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I have a .300 Wby with a 26" Shaw barrel that gets high pressure signs above about 3050fps with 180gr bullets.

I'm thinking about having it rechambered to .300 Win Mag to cut down on brass and powder costs since I'm essentially getting .300 Win velocies anyway.

What are the chances it would still be slow after a rechambering? I sure as heck don't want to trim it back if "slowness" stays with the barrel, so to speak, because I want a MV in the neighborhood of 3000fps or better.

That's your call. Remember, rifles are female and you never know how they'll go off....or what really caused it.
As for MV, my question would be, how's your accuracy? Going after speed without enough accuracy means you just miss faster.

Just a thought.....Have you chrono'ed any factory rounds in comparison? From what I remember most factory 300WM 180gr run 3150-3250. This may help determine weather you really have a barrel/chamber problem or if you need to choose a slower burning powder, which would normally give lower pressures in longer barrels.

Good point. I can't say I have. Part of the reason is, the thing shows high pressure signs so early with handloads, I'm afraid to torch the Weatherby stuff off in it. I guess I should have mentioned this in my original post, but I'm getting high pressure signs a grain or two above book minimum loads.

Also, $80 a box seems like an expensive experiment.

I'd be a bit surprised if my powders are too quick though; IMR 7828 and H1000 are the ones I've tried. They work great in my 7STW, so I just assumed they'd be good for the Weatherby as well.

Accuracy is decent, but not outstanding...about MOA.

I'm thinking aftermarket barrel WITHOUT the freebore of the Weatherby chamber...odds are I won't be doing any worse in the accuracty department, if not better. I know its still a gamble, though.

I guess another option would be to try a "slicker" bullet?

I've been shooting Accubonds and Barnes X. Is there another bullet that creates less friction? A standard cup and core flat base?

Hey I may have spoke too soon!

I went back to my personal "real numbers" list......24" factory remington barrel rechambered to 300WM with Weatherby brass, Federal magnum primer. We maxed out with H-4350 at just under 3100 fps.

With real numbers you are there!

..............V/Vaporizer brings up a very good point. If I were you, I would buy a box of 180 gr Wby ammo, try it out and don`t worry about torching your rifle. Here`s why.

When shooting Weatherby 180 gr factory ammo and you still get pressure signs, then imo, you might have a legitimate gripe to confront Weatherby with. Save the casings.

Hey guys! I`m using your 180 gr factory ammo in your rifle and I`m getting pressure signs with this and here with that,,,,so what say you? I wouldn`t even discuss any pressure signs when using your reloads. Because doing so might give them a reason to somehow de-legitimize your beef. Play dumb and keep it simple.

Could be a number of reasons, but a tight bore and/or a tight chamber or maybe both might the culprit.

Why not call Weatherby directly? They have a phone # on their site.

Whooops! In your original post you state you have a Shaw barrel. I apparently overlooked that. Sorry!

Unless Wby was using Shaw barrels, it is not a factory Wby rifle and therefore no recourse with Weatherby.

Take it to a reputable smith you may know and see what he says.

Still sounds like a tight bore, chamber or both to me.

So a tight chamber can cause high pressures before you reach a max load/velocity?

My question is who chambered the barrel? Does it have the Weatherby free bore or is the throat short? If the throat is not cut with free bore you are going to get HIGH pressure and you DO NOT want to try any factory ammo in it. Get a chamber and throat cast to find your answer. Bear

Shaw cut the chamber to factory/commercial specs

What pressure signs are you seeing?

A short throat will certainly give high pressure signs with suppossedly normal loads.

The first thing I would do is check the throat length for freebore.

If Shaw cut the chamber than throat length should not be an issue. I have several rifles set up by Shaw and they test fired them all before shipping. Have you called Chris and voiced your concerns? I had a problem with a safety they installed and they took care of it very quickly. Bear

Weatherbys are freebored to allow measurable bullet movement before contacting rifling. This is done intentionally to reduce pressures while maintaining high velocities. If your chamber does not have freebore integrated, your pressures are going to be higher than normal with any weatherby cartridge, as I understand it.

WB cartridges as I recall, run around 55-60K so you're going to see some primer flattening. The characteristics you should be looking for are excessive case lengthening, expansion just in front of the belt, etc. Also the hardness of the bullet used affects pressure (harder the bullet, more resistant it is to passage through the bore and to engraving rifling, the type of powder used affects pressure (slower the powder, lower the pressure as a rule of thumb), and since this is an aftermarket barrel, the number of grooves and lands the barrel has will affect pressures, as well as the width of the lands (in general, the more grooves and lands and the wider the lands, the higher the pressure).

If you actually have a tight barrel, you could cast a lead lap, coat it with 1200 grit diamond dust, and carefully lap the barrel. A little goes a long way when doing this.

If the throat is too tight, the case can't expand away from the bullet at firing and extreme pressures are generated. Do a cerrosafe chamber cast, slug your barrel and see what you have before rechambering. You may be surprised at what you find.

BTW, MOA accuracy is very good, especially with a heavy kicking magnum like the .300WM or even by the relatively light 7mm Magnums. Better accuracy than that is usually obtained only by a man behind a word processor.

The .300 Win. has less case capacity than the .300 Wby. Unless there is something drastically wrong with your chamber, like a short throat, I don't see how going to a smaller case will give you the velocity you are after.

Are the velocities you quoted actual chronographed speeds, or loading manual speeds?

A few years ago, I chronographed some Federal 180 grain factory loads in a .300 Wby. with a 24 inch barrel. All cartridges tested gave less than 2900 FPS, averaging somewhere in the high 2800s. Advertised velocity, IIRC, was about 3100 FPS.

I'm thinking something else is wrong. Perhaps a chamber cut a little loose at the web, rough chamber, rough locking lug recesses, etc. making primary extraction difficult.

Pressure and velocity go hand in hand. IMHO lower velocities would equate to lower pressures.

I'm just not a believer in the fast barrel-slow barrel theories. Then again I'm not a ballistician.

How many shots have you put down the tube so far?
I have been fitting Shaw barrels for a while and it seems that they need to be shot some before they settle down.I know that some will say you shouldn't have to do that,but it does make a difference.