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Link Posted: 8/15/2017 4:51:08 PM EST
[#1]
I'll have to bite the bullet (pun intended) and buy some factory ammo. I don't think that is a ridiculous idea whatsoever, even though I wince thinking about it lol.

I didn't realize Varget and 4064 were so similar, but even according to Hodgdon's data today, the max 4064 load is .1 grain less than Varget. .5 grs less 4064 at the min load though. Similar enough velocities at either end to be the considered the same results however.

Of the two loads that are apparently extra strength, the 130 is the one that shows the LEAST pressure signs out of all four loads I listed. Not saying it's safe, just that it seems odd that that one is theoretically as bad or worse than three others, but shows much less signs of pressure.

This rifle is chambered in 7.62x51.
fnh
Link Posted: 8/15/2017 5:01:49 PM EST
[#2]
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Quoted:
This rifle is chambered in 7.62x51.
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Ouch.  That's 60191psi max then.
Link Posted: 8/15/2017 10:44:36 PM EST
[#3]
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Quoted:

Ouch.  That's 60191psi max then.
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Which means nothing. The difference between .308 Win and 7.62x51 has been covered so many times it's truly comical. They were measured with two different standards but for all intents and purposes there really no different.

I don't know about M14s but my M1A can shoot ANY commercial .308 Win or NATO speck ammo. M1A's do not have port pressure sensitivity like the Garand does.

I can't help but to think of the newbe that may find this thread a think 1 or 2 grains over maximum is a proof load.

A proof load in a .308 or 7.62x51 is at least 75000 psi. Not to encourage anyone but the rifle has to be able to safety function at proof pressure too. Not just one shot to see if it can take it. This is the built in safety margin.

I never suggested that machine gun brass was in any way not good. I simply suggested that "maybe" in this one instance that it was shot in a very loose chamber.

If this was my rifle I would take a fired casing that will not chamber and size it a little at a time until the bolt will just close.

Then I would use this casing as a reference and measure the head space with a tool like the Hornady head space comparator.

Then measure some of the unfired or fully re-sized brass and compare the numbers. While your at it do some diameter measurement comparisons too.

Head separations are caused by excessively worked brass. Taking these measurements will go a long ways to solving your problem.

Motor
Link Posted: 8/16/2017 6:34:55 PM EST
[#4]
What Motor said is correct. The military uses the copper crusher method for recording/testing pressure. 52,000 c.u.p. (copper units of pressure) is approximately 60,000 psi. on the piezo electric transducer method more commonly used in the modern commercial sector. The difference between SAAMI .308 and 7.62x51mm is around 2000 psi. In other words around .5 grain of powder. Swapping primers from Winchester or Federal (the hottest) to CCI-200, CCI-250 or Remington 9.5's (the coolest) will reduce pressure close to 6000 to 7500 psi. That's equal to 2.0 grains of powder or more. Both measurement systems are accurate and useful, but need to be talked about separately.

This is why so many people have such different results when load testing. A person using the data I posted earlier (which was created using Winchester standard large rifle primers) and substituting one of the three milder primers I just mentioned (or Russian primers) will discover lower pressures and lower velocities when fired from their rifles. This is perfectly normal and safe.

This is also why some people get away with using 41.5 grains of H4895 in Lake City brass and 168 grain SMK's. They are using a softer flamed primer. It has less oomph when it ignites allowing the case to handle the larger powder charge. Using that much powder with Winchester standard large rifle primers will put you over 60,000 psi., way over. Many US military sniper rounds will test slightly over 55,000 c.u.p. This translates to close to 63,500 +/- under the psi scale. These loads are HOT and over SAAMI maximum, but not dangerously so.

There is wiggle room and loads that are slightly over maximum will not ruin you or the firearm. They are harder on the brass and rifle, but won't cause a catastrophic failure. The problems occur when people are already at the limit and then switch components that put them way over.  Flat primers, sticky bolt lift, ripped case rims, extruded or even pierced primers are warning signs that you're probably over 70,000 psi, not just 60,000. I have become more conservative in my loading practices over time and have used much of what I learned to stay that way.

I like to work up initial loads using hotter primers. This pretty much insures that I'll be safe when substituting a different brand. I like to develop my match loads using milder primers because I have found them to usually give better accuracy. I have steered clear of ball powders over the last fifteen plus years not because they don't work, but because I usually find more accurate loads over a wider charge weight when using single base extruded powders. They seem easier to work with, don't require exact powder charges to shoot well and are pretty much indifferent to high temperatures.

