Power Pistol: Why does it not group well when loaded light?

[azrocks]

In my ongoing experiments with Power Pistol (with 9mm, 124g projectiles), I've managed to do nothing more than re-invent the wheel and prove what the old hands here have said time & time again... it doesn't like to be loaded light. In other words it's good for full-power loads.

My question is why? Not just for Power Pistol, but for other similar powders / load combinations. What are the dynamics at play? Is it all related to burn rate, and if so - what exactly is happening that's causing precision issues?

 

[VAReloader]

It's possibly that a light load lays in the "side" of the case and doesn't ignite properly. I found this our trying some Silhouette in 38 spl. I talking with a tech at Ramshot, that was the reason he gave. He also stated that velocity would vary depending on the angle of the pistol, when fired, altering the burn.

Not sure that helps or is accurate but thought I would throw it out.

 

[azrocks]

It's possibly that a light load lays in the "side" of the case and doesn't ignite properly. I found this our trying some Silhouette in 38 spl. I talking with a tech at Ramshot, that was the reason he gave. He also stated that velocity would vary depending on the angle of the pistol, when fired, altering the burn.

Not sure that helps or is accurate but thought I would throw it out.

Thanks for your input, VA! I had wondered if the powder volume was at least a contributing factor. But even loaded light, my Power Pistol loads are filling up much more of the case than the lighter-shooting titegroup loads, which are grouping quite well. Not saying what you're saying aint it - just that I still don't understand things

 

[RecoilRob]

The slower burning powders that normally deliver the highest velocities seem to not burn efficiently unless the pressures are up near maximum. 296/H-110 is notorious for this, and 2400 not as bad but still far from optimum in lighter charges. Power Pistol is one of the best powders for hot loads and also likes to be run hot so it burns well...just the nature of the beast. Fast burning powders can create the same maximum pressures but the spike is much more brief so the resulting velocity will be reduced so you trade off position insensitivity for that last bit of performance.

 

[Demi-human]

This maybe dangerous, for I am thinking out loud... gunpowder needs pressure to burn quickly. Power pistol needs higher pressure to ignite through the deterrents. Something found in higher charge weights and heavier bullets. As well as 'heavier' calibers. Since it takes less time to move a lighter bullet, pressure falls off quickly and erratically. With less pressure, less burns. Even with the same velocity the barrel position relative to recoil and bullet exit could be significantly different.
I have stopped using Power Pistol in fourty-five auto becase I grew tired of wearing unburnt flakes home. With a matched set of cases, trimmed and crimped consistently, I was able to get good accuracy with two hundered and thirty grain HAPs. (For me) But still wore much powder.

 

[Galil5.56]

Don't know what you consider light/what loads you have used, but I ran it pretty light, and had good results. What issues were you having?

M9 pistol:

5.2 Power Pistol Lee 125 RN WW SPP
1090 1087 1083 1093 1100 av 1090 es 17 sd 6

Load density for above is 90%+. I stoke it up with jacketed, so can't comment on loads under 6 grains using 124/125 grain jacketed bullets. Unique with a similar burn rate (touch faster), works great at 4.7 grains with the same bullet, and is one of my most accurate loadings.

Walther P1:

4.7 grains Unique Lee 125 .358” not quenched CCI SPP Heavy LLA+JPW lube
1072 1075 1090 1077 avg 1078 ES 18 SD 7 .872" CTC 5 shots @15 yards

Of course Unique is a very easy to ignite, bulky propellant, and I have had great luck running it in .30 cal cast bullet loads, with extremely low load densities, and no filler. Now if using small charges of low load density, "slowish" ball propellants (think HS-6 or similar) in many handgun rounds (esp high volume/low max allowed pressure), and especially without enough priming, less than stellar results would not surprise me... But you never know.

 

[Demi-human]

Conversely, I can find no better propellant for +P loadings. With two-thirty hollowpoints at nearly the speed of sound one is able to stress test any home-made steel target's welding. And being, a loud and bright powder, it impresses the sense of power into onlookers. Useful for mixed company, pleasure shoots. I enjoy it, but it gets stuck in the cylinder of my powder measure, so I have learned to trickle it. Silhouette is nice metering, but not as loud. If that is a negative. Shoot well.
Demi-human

 

[243winxb]

Ball powders get a magnum primer when i load them.

Power pistol (not ball) may work better with a mag? Also.

 

[Walkalong]

It's possibly that a light load lays in the "side" of the case and doesn't ignite properly. I found this our trying some Silhouette in 38 spl. I talking with a tech at Ramshot, that was the reason he gave. He also stated that velocity would vary depending on the angle of the pistol, when fired, altering the burn.

Not sure that helps or is accurate but thought I would throw it out.

