[i][/i]To keep it short: acquired a rem mod 721 that Was chambered in 300 H&H mag, it is now in 300 win mag. The question; would a smith just ream out the chamber leaving a long throat? Or do you think the barrel was removed and the threads cut back some and reinstalled? The barrel is still 26” long.

Shoot it, the brass should fire form and you can look it over and tell maybe. Compare to a factory load.

barrel should have been cut back, thee 300 winny is fatteer at the shoulder than thee 300 H&H, and is shorter.

The previous owner should be jailed. I have a 721 in 300 H&H and it is one of my favorite rifles and calibers.

X2.

I hear yuh! But for $100 with a vortex scope on it? Why not?

3 different boxes of factory ammo only produced 1.5-2” groups at a 100 yds.

best and safest way would be make a chamber cast, you will know for sure then

Thought about doing that as well.

I do have dies, and thought about seating a bullet far enough out of the neck till I contact the rifling.

I have a suspicion that this rifle has a long throat and will take reloading with 200-220 gr bullets to be accurate.

Certainly wouldn't hurt to have someone with gages check the head space.

Cotton's suggestion would also be valuable.

So you think the barrel was shortened but its the same length??? Really??

Sorry, was referring to what would be the protocol for a procedure like this. Normal to cut back one or two threads?

the 300 H&H cartridge case length is 2.850", the 300 winny is 2.620, so to do it right a couple threads would have to come off to rechamber and have the proper leade

Weatherby calls it Freebore.

X3. Just can't fathom what some people are thinking.




For $100 into it, one can afford to put a new barrel onto her and have a shooter.

Probably had trouble finding H&H ammo and saw 300win on every counter so had it rechambered.

Ridge runner is right, probably took 4-5 threads off and rechambered it.

The difference between the length of the Win Mag and H&H is less than a 1/4". Factory rifles with a claimed 26" barrel are often more than 1/4" over or under 26", depending on manufacturer. So without having another rifle of the exact same model and caliber available to compare it to, I doubt he can tell if the barrel has been shortened with a tape measure.

Load a dummy round (no powder or primer) with the bullet seated way out and chamber it to see how far out it is to where it contacts the lands. May have to try this a few times seating the bullet at different lengths, but you can get a fairly accurate measure of throat length this way. Some guns/bullets shoot well with a significant jump to the lands, others not so much. That freebore does reduce pressure (why Weatherby designed his magnum rifles with so much of it) but can affect accuracy, it doesn't always though.

If your shooting abilities are decent, then you need to have some work done to it. If a gun like that can't be made to shoot under 1" at a hundred yards, then you don't have much.
I'd find me a competent gunsmith to take a detailed look at it and pay him to either rechamber it again or have him put a new 300 win mag barrel on it.

Ditto.
The 300H&H is one of the sexiest cartridges ever made.

Personally I’ve never liked the magnum .300’s in any configuration. Only thing worse are the hopped up 7mm’s. My .338 win mag and my .375 H&H are my babies!!

Looks like around .268 of free bore. Is that a significant amount?
(That’s a 150 gr sierra bullet)

I'd be loading 180s (or heavier possibly) in a 300 mag, so that would likely reduce that some. That is a significant amount of freebore in my opinion. Next question; how long can you load the cartridges and have them still fit in the magazine? You should be able to load them significantly longer than factory because this was originally a 300 H&H so it should have a longer magazine. If you handload I'd try loading some long 180s in it, reducing the jump to the lands and see how they group.

I know years ago when I got into long range shooting a lot of guys were loading the long Bergers touching the lands for best accuracy, and then could often only fit one in the chamber and one in the magazine because they were too long. I found not being able to fit them in the magazine unacceptable and through testing found loads in my gun that got minimal accuracy loss loaded as long as would fit in the magazine. Others intentionally built rifles like yours, barreling them in a shorter cartridge than the action and magazine was designed for, so they could load them longer than published maximum OAL. While quite a few shooters did load touching the lands, the accepted norm for safety (removing the possibility of a bullet sticking in the lands when ejecting a loaded round, for one) is to load them no closer than.010 to.015 off the lands.

The real question is how much bullet u got in the neck of the case and as was previously stated does it fit in the magazine
In actuality the real question is how does it shoot. Ive had loads shoot half moa jumping over 0.100" . The answer is in the target.

That 150 gr bullet is halfway down the neck. Not enough for me. I may try a few handloads with the 150 gr with the bullet base seated to the bottom of the case neck.
I do have some 200 gr bullets coming that I want to start handloading with. I have some Reloader 19 and imr 4350 to work with.
Thanks for the replies, very helpful!

Give us an update when you work up some loads for it. I'll be interested to see how it shoots.

Worked up a load with Reloader 19 powder and a 200 gr bullet seated just off the lands of the rifling. I was getting 1” groups at 100 yds. Total cartridge length exceeded the factory specs, but since this rifle was built on a 300 H&H action I could still put the cartridge down in the magazine.

I may do some more tweaking on the load combo to get a little better groups.

Good deal, glad ya have it shooting better.

I built a 7mm saum that I was ready to sling down over a bank until I got hold of some H4831 and now its becoming one of my better shooters.

I would guess almost all my handloads are longer than the Sammi cartridge legnth. Its like Erick Cortina said " who's Sammi, ive never met her"

Part of the joy(or not sometimes) is working up loads for a rifle. I love the experimentation!

Same powder and weight(and seating depth as the 200 gr) with 180 gr Speer grand slam got me 1.25”. Not shabby but could definitely be better.

I’ll probably try some I-4350 in the future

When you think you have a good shooting load at 100yds, better shoot it at 200.

Sometimes they open up more than one would think.

So true! I did try it at 155 yds and the elevation stayed the same and so did the groups. I do want to try and get my groups at 100 to be closer to 3/4”.