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Bullpup Rifles (Auto & Semi-Auto Centerfire) => Desert Tech MDR => Topic started by: SHORT-N-SASSY on January 28, 2018, 06:08:25 PM



Title: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on January 28, 2018, 06:08:25 PM
(https://s18.postimg.org/n7762iszt/MDR.png)
(https://deserttech.com/mdr.php (https://deserttech.com/mdr.php))

Enter: The 6.5 SOCOM ---

(https://s18.postimg.org/ywb5qmwux/PCP_D.png)

(https://s18.postimg.org/54e3bi7hl/Polymer_A.png)
(https://www.youtube.com/watch?time_continue=40&v=frA6anAX8wk (https://www.youtube.com/watch?time_continue=40&v=frA6anAX8wk))

In my view, the Desert Tech Micro Dynamic Rifle (MDR) and the polymer-cased 6.5mm SOCOM cartridge are made for each other.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Ditcher on January 28, 2018, 06:16:38 PM
How many 6.5mm cartridges do we need? lol  Why not build on something that is out there all ready? 
I hate to see how much this ammo will cost.  Guess it wont be a reloader cartridge either? 


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on January 28, 2018, 07:10:58 PM
(https://s18.postimg.org/tfx39xnp5/Derivitive.png)
(http://www.americanrifleman.org/articles/2009/10/15/innovation-in-the-american-firearms-industry/ (http://www.americanrifleman.org/articles/2009/10/15/innovation-in-the-american-firearms-industry/))

(https://s18.postimg.org/5c6blp2o9/Evolution.png)
(http://innovationtrail.org/post/innovation-gun-industry (http://innovationtrail.org/post/innovation-gun-industry))


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: spacegunz on January 28, 2018, 07:37:01 PM
In my view, the Desert Tech Micro Dynamic Rifle (MDR) and the polymer-cased 6.5mm SOCOM cartridge are made for each other.

Oh absolutely, theyíre a match made in heaven: both the MDR and polycase ammo will probably see widespread adoption circa the year 2418.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: coldboremiracle on January 28, 2018, 08:00:56 PM
In my view, the Desert Tech Micro Dynamic Rifle (MDR) and the polymer-cased 6.5mm SOCOM cartridge are made for each other.

Oh absolutely, theyíre a match made in heaven: both the MDR and polycase ammo will probably see widespread adoption circa the year 2418.
Hahahahahahahahaha


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: racky on January 28, 2018, 09:01:33 PM
S-N-S, do you know what the cost is on these new rounds????, I remember a few decades ago some ammo company was making poly shell pistol rounds, but they never caught on, if these are more affordable,and dont have, side effects, they will be popular, but maybe an initial hesitation,......remember when glock first came out, ...time will tell,....in the mean time , It sure would be nice if somebody.....anybody......, ends up making a barrel/bolt/mag kit to fit either the Tavor7 or MDR,...in.....wait its coming....6.5 GRENDEL.!!!!! ....Don't get me wrong, the 6.5 Creedmore is a awesome round,...especially for a bolt gun,...but for a 16" carbine,...maybe a little over kill,....and the grendel would be even lighter  than 6.5 CM, with still spectacular B.C's, ...Of  Course I'm not telling you anything that you dont already know better than most of us.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on January 28, 2018, 10:56:17 PM
racky,

No word on cost, yet. Here's a recent article on the 6.5 SOCOM:
(http://www.gunsholstersandgear.com/2017/11/330/new-cartridge-6-5-socom/ (http://www.gunsholstersandgear.com/2017/11/330/new-cartridge-6-5-socom/))


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Potss on January 28, 2018, 11:02:21 PM
spacegunz spot on haha.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: TNC on January 28, 2018, 11:52:26 PM
"The MDR delivers advanced firepower for the future patriot"????

