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.

  • 3358
    MEMBERS
  • 191144
    MESSAGES
  • 11
    POSTS TODAY

Discussions

For Your Amusement   General Army topics

Started 15/9/21 by stancrist; 15315 views.
hobbes154

From: hobbes154

25-Aug

JPeelen said...

For pointed bullets, for which no actual Radar drag models  are available, the British origin G7 remains to be the best allround drag model. This is in my experience totally indepedent of the bullet base shape. The drag models derived from pointed straight base projectile shape, like G6 or G8 (which is G7 without the boattail) are according to my results not superior to G7 for describing drag of bullets like Mk VII.

In that case the G7 model of Mk VII gives more energy at long range than the G6 model and the Pedersen G7 models (the G7 is between the G1 and G6 above about 1km, as can be seen in the workbook I posted).

JPeelen said...

G1 gives much better results on paper, but it is simply the wrong drag model for modern pointed bullets. If you start a calculation with a G1 ballistic coefficient obtained at high velocity, you get much too optimistic velocities at lomng ranges. For modern bullets, G1 simply creates an illusion that is very different from sobering real range results.

Thanks, I think I understand this now you've spelled it out!

  • The relation between G1 and G7 is pretty stable around Mach 2 with G1 having about twice as much drag (hence the rule of thumb that you can just divide G1 by 2 to get G7). This is where most of the measurement is done (and all that is relevant to most hunters and short-medium range target shooters, hence why G1 is still used so much).
  • However below about Mach 1.5 the relative drag of the G1 model drops sharply and stays lower than 2 (but still above 1 i.e. the G1 reference projectile is absolutely draggier than G7 at all velocities) except for a brief spike just under Mach 1 (and under Mach 0.2 but that is hardly relevant). So if you fit a G1 curve to a G7 shaped bullet using data from the "flat" zone around Mach 2, the G1 model will then under predict the drag at most slower velocities and thus give overly optimistic results.
  • By contrast the G6 is pretty similar to G7 at all supersonic velocities but much draggier at subsonic velocities (due to the lack of a boat tail?). So it will give worse results than G7 at long range when fitted to short range data.

Some good resources here http://www.jbmballistics.com/ballistics/downloads/downloads.shtml for anyone else trying to learn this stuff. (Sorry I was trying to upload some graphs but the forum wasn't liking it.)

hobbes154

From: hobbes154

25-Aug

autogun said...

Don't forget that in my revised TFW the .276 replaces the .303 only in infantry squad weapons: rifles, ARs and LMGs. The .303 (in Mk VIII form) remains in use in legacy Vickers and Browning (for AFVs) MGs.

OK, that makes sense. Still not convinced on the weapons development timeline though.

Edit: I notice you have changed "GPMG" to "LMG" ;)

  • Edited 25 August 2022 22:26  by  hobbes154
hobbes154

From: hobbes154

25-Aug

stancrist said...

M2 Ball was replaced by M2 AP as the standard combat load about midway through WWII.

Which had even more energy and recoil, yes?

What was the reason? I thought if they wanted to save lead they would have used mild steel.

stancrist

From: stancrist

26-Aug

I want to say the reason for switching from M2 Ball to M2 AP was for better barrier penetration, but I am not sure if I'm remembering correctly.

It's been well over 20 years since I read about it.  I think it was in Collector Grade's The '03 Era, if you want to check it and have access to a copy.*

*ETA:  My memory of where I read it may be faulty.  It might actually have been HWS Vol II.  See Msg 127 below.

  • Edited 26 August 2022 17:06  by  stancrist
EmericD

From: EmericD

26-Aug

stancrist said:

I want to say the reason for switching from M2 Ball to M2 AP was for better barrier penetration, but I am not sure if I'm remembering correctly.

I thought that the US ground forces started to use the APM2, after large stocks were made available by the decision of the "air force" to remove the .30" MGs and use only .50" on planes.

autogun

From: autogun

26-Aug

hobbes154 said:

Edit: I notice you have changed "GPMG" to "LMG" ;)

Such designations are relative.....

A lightweight belt-fed MG with a quick-change barrel in .276 would normally be an LMG in WW2, but on a tripod and with long-range sights could be a  GPMG.

Farmplinker

From: Farmplinker

26-Aug

Maybe the author will get the book out again now that Collector Grade is no more?

stancrist

From: stancrist

26-Aug

EmericD said:

I thought that the US ground forces started to use the APM2, after large stocks were made available by the decision of the "air force" to remove the .30" MGs and use only .50" on planes.

Can you cite an authoritative source?  I just did a brief search, but found nothing to support that idea.

The only reason for the switch from Ball to AP that I came across supports what I recalled having read:

As discussed in "A History of Modern U.S. Military Small Arms Ammunition, Vol. ll." It is further stated that "in July 1943 the Ordnance Committee reevaluated the basic ammunition requirements for ground combat and decided that, because of the large amount of metal on a modern battlefield, Armor -Piercing ammunition should take the place of Ball for general combat use."

What type of ammo was generally used during WWII? [Archive] - CMP Forums (thecmp.org)

PRM2

From: PRM2

27-Aug

In your bullet drag research, have you come across any research into the 'fumer' effect for reducing projectile base drag?

Page 306 of the Black Rifle book no.1 briefly refers to this in a section that describes the 1970s FABRL project and includes the following quote about the second phase:

'The fumer phenomenon is an approach to reducing projectile base drag by injecting heat and/or mass behind the base of the bullet. A projectile has three drag components; wave drag, skin drag, and base drag. The base drag is the result of a low pressure, "dead air region" behind the base of the bullet. The injection of heat and/or mass.. increases the pressure and approaches an equilibrium state, thereby reducing the base drug component. This effect is similar, but more pronounced than that achieved with tracer ammunition. ' 

taschoene

From: taschoene

27-Aug

The effect is well known at artillery scale -- base bleed shells use gas generators at the base of the round to reduce base drag and achieve significantly increased range.

I did find a paper about tests of fumer compounds in small-caliber ammo.  They tested with 7.62 but the ultimate application was 20mm, where they thought they could dramatically.improver penetration by increasing retained velocity/energy at long range.

https://apps.dtic.mil/sti/pdfs/ADA026147.pdf

TOP