How much can you jam?

[Mozella]

My .223 bolt gun shoots most loads best at a .005" jump with one load preferring .010" jump. None of my best recipes work better when the bullet is jammed into the rifling.

Now I'm just finishing a 6mm BR Normal rifle and I'll be hand loading that caliber too. Some folks, quite a few actually, claim best performance with .010" or more jam. This is new territory for me but if accuracy is to be found by jamming rounds, I'm all for it if it can be done safely.

My .223 loads shoot best with not too much neck tension, about .0015" or so.

My question is what happens when you try to jam a 6mm BR Norma round .010" or .020" into the lands if that round has minimum neck tension. I have no way to measure the force needed to jam a round nor do I have a way to measure seating effort. But it seems to me that it would be possible to jam a cartridge into the lands and have the bullet move relative to the case so that the "jam" is less than calculated, the seating depth is shorter than planned, and the powder might be compressed without the knowledge of the shooter.

Is this a concern or should it be a concern?

 

[Dusty Stevens]

Only concern is opening the bolt with less than .003 or so tension. You wont like the results

 

[jsthntn247]

It's called soft seating. Don't chamber until you are ready to shoot!! It can be effective though.

 

[Sniper338]

Not fun when your jammed and open the bolt and it pulls the bullet and powder goes everywhete in your action and you have a stuck bullet in the barrel... its a mess..... sounds like im not the only one whos done it!!!

 

[gilmillan1]

I like to jam bullets. My 2 f class rifles shoot better when i jam the bullets. try jamming them. i usually find a good load by playing with 20 thousands into the lands. I make groups of 3 rounds increasing 5 thousands each.

 

[Mozella]

I like to jam bullets. My 2 f class rifles shoot better when i jam the bullets. try jamming them. i usually find a good load by playing with 20 thousands into the lands. I make groups of 3 rounds increasing 5 thousands each.

Thanks for the data point. I fully intend to explore aggressive jamming with my new 6mm BR. And thanks to the others who have replied warning about the dangers of opening the bolt on a loaded round and leaving the bullet behind, stuck in the rifling. I am already aware of that potential mess. However that wasn't my question.

What I want to know is this: Will the seating depth change if you aggressively jam a round? Assuming rather light neck tension, I seems to me that when jamming a round into the lands, let's say .020" for arguments sake, one would run the risk of seating the bullet deeper into the case as you close the bolt resulting in a bullet which is perhaps jammed only .010" and which is seated .010" deeper than planned. Or, it might turn out that the bullet ends up simply touching the lands and has moved deeper into the case as the shooter closes the bolt such that it is now seated a full .020" deeper than intended. In other words, you haven't jammed the bullet at all. You simply re-seated it deeper. You get the idea.

The result would be, at the least, performance based on a false premise. Taken to an extreme, it could result in an inadvertently compressed load with unintended consequences.

I admit I don't know the relative forces associated with pushing a bullet deep into the lands vs the seating force for a round with low neck tension and that's why I'm asking the question. I imagine the answer might be dependent on several variables, neck tension and amount of jam being the two most obvious. But case neck cleanliness, neck lube, bullet coating, bullet shape, chamber and throat shape and condition, and perhaps other factors could be at play too.

Has anyone investigated this? Is there published data somewhere? Is it a concern?

I reckon it would be possible to make up several dummy rounds (to avoid spilling powder) to see just how far I can jam a round before the bullet seating depth changes, but I hate to go through that if the answer is well known to everyone except me.

 

[SDDasher]

I like to jam bullets. My 2 f class rifles shoot better when i jam the bullets. try jamming them. i usually find a good load by playing with 20 thousands into the lands. I make groups of 3 rounds increasing 5 thousands each.

I reckon it would be possible to make up several dummy rounds (to avoid spilling powder) to see just how far I can jam a round before the bullet seating depth changes, but I hate to go through that if the answer is well known to everyone except me.

Because of all the variables (most individualized to your barrel/chamber) the only way I know of determining an answer is to do as you suggest above. Good Luck.

