I just had a bunch of small hand reamers of
all sizes I collected around and got from ebay,
and found 3 that work.Last one is a taper
pin one I shortened to get exact finish size.
Also use it to ream out the crimp in reg bmg
cases.Makes priming easier with a
miniscule amount of taper.Never leaks even
at super test pressures.You could use an
end mill to get close to size also then
one hand reamer to finish.Ed

You can get chucking reamers in .001 incremental sizes. Thats the most accurate way to make correct sized holes once you have drilled them undersize.
For .50BMG I use a simple 5/16 four flute end mill in a aluminum stop set for the correct depth. I hold the end mill in the Lathe chuck and the case on a mandrel with a primer hole sized stud to support it in the tailstock. While holding the case so it doesn't turn, I advance the tailstock till the end mill bottoms in the stop. Wallah, perfectly uniformed primer pockets and no crimps.-Rob

Thanks guys.
I'm getting those hobby machines in a litte bit and I have found a supply of very large primers (cant cal em .50cal bmg primers or I get into trouble ) that will do the job nicely. So when my RMC casings turn up I can have a fiddle. Sweet hey !

I also ran into an issue with Customs about my barrel. They wont approve the import so there goes my heavy barrel from Pac-nor. BUT I did find a mob here in Oz that will make me a custom heavy barrel. Not quite the same as the Pac-nor but I have a work around sorted.

Moding the RMC cases to take (those un-named but 5/16 primers )will be very straightforeward. Remember, you need a priming tool that ARMs them i.e. flattens the cup so that the pellet is in contact with the anvil. Otherwise they wont work. I suggest you make or have made a two piece shellholder that is NMT a 0.001 fit specifically for the RMC case rims. two piece shellholders are easily machined and involve a base and top which are screwed in place and can provide a high precision fit and are very easy to make with amateur equipment. Adapt that shellholder to a .50BMG priming tool. The reason I say this, is I found in Arming the primer, the stresses will be in the rim and in my experience they either bent or tore out completely. I ruined quite a few of my RIMS THIS WAY BEFORE i gave up. You will ruin complete expensive cases! YIKES.In retrospective thinking, my modified 12 ga shellholder undoubtably had too much slop in it to work( it was designed for a 209 primer with little stresses not for arming .50BMG's). A home made two piece shell holder might avoid that expensive problem. remember,The primers should also be seated flush or NMT .003 below the case head when armed. My NEF has NEVER failed to light them off this way!-Rob

Will do Rob, Thanks for the reminder.

Gibs- Why do you need a import permit for a piece of PIPE? No offense but the gun control bureocracy in OZ is beyond my comprehension. The NRA should use it as an example of what might someday occur here. That whould scare the hell out of most americans.-Rob

Guys-Things have been relatively quiet here so I thought I'd show some Pics of my latest project. The 12GaFH Double rifle is coming along very nicely. I'm taking my time and really thinking things through as well as trying not to make any irreversible mistakes. The Zabala 10ga organ donor will soon be taked apart and sent out for re-heat treatment. However I assembled things to show you how well its coming. The monoblock was bored and threaded 15/16X32 and all convergence from the shotgun barrels removed. This is a scary step as I've just cut up a $800 perfectly good gun. The barrels are from Pac-Nor and are CM 1:20 twist. I spent alot of time writing a CNC profiling, turning and threading program. the barrels were 1.25 straight blanks and were profiled to 1.116 straight for 4" then tapering to .97 at the muzzel in 22 inches. That profile was calculated to let the gun balance over the forearm and also enable me to still use the original Zabala forearm. As you can see it fits nearly perfectly. The profiling turning to the interior dimensions and 15/16X32 threading is NOT FOR THE FAINT HEARTED! These are are a $600 pair of barrels.Lots of steel was removed and each barrel took over 6 hrs of machine time. You cant use deep cuts or high feed rates as the tool chatter even with the clever travelling rest I made for my lathe will kill the finish. Both barrels are near CLONES after this process. BTW they are so perfect the barrels when screwed into the monoblock just closed on the action as is. less than a 0.0005 clearance. Hows that for accuracy? Damn lucky! Next I have to chamber the barrels ( which will be easy with my thru the bore coolant system), make a quarter rib, front sight and make the upper and lower ribs. Regulation with the 190gr Rl-25 and 1085 Darwins will be done, then the whole thing soldered together and blued. Now You know what it will take to build the Double Rifle in 12GaFH.-Rob

Awesome stuff Senor Rob!

