M14 max bullet weight

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Here is one for the M14 gurus to ponder.

Why it is generally accepted that the heaviest bullet to shoot through an M14 is (roughly) 170 grains? You can load a 190 grain bullet to the same pressures as you can with a 150 grain bullet. Now if this were a recoil operated gun, then there's merit to this, but if you are merely measuring pressures, then there is none.

The argument that the heavier bullet is slower down the barrel therefore applies the pressure to the gas system for a longer time is not valid, as the gas piston travel is only an inch and a half (again roughly). It bottoms out regardless if the pressure is applied for 3 seconds, or 0.003 seconds. The op rod leaves contact with the gas piston for over half of it's travel. By the time the op rod returns contact to the piston, the bullet and gasses have left the chamber, and are under nearly no pressure.

I have never tried it, and have no intention to. 150 grains work fine. Merely posing the question to examine the physics behind it and get rid of some of the "mysticism" as it seems that everyone just repeats the same line: "you can't shoot heavy bullets out of the M14 because you'll wreck it" without knowing why.
 
If you turn off the gas port you can use whatever you want. You'll just have a straight pull bolt action though. I know that a 162 grain can be used safely without battering things around too much.
 
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the given parameters are 165 for hunting, 168 for target, if you don't want to bash your op-rod all to heck- if you don't care , it's 175 top end - the 175 travels at 2550 and no more , but you need an armourer and truck with spares- that's why i have 2 different bullet weights in my 308s-165s for the 14s and 180 for everything else- never even seen a 162
 
I think frontier firearms has some 168gr Match king in stock. A little pricey though at 42$/20. I haven't heard any problems with people using that ammo. When in doubt though if you aren't going to turn the gas port off try to stay lighter than heavier if possible.
 
tacoman said:
It isn't so much the bullet weight as the slower powder used for the heavier bullets that allow the pressure to peak closer to the gas port than a quicker powder which has reached peak sooner.This leaves you with a higher port pressure that you don't get with lighter bullets and quicker powders,also why hunting ammo is not as good as the military loads.
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depends on the military loads- some of that ivi stuff is minute of barn door quality- ACCURACY DEPENDS ON THE RIFLE as well as the shooter- my handloads using the m118slr recipie are 1inch groups at 100 yards, but it toom me years to develop the "sweet spot " for each rifle- i have 4 of them- an earky norc, an h&r, trw, and a springy
 
Heavier bullets will cause a stronger impulse force on the piston. The op-rod will be forced back harder.

Say you shoot a blank with the same amount of powder but no projectile, the gun probally wont cycle, so it makes sense, the heavier the projectile, the stronger the piston gets shot back.
 
If you shoot the blank, there is no useful pressure buildup in the barrel. There will be a bit, but not enough to do anything. The lack of pressure is the cause the action won't cycle, not the lack of bullet, granted the lack of bullet contributes to the lack of pressure. That is why we adjust our powder charges when we change bullet weights..... to maintain safe operating pressures.

When the bullet passes the gas port, there will be roughly 58000 psi of pressure on the gas piston until it bottoms out in the gas block, regardless whether you are shooting a:

150gr bullet with 47.3 Gr. of IMR4895

or

180gr. bullet with 44.7 Gr. of IMR4895.

See what I am getting at.....

Then the bullet leaves the barrel, and there is nothing forcing the gas to pressurize the gas block. The gasses follow the path of least resistance, out the muzzle, in effect, creating somewhat of a venturi as the moving gasses pass the gas port.

58000 psi is 58000 psi. that is the max pressure reached in the combustion chamber throughout the firing of that round.

(Load data from Hodgdon's reloading site. Do not use without consulting manuals and safe reloading practices...)
 
I was thinking of starting a thread on this same topic.

I’ve been doing a fair bit of reading on this, including most everything on this site. ARE WE REALLY SURE THAT HEAVIER BULLETS ARE BAD FOR OUR NORCS?

Before you just type YES. Here’s what I found. Below are some pressures for 308, 150gr and 180gr loads. They are extremely similar. Right at the top end the 180gr loads are often about 1000 PSI more, but that’s it. And that’s if you load your 180’s to the max. Is 1000 PSI going to make any difference? Honestly are tolerances so tight that 57.700 is okay for a lifetime, but 58,700 and your #### falls off?

Bullet Weight (Gr.) Manufacturer Powder Bullet Diam. C.O.L. Grs. Vel. (ft/s) Pressure Grs. Vel. (ft/s) Pressure
150 GR. NOS BT IMR IMR 4895 .308" 2.800" 42.6 2631 42,300 PSI 47.3C 2920 57,700 PSI
180 GR. SPR SP IMR IMR 4895 .308" 2.800" 40.5 2439 43,800 PSI 44.7C 2674 58,700 PSI

Now another kicker. With 165's - agreed to be fine for M1A's and Norc M14's, here are the numbers.

