7 mm SHERMAN SHORTMAG vs 7 SAUM

[elkaholic]

What about the seater die Rich? TIA
Mike

You would have to have a 264 seater

 

[elkaholic]

Are you using a conventional throat design or some type of hybrid design??

Trying to figure out how you're getting these remarkable velocities some are claiming, yet no pressure.

It has a conventional throat. The case is more efficient with the very short burning column, straight wall design and 40 degree shoulder. Also, because of the distance from the shoulder/neck jct. being much shorter than a SAUM, it allows for a much longer throat so that the useable case capacity is not taken up by the bullet. The case design also does allow for the pressure to be distributed a little better without stretching as easily. I wil say that SOME of the velocities listed probably did have some pretty excessive oressure, but it will outrun a SAUM with equal pressures .........Rich
p.s. If you long throated a SAUM, you could get closer to the SS velocity but that defeats the whole purpose of having a short action. You would have to run it in a long action to gain the benefit, which some people do.

 

[BlackHillsSD]

Rich, did you get my pm?

 

[elkaholic]

Rich, did you get my pm?

I did now! Did you want me to call?

 

[BlackHillsSD]

Yes that would be great.

Thanks, Ty

 

[B23]

It has a conventional throat. The case is more efficient with the very short burning column, straight wall design and 40 degree shoulder. Also, because of the distance from the shoulder/neck jct. being much shorter than a SAUM, it allows for a much longer throat so that the useable case capacity is not taken up by the bullet. The case design also does allow for the pressure to be distributed a little better without stretching as easily. I wil say that SOME of the velocities listed probably did have some pretty excessive oressure, but it will outrun a SAUM with equal pressures .........Rich
p.s. If you long throated a SAUM, you could get closer to the SS velocity but that defeats the whole purpose of having a short action. You would have to run it in a long action to gain the benefit, which some people do.

That's all well and good but using RL26 & 180 Berger bullet as the constant, isn't higher pressure needed to increase the bullets velocity?

Considering pressure monitoring equipment isn't being used and we're only going off bolt thrust, ie. bolt lift and ejector marks, couldn't the fact that this is a case with minimal body taper, which most will agree slows the exerted reward force, and that is possibly masking higher chamber pressures?

I understand you believe this to be a more efficient case design over SAAMI but aren't you packing more of the same powder in a case with slightly less capacity and using the same bullet yet getting higher verlocity? If yes, how does that not equal higher chamber pressure? Does a 40 degree shoulder some how flatten the pressure curve?

For me, the physics don't add up but I'll voluntarily admit I'm not the sharpest pencil in the box.

 

[wilkup]

That's all well and good but using RL26 & 180 Berger bullet as the constant, isn't higher pressure needed to increase the bullets velocity?

Considering pressure monitoring equipment isn't being used and we're only going off bolt thrust, ie. bolt lift and ejector marks, couldn't the fact that this is a case with minimal body taper, which most will agree slows the exerted reward force, and that is possibly masking higher chamber pressures?

I understand you believe this to be a more efficient case design over SAAMI but aren't you packing more of the same powder in a case with slightly less capacity and using the same bullet yet getting higher verlocity? If yes, how does that not equal higher chamber pressure? Does a 40 degree shoulder some how flatten the pressure curve?

For me, the physics don't add up but I'll voluntarily admit I'm not the sharpest pencil in the box.

I am one of those who've hotrodded this little shell well past what is considered safe. With that said, I'll take a stab at what's going on. I think because of the efficiency of this short little case the powder burns a bit better than other short mag cases which contributes to the higher speeds with equal pressures.

 

[trueblue]

That's all well and good but using RL26 & 180 Berger bullet as the constant, isn't higher pressure needed to increase the bullets velocity?

Considering pressure monitoring equipment isn't being used and we're only going off bolt thrust, ie. bolt lift and ejector marks, couldn't the fact that this is a case with minimal body taper, which most will agree slows the exerted reward force, and that is possibly masking higher chamber pressures?

