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Old July 22, 2023, 12:51 PM   #26
nhyrum
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Originally Posted by Unclenick View Post
Nhyrum,



Does the bolt lock back after the last round and empty clip eject? Since the gun worked fine before you tore it down and reassembled it, I assume it does that, and this demonstrates there is nothing wrong with the gas cylinder, its spring, or the operating rod.



Locking back after clip ejection proves the bolt is moving back far enough to pick up a fresh round. It sounds to me like you installed a part upside down, which spoils the gun's ability to accelerate the magazine follower up fast enough to get a round in place for pickup before the bolt is already over the top of the magazine and heading back into battery. I know I did this once when I was new to the gun, but it was over forty years ago, and I've forgotten exactly how I did it. It may have been the little piece pinned into the operating rod catch assembly that I flipped over.



Yep. That's it. Looking at the blueprint, that part is called the accelerator and it helps accelerate the follower upward.
No, the bolt doesn't even go back far enough to eject a clip.

I really do think that I've just assembled it wrong, I'll look at it the manuals and make sure I get everything in correctly

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Old July 22, 2023, 04:24 PM   #27
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Edit:

I knew this had come up before. Here's a thread where a backward follower was a problem. However, reading the last post, it looks like the operating rod catch (drawing below) was not correctly oriented to have the hook clear properly, so he had a couple of issues you can check.


Edit, Edit:

For those curious about the accelerator issue, here's the gummint drawing showing its correct orientation in the operating rod catch:

Attached Images
File Type: gif Accelerator.gif (70.9 KB, 259 views)
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Old September 9, 2023, 10:11 PM   #28
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Sorry for taking forever, gun is a little buried.

I believe I have the accelerator in correctly.


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Old September 10, 2023, 06:12 AM   #29
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Yes

The parts in the picture are assembled correctly.
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Old September 10, 2023, 11:53 AM   #30
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The parts in the picture are assembled correctly.
Thanks. I'll check what @unclenick mentioned about making sure the op rod catch was clearing and set properly

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Old September 14, 2023, 12:20 PM   #31
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Screw the gas cylinder lock back on all the way and then just back it off enough to time at the 6:00 position. By backing it off 2 whole turns, it is blocking some of the barrel gas port hole, hence the short-stroking.

Jon
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Old September 14, 2023, 02:55 PM   #32
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Originally Posted by musketjon View Post
Screw the gas cylinder lock back on all the way and then just back it off enough to time at the 6:00 position. By backing it off 2 whole turns, it is blocking some of the barrel gas port hole, hence the short-stroking.



Jon
I initially had the problem with it screwed all the way in. With it screwed all the way in, from photos I shared, it appeared it was too far back. I've tried it all the way in (which is really more like very lightly torqued after making contact - like 5 degrees of rotation), backed off a turn, or backing off till it lines up again but not torqued, and backed off an additional turn

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Last edited by nhyrum; September 15, 2023 at 10:28 AM.
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Old May 31, 2024, 09:07 PM   #33
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Sorry to revive this thread, again. I don't get out to the range as often as I'd like. It's maybe once or twice a year instead of once or twice a week.

Took it out again today, but I bought some ppu m1 garand ammo, and she runs like a dream. Seems like it was an ammo issue

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Old June 1, 2024, 07:27 AM   #34
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Thanks for letting us know!
Feed back is good!
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Old June 1, 2024, 04:11 PM   #35
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Does it now run with the heavier of your 175-grain SMK loads and the M2 Ball loads? It should. Curious business.

You can, btw, use a bent paperclip to find the gas port and see how the gas cylinder is located under it. If it is packed with carbon, a 2 mm drill is closest to the hole size needed to clear it. The original hole drill was a custom size 0.0790 -0/+0.0015", but at 0.0787", the 2mm is close enough, is probably at your Ace Hardware and can be used to clean the carbon out.
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Old June 1, 2024, 09:33 PM   #36
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No, and it didn't cycle the vintage m2 ball I had either.

When I've had it apart, the gas port is clean, but I haven't checked size.

I don't have my load data I used for the 175's at hand, but I know I did venture above the m1 service rifle book data, simply because at Max it didn't cycle, and the published loading for the m72 is above max, at 48-50 grains imr 4895.

I think I'm going to go back and just duplicate the m2, 150 grain load, then fiddle with the finding something more accurate. Right now I just need to learn iron sights(both pistol and rifle) better, and I'm not really going to see much a difference, other than the wallet being lighter

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Old June 1, 2024, 10:04 PM   #37
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Originally Posted by nhyrum View Post
No, and it didn't cycle the vintage m2 ball I had either.

When I've had it apart, the gas port is clean, but I haven't checked size.

