gatnerd

Military Guns and Ammunition

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

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NGSW Phase 2 Consolidation and info   Small Arms <20mm

Started 30/8/19 by gatnerd; 279026 views.
Gr1ff1th

From: Gr1ff1th

28-Oct

Also would you say these edge case accuracy issued with the GD Rifle + TV Neckless are a Quality Control problem or are they fundamental to the design?, because it sounds like a possible QC issue to me

nincomp

From: nincomp

28-Oct

A big question is HOW sensitive is this round to minor chamber alignment issues.  Part of the problem is that, as near as I can tell, the projectile was designed before the cartridge and is not optimized at all for this non-standard case.  The photo of the sectioned case shows that very little of the shank of the bullet extends beyond the case, leaving little to properly align the bullet in the bore while the rear part of the bullet is exposed to the turbulence from burning propellant.

  It may well turn out that a projectile with slightly different geometry or construction may be needed to reduce balloting in the barrel.  Even moving the case shoulder back slightly to expose more of the shank may be helpful (although some powder capacity would be lost).   It is also possible that a two-stage powder ignition system, with the primary "booster" more gently inserting the projectile into the throat (to avoid asymmetrical deformation) would help with accuracy.  I have no idea if this could be easily and reliably done, however.   I would imagine that a CT cartridge or the retrofit neckless discussed previously, would also benefit from this type of development to improve alignment.

Then again, as Emeric stated, there are a lot of potential issues with the proposed weapon system that could affect accuracy.  

EmericD

From: EmericD

28-Oct

Gr1ff1th said:

Thanks for your input Emeric, Do you think that it's possible that the Textron NGSW-R and AR could be having the (weakly) rumored accuracy issues or is it not likely to be true, because surely these issues would have been caught in LSAT/CTSAS and the preliminary phases of NGSW before it got to this point

Well, the goal of LSAT was to replace the 5.56 mm Minimi, not to provide a weapon family capable of hitting man-sized targets at 1200 m+, so this effect could have been forgotten...

On the other hand, the effect of an off-center chamber for CTA is well known and was investigated in-depth (for example):

https://cradpdf.drdc-rddc.gc.ca/PDFS/unc241/p804426_A1b.pdf

nincomp

From: nincomp

28-Oct

Emeric, are you aware of any work that has been done to improve in-bore bullet alignment by changing the bullet shape or construction?  For example, you mentioned the location of the center of gravity.

Thanks.

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.

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