7mm STW Reloading Thread
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coyotezapper
Well-Known Member
Pushing 75K pressure at 3300 fps. 3200 fps will put you at PMAX of 66,700 PSI depending on actual case capacity, OAL and twist. Your bbl will be shot out very quickly running your loads that hot.
I have been shooting the 7STW since Remington came out with their first rifles - 20ish years ago and I have pressure tested almost every powder including N570 ( with the 180 VLD ) with a Oehler 43 PBL and I am telling you that you are way over pressured. I am only telling you this because I would hate to see someone else think these velocities are safe and then hurt themselves. A deer or elk is not going to know the difference between 3200 and 3300 fps. Velocity=Pressure. You can't have one without the other.
WildRose
Well-Known Member
The highlighted is not necessarily true. The reason the slower burning powders were developed for large case magnums is so that we can achieve higher velocities without excessive chamber pressures and all of the corresponding problems that come from it.
coyotezapper
Well-Known Member
We are not talking burn rate, we are talking pressure. Peak pressure occurs when the bullet has only moved about 2-3" in the bore. After that the pressure drops off very fast. Slower powders help keep the bullet accelerating longer with less drop off. And yes it does keep accelerating even though the pressure is dropping. This is why it necessary to match bbl length and powder burn rate.
For example. One of the most popular choices for powder with the 308 Win is Varget and IMR4064. If you were to start a thread asking what powder to choose using a 168 or 175 grain bullet these two would have a lot of votes. Federal uses IMR4064 in their 175 GMM load. Now these two powders are only good in bbls 24" and longer. ( still ok but not optimum ) If you run a shorter bbl these powders will not get a full burn and sustained pressure will be lower due to burn rate. Now use a faster powder with the shorter bbl and you can get the same velocities as the 24" bbls but with a shorter bbl. I use H4895 with the 175 HPBT in a 20" bbl and I get an honest 2545 fps at 60K pressure. Federal claims 2560 fps, I think for their 175 GMM. Velocity=Pressure.
marioq
Well-Known Member
Wild,
When did u become a sponser? I can't send u a PM anymore!!!
When did u become a sponser? I can't send u a PM anymore!!!
WildRose
Well-Known Member
Slower burning powders allow us to achieve higher velocities with lower pressures in large cases because it's still accelerating right out the end of the barrel.
This isn't even arguable simply look at load tables.
300 Winchester Magnum Load Data - Nosler
It's also why we can achieve higher velocities with longer barrels as the velocity continues to increase the longer the pressure is contained. Powder keeps burning and expanding until it is all exhausted.
coyotezapper
Well-Known Member
I am not saying anything different than what you are saying here.
Glad to see things haven't changed much ....... You tell Em Rose
marioq
Well-Known Member
This is not related to the current discussion, but I bought a Caldwell gong the other day and set it up at 100 yards and shot my ar-10 and6.5 creed. So I took the STW to make sure it is still on target. It came with an AR-500 rating gong. Put a drill hole through it with rem 140gr corlok. I put up a new AR 550 since it is strong, drill hole #2!!!!
This round still amazes me!!!!
This round still amazes me!!!!
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Yeah. With a light bullet the STW puts enough speed on to make it fully armor piercing. They warned us about that on the range I go to and said never to shot the STW at any of the steel closer than 300 yards because they don't like buying new AR 500 plates
WildRose
Well-Known Member
Mario I'd laugh if I hadn't done the same thing myself several times over years ago.
....gun)
....gun)
To quote Elmer Keith " anyone that shoots steel at 200 yds or less with a high power rifle is asking for trouble."
I had a 338 win mag 250 grain partition come off a steel plate at 150 yds and barely missed me and went thru both sides of an army wall tent.
You can take that for what it's worth.
I had a 338 win mag 250 grain partition come off a steel plate at 150 yds and barely missed me and went thru both sides of an army wall tent.
You can take that for what it's worth.
