Jamming into the lands and pressures

[gamestalker]

So I was forming some new brass yesterday at the range, and because this new brass was so excessively short, I wanted it completely up against the bolt face during forming to reduce stretching down near the case head. Never having had a problem, but having heard for years that up to or into the lands and pressures will run significantly higher, so i used this opportunity to see just how much different pressures are with the bullets jammed into the lands. I've never had problems before with bullets jammed or close to the lands, but I thought this would be a good time to check it out.

So with both 7 mag and .270 win, I decided to run my powder charges from the bottom end of the table all the way to max, and with two different powders, RL22 and IMR-7828. I couldn't see or feel any difference with any of the cartridge / firearm / powder combinations. Even the max compressed loads were fine, nothing but nicely formed brass resulted. But I imagine that faster burners might cause an issue, but I don't use those, so...

GS

 

[jwrowland77]

Hmmmm, I might have to test a few loads out and see what happens. See if it makes any change in accuracy.

 

[nastynatesfish]

You just need to be carefull. Running jammed and working loads you'll come to see pressure faster. In my opinion. I did it with my 7 mag using h4831. I use the same charge as jammed but shorter oal and more accurate. I thing 7 mag benifits from jump due to short neck

 

[USSR]

When I was shooting my 6.5x55 in competition, I found that reducing my charge weight by 0.9gr when loading 0.020" into the lands gave me the same velocity as loading 0.012" off the lands. Hope that helps.

Don

 

[brickeyee]

If you work up the load against the lands it will be fine.

The problem comes from taking an already worked up load and THEN jamming it.

 

[gamestalker]

Ya Don, I noticed velocity was really very consistent with loads I've run off .010" as well. These loads were jammed .020", but since I have some short throats on these firearms, I still had lots of shank in the necks, so I thought that might account for the velocity being so consistent with the .010" off loads, maybe?

And of course I would never suggest anyone just jump in with an already worked up charge and jam them. Different powders, bullets, and firearms can have varied results, maybe not good results.

I've pretty much just worked with what works best and never really taken much time to run any tests or analyses to compare with. Interesting stuff though, sure has reinforced my reasoning and direction in bottle neck loading over the years.

GS

 

[spitballer]

Seating up into the lands always puts me on the low end of the data sheet and sometimes it still isn't low enough! Right now I'm using the starting load of 19.5 grains for 40 grain .224's and the group is still splitting up near the top. Must be the nosler heavy copper bases, I never get so much pressure with regular jackets. I can see seating on the lands for case-forming, for sure - good method for max pressure, gamestalker drive on.

 

[Andrew Leigh]

GS,

did you chrony you loads to measure if there was a difference or simply do visual case inspection?

 

[gamestalker]

No, I ran across the chrony, no notable difference.

I did see something interesting with both the 7mm and .270 though. As I started up from the starting charge with both the 7828 and RL22, at about 25% - 40% of the table pressures clearly were coming up based on chrony and primer appearance, no stiff bolt lift, pressures weren't in that league, so nothing excessive, just a noticeable gain. But then when I got past mid table everything settled back down. This has been the typical behavior of the of the loads I run up at the lands with these powders.

I have concluded that jamming or even up to the lands does take a small degree of velocity away when compared to .015" or more jump. But I also can see pressures seem so much easier to manage, to the extent that I couldn't get excessive pressures if I wanted to, can't get any more powder in the case. And the powder burn is always so clean in comparison, hardly any visible carbon present.

GS

 

[USSR]

I have concluded that jamming or even up to the lands does take a small degree of velocity away when compared to .015" or more jump.

I wouldn't jump to that conclusion. Things like % of powder fill, powder type, and pressure level you are operating at will influence the results. As I said, with the high pressure 6.5x55 loads I was using, I had to reduce charge weight on bullets seated into the lands to match the velocity of bullets seated off the lands.

Don

 

[gamestalker]

Don, did you experience pressure gains when you tried to match velocity with them into the lands? If so, I don't have that issue, I did lose a little bit of velocity, but nothing notable, about 30 - 40 fps.. Feed me, I'm all ears.

