Home Forums Hunting & Shooting Handguns 45 ACP +P

"special heat treat process" doesn't mean one is heat treated and the other is not, as you claimed. It only means the Super brass is heat treated differently, i.e. less than standard brass to retain more hardness.

The funny thing is I think you've made the same claim here before and got the same answer pointed out by someone else.

45 Auto +P Brass (Large Pistol primer)
45 ACP+P, 45 Automatic+P
0.892 - 0.897 O.A.L.

The 45 Auto+P is a strengthened version of the 45 Auto with the same external dimensions. A thicker web and heavier sidewall at base strengthens the case in potentially unsupported areas. This case has approximately 2 grains less internal water capacity than the standard 45 Auto.

https://www.starlinebrass.com/brass-cases/45-Auto-P-Brass/

In a case with limited capacity, when you lose 2gr water capacity, how much higher do you have to push pressures to offset the lost capacity?
Just to get equal velocities?


A question I ponder every time I hear of heavier cases to handle high pressure.


Heck, military 7.62 supposedly runs higher pressure than 308. And capacity isn't that tight in 308.

I have to believe the lab coat guys figure in the smaller boiler room effect along with the increased powder charges in the overall pressure increase equation.

Yep.

In smaller rounds, powder compaction can be critical. I remember the experiments with .38 Spec, when they seated the bullets farther and farther down in the case and observed increased pressure to the point of being dangerous.

Powder selection becomes even more critical in these low case capacity, high performance rounds.

DF

I have some data on a 1911, and a pretty generic load in .45 acp.

The load is Starline cases, CCI large pistol primers (non-magnum), Berry's 230 grain plated RN, and 5.4 grains of W231. OAL is 1.265 inches

Using default settings in Quickload (with the exception of actual bullet length and weight), I ran a prediction and got a predicted pressure of 16.2 Kpsi and 846 fps. These parameters were 25 grain case capacity and a 1.275" OAL

Actual chronograph results showed a velocity of 830 fps.

After firing, I measured the cases for capacity, and got 27.5 grains capacity versus the 25 listed as a default.

The first change in parameters I made were to give actual OAL of 1.265" instead of the default of 1.275", and predicted pressure/velocity rose to 16.8 kpsi and 852 fps.

The second change in parameters was to enter actual capacity vs default. The Pressure/velocity prediction was 14Kpsi and 819 fps, which is under the actual velocity of 830 fps.

Next was to bump the burn rate of the powder up until I matched actual velocity. That change was from a ba of 3.6500 to 3.7700, at the outer edge of industry-standard 3% variance of burn rate. That resulted in matching velocity predicted by the program, and pressure was just under 14.5 Kpsi.

I may not be dead on, but I went back and entered the hypothetical 2 grain difference in case capacity of the load above and got, at 25.5 grains, a prediction of 16.9 Kpsi and 856 fps, up from 14.5 Kpsi and 830 fps that actually resulted.

A difference of 2.5 Kpsi and 26 fps. I believe this is what you were looking for, I just took the long road getting here.

Note that seating depth has some influence, too.

I know QL is *just* a computer program, but it can be fairly accurate given the right data, to include actual velocity.

I see that I did not actually answer you question, so using the corrected measurements and, let's say 16.0 Kpsi as a benchmark pressure..

At 25.5 grains capacity, velocity is predicted to be 844 fps and 16.2 Kpsi, using 5.3 grains of powder.

At 27.5 grains capacity, velocity is predicted to be 863 fps and 16.0 Kpsi, using 5.7 grains of powder.

At 25.5 grains capacity AND 867 fps, pressure is predicted to be 17.5 Kpsi, using 5.5 grains of powder.

Absolutely.

And the faster the burn rate, the more critical seating depth and uniformity of charge from round to round becomes.

Mainsprings...

For you guys running 1911s in .45+P, .45 Super or 10mm with full loads...what weight mainspring are you running...or just using the stock one..

I have square bottom firing pin stops and 22-24# recoil springs but and still getting quite a bit of ejected case distance...

Thanks...Bob

I have 3 1911s equipped with a 17# recoil spring, 23# hammer (main) spring, extra-power firing pin spring, and the flat FP stop.

Return-to-battery is not excessively harsh, and case ejection with the load I mentioned in a previous post is 3-4 feet, and +Ps go about 5 to 6 feet.

A heavy mainspring and the flat FP stop slow reciprocating speed quite a bit.

