I might be going down the rabbit hole here, but for some time I have wanted to rechamber my Winchester Model 70 375 H&H to 375 Weatherby or 375 H&H Ackley Improved. Not for any particular practical reason - but just because.

I searched around and read the various old posts on the 375 H&H AI but I didn't see any gunsmith in the last 10 years or so. I must be way late to the party as now everybody wants a 6.5. Ha. Maybe I will make mine a 6.5-375 H&H AI.

I primarily use Hill Country Rifles here in Texas for rifle work. I took the rifle in and talked to them about it but the rechamber job wasn't something they really do. I thought I might talk to them even at DSC again about it, but more likely it would have to be a new barrel and install. This rifle has had so custom much work restocking and bedding, adding a lug to the barrel, and various work to the barrel adding custom NECG sights, recrowning, etc and to has very few shots down it that I didn't want to rebarrel it yet. I realize the Ackleyize may precipitate that rebarrel after some firings anyway.

So if anybody has a recommendation for a top quality gunsmith that would this job, or that you might have used to do a similar project, would you please post it or PM it to me and I will take it from there.

Thanks to all and Happy New Year.

I'll sell you some Wby dies cheap if you go that route

If you reload the .375hh can be a pretty flat shooter. The new Barnes 270gr LRX can be pushed out at 2800fps+ and it has a BC=.449 pair it with a 300gr Solid and there really isn’t anything you can’t hunt.

I would love to do the same thing. I have an action awaiting a barrel install. The barrel is chambered to 375H&H but I already have a 375 Ruger so i'm thinking about a 375 Weatherby instead.

other than cutting the value in half, and MIGHT have some feeding issues, this isn't a tough job .. i wouldn't do it to my rifle, but it's yours, so great --

anyone that is competent to chamber a barrel COULD do this, but they are worried about it becoming a can of worms .. and i totally understand .. there's no way to know how square the barrel couture vs the chamber is aligned, and if the gunsmith doesn't have a "conversion" reamer (belt is dull/no-cuttie-chippies) then it could be more than a bit tedious .. and it could go downhill, fast ...

One thing to consider, if yours is a CRF, remember that to do it RIGHT, the barrel needs to be set back due to the Ackley chamber headspace being .004" shorter and this would affect the location/timing of the extractor slot. The WBY conversion would not require that.

I have a375 weatherby and like it a lot My son and I have killed two bears (a nice alaskan brown and good New Mexico black bear with it) shooting factory 375 H&H 300g A-Frames with it. I've also shot some other game (deer and elk) with 375 Weatherby loads of 300g A-Frames at 2800 fps and 350g Woodleighs at 2550 fps.

The rifle weighs less than 7.5 lbs with scope so it's a little snappy with the Weatherby loads but is nice and gently with the 375 H&H rounds. It's very accurate.

If you're not going to leave your rifle a 375 H&H, I'd recommend going the 375 Weatherby route.

quote:

Originally posted by Jim Kobe:
One thing to consider, if yours is a CRF, remember that to do it RIGHT, the barrel needs to be set back due to the Ackley chamber headspace being .004" shorter and this would affect the location/timing of the extractor slot. The WBY conversion would not require that.

Jim, I assumed that the .375 AI would headspace on the belt. Is that what you are referring to?

I once bought a pre-64 Model 70 Winchester from a seller who had converted it from .375 H&H to .375 AI himself. I was planning on rebarreling it anyway, but when my gunsmith checked it over, he found .021" excessive headspace. So much for amateur craftsmanship!

It ended up a .450 Watts. This was back in the '70's, before the Lott had come on the scene.

An improved belted cartridge will still have the same headspace dimensions; so no need to worry about that; the crush fit is for rimless Ack cartridges. They will just blow out the shoulder on the first shot and then you have brass.
As for .021 excessive headspace, if you look at the SAAMI tolerances for belted brass and chambers, it is a wonder that any fit as well as they do, from the factory. Something like .018 is allowed from a min brass to a max chamber. Not ideal for sure.

quote:

Originally posted by TexKD:
I might be going down the rabbit hole here, but for some time I have wanted to rechamber my Winchester Model 70 375 H&H to 375 Weatherby or 375 H&H Ackley Improved. Not for any particular practical reason - but just because.

I searched around and read the various old posts on the 375 H&H AI but I didn't see any gunsmith in the last 10 years or so. I must be way late to the party as now everybody wants a 6.5. Ha. Maybe I will make mine a 6.5-375 H&H AI.

