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Old June 14, 2021, 07:22 AM   #1
stagpanther
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358 MGP--350 L done right?

I've though a lot about the "350 L done right" and this morning had an idea--why not try a .358 bullet in a 6.8 case? I have a 30 herret die set and a few 358 calibers--all I needed to do was widen the neck and seat a bullet. It literally took me 60 seconds to do the whole thing first try and ended up with this:



That was so brain-dead easy I thought "no way nobody has thought of this before" and I googled around--sure enough some guy came up with the same idea years ago and called it the "358 MGP." The best part is that lots of load data and testing already exists. The only thing left to do, I would think, is to take out the shoulder bump and make it a tapered straight-wall and there you have it, a hard hitting short-range street-legal cartridge even in the wierdo straight-wall hunting states.
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Old June 14, 2021, 12:51 PM   #2
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More than that, some company would have to start making the ammo and another the rifles. A lot of good ideas die on the vine for the only reason that they were never put into production...

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Old June 14, 2021, 01:45 PM   #3
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A lot of good ideas die on the vine for the only reason that they were never put into production...
Many new cartridges suffer that issue at some point in their development.
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Old June 14, 2021, 05:56 PM   #4
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Sounds like you invented a rimless 357 Herrett. I used to shoot a 357 Herrett in a Contender, and I can tell you it's plenty powerful. Right up there with the 35 Remington. Not to disparage the 350 Legend, but it's not even close.
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Old June 14, 2021, 06:30 PM   #5
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Yes I did that one about 3 years ago , had a reamer made . Built a couple of AR-15's in that cartridge . It shot about 100 fps faster than the 350 L . I dropped it for a better cartridge , more case capacity and it feeds a little better in an AR-15 than the 6.8 based case . It is a rimless 30/30 necked up to .357 , the old Herrett . Since the 350 L talk has come up I found that I still have a box of barrels and will make a couple more of the " .357 Diablo " uppers .
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Old June 14, 2021, 08:47 PM   #6
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I'm curious. What's the case capacity of the MGP?
Or for that matter, the necked-up 6.8 case?
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Old June 15, 2021, 12:56 AM   #7
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I'm curious. What's the case capacity of the MGP?
Or for that matter, the necked-up 6.8 case?
I didn't actually measure, and I suppose a lot depends on how the chamber is cut and how far out the bullets will be seated. I think I've read that using the 180 hot cors they have achieved results that surpass the 35 Remington and has been run as fast as 2500 fps, and has also been used to drive heavier and lighter bullets out of AR's. I've built quite a few different AR's and have found the 6.8 spc case to be one of the all-around best case designs in terms of reliability, robustness and adaptability for the AR 15 platform. What I can't tell is if this thing is still viable--the links for the MGP website don't seem to work.
Quote:
It is a rimless 30/30 necked up to .357 , the old Herrett . Since the 350 L talk has come up I found that I still have a box of barrels and will make a couple more of the " .357 Diablo " uppers .
I'm thinking specifically about making this a straight-wall to get the "big 5 weirdo states" hunting legal, which is the 350L's principal market draw.
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Old June 15, 2021, 01:20 AM   #8
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ernie8-
I'm confused now. The 6.8 SPC case is derived from 30 Remington brass, which is the same head size as 30-30 (essentially a rimless 30-30), so wouldn't a 357 caliber cartridge based on the 6.8 SPC be the same as a 357 caliber cartridge based on rimless 30-30? Enlighten me.

stagpanther-
there is already a .375" caliber cartridge based on the 6.8 SPC brass for the straight weall only states.
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Old June 15, 2021, 02:01 AM   #9
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The 375 FUW? (funny name).
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Old June 15, 2021, 07:03 AM   #10
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Thinking about this a bit ... case capacity (usable capacity) in a straightwall case depends on bullet diameter and OAL. There's some web and wall thickness play, but really bullet diameter is the definer.

