Saturday, May 20, 2006

Under Pressure...

Or OVER pressure as the case may be.

I fairly frequently refer to shooting +p and +p+ loads in my guns; particularly in my .45s. Of course the world most common and most favored .45 (including MY most favored .45) is the 1911, and it's variants.

A reader on the NoR forums asks "+p in a 1911, is this a kaboom waiting to happen, or is it OK for occaisonal use?"

Well the first thing is, it's entirely safe to fire most +p and +p rounds in most guns. Some manufacturers may specifically recommend against it (or may recommend only occaisonal use), and I won't counter a mnaufacturers claim; but most DON'T recommend against it for most models.

But why? Why do manufacturers recommend against it (or not), why are people concerned about it, what are the effects of it... what does +p mean?

Once again we come to a rare example of a firearms term that makes perfect logical sense. +p means "plus pressure", in other words the ammunition is loaded to a higher pressure. +p+ is plus pressure, only more so.

Of course +pressure means +power, +velocity, +recoil, and +gun wear as well. This is why most premium defensive ammnuition is loaded to +p levels, and why most match ammunition is loaded to LOWER than normal pressures (light loads are easier to control, and wear out your gun slower so you can shoot more of them).

SAAMI, the Sporting Arms and Ammunition Manufacturers Institute sets and publishes standards for factory ammunition. These standards include diameter, overall length (OAL), case length, rim and groove diameters, shoulder angle, and other basic measurements. They ALSO include the maximum chamber pressure which the ammunition can be loaded to and still be marked as a standard round.

These pressure standards are often arbitrary, and often quite low; especially on older chamberings such as those that were originally blackpowder loads, and those that were introduced before SAAMI was founded in 1926.

In many cases, these SAAMI standards were set for the weakest weapons commonly chambering a round at the time of introduction, so it could be insured that mass market ammunition was safe in any gun that would chamber it.

Obviously though, some guns are stronger than others. In fact, sometimes the same gun made today, is a lot stronger than the models of 100 years ago; because of imporoved manaufacturing techniques and metallurgy.

This is generally the case for pistols chambered in .45acp. The SAAMI specification for .45 ammo was set based on early smokeless powder technologies from prior to World War One, and is based on a standard of nominal 17,500 and proof 19,500 CUP (Copper Units of Pressure which is sorta kinda equivalent to 21,000 PSI, but the measurement can't be directly compared). Older chamberings are generaly standardized using CUP, and newer ones as PSI.

Heres a chart of SAAMI standard chamber pressures for comparison.

Many SAAMI chamberings also have a standardized +p specifications, including the .45acp +p at 21,500 cup, which works out to about 23,000 psi as measured. There are no standard +p+ specifications, but those who load commercial .45 ammo to +p+ specifications list their max at either 22,500 or 23,500 cup (up to about 25,000 psi as measured).

This is actually a relatively low pressure round, even as a pistol chambering; in comparison to some modern chamberings such as .357SIG at 40,000psi. This was very common with older chamberings because powder and matallurgical technologies available at the time made going higher in pressure very difficult.

Modern metallurgy, machining, and powders can safely and easily support far more pressure than that .45 spec, but TOO much more and you'll be reaching the limit of the BRASS used in the catridges, because in order to reliably chamber a round you need to have some clearance in the chamber.

There are manufacturers who spcifically produce heavier brass for handloaders and specialty manufacturers to use in +p and +p+ loads (important note: just being marked +p doesnt necessarily mean it's stronger brass), but because the brass is slightly different, you can't necessarily use the same load to reach the same pressure, so be careful of overpressure.

Now, all of this isn't really of much use to folks who don't handload, because any commercially manufactured pistol will be just fine with any standard commercially manufactured ammunition; and so long as the manufcature doesnt specifically recommend against it, SHOULD be fine with any commercial +p load which follows SAAMI specs.

In fact, I don’t shoot anything BUT +p or +p+ through my 1911’s excepting cheap practice ammo, which is only loaded to about 17,500 CUP (230gr RN-FMJ at 835-850fps).

The only major concern I would have with any modern 1911, is that some stock 1911 springs are a bit light. The stock springs are only 14 lbs (by original 1911 spec), and I think anyone should replace a 14lb spring with a 16 or 18lb wolff whether they are shooting +p or not. Many manufactures have in fact decided to switch to 16 or 18lb springs just for that reason.

Oh and for general 1911s, if you have an MIM slide stop or extractor, you may want to replace them with tool steel bits; but as with the recoil spring, you’d probably wan't to do that anyway. After a few thousand +p rounds they may start having problems.

If you are really concerned about shooting a lot of +p (or any +p+), shoot about 20 ronuds, look to see if there are any function issues, and if the slide is peening the frame at all. If it is, even the slightest bit, up the power of your recoil spring, and maybe add a recoil buffer. If it's still peening after that, you have a mechanical problem with your gun and need to get a gunsmith involved.

Now for handloaders, and those of us who buy non SAAMI ammunition (Cor-Bon, Buffalo Bore, Black Hills, Doubletap etc...) , theres +p and then there’s “GOD DAMN THAT’S HOT” ammo also known as +P+

There isn't an awful lot of difference in pressures between +p+ and .45 super, so not every gun is safe to shoot with these loads. Some shouldnt be fired with them at all, some should only see limited use. All my .45s are set up for .45 super, and all my .45’s have fully supported chambers, so I shoot some serious loads through them from time to time.