I don't have my load data I used for the 175's at hand, but I know I did venture above the m1 service rifle book data, simply because at Max it didn't cycle, and the published loading for the m72 is above max, at 48-50 grains imr 4895.

I think I'm going to go back and just duplicate the m2, 150 grain load, then fiddle with the finding something more accurate. Right now I just need to learn iron sights(both pistol and rifle) better, and I'm not really going to see much a difference, other than the wallet being lighter

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You have worn gas system parts.

My offer stands


I'll be glad to give it a full tech inspection if you want.

Also your match load information is too high. It was never loaded with 48-50gr of 4895.
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Old June 1, 2024, 10:13 PM   #38
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You have worn gas system parts.



My offer stands





I'll be glad to give it a full tech inspection if you want.



Also your match load information is too high. It was never loaded with 48-50gr of 4895.
I am starting to believe that to be the case. I'm just glad I didn't bend anything.

I'll send you a pm

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Old June 2, 2024, 11:01 AM   #39
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I thought, from the first post, the gun had run just fine until you disassembled and reassembled it. If so, the gas system won't suddenly go out of spec like that. It'll have a gradually increasing number of failures as it wears. Also, if you follow the reloading forum on the CMP website, you'll find folks getting good operation from loads much lighter than M2 Ball, while still others use vented gas plugs (similar effect to the loosening of the gas system) to bring down pressure for less vigorous operation, and still others have had new piston heads silver brazed onto their operating rods after having the old one cut off, shortening the rod and thereby increasing the volume the gas port is feeding, and the gun still runs. So, I am still suspicious something in your assembly is off.


Ammo:

The bulk IMR 4895 used by FA and Lake City for National Match ammo from the years 1957-1966 varied about 5% in burn rate based on the variation in charge weights they used during that period and the actual velocities they got over those years. If we take the load ranges Hodgdon posts for the 150-grain Nosler BT and the 175-grain SMK and use those bullets as surrogates for the 152 and 174.5-grain M2 and M1 Type (for M72) bullets, and we assume Hodgdon's loads are for the center values of current production IMR4895 burn rate, to produce M2 and M72 muzzle velocities would take charges of 47.6 and 47.5 grains of IMR4895, respectively, using those bullets as loaded by Hodgdon. They are remarkably close charge numbers, and, as you might guess, the heavier bullet load, with its slower exit speed, will provide the greater gas impulse to the gas cylinder, so you will get a harder shove on the gas system with the 175-grain load than with the 150-grain load.

One issue with these substitutions is the seating depth and bullet length differences are enough that the original M2 Ball bullet could have required another grain or so of powder. But that's a factor you can adjust for, as I will describe further down.

Note that 47.6 grains is below Hodgdon's starting load for the 150-grain bullet, but 47.5 grains is in the middle of their range for a 175-grain bullet, so the latter load should be backed down to 46 grains (Hodgdon's starting load) and worked up to that value.

A note on the muzzle velocities. The military traditionally measured these at 78 feet from the muzzle. In 1962, LC switched to 15 feet for M72 NM. I don't know whether the M2 standard was ever changed or not, but in 1962 LC was becoming more concerned with National Match ammunition accuracy performance and changed their test protocols some. I have worked backward from those numbers to get the following averages:

For M2 to run 2740 fps at 78 feet from the muzzle of a velocity and pressure (V&P) test barrel chambered with the powder back over the flash hole, as the military qualifies it, the equivalent velocity at 15 feet (where Hodgdon measures it per SAAMI procedure) would be 2790 fps. So, that's the number to use when adjusting Hodgdon's data for M2 velocity. (If you want to get really picky, take off one foot per second to 2789 fps to allow for the military numbers being for U.S. Army Standard Metro conditions and Hodgdon's being adjusted to an ICAO standard atmosphere.)

For M72, the 15-foot velocity would be 2680 fps.

Note that the Hodgdon data uses a Winchester case and Winchester primer. You might want to acquire a few of those particular items and some of the Nosler bullets and use the SMKs you have already and load them exactly as Hodgdon specifies, the same COL in particular. Set up with a chronograph and fire over it, handling the cartridges so the powder lays back against the flash hole. This will tell you what your gun's velocities are with that load, as compared to the Hodgdon V&P barrel, which will have much tighter chamber specs. You can then adjust your numbers proportionally. That is, if your gun gets 50 fps less than the Hodgdon V&P barrel did when you switch bullets and primers and COL around, that's the target velocity you want to hit with them fired the same way.