With that in mind, how does the 358 MGP achieve a 200fps advantage -- operating at the same pressure/same barrel length/same bullet/truly straightwall -- over the LEGEND ?
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Old June 15, 2021, 07:17 AM   #11
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With that in mind, how does the 358 MGP achieve a 200fps advantage -- operating at the same pressure/same barrel length/same bullet/truly straightwall -- over the LEGEND ?
Bigger bullet, bigger case, higher pressures is a pretty good formula. I don't know much about it--like I said all I did was have a "aha" moment and slapped something together on the press, but the data for the 358 mgp--and other straightwall variants-- is out there if you google for it.
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Old June 15, 2021, 08:07 AM   #12
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Sometimes I marvel at this straight-wall silliness--I've dropped a fair-sized deer with a plain old 44mag lever gun, and the single shot 444 marlin I bought from CVA (barreled by bergara) for $150 is very accurate. I understand the "kids need soft-shooting cartridges to like shooting" argument, but I've always thought that done right even a youth can be trained to take that "one shot" with accuracy, that adrenaline moment does a lot to dampen felt recoil. A friend of mine introduced his grandson to hunting at a young age--by 10 years of age he was shooting (and hitting with) a 7mm RUM.
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Old June 15, 2021, 08:13 AM   #13
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The 30/30 case is longer than the 6.8 case and the shoulder is a little farther forward , so more capacity . I could only get about 100 fps more with the necked 6.8 case over the straight wall 350 L with the same pressures . The AR limits the pressure you can operate at , also the case limits the pressure you can operate at with a bolt rifle . I was using 16 inch barrels as these small cases do not benefit much from longer barrels . The gas system was way different than what was needed with a .223 . There is no benefit from going above .357 dia as there is not enough case capacity for bullets weighing above the 250 of .358 dia . Also there are not any suitable bullets made for .375 that will expand well at the much lower velocities you would get . I settled on the Rimless 30/30 as it feeds best , best velocity , made from common range pick up cases and since you are turning the rim down you can go with either 6.8 or .223 bolt head . So you can make an upper to drop right on your standard .223 AR-15 . The only problem is you have to do a lot of work to make cases . The 6.8 based case on the other hand is easy to make , just neck it up . But then you have to get a different bolt head . My info is based on making working rifles , pressure testing loads , testing for accuracy and real velocity and how they worked on game . I found the 180 to 200 grain pistol bullets did the best of all the above . Not just necking up a case to photo .
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Old June 15, 2021, 08:25 AM   #14
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I started the straight wall cases about 20 years ago to get better performance for pig hunting . The first was a .45 cal version [ the later was fitted with a small rim to become the .460 S&W ] for knock down power on big pigs . I found the pistol bullets at high velocity transferred energy better than the tough 45/70 bullets . I named it after my pig hunting dog Bandit . Since then I have made straight walled .44 , .50 and .357 cartridges and stuck with the Bandit name for the straight walled cartridges I make . The bottle necked versions are named after Bandit's son Diablo . I found that the straight walled case cartridges are the most efficient with the most velocity and less muzzle blast fore the size and powder burned .
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Old June 15, 2021, 08:26 AM   #15
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But then you have to get a different bolt head . My info is based on making working rifles , pressure testing loads , testing for accuracy and real velocity and how they worked on game . I found the 180 to 200 grain pistol bullets did the best of all the above . Not just necking up a case to photo .
I was just fooling around and found that someone else had already spent a lot of time developing this cartridge, so his data is already out there. I personally would not waste any time developing yet another "microniche" cartridge since I would personally use one of the many existing straight-wall cartridges if (God forbid) I ever ended up hunting in a straight-wall only state; though I do know they get some awfully big wily deer in them sometimes. Like my state, Maine, I believe these rules have more to do with simply repressing the harvest rate than any real safety to the public.
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Old June 15, 2021, 08:30 AM   #16
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Stag , you said you have built many AR-15's . What barrel blanks do you use ? What alloy do you prefer to make your gas blocks ? Who do you use to make your reamers ? What type of pressure test tools do you use ?
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Old June 15, 2021, 08:46 AM   #17
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Stag , you said you have built many AR-15's . What barrel blanks do you use ? What alloy do you prefer to make your gas blocks ? Who do you use to make your reamers ? What type of pressure test tools do you use ?
Don't know what your point is Ernie--if it's simply "I swing a bigger pair than you because I'm more experienced than you" then I give you the road, I simply buy the components that others make and put them together. I am not a wildcat developer (though I have put together a couple that others developed).
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Old June 16, 2021, 04:26 PM   #18
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You are the one that kept contradicting my real results , without any of your own . I gave the real reasons why some things work better than others , why I though a case was better , and the pros and cons of each type . My .357 Bandit [ made into the 350 L ] gave 30/30 power to an AR-15 [ better on game than the 6.8 ] and made a very sweet little bolt rifle . I do not consider pulling out the two pins to put on another upper building an AR .
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Old June 16, 2021, 11:37 PM   #19
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Quote:
Originally Posted by ernie8
You are the one that kept contradicting my real results , without any of your own . I gave the real reasons why some things work better than others , why I though a case was better , and the pros and cons of each type . 
I don't see any real data, all I see is your opinion. I'm not saying your opinion is wrong if you have the data.

