Author Topic: .300 win mag freebore?  (Read 1338 times)

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Offline jiminpa

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.300 win mag freebore?
« on: April 25, 2003, 08:19:28 AM »
i measured my browning a bolt.300 win mag with a stoney creek tool and found the bullet is almost out of the casing before it hits the rifling! is this normal for this rifle?it measured 3.902 to the rifling with a nosler 165 gr.bullet.seems to be quite a jump for the bullet,and i think the pressure would really spike when it gets to the rifling! :eek:
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Offline Florida Jim

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.300 win mag freebore?
« Reply #1 on: April 25, 2003, 02:16:44 PM »
I also have a "a" bolt in 300 Win mag. I shoot Nosler 180 gr Protected point partitions. On the Win mag with its short neck the magazine length is the controlling factor. The above bullet is designed for the Win mag. I load mine with an overall length of 3.370" (3.340 is Saami specs). This will just clear the magazine and function reliably.

The long free bore is not any problem with pressure. Just not usually super accurate. Remember old Roy Weatherby's original rifles. He manage to get extreme speed by having a lot of freebore to reduce pressure. Weatherbys were never known for tack driving accuracy. I heard that Remington does the same on their new 700's.

Any way I load 75 gr's of reloader 22, Federal 215 primers, R-P cases. this load shoots under an inch in my "Boss" A-bolt. Averaging about 3100 and change. Start lower and work up. Nosler Manual #5 lists 75.5, but at 75.3 I started getting pressure signs.
I hope this helps

Jim

P.S
I just remembered that I worked this Load up in the summer in Florida (90 + degrees, 90 % humidity), up there in Pa you might get different results.
"The .30-06 is never a mistake"~Townsend Whelen~

Offline jiminpa

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.300 win mag freebore?
« Reply #2 on: April 28, 2003, 03:59:57 AM »
loaded up some "sample " loads this weekend.will play and see.we 're both using the same powder,i also shoot a lot of imr. turkey season started saturday,so i gotta chase them around some!! :lol:
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Offline Nobade

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.300 win mag freebore?
« Reply #3 on: April 28, 2003, 11:18:58 AM »
Lots of freebore (long throat) isn't really a problem as long as the diameter isn't too big and it's concentric to the bore. Unfortunately most factory rifles seem to be coming with fairly large diameter throats, which can be iffy if you can't touch the rifling with the bullet. Makes it interesting for us cast bullet freaks too, sometimes a bullet large enough to fill the throat can't be chambered. But I wouldn't worry too much about it in a hunting rifle - it should do just fine.
"Give me a lever long enough, and a place to stand, and I'll break the lever."

Offline KN

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.300 win mag freebore?
« Reply #4 on: April 28, 2003, 12:29:36 PM »
I did a little testing last weekend with a 223 Contender carbine I have. Shoots my regular load into about 3/4" consistently with about .130" of freebore before touching the lands. Set them out to .025" from the lands and it started vertically stringing. About 1/2" per shot out to about 3". Switched back to my regular load and it went right back to 3/4". Still scratching my head on this one.  KN

Offline Bullseye

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.300 win mag freebore?
« Reply #5 on: April 28, 2003, 01:50:45 PM »
Well KN, my opinion which is based totally on unscientific data is that a gun will not always shoot the best with the bullet barely off the rifling as is the generally accepted rule.  I think a lot of guns are like this, but others like yours might like a little more space.  I always think about my Contender barrels in 357 Max, 41 Mag and 44 Mag.  They all have a big forcing cone and their is no way you could seat the bullets to almost touch the rifling yet these barrels will shoot 5 shot 50 yard groups with the holes touching.  Would seating the bullet to touch the rifling make a difference (if you could)?  It might, but you would never know because you would not know if your 2nd-5th shot went through the first hole or missed the target all together (little bit of humor there).

I also think of factory ammo.  Some factory ammo will turn in impressive groups with factory rifles.  These bullets are a long ways from the rifling.

Bottom line for me, barely touching might help, might not help.  I just seat to the COL in the reloading manual unless I cannot make the gun shoot to satisfy me, then begin to play with COL.  But I never just assume that seating the bullet .030 off the rifling is the answer to the accuacy prayers.

Offline KN

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.300 win mag freebore?
« Reply #6 on: April 28, 2003, 04:33:02 PM »
Bullseye, I couldn't agree more. The only reason I changed my load was out of curiosity. The thing that stumps me is why it would string vertically? Iwould expect the groups to either open up or get better but I didn't expect it to string. KN

Offline Bullseye

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.300 win mag freebore?
« Reply #7 on: April 29, 2003, 05:39:57 PM »
Don't know the answer to that KN.  Strange things happen.  I was testing some 41 Mag loads with IMR 4227 last week.  One charge gave me a fairly nice round group.  Another charge gave me a nice big round group.  Another charge gave me a big vertical strung group.

These are the things that make us scratch our head and drive ourself crazy if we let it.

Offline Duffy

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.300 win mag freebore?
« Reply #8 on: April 29, 2003, 09:15:33 PM »
KN, I have the same thing happen with both of my encore bbls, 708 and 22K Hornet. The closer to the lands the worse they shoot. So far the 708 is at .045 and the Hornet's at .035 off the lands. I did notice while testing that my ES and pressures go wild when they are too close. As far as the stringing goes it could be a factor of barrel whip or vibrations set up by the pressure spikes. Check out this info, it sort of explains things.
http://home.earthlink.net/~dannewberry/index.html