What is the most overbore cartridge YOU HAVE USED?

[uncle_motorhead]

Makes sense though. I've often wondered where the appeal is on a 26 inch 10 twist 30-378 or .300 warbird or similar things…burn another 25-50 grains of powder to beat the normal .30 cal magnums by a measly 200-300feet per second. But I hear in pipes 30 inches and longer the drag racers really start to pull ahead, or more so increasing barrel length doesn't lead to the same kind of increased velocity with a .30-06 as it will with a .30-378 to use your comparison.

Total volume for the powder to burn and gasses to expand and work on the bullet as defined by case capacity and barrel internal volume makes a lot of sense compared to only considering case capacity. Case capacity tells you how much powder you can ignite but not how much work it's gonna be able to do.

By that reasoning a .30-06 is appropriate in a 24 inch barrel and definitely "overbore" in an 8 inch barrel. That makes sense to me.

Well, my 30-378 withna 26" barrel sends a 130 gr Barnes bullet out at 4030 fps, my Firebird sends a 120gr Barnes bullet out at 4050 fps, and my Warbird shooting factory Lazzeroni 180's leave at 3630. The 30-06 is 3300 for the 130, 2800 for the 180. My 7 RUM is 150 fps slower than the Firebird, both 26" barrels.

 

[uncle_motorhead]

The problem you start to run into on the really hot ones is the velocity of the gas, isn't it? I'm under the understanding the gas expansion is around 5,000 fps, so no matter what you do with standard nitro based powders you can't really get above that speed.
When I went for 4,000 fps in a 7rum, I was burning 109gr. or so aa8700 behind a 120 Sierra and hitting just a few fps below the magical 4,000 fps mark. That's nearly 1 gr. powder for every grain of bullet.

I worked for weeks to get 4000 from my 7 RUM and 120 gr (Barnes made) Lazerhead. I tried lots of powders, finally settled on 7828 at 3950. But my Firebird made 4050 pretty easily with 7828. Funny, the 30-378 made 4030 with RL22 and 25 and a 130 gr Barnes. That RUM, just not there. I got 3 7 RUM's on clearance when Gander Mtn closed. I was willing to sacrifice 1.

 

[uncle_motorhead]

22-284 with H1000. Now add a flash tube to create a front ignition case. Yes it's a labor of love to build the flash tube and modify the case.... but oh what fun!!!

Fiftydriver has been down this rabbit hole too.

I ran the front ignition flash tube a few years with my 30-378. Tried duplex loads too. No velocity gain but felt recoil and the barrel heating up was noticeably less. But so time consuming I quit when that brass was done.

 

[uncle_motorhead]

I didn't read all the replies, so this may have been covered already. When I do the accuracy qualification of our 300 WM rifles I use a load of 80.5gr of H1000 under a 180gr NBT. This usually yields a speed of around 3100-3150 depending on barrel length. The load I use for the 30-378 WBY is 100gr of H1000 under the same 180gr NBT. The speeds usually hover around 3250-3275, again, depending on barrel length. That's a pretty meager 100-125fps gain considering the huge powder, recoil, and muzzle flash increase with the Weatherby. To each their own, I guess.

But the 308 Warbird factory 180 ammo run over 3600 fps. Retumbo will get you there with the 30-378.

 

[Calvin45]

Well, my 30-378 withna 26" barrel sends a 130 gr Barnes bullet out at 4030 fps, my Firebird sends a 120gr Barnes bullet out at 4050 fps, and my Warbird shooting factory Lazzeroni 180's leave at 3630. The 30-06 is 3300 for the 130, 2800 for the 180. My 7 RUM is 150 fps slower than the Firebird, both 26" barrels.

Awesome stuff man. But even there I see a bit of a verification of my point!

The reason I say that is I have gotten the 120 grain Barnes tac-tx (300 blackout bullet originally) to 4050 fps out of my 26 inch barreled 300 Winchester magnum. Superformance powder, Peterson brass, a fed 215, and HBN treated bullets and bore. That's a hair faster than the 130 grain .30-378 load you mention and only 10'grains less bullet. The point is with these lightweights the monster 30s do no really outrun my boring old .300 Winnie in any way worth noting.

