Cartridge Considerations


New Member
Mar 8, 2002
Fairbanks, AK
Greetings and Salutations,

I am glad I found this site. Now I can ask these questions without being considered, "strange".

I have been thinking about a light-medium bore since I already have a heavy rifle and a medium. I want a rifle with punch.

I have looked at both the .338 Lazz and the .338 A-Square and find them to be virtually identical. The dimensions as follows:
Lazz and A-Square respectively.
Base: 0.581 vs 0.582
Shoulder: 0.563 vs 0.553
Case length (max): 2.82 vs 2.85
Base to Shoulder: 2.3050 vs 2.30
Base to base of neck: 2.466 vs 2.433
Shoulder length: 0.161 vs 0.133
Neck Length: 0.354 vs 0.417 (!)

Pressures (max) again Lazz vs A-Square, Lazz using 27" with a 1:12" twist and A-square using 26" with a 1:10" twist.

200gr NoslerBT 111gr Rl-25 3475fps 54,400 CUP
250gr Swift AF 103gr Rl-25 3154fps 55,900 CUP

200gr NoslerBT 105gr 7828 3360fps 60,900 PSI
250gr SierraBT 120gr A8700 3120 @ 61,600 PSI

Now A-square in their book lists max pressures in both CUP and PSI. They are 54,000 CUP and 65,000 PSI respectively. While I know full well there is no linearity between the different methods, at points with different methods it gives us a good "idea" of where things are pressure wise. Using A-Squares maxes I see Lazz running around 67,286 PSI for their max load with the 250 grain bullet. Max load I saw was at 56,400 CUP which is in the area of 67900 PSI.

This leads me to believe there really isn't any difference between the two. Also, since I can find Weatherby brass almost anywhere and Lazz available from only one source (expensive too) I should go with the A-Square.

I have wondered though, I thought more case capacity would give less pressures. When I look at the commercial reloading pages I see the .338/378 Weath. is not living up to expectations. It really isn't any better than the Lapua and vica versa. Also, a .340 Weath with a longer barrel would appear to be able to catch both. Consequently I am still on hold about the idea of lengthening the body of the A-Sq. a little. I had thought of going 0.05" extra body to 2.350" which would shorten the neck length to 0.367". Still plenty to hold the bullet. I would also take the shoulder out to 0.563 like the Lazz. If I did that it would be custom and cost ~$200 for reamers. If I left everything the same I could have the reamer rented for $50.00.

I was thinking a barrel around 29-30", chromoly (I don't like looks of stainless) with muzzle around 0.850" and heavily fluted. I would have the barrel in front of the receiver cylindrical for about 4 inches for extra support by bedding it. The rest floated. Should I have an extra lug installed so I can put another screw into the barrel ala CZ?

Any comments appreciated, thanks.

[ 03-08-2002: Message edited by: gman ]
Why not look at the 338 RUM.....It will match the Lazz and A-Square in velocity.Use less powder, brass and die's are cheaper and If you get in a pinch factory load's are pretty much every where.....Just a thought.....

It is the same as any standard magnum such as a 300 Win Mag or 300 Weatherby mag.

Can be used on any factory standard mag action and most use the Remington or Sako actions for it.

i have 2 win mod 70's in .338 win it would be no big deal to have one done up as a .338 RUM .would i have to use it as a single shot.not a problem if i did have to any way.if i went that route and went with a long barrel it would put me close to the .338 lapua,would it not,thanks,keith
You are mistaken on the 338-378. What part of expectations is it not living up to. I started working with this wildcat around 1980 and it has performed as expected and although I have found some that would come close it is still my go to rifle because I have yet to find anything that will beat it. I currently own 6-8 of them and 2-3 of them necked to 358 and they will hold a solid 100+ fps advantage over the lapua and 200 fps over the ultramag which I have a few of those also. My pet rifles average around 3600 fps with the 200 and 3350 with the 250. All of mine have 28-30 inch barrels on hunting weight rifles. It is a spectacular cartridge and if you are looking for tops in velocity you will have a hard time beating it. There are other considerations other than velocity though and that is why I have the others and continue to work with them also.
LTLR and to others here.

You are correct in the "Standard" 338/378.

The way to beat it is to Improve the case by blowing it out to a minimum tapor and putting a 35 degree shoulder on it. Now you have the powder capacity that my 338/416 IMP has except mine don't have the belt. This one will beat the velocities you mentioned quite handedly.
I am running the "300 Gr"in my 338/416 at 3310 FPS out of my ultra longrange deer and elk gun. Is is not however a carry gun.

