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Location: eastern Montana
Joined: 06/23/2007
Posts: 14
rates of twist / seating off lands

Guys - A couple of questions.

I shoot a 7-08 with a 1 in 9 1/2 twist. Other makes of the same caliber come in 1 in 10" twists.
Just out of curiousity, what would be the general rule of thumb for the bullet weight difference between the two?

Also, I learned reloading on my own and still have more to learn. How do you determine how to seat on or off the lands and does this make any significant difference. I seat according to the various manuals and then make cut back a nudge for the magazines of my particular rifles.

Thanks.

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rates of twist / seating off lands

The 1:9 twist would spin the bullet faster, therefore producing more stability than a 1:10 twist for the same bullet, in theory at least. There is no noticeable difference between the two for hunting or general range shooting, but if you were comparing 1:9 & a 1:14 twist, bullet selection is paramount, and the difference between night and day.(the heavier the bullet, the faster spin required)
A while back bullet seating was discussed here by quite a few members, a few different techniques, etc.
If I or someone else finds the topic please copy & paste it here. One way or the other you'll get a reply very soon.

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rates of twist / seating off lands

http://www.biggamehunt.net/forums/viewtopic.php?p=58026&highlight=&sid=7...

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Location: eastern Montana
Joined: 06/23/2007
Posts: 14
rates of twist / seating off lands

Thanks, guys.

Now, if I understand this correctly one is using the lands to actually seat the bullet, is that right?

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rates of twist / seating off lands

With my method you are using the lands to phsically seat the bullet,
Dons method is more of a method of measuring the distance, same thing,only different Think Think
Don will be along later today and will let you know what he thinks.

See, I'm in Nova Scotia, on the Atlantic Coast, while Don Fischer is in Oregon, on the west Coast. By the time Don gets out of the Crib, all the hard???? are answered Laugh Laugh Laugh Laugh Laugh

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Location: Antelope, Ore
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rates of twist / seating off lands

Phew! I was saved from that one! Laugh Laugh Laugh

Twists are strange thing to figure out. To many things to consider such as bullet length, dia, velocity ect. Most factory rifles are set up to stabilize the longest and heaviest bullet the manufacturer thinks will be used. Generally tho they will all handle the mid range bullets that are usually considered the hunting bullets. You have a 7-08 and in 7mm, the preferred weight bullets always seem to be 140 to 160 grs. Doesn't seem to matter whats being shot, that seems to be the bullet range for them. But some people do use 175 gr bullets, actually a lot so the twist is set to what the manufacturer feels is the best compromise twist to gain acceptable accuracy with the full range of bullets.

If your 7-08 had say a 1-8" twist, number picked out of the blue, it would stabilize the heavy bullets better than the light bullets. In fact, it might over stabilize the light bullets and render them little better than useless. Then too, if the twist is to fast and the bullet to light and fast, it is my understanding that the bullet is in danger of being torn apart by to fast a twist, no first hand experience there.

Where twist would really concern you is if you wanted to shoot very heavy bullets. Let's say you wanted to shoot some special bullet well above 175grs. You'd need to go to a faster twist barrel. A great example of that would be the fast twist 22 center fires being used to shoot 60gr and heavier bullets for what ever reason. Of course those rifles greatly over stabilize the 45 gr bullets and they become pretty much useless.

I never even shot a 7-08 but have owned three 7x57's. They are quite similar. The best bullet weight's for hunting always seemed to me to be from 139/140 gr to the 160gr bullets. But I have shot from 115gr bullets to 175gr bullets in them. the 115gr bullets usually shot well and the 175gr bullets opened up group's noticeably. The twist wasn't fast enough for the 175's but wasn't to fast for the 115's. All shot well enough for hunting purposes. The best thing to do with twist is not to concern yourself with it unless you want to shoot the heaviest bullets for the cartridge. All of those are a handloading only program.

The distance off the lands is more to do with discussion than anything else. If you jam a bullet into the lands, it can still be fired safely if the powder charge has been reduced. What might not happen is the bullet come out of the case with the case if you don't fire it. If you get the bullet to close to the lands, you may have the odd bullet just a bit longer that actually gets to them. That will jump pressures some degree but if the load is a safe one to begin with, the worst that will happen is a shot out of the group and maybe a flat primer. Somewhere between the lands and free bore is a distance where many rifles seem to handle certain bullets best so we tweak the seating depth looking for that last little bit of accuracy. I don't fool with that much but then I'm not a competitive shooter either.

What I try for is to have each round loaded so that every bullet is off the lands a bit. I'd like to give you a measurement but I haven't a clue what it is. I do know the OLL of the rounds but that doesn't tell you how far off the lands you are. You see we measure OLL from the base of the case to the tip of the bullet. Seating depth is accurately measured from the base to the point on the ogive of the bullet where it first touches the lands. Sinclair makes a tool to measure that that fits on a caliper. For that to be of any value, you'd need competition seating dies that let you adjust to thousandths of and inch. Most dies do that but it's a hit and miss deal with the course threds on our seating adjustment stems. For the vast majority of shooters I doubt it is worth the cost. Even if it were to gain you 1/4" in group size, that would be meaningless to a rifle already shooting 1" group's. Even for the highly accurate 22 CF used to shoot small varmints with, 1/4" is less than most of us can hold, even from sand bags!

Well that was a bit windy but then I've had four extra hours of sleep to think about it! neener!

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rates of twist / seating off lands

By the way, my shooting instructer is a red head and I don't argue with her!

http://i122.photobucket.com/albums/o277/DonFischer/Fat20Bikini.jpg

Hubba hubba! Eat your heart out you guy's!

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Location: eastern Montana
Joined: 06/23/2007
Posts: 14
rates of twist / seating off lands

Thanks, guys, you are very helpful as well as entertaining. Yes
By the way, my rifle has a 9 1/2" twist.
I will do both methods of determining seating off the lands and see which works for me. By coincidence, I talked to my mechanic yesterday at his shop. He happens to be a very competent benchrest shooter -- got in the state record book in June for smallest group -- and he also explained to me how to seat the bullet off the lands.

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Location: Mobile County, Alabama
Joined: 09/09/2007
Posts: 310
rates of twist / seating off lands

For the most part, seating depth is not a critical deal when it comes to accuracy. It is typically used to fine tune an already good load. For hunting rifles, I doubt there will be any noticable difference in performance. Besides, unless you single feed, you will still be limited to the length of the magazine.

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