Bull pup SBR project

[yoni]

At the risk of setting off a 556 vs 300 debate, I would ask you what advantage you see to 300 supers over 556? Energy wise, in a 10" barrel, they will be very similar with the edge going to 556, and 556 will shoot flatter due to higher velocity. And then there's availability.

I wanted something that was as short as possible, but you make a good case for adding 1 inch in barrel length and staying with the 5.56.

[georgeib]

I wanted something that was as short as possible, but you make a good case for adding 1 inch in barrel length and staying with the 5.56.

Hypothetically, if I were trying to build something as short as possible, but still maintain maximum lethality to... say 150 meters, I would look strongly at some sort of custom x95 with maybe a 7" 300 blk barrel with a short suppressor. I would shoot supersonics from it for sure. I imagine velocity would be in the 1400 fps range with 110-125 grain bullets, with probably 5-600 ft lbs of energy...

Now that I wrote that, I'm really not seeing a big enough advantage over a 357 Sig 60 grain, or 556 60 grain at 2000 fps...

[yoni]

Hypothetically, if I were trying to build something as short as possible, but still maintain maximum lethality to... say 150 meters, I would look strongly at some sort of custom x95 with maybe a 7" 300 blk barrel with a short suppressor. I would shoot supersonics from it for sure. I imagine velocity would be in the 1400 fps range with 110-125 grain bullets, with probably 5-600 ft lbs of energy...

Now that I wrote that, I'm really not seeing a big enough advantage over a 357 Sig 60 grain, or 556 60 grain at 2000 fps...

Well you won me over I just bought a new X95 in 5.56 for $1300.

[Todd.K]

So I was not thinking of subsonics in the gun.

So the question is will regular 300 blk work in the gun?

It’s not just subs. Because of the powder to bore size 300 supers use a much faster powder. This explains why it’s more efficient in shorter barrels, more like a pistol cartridge. The larger barrel diameter means more area for gas to expand into than 5.56. Faster powder expanding into a larger bore means less pressure at an equal distance down the barrel.

The short answer, with the same gas system length you can have a shorter barrel in 5.56 function than 300.

But I don’t know if the 300 starts off with the same gas system on the X95.

[georgeib]

Well you won me over I just bought a new X95 in 5.56 for $1300.

That's a great price. Interested to hear your impressions of it.

I really like short barreled 5.56, but can no longer imagine using one without, at least, a short suppressor on it. If you're going to go suppressed, at today's stage of suppressor technology, I don't think you can do better than the new Huxwrx/OSS Flow 556k. Its flow through tech is ideal for a Tavor as it doesn't increase back pressure appreciably, and is the quietest 5.56 suppressor ever tested by Pew Science at the shooter's ear. Only adds 5" to the overall length of the weapon.

[yoni]

I was on the board that evaluated the original Tavor and really didn't care for it. My old unit which can get any rifle they want rejected the Tavor and stated with 11.5" M16.

But I want a sub 19inch gun that can be deployed from backpack with out having to unfold the stock.

[mig1nc]

One of my best friends has the 13" barrel X95 SBR.

That thing is freaking tiny.


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[Ron3]

X95 has enough improvements I would call it a "2nd Generation Tavor" and the Tavor 7 a "3rd Gen".

I don't have the "Fighting from & around vehicles" training I wish I had but it seems to me bullpup rifles excell at that. Also would be perfect for checkpoints and as a common Police duty rifle. Easy to store & deploy from a vehicle without the SBR downsides.

[Ron3]

I was on the board that evaluated the original Tavor and really didn't care for it. My old unit which can get any rifle they want rejected the Tavor and stated with 11.5" M16.

But I want a sub 19inch gun that can be deployed from backpack with out having to unfold the stock.

Sounds like the bullpup you chose or an MP5K design to me.

[Clint]

Yoni,

Here is a good visual to support Todd's points.

These are our new 8" PDW barrels.

The total gas drive (pressure x duration x gas port) is roughly equal between these two, but in order to achieve that, the gas port location and sizes are quite different because the cartridge pressure curves are different.

Gas port locations can sometimes be moved further out, but at a certain point, you start to run out of available gas to drive the action and reliability suffers.

Piston systems generally have some minimum dimension for the gas block location to accommodate the push rod, return spring, bushing, etc.

Much like the standard laser marking wouldn't fit on the 300 BLK barrel, a normal piston system may not fit either, unless it can be re-designed to micro size.

It’s not just subs. Because of the powder to bore size 300 supers use a much faster powder. This explains why it’s more efficient in shorter barrels, more like a pistol cartridge. The larger barrel diameter means more area for gas to expand into than 5.56. Faster powder expanding into a larger bore means less pressure at an equal distance down the barrel.

The short answer, with the same gas system length you can have a shorter barrel in 5.56 function than 300.

But I don’t know if the 300 starts off with the same gas system on the X95.