80 degree weather? I have little experience with ball powders and don't know how extreme temp sensitivity can be. Also is this something that quickload can accurately predict? Thanks in advance!
Win 748 temp sensitivity question
- Thread starter kris6600
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Some data sources list up to 27.7 grains of Win 748 with 55 grain bullets. I believe this is higher than should be loaded even in AR's and especially in bolt rifles. My loads at 27.7 were ok in AR's at mild or cold temperatures but showed pressure signs at 90 degrees and higher. Letting a round soak in a hot chamber long enough to transfer the heat to the loaded round also showed pressure signs. At 95 degrees in my one bolt rifle showed scary high pressure signs. Letting rounds sit in the sun and getting hot also is bad. All this just to say that I do believe Win 748 does show pressure signs if working up to a near maximum load in winter and shooting the same load in hot summertime. More sensitive than other powders for 55 gr .223 loads. I shot Win 748 for a few years but I limit my Win 748 55 gr. loads to 26.5 grains maximum. I believe at 26.4-26.5 levels are safe with all primers and cases I've used and my best accuracy has been at 26.4 grains using RP 7 1/2 primers. Others results may be different from my experience with 748 powder. I now only load H335 and like it much better for 55 grain .223 loads.
rcmodel
Member in memoriam
I agree.
I have used 748 exclusively in .223 here in Kansas for over 40 years.
Winters range to -15, and summer +110.
Never noticed any difference.
But your load is 1.3 grains over the Max Load (26.3) suggested by Winchester, and later, by Hodgdon with a 55 grain bullet.
So all bets are off, as you are already over Max in 10 degree weather.
I'd back off and work up a load again when it gets hot next summer!!
Closest I ever came to blowing a rifle was with a max 30-06 load I developed in winter in 1962 with IMR-4895.
The same loads locked the bolt shut and blew primers when warmer weather arrived that summer..
rc
I have used 748 exclusively in .223 here in Kansas for over 40 years.
Winters range to -15, and summer +110.
Never noticed any difference.
But your load is 1.3 grains over the Max Load (26.3) suggested by Winchester, and later, by Hodgdon with a 55 grain bullet.
So all bets are off, as you are already over Max in 10 degree weather.
I'd back off and work up a load again when it gets hot next summer!!
Closest I ever came to blowing a rifle was with a max 30-06 load I developed in winter in 1962 with IMR-4895.
The same loads locked the bolt shut and blew primers when warmer weather arrived that summer..
rc
I tested some at 24.5 gn of w748. At 54 degrees I got 2811fps and at 28 degrees got 2674fps. This is in a 16" 1/7 twist AR with WSR primers. I was surprised there was this much difference. I tried CCI 450 mag primers when it was 28 degrees and they were actually slower at 2658 fps. They had the tightest group at .8" so I was happy with it.
Thank you. That is exactly the type of info i was hoping to get.
It is a very hot load. Lyman suggest 27.8 grains behind a 55 gr. In their ar reloading handbook. I stopped at 27.6 because i started to get paranoid since their load is more than 1 grain over everyone else's. I didn't get any pressure signs but i am definitely going to download it a bit considering the temparature at which i tested. As always thank you for the knowledge and experience.
Nature Boy
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Great. One more thing to add to the list of a hundred things to worry about in this hobby that has the potential to blow you up.
So, if I follow published load data with W748, I should still be safe regardless if it 10 deg or 100 deg? Right? (all other variables being equal)
So, if I follow published load data with W748, I should still be safe regardless if it 10 deg or 100 deg? Right? (all other variables being equal)
rcmodel
Member in memoriam
Yes, if you follow published Winchester/ Hodgdon data of 26.3 grains max.
I have seen up to 28.0C in some manuals.
rc
I have seen up to 28.0C in some manuals.
rc
I couldn't imagine 28 grains. 27.8 fills the case right to the top with military brass.
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