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Why no sabots for infantry guns?   Small Arms <20mm

Started 28-Aug by VPMudde; 2954 views.
gatnerd

From: gatnerd

30-Aug

17thfabn said:

Sounds like the World War II era 76 mm HVAP and other similar anti=tank rounds

Thank you, I wasn't aware of those (more of a gun guy then a cannon guy) but thats very much the same concept:

https://en.wikipedia.org/wiki/Armor-piercing_ammunition#APCR_and_HVAP

And the reasons for their use - sabots/APDS hadn't been perfected - is pretty much the same reason we'd be interested in Aeroshell for small arms today. It could provide a bridge between conventional copper jacketed AP rounds and future APDS sabots for small arms. 

QuintusO

From: QuintusO

30-Aug

VPMudde said:

Don't rightly know what you mean by this. A 1-in-7" twist in a 7.62 barrel is the same number of rotations per distance as a 1-in-7" 5.56. And small caliber ammunition generally has a tighter twist rate than a larger caliber to being with. The angle of the rifling will be different of course.

Correct. If your projectile needs a 1/7 to stabilize with a 5.56 bore, it will also need a 1:7 7.62 bore if using a sabot. This is a tighter twist as you point out.

VPMudde said:

But all of this still doesn't explain by what mechanism the sabot affects accuracy. That happens after exiting the barrel, no?

Separation creates interesting turbulent conditions which help knock the bullet around in complex ways. The best way to get over this is to make sure your projectile is well stabilized, and that there is reasonable muzzle pressure on uncorking (you do this via using a suppressor). A taper-fit cup sabot helps too.
 

VPMudde said:

Flechettes have their own issues, unless you know things about them that the people at AAI didn't last century. So what are you suggesting? L/D 12 bullets, but with the trailing ¾ths ground away to become fins? (there's a fancy word for that that eludes me).

Last century is a long time; we know a lot more now that they didn't then.

 

VPMudde

From: VPMudde

30-Aug

Please excuse me while I get the hang of this forum's quotation thing

EmericD said:

That's one part of the issue. The first issue with a sabot is that the force needed to extract the bullet from the case and push it into the forcing cone is more dispersed, so the internal ballistic cycle is more dispersed (more pressure and velocity deviation).

How does the sabot cause this dispersion? Wouldn't the same thing happen with light full caliber bullets al well? (say, 78gr Lehigh .308 close quarters).

EmericD said:

The second issue is that it's more difficult to achieve a perfect bullet / sabot concentricity. The more importa... [snip]

I didn't think concentricity would be that much of a problem. Good molds and a properly homogenized feed into the molder seemed enough TLC to overcome this. You could, of course, turn sabots on a lathe. Or do away with the bullet jackets altogether. No need for them if you've got a sabot to take the rifling.

EmericD said:

The third issue is that, for proper accuracy, you need to avoid the "slippery soap" effect when the bullet leaves the barrel, so you want plastic deformation and not (reversible) elastic deformation. Using a "lar... [snipp]

Perhaps there are alternatives to just clamping down on the bullet hard. A cannelure maybe, to have something for the sabot to hold on to by fit rather than compression.

Edit: getting the hang of this forum's quotation thing.

  • Edited 30 August 2021 20:17  by  VPMudde
VPMudde

From: VPMudde

30-Aug

QuintusO said:

Separation creates interesting turbulent conditions which help knock the bullet around in complex ways. The best way to get over this is to make sure your projectile is well stabilized, and that there is reasonable muzzle pressure on uncorking (you do this via using a suppressor). A taper-fit cup sabot helps too. 

You and Emeric have different ideas on what causes a saboted bullet's inaccuracy issue. I'm curious to see what you two would come up with for a solution. Me, I'm just grasping at straws with limited, but not what I believe is entirely incorrect understanding. (Not to toot my own horn or anything wink.)

QuintusO said:

Last century is a long time; we know a lot more now that they didn't then.

So what do we know now? Small diameter rods affected by otherwise non-barriers such as rain or light foliage are still small diameter rods affected by otherwise non-barriers such as rain or light foliage. 

VPMudde

From: VPMudde

30-Aug

gatnerd said:

Thank you, I wasn't aware of those (more of a gun guy then a cannon guy) but thats very much the same concept:

https://en.wikipedia.org/wiki/Armor-piercing_ammunition#APCR_and_HVAP

And the reasons for their use - sabots/APDS hadn't been perfected - is pretty much the same reason we'd be interested in Aeroshell for small arms today. It could provide a bridge between conventional copper jacketed AP rounds and future APDS sabots for small arms. 

