Port pressure in a M1a

[Uncle Ed]

A over gassed M1A can have the bolt moving to the rear when pressure is still in the barrel. And this depends on the burn rate of the powder and its port pressure, example a case head swipe.

M1A Adjustable Gas Plug
http://www.schustermfg.com/m1a-adjustable-gas-plug/
By adjusting the volume of gas in the cylinder it changes the speed of the op-rod and controls the harmonic vibration of the barrel. Even if you only shoot your M1 once in a while make it last a second lifetime. Our plug softens the blows on your op-rod and wear on the bolt lugs. Made from Hardened Tool Steel & Parkerized.

 

[Bart B.]

So when the bullet passes the gas port, the gas pressure at the gas port is a tad lower than the chamber pressure.

Yes, indeed, at that time.

 

[rammac]

A over gassed M1A can have the bolt moving to the rear when pressure is still in the barrel. And this depends on the burn rate of the powder and its port pressure, example a case head swipe.

M1A Adjustable Gas Plug
http://www.schustermfg.com/m1a-adjustable-gas-plug/
By adjusting the volume of gas in the cylinder it changes the speed of the op-rod and controls the harmonic vibration of the barrel. Even if you only shoot your M1 once in a while make it last a second lifetime. Our plug softens the blows on your op-rod and wear on the bolt lugs. Made from Hardened Tool Steel & Parkerized.

The major difference between the M1 Garand and the M14/M1A gas system is that the M14/M1A vents the gas after the piston starts to move while the M1 Garand does not so a vented gas plug does not have as much value for the M14 design. There is however some important distinctions that most people don't make when you talk about the movement of the bolt in the M14, specifically momentum. While the vented gas system pretty much precludes having too much gas in the system when the bolt opens you can still have too much momentum imparted to the bolt and it will slam to the rear with too much energy if you use the wrong powder. So while the vented plug isn't really of any value in so far as safely removing any excess gases, it does help ensure that you wont exceed the limits of recoil energy.

 

[Bart B.]

A over gassed M1A can have the bolt moving to the rear when pressure is still in the barrel.

Chamber pressure won't be much at that time. Bullets are over 10 feet out the barrel when the bolt unlocks and starts moving back.

 

[riflewoman]

Not to beat this dying horse anymore, but these vented gas plugs are fundamentally unnecessary and probably don’t work very well if they work at all. Excess gas takes time to flow through any orifice. Most of these “vents” are small enough to choke the flow so the velocity and resulting mass flow of gas will be limited. This means that excess gas will still be doing its dirty work on your operating rod even with one of these gizmos. The solution is not to “over gas” these rifles to begin with. The gas port diameters listed in the tech report might be reduced a few thousandths if you can guarantee the rifle will be kept meticulously cleaned and lubricated. Certainly parts breakage will be minimal as thes rifles were fired many thousands of rounds in their acceptance tests. Note, that the M1 barrels chambered in 308 had port sizes much larger than .0793.

 

[Uncle Ed]

Chamber pressure won't be much at that time. Bullets are over 10 feet out the barrel when the bolt unlocks and starts moving back.
View attachment 1079796

So how many people here are using issued military ammunition, and the topic is port pressure.

Glen D. Zediker
RELOADING FOR THE MATCH M14
[pay attention]

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&ved=2ahUKEwj9q6fHrqrfAhUpq1kKHTohCQoQFjAPegQIBhAC&url=http://www.zediker.com/downloads/14_loading.pdf&usg=AOvVaw0tVzg215hdzh0mGPudTRx0

The M14 has about the quickest operation of any auto-loading rifle — so much so that
the bolt can unlock before the case has fully retracted from its expanded dimensions. We’re
talking about milliseconds, but that’s all we have devoted to the entire process. The net result is that
some amount of additional expansion frequently occurs in a case fired through an M14. Com-
pounding this condition is that LC brass is liable not to contract as readily as other cases fired in
other rifles. It’s very, very (comparatively) hot and getting jerked on by an extractor, and most seem
to think this is responsible for a lot of the additional measured case growth. Don’t be fooled into thinking that brass from an M14 “fire formed” to fit the chamber; it may well have “fire deformed.” A spent case from a 14
will often have the shoulder blown farther forward than chamber specs should allow, and may
also exhibit more case head expansion than it “should.”