I primarily use Hill Country Rifles here in Texas for rifle work. I took the rifle in and talked to them about it but the rechamber job wasn't something they really do. I thought I might talk to them even at DSC again about it, but more likely it would have to be a new barrel and install. This rifle has had so custom much work restocking and bedding, adding a lug to the barrel, and various work to the barrel adding custom NECG sights, recrowning, etc and to has very few shots down it that I didn't want to rebarrel it yet. I realize the Ackleyize may precipitate that rebarrel after some firings anyway.

So if anybody has a recommendation for a top quality gunsmith that would this job, or that you might have used to do a similar project, would you please post it or PM it to me and I will take it from there.

Thanks to all and Happy New Year.

I have a .375H&H A.I. on a Whitworth I did 10-12 years back. Simple, run the AI reamer in don't let it cut the belt any further.
No issues what so ever on the Mauser style action. Ymmv with the Win-70.
Great cart. in my eyes

quote:

Originally posted by dpcd:
An improved belted cartridge will still have the same headspace dimensions; so no need to worry about that; the crush fit is for rimless Ack cartridges. They will just blow out the shoulder on the first shot and then you have brass.
As for .021 excessive headspace, if you look at the SAAMI tolerances for belted brass and chambers, it is a wonder that any fit as well as they do, from the factory. Something like .018 is allowed from a min brass to a max chamber. Not ideal for sure.

This guy is correct! I overlooked the belt issue, however it does get a little tricky reaming and just trying to "kiss" the belt without going too far. Sorry for misleading everyone.

I have a couple of AIs in smaller calibers and my comments are based on them.

If you can find some 375AI cases or rounds you might want to see how they fit in the magazine and try the initial part of the feeding cycle. On my AIs the feed fine but initial bolt stroke, until the case clears the feed lips; feels quite "sticky" and odd from the way the required pressure on the bolt handle changes as the round moves forward in the magazine. Just an annoyance but you might want to consider if this would bother you.

Yes I would want it to be a professional and pro done job both. I knew that going in, but this confirms that even more.

Maybe the better way to go is to do this in 375 Weatherby caliber instead. That was actually my first effort and what I talked to HCR about.

I am going to scratch around some at DSC on this and just see. Y'all know how it goes - by the time you get it all done then I might never use the rifle again haha.

Thank you for all the inputs Gentlemen and have a Happy New Year.

This is easy. Do what ever Matt says. They stand behind their work and know what they are talking about.

I've wanted to do the Weatherby thing too but I have killed many animals with the 375 h&h and it has just worked and also been very accurate. My big problem with the ones ive owned is they have all been too heavy.
What is your target weight for your build?

For those of you currently playing with the Weatherby must you crimp your necks or is there sufficient neck tension to hold it all together well? Also what are the velocities being achieved with 300 grain pills? What parent brass is the best?

quote:

Originally posted by Abbispa:
I've wanted to do the Weatherby thing too but I have killed many animals with the 375 h&h and it has just worked and also been very accurate.

My local GUNSMITH rechambered a Winchester M70 Classic Stainless for me in 2003.
Must have been the first thing he ever did for me,
and it was done well.
It is still the most accurate "big bore" I own, though several have been sub-0.2 MOA for three shots at 100 yards.
The .375 Weatherby has been around since 1945.
All others since then have been "me-too!"
Be sure the reamer used is the current CIP version (homologated in 2002),
revamped by Weatherby for 2001.

My big problem with the ones ive owned is they have all been too heavy.
What is your target weight for your build?

My M70 Classic Stainless with factory .375 H&H barrel has muzzle diameter of 0.720" and 24" length. Close to a #5 sporter contour.
Empty weight is 8 lbs 11 oz, in a 2.5-lbs HS Precision stock and with Leupold QRW 2-piece steel scope bases.
A #3 sporter contour (0.625" muzzle diameter at 24" length) and a 1.5-lbs stock would get it down to close to 7 lbs even,
or use a fluted #5 sporter for about the same.
A #4 sporter in a 2.0-lbs B&C Medalist stock for the M70 would make a nice, well balanced rifle at about 8 lbs even.

For those of you currently playing with the Weatherby must you crimp your necks or is there sufficient neck tension to hold it all together well?

I always crimp, just a light roll crimp, and would never do hunting ammo without it.

Also what are the velocities being achieved with 300 grain pills?

The published factory load is 2800 fps for a 300-grain Nosler Partition in a 26" barrel.
It is true. That same ammo delivers 2740 fps instrumental (5-yard) velocity in my 24" M70 re-chamber.
Easy to duplicate with H4350 handloads, if you use the Norma-made .375 Wby brass with proper headstamp.

What parent brass is the best?

The Norma .375 Wby brass is the best way to go with the .375 Wby:
It has a few grains greater water capacity, proper headstamp, and is best quality brass, made for the Weatherby factory ammo and
available as component for handloaders.
Fire-forming Winchester .375 H&H brass produces short brass, about 2.820" when uniformed,
which is 0.040" short of 2.860" .375 Wby maximum length.
Best alternative is Norma or Hornady cylindrical basic, which can be made 2.860" long, trimmed to 2.850"-2.860" for starters.

