7.62x51 NATO (.308 WCF) in the Springfield M1A

[geargnasher]

More range sessions to report, short version.

All loads are with IMR 4320, I have a bunch of it. That's forty-three twenty, not a typo. All shots fed from the magazine.

311041, 165-grain, out of a six-cavity Lee group buy mould, air cooled wheel weights....Still shooting 2" or less, repeatable round groups at 100 yards using 34 grains. 36 grains opened up the groups a bit, only shot ten one time and got about 3.5".

Lyman 311679, the John Ardito bullet. Mine drops at 209 grains with 3 clip-on 2 stick-on WW alloy. I water quenched these from the mould and today they tested 21 bhn with the Lee tool. Started at 33 grains, then 34, 35, and 36. The only thing that changed was the 36 grain load shot the smallest group at 4", the others hovered right around 5.5". The trend was clusters surrounded by flyers, mostly low-left strung flyers, could be me shooting lefty from a bipod, and these have more suds than the 311041s did and the rifle jumps a lot more.

I have no idea how fast these were going today, probably between 1900 and 2200, my Magneto Speed won't mount on the M1A unless I modify something or take off the flash hider. I only had one malfunction in 40 rounds with the 311679s, the nose didn't get pulled up high enough in the magazine and the bolt telescoped the round against the left feed ramp, looks like I need to de-nib that left nose feed tab in the magazine some more.

Gear

[fatelvis]

Thanks for the info Gear! Imr4320 huh? Sounds interesting! Does it burn clean using the 311041 34.0 grn load? Quickload says it should be moving about 1832fps.

[geargnasher]

FE, here's Bruce's data from post #34, I got 2126 average from a 24" bolt gun at 34 grains 4320 myself, but that's all I've actually checked.

In yesterday's episode, I found that while my starting-load selection with 4320 was right where I expected it be for velocities and pressures with the different bullets, the loads did NOT perform at all well as the charges were increased.

I therefore loaded three different bullet types with three incrementally-decreasing charges of 4320. The boolits were 311672, 311291, and 311467. The charges (of 4320) were 34.0, 32.0, and 30.0 grains, decreased from that starting load of yesterday, which was 36.0 grains.. I fired them in order of weight with each bullet...that is, I shot the 311291 loads in order from 30 to 32 to 34 grains, hoping to see any changes in behavior that might arise. I did see them, too.... The same order-of-fire was used with the other designs,as well.

Beginning with 311467, the 180 Loverin, the first round fired with 30.0 grains was over FOUR INCHES left of the point of aim. The next nine rounds were right in the x- and ten-ring of the 50-yd pistol center that I'm using at 50 yards (but folded in half to create a black semi-circle aiming mark). Velocity was 1816 fps average, 29 fps extreme spread, 9 fps std deviation. Group was 2.0"/9 rds/50 yds.... I didn't include the first round in the group measurement .

311467, 32.0 4320: 2000 av, 67 es, 18 sd...... and again, the FIRST round was fully four inches to the left of the group which developed in the x- and ten-rings! The remaining 9 rounds grouped 1.6".

311467, 32.0 4320: 2141 av, 63 es, 19 sd. All rounds landed within the so-called "group", which was 3.1"/10/50.

The flagrant straying of the first rounds absolutely mandates that I re-fire these loads with the addition of a dacron tuft. I strongly suspect that there's something going on with the powder positioning in the chambering of the first round, even though I just pull back the charging handle and release it to slam closed by itself. Since the same phenomenon repeated itself with 311291, although to a lesser degree, it may be that the powder is just on the edge of good burning, and the different positioning in the case might make the difference.

311291, the roundnose, illustrated clearly that yesterday's loads were driving too hard for its tastes.

311291, 30.0 4320: 1866 av, 95 es, 28 sd, 2.2"/10/50. The group was only 1/2" high, but spread pretty wide across the ten-ring.

same, 32.0 4320: 2055 av, 89 es, 27 sd, 3"/10/50.....just a loosely scattered group with nothing unusual about it.

same, 34.0 4320:2161 av, 124 es, 37 es...and a HORRIBLE 'group' (HA!), six- inches- plus in sprawl.