The 338 Tomahawk (338 RUM Improved) is right there with the velocities your posting with your 338/378 and 250 gr bullets and that's on a Regular mag action and with 250 gr bullets also. I have a friend shooting the 338 Tomahawk and is well pleased.
He has stated many times that it is so close to his 338/378 that it's not worth mentioning the difference and he is doing it with a bit less powder.

With everything considered (cost wise), one getting into this game with limited funds would be well off looking at the 338 RUM on a standard mag action rather then going to a large custom or Weatherby action to handle the 378 case head.
The cost of any of the Norma, or specialty brass for the 378 is very high.

The next written material may be of interest to some on the forum who are trying to decide between a 30 cal and the 338 cal unless you use 300 gr bullets in the 338/378 or the 338/416 IMP.

I can run the 30 cal 240 Gr Sierra MK in my Tomahawk at 3225 FPS and that bullet has a BC of .711. Compare that to "any" 338, 250 Gr at 3350 FPS and you will find that the BC of that one is only in the .587 range and that's a Sierra MK.
With long barrels on each caliber, the 240 gr will take over at 400 yards and beat the 250 gr 338 from there on out in every aspect.

Point is, the 338/378 can be beaten with a 30 cal shooting the 240 gr bullet from a factory mag action.

I still have one 30/378 and one 338/378 rifle laying around here too. Just for test purposes.
The 338/416 Rigby Imp with 300 gr bullets is my "go to" rifle for longrange and ultra longrange hunting though.

I just ran the ballistics on the 338/378 pushing the 250 Gr at 3350FPS and the Tomahawk pushing the 240 Gr at 3225 FPS. This will be interesting to many of you, I'm sure.
At 1000 yards the 338/378 with 250 gr bullets Has a remaining velocity 1916 FPS and a Foot pounds of energy of 2039 FP.
The 300 Tomahawk with 240 gr bullets at 1000 yards has a remaining velocity of 2039 FPS and a energy level of 2216 Foot pounds. Clearly the winner is the Tomahawk between the two bullets and calibers used.

My opinion would be to anyone interested in LR hunting and the 338 caliber, would be to make sure you go to the 300 gr bullet in the 338 or if you can't build a long enough barreled rifle to handle the 300 gr, you might want to consider the 300 Ultra or 300 Tomahawk with the 240 gr bullets.

Just another opinion from someone who owns or have owned the calibers mentioned.

Darryl Cassel
Darryl what sort of velocity increase does the 338 Tomahawk have over the 338UM? I have a Rem 700 338UM that I was thinking about eventually fitting with a longer barrel and stepping up to the tomahawk but I read in some of your earlier posts that the Rem action might not be able to handle the pressure that the 338 tomahawks could produce.

The 338 RUM is a fine cartridge especially when you rebarrel to a longer length.

When you improve to the Tomahawk you gain 8 to 9 more grains of powder capacity which is worth going to the improved case if you plan on a longer barrel also.

I have a friend who just put together a 338 Tomahawk on a Remington Mag action and a 34" barrel and he uses the 250 Gr Sierra MK bullet. His results are right there with the 338/378 he and I both have.

I would be a bit hesitant to shoot the 300 gr with full loads of say 108 to 110 grs of powder on the Remington but, I'm sure some are. My question to them is, do they have a long barrel on that rifle? Pressure seems to build in the longer barrels.

I know for a fact the 250 gr does well in the 338 Tomahawk with longer barrels. If you already have a 338 RUM the next step is the Tomahawk when you rebarrel. You could go to the "300" Tomahawk and shoot the 240 Gr Sierra MK with a BC of .711 which ballistically outperforms the 250 gr 338 bullet (.587 BC) all the way. The fellows shooting the 250 gr 338 don't like to hear this but, it's true.

Darryl Cassel
Hello LTLR

The 338/416 Rigby IMP I have has a minimum tapor and a 35 degree shoulder. The standard Rigby case has a much smaller capacity until you improve it.

With the improvement it does hold more powder then the standard 378 case by 12 to 15 grains of powder, depending on the case.
If you improve the 378 case to that of the 416 improved, you have nearly the same capacity. You MUST imp the 378 Case to do it though.

I have the first one Bruce Baer put together and he calls it the 33 Baer on the Rigby belt less case.

Yes, with longer barrels, you can blow the compitition away concerning velocity, in most every case or cartridge.

With an Improved case (30 Cal) I designed many years ago and a 30" barrel I was able to send the 190 gr MK out the tube at 3500 FPS.
The case was called the 308 DC Super IMP.
It had an Ackley 40 degree shoulder and I used the 8mm Mag case as the parent case.
It was blown out to a minimum tapor, the shoulder was moved slightly ahead and it would shoot 106 grs of ball powder. My good friend owns that rifle now and there are several chambered in it around the country. Clymer has the reamer.
It ended up being .002" larger in the shoulder diameter then the 308 Bear and was a longer case because I used the 8mm (375H&H) case instead of the 340 Weatherby case that Bruce did.