Bullet Weight (Gr.) Manufacturer Powder Bullet Diam. C.O.L. Grs. Vel. (ft/s) Pressure Grs. Vel. (ft/s) Pressure
165 GR. HDY SP IMR IMR 4895 .308" 2.750" 42.7 2584 49,200 PSI 45.5C 2745 58,800 PSI

That's right - 100 PSI HIGHER than the 180's at the top end...As a matter of fact, I was very hard pressed to find any 308 loads with higher pressures than the 165's loaded to the max.

Here’s another interesting thing. I don’t have photos, as Brownells removed them from their advertisement (I was going to put them in here). But when cruising their site a few months back I found something very interesting. Schuster sells an overbored gas nut for the U.S M1A rifle, that has a larger area bored out in the nut. They used to have pics of the overbored nut and the standard nut side by side for comparison.

According to them…

“This plug is bored to 58% greater volume. Greater volume and venting produces 2600 psi less pressure on the Op-Rod.”

They recommended this nut for shooters wanting to use heavy bullets in their M1A’s for hunting etc.

Pics I saw of the “overbored” nut looked EXACTLY like our Norc nuts from what I could tell, the pics of the original M1A nuts had way thicker walls and clearly less volume inside. I was seriously surprised at how thick the walls were on those standard M1A gas nuts, after only experiencing the Norc nuts. If I was a betting man, I’d say our stock Norc nuts would therefore also reduce Op-Rod pressure by at a similar amount to the “overbored” nuts from the pictures I’ve seen. That would make the pressure from 180gr full-powered loads about 1600 psi LOWER in our nocs than 150gr full powered loads in a U.S M1A. Interesting…

We’ve all also heard of fellows shooting commercial 308 ammo of an weight they can get their mitts on, in their Norc M14’s. I’ve personally never heard any first hand accounts of any damage from this. Have any of you fellows?

So. Even if U.S M1A rifles can’t handle heavier loads, are we SURE that this also applies to our Norcs? Anyone actually snapped their Op-Rods with 180’s, or been there when somebody else did it?

I’m not saying I’m convinced the “no heavy bullets” thing is a myth, but I’m personally not seeing any real evidence of it causing problems in the Norcs. And I’m seeing some things that have me seriously questioning it. Could this just be a much-repeated rumour that we inherited from U.S rifles, that doesn’t actually apply to our Chinese ones?
 
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Hmmmmm. Some stuff to ponder.
My recommendations come from a clear understanding of the amorers literature on what bullet weights the rifle was designed for. The design parameters were established, I'm guessing, around availlable military ammo of the period. Not sure if the design tested hand loadings or loadings not in standard military offering.
This a thought provoking thread. The assumption is that 180's are hard on the rifle and that assumption is based on the armorer and designers recommendations.
What I would suggest is that those wanting to brave the 180's on a regular basis, install an NM "grooved" piston from Sadlak. Mike Sadlak does his homework and this piston is specifically designed for bullet weights exceeding design limitations.
I'd love to hear what Hungry has to say on this recurring topic.
 
M14Doctor said:
Hmmmmm. Some stuff to ponder.
My recommendations come from a clear understanding of the amorers literature on what bullet weights the rifle was designed for. The design parameters were established, I'm guessing, around availlable military ammo of the period. Not sure if the design tested hand loadings or loadings not in standard military offering.
This a thought provoking thread. The assumption is that 180's are hard on the rifle and that assumption is based on the armorer and designers recommendations.
What I would suggest is that those wanting to brave the 180's on a regular basis, install an NM "grooved" piston from Sadlak. Mike Sadlak does his homework and this piston is specifically designed for bullet weights exceeding design limitations.
I'd love to hear what Hungry has to say on this recurring topic.
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What I've personally done for shooting 180's (got a great deal on a bunch of Win bulk PP's) is this. I drilled out that extra Norc gas nut I bought from you with a 1/16th hole out through the end and tried it with full powered 180gr loads (180gr win PP, 44.0 gr IMR 4895). Well, 1/16th was too big a hole and the rifle only cycle 50% of the time. I re-filled the hole with JB weld and redrilled with 1/32" and the rifle cycles smoothly, but with noteceably less slamming that with factory 150's. It cycles reliably, but just.

So, I believe that an easy fix to shoot 180's in a Norc (if a fellow is worried) is to simply drill out your gas nut with a commonly available 1/32" bit and you're done.

Really, that doesn't address the basic question of do these Norcs actually need ANY mods at all to shoot heavy bullets, though.
 
grizzly416 said:
would min loads with fast powders work with 180gr
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If you're asking me about the 1/32" hole thing, honestly I'm not sure. My loads were very near listed max (listed max for IMR 4895 loads are compressed and I don't like that, so I go with whatever the max is that is not compressed). Factory loadings for 308 win are actually fairly near max, in my experience, as this is a modern cartridge. I'd bet factory 180's would work fine with my modifications. Can't speak for near minimum loads as I never load that way myself!;)
 
The correct question to ask is not what the chamber pressure is, but rather what the pressure at the gas port is.

