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pressure and cycling semi auto
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Author:  john54 [ Fri Jul 31, 2020 9:49 am ]
Post subject:  pressure and cycling semi auto

I think I have a handle on this, but want the experience of the group for verification. I went to my local trap field and was practicing with my CZ 712. I normally use 11/8oz Remington sts at 1145 fps. I wanted to try a load with a bit less recoil and picked up a box of 1oz AA that were loaded to 1180 fps. They wouldn't cycle. Field striped my gun and sure enough it was REALLY grubby. Switched back to the 11/8 oz. shells and all was fine.

OK, went home and did a deep clean on my shotgun. Plan on going back to the range and try the 1oz shells again. I'm pretty sure they will work now, but I'll let you know.

My question is on reloading. I am planning on using Extra Light powder and the recipes show combinations of fps and chamber pressure. Am I thinking right that by using a recipe that loads to the high end of pressure, the semi-auto will be more likely to cycle and let the fps fall where it may. Example one loaded to fps value of 1,150 with a pressure of 10,060 psi. This would cycle more reliably than a load with another wad that loads to 1,150 fps and 8,810 psi.
Thanks in advance for the help. Secondary question, am I going to lose the softer recoil of the 1oz with the higher pressure load?
Thanks in advance for the help.

Author:  garrisonjoe [ Fri Jul 31, 2020 10:39 am ]
Post subject:  Re: pressure and cycling semi auto

Quote:
Secondary question, am I going to lose the softer recoil of the 1oz with the higher pressure load?


Recoil energy comes almost completely from the velocity and weight of your payload (the shot). 1 ounce of shot, at 1150 FPS, is constant. So there won't be a difference in the recoil you will feel between a high and a low chamber pressure load. With a good semiauto action soaking up some of that recoil, a 1 ounce load at that speed should be a kitten.

good luck, garrisonjoe

Author:  dogchaser37 [ Fri Jul 31, 2020 10:47 am ]
Post subject:  Re: pressure and cycling semi auto

It isn't just pressure that cycles a gas semi-auto. You also need a certain amount of powder gas.

Most gas SA's need a minimum of about 16 - 17 grains of powder to generate enough powder gas to cycle the shotgun. Some guns will run on less.....but not all and not all reliably.

Beretta SA's seem to be the least finicky with what you feed them.

Author:  Tidefanatic [ Fri Jul 31, 2020 10:53 am ]
Post subject:  Re: pressure and cycling semi auto

dogchaser37 wrote:
It isn't just pressure that cycles a gas semi-auto. You also need a certain volume of powder gas.

Most gas SA's need a minimum of about 16 - 17 grains of powder to generate enough gas volume to cycle the shot gun. Some guns will run on less.....but not all and not all reliably.

Beretta SA's seem to be the least finicky with what you feed them.


Also, not that there might not be something out there, but I`ve not heard of or seen much that a Remington V3 won`t eat.

Author:  fecmech [ Fri Jul 31, 2020 11:00 am ]
Post subject:  Re: pressure and cycling semi auto

The cycling of your action depends on port pressure and gas volume. That is the pressure and volume at the port in the barrel. My 390 Beretta will not cycle a 7/8 oz 1200fps load with extra light powder. It will cycle 1200fps 7/8oz loads with Red Dot, Promo,700x and Clays (these are actual chronographed loads). It will also cycle 3/4 oz loads with Red Dot and Promo. I think it has to do with a short sharp time pressure curve with Extra Light and less gas volume. Your gun may function just fine, you won't know till you try.
I have run into the same thing in my 20ga TriStar G2 with 3/4 oz. loads. Using a tested Promo load from SJW and also an Intl. Clays load the G2 will not reliably cycle. If I load to the same 1200 fps with Unique or WSF the G2 happily runs 100% relable. It all comes down to pressure and volume at the port.