I understand you believe this to be a more efficient case design over SAAMI but aren't you packing more of the same powder in a case with slightly less capacity and using the same bullet yet getting higher verlocity? If yes, how does that not equal higher chamber pressure? Does a 40 degree shoulder some how flatten the pressure curve?

For me, the physics don't add up but I'll voluntarily admit I'm not the sharpest pencil in the box.

Rich,
I would have to say your pressures are in the 70-75.000 range based on my experience with my SAUM.Might want to put a string gauge on it to see exactly what your pressure actually is at.

 

[bigngreen]

Iv'e built a number of 7 SAUM's throated out and several 7 SS's and using the same brass even and bullet lots the same pressure signs will put the SS faster by a margin. I have a pressure trace, the issue with it is it won't give you an actual pressure unless you have a certified calibration round to calibrate to, it's a cool tool for comparing but it won't give you an actual pressure, the SS round is so short I have not been able to get the gauge in an ideal spot since it's under a recoil lug.

 

[B23]

Iv'e built a number of 7 SAUM's throated out and several 7 SS's and using the same brass even and bullet lots the same pressure signs will put the SS faster by a margin. I have a pressure trace, the issue with it is it won't give you an actual pressure unless you have a certified calibration round to calibrate to, it's a cool tool for comparing but it won't give you an actual pressure, the SS round is so short I have not been able to get the gauge in an ideal spot since it's under a recoil lug.

And I'm not disputing the SS isn't shooting faster than a standard SAUM but in my tiny little brain it's getting there due to increased pressure. I also believe you aren't seeing the typical pressure signs of ejector marks or increased bolt lift because the SS case has less body taper than does a SAAMI SA Ultra mag and with less body taper comes less bolt thrust.

Unless a 40 degree shoulder some how flattens the pressure curve, which I've never heard and if it does please point in the direction of those findings, just calling it more efficient doesn't defy the physics, for me.

 

[elkaholic]

That's all well and good but using RL26 & 180 Berger bullet as the constant, isn't higher pressure needed to increase the bullets velocity?

Considering pressure monitoring equipment isn't being used and we're only going off bolt thrust, ie. bolt lift and ejector marks, couldn't the fact that this is a case with minimal body taper, which most will agree slows the exerted reward force, and that is possibly masking higher chamber pressures?

I understand you believe this to be a more efficient case design over SAAMI but aren't you packing more of the same powder in a case with slightly less capacity and using the same bullet yet getting higher verlocity? If yes, how does that not equal higher chamber pressure? Does a 40 degree shoulder some how flatten the pressure curve?

For me, the physics don't add up but I'll voluntarily admit I'm not the sharpest pencil in the box.

I am not so sure we are using more powder than the SAUM (at least most of us) and the capacity is very close to the same. I do agree that it likely handles pressure better, which is not a bad thing!.........Rich

 

[bigngreen]

Didn't take it like your were disputing it, just throwing that info out there. The case design certainly causes less bolt thrust, I have no doubt it is running some pressure but until a barrel is made and sent to get direct pressure testing done there is no way to have a rock solid number so we really just run on case integrity as the main identifier of what pressure we can operate at.

I have shot compared loads from some 6.5 SAUM guys and taken them and ran them in my barrels and even though the capacity is nearly identical we shoot very different velocities, in one case the load the other was shooting was at his top end and it was fire forming load in the SS with primers still rounded totally so there is something to the case shape that makes something happen different.

 

[elkaholic]

Rich,
I would have to say your pressures are in the 70-75.000 range based on my experience with my SAUM.Might want to put a string gauge on it to see exactly what your pressure actually is at.

I would not doubt that I have shot a couple at that pressure, but I don't think my loads that I use are near there. I have loaded at least 12 times with the same brass with 180's at just below 3000'. That can't happen at those pressures! .......Rich

 

[trueblue]

Rich,
If you are getting 12 reloads on your brass, that is a good sign.