Why not a blowback .223 semi-auto rifle?

[PercyShelley]

But even that is downright prosaic compared to the late WWII plans for a 15mm roller-retarded-blowback aircraft gun (I'm unsure if any were ever made), or for that matter the Becker/Oerlikon family of autocannons, which included the 20mm type 99 and 30mm mk 108. Becker/Oerlikon are often referred to as advanced primer ignition. However, if you do the math, you quickly come to the conclusion that advanced primer ignition can only effect a 50% reduction in bolt mass, and that in practice this figure is usually much lower than the ideal.

The handy US Army small arms design guide, helpfully hosted at Forgotten Weapons states that the correction factor for bolt mass on open-bolt fixed firing pin SMGs is .75, indicating that at least in small arms, API is about half as effective as the mechanical ideal.

 

[JohnKSa]

Cartridge for the largest ones was the .401 WSL, capable of flinging a 200 grain bullet at 2150 FPS. Not shabby.

Correct. The bolt had a weighted extension that extended down under the wooden fore-end of the rifle.

 

[PercyShelley]

And people will still argue that the telescoped bolt on the Sa. 23 was somehow a new development...

 

[briansmithwins]

And people will still argue that the telescoped bolt on the Sa. 23 was somehow a new development...

Didn't JMB design the first telescoped bolt, although in a pistol, not a SMG?

BSW

 

[PercyShelley]

Yes, JMB was the first, but I don't think his patent was that much earlier than the patent for the WSL rifles. A decade, tops.

 

[Swampman]

I've gotta be honest, I haven't actually read through the whole thread but in response to the original query:

"Why not a blowback .223 semi-auto rifle?"

Perhaps a better question would be: "WHY?"


For those who can't understand the difference between "blowback" and "delayed blowback", I suggest the following simple experiment.

1- Take an H&K 91/G3/PSG1

2- Remove the bolt/carrier assembly.

3- Replace it with the rollerless bolt/carrier assembly designed to function with the plastic case, short range training rounds. Add weight to bolt, put in heavier springs, whatever makes you happy... EXCEPT an actual locking system.

4- Put it in a gun vise, point it downrange and tie a really long string to the trigger.

5- Chamber an M80 ball round. (There's probably something in the design of the practice bolt to prevent this, but if you really wanna know about this stuff, you can probably figure out a way to bypass it. The path to knowledge isn't always easy...)

6- Get behind brick wall and pull trigger with long string.

7- Observe explosion, gather pieces, cry over destroyed bits of the umpteen thousand dollar rifle.

THAT is the difference between "blowback" and "delayed blowback".

In any case, H&K literature on the PSG1A1 doesn't say anything about being blowback operated, they do however mention the "locked" nature of the action.

Quote from HK website:
"It uses the famous HK delayed roller locked bolt system pioneered on the HK G3"

Link:
http://www.hk-usa.com/military_products/psg1a1_general.asp

 

[briansmithwins]

After reviewing Col. Chinn's book and some others I think I can summarize:

1) A straight blowback operated .223 would have a very heavy bolt, around 6lbs.
2) There are other problems with trying to use simple blowback at rifle pressures, gas leakage, case rupture, very slow bolt velocity.
3) There have been successful retarded blowback rifle caliber weapons. The Schwarzlose, HK series, and FAMAS are examples of successful use of the principle.
4) The quality of materials required (high stress steels) and tolerances required mean that retarded blowback rifle class weapons aren't significantly cheaper than recoil or gas operation.

BSW