Some rifles simply do not like particular powders and primers in combination. If it doesn't look promising it probably isn't. I don't waste time trying to get a bad load shooting better. I prefer to work on getting a good load shooting great.
Link Posted: 8/16/2017 7:05:27 PM EST
[#5]
Here is the text of MIL-C-46931F (dated 31 March 1989), the MIL-SPEC for the M80 7.62 NATO round, on chamber pressure:
3.7.1 Chamber pressure. The chamber pressure measurement shall be performed by either the copper-crush cylinder or EPVAT test method. However, the test method employed shall be recorded on the test results.

3.7.1.1 Chamber pressure measurement at 70° F by copper- crush cylinder test method. The average chamber pressure of the sample cartridges conditioned at 700F shall not exceed 50,000 pounds per square inch (psi). The average chamber pressure plus three standard deviations of chamber pressure shall not exceed 55,000 psi. The chamber pressure of an individual sample cartridge shall not exceed 55,000 psi.

3.7.1.2 Chamber pressure measurement at 70°F by EPVAT test method. The average chamber pressure of the sample cartridges conditioned at 70°F shall not exceed 365 MegaPascals (MPa) (52,940 psi) . The average chamber pressure plus three standard deviations of the chamber pressure shall not exceed 400 MPa (58,016 psi).  The chamber pressure of an individual sample cartridge shall not exceed 400 MPa (58,016 psi).
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Note that BOTH testing methods are approved and have specific limits which are different from each other based on the method.  Piezo testing (meeting NATO testing standards) gives a maximum average pressure of 52,940 psi.  STANAG 2310 calls for a maximum chamber pressure of 380 MPa (15 MPa greater than the SPEC above), while accepting copper crush test values of 50,000 psi (copper) (which is referred to as the USA method in the 1976 version of the STANAG).

I think we need to step away from the old "you cannot compare the two systems" and start looking at NATO requirements based on piezo methods, since SAAMI has adopted this method as well.  SAAMI's maximum (piezo) chamber pressure is 62,000 psi, which is not quite 10,000 psi greater than the NATO maximum pressure.

So yes, we can compare military and sporting ammunition pressure requirements between .308 Winchester and 7.62 NATO.  What we really need to do with that comparison is ask weapons makers whether their guns are up to the commercial pressure maxima even if they mark their barrels "7.62 NATO."  I'm fairly sure that guns built for the US market are built to handle commercial pressures.  That would include M1As, unless I am totally off.
Link Posted: 8/16/2017 8:21:58 PM EST
[#6]
NATO standard average pressure for 7.62x51 mm using the piezo electric measurement system is 61,190 psi. This is only 1810 psi lower than SAAMI .308 pressures.
Link Posted: 8/17/2017 1:15:42 AM EST
[#7]
GHPorter no you are not totally off in fact you are spot on.

In fact chamber pressure was and isn't an issue with either the M1A or the Garand either one is well capable of shooting maximum loads. It's the gas port pressure that restricts the Garand.

If you were to block off the Garand's gas port (making it a manual loader) you can safely shoot any ammo that you could in a bolt action.

Some guys modify the Garand's gas system with an adjustable device and do in fact shoot the slow burn rate powders.

Well we've gotten some what off topic but this all reverts back to what someone posted a few posts back. There's more going on with the OP'S rifle than the loads being a little too hot if in fact they even are.

If you go back and carefully look at the symptoms most if not all are symptoms of excessive head space. Either the ammo is too short or the chamber is too long.

Yes it very well could be other things or a combination. The only way to find out is to start a systematic inspection of everything.

Motor
Link Posted: 8/17/2017 6:36:24 PM EST
[#8]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Well we've gotten some what off topic but this all reverts back to what someone posted a few posts back. There's more going on with the OP'S rifle than the loads being a little too hot if in fact they even are.
Motor
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My thoughts exactly.  SAAMI allowable pressures are only slightly higher than NATO allowable pressures, and given the state of both weapon design and metallurgy, I can't see a reason to not make a rifle robust enough to handle the slightly higher pressure.

While LC (and presumably some other GI cases) are made thicker, as long as you take that into account (based on, I don't know, zillions of pages of real life experimentation and experience), you shouldn't have real issues with any load in any .308 or 7.62 rifle.

So even if those loads are a little warm for the OP's rifle, WHY are they warm when the load data seem to suggest that they should be fine?
Link Posted: 8/22/2017 11:20:30 AM EST
[#9]
How long before threads get locked?

Don't want this one to get locked before I get to shoot some of the FGMM. I need to get some, then try to find time to put a round or two through it.

