Are .45 auto rim and .45 ACP loads the same?

[dmy]

Everything I have read seems to indicate that .45 auto rim and .45 ACP loads are practically the same. However, my experience with my 625-2 is that the exact same load in an auto rim case has signs of higher pressure than when I load it in an ACP case.

I noticed it in two of my more common loads which are: 4.73 grs of 231 behind a 200 gr Hornady LSWC and 3.7 grs of Bullseye behind a Berry's plated 200 gr RNFP or SWC. All three bullets are 0.452" dia. Both loads behind all 3 bullets function perfectly out of ACP cases, but cause the case belly to expand in my auto rim cases which makes ejection somewhat difficult. All 3 bullets also seem more accurate out of my auto rim cases. I keep my revolver clean and had my chambers polished, so I know it is not caused by residue in the chambers.

My old Speer manual did have slightly lower ranges for auto rim versus ACP cartridges, but they were both pretty close. I was thinking that the pressure may be greater with auto rim because the rim forms a better seal for gases trying to escape out of the back of the cylinder. I have tried using a slight taper crimp rather than a slight roll crimp. The taper crimp seemed to have slightly less recoil and and reduced the amount of case expansion, but the case ejection was still a little sticky.

I was wondering whether anyone else who reloads .45 auto rim has the same experience?

 

[moxie]

In my experience they are exactly the same. The only difference is the rim.

Unless you are using bullets with a cannelure or crimp groove, you should be using only a light taper crimp...no roll crimp.

Trying to ascertain differences by recoil "feel", etc. is problematic. the only sure way is with a chronograph.

One advantage of the AR is the ability to use a roll crimp in bullets that can accommodate it. For example you can use a heavier bullet and load in an AR case than an ACP case because you do have the roll crimp ability, if you have the right bullet. A good choice for the AR might be the .45 Colt 255 gr. SWC hard cast from Missouri Bullet, also available in coated. It has the crimp groove. See:

Missouri Bullet Company

 

[andyo5]

I'd be careful before assuming you can use a roll crimp in a 45ACP revolver.
The case still headspaces on the case mouth. The rim allows extraction without moon clips. That's ALL the rim does.

 

[HKSmith]

I'd be careful before assuming you can use a roll crimp in a 45ACP revolver.
The case still headspaces on the case mouth. The rim allows extraction without moon clips. That's ALL the rim does.

Not true! The .45 Auto Rim cartridge headspaces on the rim, which is why the rim is so thick compared to the rim on other rimmed revolver cartridges. If you doubt this, check SAAMI specs online for the Auto Rim compared to the ACP cartridge.

 

[smokey04]

In my experience, if you check an Auto Rim[AR] case and an ACP case for water volume you will find the AR case has less case capacity. Either way, unless you are loading max. loads there will be little difference in performance.
The ACP or AR can both be loaded to equal, or better than a .45 Colt in modern guns.
If the subject really intrigues you ,try to find a copy of the article " The Best .45 Autos are Sixguns" by Skeeter Skelton, in the June 1973 issue of "Shooting Times" magazine.
For "hot rodding" the ACP you will be amazed at what can be done in the S&W 1955 Target and later versions, or if you're after ICBM ballistics try the Ruger .45 Blackhawk convertibles. You could nearly sell off your .44 Mags.! Best of luck in your pursuit. Nick

 

[growr]

I use the exact same data for either...no difference in performance for me.

Randy

PS. The 45 AR doesn't feed very well in my 1911 though......LOL!

 

[irapollock]

For what its worth, Hatcher, in his 'Textbook of Pistols and Revolvers'
lists the following data(from 1927) as factory data
45ACP 230 Gr Bullet 810fps
45ACP 200 Gr Bullet 910fps
45AR 230 Gr Bullet 810fps
45AR 255 Gr Bullet 740fps (Peters Cart. Co.)
the later matched the .45 Model of 1909's 255 Gr Bullet 738fps

So historically, from a ballistic standpoint 45ACP = 45AR. From a case dimension point, the cases capacity and dimensions are not the same:
45ACP case dia. @ mouth: 0.471"
45ACP case dia. @ head: 0.471"
45AR case dia. @ mouth: 0.472"
45AR case dia. @ web, rear: 0.475"
45ACP case dia. @ head: 0.512"
I suspect that the extra 4 mils in case dia. at the web is the source of DMY's observations about harder extraction with the AR case

 

[moxie]

I'd be careful before assuming you can use a roll crimp in a 45ACP revolver.
The case still headspaces on the case mouth. The rim allows extraction without moon clips. That's ALL the rim does.