 

[strut64]

This discussion has not taken into account the bullet design. Berger VLD's are a secant style and often jamming is preferred. Sierra SMK's are tangent style and often prefer to have a jump instead. Then there Berger Hybrids which are a mix of Secant/Tangent. I cant get the Hybrids to shoot at all in my rifle, so I cant tell you what to do with them. Go to the Berger website and read some of their blogs. There aren't any hard fast rules. In my 6 BR, a Shilen 8 twist and .272" no turn neck, the 105 VLD bullets like 10 mil jam and 107 SMK bullets prefer 20 mil jump. Every rifle is different and bullet preferences for each barrel are also.

 

[Jet]

Mozella

Not sure if this will answer your question but this is the approach I take as it realates to load devolopment.

To find jam I first find distance to the lands using a Hornady tool. I then make a dummy round and seat the bullet I intend to shoot .020" farther out of the case then what the Hornady tool measurement is. Steel wool is used to rough up the dummy round bullet. This allows me to see the rifling marks on the bullet easier. .002 neck tension is used. I chamber the round closing the bolt slowly. To remove the dummy I snap the bolt handle up quickly then remove the case. Usually, rifling marks are half as long as the width. I then measure ogive OAL and consider this maximum jam.

When I break in a new barrel, try a new powder or bullet I seat my bullets to the maximum jam. I then start with the powder charges I want to use (starting with lowest) and fire one shot with each different powder charge. All I'm looking for here is when/if excess pressure signs start to appear.

Once the acceptable range of powder weight is found I start my load testing. I always start my load testing with bullets seated at maximum jam. Once a powder weight node is found I start testing bullet seating depth, working out of maximum jam in .003 increments.

Using this method I don't worry about some of the concerns you mention since I try to find the point where pessure will spike early on and then stay away from it in future load development/testing.

As long as you are loading within safe tolerances let your target tell you what works.

Good shooting.

Rich

 

[Tim Singleton]

You need to invest a small amount of money in a Sinclair seating depth tool
You have said several times what will happen. There is a point the differing neck tension that the bullet will push back. That is considered by most to be Jam for that bullet, barrel, neck tension no way to go further into the lands. Increase neck tension with a smaller bushing seat the bullet further out and it will go a little deeper before itpushes back.

Without some way of knowing your loaded round length in the seating depth search your wasting barrel life,bullets ,powder and IMO your time

Very light neck tension and soft seating amounts to almost jumping for someone who uses quite a bit of neck tension and is able to seat the bullet further into the lands

Read JET post. Very good instructions. But you need the tools to measure base to ogive of the loaded rounds

 

[Mozella]

Mozella

Not sure if this will answer your question but this is the approach I take as it realates to load devolopment.

To find jam I first find distance to the lands using a Hornady tool. I then make a dummy round and seat the bullet I intend to shoot .020" farther out of the case then what the Hornady tool measurement is. Steel wool is used to rough up the dummy round bullet. This allows me to see the rifling marks on the bullet easier. .002 neck tension is used. I chamber the round closing the bolt slowly. To remove the dummy I snap the bolt handle up quickly then remove the case. Usually, rifling marks are half as long as the width. I then measure ogive OAL and consider this maximum jam.

......... snip .............

It answers my question with one missing part; the actual results of chambering that long cartridge. That is to say, what is the result of measuring CBTO of the .020" oversize cartridge you mentioned after closing the bolt and then ejecting the round?

Are you able to maintain the full .020" after extracting the round, giving you a genuine .020" jam, or does the cartridge exit chamber shorter than when you put it it, thus giving you something less than full .020" jam? In other words, with .002 neck tension, will chambering your long round push the bullet into the rifling or will it push it into the case or a little bit of each?

If you are willing to reveal the results of your experiments, perhaps it will save me the task of repeating your research, or at least give me a reference point.