Geeez, I hate cornball, marketing statements like that...no matter where they come from.  Stuff like that should be reserved for wannabe's and neckbeards.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: BullpupT on January 29, 2018, 07:49:56 AM
They have had those poly rounds for years now. Iím not sure about the 6.5, but the 5.56 and 7.62 have been tested with mixed results.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Steelviper on January 29, 2018, 10:35:06 AM
Would like to see more info on the 6.5 Socom since it is designed around the AR10 platform curious how it compares to the other .26 calibers (Creed and Remington)


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on January 29, 2018, 05:58:58 PM
Would like to see more info on the 6.5 Socom since it is designed around the AR10 platform curious how it compares to the other .26 calibers (Creed and Remington)

(https://s18.postimg.org/c20sot4gp/6.5.png)
(https://www.militarytimes.com/news/your-military/2017/04/18/special-operations-command-is-looking-at-a-new-6-5-mm-round-for-its-sniper-rifle/ (https://www.militarytimes.com/news/your-military/2017/04/18/special-operations-command-is-looking-at-a-new-6-5-mm-round-for-its-sniper-rifle/))

Steelviper, I think it's fair to state that the overall performance of the 6.5 SOCOM polymer-cased cartridge is similar to the 6.5mm Creedmoor and .260 Remington cartridges.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: INV136 on January 30, 2018, 01:01:33 PM
Interesting. I look forward to ballistics for this new 6.5 polymer round. I never had any interest in the MDR's ability to change out to other calibers. But, this new round has possibilities that might make an MDR caliber change kit something that I might actually want to look at. Depending on the ballistics (if they're better than the 7.62 Nato) and considering the lighter weight for carrying multiple 25 rd magazines and maybe drum magazines if they release them in this caliber.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Steelviper on January 30, 2018, 04:57:02 PM
Why not just use a polymer case 6.5 Creedmoor. Why build a entirely new cartridge how many 26 caliber .308 size round do we need (I mean .260 Rem and 6.5 Creed are already fighting for market share).

What next another polymer cased ď22 SocomĒ to compete against the 22 Nosler and .224 Valkyrie. Or how about a polymer cased fat single stack .45- .50 cal to compete against the .458 Socom, .50 Beowulf, and .450 Bushmaster.

Why not just apply the tech to existing rounds?


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on January 30, 2018, 08:52:09 PM
S-N-S, do you know what the cost is on these new rounds? . . .

racky,

I've recently come across a FAQ Page on the PCP Ammunition website ---
(https://s18.postimg.org/jlbyqw2y1/FAQ.png)
(https://www.pcpammo.com/faq/ (https://www.pcpammo.com/faq/))

And, re accuracy potential ---
(https://s18.postimg.org/nugot3vxl/about.png)
(https://www.pcpammo.com/about-2/ (https://www.pcpammo.com/about-2/))

And, re the government choosing the 6.5mm for extended-range sniping situations: It's all about projectiles with high Ballistic Coefficient --- 6.5mm projectiles are born with it. It's like adding inches to your barrel length ---
(https://s18.postimg.org/7jgkwogu1/Creedmoor.png)
(https://rifleshooter.com/2016/02/6-5-creedmoor-effect-of-barrel-length-on-velocity-cutting-up-a-creedmoor/ (https://rifleshooter.com/2016/02/6-5-creedmoor-effect-of-barrel-length-on-velocity-cutting-up-a-creedmoor/))

(https://s18.postimg.org/hjbhcxn21/Aron.png)

In view of all the above, I think a Desert Tech MDR chambered for the 6.5 SOCOM, with a 19" barrel (29.2" overall length), would be an excellent choice. Stay tuned. The future is now!





Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Sdevante on January 30, 2018, 10:14:14 PM

In view of all the above, I think a Desert Tech MDR chambered for the 6.5 SOCOM, with a 19" barrel (29.2" overall length), would be an excellent choice. Stay tuned. The future is now!

[/size][/font]


Considering they've shipped a whopping 5 rifles so far, your optimism, like your affinity for pictures rather than words, remains impressive.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: kfeltenberger on January 30, 2018, 11:50:54 PM
Sdevante:  There's really no need to get personally insulting.

