Pressure in 45 ACP revolvers

  • Last Post 06 July 2017
Eutectic posted this 07 June 2017

Years ago I ran pressure tests in a S&W 25-2 for 45 ACP load development. The pressure standards were from early Hornady data and probably +P by todays data, but quite safe in any revolver or pistol in good condition. The data was used to develop heavy cast bullet revolver loads which were published in the Fouling Shot. I used hundreds these loads in several 45 ACP revolvers including the new 625. Chronographing in the 625 gave equivalent velocity so I thought all was well.

Since I designed a new heavy 45 revolver bullet Accurate 45-248H, I decided to do another pressure test series and use the 625. Velocity and pressure was similar in the  25-2 and 625 with the jacketed pressure standards, but the pressure in the 625 with the heavy bullets was much higher.  My 625 has tighter chambers and smaller throats which was probably what pushed up the pressure with the heavy bullet loads. I had to reduce the charges and lost ~ 50 - 100 fps to get equivalent pressure in the 625.

If you are using any maximum load data, always work-up referencing known safe loads in your particular revolver.







Attached Files

Order By: Standard | Newest | Votes
BigMan54 posted this 07 June 2017

I know what you mean. I grew up shooting the .357 THOMPSON gascheck load in S&W model 27's,  Ruger Blackhawks & Colt .357/Pythons. Never a problem,  then I bought a S&W model 19. WOW ! Primers flattened & fell out & cases split. The cylinder had 3 chambers that measured. 354 & the others ran .355.-.356.

Never ASS/U/ME anything.  I should have either shot .38spl or measured the cylinder throats & Bore before shooting it for the VERY 1ST TIME & with HOT LOADS. No wonder that cop sold it so cheap.


Long time Caster/Reloader, Getting back into it after almost 10yrs. Life Member NRA 40+yrs, Life S.A.S.S. #375. Does this mean a description of me as a fumble-fingered knuckle-draggin' baboon. I also drool in my sleep. I firmly believe that true happiness is a warm gun. Did I mention how much I HATE auto-correct on this blasted tablet.

Attached Files

Ed Harris posted this 08 June 2017

GREAT topic!  

When I was at Ruger one of my assigned engineering projects was working up a smokeless proof protocol for the Ruger Old Army, because WBR, Sr. insisted that even the BP revolvers should be proofed to a suitable design standard, but it was also determined that using black powder to do so was inconvenient from a production standpoint, due to the extra attention required for cleaning, etc.

About that time Walt Kirst started making his Kartridge Conversion cylinders for the Ruger Old Army and I got him to make a cylinder for .45 ACP which I had fitted with transducer and used as a test platform.  SAAMI specification proof ammunition  for the .45 ACP was a minimum of 25,000 cup as determined by the sample average MINUS 3 standard deviations.  Maximum individual proof pressure was about 30,000 as determined by the sample average PLUS 3 standard deviations.

After having established that the Blackhawk Convertible .45 ACP/.45 Colt was fine with full charge .45 ACP (+P not yet being available at that time, 1985-86) the engineering dept. fitted an Old Army cylinder with Kistler conformal transducer and my task was to develop a smokeless cap & ball proof load which would approximate the .45 ACP proof test conditions with separate loading, using available off the shelf components.

I will not give the "recipe" but did determine that to provide SMOOTH P/T traces a 4Fg blackpowder booster dispensed with a flintlock pan charger at the bottom of the chamber was needed to ensure complete ignition of the smokeless charge. Remington 255-grain .45 Colt lead-conicals could be inserted into the Old Army chambers BACKWARDS with a chamber-capacity charge of a common, readily available shotgun powder and that combination would indeed produce 25,000 psia with VERY uniform pressures, and the minute amount of BP residue was not a problem with the normal cleaning procedures used in the plant prior to packaging revolvers and placing them into shipping.  

Incidentally, the velocity with a 255-grain lead bullet in 7-1/2" barrel with the proof load was a very uniform 1030 +/- 30 fps. I later standardized on a 15% reduction of that load, substituting a 240-grain T/C Maxi-Ball cast 1:40 tin lead for 880 fps. from my Old Army revolver and in the following years have killed seven deer with it, all one-shot kills.

So, I could suggest that pressure tested .45 ACP data which approached SAAMI MAP is quite suitable as a steady diet in modern .45 ACP revolvers such as the S&W 25, Ruger Blackhawk, etc.  Getting 900 fps with a 230-grain jacketed bullet is reality and you can cautiously do so with 255-grain cast bullet using powders such as Bullseye, W231, SR7625, PB, Universal, Unique, Red Dot, Green Dot. 


73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

Attached Files

Eutectic posted this 08 June 2017

Thanks Ed, I had wondered how they managed proofing black powder revolvers. It is pretty much impossible to get an overcharge in the cylinder. I thought they might use FFFF powder, your solution is nice.

I wondered about using 3 standard deviations I assume this is SAMMI practice. I guess I am more conservative, I use 2 SD as the limit in my development. I would reject a load requiring a 3SD margin as having more pressure variation than I want.

The heavy bullet loads I developed for 45 ACP revolver pushed 1000 fps with 250 -255 grain bullets. They worked because the bullets had very shallow seating depth, were hard alloy and sizing diameter was correct. The powders you mentioned will indeed make 900 fps and many provided excellent accuracy. For maximum velocity at safe pressure a slower burning and denser powder is required, HS-7, WW 571, and Power Pistol worked well.

These loads would be unsafe in a 1911 or any 45 semiauto, but the shallow seating and greater overall length preclude loading them in a magazine. The extended full diameter makes chambering them in a normal auto chamber impossible. You can't seat the bullets deeper because the powder fills the case. I thought this was pretty foolproof.   

Wandering in the Back Streets, wishing I was in West Virginia.


Attached Files

Dale53 posted this 05 July 2017

I found this post a very interesting and useful topic. Thanks to all the contributors. I am a certified "Old Fart" but never seem to stop learning, IF I keep my eyes open (:>).


Attached Files

shake posted this 06 July 2017

Excellent thread. Well written and informative.

Attached Files