[Evil Monkey]

I often think of myself as a person who knows everything about firearms. I am, after all, Evil Monkey. However, there are questions that linger, such as the one I'm about to ask.

Why did the Russians use a new casing for the 5.45mm instead of just taking the 7.62x39mm and necking it down?

If they necked it down, then I'm positive that the same 7.62mm magazines could have been used, considering that only the outer most bodies of the cartridges are being stacked against each other. They could have also used the same 7.62mm bolt because the case head diameter wouldn't have changed. Logistics would have been GREATLY simplified during the switch and there would have been no need for retooling to produce another type of magazine or bolt (or any other part I might be forgetting at that moment). Yet for unknown reasons to me, they decided to use another casing for the 5.45mm that had a smaller case head diameter which would require a different bolt, and less of a taper which would now require the round to use a different magazine.

[gvnwst]

less taper=more performance with same length case. I think the reason for decreasing the case head was for more mag capacity/smaller mags holding just as much.

[rcmodel]

Just a guess, but a necked down 7.62x39 case would be kind of close to a 22-250.
Probably way more powder capacity & velocity then they needed to do what they wanted to do.

In addition, the primary reason the worlds military have gone to smaller calibers is to:

* Reduce the weight of the ammo for shipping purposes.
* Reduce the amount of raw materials needed to make the ammo.
* Reduce the size of the shipping container, or make more ammo fit in the same size container.
* Reduce the weight of the ammo so the individual solder can carry more of it.

Continuing to use the same 7.62x39 case as the base for the new .22 round would not have met any of the criteria for changing calibers in the first place.

rcmodel

[Acera]

I would consider it not a good idea. Remember the need to soldier proof the gun. Less chance of a mix up and an accident. New gun, new stuff all the way around, get rid of all the old. JMHO.

[db_tanker]

a necked down 7.62x39 would be, I think, what was known as a 220 Russian. :)

I think their main goal was the reductions that rcmodel listed.

[Walkalong]

I would like to shoot one myself. I would hate to buy one just to try it.

rcmodel's reasoning sounds "sound" to me. :)

[HorseSoldier]

I think it would have been over-powered for what they wanted it to do.

Also, using the same case head/bolt and same magazines would have meant that there was a possibility of mismatching ammo in rifles, which seems to run contrary to the Soviet approach to logistics.

[max popenker]

Hi

early experiments with small-bore AK were made using 7.62x39 cases necked down to 5.6mm, but then it was found that case capacity can be decreased while keeping adequate preformance

This gave several bonus points:
1. lighter ammunition
2. soldier-proof (you cannot chamber 7.62x39 into 5.45 firearm, period; doing vice versa will cause no harm other than funny sound of shot and nil accuracy)