With 180 grainers the gap is obviously getting much bigger.

I also have a load with the the 225 eld m doing 2760…I bet your 30-378 would absolutely CRUSH that velocity with the same bullet weight.

 

[cape cove]

…I bet your 30-378 would absolutely CRUSH that velocity with the same bullet weight

You know what they say " there's no replacement for displacement."

 

[eshell]

Wait why from the muzzle?

The muzzle erodes as well, although I cannot explain why. You will often find the muzzle end will copper foul for the last couple inches while the middle area of the bore remains clean.

Before you blame cleaning, please know that I always cleaned from the chamber end and used a bore guide with Dewey rods. About half-way through the barrel life, I discovered Wipe-Out and stopped brushing entirely.

 

[uncle_motorhead]

Awesome stuff man. But even there I see a bit of a verification of my point!

The reason I say that is I have gotten the 120 grain Barnes tac-tx (300 blackout bullet originally) to 4050 fps out of my 26 inch barreled 300 Winchester magnum. Superformance powder, Peterson brass, a fed 215, and HBN treated bullets and bore. That's a hair faster than the 130 grain .30-378 load you mention and only 10'grains less bullet. The point is with these lightweights the monster 30s do no really outrun my boring old .300 Winnie in any way worth noting.

With 180 grainers the gap is obviously getting much bigger.

I also have a load with the the 225 eld m doing 2760…I bet your 30-378 would absolutely CRUSH that velocity with the same bullet weight.

The 120 is a much different bullet. Both your bore and bullet are HBN coated. I'll tell you My 300 Weatherby's are about maxed out with the same 130gr TTSX at just over 3700. And I did HBN tumble them. I have varmint rifles so I won't be testing the BO bullet in my 30-378. But my 30-378 is a full 300 fps over the 300 Wby. I haven't really played with loads in my 300 Win, because I have too much factory ammo for them. (and I've never even shot them). My 20+ years of reloading for the 30-378, 25+ years loading for the 300 Wby, lets me believe the 300 Win, will be far behind running apples to apples. By the way, I have a cheat load that runs a 120 gr Lazerhead bullet 3800 fps from a 7 Rem Mag with a 24" barrel. But my Lazzeroni Firebird pushes it out at 4050.

 

[Calvin45]

The 120 is a much different bullet. Both your bore and bullet are HBN coated. I'll tell you My 300 Weatherby's are about maxed out with the same 130gr TTSX at just over 3700. And I did HBN tumble them. I have varmint rifles so I won't be testing the BO bullet in my 30-378. But my 30-378 is a full 300 fps over the 300 Wby. I haven't really played with loads in my 300 Win, because I have too much factory ammo for them. (and I've never even shot them). My 20+ years of reloading for the 30-378, 25+ years loading for the 300 Wby, lets me believe the 300 Win, will be far behind running apples to apples. By the way, I have a cheat load that runs a 120 gr Lazerhead bullet 3800 fps from a 7 Rem Mag with a 24" barrel. But my Lazzeroni Firebird pushes it out at 4050.

Those lazzeronis have less aggressive twists don't they? I've always found running lightweights in big cases with aggressive fast twists resulted in suboptimal accuracy.

The 120 is indeed a bit different but still a copper mono with no drive bands. HBN does allow a little more juice haha. I ain't arguing with you here (And am a little jealous of your rifle inventory!) but this is kinda what I'm saying still: the huge firebird is only beating your 7rem mag by 250 fps and a couple hundred foot pounds of muzzle energy with the light 120s…I'm still guessing the difference in obtainable muzzle energy will be more pronounced when shooting heavy for caliber slugs out of each case. Of course I could be wrong, but that's just what I've generally observed.

 

[Lefty7mmstw]

The 120 is a much different bullet. Both your bore and bullet are HBN coated. I'll tell you My 300 Weatherby's are about maxed out with the same 130gr TTSX at just over 3700. And I did HBN tumble them. I have varmint rifles so I won't be testing the BO bullet in my 30-378. But my 30-378 is a full 300 fps over the 300 Wby. I haven't really played with loads in my 300 Win, because I have too much factory ammo for them. (and I've never even shot them). My 20+ years of reloading for the 30-378, 25+ years loading for the 300 Wby, lets me believe the 300 Win, will be far behind running apples to apples. By the way, I have a cheat load that runs a 120 gr Lazerhead bullet 3800 fps from a 7 Rem Mag with a 24" barrel. But my Lazzeroni Firebird pushes it out at 4050.