Author:  OldStufferA5#1911 [ Fri Jul 31, 2020 11:38 am ]
Post subject:  Re: pressure and cycling semi auto

john54 wrote:
I think I have a handle on this, but want the experience of the group for verification. I went to my local trap field and was practicing with my CZ 712. I normally use 11/8oz Remington sts at 1145 fps. I wanted to try a load with a bit less recoil and picked up a box of 1oz AA that were loaded to 1180 fps. They wouldn't cycle. Field striped my gun and sure enough it was REALLY grubby. Switched back to the 11/8 oz. shells and all was fine.

OK, went home and did a deep clean on my shotgun. Plan on going back to the range and try the 1oz shells again. I'm pretty sure they will work now, but I'll let you know.

My question is on reloading. I am planning on using Extra Light powder and the recipes show combinations of fps and chamber pressure. Am I thinking right that by using a recipe that loads to the high end of pressure, the semi-auto will be more likely to cycle and let the fps fall where it may. Example one loaded to fps value of 1,150 with a pressure of 10,060 psi. This would cycle more reliably than a load with another wad that loads to 1,150 fps and 8,810 psi.
Thanks in advance for the help. Secondary question, am I going to lose the softer recoil of the 1oz with the higher pressure load?
Thanks in advance for the help.


Gas Autoloaders (doesn't matter, shotgun, rifle, machine gun, pistol (yes a couple exist)....

CHAMBER PRESSURE has virtually NOTHING to do with the cycling function of the gun.

What drives a gas-action self-loader is gas pressure AT THE BARREL PORT(S).
If Port Pressure is too low, the gun short strokes.
If the Port Pressure is too high, the gun CAN cycle too fast, bashing itself excessively.

A load, 11,500psi, of 18 grains of Red Dot, will provide FAR LESS Port Pressure than the same shot weight 11,500psi from 40grains of Longshot.
The larger amount of slower burning powder produces maximum pressure a tiny bit later, while creating a larger gas volume "bubble", that bigger gas volume drops pressure more slowly, creating higher pressure when the projectile passes the Gas Port(s) than the smaller bubble from the Red Dot does (pressure drop is faster, port pressure is lower).

So, what a gas autoloader requires has nothing to do with Chamber Pressure at firing, it has to have The CORRECT (or at least 'ENOUGH') Port Pressure to drive it's systems, AND enough "dwell time" (length of barrel past the gas port) for the system to remain pressurized.
Saw a gas autoloader barrel off too close to the front of the gas ports, and the barrel un-corks before the system can operate, and it stops working.

Author:  cookoff013 [ Fri Jul 31, 2020 12:10 pm ]
Post subject:  Re: pressure and cycling semi auto

There are some great replies here. Ie volume of gas.

Author:  John Henry [ Fri Jul 31, 2020 1:20 pm ]
Post subject:  Re: pressure and cycling semi auto

fecmech wrote:
... My 390 Beretta will not cycle a 7/8 oz 1200fps load with extra light powder. It will cycle 1200fps 7/8oz loads with Red Dot, Promo,700x and Clays (these are actual chronographed loads). It will also cycle 3/4 oz loads with Red Dot and Promo.


That's interesting. I have yet to find an auto that will cycle my 1200 fps 3/4 oz 12 ga with red dot or exlite.

And I've tried it in several A400s, but never a 390. Glad it works for you!! What is the velocity of your 3/4 oz loads?

Author:  fecmech [ Fri Jul 31, 2020 1:43 pm ]
Post subject:  Re: pressure and cycling semi auto

Quote:
And I've tried it in several A400s, but never a 390. Glad it works for you!! What is the velocity of your 3/4 oz loads?


I use 16 grs Promo/RD for roughly1250 fps. An 87 yr old friend with shoulder problems is using 15grs of Promo in his 400 Xcell. They only eject a couple of feet but the gun ejects and feeds.