You should quit your day job and make extra strength 12Ga shotguns for a living =)

Rob:
I remember reading (too many) pages back someone voiced a concern about some of the earlier Zabalas being"soft".

Is this the reason for the heat treatment or did you make actual hardness tests or metal mass spec analysis on the receiver?
Also, is this one of the Greener crossbolt syles, I remember reading somewhere back it may not have been, I think.

( I have a 10ga.Zabala (Richland version) and an AYA 10ga,double trigger matador I'm toying with the idea of new monoblocks and rifled 12GaFH barrels, after reading this great thread.)

Bravo!

Looks like a Greener Crossbolt Mercury model?

What do you reckon the weight will be when finished?

What is the barrel length? Is that a 4" shank plus 22" of taper for 26" OAL?

What velocity with 190 grains of RL-25 and 1085-grain Darwin?

Butch Searcy still doing the heat treatment?
Searcy needs to offer one when you get the bugs worked out.
Of course that is a bigger and more powerful double than the 700 H&H Nitro Express ... so Butch could charge even more for one of those 12GaFH doubles than he does for a 700 NE. So could you, eh?

Beautiful work Rob. That is a gun that will be as strong
as any $30k double rifle. Those Zabalas are the classiest
action out there while being of good heavy construction.
Those with Greener crossbolts would hold about any load
you could stand the recoil with. Like the 35k plus
loads used in my Savage. Ed.

Rob...

You are going to start getting orders for these soon I bet.

Mere mortals might want a 20 or 28 gauge extra strength "Shotgun"

Maybe you could sell "Conversion Kits"

Thanks for all the nice comments! Lets see the barrels are 22 inches over all length. I expect velocity should be the same as my NEF but will kick harder without the brake. I tried to get 24 inches but the gun was just too muzzel heavy with my model 1/4 rib and front sight. Had to cut back to 22 to get anywhere near the right balance. Weight wise I'm trying hard for right on 14.5 lbs with perfect balance( will need some weight in the stock for this and will probably use a mercury recoil reducer. I'm going to have Butch heat treat it just to be on the safe side and yes it has the greener crossbolt. I'm trying to do nearly everything by CNC so that this gun could be replicated. I'm monitoring the costs and time involved so you all could figure out whats involved and maybe order some parts. The 12gaFh is really pushing this action and a .600NE would be a whole lot easier to do. I may also be able to make prepped monoblocks for this in the future, but they wont be cheap. I've already got 48hrs of time in this thing and $1400. Before its done I'll bet I'll put in another 50 or so hrs.-Rob

So this will be the most powerful 12Ga double shotgun in the world right?

Please tell me you are taking this to Africa with some copper switch point Darwins

Has anyone killed the big five with a shotgun before?

Totally rad, Dude...awesome and outasight...no words adequate...my tongue is hanging out and drooling and my eyes just bugged out...Amen.

Luck on your projects.

Short of a crazy Idea in a DR (and besides you've already sacrificed the length) , but just for future speculation:
What about fluting the barrels and using an alloy quarter rib to reduce the wt forward to get the 2 (or more) inches back.

Wont all the powder burn under 20" with that big of a tube?

Duggaboy- sorry but fluting would look like hell on a double rifle and the quarter rib needs to be weldable to the bottom of the 4140 barrels. Doubt there is a light weight alloy thats weldable and will blue properly and reduce the weight enough to matter. The construction of these things is really quite complicated with lots of decisions that sound good but will get you into trouble later. My intent is to make this as traditional looking as I can.
Boomstick- No all the powder doesn't burn in a 20 inch tube, it probably takes 32 inches for that. I pretty well know that I can get 1750-1800 fps out of 22 inches and that will be good enough for anything that walks this planet. Heck the entrance wound is what a .458 Lott hopes to be on exit! -Rob

quote:

Originally posted by Robgunbuilder:
Gibs- Why do you need a import permit for a piece of PIPE? No offense but the gun control bureocracy in OZ is beyond my comprehension. The NRA should use it as an example of what might someday occur here. That whould scare the hell out of most americans.-Rob

Ok, to import certain types of Firearm parts a Customs Import Permit AND a Police Approval APP is required. Barrels are one such part. I had to give all the details as to the barrels dimensions, intended use, manufacture ect ect. Well they concluded that it was NOT a shotgun barrel so I can't have it, even tho I pointed out that its basicaly a replacement for my SG's already RIFLED barrel. Simply I think they just freaked out about the size, the weight and that it was rifled. To them a SG barrel is none of the above. So no permit. I didn't even bother with the Police APP since that's a state thing and if I can't even get the bloody barrel into the country, whats the point!

