IMR 7828 / 7 STW Question

LaVec

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Feb 16, 2018
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Hello gang. I'm new here so hello to all and thanks in advance for your help. I started loading years ago based on Layne Simpson's recommendation of 80 grains of IMR 7828 behind a 160 grain TSX. I fired 40-50 rounds with no problem. Rifle is an accumark with 26 inch Barrel.Fast forward a few years and everyone is saying that 77 grains is max. I recently reloaded a few rounds with a new lot of powder (without working up,I'm new to this and made a bad mistake) and with 80 grains had a sticky Bolt and a blown primer. I can't figure out what happened or why the thoughts have changed on the max load nowadays. Rifle was clean, still new,same ambient temperature, same seating depth,new brass used. How could what was safe in 2000 be too hot today???Any help is truly appreciated.
 

7stw

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Hello gang. I'm new here so hello to all and thanks in advance for your help. I started loading years ago based on Layne Simpson's recommendation of 80 grains of IMR 7828 behind a 160 grain TSX. I fired 40-50 rounds with no problem. Rifle is an accumark with 26 inch Barrel.Fast forward a few years and everyone is saying that 77 grains is max. I recently reloaded a few rounds with a new lot of powder (without working up,I'm new to this and made a bad mistake) and with 80 grains had a sticky Bolt and a blown primer. I can't figure out what happened or why the thoughts have changed on the max load nowadays. Rifle was clean, still new,same ambient temperature, same seating depth,new brass used. How could what was safe in 2000 be too hot today???Any help is truly appreciated.
Ouch, 80 grains is a little stiff, with a 160. Don't have my manual handy, but I ewas having great luck with RL25.
Work up gradual. Once you find your node. You'll know.
The STW forum is below the reloading main thread. There's a loading section in there as well.
 

MudRunner2005

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It's possible that the powder has gradually changed burn rates over the decades, so anytime you start over, best to work up a new load. Also, powder from different lots will have slight fluctuation in burn rates, and can be slightly faster or slower. When swapping to a new lot of powder, best to start over with load development. To ensure similar performance from jug to jug, I'd recommend buying powder in bulk (8 lb. jugs with matching lot numbers). If you call and order from a company that sells online, you can specifically request matching lot numbers of powder, and they can check to see if they have the amount you are wanting to order.
 

baldhunter

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I load 77.0grs of Reloader-22 in mine with 160gr bullets.Every load I worked up with Reloader-22,I could add one more grain of 7828,so I would load 78.0grs of 7828 if I was shooting it in my rifle.I wasn't quite at max,but I quit right there because it was shooting really good.
 

Lefty7mmstw

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80 7828 has always been pretty much a top load in my rifles with 140's... 7828 is somewhat temp sensitive, so a cool weather work up may also yield high pressures in hot weather... It's best to re-work the load with a new lot of powder too, as it may be a bit different than an older lot...
 

LaVec

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Feb 16, 2018
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Thanks for the help guys. Here's a question... How much is needed to go from safe and perfect to blowing primers? I understand some powders are temp sensitive. So for instance, can a load be working fine, and 2 grains more powder start blowing primers? Can a 30 degree heat increase cause it if you were close and powder is very sensitive? Or...does it take quite a bit of pressure to go from safe to blown primer?? Thx
 

7stw

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Well, number one, is a two grain jump, is a big junp,I,and I'm assuming you aren't raising in thst interval. I mostly like to shoot while its cool, and allow a temp swing, that during hunting season, I'm not going to get a point of impact change. If you develope a load at , let's say fifty degrees, then go shoot ing at 90 degrees, I can guarantee poi, change. Particularly, if it iis a non temp stable powder. R22, will do just that, 7828, will to, if I remember right. R25, seemed to be not AS, bad, except at the extremes.
So, the answer to you question, is yes, temp swings will blow primers, and give stiff bolts, and raising the charge in too large an interval will also.
Easy does it!
 

LaVec

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Feb 16, 2018
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Thx again 7 for your help. So...just repeating my very original question about lots of powders... A lot can be as much as 5-6 % different in burn rate. So original load of 80 grains was safe. A new lot changes by only ,say 3% ,that's the equivalent of 2.4 grains increase. This could take you from safe to sorry? I know that that's the reason to work up with new lots. I just thought it would take more than 2 grains to go from perfect to sticky bolts and blown primers. Thx again!!!
 

PBR driver

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I have been loading and shooting the 7mm STW since the very early 1990's.
IMR7828 has been my powder of choice. For me it has always given great velocities and accuracy
with acceptable pressure (case expansion) limits.
Originally I worked up and followed Layne Simpsons load data written up in Shooting Times.
The 7mmSTW originally gave about 3300fps with a 160gr. Bullet using IMR7828.
Work up slowly to find the best load for your rifle no matter what ever Powder, Bullet, Primer,and Shell Casing of your choice.
 

asd9055

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This is my take on it. Years ago, my best load was with 79 grns IMR4350, 180 BT in a 300WBY. Then I retired that rifle. When I came back to loading for that round, I found out that the MAX load is down to 73 grns of IMR4350. I reached out to IMR (Hodgdon) to see if the powders changed. The response was, the powder is still the same, but the primers have changed. I have since switched to IMR7828 for the 180, but I am thinking of trying 4350. However I will work my way up.
If you have OLD recipes, before you try them again, check with modern reloading manuals or reach out to the powder/bullet manufacturers for guidance. Do not try without starting low and working up.
 

baldhunter

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Pre 7mm RUM,the 7STW loads were much higher than post 7mm Rum.I haven't shot my 7STW with a different load since I found a good load of 77.0grs of Reloader-22.I was getting 3200fps with a 160gr Accubond.If I was shooting 7828,I'd load 78.0grs.Since Reloader 26 came out,I think it would be probably better than the other two powders.I have some and need to try it.That powder gives me a bit of a jump in my 7mag loading 1.5grs more than my Reloader-22 loads.So with the 160gr Accubond in the 7STW,I plan to start at 78.5grs just to see what I get and go from there.
 

Catskills

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Jun 29, 2018
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I had the same experience. An older batch of 7828 could take 79g with a given bullet and primer, no signs of pressure, and reliable sub moa accuracy. It was shooting 3450fps. Fast forward 10 years and I‘d shot up all my old ammo. Bought new powder. I did work up with new powder and blew a primer at. 77g. Interestingly, the velocity was 100+fps slower. Sadly, the accuracy node had also changed. I ended up switching to RL 26 and found sub moa accuracy at 3350fps and called it good because I don’t need the STW long range performance since moving from the Rockies to NY. FWIW, RL26 does run a bit dirty as compared to 7828.
 
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