High pressure help

1

1stmar

New member
Guys I could use some help on this. Been reloading for over 30 years and recently made 3 changes to my load for 308. Rifle is an M1A. All loads are dispensed via a hornady autocharge pro and then dble checked on an rcbs beam scale. The autocharge is very accurate and consistent. My previous load was 168SMK LC brass CCI primers and 42.5 grains of 4064. The changes I made are: 1. 165 gr hornady sp (3040) 2. Various COL 3. Hornady one shot.

I have tried various COL from 2.168 - 2.218. These COL are measured with a hornady comparator so not true COL. 2.168 was right at the recommended COL. Velocities were consistently between 2500-2570 for all depths. Nothing hand fed were too long or seemed to reach lands. I had 3 high pressure rounds that did not extract over 60 firings. They were at various different COLs including the min and the max I was using. The 60 firings were 3 different reloading sessions and range sessions.

Here is what I thought was going on and why. When I received the first high pressure load I inspected the case and found what you would expect, extractor mark on rim. I went back and dble checked the remaining rounds (all the same COL) at the time, and they were spot on at 42.5. When I did so I noticed that cartridges were difficult to break down with an impact tool. I use no crimp. I then reassembled the cartridges after weighing and reloaded another 20. Not satisfied that I understood what happened I decided to adjust the COL thinking maybe they were too long and possibly jammed in the lands. When I decided to reduce the COL (a day later) you could feel them break loose as if they were glued to the case. I immediately thought it was the one shot.

Searching for previous posts I found a post that one of the ingredients in one shot is actually used in gluing shoe soles. I then thought perhaps I didn’t shake the can enough. I did some testing with the cartridges to see if I could recreate the stickiness and was able to do so. I then made very sure I shook the can exceptionally well and reloaded another 20. I still got a high pressure round this time at the 2.168 COL. I’m pretty convinced it’s the one shot and will be going back to hornady unique. Has anyone experienced anything like this with one shot? Thoughts on anything else it could be? BTW even the high pressure round chronographed at 2569.

Thanks for taking the time to read this lengthy post, I didn’t intend to make it this long.
 
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How are you defining high pressure exactly? Something about not extracting? I wonder if your powder is borderline for creating too much port pressure causing the gun to try extracting before the pressure drops enough to allow the case to disengage from the chamber.

Most semiauto function by firing and using a powder the reaches max pressure very quick. Then the bullet travels past the port. With the bullet still in the barrel, but chamber pressure dropping fast, gas surges through the port and pushes on a piston or something else to unlock and cycle the action.

The key point is you need reduced chamber pressure and port pressure within spec to open the bolt easily.

Too high of chamber pressure or too high of port pressure really adds a lot of harshness to this cycle damaging gas systems, damaging cases, etc. So, that said, I would look into what powders work well with M1A.

For example, in M1 Garand which I have looked into….H4831, R19, etc are great 30’06 powders, but are out of balance in a M1 Garand. Faster burning powders like IMR 4064, H4195and some others deliver slightly less velocity, but fewer bent op rods and chewed up brass.

Often there is a port tuning option too, but I have not looked into that much.

You can go down the One Shot rabbit hole, but it is a proven commodity in my opinion. You might try case wax by Imperial or Creedmoor Sports. It has many advantages in sizing.

I have seen bullet weld, but more often I’ve seen rifle rounds with std 0.003” neck tension and moderately sized <250gr bullets don’t like to work with impact pullers. Try a collet puller. There is a neck weld issue, but it is much rarer and seem to be corrosion related. Brushing necks and/or lubing necks with graphite seems to be the solution.
 
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After the failure to extract, the only way I could pull back the op rod a. D eject a case was by banging on the charging handle several times. Additionally there was an extractor mark. I would say the primers were flat.

I’m not sure what powder would be more appropriate but I will say I have 3 garands and an M1a and I use 4064 in all of them without issue and 1 of the garands is a 308. Been running them with 47 gr of 4064 (30-06) and 42.5 gr (308) for 10 years. I don’t think it’s the powder.

I’m not sure if waiting till the chamber/case cooled down if I’d been able to pull back on the op rod, perhaps I should have waited. The cases have been reloaded several times (full length) , perhaps the beginnings of case head separation? I have the last case it happened too and will look for signs today. Somehow I think it is either lube (my first inclination) or case.
 
Hmmm. Are the cases all the same headstamps with the same load history? 308 has more weight and capacity variation by headstamp and lot than any other cartridge I load for. Check the weight of the ones that went over-pressure to compare to your others.

Carbon inside a case neck is usually a good thing. It helps lube the bullet seating process. But if you think it may react with something, you can try sticking a bore brush in and giving it a couple of turns to roughen the inside of the neck a little. Then apply a dry lube to the inside of the neck with motor mica or graphite before seating the bullets. You can also use a swab to apply a mix of graphite powder and alcohol and then let the alcohol dry.

You found some sticking bullets, but have you had any cartridges for which removing the bullet was super easy? I'm thinking a loose bullet could fly forward upon chambering and start out seated into the lands. That could raise pressure by maybe 20%.

Are there any marks on the high-pressure cases that look unusual?

You are double-checking charge weight, but are you ever charging and then dumping the charge and re-charging any cases? If so, is it possible some One Shot got into the bottom of a case and stuck some unburned powder in it that didn't dump out with the rest?
 