311672 did pretty well to begin with.

311672, 30. 0 4320: 1868 av, 79 es, 30 sd, 1.3"/10/50. Nice group, compared to some others!

same, 32.0 4320: 1976 av, 80 es, no sd reading, 1.6"/9/50... the tenth round was a flyer two inches out at 10:00, no explanation. It was called "good".

same, 34.0 4320: 2116 av, 116 es (high!), no sd reading, 2.5"/10/50....just a general loosening of the group as it neared the load levels from yesterday.

All rounds fired today functioned the rifle perfectly.

The Nevada zephyrs were out in force! It was so bad that I eventually found a BRICK (no kidding) which I used to dampen the flailing-around of my chronograph boom. I did this by duct-taping from the brick on the ground up to the outer end of the boom with considerable tension on the tape. I also had to run duct-tape from the boom just outside the rear doors of the van to the upwind side of the vehicle, to keep the boom from slewing violently down-wind in the gusts (I did this first, and added the brick rig later). The normal retaining notches were not up to the job in the gale.

I estimate the gusts at around 40 mph, and today was the first time I've felt the van actually moving very much in wind. It has a one-ton suspension, so it's pretty stiff. In the lulls which came occasionally, I'd sometimes fire three or four rounds in quick succession to take advantage of the condition. All the wind whistling through Der 'wagen kept barrel heat well under control. At only fifty yards, and with the wind mostly fish-tailing or quartering from behind, I don't believe it affected my results very much.

The learning process goes on....

Here's the deal with the 210 grain bullet and 4320: Port pressure starts to get real close to 12K psi right around 34 grains, and is past that by 36 grains, in the upper 13K range. I'd say that in an M1A 35 grains of 4320 should be considered maximum for the gas system behind that bullet weight. Problem is, 36 grains is right where the powder really starts to work correctly, and I think closer to 38 grains would be about right for the alloy I was using (3 coww 2 soww, water quenched), but the gas system can't take it. I don't have data on the lighter bullets, but this goes to show that the rule of NEVER running anything slower-burning than 4064 is a sound one, unless you're going to reduce it considerably, and reducing it enough to be safe for the gas system may put it below the ideal burn rate of the powder. I also think this factor is worse for the lighter bullets, as not as much energy is consumed early in the barrel and port pressure is likely higher with lighter bullets.

I'm planning to step up to 3031 and re-try the heavy 311679 bullets (they're listed at 196 grain, but mine are 211 with gas check), the rifle seems to like them. I also have a 160-ish grain bullet to try as well, I only messed with the Ardito bullet because I had the mould and the bullet fit the M1A throat and magazines very well, and fed very well.

Oh, and at 34 grains, the 4320 burned clean as a whistle, one of the really nice things about those IMR stick powders, they're clean even when charges are reduced a bit.

Gear

[geargnasher]

One more tidbit, 34 grains of 4320 calculates to 2008 fps MV with the 311679 from a 22" barrel.

Gear

[tomme boy]

Gear, please explain the port pressure for me. Wouldn't it be higher if it was a jacketed being shot?

[cbrick]

Trying to use BruceB's loads but that's kinda tough when ya have neither the molds or the powder he used. Viht N-140 is right close in burn rate to 4320 and is a short (very short) stick powder.

Here's the best the M1A has done for me so far, 4th time out with it. First time didn't count for nuthin, couldn't see either the open sights or the target. Put on a Nikon 9X, much better. Second outing I used the XCB bullet and 311365 with both 34.5 gr and 35.0 gr N-140. Not good, it did keep most shots on the 8 1/2 x 11 paper but . . .

Next time I tried the RCBS 180 SP with the same two powder charges and learned a big lesson with seating depth, while groups (using that term loosely) were better, not good.