As for the polymer cased ammo, one thing that they don't seem to discuss is the heat and how the case manages it.  In brass or steel cased ammo, the case helps retain heat and prevents all that was generated from being transferred to the chamber.  How does the polymer cased ammo handle this?  For a bolt gun, I don't see an issue, or even a semi-auto that will fire a handful of shots, but for something that will be firing a lot of rounds in a short time, I see heat being a potential issue.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Steelviper on January 30, 2018, 11:58:07 PM
Sdevante:  There's really no need to get personally insulting.

As for the polymer cased ammo, one thing that they don't seem to discuss is the heat and how the case manages it.  In brass or steel cased ammo, the case helps retain heat and prevents all that was generated from being transferred to the chamber.  How does the polymer cased ammo handle this?  For a bolt gun, I don't see an issue, or even a semi-auto that will fire a handful of shots, but for something that will be firing a lot of rounds in a short time, I see heat being a potential issue.

Exactly- brass acts as a giant heat sink.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on January 31, 2018, 01:42:35 AM
(https://s18.postimg.org/567txk1vd/Heat.png)
(https://www.pcpammo.com/faq/ (https://www.pcpammo.com/faq/))


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Clarke-Sensei on January 31, 2018, 02:32:08 AM
I just wonder why 6.5 SOCOM is brought up. If the polymer case is it's only selling point, it comes off as a far more niche item, especially if tests show no solid advantage over its contemporaries besides weight.

The MDR is better off getting past its current state to proper production and evaluation, and just working with either their own or ES Tactical's 6.5 CM kit. A 6.5 SOCOM kit will likely be far more niche due to the proprietary nature of the ammo, and I don't know how many people will justify SOCOM in lieu of CM's market.





Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: EWTHeckman on January 31, 2018, 07:31:37 AM
I just wonder why 6.5 SOCOM is brought up. If the polymer case is it's only selling point, it comes off as a far more niche item, especially if tests show no solid advantage over its contemporaries besides weight.

When it comes to the military, weight is a very big deal. There is a lot of concern about how much weight soldiers are already having to carry, so paring that weight down without giving up anything important is a major goal of the military.

Of course, weight isn't quite as big a deal for those of us not engaged in warfare. But whatever round the military uses tends to be much more cost effective for us. In my opinion, that's a good reason to discuss the military's likely direction.

I have to say that it bugs me that PCP is using a polymer for military only rounds that would be needed by civilians. (There are places in this country where it routinely gets below zero.) For the love of God, why?!?


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Clarke-Sensei on January 31, 2018, 04:27:01 PM
I just wonder why 6.5 SOCOM is brought up. If the polymer case is it's only selling point, it comes off as a far more niche item, especially if tests show no solid advantage over its contemporaries besides weight.

When it comes to the military, weight is a very big deal. There is a lot of concern about how much weight soldiers are already having to carry, so paring that weight down without giving up anything important is a major goal of the military.

Of course, weight isn't quite as big a deal for those of us not engaged in warfare. But whatever round the military uses tends to be much more cost effective for us. In my opinion, that's a good reason to discuss the military's likely direction.

I have to say that it bugs me that PCP is using a polymer for military only rounds that would be needed by civilians. (There are places in this country where it routinely gets below zero.) For the love of God, why?!?

I understand the desire for reducing weight for military uses, but unless the use of polymer cases really takes off with more manufacturers, it's fairly unlikely the U.S. military would adopt the change. Plus, It's not like our defense funds are being properly utilized by our government anyways.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: kfeltenberger on January 31, 2018, 10:18:06 PM
I have to say that it bugs me that PCP is using a polymer for military only rounds that would be needed by civilians. (There are places in this country where it routinely gets below zero.) For the love of God, why?!?

Because they can probably make a crapton of money selling "military" spec ammo, at a premium, on the grey market to unscrupulous dealers who will then mark it up even more.



Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: kfeltenberger on January 31, 2018, 11:00:28 PM
This is more of an overview of DT, but coverage of the MDR starts at about 10:15 or so.

https://youtu.be/ahqjiSCTAmY (https://youtu.be/ahqjiSCTAmY)

MDR coverage:

https://youtu.be/ahqjiSCTAmY?t=10m15s (https://youtu.be/ahqjiSCTAmY?t=10m15s)


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: Steelviper on February 01, 2018, 12:21:30 AM
Great vid- thanks


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: spacegunz on February 01, 2018, 01:16:23 AM
It was funny when they blamed the PMAG pre-emptively, saying that it probably wonít drop free because itís a bad PMAG. Youíre at shot show and thereís nothing you can do to replace the one PMAG you apparently have? Youíre at shot show and you only thought to bring one PMAG for your demos? [sigh]

Anyway regarding polycase ammo: thatís a very interesting quote where they say it actually ďreducesĒ heat transmission to the barrel. The heat has to go somewhere, so presumably itís going to go down the barrel. Just because it doesnít transmit through the polymer doesnít mean it doesnít find itís way into the barrel further down; though, that would be really cool if it turns out most of the heat just leaves the barrel. Probably would heat up a suppressor faster, though.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: kfeltenberger on February 01, 2018, 02:49:35 AM
Anyway regarding polycase ammo: thatís a very interesting quote where they say it actually ďreducesĒ heat transmission to the barrel. The heat has to go somewhere, so presumably itís going to go down the barrel. Just because it doesnít transmit through the polymer doesnít mean it doesnít find itís way into the barrel further down; though, that would be really cool if it turns out most of the heat just leaves the barrel. Probably would heat up a suppressor faster, though.

What they could be implying is that it takes more calories of heat to raise the temperature of the polymer case than it does the brass case; if this is the case, then it makes sense. 

I remember attending an assembly back in 1980 that was given by by NASA (several residents in our district were NASA engineers and we were within commuting distance to Goddard SFC) about the Space Shuttle and the future of the space program.  Before they started talking, they lit a blowtorch and set it on a stand, then on a wire frame, they put a black block that was touched by the flame.  In moments the block started glowing red.  Then they gave the lecture and ended it talking about the Shuttle and some of the technology that had been designed just for the Orbiter.  One of them was the formula for the heat resistant tiles.  At this, one of the speakers turned off the torch and after another comment, picked it up with their bare hand and tossed it into the audience.

The block had returned to room temperature within moments of the the heat being removed.  I've always thought that this had potential firearms applications.  Based on the promo materials, it sounds like what the Strightjacket/Dracos barrel uses.  Even if it isn't, there's a place for this in the industry.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on February 01, 2018, 06:56:57 AM
Considering the painfully slow evolution of arms and ammunition design in our country, I submit that the overall scope of the Desert Tech MDR design represents a new day in this ongoing saga:

A Brief History of Firearms (http://www.nramuseum.org/gun-info-research/a-brief-history-of-firearms.aspx (http://www.nramuseum.org/gun-info-research/a-brief-history-of-firearms.aspx))

The History and Evolution of Rifles (https://www.returnofkings.com/81014/the-history-and-evolution-of-rifles (https://www.returnofkings.com/81014/the-history-and-evolution-of-rifles))

(https://s18.postimg.org/uc0ifo1p5/all.png)
(https://www.all4shooters.com/en/Shooting/technics/Bullpup-assault-weapons-evolution-from-1970s-to-our-days/?p=2 (https://www.all4shooters.com/en/Shooting/technics/Bullpup-assault-weapons-evolution-from-1970s-to-our-days/?p=2))

And, I submit that the Voice of our Bullpup Forum plays no small part in what the future of firearms technology has in store for us.

To all our new Bullpup Forum Members, Welcome aboard!