As for load density, I was working all the way up to max charge with both the 7 mag. and the .270, and charges were very compressed, probably some where around 95% - 97% load density, well above the top of the shoulders. I just finished processing most of the brass, and nothing at all looks to be on the upper edge, no scorched brass, split necks, or loose primer pockets. Both rifles have rather short throats too, so the bullets were completely into the necks, even though they were pretty hard jammed into the lands.

GS

 

[rg1]

A reloading friend with his 7MM Rem Mag had a load that shot sub moa in his rifle with loads at maximum in some manuals and slightly over in others. Didn't know it until at the range and when he fired his first round it was much louder than normal. Everyone around stopped to look. The round was stuck in the chamber so tightly that it took a sandbag against the bolt and pounding to open the action. He had taken his favorite maximum load and seated out to touch the lands. Thank goodness he was shooting a strong Remington action and there was no Ka-Boom. He'd read all the hype about best accuracy is with bullets touching the lands. A combination of errors that could have been bad for one's health and ruining a good rifle. Loads need to be reduced with bullets touching or jammed into the lands and in most factory hunting rifles I doubt you'd see any worthwhile accuracy improvements. Plus in a hunting rifle it's asking for a jammed rifle possibly when you need a follow-up shot quick. Some places a round that may keep the bolt from closing could be hazardous also if your quarry has teeth that bites, horns, or hooves.

 

[Andrew Leigh]

GS,

As all bullets we loaded into the lands the initial inertia would have been the same so the variability of jump was removed however one cannot escape the effect of the additional powder surely?

A quick QL simulation on a 150gr with RL-22 into the lands at 94% load density comes in at 53 gr and a pressure of 54 862psi. Upon lifting that to 55gr. or 97.5% load density the pressure rises to 60 524psi.

As an avid student of hand loading I would love to simulate that in QL for my own edification and to see what was going on. If you are willing to provide the info then this would help, only one calibre would be necessary, the .270 would be fine;

Barrel length
COL
The exact bullet
The powder type
Average speed per powder weight and what that powder weight was
If possible the H2O capacity of the fire formed cases, maybe to late now.

What I will do is to work your velocities back to a pressure and plot a graph. I have never loaded off the lands an am keen to do so, this information would be rather valuable for me.

Certainly loading off the lands and approaching them makes a rather large difference, I have done a little work on this. My research on a .308 shows that pressure drops as you seat further out, to a point and then it lifts dramatically. Here I started 2.00mm (0.08") from the lands and the change come at 1.00mm (0.04") when the pressure rise dramatically.

The curve marked cartridge pressure is actually the QL simulation (QL does not compensate for the inertia approaching the lands, on the pressure when on the lands). The curve marked inertia pressure is the actual plot of chronied results being converted back to a pressure in QL.

 

[gamestalker]

Don, if you would like the chrony numbers I would be happy to share with you. Maybe you'll have some insight to offer, I'm always interested in picking someone brain with experience. Speaking of, an old friend of mine got me into this back in the 80's, you might know him, Bob Jensen. I just happened to be dating his daughter, I didn't have two nickels to rub together back then, still don't, but Bob and a couple other BR shooters kind of took my under their wings and taught me a lot about how to make a production rig shoot better. This was just one of multiple techniques that lead to getting much better results with my 700's and Savages at the time.

RG1, these type of things happen because someone doesn't do their home work, there is much to be aware of, such as a proper work up. There are those combinations that do function well under such conditions, and those which do not. To simply imply that seating up to or jamming into the lands, or loading at the upper end of the table while doing so is hazardous, and will certainly result in bad things happening, is simply not true, or accurate. Now, have I ever seen someone KB a rifle when loading like this, absolutely. But in every single circumstance it was 100% a lack of knowledge and procedure that got them. Further more, most would have very likely still have experienced a catastrophic event, even if they were seated off the lands. The right way, vs, the wrong way to reload.

GS

 

[gamestalker]

I'll get that data to you in the morning Andrew, I'm curious as well.

