How much bottleneck can be tolerated in a SS BPCR cartridge safely???

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  • Last Post 23 August 2013
corerf posted this 02 March 2012

Heres the deal, there is nothing new under the sun. But I'd like to expand on several variants of the 40-82 cartridge, known as the 40-65 ron long, 40-65 long neck and the 40-82 crossno. All of these are 45-xxx parent brass necked to 40 cal to accept a .408 bullet and handle larger volumes of powder.

The idea is to make the 40 cal, with higher BC (above 400 gr) more competitive in long range.

Several folks have done their own deal with multiple dies, using a 40-65 die, running only part way down a 45-90 brass and making a pseudo two die system with a spacer at base to keep the case head fat like the parent brass.

I'd like to go a step further but I am treading in deep dookey potentially. Like a massive boom and the loss of my favorite body part, my head.

I'd like to take a 50-140 and neck all the way down to 40. Now this would be a neck, not a shoulder but the worry is, when the BP burns will the BP see a shoulder, a neck or a complete obstruction???

I have looked at an awful lot of BPCR rounds and NONE have that an extreme diameter change. I'd like to go fatter than the 45-70 case head, to some extent for efficiency (I am drawing a parallel to the 284 win, 308 win, etc where the powder column burn characteristic is “better” than say the 30-06. Same work performed in a shorter package, or very nearly). That and I can jam more BP in!

Secondly I'd like to have the ability to throat for 400+ gr bullets, not express stuff, and get the velocity upwards of 1500 where a 1-18 twist, or 1-16 twist will stabilize out to as close to 1k yards without worry of stripping rifling. Folks are saying that the 1-14.5 GM barrel will strip but it also is up to the 1000 yard task. An extra 100-150 fps is what I am trying to achieve. That and creating my own deal, for the sake of wasting money and doing it...... good or bad.

So the case head would be somewhere near 565 for about 1 inch, then reduce fairly quick to 505 (a shoulder similar to the 30-30 neck-body junction) The taper to the 40 cal neck would be following the 505 to 425 inch body of the 40-65 win.

So in other words, the case head is blown straight in fire form to the full diameter of 565, then taper as the natural 50-140. Then a 505 to 425 taper for an about 1.15, then a .75 or so neck.

The BP will only see the basic 50 cal base and a basic 40-65 cartridge, the neck wont exist as its essentially become part of the bore due to a deeply seated bullet. The neck woud be very long, as long as the 40-65 FL die allows me to press in, potentially 3/4 inch. I'd like to use the Snover bullet or longer as the basis and have all grease grooves in the neck and have the bullet ALL in the neck. This is an application specific cartridge!

Dies used to form would be 50-140 FL die mutilated to be used as a base sizer. The 40-65 die with a machined spacer would do the upper half, granted it can size and NOT crush the long neck. So far what I have read is it will go long with no issues.

Lastly I can use another carbide die, for multiple shots to just neck size. Like a pistol die.

The biq question, is there a limit to how much BP you can stack under a projectile with a severe overbore condition? and is the pressure going to peak so violently that it destroys my (Argentine) Rolling Block?

Anyway, any body????? Any thoughts (directed toward the project, not away from the project) would be appreciated.

Sharps built the 44-100 and it worked well. The 50-140 is just a fatter head version with a smaller mouth. I am nuts but not too nuts.

I think this can work, maybe kick like its been dropped form a 30 story building, not be accurate, etc..... but it will work.

Mike

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TRKakaCatWhisperer posted this 02 March 2012

405 Win ?

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corerf posted this 02 March 2012

Thought about it prior and is still an option, with reduced neck diameter. But I wanted more capacity.

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32ideal posted this 02 March 2012

Go to the 40-90 Sharps Straight or Bottle neck case, more than enough capacity I would think. If to much you could shorten them to your needs.

Mike

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Tom Acheson posted this 02 March 2012

Not sure if this helps but....my Model 74 C. Sharps .40-70 1:16 Badger using 68.0 of Swiss 1/12 has on several range trips chrono'd between 1323 and 1330 fps, using a 420-grain 16:1 Paul Jones Money bullet. Using 69.0-grains it went at 1362 fps. Getting closer to your 1500 fps target.

Tom

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corerf posted this 02 March 2012

To Tom: how much of the money bullet is in the case?to 32 ideal, any idea where I can get a dimensional drawing of the 40-90 sbn?

Is rather not build my own.... But I want all the bullet in the neck, and a large capacity.

32ideal, what is the parent case for the 40-90 sbn?

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Tom Acheson posted this 02 March 2012

The OAL touching the lands is 3.480” Subtract 2.5” for the 405 Winch. Hornady case and that leaves 0.980” exposed. The bullet is about 1.375” long that means about 0.395” of the bullet is in the case. (I use a 0.060” thick ploy wad on top of the powder and a waxed paper wad in the case above the primer and a FC 150 primer.) This exposes 2 of the 4 lube grooves. I can't recall the amount of compression but it ain't much.

Tom

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Brodie posted this 03 March 2012

Tom:  I don't think that the “shoulder” of your proposed case would be a problem.  Just look at the 577/450 which if I am visualizing your proposed cartridge correctly would be about the same.  But , why wildcat a BPCR  round.  They won't let you use it in the matches..  Brodie

B.E.Brickey

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303PV posted this 03 March 2012

What about the 9.5x60R Turkish. It was used in a Peabody rifle.

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corerf posted this 03 March 2012

Old Coot,

Thank you! Thats the dimensions I wanted to see. .130 case reduction, over a very short distance. Its a real shoulder/

303PV, I could only find a 9.5x47R but too has a sharper shoulder than most.

In general:

I did some reading where folks have had severe fouling just ahead of the throat due to the powder being blown forward and doing most of the combustion at the first inch of barrel. BUT I think they are short seating to boot capacity (in ref to the 40-90 Sharps). I would be seating as deep as possible and hopefully with a throat full, tight, I would not see that problem.

You guys are giving me hope.

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delmarskid1 posted this 03 March 2012

Some people have good results using black in bottle necked cartridges. They change a few procedures. They do not compress the powder and use pistol primers. This may be how they avoid the throat fouling that you mentioned. For curiosity's sake I loaded pyrodex pistol powder in an '06 and a .375HH. The .375 worked well. The '06 was a mistake. Bad fouling in the throat. I didn't know about black powder bullet lubes then. It may have made a difference.

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corerf posted this 04 March 2012

That's huge info and makes complete sense.

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lkydvl posted this 11 May 2012

Your thinking is a mix of both BP and smokeless cartridge loading. Forget ANYTHING related to smokeless when loading BP.

Its nigh unto impossible to overload a BP cartridge to the point of overpressure. It just does not burn in that fashion like smokeless does. Excess will leave more fouling in the barrel, more burning outside the barrel and unburnt powder on the ground ahead of you.

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Michael K posted this 12 May 2012

You could look into the old .40-110 Win Express. 3.25” case length with a .532 base and a .485 shoulder dia. which is within about 0.010 of the 50-140 and it does carry the nice long you are seeking. There are of coarse the more obscure 40-90 Bullard or 40-90 Peabody rounds. They seem more like a 1870-80s version of a modern short mag. Hmmm, reckon they could be refered to as BPSMs. Michael

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vol423 posted this 23 August 2013

There is a cartridge that is technically the 40-85 but it is made by necking up a 9,3X74R cartridge to 40 caliber.  It  is just about the best long range setup you can get and it is entirely legal for  the matches.

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