[HFQ SPOILER] Rile adaptations

This is a question for some of the local firearms experts.

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I have a question about the rifle grenades. From the description, the ICA is using the V-B grenade model for their rifle grenades. I went online and did some reading, but something isn't making sense to me.
If you have a passage for the bullet to pass through the grenade, how do you capture enough muzzle blast behind the grenade to propel it? From the diagrams I could find, the adapter allows the gasses to spread within a confined space which would impart some acceleration; but how do you keep the bulk of the gasses from simply escaping down the bullet passage?

eldrwyrm wrote:This is a question for some of the local firearms experts.

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I have a question about the rifle grenades. From the description, the ICA is using the V-B grenade model for their rifle grenades. I went online and did some reading, but something isn't making sense to me.
If you have a passage for the bullet to pass through the grenade, how do you capture enough muzzle blast behind the grenade to propel it? From the diagrams I could find, the adapter allows the gasses to spread within a confined space which would impart some acceleration; but how do you keep the bulk of the gasses from simply escaping down the bullet passage?

The rifle grenades I have seen used were the "Mills Bomb" type fired from a muzzle-mounted cup and using a special blank cartridge as propellant.

No "bullet passage" needed

A second type had a rod down the rifle barrel and, again, a blank as propellant.

There is an excellent article in Wikipedia

I found a diagram of a V-B grenade. It looks like there's a space for the gas to expand beyond the muzzle of the rifle. It looks like the bullet travels through a hole that's aligned with the muzzle of the rifle, and the gas expands into the space. The gas is moving at the same velocity as the bullet, so, the grenade captures it before the bullet exits the hole.

It worked for the French Army.

One marked advantage of the design is that you don't need special ammo- like blanks- to fire the grenades. That simplifies the logistics all the way up the line. Thre's no need to develop it, to make it (thereby saving those common components for live ammunition), no need to transport it and to issue it- and make sure it is issued with the grenades themselves.

It prevents a situation where you have plenty of grenades but no way to fire them. It also keeps the inevitable mistake of some trooper forgetting to load a blank under the stress of combat and blowing up his gun and/or the grenade.

If troops in the Civil War could forget to cap their rifles- but keep (dry)firing and (re)loading them, it would be easy for someone to throw a live round in the chamber instead of a blank. I've read account of where there were rifles picked up after several battles during the Civil War that had 4 or 5 charges and projectiles rammed down one top of the other in the barrel but no cap on the nipple. If a soldier can forget something as essential and basic as that (loading was something they were drilled on relentlessly), doing something different like loading a blank instead of a live round would be easy to screw up under combat conditions. Or they could load the blank, get interrupted during the final preparations for firing a grenade and need a live round instead, only to end up merely making harsh noises at the enemy.

As to how it works, I haven't looked into it but there's probably either a small expansion chamber of some sort near the muzzle at the base of the launcher. This would let the gasses expand slightly and have a place for them to 'push' at the base of the grenade. Or the grenade's fit is so loose in the launcher that there's not enough friction with the sidewalls of the launcher (they are described as a 'cup') that the gasses passing through the small hole in the middle could launch it.