Totally different application. Many powders suffer from powder position in the .38 Spl where there is a lot of extra space in the case for the powder to move around in, compared to the small 9MM case where most powders give a very good fill. I test powder position all the time, and you are right, it can make a big difference, with some powders being worse than others, while some do much better than average. It makes the biggest difference in big cases where the load density is poor like in .38 Spl with typical fast powders used in it. .45 Colt is another one. The auto calibers like .3 ACP, 9MM, .40, and even .45 ACP are much less susceptible to differences in velocity due to powder position simply because the load density is almost always very good.

The slow for the caliber powders seem to be less forgiving of being downloaded.

 

[Walkalong]

This maybe dangerous, for I am thinking out loud..

Sounds like you have a good grasp of it.

 

[ATLDave]

Slower powders are slower precisely because their grain shape and chemical coatings are chosen/applied in order to retard/deter burning. That resistance/retardation is designed to yield the intended burn rate/gas volume when working within a certain pressure range. Below that range, those same features can interfere with complete burning/ignition of the powder. Among other things, this can cause variation from cartridge to cartridge over how much, and when during the deflagration process, of the powder load gets burned at all.

If you want to play with light loads, a faster powder is generally the way to go. Many powders can be safely downloaded to the point where stuck bullets or an inability to cycle the action are the limiting factor... but mid-slow powders aren't generally good for that application.

 

[azrocks]

I appreciate your responses, gents! Much to learn and I'm still playing catch-up!.

ATLDave: That makes a lot of sense. Thanks for the input.

I went out yesterday and tested some titegroup loads under the same bullets (Precision Delta 124g FMJs) with the same OAL (1.140). Despite the significantly decreased powder volume, my group sizes shrank significantly with far less recoil (the best loads were 3.7, 3.8, & 3.9g TG) I had to run at least 5.6g PP to get group sizes as small as those, and that brought with it significantly more recoil, flash, and bark.

 

[RealGun]

In my ongoing experiments with Power Pistol (with 9mm, 124g projectiles), I've managed to do nothing more than re-invent the wheel and prove what the old hands here have said time & time again... it doesn't like to be loaded light. In other words it's good for full-power loads.

My question is why? Not just for Power Pistol, but for other similar powders / load combinations. What are the dynamics at play? Is it all related to burn rate, and if so - what exactly is happening that's causing precision issues?

If ignition is incomplete, there will a slightly different charge behind every shot.

 

[rsrocket1]

BE-86 is close to PP in terms of "slowness". At least it's slower than Unique. Plus it is very fine grained so it meters very well. In general if you want light loads, go with Clays, Red Dot, Titewad, e3, Extra Lite, Nitro100, N310. But for 9mm, Green Dot and Unique are about as fast a powder as I would like, the other powders may reach max SAAMI pressure before you get the bullet to go fast enough to operate the action.

Download 9mm? If you want to down load 9mm, use a .22lr or airsoft gun

 

[ATLDave]

But for 9mm, Green Dot and Unique are about as fast a powder as I would like, the other powders may reach max SAAMI pressure before you get the bullet to go fast enough to operate the action.

Download 9mm? If you want to down load 9mm, use a .22lr or airsoft gun

That's silly. Plenty of soft-shooting rounds are made in 9mm with fast powders. Millions of such rounds get shot a year by Steel Challenge and USPSA competitors.

 

[bluetopper]

Light charges of slower burning powders may not burn completely, therefore not consistently, and pressures will be vary.

 

[RecoilRob]

That's silly. Plenty of soft-shooting rounds are made in 9mm with fast powders. Millions of such rounds get shot a year by Steel Challenge and USPSA competitors.

3.8 WW231 under a 154 grain cast boat-tail from a Lyman mould shoots extremely well at full velocity (960 or so from 4") and will operate any gun in the cabinet positively while being easy on the shooter. Being as most autoloading pistols are recoil operated, a heavy bullet can generate the momentum needed to cycle them with much less velocity than a lighter bullet while creating much less muzzle blast and flash. The heavy bullet 231 loads are relatively pleasant to shoot indoors and work most excellently in a supressed application.

 

[jlove1974]

I bought a lb of power pistol a few years ago. Tried it in 45acp, and put it back on the shelf. I think it's still 7/8th full. CFE-P, Unique, TG, and red dot all cover the same basic slow to fast range I need for .40, .45, and 9mm without the flash and recoil that I found PP to give me no matter what it's loaded in.

 

[RealGun]

I bought a lb of power pistol a few years ago. Tried it in 45acp, and put it back on the shelf. I think it's still 7/8th full. CFE-P, Unique, TG, and red dot all cover the same basic slow to fast range I need for .40, .45, and 9mm without the flash and recoil that I found PP to give me no matter what it's loaded in.

Among those cartridges, I believe it is best suited for 40 S&W. I made a commitment to it for 40 but later found it among the best for 45 Colt jacketed. It has a smart ignition that I like better than some of the lazy cowboy loads, still within 14k psi boundaries. Got it from Hornady #9.