Been shooting the the 7mm/338 Lapua Short this week (we call it the 7mm LSM or 7mm Fatso, I'll post a pic one day and you'll see why) with 24N41. It proved to be a tad faster than H50BMG, with 84gns of 24N41 behind a 180gn Berger giving 65,000 psi, 86.5gns of H50BMG giving 64,500 psi and 87gns of H870 giving 64,100 psi. These were 3 shot averages after a fouler. Pressure also started to climb quickly as you fired more groups, requiring a reduction in powder charge, similar to 20N29. They must be of a similar composition. You need to be careful of these 2 slowest N powders with max loads judging by my experiences. They produce good velocity though.
In perfect conditions you might stretch your 7mm-08 load to 600 yards if the accuracy is good enough, you'd need better than 3/4 moa at 600 yards and preferably 1/2 moa.
The wind is what will get you, if you've done all your other calculations right, and a .48 or thereabouts BC at 2800 to 2900 fps will get blown about a fair bit. From the many deer I've seen killed at long range, I'd be limiting myself to 400 yards with that combo. Of course, I've got bigger guns for the long shots!
You'd have to give me some more specs before I could recommend something, like max. all up rifle weight you can manage, depending on how far you're going to carry it. Also, will you use a muzzle brake? When you combine this with how much recoil you can handle, this will give you an idea of what sort of gun will suit you, and what its capabilities will be. Let me know these things and I'll suggest what I would do in your situation.
I guess my requirements would be as follows.
- capable of shooting deer/Tahr out to 750yds
- not too heavy, would prefer a hunting type stock rather than strictly tactical- maybe 11 lb all up.
- I have not had any experience with muzzle brakes, if they reduce recoil without any disadvantages I would definitely want one!
-Flexible with Calibre, but would prefer one that is not going to give me a beating
At the end of the day I am not really interested in taking animals over 1000yds (would like to have a go but don't want a 20lb rifle!)
Greg, Thats great information, and indicates once again how much lot to lot variation plays a part.
My recent tests with H50BMG in my 257W had that powder about at least 1 grain slower burning than the lot of H870 I am using. Yet your results are the reverse.
On the basis of your test with Viht 24N41 being a tad faster burning than H50BMG, I may not bother with it, and just continue with my order of 20N29, and also order the double base Viht N570 which was released recently.
According to one report, Viht N570 is supposed to be slower burning than N170, and similar in burning rate to H50BMG.
A photo of 7mm Fatso would be great. Regards, Brian.
it depends how you are judging burning rate. If you are comparing velocity achieved versus powder weight then H50BMG appears slower as it takes slightly more powder to equal H870's velocity, but pressure will be slightly higher as well. I measure pressure with a strain gauge setup on an Oehler 43. When you compare charge weight versus pressure, H50BMG is slightly faster than H870. Different lots of H870 can vary quite a bit though, I always chronograph and pressure test when I open a new tin.
with an 11 pound all up rifle weight, you can pretty much choose any calibre you wish and recoil won't be a problem if you brake it. If you want to stick with a factory calibre, I would choose the 7mm RUM, especially as Nosler are now making quality 300 RUM brass you can neck down. If you want the hottest 7mm wildcat, Kirby's 7mmAM or another version based on the 338 Lapua case would be it. A 26 to 30" number six or seven contour barrel from one of the top barrel makers would be my choice, depending on your portability requirements. A one in nine twist will stabilise any of the good long-range bullets, but I haven't had much success stabilising the 200 grain Wildcat ULD's in a 9 inch twist to 1000 yards, although others have. I have a one in 8 twist barrel coming to try these ULD's beyond 1000 yards where they should come in to their own. Either a trued Remington action or one of the custom actions if you can afford it. A varmint style stock with a round, slightly wider forend from Macmillan, HS precision, Lone Wolf or one of the other top stock makers. The Leupold Mk4 4.5-14x50 you already have will work fine out to 1000 yards.
These are just my suggestions, but the big 7mm's have the best compromise of ballistics, manageable recoil and killing power for rifles about the 10 pound mark.
Thanks for that info Greg, very useful. Have you done much shooting with the 7mm RUM?, there certainly is a good range of projectiles in 7MM calibres. Who would be a good gunsmith to use to build such a rifle?, are muzzle brakes custom made for each rifle?
This long range stuff is all new to me. Only ten years ago I thought 150yds was a long shot, now 300 - 350yd shots are bread and butter. It would be interesting to push it a bit further.
I suppose the extra weight of a 10-11 lb rifle plus the muzzle brake and decent recoil pad would make the recoil bearable.