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Velocity Question

It’s really complex, and I don’t understand it completely, but I know more or less what happens. Setting aside powder burn rate, you have a rise to peak pressure that is rapid acceleration, rapid creation of gasses, medium acceleration as powder continues to burn and expand. Slow acceleration after the powder gas burned out but the gasses are still expanding, then finally deceleration where friction becomes greater than remaining pressure in the barrel.

Here’s the basics.
Pressure over time overcoming resistance. That three lines on a graph. If we use the load data pictured at the start of the thread and look at Accurate #2 and 5744 with the 190 grain subx bullet. They both exit the barrel at say 1050 fps after starting at 0 and traveling 24”. The #2 load does it with 60% less powder while creating 60% more pressure. What we don’t know is the time it took to create that velocity. All we know is that after traveling the same distance, they were at the same speed. That means that before that intersection one bullet was traveling slower than the other and after that point the other bullet was traveling slower. One rate of acceleration after the initial slower boost finally overcame the other. This is where you need to know time in the barrel vs distance traveled. They will be different for each load.

Smokeless powder needs containment to be effective, if it can’t build pressure, if the gasses created by burning aren’t contained, pressure can not build up. If you throw a loaded round in the fire, if you’re hit by anything, it’s likely to be the primer. The lightest component. Then whatever is lighter, the brass or the bullet. In theory if the primer pops out and the flash hole is big enough, there may not be enough pressure to separate the brass from the bullet.

Now the fun part.
Peak pressure is the point where volumetric efficiency changes. Powder needs containment to build pressure. A moving bullet is more or less a pressure relief valve. As the bullet moves, the volume of the containment vessel increases. The burn rate and rate gasses expanding decreases. How this plays out is that a 30 caliber bullet driven by the exact same powder charge will have less muzzle velocity than a 22 caliber bullet of the same weight and same barrel length. You have the same potential energy in a larger container, less energy will be developed in the larger container.

Resistance of the bullet traveling down the barrel, changes the rate of expansion. Bearing surface length, weight, lube if it’s a cast bullet all change the equation. Remember the bullet is the pressure relief valve, if the bullet doesn’t move, hopefully the primer pops and the pressure has a place to go. If that’s not enough relief stronger parts start to let loose.

That’s the premise of a 125 grain bullet using the same charge weight to match the velocity of a 240 grain bullet. There is so little resistance provided by the 125 grain bullet, the powder develops so little pressure that you have to add more powder. Basically the burn rate has changed, peak pressure has changed and the lighter bullet is followed out the muzzle by a measurable amount partially and totally un burned powder. This is manipulation of a burn rate. It’s possible to turn a fast burning powder, into a slow burning powder. Tougher to turn a slow powder into a fast powder.

Fast powders for subsonic is more about sound than velocity. The higher the peak pressure, the lower the muzzle pressure. The lower the muzzle pressure, the lower the sound signature. If all the powder burns it’s a plus so combustible powder is not filling your suppressor turning it into a bomb.

With supers you don’t have an artificial velocity limit. You load to a pressure point. With subs pressure is rarely a limiting factor, you load to a specific velocity window. it has a different set of variables a different set of factors that require a slightly different approach. There has been years of refining most cartridges that see today. There is a road map. This cartridge in that length barrel with this weight bullet performs best at this velocity. That’s not really science and engineering, it’s experience. All the fancy equations do is cut down development time when changing components, burning out a barrel about the time you have your load developed. Subsonic shooting Does not have that kind of data base yet.

I’m not knocking the science but the phrase “listen to the target” trumps the equation says every day.

None of this is any different shooting supers. It’s just velocity hides a lot of issues. If you have a 200 grain bullet at 3000 fps and SD’s in the low teens, it may not show up on target until 1000 yards. At 1000 fps it shows at 50. You actually need tighter tolerances to shoot subs MOA at any distance than you do supers.