Your Junta read this entire thread before reaching their conclusion no doubt.

I think it is simply that given the dimensions and the word SHOTGUN Barrel in the same sentence threw them into a spin. It didnt compute, ergo - Delete!

Rob:
I luv the look of you SxS SGFH, I dare you to fire both barrels at the same time when its done.

quote:

Originally posted by Robgunbuilder:
Duggaboy- sorry but fluting would look like hell on a double rifle and the quarter rib needs to be weldable to the bottom of the 4140 barrels. Doubt there is a light weight alloy thats weldable and will blue properly and reduce the weight enough to matter. The construction of these things is really quite complicated with lots of decisions that sound good but will get you into trouble later. My intent is to make this as traditional looking as I can.
-Rob

It was a "what if" and I do understand the complexities you are facing( having observed several different ones under construction or re-barrelling) though I have not completed one myself.

Your choice of the traditional look is appropriate.

Having seen a few octagonal DR's and one triagonal example, the aspect of micro-fluting still has some appeal to me for the future.

My thought as to the quarter rib was to dove-tail or bond an alloy super structure on to a joined barrel assembly.

You are most likely correct that in the end all the excess frittering would not pay off in significant enough weight reduction.

But day-dreaming is what gets us into these projects ,ain't it?

Both barrels at the same time going off with no brakes. EEKS! Thats gotta hurt! No plans to do that.
Yup, I'm going for as close to the classsic look and handling as I can get. I have a original Jeffery 450#2 that I'm using as a model. I'll have to make some compromises but I want it to be elegant when done. I'd be interested in some pics of that octagonal DR if you can post em just to keep an open mind.
Gibs- I absolutely cannot comprehend whats been allowed to happen in OZ. That level of bureocracy and governmental control is like a bad dream. I always thought one of the main purposes of having guns was to never let anything like that happen. Now I'm gonna run out and get a MaDeuce .50 for brass production for my DR. In your case, keep figuring a way around its fun and entertainment.-Rob

quote:

Originally posted by Robgunbuilder:
Both barrels at the same time going off with no brakes. EEKS! Thats gotta hurt! No plans to do that.

You big Girls Blouse You!!! An here I thought you was maken real mens guns. Seriously tho, looking good Rob. Cant wait to see how it looks all done.

quote:

Originally posted by Robgunbuilder:Gibs- I absolutely cannot comprehend whats been allowed to happen in OZ. That level of bureocracy and governmental control is like a bad dream. I always thought one of the main purposes of having guns was to never let anything like that happen. Now I'm gonna run out and get a MaDeuce .50 for brass production for my DR. In your case, keep figuring a way around its fun and entertainment.-Rob

Unlike the USA, Australia never evolved the same way. For startes we never had a War of Independance, we just voted. Second we also dont have the large number of private firearm owners that the USA has. For a country of only 25 odd million people, the number of private firearm owners would be lucky to get to 500 000 (maybe a bit more, no real hard facts on that figure anywhere). Our National shooting body SSAA has only some 200 000 odd members. Just not enough to make a real political impact. We are regualy targeted as the scape goat ever time some loon gos nutzoid with a firearm and the general public have been cond by the media that Anti Firearm Laws will improve such type of violance, which of course is pure bunk. But they swallow it whole desperatly believeing it will be a quick fix and they can blisfully go about their lives pretending that the Government of the day has their best interests at heart.......yeah right!
We are just an easy target to pacify the public, Ohh theres been another a shooting, let beat up on the LAWFUL firearm owners, that way we can say we did something! Until we have enough firearm owners in this country to actualy make the pollies sweat bricks, we are on our own. And last, we do not have the right to bare arms. We dont even have a constition like the US does, we have a Bill of Rights, that Bill can be change any damn time the polllies like. We do have a constition, but its only for how the government is formed and what powers they get, not one bit about the rights of the people. Thats left to the Bill of Rights. And in there we dont even have the Right of Freedom of Speach technicaly. So yeah, never let the bastards take away your 2nd amendment or you will be as screwed as we are.