Respectfully disagree. They headspace on the moonclip for ACPs or the rim for ARs.

In fact many of the more recently produced 325/625 chambers either don't have the "shelf" that permits headspacing on the case mouth for ACPs without moon clips or the shelves are cut too deep to be of any use. S&W chooses to ignore this, knowing that the ACP cartridges will headspace just fine on the moon clips.

 

[fredj338]

I've loaded identical loads in my M625/4" & they are almost the same as my 1911/Comm. I then double checked with 45acp loads in the same gun, no real diff. Any pressure signs you are seeing is brass specific. Measure the internal volume of your 45AR cases, see if they are significantly less.
What you are likely seeing is the 45AR brass is thinner in the head area & you are getting some case expansion there. I've loaded some pretty stiff loads using 250gr LSWHP, 850fps. In acp or Ar brass, case head exp is minimal.

 

[fredj338]

I'd be careful before assuming you can use a roll crimp in a 45ACP revolver.
The case still headspaces on the case mouth. The rim allows extraction without moon clips. That's ALL the rim does.

Not really. Once you go to a moon clip, the headspace is off the false rim of the clip. Most 45acp brass wont even come close to headspace on the mouth in a M625.

 

[alwslate]

dmy you're not seeing signs of excessive pressure with your loads
which are basically at starting level. Isn't this the second time you
have brought up this issue of swollen AR brass in the middle of the
case? If you're actually seeing this it isn't because of high pressure.

 

[BLUEDOT37]

In my experience, if you check an Auto Rim[AR] case and an ACP case for water volume you will find the AR case has less case capacity.

I've not checked other brands but using new Starline brass, I've measured a capacity of 27.3grs/H²O for their 45ACP brass & 27.4grs/H²O for their 45AR brass.

Their 45AR brass is equally as strong as their 45 Super brass, which holds 26.8grs/H²O.

.

 

[forestswin]

Dmy
I would just like to note the Hornady 200 gr. Swc is a soft swaged bullet, not a cast bullet. Load data is different for swaged than cast.
I also notice the starting charge for the Hornady is 5.4 grains of Win231 at 800 fps as shown in the Hornady handbook.

 

[TAROMAN]

Same load in AR brass for my 625s and ACP brass for my 1911s.
200 LSWC over 4.2 grains of N310.
Works equally well in both platforms.
And the 255 grain pin smashers for the AR are a hoot, too.

 

[Groo01]

Groo here
The thing about AR brass is that it is not constant between
makers.
Starline [ best] can handle 45super + pressures but Rem
is very soft and will show pressure much faster.
Is your brass Rem?
If so get some Starline, keep the Rem for very light target loads.

 

[moxie]

"not constant between
makers."

That's true of any caliber. Not only that, but the same maker's brass will vary from lot to lot and over time.

 

[S&WIowegan]

I started out using Remington 45 Auto Rim brass since they were the only game in town at the time. Later on Starline produced 45 AR occasionally but I have never used it. Never had any problem with Rem. AR brass. If your AR brass is showing swelling near the rim, my question would be "are your cylinder chambers chamfered?".

 

[moxie]

Excellent point!!

 

[H Richard]

If you are getting swelling of the brass at the base where a chamber is chamfered, that is at the thickest part of the brass in the web, and that would be an indication you have reached "beyond" the loading limit.

 

[dmy]

thanks all

Very good and valuable info. Yes, this is the second time I have written about swollen auto rim cases. I only have Remington AR brass because that was the only thing available at the time. I presumed that Remington would be decent quality. Most of the swelling is near the rim, but my chambers are not chamfered. I will have to buy some Starling and see if I have the same problem. Again, thanks everyone.