H2o capacity is too late, I've already formed all the brass. But maybe we can come up with an approximate, since it was new Win. brass? Maybe you have 1 or 2 new pieces of .270 Win. Winchester brass, I might as well, I'll dig around.

But I did record all the powder charges and velocities at each increment. I'm just guessing at the load density, but the powder charges from about mid table up were well into the necks with both 7828 and RL22, more so at 75% table and up, of course.

Thanks!

GS

 

[Andrew Leigh]

Awesome, look forward to the exercise.

 

[stubbicatt]

I did my load development for my F open rifle with a "0" to ".010" jam and found a good load that way. Once I arrived at a consistent powder charge I began experimenting with seating deeper and found a great load with .010" jump.

The down side of a jump is the need to frequently measure your throat erosion to keep the jump the same.

A shooting buddy soft seats his bullets at +.025" and his rifle shoots very well. As he says, don't have to worry about seating depth ever again as he doesn't have to chase the rifling over the life of his barrels.

 

[gamestalker]

I sometimes like to soft seat and have had some very good results doing it. But with hunting loads this isn't a recommended technique, I get lots of criticism just seating up to the lands with my hunting loads as it is.

And yes, throats do change some over time, very good point, but I always re-access that aspect with each new batch.

GS

 

[USSR]

Don, did you experience pressure gains when you tried to match velocity with them into the lands? If so, I don't have that issue, I did lose a little bit of velocity, but nothing notable, about 30 - 40 fps.. Feed me, I'm all ears.

I have neither a copper crusher gauge nor an electric piezo gauge to measure pressure, so no way of knowing pressure. I use Lapua brass which is very tough, and it will take pressure well above 60k psi without showing pressure signs. However, velocity is a by-product of pressure, so if I am getting more or less velocity using the same components, and the only difference is the dynamic of whether the bullet gets a running start before meeting the resistance of the bullet contacting the lands or meeting the resistance immediately upon ignition, then this is the best indicator of pressure that I have available to me.

Don

 

[brickeyee]

Keep in mind velocity represents the average pressure down the barrel.
It is NOT the peak pressure.

 

[USSR]

Keep in mind velocity represents the average pressure down the barrel.
It is NOT the peak pressure.

True, but the average pressure can be influenced by a spike in the peak pressure.

Don

 

[gamestalker]

Aside from where the bullet is in relation to the lands, doesn't the pressure curve and peak pressure both influence velocity? An example of what I'm referring to is powder "A" produces lower peak pressures than powder "B", but powder "A" produces higher velocities. I often pick powders based on this particular element, which I surmise is why I probably don't ever experience evidence of excessive pressures. Way back when I was mentored about jamming and working up to max or near max charges, one of the primary key elements was powder choice.

Since I don't usually spring for the good brass, Lapua, I am forced to make things work with standard production brass, as it were. This fact alone, keeps me very aware of my workings and results, which in a way seems to maybe have it's advantages in identifying pressure signs slightly easier I think? Either way, all has been good in jammed / high end table charge territory for me. Now and then I do encounter the unusual, but nothing representing an excessive pressure situation.

GS

 

[Andrew Leigh]

Just on the side GS, your experiences would have been a little different if you had done this exercise with a mono bullet. Methinks that the Speers probably have a very soft lead core which presents less inertia when engaging with the rifling.

 

[gamestalker]

Oh definitely Don, mono's are a totally different world in this regard. But this is why I have started this thread, although I have had great results with this, I want to learn more about the physics involved.

I typically only jam when forming, and generally seat up to the lands with most of my range and field loads for better than 2-1/2 decades, and with just about every common cup and core, Sierra, Nosler, Hornady, and Speer of course. Variations of those include the Speer GS, HC, BTSP, Ballistic Tip ST, GK's, Accubond, Partitions, well you get the idea. Some have certainly demonstrated visibly higher pressures, some not, but none have put me questionably over the top. That's not to say that I haven't backed off a tad with a few, but no catastrophic failures, and also because an accuracy node was located at a lower charge or slightly shorter OAL with a particular bullet or rifle.

GS