Gibs - been to Oz probably 5 times and hunted big time near Darwin for banteng and Water buff.Had a fabulous time and have always felt you guys were more like brothers than anything else.I feel for you. Your right the 2nd amendment is the most important piece of our constitution andfeel certain we will never ever let it be taken away. -Rob

The main differences between the US and Australia regarding gun laws are size and demographics.

The US has the muscle to tell the Euro UN to fuck off, which is the major generator of the anti gun sentiment. We are too small.

The second reason for the US's strength is its structure of large rural voting centres, basically keeping the city slickers in balance.

Australia, despite its 'outback' reputation has very few people in the outback. 85% of Australians live within spitting distance of the 4 or 5 major cities.

In other words the cities make a law and the whole state crumbles 9 to 1.

Also the biggest reason gun owners don't battle anti laws well, and this is now a problem in the US too, is they support the same agendas anti-ing other sports and living styles.

Get 100 gunowners together and you will find 99 of them with personal views on banning anything ranging from fast cars, 4x4's, knives, violent sport, video games, crossbows, dangerous dog breeds and the list goes on and on.

The one guy who is open to everything else is the guy you need on the team to really fight for guns.

The other 99 guys are almost as dangerous as the anti's themselves when it comes time to ban things as he sells every other group down the tube without even realising it.

Divided you fall.

Karl,
Welcome back.
We are in some worrisome times in the USA for sure. The latest crock here is that US guns are flooding into Mexico. We need to go protect Mexico against the threat from the USA guns, which are only 15% of the world of guns being used by the drug cartel!!!
Forget about protecting the USA from illegal immigration and drugs!!!
So, when our forces finally muster down to the border, will they point their weapons back at us or toward Mexico????
After all, the Homeland's military veterans are a terrorist threat from within, same as the pro-lifers.

I got QuickLOAD finally. I am dangerous now too.

Rob,
I am ignoring the base shape of the slugs and letting QuickLOAD calculate the bore area on my first run through some approximations:

12GaFH case capacity: 340.0 grains H2O
case length: 3.850"
1085 gr. Brass Darwin slug length: 1.350"
COL: 4.180" (FN showing .330" nose length)
etc.

22" barrel:

RL-19

190.0 gr. (88.7% filling)
1764 fps
24,386 psi
7500 ft.lbs.

200.0 gr. (93.4% filling)
1863 fps
27,889 psi
8360 ft.lbs.

210.0 gr. (98.1% filling)
1964 fps
31,948 psi
9293 ft.lbs.

215.0 (100.4% = compressed)
2016 fps
34,217 psi
9787 ft.lbs.

220.0 gr. (102.7% = compressed)
2068 fps
36,669 psi
10,300 ft.lbs.

H4350

205.0 gr. (96.2% filling)
2045 fps
34,673 psi
10,079 ft.lbs.

The smaller-bore 700 H&H Nitro Express truly eats the dust of the 12GaFH, and it does so at higher pressure than the shotgun.
Even a 12GaFH with a 22" barrel outperforms the 700 NE at pressures well below the CIP max for the 700 NE.
Bigger bore and bigger case counts for something.
Same SD slugs too.

Alas, QuickLOAD does not know what to do with the 15 grains of Blue Dot starter.

My best approximation so far is to figure that X grains of H50BMG plus 15 grains of Blue Dot (X + 15 grain total) set off by the 209 ...
burns faster, like X + 3.6 grains of Retumbo.

So ...
24" barrel
1382-grain Hard Lead Darwin
1.375" slug length
4.225" COL:

200.0 grains H50BMG X 15 grains Blue Dot
(91.2% fill with the H50BMG alone, leaves plenty of room for the Blue Dot 15-grain starter powder)
= 203.6 grains of Retumbo:

1536 fps
20,558 psi
7242 ft.lbs.

Amazing low pressure!

That too will give a greater TKO than the 700 NE, with the added benefit of
penetrating like an overgrown 45-70 Govt. Hammerhead.

