Art? Steve? M1A again...

[Edward429451]

Art & Steve, awhile back we discussed heavy bullets and powders for the M!A and the possibility of bending the op rod and such. Art explained time & pressure peaks and such, and Steve talked weights, IIRC.

I posted the same question on a different board and this other guy came up with a different answer than what I was told here so I thought I'd run this by you guys to see what you think, what I missed, where he's wrong, or right. OK? Heres his post:

With the m14/m1a you don't need to worry about bending your op rod. They are limited which means after the bullet passes the gas port in the barrel it vents into the piston where it builds pressure until it gets enough to work the action. Then the piston moves back and blocks the rest of the gas from entering the piston area. On the m1 Garand it continues to build until the bullet actually leaves the barrel. So if you shoot heavier than 165 regularly you can bend the op rod on a Garand, but not the m14. I did see a article on line somewhere about the m14 that said you would bend your op rod but he must have been confused or someone gave him bad info. Anyways if you wanted to make double extra sure you can shut off gas system (turn it to grenade mode) and shoot all you want. Well happy shootin' Shayne
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I can see what he's sayin, but would like to be very clear on this and I know you two guys are very well versed in the mechanics of the rifle and welcome your input. Thanks.

 

[Jon Coppenbarger]

I'am not steve or art but shot m1a's in matches from about 1984 to 1993
had witnessed them blow apart but have never seen a bent op rod not that it could not happen.

what we were always worried about was loading to hot for conditions and making a bomb out of the rifle so much at some matches we kept the ammo in a cooler in the summer.
when you are trying to push the envelope well!

 

[Steve Smith]

I know John Volk has bent plenty and has seen more bent...not to mention guns disassemble themselves.

JC121 liked the 180s but everyone else I know used 175s...I wouldn't go over the 180s that Jon used. I had good accuracy out of 175s for the very short time I used them.

BTW, I see what that guy is saying too. I THINK that a bent op rod is more likely to come from using a too-fast powder than from using a too-heavy bullet. Using a overly heavy bullet will tax your gun heavily, but a overly fast powder will peak too quickly, overcoming the "advantage" of the short gas system. Of course, a heavier bullet can effectively make a powder burn faster, (the bullet is moving slower) so you get the same effect. Stick with powders such as Varget, RL-15, and the old favorite IMR-4895 and bullets at 180 and less. Thousands have gone before you...heed their findings.

I have talked to some of the M14 "greats" and heard them talk about how you could hear the action "banging around" with those heavy 175 grain loads on a hot day...wow! When I was tinkering with an M1A I was plinking in comparison to what I do now...I never made a gun "bang aroud " like that!

 

[Jon Coppenbarger]

I had luck with my rifles but back when I shot I really only had the choice of 168 smk or the 180 smk's did not look at the hornady's after having inconsitant bullet weights with the hornady 168's I'am totally guessing that 175's are hornady but really not sure maybe there sierra? never tried them.
did start playing around with190 smk's right before I hung the m1a up in 93.
but I have the same problem today as I did back then.
I liked different loads at different ranges.
for me it was 168's at 200 and 180's at anything farther out.
but like alot of guys they like to use the same load all the way across and some day I hope to do that but its not in my near furture.

man I did see a few come apart in those days but never one of mine.

 

[Art Eatman]

To make the op-rod cycle, you need a force. It's the old Force = presure times area, where the area is that of the piston.

So: The higher the pressure behind the bullet, the greater the force on the op-rod.

It's less the weight of the bullet, then, than it is the pressure curve of a particular type of powder. Slower-burning powders maintain the pressure longer as the bullet travels down the barrel. With faster-burning powders, the pressure curve drops off more rapidly.

The amount of gas pressure to act on the piston for any powder also depends on the diameter of the gas port. Bigger hole, more pressure; smaller hole, less pressure. This is because the gas pressure goes to zero as the bullet exits the muzzle.

Unless you rework the diameter of the gas port, then, you're limited as to what you can do with an M1 or an M1A. You can shoot any weight of bullet you want, but you're limited as to how much powder of what sort you can use. I don't know about the M1A, but I have read that the M1 is designed for 2,000 psi at the port.

SFAIK,

Art

 

[Edward429451]

Thousands have gone before you...heed their findings.

