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Discussion Starter · #1 · (Edited)
For some background, I've been impressed with the American Eagle 158gr round from my 4" GP100. It pushes the bullet to a stout 1320 fps. So I hold that as a bit of a benchmark for handloads. However, as of yet I have not been able to reach it.

Initially I used 300-MP. 17.0 grains, which is the max in the Hornady book. I worked up to this with a Nosler 158gr, because that's what I happened to have. This resulted in a middling 1175 fps on average from my GP100.

Speer has data going up to 18.6 grains of 300-MP. However, I did not feel comfortable using that without using all the same components. Initially I couldn't find Speer bullets, but recently I have been able to get them. I was using Federal cases and primers already. So today I tested up to 18.4 grains of 300-MP. However, they were only going about 1220 fps, still 100 fps short of the AE factory stuff. They sizzle out of the 16" Rossi at 1850 fps, though, about 50fps faster than AE from that gun!

I also have considered that in the short barrel, perhaps the 300-MP loads don't develop full pressure due to case capacity limitations (I wouldn't use this logic to exceed book loads, just to pursue other avenues). So perhaps a slightly faster powder would actually be faster from the 4" GP. 800x seems a good choice, but also it's the only other powder I have. There isn't a lot of data for it in .357, but Nosler has data with their bullet and Fed cases. They go up to 8.7 grains. However, 8.5 grains only reached 1045 fps from my GP100. Interestingly, they show ~1450 fps from an 8" gun. But from my 16" Rossi it was only reaching 1440 fps.

So, still no dice on doing what the AE ammo does. No big deal, but it was interesting trying. 300MP for me in .44 Mag is a different story, though. It outperforms American Eagle and Remington UMC easily with published loads. That said, that's from a longer 8" revolver, so that may have something to do with it as well.

In some ways it seems like my GP100 is "slow". But factory ammo from it seems to do just fine. So who knows.

300MP is amazing in the carbine, though. Even dropping a grain to 17.5 results in 1770 fps for a 158gr bullet.

As an aside, I've noticed I get a lot of partially burned 800x all over the shooting table sometimes. They also had fairly high extreme spreads and SD's. Though most of my 800x loads use plated bullets which means mild crimps, so perhaps that is more the problem than anything else. Also it's easy to see the 800x flakes, I suppose unburned 300-MP could be everywhere too, but it's so fine it wouldn't be that obvious.
 

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1320fps from a 4" barrel is quite fast. Not knowing your bullet dimensions or COL, I am missing some key speculation data. I get the absolute best speeds from Lil'Gun in 357 magnum. My 158gr Lil'Gun self defense load is 1250+ fps using a whopping 16.9gr powder, but it is flat nose, soft point. I thought I was getting great 4" speed at 1250fps but clearly I am shooting slow. H-110 also gives some great speeds from a 4" barrel.

Keep in mind that you will probably get a large fireball too. Slow powder and short barrel means a lot of powder will burn in the air. From your carbine, these powders will give a 357 magnum bullet quite a lot of speed. Probably around 1800fps.

Wish I knew more about 300-MP. It may be very comparable to the H110 and Lil'Gun. The powder weight you reference certainly makes it sound similar.
 

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...Wish I knew more about 300-MP. It may be very comparable to the H110 and Lil'Gun. The powder weight you reference certainly makes it sound similar.
It's close on the burn charts. There are rumors it's made in the same plant and is the same as H110/296.
 

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Nope, Federal 100 in everything.
I would highly recommend magnum primers. There's a chance that you are not fully burning the powder due to not using magnum primers. The data in the Hornady 9th used WSPM primers shot in an eight inch Python. Like most slow burning magnum powders longer barrels are their friends.
 

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I agree that American Eagle .357 SJSP is some powerful ammo.

I have clocked lead 158 gr TCFP in the 1300 FPS speed range using H110 in my 4" GP100.

I have clocked jacked 125 gr at 1400+ in the same gun using H110.

I don't think you will gain any velocity with 300MP using magnum primers, maybe more consistency.

What kind of crimp are you using?
 

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Discussion Starter · #8 ·
1320fps from a 4" barrel is quite fast. Not knowing your bullet dimensions or COL, I am missing some key speculation data. I get the absolute best speeds from Lil'Gun in 357 magnum. My 158gr Lil'Gun self defense load is 1250+ fps using a whopping 16.9gr powder, but it is flat nose, soft point. I thought I was getting great 4" speed at 1250fps but clearly I am shooting slow. H-110 also gives some great speeds from a 4" barrel.
That's interesting to know your max loads with magnum powders are in the same ballpark. I guess the AE stuff has some magic in it. I don't bother too much with OAL when loading revolver rounds. They are seated to the cannelure. I just went and measured a few. The Speer/300MP's are just over 1.590". The Nosler/800x's are around 1.595-1.600".

300-MP is made at St Mark's, just like H-110. From what I have read, Alliant spec'd a powder that was slower burning than H-110. Most of the Hornady data has larger charge weights for 300-MP than H-110/W296, though that isn't absolutely true in every cartridge/bullet.

I agree that American Eagle .357 SJSP is some powerful ammo.

I have clocked lead 158 gr TCFP in the 1300 FPS speed range using H110 in my 4" GP100.

I have clocked jacked 125 gr at 1400+ in the same gun using H110.

I don't think you will gain any velocity with 300MP using magnum primers, maybe more consistency.

What kind of crimp are you using?
I don't have to reach 1300+ fps, it just seemed like a good benchmark since factory ammo does it. Lead would probably help, but the AE load is jacketed. It's no big deal, but I am a little surprised that reasonable handloading can't equal it.