Yes the starter powder is still adding to the charge,
say like blue dot and HBMG added together would be
little faster, take total, call it Retumbo or RE25.
Calculate for those two, and see what matches the chrono
results that you got.Then you'd know the amount
of speedup blue dot gave. For pressure
and velocity you have to include it in
the calculations the program is doing.
The 200gr HBMG and 15gr Blue Dot load
you list above that the program shows,
at 1536 fps, you chronoed at little over 1600.
So that would reflect the starter powder.Ed

RIP- Wow now equipped with Quickload you truly have become dangerous! Good data though. I have yet to try Rl-19 and probably should. That data with H-50BMG at 200grs seems close to what I got and yes with a starter powder I agree the charge acts more like Rl-25. I've been busy figuring out how to make DR concave ribs and a reral elegant 1/4 rib. Thats next on the to do list. I've shown the 12GaFH DR to a few locals and I guess my stock has risen a bit. Cant wait to start regulating the beast. I have to carefully consider some loads like the 200gr H50BMG as the issue of a accidental double really has me thinking. A double at Full power probably is a trip to the hospital.-Rob

Ed,
I believe you first offered the idea that the starter powder changes the burn rate of the H50BMG.

I ran with that idea and this was my result.
I clarified the above, as below:

quote:

24" barrel
1382-grain Hard Lead Darwin
1.375" slug length
4.225" COL:

200.0 grains H50BMG X 15 grains Blue Dot
(91.2% fill with the H50BMG alone, leaves plenty of room for the Blue Dot 15-grain starter powder)
= 203.6 grains of Retumbo equivalent:

1536 fps
20,558 psi
7242 ft.lbs.

I did the estimation process just as you recommended, based on my chrono data using Rob's 1085-grain Brass Darwins in my loads.
My formula got me to within 1 fps with Quickload.

200xH50BMG + 15xBD = 203.6xRetumbo

This neglects the effect on burn rate caused by a heavier slug.

I will refine the "formula" when I have some data from my gun with the heavier slugs.

H50BMG is horribly inefficient in the 12gaFH, Blue Dot starter seems to improve that.

After 6 months of waiting for Lee to make the sizing die, I got a cute notice that I should keep waiting when I emailed them last week ...

I am waiting for a reamer from Dave Kiff to make my own sizing die ...

Now I see that Brownells has shelf stock of Clymer .730" back-bore reamers, cheap!

I am getting impatient.

Will order some stuff from Brownells now ...

and go try the load approximation with RL-25 as you suggested.

Rob,
Yes, I are truly dangerous now, a U.S. Military veteran in possession of QuickLOAD!
Nice to finally join the club!
I'll go play with RL-25 now.

Assuming the QuickLoad assumptions noted above are representataive of Rob's 12GaFH with
Nohbozo brass and CCI-35 primer
1085-grain Brass Darwin
22" effective barrel length (24" in parentheses for comparison):

RL-25

210.7 grains RL-25 = 98.9% fill
23,827 psi
1767 fps (1812 fps)
7521 ft.lbs. (7910 ft.lbs.)
(this load is exactly equivalent to my chrono data for 230-grain-H50BMG + 15-grain-BlueDot,
but remember my brass is different)

212.98 grains RL-25 = 100.0% fill
24,550 psi
1789 fps (1835 fps)
7711 ft.lbs. (8109 ft.lbs.)

222.63 grains RL-25 = 105.0% compressed load
28,286 psi
1896 fps (1944 fps)
8664 ft.lbs. (9104 ft.lbs.)

Eventually we shall see how this jives with reality.

From this it appears that the Blue Dot starter changes the burn rate of H50BMG to something closer to Retumbo than to the RL-25.
Retumbo is faster than RL-25.

RIP- My 220gr load of Rl-25 did 1757 as I remember. Thats incredibly close to the predicted values. Actually I've found Quickload to be remarkably accurate at predicting the velocities of the 12GaFH.-Rob

Rob,
Lot-to-lot powder variation and the 'puter uses a lot that is on the bulky and fast side of the spectrum of lots as a safety factor? Close enough.

I am not finished trying the X15-H50BMG loads yet.
Certainly looks like I could go to faster powders too.

Simply switching bullet weights from 1085 grains to 1382 grains, other parameters the same,
usually only drops the velocity by about 40 fps, and ups the pressure by about 4000 psi.

I suppose the bigger change comes from increased recoil:

I looked up this Quickloads program, looks to be rather handy. Sadly will have to wait a bit, to many other things on the go atm. Thanks for the info, even if it was only in passing.

RIP- I went the other way with 350 gr aluminum bullets at 3000 fps. That took 190 gr of IMR 3031 and was a hoot! I'm surprised a little by upping the bullet weight to 1382gr that you only lose 40 fps. I would have thought more. Yes the recoil will be stouter!-Rob

Rob,
Oh boy! I can try the aluminum QuickLOADs next!
The above was from my first doodlings with QuickLOAD.