 

[Uncle Ed]

Read the link below, starting at post #42 there are Quickload charts. Please note the data is for the 7.62x51 and not the .308.

IMR-3031 in the FAL..
https://www.falfiles.com/forums/showthread.php?t=287067

 

[rammac]

Unless your rifle is a military surplus rifle there is no need to use the specs for a 7.62x51mm cartridge other than to be more precise with your data IF you have a true 7.62x51mm chamber.

• There are only small differences in the blueprint specs for the two cartridges, none are critical.
• There are small differences between the chamber specs that aren't of any importance unless you are shooting a military surplus rifle.
• The 7.62x51mm chamber is actually larger than the .308 Win chamber specs in most of the few features that differ so the 7.62x51mm chamber can shoot the .308 Win ammo safely.
• 7.62x51mm ammo MIGHT be a problem in a .308 Win chamber IF the ammo was built to the maximum military specs but since there are no 7.62x51mm ammunition dies (unless a government had special dies built for use in their ammo plants) most ammo is built to .308 Win specs.
• Springfield Armory doesn't cut the chambers to military specs, they use .308 Winchester specs.

Many of us have used many millions of military surplus cartridges in the M1A rifles over the last 44 years of the rifle's production life and it has never earned a reputation for not being able to handle both .308 Win and 7.62x51mm ammo.

 

[Bart B.]

The M14 has about the quickest operation of any auto-loading rifle — so much so that the bolt can unlock before the case has fully retracted from its expanded dimensions.

In spite of M14 bolts taking 25% longer to unlock than M1 bolts?

 

[Bart B.]

So how many people here are using issued military ammunition, and the topic is port pressure.

I don't know nor care what ammo is used. Do a survey.

My data puts the part's moving timing up for those who might want to know when things change position relative to primer strike.

 

[Uncle Ed]

In spite of M14 bolts taking 25% longer to unlock than M1 bolts?

If you want to argue with Glen D. Zediker who wrote the book I quoted then send him a email.

And tell us what books on the M1A have you written and had published.

On top of this there is so much reloading data for the 7.62 rifles I see no use for Quickload.

 

[Zero333]

Only your rifle can tell what powder and charge weight it prefers.

I load the 40.5 or 41.5 gr H-4895 with 168 hornyday bthp/amax in my M1A 18.5" bbl. Action sounds and feels perfect with these load.

I tried 41.5 gr of Varget and the action sounded/felt rougher. But still worked normally.

I was wondering about the same thing as you and Quickload port pressure to find a ball powder to work with on my XL650. But running different powders in QL showed little difference in port pressure to make a educated guess.

According to QL I should be able to use every powder from H335 up h414 and everything in between. But in reality I know this is not the case, so I will have to try different ball powders to see what works best.

In QL I was looking for port pressure around 12,500 psi around the 15" area.

 

[Bart B.]

If you want to argue with Glen D. Zediker who wrote the book I quoted then send him a email.

And tell us what books on the M1A have you written and had published.

All that instead of "yes"..... ... . hmmmmmm

I may well laugh for days after reading Zediker's remark "Probably the best factory ammunition for a match-grade M14 is Lake City Match (LCM) M852." Its accuracy spec was the same as M118, 7 inches average ES, therefore max ES about 12 inches; in bolt action test barrels. Federal Gold Medal match easily halved those numbers in rebuilt M14NM rifles

 

[Uncle Ed]

All that instead of "yes"..... ... . hmmmmmm

There is no ego compensation in Quickload................

