gatnerd

Military Guns and Ammunition

Hosted by gatnerd

This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.

  • 3274
    MEMBERS
  • 185868
    MESSAGES
  • 0
    POSTS TODAY

Discussions

NGSW Phase 2 Consolidation and info   Small Arms <20mm

Started 30/8/19 by gatnerd; 314228 views.
poliorcetes

From: poliorcetes

28-Oct

roguetechie said:

A very important thing to note is that TV can absolutely ratchet the pressures up if necessary AND they're getting enough of an efficiency bump in a cartridge this size to potentially get a little more MV out of any given peak pressure.

Although steel base would guarantee back extraction, I wonder why the leckless format: would it be related to the plasticity of polymer at huge pressures?

Maybe CT has a bigger pressure margin because plasticity works in favor of the design (sealing the forward part of the chamber)

poliorcetes

From: poliorcetes

28-Oct

EmericD said:

My understanding is that the "out of alignment" chamber is much more acute with the Textron CT moving chamber design.

What would be the cause of such disalignment? Debris in the "chamber receiver"?

renatohm

From: renatohm

28-Oct

A movable chamber that is separate from the barrel, not unlike cylinders in revolvers, and we do know that a disalignment will affect accuracy.

Gr1ff1th

From: Gr1ff1th

29-Oct

CT has the highest potential pressure out of all of them, due to the fully supported cartridge in the chamber

gatnerd

From: gatnerd

29-Oct

EmericD said:

I've just had some information "straight" from GD, and it's true that they experienced accuracy problems in some cases.

Great info, thanks for sharing.

Alas, not great news. I guess given these issues for TV (and assumed textron), SIG actually has a solid chance? 

Do you think if TV used a more substantial internal neck that the accuracy issue would resolve itself?

Our early 'reports' out of youtube show pretty solid accuracy for TV's .308 conventionally necked rounds out of this AR10:

https://youtu.be/zxomPhgSaxA?t=575

And very good groups from bolt guns:

https://youtu.be/Zt10UNnGb4w?t=50

EmericD

From: EmericD

29-Oct

gatnerd said:

Do you think if TV used a more substantial internal neck that the accuracy issue would resolve itself?

At least it will help. I dunno if that will resolve everything because the polymer part will be thicker than with a neck, and the case / chamber concentricity should be improved. Maybe with something like an "O" ring on the front part of the case, or some groove / flange in this area.

I was also been told that one test bullet was very "front heavy", so avoiding in-bore yaw was challenging for everyone.

Gr1ff1th

From: Gr1ff1th

29-Oct

"My understanding is that the "out of alignment" chamber is much more acute with the Textron CT moving chamber design."

Does this mean that you've heard on the grapevine that the Textron is having issues currently, or am I misinterpreting what you're saying?

Edit : If I'm reading this right it says that even a 0.254mm misalignment can result in a 3-4 MOA shift, and a 0.54mm misalignment will result in a 12 MOA shift, these tolerances seem to be pretty tight for a combat rifle, I really hope this isn't an issue in the Textron NGSW

  • Edited 29 October 2021 5:54  by  Gr1ff1th
gatnerd

From: gatnerd

29-Oct

EmericD said:

I was also been told that one test bullet was very "front heavy", so avoiding in-bore yaw was challenging for everyone.

Ah, Tungsten EPR I assume?

That was something I had wondered about awhile back - if they just took the EPR design, and swapped out the steel tip for tungsten, then the projectile would be very front heavy (as opposed to the preferred rearward weight balance.) Also the projectile would be pretty radically different in overall weight. 

Would a full length, exposed tip penetrator design fix the front heavy issue? 

I recall awhile back you had mentioned 'acoustic impedance' of alternative materials to copper/steel for the base of the EPR to work better with tungsten than Nammo's 'powerball' steel base/tunsgten tip. If thats still happening, and the alternate material is less dense then steel/copper, that would exacerbate the front heavyness as well?

gatnerd

From: gatnerd

29-Oct

Gr1ff1th said:

If I'm reading this right it says that even a 0.254mm misalignment can result in a 3-4 MOA shift, and a 0.54mm misalignment will result in a 12 MOA shift, these tolerances seem to be pretty tight for a combat rifle, I really hope this isn't an issue in the Textron NGSW

Those would be tight tolerances. 0.254 is .01", only slightly more than the standard .008" gap between a revolver cylinder and barrel. 

For that chart, Delphi rendered it unreadable. You you think you could upload it using ImgBB? Thats the best way to share photos on this forum. Its free and fast.

https://imgbb.com/

Then you can share the link to the upload, or upload it using the little photo icon 'from website' using that link. Whereas rendering 'from computer' often compresses the image to death.

Gr1ff1th

From: Gr1ff1th

29-Oct

Here are some relevant extracts from the study Emeric linked earlier, about the specifics of the effects of chamber misalignment, along with a nice picture of the kind of yaw at 0.54 milimetres for a visual aid

 

  • Edited 29 October 2021 6:52  by  Gr1ff1th
TOP