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.

My post was all about SAAMI specs being worthless compared to what can ACTUALLY be done with the cartridge. You are arguing with a scientist, by the way, which is only going to make you look ignorant.

Pressure limits are all about brass dimensions, action steel dimensions, and strength of locking mechanisms. If one understands some basics about all of these, one can handload above "dummy light" specs and be completely safe. In my experience, handloaders used to be a bunch of curious experimenters who wanted to understand the limitations of their equipment. Now it seems like the bulk of them have become nannying bitches who want to be protected by some "official".

The data for all platforms in 357 Mag are all the same. That said, if one compares the steel of the action/chamber of a lever gun in 357 to the weakest revolver chambered in same cartridge, then looks at the back-thrust force on the 357 lever action compared to bigger cartridges based on the same platform, one comes to the conclusion that one can safely step well above SAAMI-spec data and be nowhere near any red line. The same holds true exactly for the Contender platform. Lots of chamber steel, and the locking mechanism is designed to handle back thrust at much higher pressures for same cartridge dimension, or same pressures for much larger cylinder. Thus, Contenders will easily digest scorching loads in 357.

I don't recommend anyone try to step above the reloading data unless they understand all of what I have only named here, but not described in any detail. What I am trying to say, in layman's terms, is that every platform has its limitations, but that some have far fewer than others. In the case of relatively small-bore revolver cartridges, many lever guns and all Contenders are designed to handle pressures far beyond what is safe in the relatively weak mechanisms found on some revolvers. If you understand this, and understand the burn curves of the powers you are using (through much experimentation), you can safely exceed the data for the 357 in strong platforms. The brass will not even be phased.

Again, this isn't a license to fill a case with a high-intensity, fast-burning powder, then stick a big bullet on top, thinking that your gun can handle whatever. And in reality, those of us who don't have access to calibrated testing equipment have no idea what pressures we are running with our ammo. It could be that our "hot" loads are actually within or close to SAAMI spec in our guns, or it could be that book loads that we imagine are safe are well above SAAMI spec in our guns.

Following the "rules" doesn't guarantee that nothing will go wrong, and stepping outside the "rules" does not guarantee that one is actually incurring any additional risk.

Scientist or not and certainly not worried about looking ignorant the thing is SAAMI Specs say one reading for CUP and another in PSI.
We aren't worried about converting the two. Who cares anyway?
We all know anyone can load above SAAMI Specs. That isnt anything new. We are individuals. We can choose to do whatever we want as long as it doesnt hurt anyone else.
I know I do.

Well, for a while I did. I have a wonderful old milsurp Swede, and I have pressure measuring equipment. I needed to know a reasonable limit for loads for it. Turns out it is about 52 KPSI. The conversion came in handy for that and a couple of other special situations. A few years after I came up with my conversion, I was delighted to find that Dr. Floyd Brownell had done the same thing a few decades earlier.



Got a mouse in your pocket?

You are entirely welcome. Glad to be of assistance.

Just for everybody's reference, the conversion holds for rifle cartridges from 35 KPSI to 62 KPSI, and is within plus or minus 1 KPSI in the middle of the range, and plus or minus 2 KPSI at the ends. That's better precision than you'll get out of copper crusher, and about as good as you'll get out of piezo or strain equipment.

Well, my mouse and I appreciated your well thought out and designed answer. The precision of any test is dependant mostly on the tech or doofus that is conducting it.
Still this isnt about your knowledge but about what SAAMI Specs says. Accurate or not. What you, me or anyone else does with it is up to them.
But, what SAAMI Specs says is what SAAMI Spec says. Dont need a conversion theory for that.

I knew there must be a reason I was enjoying your posts so much!

Yes, the gas cannot read the headstamp. All it "knows" is how much brass and steel is between it and the outside world, and what the geometry is. In modern actions, I load my 7x57 and my modern 6.5x55 to about 58-59 KPSI.

SAAMI specs were created so that ammunition made to them will be work and be safe in practically all firearms.

Most of us know SAAMI Specs are designed to accommodate the weakest link in the chain.. This is nothing new. But what SAAMI Specs says is what they say. Regardless what it is based on.
Still the individual is the guiding light of his destination on his load developement. Load data is just a guide. The individual can choose to follow it or not.
Still SAAMI Specs has their rules and ways of doing things.

Now that we're all in agreement...my favorite load in 357 for SERIOUS business is a NOE mould-cast 230 gr WLN designed for rifle rounds that I seat to give about .01" clearance from cylinder face in RBH and crimp with Lee FCD over 12 grains 110/296 in non-Winchester brass using CCI550's. It is just barely subsonic, near 1100, and hits harder than anything I've ever seen from a 357 handgun. It doesn't feed in unaltered lever guns, though.