Yesterday I used the RCBS 180 SP, 28.0 gr N-140 seated to 2.670" COAL. That's the group below. I have no real idea what the velocity might be with these reduced loads, cycling was flawless with all loads & bullets tried so far. I don't know if anything can be learned from how far and where it throws spent brass but it was in the same place with both 35 gr and with 28 gr.



7 shots in above target, the first three were on a different target and the spotter did not see the hits so figuring possibly low off target I moved to this higher target on the same backer board and printed this 7 shot group. Of the first three shots on the other target the first two were low (in fact in the bar code at low left) and one was in the middle of this group on this target. In effect this target is an 8 shot group. As a 10 shot group the first two were low by 3 1/2 inches. barrel was not cleaned since the last shooting. With the bore scope I can say that both the bore and the gas port are spotless. Not even powder soot.

The RCBS 180 SP's were cast, sized & lubed 6 years ago. Sized with a .311" Star die to .3105" with my alloy.
Brass sized in an RCBS small base F/L die & checked in a Wilson gage for fit.
Brass is Fed commercial.
CCI #34 primer. Primer pockets uniformed with the Sinclair tool and seated primers are .005" below flush as is recommended in the M1A with the free floating firing pin.
Lube - LBT Blue.

The RCBS 150 FP also shot yesterday at 30 gr didn't fair quite as well but not real bad. Worth further testing.

Not bragging groups but definitely headed in the right direction. I've got other bullets & powders to try yet but it's a start.

Rick

[geargnasher]

Gear, please explain the port pressure for me. Wouldn't it be higher if it was a jacketed being shot?

The gas port is about 12" or so down the barrel from the base of the bullet before firing. If the powder burns too slowly, it can carry too much pressure for the gas system at that point and damage the gun. Powders that are too fast peter out, even at maximum chamber pressure, before the gas carries to the port. That means there's an operating window we have to stay in, and it's max at 12" is 12,000psi per the design parameters of the gun. Too much below that and gas volume is too low to cycle the action. Forgive me if you already know this...

Second part, I really don't know. My suspicion is the pressure curve depends a good bit on how much energy the powder expends on engraving the bullet. I suppose, when I pony up and get my own software, I can run the numbers with a jacketed bullet instead and see what the QL folks already know that I don't. At these pressure levels, though, I'm going to wager that there isn't really that much difference either engraving or at the port or even muzzle between jacketed and WD cast of the same weight.

Gear

[tomme boy]

I know nothing about this rifle other than I want one but can't afford one. Have you tried Varget yet? I used to use a lot of the 4320 in 308. But Varget or rl15 always gave me better groups. 4320 was always top speed wise out the barrel, but I always found the other two would always give better accuracy. If the gun did not like Varget, it liked rl15. Or the other way around. This was for a bolt rifle so I don't know if the burn rate would be OK or not. It should be as they are a little faster than 4320.

[BruceB]

[QUOTE=tomme boy;3137650] Have you tried Varget yet? QUOTE

There have been numerous inquiries from people wondering about their own "pet" powders.

Look at a burn-rate chart!

There are literally scores of powders which would function in an M1A. It would be flatly impossible for one person to to work up loads for ALL of them, and even then the manufacturers keep adding new ones.

We have to take some careful steps on our own, or else wait for someone else to do the basic work.

In the case of Varget: find OTHER powders with near the same burning rate, and see which of them have been tried during this thread, or MAYBE in the Lyman cast handbook.

Then reduce the load somewhat, and begin from there.

One of the requirement s of loading cast bullets, in many situations, is a willingness to experiment within safe limits. Otherwise, we would be restricted to mostly-unsatisfactory information from published sources, and I INCLUDE the Lyman handbooks in that statement.

[BruceB]

Trying to use BruceB's loads but that's kinda tough when ya have neither the molds or the powder he used. Rick

The specific bullet designs used don't matter much from a pressure standpoint.

For example, I used the 311466 a lot, at about 150 grains.

ANY .30-caliber bullet of 150 grains +/- 10 grains will work safely with my starting data. Same applies to other weight brackets.... if the design is reasonably close to the weight i used, TRY IT!

