Home Forums Reloading Handgun Reloading Reloading 357Mag w/ Power Pro 300-MP

Anyone experimented with this newish powder? Hornady shows max loads being ~150fps faster than the old standby of H110/W296? Curious if anyone has tried it, what kind of accuracy you are getting and if the velocity gain is real. I just picked up a T/C Contender in 357mag and am considering taking it with me for mule deer this fall. An extra 150 fps and 10" barrel with no cylinder gap should have a 158gr bullet in the 1700-1800fps range. That all sounds pretty good in theory, just wondering if anyone has actual real life experience?

I am still working on my first pound. Using a 4 5/8" Blackhawk have pushed 158gr XTP's to 1,222 fps and 158gr LSWC hard cast to 1,293 fps with no problems. As a point of reference, in the same gun factory federal AE 158 gr JSP runs 1,178 fps. Cast load data is scarce. There was an article in handloader a while back with some good jacketed and cast data. Google it up, as I believe it is online. For some reason, Alliant is specific in using federal standard (non magnum) primers. That's what I used.

I have a lb of 300-MP but I've yet to try it. In my experience, the reason why 357's are so lack-luster in performance has to do with the handcuffing of pressure by SAAMI standards. In a sturdy revolver, a lever gun, or a Contender, the MAP of 35k is silly, and loading with a pressure ceiling of 40k or 42k really turns it into a different animal. It isn't hard on the brass, it isn't hard on the guns, and it isn't such a sissy anymore. Which is the reason I like 110/296 in 357. If you load to 100% load density, there isn't a bullet you can stick in a 357 case that will cause any problems in the platforms I named. By sticking 357's into small, comparatively weak guns, and then handicapping the MAP, people get the illusion that they are shooting a "magnum" with their wee snubby. No, that isn't a "magnum", it is basically a 9mm+P. A "magnum" is standard bullets doing 1500 from common barrel lengths, and I don't mean 125's. A "magnum" is the original iteration of the 357, which, after it was designed, was taken to the Western states and used to kill everything from pronghorn to bull moose at ranges that some consider only for rifles and scopes. Rant over.

I've heard bad things about shooting Lil Gun in guns with a cylinder gap, and I don't do it because I don't want to find out, but a 357 in Contender or lever gun Lil Gun will match or top the numbers I've seen for 300-MP. It makes me wonder if 300-MP might also be guilty of the dreaded flame-cutting that Lil Gun shooters have claimed in revolvers. I don't know. But if I had a Contender in 357, along with 300-MP, I'd be trying LG. Don't be afraid to fill up the case, either. I've seen some amazing things out of lever 357's and Lil Gun with bullets 158-200gr, both in velocity and accuracy, with compressed charges of Lil Gun. Like 1900+ with 158gr bullets out of a 20" bbl. You'd surely get 1700-1800 out of a 10" with same loads of Lil Gun.

As reloaders, we get to do what factory fodder shooters don't, and that freedom comes with responsibility. As always, this info is for people who understand the responsibility involved.

I avoid lilgun for the same reasons. According to the all-knowing inter web, isn't just flame cutting, it actually 'melts' the rifling in barrels.

I've not seen any "melted rifling" in several guns in which I shoot Lil Gun. And at pressures far beyond anything shot in a 357. With thousands of rounds of said Lil Gun-charged rounds being fired, I think I'm safe. And that the rest of you are too, unless your barrels are made from recycled milk jugs or something.

I think the source of the original lil gun claims was the president of freedom arms. One would think if it was truly and issue it would be all over the place on the web. I'll still avoid it if for no other reason than I already have loads with other powders that work for me. In any event, 300-MP seems to do what I need it to do in the .357, topping factory velocities with loads slightly under book max. It also meters well.

You ar3 correct the factory loaded 357 mag was once loade to 40,000 CUPS which is close to 43,500 PSI. That’s why the original factory Ammo were much faster the SAAMI factory Ammo of today.

A 4” barreled revolver with a 158 grain JHP should be near 1400 FPS loade to 40,000 PSI.

Here's another question - is it safe to use 'Rifle Data' for a Contender pistol? I'm assuming it would be fine but thought I'd ask. I will work up from middle of the road book loads but just looking for some info first.