My prediction is that if you were to glue a strain gauge as close as possible to the gas port of an M14, you would find that given equal chamber pressures, the heavier bullet load would tend to give higher port pressures. The heavier bullet has greater inertia and generally a longer bearing surface and thus resists being accelerated to a greater extent than a lighter one. This means that the pressure will drop off from peak chamber pressure at a lower rate than with the light bullet.

A higher port pressure will still be harder on the gas system, even if the port is only open for an instant, because the gas pressure will accelerate the piston more rapidly and thus strike the operating rod more forcefully during the brief period that the port is open to the barrel and not closed off by the piston.
 
Man I love this thread. It's got me leafing through my manuals re reading all the stuff on port pressures and bullet weights. Good stuff.
Coincidentally, I have been working on paper and have nearly completed a piece on understanding the M14 Gas System. Nothing I post will be my thoughts on this, all info will be from proven sources.
I'll post it up in next couple days.
 
The 175 gr Sierra MK's were found to batter and then break the op rods of the USMC Teams back in 1997. Nothing fancy, just lots of beating up of the op rods. :rolleyes:

This is old information! This is not a recent discovery. Then in 1997, the US Army AMTU beat the Marine Teams at Camp Perry with the M16A2's. The USMC abandoned the M14 platform the next year. I've got the book downstairs, John Feamster's book : Black Magic: The Ultra Accurate AR-15 (Paperback) everything is a royal mess from my last move. ;)

Hope this helps,

Barney
 
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Hungry said:
The 175 gr Sierra MK's were found to batter and then break the op rods of the USMC Teams back in 1997. Nothing fancy, just lots of beating up of the op rods. :rolleyes:

This is old information! This is not a recent discovery. Then in 1997, the US Army AMTU beat the Marine Teams at Camp Perry with the M16A2's. The USMC abandoned the M14 platform the next year. I've got the book downstairs, John Feamster's book : Black Magic: The Ultra Accurate AR-15 (Paperback) everything is a royal mess from my last move. ;)

Hope this helps,

Barney
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Why do you need to bring us down with all these facts Hungry??? :D:(
 
Once the gas piston breaks contact with the op rod, the only resistance is the recoil spring, the friction of the op rod/bolt system, and extracting the brass. None of that changes regardless of the load being used.

Using a (considerably) heavier piece of brass would have an effect on the op rod, stressing where it doglegs to the side to come out from under the barrel, but that's a pretty beefy area. It would appear that the only possible weak spots would be the retainer tang, and possibly (as a stretch) the dogleg, both only being damaged or worn by lateral movement.

Alternatively, assuming there is no possible way to safely shoot heavier bullets, and dropping any relevant argument to the contrary, two modifications could be:

1: Stretch the factory spring (or buy a stiffer one) to slow down the op rod.
2: Create a detent to rotate the gas selector only partially.

Both would of course involve a lot of testing for either spring resistance, or gas selector position, but would be very functional, and easy mods to accomplish.

But I am still running with the original argument.......;)
 
archie_james_c said:
Why do you need to bring us down with all these facts Hungry??? :D:(
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b/c there/s still a lot of dealers willing to flog 180 bullets to a whole new generation of m14 owners( basically anybody with a norc after 1990 or so) that haven't taken the time to READ up on the m14 and it's action, or didn't have it drilled into them at basic- i'll fully admit hungry et al have taught me a few things too, and i was through the system- let's face it, you shoot what you're issued, and the mods used by the camp perry boys never come up for the average soldier- also when the m14 was issued, everybody had a 308/7.62x51 of some sort,and everybody used the 147 grain bullet- it was the r&d guys that got us shooting 173s in country( lake city m118)back in the early 70's - and an awful lot of us like the 180 for evrything, and are of the mind b/c it's a 308win, it SHOULD take all 308 loads- well, just like it's GARAND forefathers, it CAN'T- while nobody discusses it, the other end of the spectrum does just as poorly- under 147s, i've found misfeeds, short strokes, light firing pin strikes and a bunch of other stuff even though i've stepped up the powder to compensate for the lighter bullet-
question: HAS ANYONE GOT DATA ON FEEDING 180'S AND HEAVIER THROUGH SOMETHING LIKE AN FN OR G3?- do they suffer the same way?
 
A little girl and her mom are baking bread. They knead the dough, roll it into what starts to look like a loaf, and the mom puts it on the cookie sheet. She takes a knife and cuts about 2" off of each end.

The little girl asks "Mom, how come you cut the ends off the loaf of bread before you bake it?"

Mom replies "Ohhh, that is a great question. You should go ask you grandmother that"

Girl goes to grandma later that day "Gramma, how come when you are baking bread, you have to cut the ends off?"

Grandma replies "Well you just have to or it won't work. My mother showed me to do that when I was a little girl"

So the little girl takes it upon herself to ask Great Grandma "Why do you cut the ends off the loaf of bread when you bake?"

Grandma replies "Because your great grandfather and I got a really small bread box for our wedding in 1912, and a whole loaf of bread would not fit. I don't know why the hell everyone else does it though."
 
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