 

[Bart B.]

There is no ego compensation in Quickload................

I see no value in Quickload either.

 

[riflewoman]

If you want to argue with Glen D. Zediker who wrote the book I quoted then send him a email.
And tell us what books on the M1A have you written and had published.
.

Mr Zediker, to my knowledge, is a shooter, reloader and writer. I do not think he has an engineering or mechanical background. So his statements that the M1A has a harsher operating cycle is flat out wrong. The design engineers at Springfield armory in Massachusetts worked very hard on the gas system and operating dwell of the M14 to eliminate the abrupt operation of the M1. The fundamental reason the cases are larger after firing in an M14/M1A is the larger chamber. Just cutoff the gas system and operate the bolt manually. The cases will be just as big as when fired with the gas system. The statement that the cases are larger because they’re extracted while still hot indicates that Mr Zediker does not understand thermal expansion and contraction.

The M14 was designed in the early 1950s with the G3 and FAL as contemporaries. Compared to those, the M14 has a much better primary extraction and better operating characteristics.

 

[Uncle Ed]

What Mr. Zediker said was the extracted cases can be longer than the chamber because the shoulder has moved forward. And all you need to do is use a Hornady cartridge case headspace gauge and measure the fired cases.

Below is what Mr. Zediker stated.

"A spent case from a M14/M1A will often have the shoulder blown farther forward than chamber specs should allow"

Meaning a fired case after ejection will be longer to the case shoulder than the chamber. Meaning you can't measure a fired case and set the die up for .003 shoulder bump and expect the case to chamber. And you do not need to be a Engineer to figure this out.

And all this posting BS over a Quickload port pressure guesstimates.

 

[rammac]

In his own book Zediker explains that he is simply a writer who started his shooting hobby in order to learn about the sport so he could write about firearms and competition shooting. His book is actually a compilation of information he gleaned from other shooters, it isn't based on anything scientifically proven and there are quite a few errors in it. It's a fairly useful book for beginners but it's really not very accurate or informative once you've advanced past the basics of firearms physics.

As for QuickLoad, it is used by several bullet manufacturers as the basis of their reloading manuals. Bryan Litz uses it to build his reloading data for the Berger Bullets reloading manual. The manual includes a section that discusses the attributes of QuickLoad; which is a pretty convincing recommendation for the software since Bryan Litz is a formally trained expert in ballistics and is recognized as one of the leading experts in modern ballistics. There are other reloading manuals that were written using QuickLoad data but I don't recall which ones. You could call Ed Dillon at Necos.com and ask him who else uses the software for developing their reloading manuals, I'm sure he would be more than happy to explain just how popular the software is with real ballisticians.

But like all computer software, garbage in = garbage out. If you don't bother to learn how to use the software then you will never see it's usefulness. Unfortunately there are way too many people that are either too lazy to actually read the software's instructions or they are simply too ignorant to understand how legitimate the science is that the developer used to build the software. Not that I'm an expert with the software nor am I a ballistician but I have had enough education in the field of engineering that I'm able to understand more than most so I tend to keep an open mind about the current tools that are available rather than just scoff at anything that is more modern than a stone tablet and a chisel.

 

[rammac]

...Meaning a fired case after ejection will be longer to the case shoulder than the chamber. Meaning you can't measure a fired case and set the die up for .003 shoulder bump and expect the case to chamber. And you do not need to be a Engineer to figure this out...

No, you don't need to be an engineer to reload for the M1A rifle but I suspect that you have your share of misunderstandings about how the rifle works.

Do you know how to mitigate over-expanded cases?

 

[cfreeman]

No, you don't need to be an engineer to reload for the M1A rifle but I suspect that you have your share of misunderstandings about how the rifle works.

Do you know how to mitigate over-expanded cases?

Not trying to be a smartass at all or get into this pissing contest, but I would like to know how to mitigate overexpanded cases. Seriously.