I would *assume* if the case looks terrible, velocity isn't going to be quite so important to measure, as something else is going on? Only reason I'm asking is that I can shoot rounds through the gun pretty easily, but running across the chronograph will take much more time.
Link Posted: 8/22/2017 11:31:04 AM EST
[#10]
Link Posted: 8/22/2017 12:55:46 PM EST
[#11]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
How long before threads get locked?

Don't want this one to get locked before I get to shoot some of the FGMM. I need to get some, then try to find time to put a round or two through it.

I would *assume* if the case looks terrible, velocity isn't going to be quite so important to measure, as something else is going on? Only reason I'm asking is that I can shoot rounds through the gun pretty easily, but running across the chronograph will take much more time.
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If your brass looks the same as your reloads then I'd call DPMS for an RMA.
Link Posted: 8/22/2017 3:16:10 PM EST
[#12]
I did mean archives, apologies.
Link Posted: 8/22/2017 4:47:58 PM EST
[#13]
Link Posted: 8/23/2017 6:44:14 AM EST
[#14]
Tried once fired machine gun brass, once.  It came unsized and took 2 sizing's to get it to function.  All that work for one load and the separation ring showed. Never bought once fired military 308 again. Every single gun is different, including full autos.  Might want to check into better brass.

Good move to at least try some factory rounds, to give you a baseline.  From 16 in ar-10, standard 155 gn surplus military ball drops to slightly less than 2600 fps.  If you are getting more than 2750 fps with 125 gn loads, you best be careful.

One thing that may not have been previously mentioned is your handloading procedure.  When trying the lighter than 150 grainers in 16 incher, the bullets were pulling, not setting back.  Would load dummy rounds of what ever bullet/procedure you are using, measure col and shoulder datum, load dummy round in mag and release bolt from fully locked back.  Then measure again to learn if anything changed.  Would also do this with the factory round, being careful.  Every rifle is different, and helps to know your chamber.

Might want to check for case head swipe, which seems fairly common in 16 in ar-10 style. If it's there, may indicate timing issue.

Mine 16 inch has 1:10 twist, and simply won't shoot anything less than 160 grainers accurately enough to bother with. Have not tried anything heavier than 175 grains, and ain't planning on it.
Link Posted: 8/23/2017 7:40:13 AM EST
[#15]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Tried once fired machine gun brass, once.  It came unsized and took 2 sizing's to get it to function.  All that work for one load and the separation ring showed. Never bought once fired military 308 again. Every single gun is different, including full autos.  Might want to check into better brass.

Good move to at least try some factory rounds, to give you a baseline.  From 16 in ar-10, standard 155 gn surplus military ball drops to slightly less than 2600 fps.  If you are getting more than 2750 fps with 125 gn loads, you best be careful.

One thing that may not have been previously mentioned is your handloading procedure.  When trying the lighter than 150 grainers in 16 incher, the bullets were pulling, not setting back.  Would load dummy rounds of what ever bullet/procedure you are using, measure col and shoulder datum, load dummy round in mag and release bolt from fully locked back.  Then measure again to learn if anything changed.  Would also do this with the factory round, being careful.  Every rifle is different, and helps to know your chamber.

Might want to check for case head swipe, which seems fairly common in 16 in ar-10 style. If it's there, may indicate timing issue.

Mine 16 inch has 1:10 twist, and simply won't shoot anything less than 160 grainers accurately enough to bother with. Have not tried anything heavier than 175 grains, and ain't planning on it.
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I shoot a lot of LC 7.62x51 brass.

I actually buy it on 40lb lots. The trick is to get a Redding small body resizer, works the first time everytime.
Link Posted: 8/23/2017 8:57:22 AM EST
[#16]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
Tried once fired machine gun brass, once.  It came unsized and took 2 sizing's to get it to function.  All that work for one load and the separation ring showed. Never bought once fired military 308 again. Every single gun is different, including full autos.  Might want to check into better brass.

Good move to at least try some factory rounds, to give you a baseline.  From 16 in ar-10, standard 155 gn surplus military ball drops to slightly less than 2600 fps.  If you are getting more than 2750 fps with 125 gn loads, you best be careful.

One thing that may not have been previously mentioned is your handloading procedure.  When trying the lighter than 150 grainers in 16 incher, the bullets were pulling, not setting back.  Would load dummy rounds of what ever bullet/procedure you are using, measure col and shoulder datum, load dummy round in mag and release bolt from fully locked back.  Then measure again to learn if anything changed.  Would also do this with the factory round, being careful.  Every rifle is different, and helps to know your chamber.