As to the powders, select something with a burning rate close to the listed powder, reduce the charge a bit, and have at it. There's a lot of room before pressures get high, and the few cases where I generated higher pressures are clearly stated.

[tomme boy]

Bruce Varget is in the burn rate for the proper operating of the gun. That is why I was asking.

[BruceB]

Yes indeed, there's NO doubt in my mind that a Varget load can be found which will function the M1A perfectly.

It just happens to be one of those (many) powders that I haven't yet gotten around to using in ANY of the dozen-odd cartridges that I still load.

In spite of current scarcities, we really are privileged to have so many options in smokeless powder. It's particularly nice to discover that the M1A works well with an incredible number of powders with widely-varied burn rates.

[geargnasher]

Tomme, there are two upper limits and two lower limits to operate the M1A, and like Bruce says, LOTS of powders will work between them.

The upper limits are port pressure (12,000 PSI is what my research keeps turning up) and chamber pressure, which is whatever SAAMI says it is for the .308, or what your rifle tells you it can safely stand.

The lower limit for semi-auto function is whatever minimum port pressure will operate the action satisfactorily, and whatever minimum pressure will obturate the brass to the chamber so the chamber doesn't get all mucky with lube and powder residue in a short time and begin causing malfunctions.

Pistol/shotgun powders like Unique don't work because they burn too quickly and would exceed the chamber pressure limits long before you got enough of it in there to bring port pressure up enough to cycle the gun. Powders slower than 4064, like the 4320 Bruce and I both experimented with and the 4831 he used, will work, BUT the pressure stays higher, longer than is ideal and port pressure exceeds the 12K limit before enough powder can be used to get chamber pressure up to what the powder likes to burn at and what it takes to really obturate the brass. You can't load anything slower than 4064 to the maximum chamber pressure with typical weight bullets without seriously overpressuring the gas system and possibly cracking the receiver. That's why powders in the 4198 to 4064 rate are usually recommended, you can load them up to charge weights where they burn well without them burning too long and making too much port pressure. It's a matter of timing.

Varget falls in the range of plenty usable, and probably safe for the gas system unless you really start pushing the chamber pressure limits. It would be handy to have Quickload to give you an approximation of port pressure vs. charge weight, then you'd know where your upper limits are when you compare that to loading data for the equivalent weight jacketed bullet.

With something faster like 4198 or RX7, you'll reach maximum chamber pressure before you ever overpressure the port, so if you stick with published data all you have to do is find your accuracy point. Or if you have it, use the powder the rifle was built around: Some flavor of 4895.

Gear

[BruceB]

Tomme, there are two upper limits and two lower limits to operate the M1A, and like Bruce says, LOTS of powders will work between them.

The upper limits are port pressure (12,000 PSI is what my research keeps turning up) and chamber pressure limit for semi-auto function is whatever minimum port pressure will operate the BUT the pressure stays higher, longer than is ideal and port pressure exceeds the 12K limit before enough powder can be used to get chamber pressure up to what the powder likes to burn at and what it takes to really obturate the brass. You can't load anything slower than 4064 to the maximum chamber pressure with typical weight bullets without seriously overpressuring the gas system and possibly cracking the receiver.

With something faster like 4198 or RX7, you'll reach maximum chamber pressure before you ever overpressure the port, so if you stick with published data all you have to do is find your accuracy point. Or if you have it, use the powder the rifle was built around: Some flavor of 4895.

Gear

"Published Data"????

This whole thread was begun simply due to the woeful LACK of "published data". NOT a lack of data for the .308/7.62x51, but data for the M1A/M14 rifle SPECIFICALLY.

This matter of suitable powders was addressed quite early in the thread, and was re-visited throughout the course of the exercise.

THE RIFLE will decide what charges and powders will work. The actual PSI figures are immaterial, because either the rifle will work, or.... it won't.

IF the ejection pattern of a cast-bullet load is similar to the pattern derived from a "standard" jacketed load, then gas port pressure is also similar to that of the jacketed load. It doesn't matter WHAT powder is used, so long as port pressure is similar to that of the jacketed load or below, and as long as the chamber pressure is safe while delivering that port pressure.