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: whiskey91lima on February 01, 2018, 01:23:43 PM
Anyway regarding polycase ammo: thatís a very interesting quote where they say it actually ďreducesĒ heat transmission to the barrel. The heat has to go somewhere, so presumably itís going to go down the barrel. Just because it doesnít transmit through the polymer doesnít mean it doesnít find itís way into the barrel further down; though, that would be really cool if it turns out most of the heat just leaves the barrel. Probably would heat up a suppressor faster, though.

What they could be implying is that it takes more calories of heat to raise the temperature of the polymer case than it does the brass case; if this is the case, then it makes sense. 

I remember attending an assembly back in 1980 that was given by by NASA (several residents in our district were NASA engineers and we were within commuting distance to Goddard SFC) about the Space Shuttle and the future of the space program.  Before they started talking, they lit a blowtorch and set it on a stand, then on a wire frame, they put a black block that was touched by the flame.  In moments the block started glowing red.  Then they gave the lecture and ended it talking about the Shuttle and some of the technology that had been designed just for the Orbiter.  One of them was the formula for the heat resistant tiles.  At this, one of the speakers turned off the torch and after another comment, picked it up with their bare hand and tossed it into the audience.

The block had returned to room temperature within moments of the the heat being removed.  I've always thought that this had potential firearms applications.  Based on the promo materials, it sounds like what the Strightjacket/Dracos barrel uses.  Even if it isn't, there's a place for this in the industry.

Itís my understanding that most of the heat in the barrel comes from friction from the bullet passing through the barrel and compression waves from both the bullet and explosion. Heat in the gas system is predominantly from the gas. Usually the chamber is lower in temperature than down the barrel. Though correct me if Iím wrong.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: SHORT-N-SASSY on February 10, 2018, 06:29:52 AM
S-N-S, . . . It sure would be nice if somebody.....anybody......, ends up making a barrel/bolt/mag kit to fit either the Tavor7 or MDR,...in.....wait its coming....6.5 GRENDEL.!!!!! ....Don't get me wrong, the 6.5 Creedmore is a awesome round,...especially for a bolt gun,...but for a 16" carbine,...maybe a little over kill,....and the grendel would be even lighter  than 6.5 CM, with still spectacular B.C's, ...Of  Course I'm not telling you anything that you dont already know better than most of us.

racky,

I'm on it ---

(https://s18.postimg.org/mqn0hc1zt/Eric.png)
(http://www.65grendel.com/forum/showthread.php?7764.Desert-Tactical-Arms&p=182584&viewfull=1#post182584 (http://www.65grendel.com/forum/showthread.php?7764.Desert-Tactical-Arms&p=182584&viewfull=1#post182584))



Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: ShootingSight on February 10, 2018, 10:51:20 AM
Without regard to the word 'mostly', the heat in the barrel is the sum total of heat transmitted into the chamber wall via the case, plus the heat transmitted intot he barrel from the gas, plus heat from the friction of the bullet.  The balance of the energy created through combustion of the powder either goes into heating the case, heating the bullet, accelerating the bullet in the form of kinetic energy, or accelerating the rifle comppnents in recoil, or is retained in the heat of the exhaust gasses (I might have missed a factor or two, but you get my point).  Without exception, the sum total of these amounts of energy must equal exactly 100% of the energy produced, as nature does not allow remainders or shortfalls in thermodynamics.

The amount of energy that gets into the chamber wall via the case wall is driven by several factors: the thermal capacity of the case material, the thermal conductivity of the case wall, and the thickness of the case wall.  You also get into boiling point and latent heats if you are vaporizing materials during combustion.  So if I design a case wall in polymer, that is thicker than brass, has a lower thermal conductivity than brass (ie plastic is a better insulator than metal), it probably does not have a higher thermal capacity than brass, but it will likely boil off more molecules which absorbs heat rather than transmitting it  .... and I run the math, it is well possible that less energy gets transferred to the chamber wall.

Coming back to the bit that it all needs to total 100%, if 1 component is diminished, almost all other components will increment slightly to make up the difference - the barrel will be slightly hotter, the bullet will have a slightly greater velocity.  Not all will rise by the same amount - the physics governing each interaction will divvy it up as it happens.

