Your favorite SBR length

calicojack · Jul 5, 2020

teratos said:
Same effect as jumping of a diving board vs jumping off the Golden Gate Bridge.

I have heard that jumping off a high span bridge into water is like hitting concrete.

teratos · Jul 5, 2020

calicojack said:
I have heard that jumping off a high span bridge into water is like hitting concrete.

Yep. Same as a projectile. The faster it is going, the more energy it carries. The barrier pushes energy back into the object hitting it. In this case, causing fragmentation. There is a term for it, but I took physics 30 years ago.....

calicojack · Jul 5, 2020

teratos said:
Yep. Same as a projectile. The faster it is going, the more energy it carries. The barrier pushes energy back into the object hitting it. In this case, causing fragmentation. There is a term for it, but I took physics 30 years ago.....

Oh, well in that case - I double down on my 14.5" SBR recommendation

Biggfoot44 · Jul 5, 2020

If you are having a 29in OAL parameter , might as well have more bbl length than a trick buttstock . More velocity , longer dwell time , etc .

calicojack · Jul 6, 2020

teratos said:
Curious about the “specialty ammo” remark. My 10.5 shorties cycle everything I throw at them just fine running suppressed. Am I missing something?

I'll say this about my gov profile 10.5" SBR; it's a shooter. That little f*k is accurate. Not 100% sure why (PSA barrel), but it is.

A buddy of mine shot it [while I was present] and said "I want one of these!". Then I explained the Federal and State requirements. Then he said "never mind". :sad20:

Dezus · Jul 6, 2020

calicojack said:
I'll say this about my gov profile 10.5" SBR; it's a shooter. That little f*k is accurate. Not 100% sure why (PSA barrel), but it is.

A buddy of mine shot it and said "I want one of these!". Then I explained the Federal and State requirements. Then he said "never mind".

I feel that, I shrugged off the whole NFA thing for the longest time, then I bought a can and now I'm waaaaaayyyyy down the rabbit hole.

calicojack · Jul 6, 2020

Dezus said:
I feel that, I shrugged off the whole NFA thing for the longest time, then I bought a can and now I'm waaaaaayyyyy down the rabbit hole.

LOL! Yep - I have a rimfire can and a 30 cal can in jail. Can't wait to get that thing.

outrider58 · Jul 6, 2020

teratos said:
Yep. Same as a projectile. The faster it is going, the more energy it carries. The barrier pushes energy back into the object hitting it. In this case, causing fragmentation. There is a term for it, but I took physics 30 years ago.....

I think it's 'the bullsh!t to benefit ratio'...I could be mistaken though...

erwos · Jul 6, 2020

Biggfoot44 said:
If you are having a 29in OAL parameter , might as well have more bbl length than a trick buttstock . More velocity , longer dwell time , etc .

I completely agree with this. Some of the insane stuff I see trying to get these things over 29"... the juice is not always worth the squeeze.

woodline · Jul 6, 2020

outrider58 said:
I think it's 'the bullsh!t to benefit ratio'...I could be mistaken though...

I’m not sure you’re making your stance on terminal ballistics vs marksmanship in short range weapons clear. Maybe you should reiterate it a few more times.

woodline · Jul 6, 2020

If you want the shortest possible OAL and feel marksmanship is the only important factor, I highly recommend a rimfire SBR instead of centerfire. Maryland OAL rules don’t apply to rimfire weapons. They poke good holes in things too.

GutPile · Jul 8, 2020

11.5 here but I really enjoy my 14.5. I know it sounds stupid but I like the way it feels/handles vs my full length 16 inchers.

outphase84 · Jul 8, 2020

teratos said:
The slower the projectile goes, the more problems you will have with over-penetration. With M193 ammo, the projectile is moving so fast, it fragments easily when hitting a barrier because of the energy it carries. Same effect as jumping of a diving board vs jumping off the Golden Gate Bridge. Believe it or not, slower projectiles like pistol rounds, buckshot etc. are much more likely to go through multiple sheets of drywall.

Shorter barrel, less velocity.

Yeah, no. That's wildly inaccurate.

Slower projectiles like pistol rounds overpenetrate more because of where their kinetic energy comes from. Heavy rounds that move slow impart most of their force from their mass. Going through drywall reduces acceleration, but not mass, so they retain force pretty well.

5.56, on the other hand, uses very light rounds moving very quickly. Striking solid objects removes acceleration, which is where the bulk of their force comes from, which means a drastic reduction in force.

Increasing velocity increases overpenetration. Period.

Your golden gate bridge comparison is actually quite an apt comparison, but not in the way you thought it would be. Jumping off of a diving board, you can dive 9 or 10 feet down without swimming. People who have ended up in a dive off of the golden gate bridge go *significantly* deeper, and many have survived. There was a teenager a couple years ago that not only survived a dive, but was swimming back to shore when the coast guard picked him up.

Pinecone · Jul 8, 2020

Heck, there was a Marine F8 pilot who punched out in excess of 15K feet, no chute, hit the water and broke both ankles.

EDIT - also broke his pelvis and cracked a vertebra. Still not to bad for that long of a fall.

https://uss-la-ca135.org/60/1960Judkins-Knott.html

I thought there was another one from something around 40K feet, but I cannot find anything on it.