Author:  john54 [ Fri Jul 31, 2020 3:48 pm ]
Post subject:  Re: pressure and cycling semi auto

Thanks for all the information. I just got back from the Trap range and the nice and clean CZ-712 cycled the 1oz AA's 1180 fps. just fine. I was a little worried for a bit. I had set up for 1oz loads and had started thinking of the money I had wasted because it wouldn't cycle them. I did notice the difference in recoil between the 1oz and the 11/8 oz. Not much, but significant.

Author:  oneounceload [ Fri Jul 31, 2020 5:25 pm ]
Post subject:  Re: pressure and cycling semi auto

John Henry wrote:
fecmech wrote:
... My 390 Beretta will not cycle a 7/8 oz 1200fps load with extra light powder. It will cycle 1200fps 7/8oz loads with Red Dot, Promo,700x and Clays (these are actual chronographed loads). It will also cycle 3/4 oz loads with Red Dot and Promo.


That's interesting. I have yet to find an auto that will cycle my 1200 fps 3/4 oz 12 ga with red dot or exlite.

And I've tried it in several A400s, but never a 390. Glad it works for you!! What is the velocity of your 3/4 oz loads?



I got my A400s to run 3/4 @ 1210, but got a lot of residue in the barrel; bumped the charge up to run @1275 and performance was much improved. This was with Titewad, not RD or Promo.

Author:  rsrocket1 [ Fri Jul 31, 2020 6:54 pm ]
Post subject:  Re: pressure and cycling semi auto

I use 18.5-19g of Red Dot, Titewad, Clays, Titegroup under 3/4 oz of reclaimed shot for 1300 fps and it works great on the skeet range at any temperature down to the 40's (doesn't get any colder here during the hours I shoot). It feels nice and crisp with no "whoosh" and no residue in my Remington 1100 gas gun. When I tried for 1200 fps, I would foul up the gas system within a hundred shots so I had to do a quick spray and clean using Rem Oil on the magazine tube between rounds. I don't have to do this anymore and can go many hundreds of shots between cleanings if I want (but I don't).

Author:  cookoff013 [ Sat Aug 01, 2020 2:29 am ]
Post subject:  Re: pressure and cycling semi auto

Most european light loads run 1400fps estimated. Thats 7/8oz.

Author:  Denver1911 [ Sat Aug 01, 2020 5:53 am ]
Post subject:  Re: pressure and cycling semi auto

I have to ask:

How can different powders have different volumes of gas at the ports?

Volume of the cylinder is pi * r^2 * h. Pi is constant. r is half the barrels diameter. h is the distance from back to the hull to the ports. These don’t change by powder. The gas fills the allotted volume.

Do you mean mass?

Author:  RandyWakeman [ Sat Aug 01, 2020 6:52 am ]
Post subject:  Re: pressure and cycling semi auto

Denver1911 wrote:
I have to ask:

How can different powders have different volumes of gas at the ports?


Quote:
For example, an AL sized cylinder is filled with nitrogen at 2000 psi. What is the gas volume of nitrogen from the cylinder?

P(1) is 2000 psi
V(1) is the internal volume of AL cylinder 29.5 liter*
P(2) is 14.7 psi
V(2) is the unknown volume of gas

Solving the equation above for V(2) gives:
V(2) = [p(1) x V(1)]/P(2) = (2000 psi x 29.5 liters)/14.7 psi = 4013 liters

(approximately 140 cu. ft.)


More pressure means more volume.

Author:  Denver1911 [ Sat Aug 01, 2020 7:19 am ]
Post subject:  Re: pressure and cycling semi auto

RandyWakeman wrote:
Denver1911 wrote:
I have to ask:

How can different powders have different volumes of gas at the ports?


Quote:
For example, an AL sized cylinder is filled with nitrogen at 2000 psi. What is the gas volume of nitrogen from the cylinder?

P(1) is 2000 psi
V(1) is the internal volume of AL cylinder 29.5 liter*
P(2) is 14.7 psi
V(2) is the unknown volume of gas

Solving the equation above for V(2) gives:
V(2) = [p(1) x V(1)]/P(2) = (2000 psi x 29.5 liters)/14.7 psi = 4013 liters

(approximately 140 cu. ft.)


