Another look at strength of the .44 spl flattops

[Deep Six]

After reading some of the threads lately about the strength of the new model .44 special flattops, I decided to do a little investigating myself. First off let me share a little bit about myself. I am a mechanical engineer with a background in pressure vessel stress analysis working in the commercial nuclear power industry. While I’m no gun designer (my dream job!!!), pressure vessel stress analysis has some application in firearms. In this post I will primarily compare the .44 spl Flattop with the full-size NMB in .45 Colt. Please note that the following is my personal opinion and is presented for the purposes of casual discussion about the hobby we all share. Please do not take this as a professional analysis of any firearm or recommendation as to the safety of any particular load. Always start with the published starting charge and work up from there using your best judgment.
To start, I measured various revolvers from my collection using a digital caliper:
-------------------------------------NM Flattop-----NMB Bisley-----NM Flattop-----Redhawk-----S&W 629-6
-------------------------------------.44 Spl---------.45 Colt--------.41 Mag--------.44 Mag-------.44 Mag
Cylinder Diameter:----------------1.675”-----------1.731”---------1.731”---------1.782”---------1.709”
Cylinder Length:-------------------1.610”-----------1.705”---------1.672”---------1.750”---------1.702”
Cyl Outer Wall Thickness:---------0.085”-----------0.076”---------0.099”---------0.117”---------0.078
Cyl Web (between
charge holes) Thickness:----------0.064”-----------0.064”---------0.111”---------0.085”---------0.085”
Forcing Cone OD:------------------0.622”-----------0.622”---------0.622”---------0.685”---------0.625”
Top Strap Thickness:--------------0.248”-----------0.250”---------0.247”---------0.270”---------0.217”
Top Strap Width:------------------0.703”-----------0.720”----------0.713”---------0.705”---------0.665”
Charge Hole Diameter:------------0.460”-----------0.482”---------0.440”----------0.460”--------0.460”

The pressure generated inside the cylinder when a round is fired produces tri-axial stress in the wall of the cylinder. While a gun designer would be concerned with all three stress components, hoop stress is the only relevant consideration for the purposes of comparing the two revolvers. Hoop stress is given by the equation S = (P)(D) / (2t), where S is the hoop stress, P is the internal pressure, D is the mean diameter, and t is the wall thickness.

Since the wall thickness varies, use the minimum value. For the .44 spl, t is 0.065” at the web and D is 0.460+0.065 = 0.525”. For the .45 Colt, t is 0.065” at the web and D is 0.482+0.065 = 0.547”. If we use the same pressure load in both revolvers, the hoop stress is:

For the .44 spl: S = (P)(0.525) / (0.130) = 4.0385(P)
For the .45 Colt: S = (P)(0.547) / (0.130) = 4.2077(P)

Comparing the two, we see that for equal pressure loads, the hoop stress generated in the 45 is 4.2077/4.0385 = 1.042 times the hoop stress generated in the 44 spl. While the cylinder bolt notches definitely cause a stress concentration, they can be assumed to affect both guns equally for this comparison.

The forcing cone diameters of the two guns are the same. The top strap is slightly smaller on the flattop with a cross sectional area of (0.248)x(0.703) = 0.1743 in2 compared with the full size NMB at (0.250)x(0.720) = 0.1800 in2. The tensile load induced in the top strap will be proportional to the square of the inside diameter of the cases. For an equal pressure charge, the tensile load in the top strap of the .44 spl will be (0.430^2)/(0.452^2) = 0.905 times that of the .45 Colt. Since tensile stress is equal to tensileload divided by area, the tensile stress in the .44 spl will actually be slightly lower for equal pressure charges.

Obviously this is all based on the assumption that Ruger is using the same grade and specification of steel in both guns. I personally have no reason to doubt this.

This leads me to three conclusions:


If a given pressure level is considered safe in a full size NMB in .45 Colt, I would consider the same pressure level to be safe in the .44 spl flattop.
The .41 flattop and Redhawk have a lot more wall thickness and therefore pressure capacity than the .44 spl or .45 Colt.
S&W is obviously comfortable with lower factors of safety than Ruger, as reflected in the dimensions shown above.


Comments?

[Ballard]

With the flat top .44 special, Ross Seyfried is happy with a 280gr WFN at 1100 fps. That is good enough for me. By the way, where in N. IL are you?

[Deep Six]

Southwest of Rockford a ways.

[shoot-n-lead]

Deep Six...that is a very interesting analysis.

And, from my unqualified perspective, it comes to a very plausible conclusion.

Thanks for posting your findings...more food for thought.

[DougGuy]

Sounds good on paper, but published data for Ruger/TC Only loads for the full sized NMBH .45 basically tops off at 30,000psi. All things being proportionally smaller yet near the same thickness between the NMBH .45 and NMFT .44 you would think it could stand the same or similar pressure ceilings.

Question is, why would anyone want to load a .44 Special to the same 30,000psi ceiling as the NMBH .45 when we have the .44 magnum?