In this thread I'm hoping to get towards that perfected -DS part. Though Aeroshell (and polymer jackets in general) are a nice and relevant development for sure, and provide some of the same benefits. The polymers and manufacturing techniques used there could be used in making a proper discarding sabot for small arms.

I just also really want that extra velocity and ultra sleek aerodynamics to happen no_mouth

gatnerd

From: gatnerd

30-Aug

VPMudde said:

I just also really want that extra velocity and ultra sleek aerodynamics to happen

Yep, the pairing of sabots with VLD projectiles is pretty much the holy grail for small arms development. 

Its a substantial challenge. On the plus side, theres never been an easier time to experiment with this.

-3D printing would allow the rapid prototyping of different sabot configurations

-.300 Blackout provides an ideal off the shelf sabot launching cartridge (plenty of ogive space + 1/7 barrel twist for .224 vld)

Off the top of my head, configuring a 2 piece sabot that it 'clips into' a groove in the bullet, and also closely follows the contours of the bullet, may be promising. And while that would be a bitch to machine it would be straightforward for a good 3D printer. 

Cutting Edge's line of rifle bullets have a groove already that could serve as a off the shelf jumping off point.

On the much more extreme side, Elite and Vanguards 5.7x28 projectile is very groovy in terms of where a sabot could clamp on:

VPMudde

From: VPMudde

31-Aug

  • Edited 31 August 2021 11:03  by  VPMudde
smg762

From: smg762

31-Aug

As well as the increased piston area, does a sabot also get more speed thanks to its squishyness when contacting the rifling?

 And if so would the same apply to 9mm syntech ammo or the aeroshell rounds? 

If one went the non-discarding route, how much would the plastic jacket weigh if you scaled the aeroshell down to 556..? (Assuming a long 32mm bullet)

roguetechie

From: roguetechie

3-Sep

Squishiness is not going to be a factor in a sabot getting more MV especially since you don't want a sabot to get squishy since that's an incredibly good way to have the bullet start balloting it's way down the barrel potentially causing the nose to ram into the inside of the barrel walls.

This is something you want to avoid naturally.

Now that being said, I wonder if with any one of several manufacturing tricks we can do now that we couldn't in any sort of quantity even a few years ago there might not be some way to use a shear thickening compound maybe formed into a tiny o ring to "grip" the projectile while under acceleration down the barrel without the need for a canelure or other grooves which are going to rob precious aerodynamic performance in free flight.

Assuming that you run Textron or TV cases there's potentially going to be more room in production facilities for tooling and etc to do things with projectile construction that just weren't feasible to do before. 

I also believe that now is the time to start pushing for projects to look into these things before the usual suspects can cut the staffing and square footage at our national ammo production facilities back to the bone thereby robbing us of the ability to put these things into effect say 5 years from now.

We have been very poor stewards of our defense industrial base up to now and because of it there's worryingly little defense industrial base left.

Whatever we eventually do, the important thing right now is to make sure that the usual suspects don't take the "opportunity" once a winner for ngsw is picked to cut even more stuff we won't ever be able to replace like has happened so many times already.

To a degree it may even be a good thing to embark on something that "needs" way more resources than ideal in the short term just to make sure whatever good solution emerges in the medium term has what's necessary when we figure it out.

VPMudde

From: VPMudde

3-Sep

roguetechie said:

I also believe that now is the time to start pushing for projects to look into these things before the usual suspects can cut the staffing and square footage at our national ammo production facilities back to the bone thereby robbing us of the ability to put these things into effect say 5 years from now.

[snip]

To a degree it may even be a good thing to embark on something that "needs" way more resources than ideal in the short term just to make sure whatever good solution emerges in the medium term has what's necessary when we figure it out.

APTC looks to be the one to watch. One of the program's products is "scalable, caliber-agnostic munition technology which can be 
leveraged by future efforts". It has it's milestone C expected Q1 of 2023.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2015/smallarms/Panel_PMMAS_SMALL_MED_NDIA_FINAL_29MAY15.pdf&ved=2ahUKEwi1nOPj3uPyAhVKDuwKHbLLA1cQFnoECDcQAQ&usg=AOvVaw1Dmdl_uYChKoVVahCCLD6a

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.globalsecurity.org/military/library/budget/fy2020/army-peds/U_0603639A_4_PB_2020.pdf&ved=2ahUKEwi1nOPj3uPyAhVKDuwKHbLLA1cQFnoECDAQAQ&usg=AOvVaw1pioGfjO9MG4Pp9H6l37nm

So,  putting and 1 and 1 together: Not much longer until 6.8mm sabot magnum and it's 1400m/s 5mm VLDs...

edit: botched copying a link

  • Edited 03 September 2021 18:23  by  VPMudde
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