What real world velocites and pressures were you getting from your Diablo and Bandit cartridges?

How does your rimless .30/30 case differ in dimensions from the 6.8 case?

Will your rimless .30/30 case have a COAL that's useable in an AR-15 magazine?
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Old June 16, 2021, 11:48 PM   #20
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ernie8-
The 357 Herrett uses a 30-30 case trimmed to 1.75" long to achieve 2200 fps with a 180 gr bullet out of a 10" barrel. I never tried anything heavier, never really wanted to. The 6.8 SPC case is 1.68", so you might sacrifice some velocity, but running the cartridge out of a longer barrel should get you similar or slightly higher velocities. Right? Do you have to drop down to lower pressures to run these in an AR15?
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Old June 17, 2021, 12:02 AM   #21
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I personally would not waste any time developing yet another "microniche" cartridge since I would personally use one of the many existing straight-wall cartridges if (God forbid) I ever ended up hunting in a straight-wall only state;
There are a lot of the "micro-niche" cartridges out there. One of my customers built a 45 Raptor, which is supposedly better than the 45 Hamr, which is better than the 450 Bushmaster, and so on. And every custom gunsmith has come up with his own version of an existing cartridge, tweaked to be slightly different than other similar cartridges, and come up with a dozen reasons why his is better than the other one. They can't all be right. But creative people create stuff, unique or not. I did my apprenticeship in a custom gunsmith shop of some note, and they had a whole line of cartridges they would chamber rifles in, and every one of them was better than commercial cartridges according to them.
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Old June 17, 2021, 12:11 AM   #22
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A question.....

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Old June 17, 2021, 06:35 AM   #23
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Uhhhh--bigger case volume and bigger bullet.

Quote:
You are the one that kept contradicting my real results , without any of your own . I gave the real reasons why some things work better than others , why I though a case was better , and the pros and cons of each type . My .357 Bandit [ made into the 350 L ] gave 30/30 power to an AR-15 [ better on game than the 6.8 ] and made a very sweet little bolt rifle . I do not consider pulling out the two pins to put on another upper building an AR .
I don't have the slightest idea what you are talking about--I haven't contradicted anything you have said. This MGP was conjured up by another guy some 16 years ago or so. Track him down and huff and puff and kick sand in his face if you want. You bring up these ad hominem questions/comments which are not contributing much of anything to the conversation.
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Old June 17, 2021, 10:07 AM   #24
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At the end of the day it's a wonderful solution searching for a problem.
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Old June 17, 2021, 04:41 PM   #25
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Uhhhh--bigger case volume and bigger bullet.
Uuhhhh. No.
358/356 R-squared says only 1% increase in straightwall case volume.
It may be angels on the head of a pin at this point, but all these other
wunnerful cases that give wunnerfully-better performance need "a bit"
more explanation.


.

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