I've covered it before, but jsut briefly heres the difference between a supported chamber and an unsupported chamber: a standard 1911 has a relatively loose chamber, with a large crescent taken out of the bottom edge of the chamber forward of the case headto facilitate feeding. Many modern .45acp weapons, including many 1911's have match specification barrels with fully supported chambers, by using a feed ramp either built into the frame of the pistol, or integral to the barrel, which leaves almost none of the case in fornt of the case head unsupported. This allows for higher pressure loadings with lest risk of case rupture.

It should be noted that glocks have a partially unsupported chamber; though it offers more support than a traditional 1911 chamber. A gun like the H&K USP has a fully supported chamber, and in fact comes from the factory rated for .45 super.

The safe limit for .45 BRASS in those guns is around 185gr at 1350fps. Obviously you want to back off a bit from that, but a 185gr +p+ at 1250fps is perfectly safe in a fully supported chamber (it should be safe in an unsupported chamber, but you can't be sure without testing it), and at 1150 fps +p from just about any gun (that's appx. 22,500 cup). For 230gr loads the safe max velocity is about 1100-1150fps +p+ and 1000-1050fps +p should be safe for almost any gun (950fps is the standard 230gr+p).

Just as an example by the way, these are the +p+ loadings doubletap specifies:

165gr JHP at 1325fps/643ftlbs
185gr JHP at 1225fps/616ftlbs
200gr JHP at 1125fps/562ftlbs
230gr JHP at 1010fps/521ftlbs

This is in comparison to standard pressure loads:

165gr FMJ at 1150fps/485ftlbs
185gr FMJ at 1050fps/452ftlbs
200gr FMJ at 950fps/400ftlbs
230gr FMJ at 850fps/368ftlbs

Those ratings come from a 5” 1911 shooting RN-FMJ, JHP, or JSWC. Expect a bit higher velocity out of a polygonally rifled barrel of the same length (or the same velocity for a 4" polygonal barrel, which is more likely) . Oh and for those of you wondering about .45 super; you get about 100fps and a maximum of about 150fps over and above the +p+ loads (or up to 300 or so fps over standard pressure .45acp) at a given weight. The +p+ loads are actually touching on .45 super territory.

Also compare to .40 S&W in similar bullet weights, (a much higher pressure loading) at +p+ levels. These ratings are from a 4" polygonal barrel, which should be similar to a 5" 1911.

165gr JHP at 1225fps/550ftlbs
180gr JHP at 1100fps/484ftlbs
200gr JHP at 1050fps/490ftlbs

You can see that +p+ .40 s&w at the same bullet weights is somewhat more powerful than standard pressure .45acp, and somewhat less powerful than +p+ (+p .40 is either the same as or a bit more powerful than +p .45 because of the relatively low SAAMI +p .45 pressure ceiling). The reason there aren't as large gains in .40 S&W between standard pressure +p and +p+ in comparison to the .45acp; is because the .40 already a high pressure round, with a much lower pressure overhead as compared to standard .45acp.

Now comes the heresy...
For those who deride the .40 as "short and weak" in comparison to the .45, looking at those numbers you should think again. There is very little diameter differential there, and the bottom to mid range of .45 weights are the same as the mid to top range of .40 weights.

Of course the .45 gives you a higher power and weight ceiling (which means more velocity per weight, and more weight availabe in general) and is more versatile; but I don't think there's going to be much difference shooting someone with a 165gr .40 and a 165gr .45 loaded to the same velocity; or a 200gr etc...
Anyway back to the main story...

Don't shoot lead loads as hot as those max loads from a conventional barrel unless you really love scrubbing, and don't shoot lead loads at that high pressure AT ALL from a polygonally rifled barrel (even hardcast will flow too much at those velocities and pressures, and can produce dangerous overpressure).

As long as you are sure of the strength of your brass, you can generally load +p rounds in standard brass with no problems, but I would recommend never loading any +p+ rounds unless you are using heavier duty brass; either +p rated brass or .45 super brass (which is essentially cut down .308 rifle brass and can handle about 70% more pressure than .45acp).

If you buy commercial +p+ rounds from a reputable manufacturer like Buffalo Bore or Doubletap you can bet their brass is rated for it.

Also, don't reload any brass that you've loaded to +p+ levels, again unless it is +p rated or .45 super brass. Don't reload it at ALL if it was shot from an unsupported chamber. Also obviously, you don't want to use range pickups to load +p or +p+ rounds (because you don't know how much wear they have); use only pristine or at most known once fired brass (and I'd be leery of once fired) for +p and absolutely only pristine brass for +p+.

Oh and dont be surprised if you like the hot loads a lot. I find them much mroe fun to shoot, especially doubletaps and rapid fire excercises. Yes theres a lot more snap, but in a full sized gun I just find they feel better, and you can recover from recoil faster.

Of course I wouldn't want to shoot those same loads from a G36; which is pretty much why I sold mine.

What can I say, I'm a recoil and velocity junky... Lord I really need a 10mm.