I called the cartridge the poor mans 30/378 and Bruce Baer says the same as I do concerning the match up between the 30/378 and the Improved 8mm or 340 Weathetby. Either of the improved 30 cals will stay with the 30/378 with a tad bit less powder.
This is especially true with bullets up to the 220 gr MK.

The best I ever did with the 30/378 and the 190 gr bullet coming out of my 37" barrel was 3600 FPS. The 30" tube and the 30 DC Super IMP did 3500 FPS with the same bullet. Ray Romain has the basic same case with his name on it also. His is called the 30/375 Romain and will walk right along with mine.

I mentioned many times on this forum that you don't really need to go to big actions and 378 size cases with the 30 caliber diameter cartridges. The Improved 300 Weatherbys and 300 ULTRA (without Improving it) will do it.
We prooved this many years ago.

I still have a long barreled 30/378 laying around but, seldom ever shoot it any longer.

Good shooting no matter what cartridge you use. It's still fun & smell of burning powder still makes me horney even in my older age. Of course diesel smoke does that to every time I fire up the Dodge Cummins of mine.

Darryl Cassel

[ 08-21-2002: Message edited by: Darryl Cassel ]
Remember my velocities are out of a 28" barrel hunting rifle. I think the velocities you posted from a 30 caliber tomahawk and 240 grain bullets were out of much longer barrels. When I said I haven't found anything that beat the 338-378 I thought we were talking about buying a factory rifle. I just didn't explain good enough.

I have several rifles off the ultramag case and agree improving it is the way to go on a budget. I have two in 338 using the full length 300 case and improved version. They are exceptional rifles and these along with the lapua and 338-378 wby are all right in there within probably 100 fps using the same barrel lengths. Really your individual barrel could make the difference on which would be faster. I have a 26" standard 300 weatherby that I love to show off to 30-378 owners. My accuracy load with a 180 grain bullet is 3475 fps, with the 200 grain bullet it is 3275 fps. Some barrels are just crazy.
I have never worked with the 416 rigby case and had no idea it had more powder capacity than the 378 wby case. I think I talked to you once before about yours but didn't realize it held more powder. Now I have got to have one of those. I have two ruger number one's in 416 rigby down in the shop that I planned to build something off the 378 case with. Now I may try the Rigby. Is yours an improved version of the rigby or just necked to 338?
As always thanks for all the info. I have never been a fan of the 30-378 and have advised people against it on forums since it got popular around 1997 I think. I tried it and it was a barrel burner like no other I have fooled with. It was very finicky to work with at top velocity loads and like you say could come very close to it with other cases that were not as bad at torching barrels. But that is just my opinion. I know there are many people out there who adore the cartridge. That is the reason I just fool with the 378 case in 338 and 358. I did build an 8mm-378 and thought it did much better than the 30-378 but the limited bullets wouldn't let it reach it's potential.

I also like your 6.5 gibbs you were talking about over on another thread. I think he was rechambering a 25 and wanted to stick with that caliber but I prefer the 6.5 and with the new 120 grain lost river bullets (.687 BC) it is one of my favorite rifles. In my arsenal it is about the best I have in a flat shooting, light recoil rifle for deer size stuff. I would not hesitate using my 358 or 338 gibbs on anything in north america. I liked the 240 gibbs so much as a varminter I got three of them with tight neck chambers. I am shooting the 70 grain ballistic tips at 4100 fps. One is twisted just for the 107 matchking and it is a great long range varminter.
Hello LTLR

Yes, the Gibbs line seems to work great in about any caliber Rocky chamber them to.

The 6.5 Gibbs with an 8 twist shooting the 142 Sierra MK is one of my favorite calibers.
It will do the job further downrange then my 25 Gibbs will. The 30 Gibbs is a dandy also and VERY easy to work with. With 180 and especially 190 gr Sierra MKs, they are fantastic.
To keep from wasting barrel steel, I fireform with the standard loading of the parent case while out woodchuck hunting or breaking in the barrel, which usually takes me about 30-35 rounds to do.

Keep shooting and let us know how the rifles are doing.
Anyone who has the time to use the equipment they have gathered and have several years of experiance doing so, as it sounds you do, is an asset to the forum.


PS Burn that powder and smell it----It will do wonders for you. You wife or girlfriend may want you to go to the range "More Often"
Just a little something from my "bag of tricks." It worked so good, even my wife shoots and hunts with me.
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