Cases are all LC 11. I have not Checked weight. The last high pressure round was 2nd in the magazine so possibly moved forward into the lands. One of the reasons I liked h1s was seating seemed smoother and COL seemed more consistent so again maybe not enough tension. Powder was the end of an 8lb keg so did too off from new keg. 43.6 is max and I’m at 42.5 so skeptical mixed lots would cause it. Additionally, that was the last reloading session so wouldn’t explain other high pressure loads.
Thinking that it might be hs1, I did clean the last 20 necks after sizing w a qtip thar had carb cleaner on it. Waited at least 30 min to dry. This was only done on the last reloading session when searching for answers.
 
You changed the bullet. You changed COAL. You changed your sizing lube.

Now you have a problem and don't know what might be causing it??

Change back. Change one thing at a time. test between changes. Troubleshooting is a PITA, but if not done right, you don't get the right answer, usually.

I never had good luck with Hornady one shot lube. Always took more than one shot, usually 2-3 to get my cases sufficiently lubed. I've had much better luck with the RCBS stuff in a pump spray (NOT AEROSOL) bottle.

I tumble in dry corncob, decap, (Lee punch and hammer) lube then size, and then tumble again, to remove the lube. I literally do nothing to the inside of the case necks. If I get that "crunch" sound from the expander ball dragging on its way out, that tells me to use a little more lube, or give the brass more time for the lube to "migrate" enough.

The bullet you are now using is a flat base bullet. The powder charge is about a grain heavier than max listed in my Hornady book for the 168gr boatail in the service rifle section. That charge is, however right in the middle of my Lyman book's .308 data.

Comparator readings tell me nothing useful. Measure COAL from case base to bullet tip. For the bullet you named, Hornady says max coal should be 2.750".
 
Thanks 44 Amp. I am doing that right now. Going back to hornady unque for lube. I liked the hs1 inside the neck as the drag across the expander was smoother thinking I might get better concentricity. But it isn’t worth this headache or damaging my op rod.
 
DO you have any of the original OLD loaded cartridges laying about?

If you do, id measure them in the new measuring device you have in order to get a baseline dimension.

Have any of the old bullets left? Should measure them and compare with the new, the section of bullet between base and cannelure is important... Especially since some seating die instructions just say to go through bullet cannelure.

Have had hornady factory boxes of bullets that had cannelure in multiple places. same bullets, same over dimensions but in the ones i have its normal to seat to one depth, and put laoded rounds side by side and some will have cannelures .3" above the case mouth... while all others are seated properly in cannelure.

The "sticky" of the lube should not be an issue.. ever pulled down military surplus 7.62x51?
 
The self venting gas system on the M14 (M1A) generally prevents the kind of op rod damage that can happen in GI condition M1 Garands. Not saying one can't bend the op rod on an M14, but the different gas system, and the different shape and size of the M14 op rod makes it much less likely.

With the M1 system, the port is very clost to the muzzle and the gas cylinder is subject to full barrel pressure until the bullet exits the barrel. With too high a port pressure, this results in an extra hard "shove" to the gas piston.

The M14 system ports the gas several inches back from the muzzle, and as the gas piston begins to move, it blocks additional pressure from the barrel, and then as it moves further, the op rod is already moving, so there's nothing for the extra pressure to push, ensuring a constant, "in spec" push on the piston, even when the port pressure is too high, it seldom gets to the point of damaging the mechanism. It usually works. :D
 
OP. You had failure to extract. The extractor jumped the rim. You rehooked the extractor to the rim and you needed a mallet to the the brass out. You noticed damage marks on the rim. Is that what happened?

Was the primer cratered? Any ejector hole impression / swipe mark on the brass head? Not sure you really had high pressure.

-TL

Sent from my SM-N960U using Tapatalk
 
Ok guys i think with your help I have figured out some things:
-Loaded up 42.5 gr and noticed that it fills the case right to the bottom of the neck. Got me thinking about Uncle Nicks post and 44 AMPs about case volume and different load manuals listing different max charges. I have 3 that all list 43.6 as max and compressed. With lc brass I don’t think I could get 43.6 and a bullet seated.
-max col was listed at 2.775. I started well past that in my last reloading session and worked down to that. Thinking at the time was I was possibly jammed in the lands increasing pressure. The last high pressure round I had was at list max col, the shortest rounds I had. I think that was a compressed load or very close to it.

Just fired 10 rds of 42.5, 42 at 30thousands longer than listed max. No issues. Then I fired 5 rds of 168 42.5 that I had previously loaded. I noticed a significant difference in ejection. The hornady rounds, even at 42gr, were ejecting 10-13 ft away, the 168 were dropping by my bench about 3 feet.

I think it was amp that brought up the flat base vs the boat tail. I believe that makes a significant difference.

Can’t thank you guys enough for getting me on the right path. You all were spot on. Agree on the last comments about stickiness. Last rounds I loaded were with unique but will try hs1 again.

Thanks again
 
Hornady 1-shot's N-Hexane is a solvent (not a glue or glue-precursor, material)

> "... used as cleaning agent in the printing, textile, furniture,
> and shoemaking industries.

I cannot find anywhere that it has an effect on metals/brass.
 
Thanks mehavey. I’m going to try it again and clean the neck w alcohol or carb cleaner. Bullets seem to seat smoother and I get more consistent depth.
 
I've used Hornady 1-shot for a couple of years now (since I quit bad-mouthing it and
read the directions :D )

But I admit I spray the cases lying all one direction/on horizontal surface -- no spray inside
the case/neck -- and so haven't experienced what you describe
 
Not sure what to make of this but:

In industry, hexanes are used in the formulation of glues for shoes, leather products, and roofing.

https://en.m.wikipedia.org/wiki/Hexane

In the end I don’t think it contributes to the high pressure I was seeing but not sure of how it affects accuracy. If i continue to use it I will clean the inside of the necks.
 
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