I use an FCD for the crimp, I'd describe it as medium-heavy. It's pretty rolled into the bullet, but not to where it is flattening back out or anything. I could try to get some pictures, though I don't know if it will be possible to get anything decent.

I agree, I don't think magnum primers will bump the speed, but might slow it in the carbine as I'd likely have to back off the charge weight a bit. The Alliant data is for regular Federal primers, so that is what I use. The 300-MP loads have been pretty consistent in terms of the extremes and SD's. Perhaps with 800x that would help, it has been more inconsistent. Though again, mostly I use it in medium loads with plated bullets, which may also be the problem. I don't know if magnum primers would help in that case, maybe? I don't own any magnum primers right now, but will keep an eye out for them.

As an aside, I have chronographed some 158gr jacketed bullets at over 1400 fps from a 4" GP100. A friend bought his GP used, and bought some "new" ammo from the same guy. They were clearly reloads, but he shot them anyway. When he touched off the first one, it was stout! He could barely get the case out (if he'd shot all 6, he probably wouldn't have been able to). I happened to have the chrono, so he shot two over it. They were a little over 1400 fps. I took the rest of the bullets and pulled them, they were a 158gr jacketed soft point (very round-nose shaped, though). And they were loaded with anywhere from 14.1-14.8 grains of powder. I can't swear to it, but it seemed to clearly be Blue Dot from the black and blue dots of powder. If that is really what it was, I guess it's a testament to how tough the GP is. His gun seems to be a fine shooter, that bit of abuse aside.
 

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Aurora40, I decided to run some possibilities through Quick Load. I used the Speer TMJ FN 4207 as the model because you mentioned Speer. My version of QL doesn't have the 300-MP powder but you did get me to look at the Accurate powder burn chart. They list it on the same line as H110/296 as you said. Keeping with 3500psi, QL claims 1233fps from H110 and 1267fps from Lil'Gun from a 4" barrel. I had to extend the COL to 1.61" to get the bullets that fast. COL has an important relationship to pressure and speed. I didn't check every powder, but all the ones I scanned are below 1300fps. If I run the Lil'Gun up to a proof load close to 40Kpsi, I get 1320fps. H110 gets there at 42Kpsi, another dangerous proof load.

Then there is your friends 1400fps experience. I plugged 14.1gr BlueDot using that same Speer bullet and COL. Quick Load claims 1481fps at 60Kpsi. And you found 14.1gr to 14.8gr variation! I imagine these would feel stout!

I am anxious to get a GP-100.
 

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Okay, so with all these posts about velocity, where's the talk about accuracy?
 

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Some of my favorite 158 gr .357 Magnum loads:

158 XTP/18.6 300MP = 1230 fps 4" barrel
158 XTP/17.0 Lil Gun = 1270 fps 4" barrel
158 XTP/15.0 2400 = 1214 4" barrel

158 LSWC/17.0 Lil Gun = 1341 fps 4" barrel
158 LSWC/14.5 2400 = 1341 fps 4" barrel

(not a typo, both 2400 and Lil Gun gave averages of exactly 1341 fps)

Adequate accuracy with all loads. BUT, my go to load because of great accuracy is the Alliant 2400 loads in both JHP and LSWC. Guns used are GP100 and Smith 66. All loads chronographed by myself.
 

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Discussion Starter · #13 ·
Thanks guys. BigSteve, it's good to see you had similar results with 300-MP. DAardvark, that Quickload data is quite interesting. It looks like matching the American Eagle ammo is not gonna happen with safe loads. Also, 60k PSI from those blue dot loads!?! Hopefully they weren't making that much, but if so, it's pretty amazing the gun held together.

Try 'Lil Gun when you get the chance, never go back.
You think it would reach faster velocities from a handgun? BigSteve's tests show an improvement, but not a huge one. Or is there some other aspect of it that is more compelling? I'm still on the whole impressed with 300-MP. From carbines it is excellent, and it has worked well for me in .44 Magnum to deliver top-end velocities.
 

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Blue, well said, but to each his own. Some are interested in pie plate accuracy out at 25 yds, presumably for defense loads or very close in deer with all the speed they can get. Me, I'm a believer in Keith's old adage, 1200 fps is about all you need in any loading for the lower 48, or you'd better get a bigger, read longer barrel, gun. 1200 fps was his load from a .44 Special...but he went to almost 1400 in the .44 Magnum, buy much above 1200 though, maybe 99% of the shooting fraternity can't control the piece good enough the get 2nd shot hits in a timely manner, and that includes the .357 Magnum.

My goal is a 2" or less group at 25 yds from rest, velocity is always secondary, and more is not always better for the intended purpose. No disrespect stated or implied to those who frequent the speed limits of the envelope either...it's just not for me, and I don't want to shoot next to them on any range, either.

Rod
 

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Discussion Starter · #15 ·
No disrespect stated or implied to those who frequent the speed limits of the envelope either...it's just not for me, and I don't want to shoot next to them on any range, either.
Haha, yeah no disrespect is stated or implied when you say you don't want to be next to them on any range. :rolleyes:

I was pretty content to just ignore posts like BlueMountains, but what the hell... There are always people who feel the need to visit a thread that they clearly have no interest in, just to state that their interests lie elsewhere. You want to talk about shooting a handgun from a rest or about loading for accuracy, there are thousands of threads on the forum already. I bet more than a few already deal with that. And in case they don't, the forum has a very conveniently included means to start your own new one:

 

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aurora40,
I was only trying to find out if anyone loading to the higher velocities were still getting good accuracy with those rounds. It is pretty important after all. Without accuracy, velocity means nothing.
 
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