We most certainly can and do run powders a lot slower than 4064.

Likewise, we can and do run powders a lot quicker than the 'medium burners'.

Also likewise, we can and do run bullets outside the 'normal' weight categories commonly accepted for the .308/7.62.

The 4831s and 4350s etc are generally considered too slow-burning for these rifles.... WITH JACKETED BULLETS. With cast bullets, these slow-burners work exceedingly well in the M1A, offering a longer pressure curve to keep port pressures high enough for good function, and chamber pressures low enough for gentle acceleration of the bullets

Don't confuse all the warnings about slow powder and JACKETED bullets in M1A rifles, with the way things work with CAST bullets.

My M1A, the "test-bed" for this whole thread, functions perfectly with powders as 'slow' as H4831 all the way down to XMP5744 in the fast-burners.... PERFECTLY, meaning good accuracy, decent brass life, 100% mechanical function, and so on.

My rifle has fired roughly 7000 cast-bullet rounds, and shows absolutely zero bad effects from this marathon.

The 4831s can leave more crud on brass or in the rifle (not the bore) , but they do work and work well. Given a choice, I find IMR 4831 and 4350 run a bit cleaner than the "H" version of 4831. Operating pressures are safe in all regards, as long as normal due care is taken. There is no risk of receiver or op-rod damage with proper loads of the slow powders.

This rifle design, for a cast-bullet shooter, is amazingly flexible and rewarding. Without bragging too much (I hope), THIS THREAD now constitutes the "published data" for cast bullets in M1A rifles. The various handbooks are pathetically inadequate in dealing with this subject.

[tomme boy]

So with Quickload, we can estimate the PSI at a certain spot in the barrel?

So the engraving of the bullet is what seems to be changing the speed of the powder? On how it burns? Comparing jacketed to lead. The jacketed increases the peak PSI sooner and burns up more powder faster? And that same powder with lead would burn longer and the peak would be right at the port????

I am just trying to understand how the powders are reacting for this platform. So do they make a adjustable gas port so if you found that a certain faster powder in the mid range burn rates has a lower chamber psi but a high port psi could be dialed down to make work better?

I am not trying to argue. I want to understand what can be done with this.

[cbrick]

I started with N-140 mostly because I have it. Second that it is the same burn rate as 4320, Varget, RL 15 & 2520. Burns very clean even when reduced. I've gone as high as 35 gr and as low as 28 gr. Tried 4 different bullets from 150 to 188 gr. Haven't found a load that didn't cycle the action perfectly or a bullet yet that didn't cycle & feed perfectly.

I've got about 12 30 cal molds but unfortunately none match up with Bruces. Anybody have any idea how many 30 cal molds there are? Wow. A guy could have 100 30 cal molds and not have nearly all of them. I've got a SAECO 160 I want to try and a few others. Want to try the MP 180 silhouette bullet, I don't have that but this morning winelover said I could borrow his.

Popper posted some 308 N-140 loads (not an M1A) in another thread and results looked good, I looked briefly for that thread and haven't found it yet. Wanna see what bullet he used (maybe I have it) and at what starting charges, the best I've gotten so far is with very reduced charges and the RCBS 180 SP, a bore rider seated very deep.

I've been using civilian brass but yesterday 500 mixed headstamp once fired military cases showed up from Monmouth Brass, a member here. I bet you all are jealous that I get to deal with all those primer crimps, primer pockets and brass prep.

Life would be so much simpler and cheaper if only I didn't like to jerk on a trigger quite so much.

Rick

[geargnasher]

Rick, check the pockets before you even set up your swager, all the wcc08 I just got from them had pockets identical to commercial, only needed depth uniforming.