I don't know about the 300win being a slouch. I'm running a 165 Hdy interlock to 3280 fps with my rifle and I've seen 3150 fps with 180's easily with slow enough powders. My brother's #1 300win was up to 3250 fps with a heavy dose of Retumbo and a 180 when he had it. We are working with v570 and 200 grain pills right now but I haven't had a chrono on either (my Browning or my son's Savage Impulse) rifle yet with it. The Savage tossed a .4" group at 100 with 200eld-x pills and v570 so I loaded 50 to wring it out a bit.

I'm loading for a buddy's 300roy in a crapumark rifle; with factory ammo it was a shotgun. We started stuffing heavier pills in it to fill the throat and accuracy came in. With a 220 Sierra hpbt or 225 Hdy hpbt at 2700 fps with 7828 it's good for 1 to 1.5" at 200 depending on conditions. We've tried for a bit more, but accuracy goes to pot.
Both my 300 rum rifles are running either a 180 at 3300 fps or a 225 Hdy hpbt at 3,000 fps. There's a bit more on tap, but they shoot well there.

 

[Calvin45]

I ran the front ignition flash tube a few years with my 30-378. Tried duplex loads too. No velocity gain but felt recoil and the barrel heating up was noticeably less. But so time consuming I quit when that brass was done.

Something about duplex loads and ".30-378" being in the same sentence gives me a major "pucker factor"

But that's really cool about the front ignition flash tubes…I understand it'd be a lot of work and fiddling around which is exactly why I need to try this some day haha. The premise makes a lot of sense to me.

Do you think it would be worth doing in less overbore rounds as well? I've heard of guys doing this with the .22-284 wildcat specifically. Please do share more about this, what you learned and if there's any "rookie mistakes" to watch out for when doing this? Did you make the flash tubes yourself? Do you like drill out and tap the primer pocket, thread a tube into it, and seat the primer in the tube itself?

 

[JamesWilson5]

6.5 300 weatherby for me

 

[QuietTexan]

20 WSSM would be one ridiculously extreme looking round….in a good way!

I'm hopeful for the WSSM to work well being shorter and fatter versus the 20-250AI. I have 10,000+ Berger 55gn bullets and a stack of 8 twist 204 blanks ready to find out what happens with those two.

I normally go in for the "big hole" theory when shooting pigs, but I figure if I can get a .204 55gn bullet to hit at 3200FPS it should act like a 223 Rem right? Same weight, same velocity (realistically more), just a longer, skinnier bullet when it hits.

I've been intrigued by the WSSM concept for a long time. One of my crazy long-term projects to to scale a PPC/WSSM/whatever is closest to a 30 cal on a Cheytac case.

On the opposite end of the spectrum I ordered a 338 Dasher reamer yesterday. I wish I could get Hammer to make a .338 version of their 101 Blackout Hammer for supers from 8.6BLK/ 338 Dasher. @RockyMtnMT can you make my dreams come true???

 

[Calvin45]

I'm hopeful for the WSSM to work well being shorter and fatter versus the 20-250AI. I have 10,000+ Berger 55gn bullets and a stack of 8 twist 204 blanks ready to find out what happens with those two.

I normally go in for the "big hole" theory when shooting pigs, but I figure if I can get a .204 55gn bullet to hit at 3200FPS it should act like a 223 Rem right? Same weight, same velocity (realistically more), just a longer, skinnier bullet when it hits.

I've been intrigued by the WSSM concept for a long time. One of my crazy long-term projects to to scale a PPC/WSSM/whatever is closest to a 30 cal on a Cheytac case.

On the opposite end of the spectrum I ordered a 338 Dasher reamer yesterday. I wish I could get Hammer to make a .338 version of their 101 Blackout Hammer for supers 8.6BLK/ 338 Dasher. @RockyMtnMT can you make my dreams come true???

Sounds like an expensive experiment! I'll be waiting for updates