Might want to check for case head swipe, which seems fairly common in 16 in ar-10 style. If it's there, may indicate timing issue.

Mine 16 inch has 1:10 twist, and simply won't shoot anything less than 160 grainers accurately enough to bother with. Have not tried anything heavier than 175 grains, and ain't planning on it.
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7.62 brass is fine OP has some other problem.
Link Posted: 8/23/2017 10:45:34 AM EST
[#17]
Military 7.62mm chambers can be, and usually are considerably longer headspaced than commercial .308. Combined with the violent extraction process and you end up with these issues.

If you want brand new military brass that's virtually identical to Lake City buy some IMI Match from Widener's Reloading Supply. At $295.00 per 1000 you can't go wrong. This is my first pick when loading .308 semi-auto rifles.
Link Posted: 8/23/2017 3:41:42 PM EST
[#18]
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Quoted:
Military 7.62mm chambers can be, and usually are considerably longer headspaced than commercial .308. Combined with the violent extraction process and you end up with these issues.

If you want brand new military brass that's virtually identical to Lake City buy some IMI Match from Widener's Reloading Supply. At $295.00 per 1000 you can't go wrong. This is my first pick when loading .308 semi-auto rifles.
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Cite?  Has not been my experience in resizing well over 8000 rnds of 7.62 brass over the past decade.
Link Posted: 8/23/2017 5:32:41 PM EST
[#19]
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Quoted:


Cite?  Has not been my experience in resizing well over 8000 rnds of 7.62 brass over the past decade.
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As part of another project, I just randomly checked the headspace dimension on 50 once-fired LC 11 cases that were definitely machinegun fired.  Link marks are a dead giveaway, and do not look at all like magazine lip marks.

Of the 50 cases, 44 had their headspace dimension within SAAMI specs of between 1.627" and 1.634", with the majority being between 1.630" and 1.632".  7.62 NATO specs allow for a headspace length of between 1.626" and 1.6232".  This random sample from 1200 cases had only 3 cases with a headspace dimension of greater than 1.634" - they were 1.637, 1.636 and 1.638 in order of discovery.  The remaining three cases were UNDER 1.627" - they ranged from 1.620 to 1.623".

Modern machinegun fired 7.62 brass will be fired almost exclusively in the M240 machinegun.  Unlike the (essentially) retired M60, the M240 does not destroy cases, nor do they grow excessively when fired in this gun.  YES, the headspace specs for the M240 are outside of SAAMI specs (1.625 - 1.640" as far as I can determine, versus 1.630 to 1.640" per SAAMI).  But (apparently) so what?  I do not believe that this is a real problem for handloaders buying modern once-fired GI brass.
Link Posted: 8/23/2017 5:47:51 PM EST
[#20]
Compare 7.62x51mm headspace dimensions vs. .308. Headspace that is acceptable for 7.62x51mm will fail a "field-gage" in .308. A .308 field gage is the dead end for the civilian owned rifle. That's when it needs to be removed from service. The military allows for a much longer chamber in their blueprints.

I have never had problems resizing brass fired from my M1-A's or AR-10's, however every piece of brass I brought back from Camp Perry in the 1980's and virtually all "once fired" sold as surplus is a wrestling match. Like posters have already mentioned, many times that brass had to be resized twice to get the dimensions I needed. The simple fact that so many individuals have had this experience when resizing 7.62mm "once fired" lends credence to my views.

When these specific "once fired" cases require much more effort to resize what has changed?
Link Posted: 8/23/2017 7:19:39 PM EST
[#21]
Diameter, usually.  Increased diameter can be an issue, even when shoulder location isn't.  Sometimes the diameter is a really big problem, particularly if the chamber the case was fired in is a bit oversized throughout.

I have also found that I need a LOT more lube to get these cases to size without hurting my shoulder.  I am not sure what's going on, since the ones I'm working on don't seem to be really blown out.  (Maybe I'm spoiled with 5.56mm and 9mm cases that take relatively little effort to size...)
Link Posted: 8/23/2017 11:46:37 PM EST
[#22]
Discussion ForumsJump to Quoted PostQuote History
Quoted:

As part of another project, I just randomly checked the headspace dimension on 50 once-fired LC 11 cases that were definitely machinegun fired.  Link marks are a dead giveaway, and do not look at all like magazine lip marks.