Bruce, jacketed published data. I was explaining to Tomme that you can go with a jacketed book max of RX7 with an equivalent cast bullet and not be over pressure for the port. If you're comfortable judging port pressure by ejection patterns, fine, but I am not now that I've seen some QL numbers for some of the slower powders, even at 6-8 grains below starting jacketed loads from published sources. There's a reason not to go slow, you have to keep loads reduced down to the "no data" land between cast and jacketed published information to keep from beating up the gun, and who knows where the danger point is? I can tell you not to ever put more than 36 grains of 4320 in a case intended for the M1A, and my rifle will concur as the extractor starts peeling back the case rims. A quick look at pressure data indicates port pressure going over 14K, and I can feel the bolt slamming the receiver, gives me a headache.

I'll continue to put up the cast-relevant data I generate if that is agreeable, but I tend to have a different approach to this than some, I'm going for around 22-2300 fps and under 2 MOA at at least 300 yards, this is a coyote and silly-wet getter for me. Lots of things can be made to work, but some are better than others, and port pressure and timing is something everyone reading this thread needs to be aware of, if academically for no other reason. Tomme asked, and as I didn't see much info on it covered here, I endeavored to fill that gap with the information I've been able to come up with.

Tomme,

"So with Quickload, we can estimate the PSI at a certain spot in the barrel?" Absolutely.

"So the engraving of the bullet is what seems to be changing the speed of the powder?" Speculation on my part, a quick comparison with QL should answer that, and I haven't bought the program myself just yet.

"On how it burns? Comparing jacketed to lead. The jacketed increases the peak PSI sooner and burns up more powder faster? And that same powder with lead would burn longer and the peak would be right at the port????" Could be. I know that seating depth and alloy change the pressure curve, I assume jacketed would change it a lot more. Problem is I never studied jacketed pressure data that closely. When I get QL I'll answer this.

"I am just trying to understand how the powders are reacting for this platform. So do they make a adjustable gas port so if you found that a certain faster powder in the mid range burn rates has a lower chamber psi but a high port psi could be dialed down to make work better?" I had the same thought. Internet wisdom from experienced M1/M14 builders does not concur, but then again they don't know boolits very well, either. That's the whole reason BruceB started this thread, and it is STILL about the only load data resource on the entire internet, maybe anywhere outside of a few people's personal notes, for shooting cast bullets in the M1A platform.

Gear

[cbrick]

I uniform all pockets anyway. I got the shop manual that Sgt Mike posted about several pages back. An outstanding book by the way. It delves deep into high level armorer level topics but there is info aplenty even for those that don't wish to set up a machine shop. One of the first topics covered is slam fires, the free floating firing pin, the cause of most slam fires and the cure. Primers must be seated .005" below flush, primers higher than this run a risk of a slam fire with the bolt out of battery which would be super bad stuff. Next is the use of #34 primers for the harder cups and less sensitive compound just as Bruce recommended. I did have a double tap with mine using Fed 210's before the #34's got here, that's why I parked it until I had them.

Regarding the port pressure serious damage can occur before you realize it. With too much port pressure the operating rod can be bent which changes it's length and firing in this condition can prevent the bolt from closing fully. In other words, out of battery. Port pressure is a topic worth noting.

Rick

[geargnasher]

Rick, in that manual have you come across anything that corroborates the 12K psi port max that I've read about?

I think it's important that people reading this realize that while they can use slow-burning powders with reduced loads in the M1A, they have to stop adding powder at a certain point due to the resulting long pressure curve and port maximum and find a safe balance (if any is to be had) between under-volume charges/SEE risk and excessive port pressure that will most certainly damage the rifle.

Gear

[cbrick]

They didn't mention specific numbers for port pressure, a bent operating rod was discussed as part of the section on slam fires. The book is not a loading manual by any stretch but it goes into detail about the primer pocket depth, seating depth as one of the reasons for slam fires. Just so happens that how they describe pocket uniforming and primer seating is exactly what I've been doing with match ammo for many years, as an accuracy trick though not for slam fires. They even mention the same Sinclair uniforming tool that I use. Even though I had done this with the Fed 210's and my primers were seated .005" below flush I did have a slam fire. I was lucky in that it was not out of battery but an eye opener anyway.

I'm with Bruce and the book and highly recommend the use of CCI #34 military primers.

Rick