Edit to add
Once all that sinks in, we can talk about the relationship between gas pressure and volume need to cycle a gas operated semi auto, and why burn rate makes a difference.
I understand now!!! Too many changes in variables and limited ballistic testing in this new field of shooting!!! You made really rethink when you stated that your 12" barrel was producing higher MV than your longer barrels!!!! I was not grasping the concept until you force me to think!!!! I was relying on memory!!!
 
I understand now!!! Too many changes in variables and limited ballistic testing in this new field of shooting!!! You made really rethink when you stated that your 12" barrel was producing higher MV than your longer barrels!!!! I was not grasping the concept until you force me to think!!!! I was relying on memory!!!
Let me make sure I didn’t confuse you with that. I have a 12” barrel that shoots the same super sonic load faster than most 16 “ barrels. It’s just an anomaly.

The higher velocity in shorter barrels with subs is completely different, and can happen for a couple of reasons.

When the volume of gas created by the powder charge stops expanding, it’s impossible for the bullet to gain velocity. Friction will then cause a drop in velocity. Bullets in a barrel don’t coast very well. This is why muzzle pressure is a good thing to monitor with subs. On a good day I can push a bullet through a barrel by hand, once it’s fully engraved. But even engraved the pressure required to get the bullet moving is 5 times, or whatever, to keep it moving.

A slow powder in a long barrel will still be burning powder and creating pressure, expanding gasses, at 20” In our example of #2 vs 5744. The #2 load burned alll the powder 10” inches back and was relying on the expanding gasses to keep pushing it. Slower and slower all the time until slow increase in speed became no increase in speed and finally loss of velocity.

The most important thing to remember is that leaving from the same place and traveling at the same speed at a certain distance, is completely irrelevant to the highest speed obtained in between stop and start, or even average speed.

Two planes leave San Diego and landed in Phoenix. Both have an airspeed of 200 mph on touch down. Both flights were non stop and took the same route. One took an hour. The other took two hours. Why?
 
Let me make sure I didn’t confuse you with that. I have a 12” barrel that shoots the same super sonic load faster than most 16 “ barrels. It’s just an anomaly.

The higher velocity in shorter barrels with subs is completely different, and can happen for a couple of reasons.

When the volume of gas created by the powder charge stops expanding, it’s impossible for the bullet to gain velocity. Friction will then cause a drop in velocity. Bullets in a barrel don’t coast very well. This is why muzzle pressure is a good thing to monitor with subs. On a good day I can push a bullet through a barrel by hand, once it’s fully engraved. But even engraved the pressure required to get the bullet moving is 5 times, or whatever, to keep it moving.

A slow powder in a long barrel will still be burning powder and creating pressure, expanding gasses, at 20” In our example of #2 vs 5744. The #2 load burned alll the powder 10” inches back and was relying on the expanding gasses to keep pushing it. Slower and slower all the time until slow increase in speed became no increase in speed and finally loss of velocity.

The most important thing to remember is that leaving from the same place and traveling at the same speed at a certain distance, is completely irrelevant to the highest speed obtained in between stop and start, or even average speed.

Two planes leave San Diego and landed in Phoenix. Both have an airspeed of 200 mph on touch down. Both flights were non stop and took the same route. One took an hour. The other took two hours. Why?

If the two planes are the same models which I'm going to assume, one was fully loaded with full fuel bladders and at max cargo weight!!! Slower acceleration for take off and had to utilize the full runway, slower climbing to cruising altitude, and slower to get to cruising speed!! It also had to throttle back soon to hold the 200mph landing!! Plus, the moment on this plane required the full runway to stop!!! The other plane, has just enough fuel for the trip, and is flying empty!!! Faster acceleration down the runway for liftoff and used less runway, faster to cruising altitude, and faster at obtaining cruising speed, faster decent, easier to slow down to 200mph on landing, and easier and quicker stop!!! The take off, the climb, getting to cruising speed, the decent, and landings are all acceleration problem!!! Plus, the lighter plane had a longer time in fast cruising speed!!!! The fully loaded plane just got to cruising speed and had to start the decent!!! Spent little to no time at fast cruising speed!!!
 
