Load development issue

A

American Gunner 3006

Inactive
The rifle: Winchester 70, 7mm rem mag
The bullet: Barnes 150 ttsx
The powder: 62.5 H4350

The issue: Three shots at 100 yards gives a 5-6" spread vertically but they are all dead in line. Firing through a chronograph at 3124, 3125, 3145 fps (21 fps extreme spread). Action on the rifle is glass bedded and everything is tight.

The question: What would cause that kind of spread with such consistent velocities?
 
Try moving the front sandbag under the magazine floor plate and keep all pressure off the front end of the stock. Also, if your barrel is long and whippy and if you have a load for which the bullet exits right when the muzzle in the midst of a vertical position swing, the spread is easy to get. I would try both load tuning and changing the support position on the rifle.
 
That much vertical spread is most likely caused by inconsistent vertical position of the stock butt in your shoulder for each shot. The more recoil the rifle has, the more vertical spread the groups will have. The lower the butt is, the higher shots go because there's less resistance making the muzzle axis point higher when bullets leave.

This happens with 22 rimfire match rifles even with their bullets taking near 3 times as long to leave the barrel.
 
Bart B wrote:

That much vertical spread is most likely caused by inconsistent vertical position of the stock butt in your shoulder for each shot. The more recoil the rifle has, the more vertical spread the groups will have. The lower the butt is, the higher shots go because there's less resistance making the muzzle axis point higher when bullets leave.

This happens with 22 rimfire match rifles even with their bullets taking near 3 times as long to leave the barrel.
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Along this same line;

I even get vertical stringing with a 22LR off the bench,
if my shoulder isn't tight to the rifle's butt.
 
Could be any of the above. Could also be barrel heat. I have a 7mmSTW (just a bit faster than your 7mm Mag) The first shot out of a clean cold barrel prints 2 inches high. Second shot about an inch high. Every shot there after, as long as the barrel stays warm, is dead on.
 
Regarding point of impact changing as barrel heats up, the most common cause is not the barrel. It's the receiver face not being squared up to the barrel tenon axis. As the barrel heats up and expands, it bears harder on one place around the receiver face. That causes the barrel to whip more in that direction.

When all is squared up correctly, no point of impact change across 10 shots fired once every 5 seconds in highpower rifle rapid fire matches. In one test starting with a cold 308 Win barrel, 40 shots were fired about 10 to 15 seconds apart and the extreme spread at 600 yards was 1.9 inches
 
Regarding point of impact changing as barrel heats up, the most common cause is notRegarding point of impact changing as barrel heats up, the most common cause is not the barrel. It's the receiver face not being squared up to the barrel tenon axis. As the barrel heats up and expands, it bears harder on one place around the receiver face.
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what about actions that use a barrel nut system where the barrel never touches a receiver face?
 
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