Melnic · Jul 8, 2020

Dezus said:
They measure it with the stock collapsed or a brace removed. It used to be brace/stock fully extended was the OAL

When did that change?
Does that mean we have to make our stocks "non collapsable"?
Is there another thread on this I missed?

outrider58 · Jul 8, 2020

outphase84 said:
Yeah, no. That's wildly inaccurate.

Slower projectiles like pistol rounds overpenetrate more because of where their kinetic energy comes from. Heavy rounds that move slow impart most of their force from their mass. Going through drywall reduces acceleration, but not mass, so they retain force pretty well.

5.56, on the other hand, uses very light rounds moving very quickly. Striking solid objects removes acceleration, which is where the bulk of their force comes from, which means a drastic reduction in force.

Increasing velocity increases overpenetration. Period.

Your golden gate bridge comparison is actually quite an apt comparison, but not in the way you thought it would be. Jumping off of a diving board, you can dive 9 or 10 feet down without swimming. People who have ended up in a dive off of the golden gate bridge go *significantly* deeper, and many have survived. There was a teenager a couple years ago that not only survived a dive, but was swimming back to shore when the coast guard picked him up.

You missed one important aspect in your analysis, projectile construction.

...and jumping out of an airplane without a parachute into water is another poor equivalent. There have been plenty of people who have burned in on dry land and survived. No penetration. Believe what you like, I call that an act of God.

Yes, I know, the latter was not your example.

woodline · Jul 8, 2020

outphase84 said:
Increasing velocity increases overpenetration. Period.

This would be true if every bullet just ice picked through media and didn’t exhibit effects that vary based on velocity. The effect of impact velocity on the structural integrity (or lack thereof) of a projectile is technically separate from what you’re talking about in your post (parts of which I agree with), but pertinent to the conversation at hand.

This is why time and time again one can see testing of handgun projectiles that are designed to expand and penetrate consistently in a given velocity range fail to do when tested outside of that range. Often the overpenetrate when going too slow, and underpenetrate when moving too fast.

Another example would be the infamous SS109 projectile. Once fleet yaw effect is accounted for, fragmentation is still velocity dependent. Above a certain range, it fragments and tumbles reliably, decreasing overall penetration while improving energy transfer. Below that threshold, it retains momentum for longer and icepicks straight through. The trade off is a degree of barrier blindness, or the ability to poke a hole in something hard and then continue on to do its job on soft fleshy things.

Meanwhile something like a 62gr bthp loaded to the same velocity as m855 will have very different effects from m855 depending on what it strikes.

These are anecdotes but speak to why I feel it is beneficial to use projectiles that have the best chance of functioning consistently within specification with a given firearm ASSUMING good reliability, availability, and cost. But if you just care about poking holes in the right places, that is still better than harsh words. At work we have the choice between different projectiles based on what length barrel we are using and what we need the projectile to do. Oddly enough those of us running 10.5” guns don’t seem to pick green tip much when we have m855a1, mk262 or 70gr improved tsx available.

woodline · Jul 8, 2020

outrider58 said:
You missed one important aspect in your analysis, projectile construction.

Beat me to it.

teratos · Jul 8, 2020

outphase84 said:
Yeah, no. That's wildly inaccurate.

Slower projectiles like pistol rounds overpenetrate more because of where their kinetic energy comes from. Heavy rounds that move slow impart most of their force from their mass. Going through drywall reduces acceleration, but not mass, so they retain force pretty well.

5.56, on the other hand, uses very light rounds moving very quickly. Striking solid objects removes acceleration, which is where the bulk of their force comes from, which means a drastic reduction in force.

Increasing velocity increases overpenetration.

The force dissipates when it hits something, yes. In the case of 5.56, the bullet often fragments. I never said anything about conservation of mass, etc. so wasn't technically wrong. Yes, increasing velocity will increase over-penetration, but other factors are at play. So nothing I said was "wildly inaccurate"

outphase84 said:
Your golden gate bridge comparison is actually quite an apt comparison, but not in the way you thought it would be. Jumping off of a diving board, you can dive 9 or 10 feet down without swimming. People who have ended up in a dive off of the golden gate bridge go *significantly* deeper, and many have survived. There was a teenager a couple years ago that not only survived a dive, but was swimming back to shore when the coast guard picked him up.

Why do people break bones, then? It has to do with the force with which they hit. You know, mass and velocity. 95% of the people die FROM THE IMPACT, not going too deep. The faster you hit something, the more energy is involved in the equation.

https://www.quora.com/What-kills-Go...ter-breaking-all-your-bones-or-something-else

Great first post, though.

shadow116 · Jul 8, 2020

outphase84 said:
Yeah, no. That's wildly inaccurate.

Slower projectiles like pistol rounds overpenetrate more because of where their kinetic energy comes from. Heavy rounds that move slow impart most of their force from their mass. Going through drywall reduces acceleration, but not mass, so they retain force pretty well.

5.56, on the other hand, uses very light rounds moving very quickly. Striking solid objects removes acceleration, which is where the bulk of their force comes from, which means a drastic reduction in force.

Increasing velocity increases overpenetration. Period.

Yeah, Not only no, but hell no.

Some of your statement could be applied to the exterior ballistics of the 5.56/.223 round.

But, years and years of research into the terminal ballistics of actual 5.56 rounds completely invalidates your statement.

Your favorite SBR length

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