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If the two planes are the same models which I'm going to assume, one was fully loaded with full fuel bladders and at max cargo weight!!! Slower acceleration for take off, slower climbing to cruising altitude, and slower to get to cruising speed!! It also had to throttle back soon to hold the 200mph landing!! Plus, the moment on this plane required the full runway to stop!!! The other plane, has just enough fuel for the trip, and is flying empty!!! Faster acceleration down the runway for liftoff, faster to cruising altitude, and faster at obtaining cruising speed, faster decent, easier to slow down to 200mph on landing, and easier and quicker stop!!! The take off, the climb, getting to cruising speed, the decent, and landings are all acceleration problem!!! Plus, the lighter plane had a longer time in fast cruising speed!!!! The fully loaded plane just got to cruising altitude and had to start the decent!!! Spent little to no time at fast cruising speed!!!
That’s engineer thinking it’s simpler than that.

One flight was in the winter, the other in the summer. Arizona does not recognize daylight savings time. So half the year you leave San Diego at 1, arrive at 2. The other half the year you leave at 1, arrive at 3.

It’s better than flying the other way where half the year you cease to exist until time catches up. ;)

Sorry about that, just thought you needed to step away from the calculator for a minute.
 
That’s engineer thinking it’s simpler than that.

One flight was in the winter, the other in the summer. Arizona does not recognize daylight savings time. So half the year you leave San Diego at 1, arrive at 2. The other half the year you leave at 1, arrive at 3.

It’s better than flying the other way where half the year you cease to exist until time catches up. ;)

Sorry about that, just thought you needed to step away from the calculator for a minute.
Billiant!! Yah got the tater!!!!!
I spend way too much time thinking in the BOX!!!
BRAVO!!!!!

Here's another logic problem!!
A man is died from drowning and there are 52 bicycles around him!!!
What event caused him to drown?
HINT: A ______ _________!!!!!!!
 
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Billiant!! Yah got the tater!!!!!
I spend way too much time thinking in the BOX!!!
BRAVO!!!!!

Here's another logic problem!!
A man is died from drowning and there are 52 bicycles around him!!!
What event caused him to drown?
He was caught using marked cards at poker, so they through him in the River along with his
IMG_7840.jpeg
 
Wild Bill

I got an AR10, and a suppressor and after looking at the reloading manual and seeing barrel length it got me wondering what differences would I have since I am using a 16” barrel and load data was generated with the longer barrel. I noticed my speeds were faster eventhough I was doing what the book stated as a safe load. I then dabbled with the Clays powder and will continue to as of now I like that powder over totegroup and H4895
 
So my next conundrum is this. So this rifle is from Bear Creek Arsenal. Overall pretty happy. When I first put the suppressor on the BCG wouldn’t cycle so it was basically a single shot rifle.

1) removed the existing buffer weight and spring and replaced with my AR15 buffer weight and spring and gun cycles. Sometimes it locks the bolt back and sometimes it doesn’t. I still have to play with the gas block and will do that once I get a subsonic load I like.

2). I weighed the original buffer weight and it maxed at my scale at 1500 grams. The AR15 buffer weight is considerably lighter hence the cycling of the action.

3). A couple of pics of what I am seeing. Now with the gas block where it is adjusted to now I am getting ejections between 3-5 o’clock. My buddy was with me this past weekend and he noticed that the BCG wasn’t or seemed to not go back far enough. When I was shooting with my daughter we noticed the same thing.


Thoughts

Thank you

Travis
 

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So my next conundrum is this. So this rifle is from Bear Creek Arsenal. Overall pretty happy. When I first put the suppressor on the BCG wouldn’t cycle so it was basically a single shot rifle.

1) removed the existing buffer weight and spring and replaced with my AR15 buffer weight and spring and gun cycles. Sometimes it locks the bolt back and sometimes it doesn’t. I still have to play with the gas block and will do that once I get a subsonic load I like.

2). I weighed the original buffer weight and it maxed at my scale at 1500 grams. The AR15 buffer weight is considerably lighter hence the cycling of the action.