Of the 50 cases, 44 had their headspace dimension within SAAMI specs of between 1.627" and 1.634", with the majority being between 1.630" and 1.632".  7.62 NATO specs allow for a headspace length of between 1.626" and 1.6232".  This random sample from 1200 cases had only 3 cases with a headspace dimension of greater than 1.634" - they were 1.637, 1.636 and 1.638 in order of discovery.  The remaining three cases were UNDER 1.627" - they ranged from 1.620 to 1.623".

Modern machinegun fired 7.62 brass will be fired almost exclusively in the M240 machinegun.  Unlike the (essentially) retired M60, the M240 does not destroy cases, nor do they grow excessively when fired in this gun.  YES, the headspace specs for the M240 are outside of SAAMI specs (1.625 - 1.640" as far as I can determine, versus 1.630 to 1.640" per SAAMI).  But (apparently) so what?  I do not believe that this is a real problem for handloaders buying modern once-fired GI brass.
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Excellent post. This is exactly what I've found to be true outside of internet claims.
Link Posted: 8/24/2017 6:49:48 AM EST
[#23]
Can not speak to modern mg, have not used once fired military 308 in over a decade.  However am in possession of FAL with military chamber.  After firing standard round in this rifle, it must be small based to function properly in newer Rock River with tighter chamber.  Small based to size down base dia.  Like others have said, every rifle is different, and there is a plus and minus in specs.  Have 2 bolt target 308s that less shoulder datum than new brass, by .001-.002 inch.

The originator of this post certainly appears to have got some cases that were shot in something that allowed the case shoulder to stretch excessively.  That separation ring is a strong indicator.  Course there may be some that use the brass repeatedly, then sell it off.  This may show up at the rim.

Over the pasty decade, a lot of manufactures are making more accurate rifles, especially 223 and 308 ar's.  Apparently a lot of them incorporate tighter chamber dimensions to help with this.  There are no hard and fast "rules", you just adapt to what works for your specific situation.
Link Posted: 8/27/2017 3:17:54 AM EST
[#24]
Test fired the 168gr FGMM today.

While I couldn't chronograph it, the cartridge case and primer both look good. Much less evidence of pressure (what I'd consider "normal") compared to the loads I previously listed. I need to chronograph now, and see if the FGMM velocity is less than what I'm getting with my previous listed loads. I'm assuming it has to be, but I don't like assuming if I don't have to, and the chronograph will tell me.

I'm going to have to go back and look at some of my lighter loads, but I notice even on the FGMM the extractor is digging into the case rim enough to see it pretty easily. Making me wonder if these casings aren't really a bad idea to re-use (at least for important activities). I can imagine that in the unlikely event the rim lines up with the extractor the same way twice, it may tear the rim off. I've not taken the time to look at say, 5.56 that is once fired, but I assume it's not particularly normal to dig in a significant amount? Obviously on the "heavy" handloads, the bend in the rim was visible from the bottom where the metal creased, the FGMM is not that bad thankfully.
Link Posted: 8/27/2017 5:17:22 AM EST
[#25]
I've seen plenty of 5.56 with digs in the rim, very few visibly pull the rim back when observed from the side. Probably a combo of overgassed and snug headspace with those rifles.
Link Posted: 8/31/2017 2:00:45 PM EST
[#26]
Just to play around (since I now have a bunch of rounds I have to take apart) I took one of the 41.6gr 190 ABLR rounds and stretched it out to 2.96" and test fired. Noticeable reduction in pressure signs all around. Doesn't help me, way over mag length, and it's easier to just pull the bullets and load something that works, but for science.

I may also try another can of Varget. I got a sealed 8lb can a couple of years back I started taking powder from, but because I don't know how they were stored before I got them, I'm wondering if perhaps there is something off with the powder itself. It's not likely, but worth checking I figure.
Link Posted: 9/21/2017 12:07:02 PM EST
[#27]
Dredging this up, not really wanting to change the topic too much, but I like tinkering as much as most here I'm guessing...

Lengthening the gas system *should* reduce stress on brass, no? Toying with the idea of going with a longer barrel (if I can find one), but either way, thinking a longer gas system would be interesting to see what happens with loads that are apparently safe but showing some brass stress. Mainly stretch and heavy load on the extractor groove.

Not finding a whole lot of information on gas length that relates specific experience with the brass. There is some anecdotal info, but my thought are that a reduction in dwell time, coupled with more time for pressure to drop with the longer system, would make extraction easier.

I've got adjustable gas already, and I'm three clicks from fully closed, so there is definitely more than enough gas to work it as-is (16"/mid-length gas) Since I won't be asking the gun to digest all ammo out there, any finickyness that may come won't be of particular concern.
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