You load some very hot loads. I was a 20 pound Wilson flat wire recoil spring stock mainspring and do not use a squarebottom firing pin stop. With Underwood 45 Super Ammo I get about 8’ ejected bras. I make sure that the barrel lugs are fitted properly to the lugs in th3 slide, I believe this is a key factor.

I'm setting up a custom Govt. all steel .45 for +P/Super loads. I ordered a 17# Wilson flat wire recoil spring kit, heavier firing pin spring and will use the full powered factory main spring (23#, IIRC).

I ordered a square bottom firing pin stop and will fit it. I'm not going with heavier recoil spring based on info from this thread. If rearward slide velocity is slowed, no need to slam the slide back into battery with more power than needed.

I ordered 100 Starline .45 Super cases, already have 500 Starline ACP cases. Will see how much difference the brass makes. The barrel is std. Colt fitted to a Micro bushing. Will be watching for case expansion as the std. Colt barrel doesn't fully support the case body.

I'm going to be shooting 185 and 200 gr. XTP's over AA-7 with std. Fed primers.

DF

That'll be a fun project DF, shoot a pig with that thing.

BTW, iirc JWP says that 45 cal 185 gr XTP is a tough little customer, really good penetration and wound channels.

You have the right idea.

Read through this thread. https://www.1911addicts.com/threads/flat-bottom-fps.2982/

This gun is a Colt 1911 made in 1951. I fit a commander hammer, did the trigger job with aftermarket trigger, stippled the front strap and had it hard chromed. Slide is blue, fitted with S&W sights. You don't see that much any more, was the thing to do back in the '60's. I'll post photos when I get it put back together.

DF

That's pretty much what I did too in various 1911 pistols (both for hot 45 loads and for 10mm). I may have used 22# or 24# main springs, but in the same ballpark anyway.

Like you said, that setup still runs standard pressure ammo easily, but handles hot loads really well. I was pushing certain 230gr cast bullets a touch over 1,000 fps, and the 200gr XTP to about 1,110 in standard brass safely. That's close to what some here are posting for 45 Super loads; the big difference is having a gun set up to handle it.

The recoil spring weight really does very little to affect locked time in a 1911. It's become popular because it's one of the only options in striker fired pistols, and it's an easy change, but it's not nearly as effective as a FBFPS and heavy mainspring.

The best way to make sure the slide and barrel aren’t unlocking prematurely is to make sure the barrel and slide locking lugs are mated properly.

My smith doesnt like the flat bottom firing pin stops and neither does this Smith.


Joe C
Joe C
Custom Pistolsmith
Sponsor
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Sep 11, 2011
grainfed said: ↑
Joe C.........

Very curious to read your reasons why you would leave the FPS alone.....?????

tw
TW,

I would be glad to talk to you about is privately sometime if you would like. Feel free to give me a call anytime. Oh heck, nevermind...I'll just type out some of my thoughts for ya'll to mull and give your feedback about...

It's my opinion, based on observations, that it is better to control recoil by using the springs rather than alter the mechanical attributes. For one thing, it is possible to crack the hammer, depending on the type of hammer, if you use the flat FPS which as you can imagine can cause all kinds of problems (I have seen this happen). You also risk inducing failures to feed by using the flat FPS because you are mechanically impeding the rearward travel of the slide in such a sudden manner.

By asking the slide to overcome the spring weight AND flat FPS from a dead stop you are unnecessarily causing a delay that does not need to be there. This can also affect the speed of getting off a double tap as the slide has now been delayed (one of the reasons open guns often have the FPS filed at an aggravated angle forward) . If the gun is sprung properly it has been my experience that you get the same or better results as using the flat FPS without slowing down the action of the gun and potentially damaging something. But again, it's just my opinion...it seems that much of this has been forgotten or pushed to the wayside in the pursuit of the "quick fix" for recoil by using the flat FPS.


https://www.1911addicts.com/threads/flat-bottom-fps.2982/

That smith must be talking about light target loads, or else he completely missed the point. The entire reason for changing to a FBFPS is to cause that delay, that does need to be there for hotter loads. That's the whole point.

From his writing it also sounds like he's never actually compared ejection distance with different springs to see how little effect it really has. The ejection distance is directly related to slide speed.

The fact is there are plenty of smiths out there, and manufacturers too, who have their own opinions on how to do something without really having the facts to back it up, so they make up a theory. What you've posted is a great example of that.