3). A couple of pics of what I am seeing. Now with the gas block where it is adjusted to now I am getting ejections between 3-5 o’clock. My buddy was with me this past weekend and he noticed that the BCG wasn’t or seemed to not go back far enough. When I was shooting with my daughter we noticed the same thing.


Thoughts

Thank you

Travis
Until you start playing with the porting adjustment, don't worry about changing weights or springs!!! If you are at full open porting, there are several spring options availability for closing the porting a little (for fine tuning the flow later after spring change) and make full cycling possible!! Less or more on the spring coefficient, longer spring (more coils), shorter spring (less coils), spring wire size!!!!!

I personally liked the simplicity of Mimi-14 design (180, 181, 182 series)!!! It lacked porting adjustment!! I thought Ruger should have made an optional port flow control!!! NOPE!!!! They instead made a fixed, positive stationary lug extractor with the introduction of the new Ranch Rifle!!! What a POS!!! They cut cost of manufacturing (extractor spring and plunger) vs a milled slot in the bolt and fixed lug in the receiver!! After the new Ranch Rifle introduction, and shooting a few friends new minis, I looked the other way, and have no desire at another Ruger mini purchase since the mid 90s!!! RUGER LOST A CUSTOMER WITH THE NEW RANCH RIFLE DESIGN!!! The early 18x (0, 1, 2) series were awesome!!!

The thing about the old minis is the ease of break down for cleaning an assembly!!! The design itself is simple!! To disassemble the mini, yank, or pry the back end of the trigger guard open!!! This unlocks the trigger/sear assembly from the receiver/barrel with the stock sandwiched between the two assemblies!! Drop the trigger assembly out of the stock and receiver, separate the receiver from the stock but lift up on the receiver and shoving forward!!! Pull back on the piston spring closest to the receiver, pull the string outward clearing the receiver and then clear the spring from the piston spring well!! Slid the piston/action lever back and pull it out of the receiver slot!! Next giggle the front of rotary bolt out the slot, turn front of the bolt outward of the receiver, twist the back of the bolt out of its slot!!! 7 pieces of single components and assemblies including the hand guard!!! SIMPLE, SIMPLE, SIMPLE! And no tools required!!! Unless you want to use the point of a loaded round inserted into the rear trigger guard hole to pry the guard open!!!

When the minis and Colt ARs first came out, the full auto Mini (M114 series) published rate of fire was 550 round/min!!! The full auto M16 (Stoner) had a rate of fire at 500 rounds/min!!!!! Colt bought out Stoner which was having severe financial problems with their government M16 contract!!!
Colt was able to renew a government contract with the rights to buy the Stoner PP Rights!!!

WHEN LOOKING BACK AT AR10S AND AR15S, EVERYONE THINK COLT!!!
IT'S ACTUALLY IS STONER!!!!!!!!!!
 
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The first question really is do you want to modify the rifle to shoot the the one load?
Or develop loads to work in the rifle?

It’s two completely different approaches.
 
So my next conundrum is this. So this rifle is from Bear Creek Arsenal. Overall pretty happy. When I first put the suppressor on the BCG wouldn’t cycle so it was basically a single shot rifle.

1) removed the existing buffer weight and spring and replaced with my AR15 buffer weight and spring and gun cycles. Sometimes it locks the bolt back and sometimes it doesn’t. I still have to play with the gas block and will do that once I get a subsonic load I like.

2). I weighed the original buffer weight and it maxed at my scale at 1500 grams. The AR15 buffer weight is considerably lighter hence the cycling of the action.

3). A couple of pics of what I am seeing. Now with the gas block where it is adjusted to now I am getting ejections between 3-5 o’clock. My buddy was with me this past weekend and he noticed that the BCG wasn’t or seemed to not go back far enough. When I was shooting with my daughter we noticed the same thing.


Thoughts

Thank you

Travis
Sounds like your system is still under-gassed for the buffer/spring with the ammo you are using.

I would move up the priority on the gas block testing unless you are okay with a single shot.

The AR15 platform is flexible, but with that said there still needs to be a balance between the gas port pressure and the mechanism.