The only SAAMI spec for .357 is for handguns. People used to exceed that in carbines, but it really wasn't a good idea. A quick check of Hodgden's data shows the same data for both rifle and pistol, Alliant shows only pistol data.

SAAMI Specs on the 357 Magnum is 45,000 CUP if measured on a copper crusher pressure equipment or 35,000 PSI if measured on a Peizo transducer pressure equipment. Using the same reference ammo for both systems .
Thismis easy to check to see on SAAMI's site.

Nope, the old method was 40,000 CUP, which is close to 43,500 PSI. THE NEW pizero PSI pressure is SAAMI max average at 36,000 PSI

Argue with SAAMI. I am not going to argue with you. In the old days of the 357 only CUP was used NOT PSI although many including Keith called it PSI.
IT WAS NOT . it was Copper Units Of Pressure.
Again argue with SAAMI.

I know it was CUP and the6 are not PSI. The CUP and PSI are not the same. You are dead wrong on the 45, 000 CUP being 35!00 PSI, the numbers I posted ar3 correct according to Denton Bromwell’s CUP to PSI conversion.

There is no conversion system. When a ballistic lab references a pressure gun, be it a copper crusher system or a piezo transduce pressure gun they use the same reference ammo.
Just like some rifles such as a 458 Mag has a piezo pressure it also has a copper crusher pressure. Depending on the system thatis used.
Sometimes they are used in conjunction with each other. BUT THEY ALL USE THE SAME REFERENCE AMMO. There is no reference ammo for each one.

Yes there is a mathematical conversion, here you go

https://www.shootingsoftware.com/ftp/psicuparticle2.pdf

Yes there is a mathematical conversion, here you go

https://www.shootingsoftware.com/ftp/psicuparticle2.pdf[/quote]

My understanding is that was written 2002. I do know that ballisticians more recently says there is no ACCURATE way to convert the figures.
Still doesnt matter. All that matters is what a pressure gun gives as far as pressure.
Still, regardless, both types of pressure guns uses the same reference ammo.
SAAMI still sayS for the 357 Mag is the MAP average in CUP is 45,000CUP and 35,000PSI depending if tested on a copper crusher system or a Piezo Transducer system.
Evidentally SAAMI is stupid I guess. Wonder why ballistic labs go by their findings?

Why are wrong on the 45,000 CUP in the old days it was 40,000 CUP never 45,000 and only PSI is used today


https://saami.org/wp-content/uploads/2018/01/Z299-3_ANSI-SAAMI_CFPandR.pdf#page=10

Denton’s maths conversion is as accurate enough I’ve talked with Denton and it has been discussed on this web site as well as other.

On page 20 of SAAMI Specs the pressure is listed in CUP's is 45,000 on a copper crusher pressure gun. On page 28 you will see it is 35,000 PSI on Piezo transducer pressure gun.
Do the conversion factor on, lets say 4 of you favorite calibers and see if the conversion is correct. Doesnt really matter,it still doesnt change,SAAMI Specs. So whether it is right or wrong SAAMI specs is still what the Loading companies go by.

CUP increases in an orderly way as pressure increases.

The reading on piezo equipment increases in an orderly way as pressure increases.

Simple rules of math require that there is therefore a conversion between the two.

If you draw 10 cartridges from a large lot of near identical ammunition and test them with either system, and then draw another 10 and do another test you will almost never get exactly the same answer. But you can test the first 10 on one system and the next 10 on the other, and repeat that with several different pressure cartridges, and build up the conversion formula.

I took a simpler path, and just did the same thing with the CUP spec vs. the PSI spec. The resulting formula is about as good as the result as you would get from the method above. It works from 35 KPSI to 60 KPSI.

It doesnt matter about your conversion theory. All that matters is what SAAMI Specs tells the loading companies they must abide by if they are members such as most are.
Who cares about a conversion theory? If SAAMI Specs says 45,000CUP AND 35,000PSI that is what they mean. They also set parameters on how much each pressure can vary with a maximum high in each shot string. And how high the average can vary depending on other senarios.
So, while we appreciate individuals such as yourself giving of your vast knowledge, this is where it is not really relavent to the conversation. The conversation is what SAAMI Specs says and not how to use a conversion theory.