Pay attention to keeping the powder back. Testing with National Match ammo years ago, I found the difference between the powder being back over the flash hole (tipped the loaded rifle's muzzle up before slowly bringing it down level to fire) and having it forward in the case (tipped muzzle down before slowly bringing it up level to fire) was about 80 fps. It was also the difference between a noticeably flattened (though not excessively) and a rounded primer, I knew the pressure difference was following it at almost 7000 psi difference.

Also, note that the test gun does not have to be your Garand. The Hodgdon gun was not, and the military V&P barrel was not. A bolt rifle with positive feed makes it a little easier to keep powder oriented the way you want as you close the chamber. Just use the same ratio of your gun's velocity to the V&P barrel gun's velocity to get translated to your components and develop that load in the same gun.
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Old June 2, 2024, 10:20 PM   #40
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If you need a good grease for your M1 try one of these. They work great.



I need to get out and shoot mine soon.

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Old June 2, 2024, 10:49 PM   #41
nhyrum
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Quote:
Originally Posted by Unclenick View Post
I thought, from the first post, the gun had run just fine until you disassembled and reassembled it. If so, the gas system won't suddenly go out of spec like that. It'll have a gradually increasing number of failures as it wears. Also, if you follow the reloading forum on the CMP website, you'll find folks getting good operation from loads much lighter than M2 Ball, while still others use vented gas plugs (similar effect to the loosening of the gas system) to bring down pressure for less vigorous operation, and still others have had new piston heads silver brazed onto their operating rods after having the old one cut off, shortening the rod and thereby increasing the volume the gas port is feeding, and the gun still runs. So, I am still suspicious something in your assembly is off.





Ammo:



The bulk IMR 4895 used by FA and Lake City for National Match ammo from the years 1957-1966 varied about 5% in burn rate based on the variation in charge weights they used during that period and the actual velocities they got over those years. If we take the load ranges Hodgdon posts for the 150-grain Nosler BT and the 175-grain SMK and use those bullets as surrogates for the 152 and 174.5-grain M2 and M1 Type (for M72) bullets, and we assume Hodgdon's loads are for the center values of current production IMR4895 burn rate, to produce M2 and M72 muzzle velocities would take charges of 47.6 and 47.5 grains of IMR4895, respectively, using those bullets as loaded by Hodgdon. They are remarkably close charge numbers, and, as you might guess, the heavier bullet load, with its slower exit speed, will provide the greater gas impulse to the gas cylinder, so you will get a harder shove on the gas system with the 175-grain load than with the 150-grain load.



One issue with these substitutions is the seating depth and bullet length differences are enough that the original M2 Ball bullet could have required another grain or so of powder. But that's a factor you can adjust for, as I will describe further down.



Note that 47.6 grains is below Hodgdon's starting load for the 150-grain bullet, but 47.5 grains is in the middle of their range for a 175-grain bullet, so the latter load should be backed down to 46 grains (Hodgdon's starting load) and worked up to that value.



A note on the muzzle velocities. The military traditionally measured these at 78 feet from the muzzle. In 1962, LC switched to 15 feet for M72 NM. I don't know whether the M2 standard was ever changed or not, but in 1962 LC was becoming more concerned with National Match ammunition accuracy performance and changed their test protocols some. I have worked backward from those numbers to get the following averages:



For M2 to run 2740 fps at 78 feet from the muzzle of a velocity and pressure (V&P) test barrel chambered with the powder back over the flash hole, as the military qualifies it, the equivalent velocity at 15 feet (where Hodgdon measures it per SAAMI procedure) would be 2790 fps. So, that's the number to use when adjusting Hodgdon's data for M2 velocity. (If you want to get really picky, take off one foot per second to 2789 fps to allow for the military numbers being for U.S. Army Standard Metro conditions and Hodgdon's being adjusted to an ICAO standard atmosphere.)



For M72, the 15-foot velocity would be 2680 fps.



Note that the Hodgdon data uses a Winchester case and Winchester primer. You might want to acquire a few of those particular items and some of the Nosler bullets and use the SMKs you have already and load them exactly as Hodgdon specifies, the same COL in particular. Set up with a chronograph and fire over it, handling the cartridges so the powder lays back against the flash hole. This will tell you what your gun's velocities are with that load, as compared to the Hodgdon V&P barrel, which will have much tighter chamber specs. You can then adjust your numbers proportionally. That is, if your gun gets 50 fps less than the Hodgdon V&P barrel did when you switch bullets and primers and COL around, that's the target velocity you want to hit with them fired the same way.



Pay attention to keeping the powder back. Testing with National Match ammo years ago, I found the difference between the powder being back over the flash hole (tipped the loaded rifle's muzzle up before slowly bringing it down level to fire) and having it forward in the case (tipped muzzle down before slowly bringing it up level to fire) was about 80 fps. It was also the difference between a noticeably flattened (though not excessively) and a rounded primer, I knew the pressure difference was following it at almost 7000 psi difference.