So without attributing proportions, if heat to the chamber is diminished by the case, all other aspects will absorb that extra energy in some proportion.


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: readr1 on February 10, 2018, 10:15:54 PM
Without regard to the word 'mostly', the heat in the barrel is the sum total of heat transmitted into the chamber wall via the case, plus the heat transmitted intot he barrel from the gas, plus heat from the friction of the bullet.  The balance of the energy created through combustion of the powder either goes into heating the case, heating the bullet, accelerating the bullet in the form of kinetic energy, or accelerating the rifle comppnents in recoil, or is retained in the heat of the exhaust gasses (I might have missed a factor or two, but you get my point).  Without exception, the sum total of these amounts of energy must equal exactly 100% of the energy produced, as nature does not allow remainders or shortfalls in thermodynamics.

The amount of energy that gets into the chamber wall via the case wall is driven by several factors: the thermal capacity of the case material, the thermal conductivity of the case wall, and the thickness of the case wall.  You also get into boiling point and latent heats if you are vaporizing materials during combustion.  So if I design a case wall in polymer, that is thicker than brass, has a lower thermal conductivity than brass (ie plastic is a better insulator than metal), it probably does not have a higher thermal capacity than brass, but it will likely boil off more molecules which absorbs heat rather than transmitting it  .... and I run the math, it is well possible that less energy gets transferred to the chamber wall.

Coming back to the bit that it all needs to total 100%, if 1 component is diminished, almost all other components will increment slightly to make up the difference - the barrel will be slightly hotter, the bullet will have a slightly greater velocity.  Not all will rise by the same amount - the physics governing each interaction will divvy it up as it happens.

So without attributing proportions, if heat to the chamber is diminished by the case, all other aspects will absorb that extra energy in some proportion.

No fair!!! You can't just bring logic and science into an argument like that! Thats like using a nuke to kill a fly...


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: ShootingSight on February 11, 2018, 02:57:27 PM
Sorry.  I was drinking my coffee, trying to wake up, and I started thinking about it.  There are some seriously cool thermodynamics happening in a chamber during combustion.

Wanna know how all the powder in a case ignites?  It is not from the flame front moving from rear to front in the case.  It is because as the powder in the back of the case goes up, it generates an intense pressure spike in the case.  When you compress air, it gets hot.  So as this pressure wave propagates to the front of the case, the air around the powder compresses and gets so hot, all the powder ignites at the same time.  This is why you can put powder on a table and light it uncompressed, and it just fizzles, but in a confined space it burns a lot more quickly.

Art


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: EWTHeckman on February 11, 2018, 08:56:07 PM
So as this pressure wave propagates to the front of the case, the air around the powder compresses and gets so hot, all the powder ignites at the same time.

So pretty much like a diesel engine or gasoline engine running too low an octane works? Pretty cool.

I can add this to the list of things I learned today. Thanks!


Title: Re: "The MDR delivers advanced firepower for the future patriot."
Post by: ShootingSight on February 12, 2018, 08:50:52 AM
Exactly.  Knocking in a car engine comes when the air in the cylinder compresses and heats up.  If it gets hotter than the boiling point of the fuel, the tiny droplets of fuel vaporize, and burn faster as a gas, rather than being liquid droplets that burn on the surface, and take a slightly longer time to burn.  A smooth running engine relies on the fuel still being liquid upon ignition.  Higher octane gas has a higher boiling point, so can withstand greater compression without causing knocking.

In a gun, it gets funkier than that.  While the powder starts burning at the back, the pressure wave propagates forward.  The leading edge of the shockwave, not quite hot enough to ignite the powder will get to the case shoulder and reflect back and converge on a spot that is coaxial and slightly aft of the shoulder.  This point of convergence is hotter than the leading edge of the shockwave, so after the powder has ignited by the primer, a second point of ignition will start at the front of the case, and burn backwards.  Who'd 'a thunk it.