When you try for subsonic using low pressure, it gets more important to have the gas port pressure to finish the job. Not every bbl and gas port length will combine with a set of hardware that will provide reliable function.

What is the gas port length of your bbl?
 
This is more fun and games with subs in rifles not designed to shoot them.

The first thing to check is the rifle itself. If it or the carrier group has less than a few hundred rounds, give it time. Which buffer are you using, standard, H1….?
Make sure it’s squeaky clean and well lubed. Subs are notoriously dirty and back pressure from the suppressors makes sure all extra carbon goes where you need it least.
Check for leaks at the gas block, both between the block and barrel and tube, also under the key on the carrier. People brag about a properly staked key for a reason. Carbon tracks anywhere they aren’t supposed to be are a good indicator of a gas leak.
If opening the gas block more does not help, allowing more gas, you have to create it. Many people drill out the port, to me that’s absolutely the last resort.

Time to look at the load. This will drive the folks that shoot short jumps or jams and argue that moving the bullet does not drop pressure or velocity.
Since you’re right on the edge or reliability, adjusting the current load might work. If velocity allows, you can simply add powder. If not hopefully you can move the bullet out. This is how I work up a load with powder that is too fast for the application. Quickload is priceless for this type of thing because of being able to look at both peak and muzzle pressure. I’m more concerned with muzzle pressure.

The first thing is to set priorities, with a semi auto, it has to cycle. Accuracy, sound signature, gas in your face all don’t really matter if it won’t go pew pew pew. Last round lock back is negotiable as long as you can dump what’s in the magazine.

Where I start
Seat the bullet as long as practical, leave enough in the case to not fall out. The 190 SubX may not be the best profile to work with. The 175 allows you to seat a much longer length. The short fat nose of the 190 can limit seating depth adjustment severely. I pick a powder charge that should be 11-1200 fps. If that won’t cycle, there’s not much sense in chasing that powder bullet combination. That’s another reason to start high and work a new load down.

If f it cycles, great I can start working on velocity. I start reducing powder charge until the velocity is too low, or it stops. Locking back. That is the pont where reliabllity is falling off. But you have established a minimum charge weight needed to cycle that bullet combination. Hopefully you have a charge weight that is also below target velocity, if so you can start tuning your load. Seat the bullet deeper, the velocity will start to increase, pay attention to your groups. +/- 50fps won’t mean squat for effective range. But 2 MOA vs 1/2 MOA is huge. Don’t get hung up on velocity once the speed is subsonic on the coldest day you will ever shoot.

It’s f you have a load like you listed above, right velocity, reasonably accurate just not quit cycling reliably, this is when you start moving the bullet in and out watching the changes in cycling. if you want to maintain velocity and hope fully improve cycling or lock back adding .1 to the powder charge and moving the bullet out .010” is a pretty hood rule of thumb to increase available gas and pressure, without changing velocity. Same works in reverse, drooo ok the charge .1 grain drop the seated depth .010”. This varies some with case capacity. But it’s a hood place to start.

Sometimes you just have a combination that won’t work. I had a problem with Lehigh 194’s and a certain powder. Bullet weight can change burn rate enough to change cycling, same powder charge would cycle certain 150 bullets. So it wasn’t really a weight or bullet drag issue.

The problem was that the chosen powder did not create enough pressure to obturate the base of the 194. The copper was just too hard and gasses blew by the bullet. Faster powder was the answer.

Lots of new possible problems and solutions
 
Sounds like your system is still under-gassed for the buffer/spring with the ammo you are using.

I would move up the priority on the gas block testing unless you are okay with a single shot.

The AR15 platform is flexible, but with that said there still needs to be a balance between the gas port pressure and the mechanism.

When you try for subsonic using low pressure, it gets more important to have the gas port pressure to finish the job. Not every bbl and gas port length will combine with a set of hardware that will provide reliable function.

What is the gas port length of your bbl?
Carbine length. Barrel is 16” in length. I am going to call Bear Creek and see what buffer weight they use it seems to far exceed what an H3 should be
 

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