I have not read any of the manuals or instructions, just fired up QuickLOAD and started inputting.

I was surprised that the velocity was so close between 1085 and 1382-grain slugs.
Peak chamber pressure changes were more significant than velocity, but only around 4000 psi different.

Most of the muzzle pressures were around 5000 psi.

I am going to "study up" on "bore area" and see if I can refine the default value calculated from the .729" groove input.

I guess you have to calculate the area of the .729" circle and subtract away the area covered by the rifling in cross section to .719" bore diameter?

The proper number of grooves and the .005" rifling height might not have been applied by the default?

RIP- you can get pretty sophisticated and define the cartridge case dimensions and bullet design. They have an effect as well as the rifling pattern etc. yes these loadings run about 6000lb muzzel pressure. Thats why I kept my muzzel thickness no NLT .97. I used Quickload to develop the .600Ok, .600RLG, 700RLG and the 12GaFH. I found it to be pretty reliable and safe. A wise, fun and very useful investment.
Those Al Darwins screem out of the NEF and have very light recoil. I now put a little Rooster Red lube on them too. Lotsa fun and really gets the attention of those at the range.-Rob

quote:

Originally posted by RIP:
Karl,
Welcome back.
We are in some worrisome times in the USA for sure. The latest crock here is that US guns are flooding into Mexico. We need to go protect Mexico against the threat from the USA guns, which are only 15% of the world of guns being used by the drug cartel!!!
Forget about protecting the USA from illegal immigration and drugs!!!
So, when our forces finally muster down to the border, will they point their weapons back at us or toward Mexico????
After all, the Homeland's military veterans are a terrorist threat from within, same as the pro-lifers.

Rip thanks. I always seem to drop in with something cheery don't I
I am in the 4th world right now(ie the 3rd world with more loud noises) seeing the effects of when people get tied up with so much bullshit, like the policies you mention above, they eventually forget their constitutions.

But back on target. Did anyone find one of the CSA or tonolini guns to test the 12ga FH yet? Regrettably I have not

Karl.

quote:

Originally posted by Karl:

But back on target. Did anyone find one of the CSA or tonolini guns to test the 12ga FH yet? Regrettably I have not

Karl.

Karl,
Ed is still waiting to pounce on one, and I would too if I could find one.
I had a guy look around at the Tulsa show.
He could not even find another 10 gauge Zabala.
I have one of those but it is a model from the last year they imported them here and has no third fastener/GreenerXbolt ... I am still looking to collect one like Rob's.

Rob's most excellent adventure in building the DR will surely provide jollies for all.
Even he feels that his stock has risen, and I second the notion.
We only fear a trip to hospital for Rob, a minor inconvenience, if he should accidentally double-fire it,
and Rob firsted that notion.

I am getting closer to Rob's chrono data with QuickLOAD.
I stupidly ignored the "Shot Start/initiation Pressure," and the "Weighting Factor" for cylindrical case shape. Now corrected:

12GaFH No.1
NohBozo Brass
CCI-35
1085-grain Brass Darwin
22" barrel:

220.0 grains of RL-25

1799 fps (Rob's actual velocity was 1757 fps)
25,084 psi peak chamber pressure
6428 psi muzzle pressure
7800 ft.lbs. KE of slug

10.5 pound gun weight recoil (NEF):
152.7 ft.lbs.
30.58 fps

Should be really gentle in a 14-pound double, and Rob's muzzle brake gentles the 10.5# NEF also.
No worries about hospital!


I am still ignoring bullet shape factors regarding the base of the bullet, corrections there will lower the pressure and velocity a wee bit.

I am still using the default "Cross Section Area of Bore" = 0.41113 in.^2
This is 98.499% of the area of a .729" smooth bore.

A circle of .729" diameter (groove) has an area of 0.4173936 in.^2,
and a circle of .719" diameter (bore/land) has an area of 0.4060210 in.^2.

In the program, increasing the "Cross Section Area of Bore" all the way to a .729" cylinder smooth bore causes only a decrease of about 20 fps velocity. Just a trifle.

"Indians vow to endeavor to persevere."
24" NEF-er with 1382-grain Lead Darwin using 215.0 grains of "X15H50BMG" powder with CCI-209 primer:

1583 fps
21,760 psi chamber
5878 psi muzzle
7686 ft.lbs. KE

11.5 pound gun recoil:
164.98 ft.lbs
30.37 fps
and greatly lessened from that by VAIS (C) brake.