 

[BoydAllen]

First of all let me give you a little benchrest history as I answer your question. The use of jam in reloading came from early short range benchrest. If the word is used as it should be, as it originally was, it is the maximum length that a round can be loaded to, without the bullet being pushed into the case as the round is chambered. This is usually found by loading a little long, measuring the round's length, chambering it, and then measuring again. If the round is shorter after chambering, that shorter length has the bullet seated at jam, which is used to denote a specific loaded length for that bullet, chamber, and neck tension. Things like the condition of the inside of the neck will effect it, as will neck thickness, and how hard the brass is. Shooters will speak of seating bullets at jam, or off (or shorter than)jam by so many thousandths. Some time later, with the advent of the internet, people picked up on the word, and started using it in a much less precise manner, to denote seating into the rifling, usually by some unspecified amount.

Getting to your question, if you seat a bullet .020 longer than where you think it would be just touching the rifling, and then measure the round form tip to head, and then chamber and extract it, you are likely to find that it has grown shorter, that the bullet has been pushed back into the case. This length, which at that point could be better measured off the ogive, is jam for that neck tension, in that rifle, for that brass. If the round is not shortened, you can load another test a bit longer and do the same thing, until the bullet is pushed into the case when chambered.

Different throat angles, different bullet shapes, different neck thicknesses, neck interior finishes, hardnesses, and neck tensions will give different results. If you are planning to seat into the rifling, working from jam may be useful.

As to not finding best accuracy with bullets seated into the rifling, I would guess that you worked up a load with the bullets jumping a bit, and then seated longer, into the rifling. The problem with this approach is that when comparing pressures with the same powder charge that were jumped or seated to touch or slightly into the rifling, there is a difference in pressure of 5-6,000 PSI which will have a similar effect to upping your powder charge. To properly explore a rifle/bullet combination's potential accuracy with bullets seated into the rifling, you need to start looking for a charge weight with the bullet seated to that length.

For your BR I suggest that you seat bullets so that the rifling makes marks that are half or less long than wide and then testing powder charges, starting low, and working up in increments of .3 grain until you feel the bolt lift increase after firing. This would be will brass that is FL sized using a properly fitted FL bushing die. A couple of thousandths neck tension should be adequate. If you continue until pressure stops you, your are likely to find more than one accuracy node, and their spacing may be somewhat uniform.

 

[Mozella]

..... snip ........
Getting to your question, if you seat a bullet .020 longer than where you think it would be just touching the rifling, and then measure the round form tip to head, and then chamber and extract it, you are likely to find that it has grown shorter, that the bullet has been pushed back into the case. ......... snip ........

Thank you for answering my question. This is exactly what I would expect to happen, but I have yet to encounter this mentioned as a reloading "tip" or point of discussion. I've read quite a bit about seating depth and I don't recall any mention of this issue. Of course, that doesn't mean it doesn't exist, but if it's "out there" it's not well publicized. Sure, there are plenty of people who say things like "My gun shoots best with the bullet jammed into the rifling by .010"." However, I don't remember reading anything similar to your post.

None of my several reloading manuals mention this point except that several of them say to never seat bullets so long that they touch the rifling. Neither do the instructions included with my various seating dies make mention of seating bullets in this way.

Several years ago Eric Stecker wrote a detailed article about seating depth for Berger VLD bullets and he recommends that target shooters should try different seating depths between .010" into the rifling and .120" jump in .040" to .050" increments in order to find the "sweet spot". But he never mentioned the idea that jamming these bullets might change the original seated length.

Thanks for not only confirming what I suspected, and providing some useful tips as well. This seems to me a rather important bit of knowledge for anyone experimenting with seating bullets into the rifling not only so that the reloader can know what is actually happening (as opposed to guessing) but also because there might be some safety concerns too under certain circumstances.

I'll proceed with my seating depth experimenting with some assurance that what I supposed would happen has been studied by someone else. Thanks again for your excellent post.