In 2.5-pound HS Precision stock:



Switching my M70 Classic Stainless to the 2.0-pound B&C Medalist stock would take off a half pound,
making it 8 lbs 3 oz, without scope.
Not bad. A little muzzle heavy.

If I were building another .375 Weatherby?
M70 action.
#4 sporter contour barrel.
B&C Medalist stock.

That would also be the recipe for a lightweight .458 WIN LongCOL.
The ultimate, well under 8 pounds.

Those two rifles would be the ultimate, redundant, safari battery, able to use factory .375 H&H and .458 Win.Mag. ammo to excellent effect in a pinch,
if your handloads ever got lost.

Rip ...

All my rifles seem to come out heavier than others.

This 375 compete with its McMillan Supergrade McWoody stock with magnum fill, NECG sights, barrel band, 24 inch barrel, Sunny Hill box and metal, plus the Talley steel bases and rings and its Leupold VX6 2-12 Firedot it tips my scale at 10 lbs and a few ounces unloaded. So at that weight it can soak up a little more recoil I believe. 9 lbs or 9.5 would be great, but as it is it is a solid go anywhere package that shoots well too.

Yes I am going to visit with Matt again at DSC and see what we can do or where he has an idea can complete this.

Thanks for joining in guys and I remember the big thread RIP had going before on it.

My CZ 550 blued/walnut 500 Jeffery weighs 12 lbs with a Leupold 1.5-5x scope. Our (my son's and mine) Rem XCR II in 375 Weatherby is shockingly light. 7.5 lbs with Leupold 2-7x Firedot scope I was a bit nervous the first time I shot it but it's accurate, reliable and it's squishy plastic stock must soak up the recoil. Its a pleasure with 375 H&H factory rounds and a bit snappy not bad with 375 Weatherby loads.

I found out as many professional have said that the slower velocity of the std. 375 is a better killer of DG..I agree with that concept to the degree that its a waste of time trying to improve a perfect caliber...but hey if you just want to, that's the best reason in the world to do it...It will be hard to sell is the down side imo..

TexKD, I may be late to the discussion but if you are still interested in re-chambering your .375 H&H to Ackely Improved or Weatherby, I suggest that you talk to Kerry O'Day at Match Grade Arms in Spring, Tx, just north of Houston. He is at SCI and will be at DSC and also at HSC later this month. Or you can contact him as follows:

MG Arms Incorporated
6030 Treaschwig Road | Spring, TX 77373
info@mgarmsinc.com
Fax: 281-821-6387 | Phone: 281-821-8282

Kerry rechambered my SAKO AV .375 H&H to Ackley Improved about 15 years ago. It has taken everything from duiker to elephant and a lot of critters in between. I like it because it shoots relatively flat and hits extremely hard for a .375 caliber. Kerry also professionally loads my ammunition. I prefer the 270 gr. Barnes TTX as a "soft" and the .300 gr. Speer Breakaways as a "solid". Both bullets will shoot half inch at 100 yards Plenty accurate to take a Tommy at relatively long distance and plenty of punch to drop an elephant if placed right. Also, you can shoot regular .375 H&H or .375 Weatherby if necessary. Kerry is a good guy and will make you happy with whatever you choose to do.


Gene Human

Question: do you lose velocity shooting H+H out of AI or weatherby chamber?

A little bit I believe. I get right around 2500 fps shooting Remington Safari 300g 375 H&H A-Frames out of our Rem XCR II in 375 Weatherby (it has a 24" barrel). Rip would know for sure though.

Thank you Gene. I will definitely talk to him at one or both of the shows. Thanks for referring me and I will let him know.

quote:

Originally posted by chuck375:
A little bit I believe. I get right around 2500 fps shooting Remington Safari 300g 375 H&H A-Frames out of our Rem XCR II in 375 Weatherby (it has a 24" barrel). Rip would know for sure though.

chuck375,

Thanks for the cue.
I will take it from here.

Weatherby factory load by Norma, .375 Weatherby (Norma brass and primer):
Advertised velocity is 2800 fps MV in a 26” barrel, so the below 24” velocity supports the claim very well,
allowing for not so good ThermoBallisticIndependence of suspected Norma powders.

