SBR or pistol

[Beiruty]

My choice for now...
https://photos.app.goo.gl/oRTeDBfo8PTjCw679

[The Annoyed Man]

If you need a real Personal Protection SBR, here is your best choice

A Binford nail gun? Not practical because you need an air hose.

[jb2012]

As mentioned, the pistol is slightly more versatile, but also braces have come leaps and bounds from what they were originally. You really won’t gain anything by having a stock except... having an actual stock.

I would advise staying away from springfield, however that’s another story.

[MaduroBU]

Here is how I think this issue. I'm not putting it forth as the only way, just as a thought experiment that may be useful.

A cartridge and the barrel are a single pressure vessel, much like the piston in an internal combustion engine (replacing the air/fuel mix with nitrated hydrocarbons and eliminating the ability to reciprocate). In general, the higher the initial pressure and the lower the final pressure, the more efficient the piston will be at converting chemical energy into motion (see Carnot's theorem of heat engines, where pressure is replaced by heat in a more rigorous and technically correct explanation....but it's much easier to think in terms of pressure for our limited purposes).

The greater the ratio of expansion volume (bore area*length) to chemical energy (powder charge weight, ignoring small differences in smokeless powder energy content from, say, more nitroglycerine), the more of that energy will be converted into motion of the projectile. This is why black powder arms have huge barrels: adding expansion volume was all those designers and Smith's could do because the chemistry (black powder and early nitrocellulose) and materials science (barrel steel and later case brass) put hard limits on their maximum initial pressures. All they could do was wring every foot-pound out of a low power system. Smokeless powder changed that, allowing far higher initial pressures to produce very high velocities from small expansion volumes. This led to everything becoming a "carbine" (historically, a rifle with a 24" barrel was a carbine, c.f. the Mauser 98k).

This technological revolution doesnt change the laws of physics; it merely improved our ability to harness them. Today, we have the ability to generate useful velocities with extremely short barrels, and the tradeoff is muzzle blast. The high initial pressure that can be so useful can produce deafening and blinding blast rather than useful velocity if not given a sufficient expansion volume.

To that end, I suggest a website called ballistics by the inch, at bbti.com, where they shot a variety of calibers out of varying length firearms. There is also a software package called Quickload which can estimate the effects of barrel length, powder burn rate, charge weight, and bullet mass on velocity and muzzle exit pressure. I'd be happy to run a few numbers for you if you like since the program isn't cheap and has limited utility for most folks.

David Ricardo once said in reference to WW2 aircraft engines (supercharging was just taking hold then) that we must get away from measuring engine power in displacement and instead think instead of how much air the engine can be made to efficiently consume. When building pistol or rifle, we must think in terms of how much powder a barrel length of our chosen length can be made to efficiently consume. That's why folks are suggesting the .300 Blackout/Whisper over the 5.56 NATO for your chosen barrel length.

My preference is a .357 Sig with a 5.7" barrel or a 7.62x40 WT in a bullpup with a 16.5" barrel. The IWI bullpup shotgun might be the best choice for a pure home defense gun.

[The Annoyed Man]

Very good explanation of pressure and volume, but I have to ask what’s the advantage of 7.62x40 WT over 7.62×35mm (.300 Blackout)? Wikipedia says that:

Wilson had been hunting feral hogs with both the .30 Remington AR and .300 AAC Blackout. However, since most feral hog hunting is performed at night, he did not like looking for proprietary brass cases after he had fired them and designed the 7.62 X 40mm around the inexpensive and readily available 5.56 NATO cartridge.

Well... the 7.62x40mm is also a proprietary case, and .300 Blackout cases can also be made from inexpensive 5.56 brass. Even the bullet weight range is similar up to a point....except the Blackout range includes heavy subsonics.

I’m not knocking the WT cartridge, but I’m unclear as to its advantages over .300 Blackout. Please enlighten me.

[montgomery]

My main interest is something easily transportable but more capable than a G26 or similar.

Speaking of transportable, if you go SBR route, you need permission from ATF to take it out of state, including dates and locations.

[LDB415]

If you need a real Personal Protection SBR, here is your best choice

A Binford nail gun? Not practical because you need an air hose.

That might be good if the not Pamela Anderson assistant was in charge of it.

