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Location: CA Central Coast
Joined: 12/01/2005
Posts: 151
how deep are lands/grooves supposed to be?

Hi, all -

After suffering through some consistently below-average chronograph readings (with several bullet/powder combinations), I've begun to think that my barrel might be a little tired. I bought the gun (a Sako AV in 7mm mag) used a few months ago.

Today I "slugged" the barrel -- I drove a bullet through from muzzle to breech. The outer diameter remained unchanged at .284" and the inner went to .280". This is exactly half the reduction I thought I'd see, as I was told in hunter safety training that grooves are usually .004" deep.

So, I ask the rifle mavens here...does it sound like my barrel is worn out? I'm really at a loss to explain the lower velocities I've been getting, but before I decide to invest in a new barrel, I'd like to make sure that this one truly is bad. Thanks for any input.

Don Fischer's picture
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Moderator
Location: Antelope, Ore
Joined: 03/24/2005
Posts: 3173
how deep are lands/grooves supposed to be?

Have a gunsmith put a bore scope in it. My 30-06 won't come up to velocities either. I inherited it from an old friend that shot a lot of old military primers thru it and didn't clean it very well. The barrel is pitted, low velocities but it shoots fine. Though of a re-bore to 338-06 but it's a very expenaise rifle. So I use it as is, like having a high grade 300 Sav!

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Location: CA Central Coast
Joined: 12/01/2005
Posts: 151
how deep are lands/grooves supposed to be?

Thanks for the suggestion, Don. I'd do that if there were a gunsmith close to me, but the nearest one is quite a ways away. Today, I repeated the test with soft lead slugs (yesterday I used copper) and the land measurements were more consistent with the .004" I'd heard earlier. It did feel a little "easy" in the middle of the barrel on one test, but not on the other, so...I don't know what to think.

I may just leave it alone, or I might consider your idea of barreling it up to something bigger. I guess I could get another rifle in 7mm RM, and turn this into a 375 H&H or something...

I also have a real problem with the trigger on this rifle, but that's another story for another time.