If I owned a contender in 357(which, due to their horrible chamber reamers, use what amounts to a forcing cone-style throat), I'd load the biggest bullets I desired to the longest length that would still chamber easily, FCD them there, and fill up the empty space in the case with 110/296, or Lil Gun, or 300-MP. I tried this in 44 mag 10" Contender using 300gr cast bullets, and got FAR more velocity and recoil than I wanted to, but it should work pretty slick in a 357. I could get 24 gr 110/296 easily into the 44 mag case, seating at 1.8". They weren't fun to shoot. Consequently, I filed the feed ramp stop back on a 44 Marlin and can shoot 1.78" cartridges, which allows 22gr of 110/296 behind a 300 or 23 behind a 285. Those are good times. I hope the OP has some good times with his project.

Well last night I picked up a pound of 300MP loaded up 3 each at 16.0, 16.5, and 17.0 gr with 158gr Hornady XTP HPs, CCI 550's per Hornady Manual. Shot them this morning. Stout but no obvious pressure signs. 16.0's got around 1425, 16.5 around 1450 and 17 about 1500 fps. Was hard to tell exactly because the damn wind was blowing about 25mph and I don't think I was perfectly aligned with my chronograph. I think if I get aligned better that the velocities will be higher. (I shot a couple of my standard 14.5gr IMR 4227/158gr and was 100fps off of normal.) I was only shooting 25 yards due to wind. All 3 groups were quarter size or less, one group all touching - the others 2 would touch and one stray. Think I'll load a few more in the 16.5gr-17gr range and try them again on a nicer day.

FWIW: I have a box of Fed Am Eagle 158gr FP's - they chrono right at 1600 fps from my contender. Primers flatten out a bit but not excessively. Those are pretty sporty, touch one of those off and the action release pops you pretty good if holding with 2 hands around the grip.

As for the long throat Contender issue, I'm not really sure how much jump this barrel has. I do know that the other day I shot a 3 shot group that fit completely under a quarter at 50 yards with the IMR 4227 load and 158gr XTPs. Typical groups have not been much bigger hanging right around 1". If it will shoot like that I guess I really don't care what the jump is.

More fun than a barrel of monkeys!

Good looking firearm. You dont put the fingers of the support hand behind the trigger guard. If you ever shoot a hard kicker you will find that out quickly.
Good shooting too. Let us know what you find out about the charge you settle on.

Alliant list 18.6 with a 158 gr GDHP and standard primers.

Saw that - went with Hornady Data - they max out at 17.0gr but with a magnum primer and 158gr XTP bullets. Seems like it may be a bit conservative but still plenty stout enough for me. 1500+ fps from a 357 Mag is pretty amazing. I do believe any deer under 100 yards would not last long hit with a XTP FP going that fast.

As for keeping your support hand fingers in front of the trigger guard......well one good smack and I now keep my fingers in front of it. lol.

Been way too long since I messed with a Contender, making up for it now!

I used Alliant data and standard (actually match) fed primers for my load work up. Not mag primers. I think Hornady is lower because of the mag primers, but I'm not sure.

Works good in 30 carbine.

I tried that that powder out of a 4 inch 620. I found that h110 seemed to be a bit more accurate and I don't think that the 300 mp was any faster. That was just with federal primers, 158 xtp's, and starline cases.

158 XTP
16 GRAIns h110
starline case
federal mag primer

1280 fps 4 inch smith 620.

Wind finally died down last night so I shot 3 each at 16.5gr, 16.8gr and 17.0 gr. All shot right about 1500 fps and were 1" accurate at 50 yards. I need to try them again to confirm but going over 16.5 really did not increase the velocity as much as I thought. FWIW 16.5 is a full case, maybe a tad compressed.

I really don't think 300 MP is doing anything that H110 or W296 won't do and I'll probably go with one of those when this powder is used up. Which should be pretty quick because this T/C is ridiculously fun to shoot.

One more note about jump to lands in .357 barrel - it really does not seem to matter. After messing with the 300 MP loads I put 3) 38 special loads with Hornady 158gr LSWC HP's and 4.3gr of Unique through it and printed a pretty little cloverleaf at 50 yards. Accuracy of this handgun is amazing.

And, .22 K-Hornet.

DF

And .22 (Vanilla) Hornet.

Got back out shooting the T/C 357Mag with 300 M-P yesterday. Tried 3 @ 16.5, 3 @ 16.7 and 6 @ 17.0 with 158gr XTP HP's. Was getting about 1525 on the 16.5's and up to 1550 on the 17.0's. Must be about optimal as powder increase really is not making much difference. Accuracy at 50 yards was impressive. All 12 shots were within 1 1/2". A 6 shot group of the 17.0's, 5 of the 6 were in 1" and one just a tad high opened it up to 1.5". (I think I have a bit of parallax in my scope giving a bit of vertical stringing) I believe I have found a good stout hunting load. I would like to find some 158gr XTP FP's and see if they shoot the same as I believe that will be my bullet of choice this fall. Fun stuff.