Unknown Norma Powder (N-204?) 88.5 grains
300-grain Nosler Partition
COL = 3.565"
5-yard Instrumental velocity = 2734 fps (needs correction to MV for BC = 0.398, add about 10 fps)
100-yard 3-shot group: 1.1"

Factory .375 H&H ammo fired in this same 24"-barreled Winchester M70 Classic Stainless rifle,
Remington Factory-Loaded 300-grain Swift A-Frame, advertised at 2530 fps MV,
before and after the simple re-chambering from .375 H&H to .375 Weatherby:

(5-yard Instrumental Velocity, not corrected to MV. For BC = 0.325 that would add more than 10 fps to IV to get MV)
Before: 2473 fps ... 1.0" 100-yard 3-shot group
After: 2367 fps ... 0.8" 100-yard 3-shot group

Factory .375 H&H A-Frame load lost only 106 fps when fired in the same rifle after re-chambering to .375 Weatherby.
Some people say that slowing down the .375 H&H makes it more deadly.

That is only true for bullets that fall apart on impact at higher speed.

Re-chambering the rifle to .375 Wby made it more accurate with the .375 H&H factory load.

Slowing it down also reduces the recoil of the factory loads. Maybe that is why I shot it more accurately?

Another handy thing, indeed, a possible TRIP SAVER thing:

When the point of impact of the above .375 Weatherby factory load is +3.0” at 100 yards, the POI of the above .375 H&H factory load is +1.3” at 100 yards, IN THIS RIFLE:



Here is how the .375 Wby cleans up the .375 H&H in a simple re-chamber.
The shoulders only are shown here,
but it is a complete cleanup everywhere,
from old .375 H&H to new .375 WBY.
Just stay off the belt.



Rip ...

The Guru ^^^

Thank you RIP. I know you had the other thread going on this before. I got hooked then Ha. So I was getting back to this job and looking around.

I am going to talk to MG in a week.

Thanks for joining in.

Is it worth it in shorter barrels? II hacked my stainless M70 alaska gun to 20". Will it recover any velocity or just make a lot of noise?

It is worth noting that the biggest shooter on AR by far is Saeed. Ass most of you know he uses the 375/404 Improved, basically a 375 RUM.

He has also used the 375 Lazzeroni, basically rimless version of the 378 Wby.

With 300 grainers he has been from top 378 velocities down to H&H ballistics. However, the load he has now used for years is a backed off 375/404 load that is right on 375 Wby ballistics.

Yes that has been Noted. But thanks.

Also, while I am pretty sure it is - but after the H & H case is fired in the 375 Weatherby chamber, I assume that the case has now been fire formed and is now Weatherby-ized ( New Term ).

quote:

Originally posted by TexKD:
Yes that has been Noted. But thanks.

Also, while I am pretty sure it is - but after the H & H case is fired in the 375 Weatherby chamber, I assume that the case has now been fire formed and is now Weatherby-ized ( New Term ).

Correct.

I have had the 358 STA a heap more times than 375 Imp and ideas as 375 H&H necked down. Full 358 loads simply won't fit the necked down 375 case. I worked couple of reduced loads that shot to the same point in the 375 case as the fireformed.

I also used 340 Wby necked up brass. Wby brass is slightly bigger in capacity than case dimensions would suggest as it is very thin in the walls.

Yep, just fire any .375 H&H in the .375 Wby chamber.

Handloaders have the choice of new Norma made Weatherby brass with proper headstamp readily available now. This brass is about 20 grains lighter, and has about 3 grains greater water capacity than my brass formed from Hornady basic. Using the Norma brass will lower pressures and velocities versus these loads in Hornady brass, so 0.5 to 1.0 grains more powder, depending on type powder, might be used in Norma brass. A comparison of brass is shown below, also including the Winchester WW-Super .375 H&H brass that has been fire formed to .375 Weatherby (beware the shorterWW brass):

Norma Hornady WW-Super

2.860 2.850 2.832 (case length in inches)

228.3 248.4 248.7 (case weight in grains)

111.5 108.2 108.4 (overflow water capacity)



Hornady basic cylindrical FL-sized, trimmed to 2.850", and fire-formed, annealed.
Best substitute for Norma brass with proper headstamp.
Norma factory load is second from left above.

Rip ...

Thanks.

The new brass I currently have is both Winchester Super brass in 375 H&H or Federal nickel brass in 375. Plus the factory loads I have are all Federal in the nickel safari cases.

But browsing on Midway a couple of days ago I saw that Weatherby branded 375 Wby brass was available, but just out of stock at this time. You guys probably got it all already . .

100 - 150 pieces of Wby stamped brass plus what I have is probably a lifetime supply.

Its definatly a caliber that needs a monolithic bullet on DG IMO..The monolithic has made big changes in the DG gun world IMO..

Thank you Gene.

I had a great time meeting and talking with MG in Dallas and we will get it done. Plus a rifle for my daughter too.

You are very welcome. I am certain you will be pleased. Will you be attending HSC?

Gene