More pressure means more volume.


Uh .. no. Volume is a measure of .. volume. You can’t fit 4013 liter of gas inside of a 29.5 liter container .. if you put it in there, it becomes 29.5 liter of gas. Albeit at a different temperature and pressure. But once inside the container it is 29.5 liters.

Maybe you mean “volume at standard pressure?”

Author:  dogchaser37 [ Sat Aug 01, 2020 8:11 am ]
Post subject:  Re: pressure and cycling semi auto

Denver, gas is compressible. Increase gas pressure in a vessel, means an increased amount/weight of gas is in that vessel.

All powders are different and they all produce varying amounts of powder gas, per grain of powder.

Author:  Denver1911 [ Sat Aug 01, 2020 9:21 am ]
Post subject:  Re: pressure and cycling semi auto

dogchaser37 wrote:
Denver, gas is compressible. Increase gas pressure in a vessel, means an increased volume of gas is in that vessel.

All powders are different and they all produce varying amounts of powder gas, per grain of powder.


I’m still going with no. The volume of gas in a 1 liter container is .. 1 liter. It may have been at a different volume before it was compressed and put in the container when it was at a different pressure, but once inside the container it is 1 liter. pv=nRt and all that. If you have a fixed mass of gas (n) and it’s at room temperature at 1 atmosphere, then you compress it, you still have a fixed mass of gas. Pressure goes up, temperature goes up, and volume goes down. So, yes, gas is compressible. But when you compress it .. volume changes. I know I am right, so I’ll not derail the thread any further. All replies will be read and if they refute the claim that the volume of gas contained inside the cylinder between shell bottom and ports is different for different powders .. they will be ignored as factually incorrect. Volume of different gasses inside a fixed contained is always fixed. Mass may be different. Pressure may be different. And temperature may be different. But a fixed volume is .. well .. a fixed volume. No more thread derailing from me, so if you disbelieve this, I can’t help you. Look it up.

Author:  garrisonjoe [ Sat Aug 01, 2020 9:32 am ]
Post subject:  Re: pressure and cycling semi auto

You two or three are talking past each other. The volume of the tank is constant. The AMOUNT of gas in the tank increases with pressure. When pumped into the tank, the volume of the gas is the same as the volume of the tank. You can't talk accurately about AMOUNT of a gas unless you talk the WEIGHT of the gas (or the moles of gas, more precisely, and what a chemist would do).

Using the term VOLUME of gas always requires you to consider the PRESSURE it is at. A volume of a gas is not an accurate way to specify the AMOUNT of gas, unless you also specify the temperature and pressure it is at. Gases are hard to measure because of that. Liquids like water or hydraulic fluid are easy to specify by volume, because those liquids do not change volume as pressure increases.

Now, most shotgun powders generate close to the same weight of gas from the same weight of powder. Some generate it faster (faster powders), some slower (amazingly, called slower powders). The magic rule of thumb that about 18 grains of powder will make enough gas in a 1 or 9/8 ounce load to work a gas semiauto comes from the fact that all the smokeless powders have nitrocellulose as the main component. It burns to make mostly carbon dioxide and steam (gases). The weight of nitrocellulose (close to the same in most powders) burns to make the same WEIGHT of gases for most powders, but at different speeds and peak pressures and port pressures depending upon the exact powder and the speed deterrent additives. And substituting nitroglycerin for some of the nitrocellulose (as double base powders do), boosts the amount of gas produced just a little bit, and adjusts the speed of the burn.

Quote:
More pressure means more volume.

Nope, more pressure means more amount of gas fits (has been generated) in the barrel space at the time of measurement.


good luck, garrisonjoe

(corrected a key-bounce on "1 ounce" that my keyboard has started doing!)

Author:  dogchaser37 [ Sat Aug 01, 2020 10:29 am ]
Post subject:  Re: pressure and cycling semi auto

garrisonjoe, Denver,

Yup I should have said amount not volume. I will edit my post.

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