Works best with heavier bullet weights for caliber. My 24" 300WM shoots very well with 79gr of Retumbo with 210's. My 6.5x284's with 24/26" barrels, 59gr with 140's. You should have no problem with 168's in your 7mm, but I'd give the 140's a try.
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magnummainiac is right in that barrel lenght means litte to nothing when it comes to picking a powder. What works in a 7mag using a 28 in barrel is going to work in a 20 inch barrel. Most of the powder is burned before the bullet clears the chamber. Heavier bullets can take advantage of slower powders because it takes more to get them moving so it gives a slow powder a nano second more to burn. Like i said ive loaded for the 7 mag for many years. Ive found that with 140s and 150s 4831 will give me all the velocity that can be had. Step up to 160s and powders like 7828 and re22 do real well. I dont load 175 bullets. I use my guns for hunting and never saw what there was to be gained by using a bullet that heavy. Maybe in a 7 ultra but in my opinion the 7mag is most effecient with 150-160 grain bullets for hunting. I could care less which grouped better at a 1000 yards. I hunt deer not paper targets. you have to keep in mind that even 4831 is a slow burning powder. When i started loading it was the slowest powder available to us. Just like with all the new super duper deer bullets that the new guys just have to have. the powder manufactures get in on it too. They push super slow powders best used in a 50 bmg and convince us we need them for a bloody 2506. When in fact good old cup and core bullets and some 4831 still makes most cartridges, even the magnums run at top efficentcy in the deer fields. Some guys look for the last fps they can get. they will do about anything to gain 50 fps. Me i load even magnums for accuracy. Id much rather have a load that does 3000 with a 150 and shoots 1/2 inch groups then one that shoots 3200 and shoots 2 inch groups. Yes i admit ive fooled with retumbo, h1000 and re25 and still use a little re25. But i use it for heavy bullet loads in the 300 ultra. Ive tried all three in about every magnum round going and keep comming back to 4831 in the 7 mag. It gives top velocitys and top accuracy with hunting weight bullets.
personaly i think retumbo is to slow for the 7mag with any barrel lenght. Ive loaded the 7 rem mag for 20 years and have allways had my best luck with powders like hodgdon 4831, imr483 and 7828 and re19 and re22. Any slower then these powders and your not going to gain velocity your just going to use more powder.
You're taking a lot of proven factual data and replacing it with your opinion. Granted, you've collected a lot of data to form your opinion and I respect that. You can use what you think is best. However, Retumbo works extremely well in the 7RM with good hunting weight bullets between 168 and 190 grains with fantastic accuracy in most instances when used in a properly developed load. Also, none of the powders you listed will come close to reaching the velocity obtained from using Retumbo. To say a powder is too slow is to say I cannot get enough of "said" powder in the case to produce full pressure. Retumbo, however, does not fit this description for the 7RM.
[QUOTE=lloydsmale;891200]magnummainiac is right in that barrel lenght means litte to nothing when it comes to picking a powder. What works in a 7mag using a 28 in barrel is going to work in a 20 inch barrel. Most of the powder is burned before the bullet clears the chamber. Heavier bullets can take advantage of slower powders because it takes more to get them moving so it gives a slow powder a nano second more to burn. QUOTE]
OK, so anybody, help me wrap my head around this, cause I am struggling....... I saw a guy load a couple ( three if memoery is correct ) shells at max load, shoot through a chrony, then added 1 grain of powder and gained 50 fps, then added another grain and gained another 50 fps. Then did it again and gained only 15 fps. ( Not very intelligent , I know ) Why did the last round not gain the additional 50 fps like the others unless there was unburnt powder no longer pushing the projectile?
No, I don't remember the rifle, or the load. It was some time ago.
I load my cartridges down if needed for accuracy so this is not about gaining speed. It is about using what is at my disposal.
Seems the general consensus agrees a 24 inch barrel will do. Thanks all!
Why handicap yourself with the 140-grain bullets? If you really look at the data, the 160-grainers give up nothing to the 140s and do it at a longer range. Retumbo is a very slow powder and should work well, but use heavier bullets. You are not using a 7 mag to its potential with a 140.
The only reason that I have some 139 Hornadys loaded is that I am trying to use them up. After they are gone, it will be only 160 Partitions for me.
If you insist on 140-grainers try some RL22. I have an under-max load that pushes the 139 Hornady to 3100 from a 26-inch barrel. It is a great deer load, but the 160s are superior.
I get 3006 fps from my 26-inch Remington with the 160 partition and RL25. This is not much slower than the 139 and definitely hits harder.
I started loading for the 7 Mag in about 1975. I always wished my old 7 Mag was a 26". I never could get published velocities without major pressure signs. My buddies with 26" barrels always topped my speed with about 10 less grains of 4831.
I came into this thinking the Retumbo wasn't really suited to the 7 Mag but after consulting the IMR/Hodgdon online reloading center I see Retumbo is considered a top velocity choice for 140 and up. I am very certain the 26" will show a pretty good velocity advantage over the 24". 4831 sure did.
If Retumbo is what you got I say go burn it up.
__________________ Build a man a fire and you heat him for a day. Set him on fire and you heat him for life.