 

[savagedasher]

I can think of more reasons not to jam. Here is a few Excess pressure on bullet start. That is cause loose primer pockets and flat primers. Seating bullets in the lands neck tension and case hardness can be paramount. Jamming many of times if you try to take a loaded round out the bullet pulls. I never have got Low ES or SD with bullets that had to be jammed. I shoot bullet that like to be Jumped or the reasons above .
Larry

 

[BoydAllen]

If you work up the load with bullets seating into the rifling, and pay any attention at all to pressure signs, I have never seen a pressure issue arise. It is only when someone chooses to take a shortcut and move bullets out using a load that was worked up jumping that this will happen. I can't tell you how many fellows that I run into that do not have an organized method for working up loads, and who have a fear of seating into the rifling. Recently I was have been helping a shooter get started with a custom bolt action .308 and had to overcome the fact that everything that he had read had been about jumped bullets. After he shot his first ten shots he called me, all of the bullet holes were cutting each other. I told him a specific amount that I wanted him into the lands, and what the bullet marks should look, and started his charge investigation at the lowest charge in the manual. Since then he has stair stepped up gradually and I think that he will run out of space in the case without encountering any excessive pressure. In the future, I will encourage him to investigate all seating depths, including jumped. On that subject there is a good "article" in the Berger manual on about page 202, that describes an unconventional method for working up loads jumping VLDs quite a lot, I think that everyone would benefit from reading it. Sometime later I asked a Berger reloading tech if that method works with all bullet shapes, and he said that it does.

 

[savagedasher]

I can think of more reasons not to jam. Here is a few Excess pressure on bullet start. That is cause loose primer pockets and flat primers. Seating bullets in the lands neck tension and case hardness can be paramount. Jamming many of times if you try to take a loaded round out the bullet pulls. I never have got Low ES or SD with bullets that had to be jammed. I shoot bullet that like to be Jumped or the reasons above .
Larry

Larry

How much pressure difference are you talking... say from 010-Off to 010-IN, how much pressure indifference in a Dasher?

Explain how case hardness can be paramount from In to Off?

Your ES/SD experience could very well be isolated more so to your own bullet choices and calibers, could it not. If not, how do so many that seat into the rifling have such good results. I personally can say just the opposite, and find lowest ES/SD to occur into the rifling from more bullets and calibers then not.

Donovan

I don't know the pressure difference but the primers show a big difference
If a case is soft and the other is hard the seating depth will be different. Jumping I have good luck annealed and not.
Bullet choice Yes I don't shoot bullets in the lands. Larry

 

[Jet]

Mozella

Not sure if this will answer your question but this is the approach I take as it realates to load devolopment.

To find jam I first find distance to the lands using a Hornady tool. I then make a dummy round and seat the bullet I intend to shoot .020" farther out of the case then what the Hornady tool measurement is. Steel wool is used to rough up the dummy round bullet. This allows me to see the rifling marks on the bullet easier. .002 neck tension is used. I chamber the round closing the bolt slowly. To remove the dummy I snap the bolt handle up quickly then remove the case. Usually, rifling marks are half as long as the width. I then measure ogive OAL and consider this maximum jam.

......... snip .............

It answers my question with one missing part; the actual results of chambering that long cartridge. That is to say, what is the result of measuring CBTO of the .020" oversize cartridge you mentioned after closing the bolt and then ejecting the round?

Are you able to maintain the full .020" after extracting the round, giving you a genuine .020" jam, or does the cartridge exit chamber shorter than when you put it it, thus giving you something less than full .020" jam? In other words, with .002 neck tension, will chambering your long round push the bullet into the rifling or will it push it into the case or a little bit of each?

If you are willing to reveal the results of your experiments, perhaps it will save me the task of repeating your research, or at least give me a reference point.

Mozella

I just did a jam test on one rifle. This rifle has a Krieger barrel with 764 rounds fired on it. It is a 4 groove and has a.237 bore. Bullet used is a Berger 105 Hybrid and .002 neck tension was used.

Jam found using the Hornady tool is 1.855.

Dummy bullet made and seated to 1.875. Used process stated above and jam is 1.869.

