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gain twist rifling   General Military Discussion

Started 9-Aug by smg762; 3177 views.
smg762

From: smg762

15-Aug

I was looking at the aeroshell thread and there was a notion of .270s at 4000fps...using a fabrl bullet. Kind of similar to what im after. Just seems like a 70grain would struggle to stabilise.  With a 70grain .270 fabrl, would it actully match the BC of a 170grain in terms of real retained energy. and what sort of twist did the fabrl or cetme have.

Id have thought a hollow aluminium bullet is best for a cetme bullet, to allow the core to take up most of he weight.

  • Edited 15 August 2021 17:33  by  smg762
DavidPawley

From: DavidPawley

16-Aug

Huh?

I recognise words there but I don’t think that you are writing in English.

roguetechie

From: roguetechie

17-Aug

Ok let's break this down.

So what you want is something in .270 that can get to very high velocities (let's say 3500+ fps because 4000 is getting into territory you don't want to be in if you don't really have to be)

You would also like this projectile to have a similar retained energy (let's say at 1 kilometer) to a  conventional 170 grain 270 projectile (and let's say at least as good terminal effects as your stretch goal because retained energy is meaningless unless your projectile can dump it effectively into your target)

You want to do this with a very lightweight for caliber projectile. This can be either aeroshell or something else like it and preferably full caliber right?

Do you want this round/loading to be compatible with the Same rifling twist of your 170 grain comparison projectile? (That's probably going to be pretty tough)

You think you'd like the projector itself to be similar to 5.56 fabrl / 7.92x41 cetme.

You think that you would need or want a hollow aluminum projectile in order to make room and save weight for the core. (This directly conflicts with your desire for a good BC in order to match retained energy of the 170 grain round)

What exactly are you trying to make this projectile do?

What is your priority media (flesh cinder block sand bag lethal behind armor wound at x Meters with x armor class?) to penetrate and what terminal effect do you want in that material?

What are the next 3 most important things to penetrate/have good terminal effect against?

If we can get a better idea of what you want to do we can give you better answers

smg762

From: smg762

17-Aug

Well the idea was that the cetme shape would allow 3700fps and still retain energy well. Then you add a .17 rod and its a super penetrator. Same end goal as aeroshell.

Im really curious about twist rates, in terms of, would a cetme bullet allow slow rates, to enable these overbore energies.

My round with 3300ft lbs strikes with 2600 at 300m...the core strikes with 1700 which is pretty cool. 

Oh, last question....if u recall darpa guided bullets in the news a while back.....google the pics.

I was surprised that apparently they need no spin despite having only tiny fins...could one really go smoothbore just by adding this sort of thing to your bullet?

  • Edited 17 August 2021 10:51  by  smg762
EmericD

From: EmericD

17-Aug

smg762 said:

Oh, last question....if u recall darpa guided bullets in the news a while back.....google the pics. I was surprised that apparently they need no spin despite having only tiny fins...could one really go smoothbore just by adding this sort of thing to your bullet?

The bullet was ~4 cm long, with fins at the rear, just like an arrow. The fins generate drag behind the bullet CoG, enabling proper aerodynamic stability.

JPeelen

From: JPeelen

17-Aug

Keep in mind the videos were a publicity stunt. The bullets were not guided at all. They were simply dumb, finned projectiles. And the circling motion of the trajectory --doubtless intended to give the impression of guidance to the unwary-- was due to the asymmetry of the fins, which is unavoidable with small calibers of 12.7 mm and below. 

This is why real world fin stabilized projectiles have slightly canted fins, inducing rotation to compensate for asymmetries. 

smg762

From: smg762

18-Aug

Well i was curipus about the inset fins....they dont stick out...lile a mortar round.  Is this really doable... would it work as a dedicated smoohbore bullet.

Also if one had fins that were intentially slightly too small, would the bullet work with a slow twist like 1 in 40.

for example a 204 often needs fast twists and this isnt too efficient...if u had 4 fins near the front of a VLD could you lower the twis5 rate and would it still stabilise

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