BTW, I was a welder for near half a century, and spent some very informative years welding in vessel shop. We were on the coast and had a barge slip right up the middle of the shop and HEAVY overhead cranes, we built the big stuff, 3 1/2" and 4" wall thickhess were common, as was test pressures in excess of 20,000psi for some of our hi strength alloy tanks. Stress relieving was a TRIP, seeing nearly a thousand tons of steel sitting in a gas oven so red hot you could dang near see through it.. I thought I was a welder when I went there. When I left, I *knew* I was...

[shoot-n-lead]

Question is, why would anyone want to load a .44 Special to the same 30,000psi ceiling as the NMBH .45 when we have the .44 magnum?


Now that is where I am...the 44 special at moderate loads...IS...the handgun for me...smaller gun that will do almost anything that I need to have done with a handgun. I LOVE'EM.

Matter of fact, I am to the point of dumping my colts because they really serve no purpose in my arsenal, other than take up space in the safe. If I had it to do over, I would not even go down the .45 colt road. If I need more than the special...I can just reach and get the 44 mag...and use most of the same bullets and molds.

[doc1876]

just leave an address as to where this dump is!!!!

[Frank46]

The weak spot on a barrel is usually the forceing cone. When you stop and think about it after the bullet leaves the cylinder and enters the forceing cone which serves to guide the bullet down the barrel. But as things go that doesn't always work out. Assuming everything lines up properly and in many cases it does the forcing cone takes a beating everytime a bullet hits it. We've all heard about the model 19 when fed a diet of 125 grain screamers and the result is a cracked forcing cone. And now with revolvers with new exotic alloys the front of the cylinder and the forcing cone end up looking like they have been sandblasted. Then we have thread constrictions where the bbl is screwed into the revolver frame. By heavily tourqing the barrel in the frame the metal is compressed and dimensions change. Either shooting with jacketed bullets or firelapping are the two fixes for this. I've seen many pics of some barrels forcing cones. Some do look nice but a lot look like the guy was three sheets to the wind when it came time to cut the forcing cone. And you look at the forcing cones that have been recut and it's like night and day. Just my two cents on the topic. Frank

[shoot-n-lead]

just leave an address as to where this dump is!!!!

I am gonna keep a Williams Distributors stainless, but the others will be on the Swap & Sell...along with multiple molds, holsters and brass, soon.

[Ballard]

Deep six, I am SE of Rockford a ways

[doc1876]

and here I gotta pay the guys for the soffit and facia on the house!!! I told the city there were more important things than that stuff!!

[MakeMineA10mm]

In another thread about this topic, Dale53 and Larry-in-MT posted there was an article in Handloader 260 about the Ruger Lipsey 44 Specials and their strength/level of handloads they can handle. I get the yearly DVDs from Wolfe and went to the shelf and broke out the 2009 one and pulled up the article. In it is an interesting quote from Brian Pearce:

"They (Ruger New Model Blackhawk 44 Specials) are constructed of modern chrome-moly 4140 steel, which usually has a Rockwell Hardness of between 36 and 38. In carefully measuring chamber wall thickness and in having some knowledge of the breaking point of this frame and cylinder, it will safely digest a steady diet of handloads that generate up to 25,000 psi, or what I termed Category Three handloads as presented in previous editions of Handloader Magazine."

That's pretty definitive. I also like that Pearce has some advanced knowledge of "the breaking point of this frame and cylinder." If Pearce says that, I will take that to the bank.

[jrayborn]

Is there any difference in strength between blued steel and stainless steel cylinders?

[Deep Six]

Without knowing the exact alloy and grade of both types, it's impossible to say for sure. Generally, stainless has a lower yield strength than chromoly steel, but there are several martensitic stainless alloys that have very high yield strength. Also keep in mind that yield strength is only one of several important characteristics that needs to be considered. Obviously Ruger has a stainless alloy that they are comfortable using in place of the chromoly steel.

[MakeMineA10mm]

Agree with Deep Six.

I own an early S&W 629-1, and back in 1985, shortly after they were released, they were recalled. Their steel supplier had messed up the heat treat on a couple-3 of the rods they sent to S&W to make into 629 and 624 cylinders. Smith did a mark less test on each and every gun's cylinder, and put a small red sticker on the box label.

So, just as with chrome-Molly, I'd say the heat treat of the stainless has a lot to do with it as well as the grade of steel used.

My guess is the hidden question in your post, jrayborn, is if a stainless steel mid-size 44 Special is as strong as the chrome-molly version we've been discussing. For that answer I can't say definitively, but I'd agree with Deep Six' principle that Ruger must use a stainless steel and heat treat they are comfortable with, including a safety margin.

[jrayborn]

No real hidden question, and I didn't think we could get a great answer without knowing the specifics. The yield strength generally being lower is a great answer, and is pretty much what I was interested in, unless someone was more familiar on Ruger steels specifically its probably as close as we'll get :) Thanks!

I have machined some nasty "stainless" steels so certainly there are differences, I know very little about metallurgy and have both styles of ruger revolver and have always been curious.