Brilliant, terrible or diminishing returns

[sqlbullet]

My recent acquisition of a Fusion 1911 sparked some renewed research into 9X23 Win and very heavy 38 Super Comp loads.  I find the 9X23 very interesting as a case study:  Ramped frame design with a very strong cartridge case head to enable 50K psi internal ballistics pressures.

This got me thinking about 10mm Auto.

6.8 SPC offers a potential brass source for a 55K PSI capable case head, with some trimming and reaming. So brass can be sourced for a wildcat experiment relatively easily.

A web search turned up that this was not an original idea.  But, it appears previous endeavours didn't get past the ideation phase.  I would guess that the brass reaming was the first hurdle.

Next came the question of gun strength.  I spent about 10 hours over the holiday weekend dusting off engineering books and collaborating with family members that are engineers. The math says a 1911 barrel would have a safety margin that is acceptable:  1.4 in 4140 (fully annealed), 1.5 in 416R. Most 1911 barrels in carbon steel are hardened and normalized, which would boost that margin to 2.2.

The Tanfoglio guns get a bit more interesting since I don't have good data on there barrel steel.  I assume it is 4140 or a similar arsenal steel, and that it is significantly hardened and normalized. With that assumption the safety margin is at least 1.6 in arsenal steel.  If they are using 416R the margin is below an acceptable threshold at 1.1, unless they are using some trick in the hardening process to exceed the typical 416R yield values.

So, testing in 1911 :-)

Next came the question of the action strength.  Due to the complexity of the geometries in the action, this is really a challenge for software that I no longer have a license for.  As a smoke test I calculated the lbs-force in a 460 Rowland and compared it to a 50K PSI 10mm round.  The 10mm is less but only by about 2%.

I would add here that this is being approached as a wildcat exercise.  A "production" implementation would require significantly more review.  I am trying to ensure I won't blow up my guns if I get to the testing ammo phase.

With this diligence completed, I stepped into a review of the internal ballistics.  No sense in doing this if there is not a meaningful gain in velocity over 10mm Auto.

This is where my excitement diminished a bit.  I was optimistically hoping to see a 20% + gain in velocity for mid-weight bullets and more for light bullets.  Realistically it appears the gains would be 12-13% for the bullets 135 and less, and about 8-9% for mid-weight bullets.  This gives a 135 grain JHP at a probable 1800 fps, and a 155 grain at a probable 1630 fps.

If 20% or a bit more was accessible, then I would be ordering a reamer for Forster.  But 10% is not so exciting given the reward.

[The_Shadow]

Mitch, the 6.8 SPC is the case I used for my snake shot loads for 10mm only because I didn't have an 10mm Mag cases to use for my project.

The case was cut down to length so that I could form the neck area to 9mm sizing with the 9x25Dillon dies to head space off the neck but also allow the neck area to hold even more lead shot as it sort of takes the place of a projectile as loaded. 108.6 grains of #9 shot capped with a 357 gas check.

[The_Shadow]

I am tracking what you are saying about the 6.8SPC case being stronger than the 10mm.  Max Loads for 10mm my provide more pressure due to the 6.8 case volume.
I'll try to follow your progress should you try to develop some loads.

I remember where some 800X original loadings were really too strong for the 10mm cases...
this is one such loading
Underwood 135gr Nosler JHP
Ballistics Information: 10mm Auto
Muzzle Velocity: 1600 fps
Muzzle Energy: 767 ft. lbs
Pictures: Before/After disassembly:
Brass Make/Headstamp: Star Line - Brass
Bullet Make/Weight/Construction/Info; Length 0.4880"/Dia. 0.400": Nosler 135gr. JHP
actual weight 135.2 grains
C.O.A.L.: 1.2520"
Primer: Brass color
Case: Diameter 0.4215" Crimp Diameter 0.4210" Length 0.9870"
Powder Description/Positive ID/Type/Charge Weight: IMR800X 11.8 grains
Picture of powder:
Tested Velocity: 1738 fps

After the Shot
Case Data: expansion measurement's: Diameter 0.4325" "Smiled" 0.4295" primer blown out, no ejection, case stayed in the chamber but loose. 

WARNING! yet the old 800X data was shown as and was too much