Many vaiables come into play. Bullet make and style, neck tension, barrel manufacturer, round count on barrel, etc.

Recommend you experement a bit so you can see differences.

Good Shooting.

Rich

 

[Tim Singleton]

Mozella

Not sure if this will answer your question but this is the approach I take as it realates to load devolopment.

To find jam I first find distance to the lands using a Hornady tool. I then make a dummy round and seat the bullet I intend to shoot .020" farther out of the case then what the Hornady tool measurement is. Steel wool is used to rough up the dummy round bullet. This allows me to see the rifling marks on the bullet easier. .002 neck tension is used. I chamber the round closing the bolt slowly. To remove the dummy I snap the bolt handle up quickly then remove the case. Usually, rifling marks are half as long as the width. I then measure ogive OAL and consider this maximum jam.

......... snip .............

It answers my question with one missing part; the actual results of chambering that long cartridge. That is to say, what is the result of measuring CBTO of the .020" oversize cartridge you mentioned after closing the bolt and then ejecting the round?

Are you able to maintain the full .020" after extracting the round, giving you a genuine .020" jam, or does the cartridge exit chamber shorter than when you put it it, thus giving you something less than full .020" jam? In other words, with .002 neck tension, will chambering your long round push the bullet into the rifling or will it push it into the case or a little bit of each?

If you are willing to reveal the results of your experiments, perhaps it will save me the task of repeating your research, or at least give me a reference point.

Mozella

I just did a jam test on one rifle. This rifle has a Krieger barrel with 764 rounds fired on it. It is a 4 groove and has a.237 bore. Bullet used is a Berger 105 Hybrid and .002 neck tension was used.

Jam found using the Hornady tool is 1.855.

Dummy bullet made and seated to 1.875. Used process stated above and jam is 1.869.

Many vaiables come into play. Bullet make and style, neck tension, barrel manufacturer, round count on barrel, etc.

Recommend you experement a bit so you can see differences.

Good Shooting.

Rich

That's the problem IMO with the hornady tool. There is no neck tension. They basically find what most call touch. And really not a good job of that a case not fired in your chamber or sized the amount that you size brass. You are pushing a flexible plastic rod against a piece of brass that doesn't fit your chamber well. A lot of people use them and find a starting place. But again not a very accurate tool as shown by Jet's testing.
No substitute for a dummy round with the neck tension you plan to shoot

 

[swd]

There's some damn good information here that should be a sticky some where. Thank you Boyd and all.

 

[savagedasher]

I don't know the pressure difference but the primers show a big difference
If a case is soft and the other is hard the seating depth will be different. Jumping I have good luck annealed and not.
Bullet choice Yes I don't shoot bullets in the lands. Larry

Myself, I see very little vertical POI change on the targets, very little velocity variance on the chronographs, very little pressure variance on the pressure trace system, and never much difference (if any at all) on the primers. From say 010-OFF to 010-IN, a spread of 20-fps <> 1000-psi would be typical to what I see. My experience is, lowest ES to both pressure and velocity comes from the best seating positions, no matter what the position. The only time I see much for actual pressure increase from seating, is when at a "Hard Jam" (of say +025-IN) or at a "Big Jump" (from excessive compression). Which has been pretty universal to most all calibers, bullets, and powders in my experience.

Donovan

I have found the same . But with the lead angle of the reamer I feel any thing less then .020 jump is still jam. From touch to jam can be in excess of .030 depending on bullet shape and lead angle if the reamer and how it is found.
I shoot a compressed Using the number on QL 108% full .Using a 14'' long drop tube and a slow pour my bullet stay seated. I only size .150 of the neck for seating also.
A friend not using a long drop tube with the same load same chamber when the bullets moved forward his primers showed excess pressure. The ones that the bullet moved forward with less compression and jammed all showed over pressure on the primers.
I fell any thing less then.020 off is not a problem. .020 forward pressure go up. How much, enough for it to show on the primers. Larry