[MaduroBU]

Very good explanation of pressure and volume, but I have to ask what’s the advantage of 7.62x40 WT over 7.62×35mm (.300 Blackout)? Wikipedia says that:

Wilson had been hunting feral hogs with both the .30 Remington AR and .300 AAC Blackout. However, since most feral hog hunting is performed at night, he did not like looking for proprietary brass cases after he had fired them and designed the 7.62 X 40mm around the inexpensive and readily available 5.56 NATO cartridge.

Well... the 7.62x40mm is also a proprietary case, and .300 Blackout cases can also be made from inexpensive 5.56 brass. Even the bullet weight range is similar up to a point....except the Blackout range includes heavy subsonics.

I’m not knocking the WT cartridge, but I’m unclear as to its advantages over .300 Blackout. Please enlighten me.

If you're limited to buying factory ammo, the 7.62x40 is awful. Wilson relaunched a slightly modified (and worse) version called the .300 HAMR that means even the maker will probably stop selling ammo for it. It is also useless if you want subsonics.

The advantage is 2-300 FPS with 150 gr bullets, matching a .30-30 at 100 yards and beating it thereafter. The .300 Whisper was built to replace the MP5-SD using a standard 5.56 platform. The 7.62x40 was built to replace the .30-30 and 7.62x39. While the lack of factory ammo is a huge issue for most folks, the round is a reader's dream. It is NOT a proprietary case (the reason that Bill Wilson hired Kurt Buchert was partially that he got sick of losing 6.8 SPC cases while killing hogs at night on his ranch), but a cut and resized 5.56 NATO case. Most of my brass was made from range pickups that I cut, formed, annealed, and fireformed. As long as I can get 5.56 NATO cases and primers, 150 grain .308 bullets, and either CFE BLK or revolver powder, I don't need to care what factory ammo prices do.

[The Annoyed Man]

Very good explanation of pressure and volume, but I have to ask what’s the advantage of 7.62x40 WT over 7.62×35mm (.300 Blackout)? Wikipedia says that:

Wilson had been hunting feral hogs with both the .30 Remington AR and .300 AAC Blackout. However, since most feral hog hunting is performed at night, he did not like looking for proprietary brass cases after he had fired them and designed the 7.62 X 40mm around the inexpensive and readily available 5.56 NATO cartridge.

Well... the 7.62x40mm is also a proprietary case, and .300 Blackout cases can also be made from inexpensive 5.56 brass. Even the bullet weight range is similar up to a point....except the Blackout range includes heavy subsonics.

I’m not knocking the WT cartridge, but I’m unclear as to its advantages over .300 Blackout. Please enlighten me.

If you're limited to buying factory ammo, the 7.62x40 is awful. Wilson relaunched a slightly modified (and worse) version called the .300 HAMR that means even the maker will probably stop selling ammo for it. It is also useless if you want subsonics.

The advantage is 2-300 FPS with 150 gr bullets, matching a .30-30 at 100 yards and beating it thereafter. The .300 Whisper was built to replace the MP5-SD using a standard 5.56 platform. The 7.62x40 was built to replace the .30-30 and 7.62x39. While the lack of factory ammo is a huge issue for most folks, the round is a reader's dream. It is NOT a proprietary case (the reason that Bill Wilson hired Kurt Buchert was partially that he got sick of losing 6.8 SPC cases while killing hogs at night on his ranch), but a cut and resized 5.56 NATO case. Most of my brass was made from range pickups that I cut, formed, annealed, and fireformed. As long as I can get 5.56 NATO cases and primers, 150 grain .308 bullets, and either CFE BLK or revolver powder, I don't need to care what factory ammo prices do.

Thanks for the explanation. I have about 50-60 lbs of mixed 5.56/.223 brass that needs cleaning and sorting. I’ve been saving it because I do reload, but I’m not so involved in it that I’ve tried reforming it into other chamberings. Also, I own a .30-30 rifle, so maybe I'm not that motivated to try it. Plus, my wife is probably tired of me building new ARs.

[carlson1]

I haven’t read all of the post, but if I had it to do it all over again I would not do a SBR I would just do an AR pistol. I have a Daniel Defense MK18 10.3” barrel, SBA3 adjustable pistol brace, and a Law Tactical Adapter. Folds up nicely. It shoots fantastic and goes right into a backpack nice and neat.

[AdioSS]

Have you considered a piston driven pistol instead of DI?
My first 5.56 anything was a Keltec PLR-16. 9.5” barrel, AR mag compatible, no buffer tube, lightweight polymer frame.

[03Lightningrocks]

There is also the Sig 556 pistol