Gotcha, Bear in mind here that while I've been shooting for decades and even reloading for just about as long, its only been with pistol rounds. Pistol cartridge reloading is fairly well cut & dried. Rifle cartridge reloading is not. So in actuallity I'm kind of a newbie to the rifle stuff, which I've only been doing for a couple three years now. I'm just trying to take all this in and put it all together in a way I can understand, and certainly bow to you guys superior experiance in this. If I ask a question that seems to suggest that you were incorrect about something, thats not me telling you that you were wrong, Thats me saying, Professor, I heard something that didnt mesh with what you taught me, and could you explain it for me again to try to bring in the loose ends of the picture I'm drawing..So dont take offense at my questions. If I thought you guys were wrong, I wouldnt come to you for advice! (I thought I caught the slightest hint of taking offense there somewhere)

That said, I think I'm getting it now. Shayne's not taking into account the powders, ignoring the pressure curve science and only thinking mechanics. I'm not looking to push the envelope as much as just looking for a general purpose load for all occasions or at least a way to use all those heavies up (better part of a 1000). I kinda wish they was all 168's at this point, cause I'm not likely to need to shoot past 200 anyway.

I had fairly good results with the 4895. Not spectacular but I'll keep tinkering with it and see what I can do. The 4064 was significantly better but hand weighing is a (small) drag (I still haven't chamfered the powder bar on the Dillon). I got some BLC-2 also and I'll have to finish it up before I go get more (RL-15 or Varget). I hope the BLC-2 does good cause it meters very precise. I just recently finished some 900-1000 55gr 223's, and every time I checked a charge, it was spooky right on the money with no variation at all. I expected some and didn't get any. Weird.

Anyway, Thanks. These threads are so much more fun than the L&P threads. I gotta learn to stay out of those threads! I very much appreciate you experts time and patience with my questions, and rest assured, I will heed your advice.

 

[Steve Smith]

I am NOT a professor NOR an Expert!

No offense taken!

 

[Edward429451]

Professor,

Aw, you're just being modest. Experts can't be self proclaimed, others must do it for them in recognition. So wear it!

 

[Steve Smith]

Just because the NRA calls me an "Expert" doesn't mean I go around pontificating. And I CAN be told things! lol!

BTW, JC121 is "Master Jon"

 

[Edward429451]

Steve Smith. Draftee to the office of "Pope of the M1A"

You'll need a cool tall hat.

 

[Steve Smith]

Nope...not enough experiece with that thing...Sven might come along soon, though.

 

[Ekie]

I don't have any experiance with the cast receiver M1A, but have heard many report from actual experiance that shooting 190 grain bullets can crack the cast receiver. Back "in the day" the 168 was the king, and I don't recall many shooting the 190s any who.

 

[Jon Coppenbarger]

man I just cheated back in those days as I had my m1a's built by the same guys who were winning national titles with them and with the rifles always came the best loads and while competing with all those guys we exchanged what each was doing and what worked for one guy and what did not work.

it was simple back then as we all shot either 4895 in about 80% of the rifles and a few of us went with 4064.

for short courses like reduced matches 4895 was my ticket and for across the course 4064 was all I shot the last 4 or 5 years I did it.
that was it and it was simple.
we always small based our brass checked every piece by dropping it into the chamber to see if it was sized right.
dropped our load in depending on the distance and temp. and popped a round in it and of to the races.

back then we even used mexican match some times if we were low on ammo and wanted to shoot a reduced course match.
nothing like a usgi ball ammo , we just pulled the tip and dropped in a 168 and off to th ematch.
please I'am not saying that is the thing to do but it happens

 

[Edward429451]

Whats Mexican Match? I've heard of it but never got the details.

 

[Steve Smith]

Match bullet in an otherwise gi cartridge. (gi primer, case, and powder)

 

[Grump]

My mentors called Mexican Match the stuff made from M118 173-gr Match ammo. Not many were doing it when "Special Ball" appeared. I suppose there's some small danger of high pressures if you do it with M80 ball, since your replacement bullet is also boat-tail (both have short bearing surfaces, so no "advantage" pressure-wise) but is 21 grains heavier.

INTERESTINGLY ENOUGH, an old NRA article on WW748 as a service rifle alternative (early 1980s) published port pressures for various loads, ranging from Sierra 150-gr MKs to the 190s. Guess which one had the highest port pressure, at 12,800 CUP? The 150-grain!

The M14 gas system is designed for 12,500, +/- 2,000, so there really was no problem.

Sure wish we could still get hard technical data like that.

As far as bending the op rod goes, I was VERY skeptical about being able to bend that short li'l ol' thang until I fired a round when the op rod was out of the disassembly notch. Interesting jam, reduced with the heel of the boot. But the op rod was bent where the skinny part alongside the receiver bends down to join the underbarrel tube. It was FAR easier to straighten out than I thought it should be!