Also, note that the test gun does not have to be your Garand. The Hodgdon gun was not, and the military V&P barrel was not. A bolt rifle with positive feed makes it a little easier to keep powder oriented the way you want as you close the chamber. Just use the same ratio of your gun's velocity to the V&P barrel gun's velocity to get translated to your components and develop that load in the same gun.
Yes, it started that way. I think what happened was a combination of good ammo, assembled wrong, then bad ammo, assembled right.

Powder with the burn rate appropriate to the garand are not anywhere near my normal powder. 9mm, 10mm, and a 454 casull handguns, a 300 bo and a 300 rum. And I loaded the ammo some time ago, and it was a time when loading supplies were near impossible to get, so I doubt I was able to acquire the correct powder.

But, now I have at least a good starting point. The rifle functions with factory ammo specific to the rifle. Once I get my bench set back up, I will start first with duplicating the factory m2 and verifying with a chronograph, since on all my range trips, the 9v battery was dead, because I'd buy a new battery after the last range trip, put it in to make sure the Chrono still worked, then put it away for near a year, and next time, dead. On to USB rechargeable batteries. That way I can see if my loads are producing the velocity they should, with the correct powder

hold on, let my dry my eyes, been a while since I've bought reloading supplies...

If those function, I'll maybe try some 168's. I don't have the 300 blackout anymore, and I don't think a 230 Berger would work well, so I'll have to buy bullets anyway, and 150's are still cheap.

I also have exhausted my confidence in my ability to get the rifle together any more correct. I've assembled it with 3 or 4 manuals and like started above, it functions with factory ammo, so it's together right enough. The problems with my load could be any combination of just the wrong enough powder and just the right amount of wear. I don't know, but at least I have a clean starting point. Having someone with the tools and expertise I don't have to measure and gauge everything, and maybe replace worn parts doesn't seem like a bad option.

Ive been using #2 red tacky grease. I want to say it works well, as others say, but who knows if maybe it's part of the issue

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Old June 3, 2024, 11:04 AM   #42
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Nyrhum,

Thanks for the clarification. It seems I wasn't following the stages of this evolution very well.

Yes, the wrong powders can be the whole issue. Fast powders hit their pressure peak before there is much expansion, so they peak in a smaller volume than the correct ones do, and that means you have to use an amount that makes too little gas, so the pressure has dropped too far by the time the bullet gets to the muzzle. If you use slow powders, they often burn incompletely unless the bullet is very heavy. The result is, again, low gas port pressure, plus a lot of unburned powder tossed out and sometimes driven into the gas port, partially obstructing it. Also, if you do get the slow powders to burn completely, they make more gas, which over-pressurizes the gas cylinder and drives the op-rod back too fast. I've watched videos of the op-rod speed shooting commercial ammo with heavy bullets and slower powders. It doesn't instantly destroy the gun or anything, but you can see the op-rod taking about 20% less time to get to the full counterbattery position. That is 20% less time or about 25% higher average op-rod velocity. The kinetic energy of the op-rod is proportional to the square of its velocity, so this is 156% of its normal KE, and KE is proportional to the force needed to stop its motion, so the battering of the frame and rod is 156% of normal. It's a good way to wear your gun and op-rod out faster.

This is a subject that causes confusion, but the op-rod normally sees something on the order of 500 lbs of force on the piston briefly at peak pressure. This drops rapidly because the piston isn't a very tight fit; plus, it starts moving backward, expanding the space the gas is in. That short, high-pressure application is analogous to a pitcher throwing a fastball. It puts enough velocity and inertia into the op-rod that it coasts through unlocking the bolt, extracting the casing, and compressing the op-rod spring. Imagine trying to push the op-rod handle hard enough over a length of a quarter to half an inch or so that it has enough speed to just coast the rest of the way through the cycle. That gives you a sense of what the op-rod has to put up with.

I've had good luck with the Everready lithium 9V batteries, but they are a tight fit in many spaces and run a little more voltage than most lithium. I've also been using rechargeables, but they run slightly low voltage, so your gizmo has to be cool with that. One advantage to lithium of either sort is its internal resistance is lower at low temperatures than the alkaline and carbon-zinc batteries have, so it prevents display fading in lower temperatures.

For lubrication, I've played with different approaches. The main thing you want to avoid is gun oil, as it warms up and spreads around and winds up not only in the bedding (if you have any) but also gets misted into your glasses. High-temperature, high-tack, and high-pressure greases are generally the way to go. This one from Slip2000 is good. I also want to try this one this stuff when it is available again.
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