But, I've also never heard a first-hand report of anyone even SEEING or having a personal acquaintance actually reporting a bent M1A op-rod.

 

[Art Eatman]

Grump, do you have that data reasonably handy? It would be interesting to have it for those folks loading for the Garand and the M1A.

What year and month is that issue?

Art

 

[Grump]

And the DATA says!

Contains some load data reportedly at SAAMI max. Use at your own risk, including the risk that the original source may be incorrect or misprinted, and that the person posting may not type so grate. YOU are the only one responsible!

From
C.E. Harris, _A Service Rifle Powder Alternative_, TAR, March 1984, pp. 35-35, 78.

Quoted and/or paraphrased under "fair use" educational and discussion purposes. Trust me. I'm a lawyer.

All data using Lake City Match brass, once-fired, WLR primers. Port pressure from a USGI port pressure gauge, breech pressure is CUP from SAAMI chambered test barrel, velocity at 15 feet (USGI velocities are at 78 feet).

Bullet---------------- Charge 748----Vel--------Breech-------Port
Sierra 150-gr MK-------- 45.5 -------- 2731 --- 42,600 -------- 12,830 (okay, I was off a bit)
Sierra 168-gr Int'l ------ 43.0 -------- 2587 --- 48,800 -------- 11,480
Lapua 170 FMJBT ------- 42.5 -------- 2535 --- 46,600 -------- 10,640
LC 173-gr M118 FMJBT - 42.5 MAX -- 2608 --- 52,400 -------- 11,350
Sierra 180-gr MK -------- 42.0 -------- 2569 --- 49,500 -------- 11,480
Lapua 185-gr FMJBT ---- 41.5 -------- 2470 --- 48,700 -------- 10,560
SIERRA 190-gr MK!! ---- 41.0 -------- 2450 --- 50,500 -------- 9,940

The SAAMI CUP breech pressure protocol uses undrilled cases, while the military standard uses drilled. This results in higher pressures recorded with SAAMI (more pressure build before the case blows out and impinges on the copper crusher) than with military tests.

If I remember correctly, the military pressure standards for 7.62 NATO is still lower than commercial SAAMI, though it may not be as much as the raw numbers might seem to indicate...

Strange now, isn't it--the lowest port pressures were with the heaviest bullets.

Too bad we don't have similar data with 4895, 4064, RL-15 and Varget, eh?:banghead:

These seven loads were tested from three barrels, plus "control" groups using Federal #308M and statistically average M118 (LC 77 Match, 2.4-inch mean radius at 600 yards = about 7.2-inch 10-round groups from heavy test barrel fixtures). All barrels were mounted on the same Rem 700 action, and differed slightly in their chamber/throat details. Only 3 of the 21 total load/barrel combos averaged less than 1 MOA, in 10 consecutive 5-round groups per combo.

edited for colums formatting

 

[Steve Smith]

Well, obviously that it with only one powder, and it does not take into account dwell time at that pressure. Years of field experiments show that the heavier bullets produce the failure, when the light bullets do not. Prehaps the dwell time is more of a factor than we would initially believe, OR in conjunction with the dwell time, the case may still be quite expanded, since the period with the highest pressure will be extended with a heavier bullet.

 

[Art Eatman]

The heavier bullet causes equal pressures for a smaller charge of powder. However, a smaller charge of powder produces a smaller total volume of gas. Since the volume of the barrel is a constant, the pressure of this smaller volume of gas is more quickly reduced as the bullet nears the muzzle.

, Art

 

[Steve Smith]

FWIW, I am happy to see a technical discussion here! I get bored with the "What bling do I need for my whatsits now?" threads!

 

[Edward429451]

So can it be reasonably assumed that different powders would act similarly or would that be a dumb assumption, b/c they're different powders and results could be anything until tested for sure.

I'm sticking to established loads until I clear this foggy issue up.

 

[Grump]

The 1984 NRA loads are established, using LC brass. Port pressure is no problem with 748, using 190-gr bullets, but you must also stay within the safe breech pressure limits.

No hot-rodding 190s past 2450 fps (15 feet instrumental) in .308 in an M1A using 748. In fact, those loads are arguably easier on the rifle than "standard" ammo.

Now that's easy, isn't it?

 

[Edward429451]

Yeah. Easy.

Anybody use 748? I never heard of it. Is it available?

 

[Steve Smith]

I've heard of that load, but 2450 is considered pretty soft for a long distance load.

Ed, oughtta be able to get 748 from Bartlett or hi-techammo.