What do you call "Jam"

[jelrod1]

With the seemingly different terminology floating around just wondering what you guys call jam? I usually remove the firing pin assembly from the bolt to test a new bullet. I then load a normally sized case with no primer or powder with the bullet seated long. Then I incrementally seat deeper until the bolt will finally close. This is the longest a round can be and the bolt still close and I call that jam. Anything shorter I call jam minus .005 and so on. I have used the hornady gage to find "touch" also but prefer this way.

Just wondering if I'm wrong in my terminology and how you get there. On forums you see "jammed .01" and things like that and I just don't see how that's possible. I can understand "into the lands" from touch or "jam -.005 "

 

[ShootDots]

I understand exactly where you are coming from... I look at it this way: If you KNOW what the dimension(s) are for your bullets in relation to the lands and GO INTO the lands, no matter how far, you are, in simplest terms "jamming" the bullet. Example: If my 6.5 x 284, which uses 140 Hybrids, has them "touching the lands" at 2.443" (which it actually is at this moment) then going to 2.450 will "jam" the bullet 0.007K... TECHNICALLY anytime you run the bullet INTO the lands, it is a jam... Some people do not call it a jam til it makes "marks" of some sort on a bullet.. I see varying terms like 5thou less than jam; or jam + 5thou... I don't know what nebulous terminology that is.. If you place the bullet SOMEWHERE INTO the lands, you have, BY DEFINITION, a jam! At any rate, this may be one of those topics that holds as many opinions as there are bullets to jam!! LOL!!

 

[savageshooter86]

Boyd helped me on this one and Tony Boyer talks about it in his book. But like others said it only matters what you call/refer to "jam". I use the Hornady tool and find "touching the lands"(I also did this by using dummy round and finding where the rifling marks just started to fade away on a polished bullet) and both measurements were very very close. I then refer to anything longer than this as +xx. Anything shorter I call -xx.

***The old school term for JAM is removing firing pin, seating dummy bullet way long and closing the bolt. Whatever the round comes out as is your "jam". The rifling is seating your bullet. If you repeat on a few cases/bullet and the reading is close to the same, then you are at "jam". But like Donovan stated this reading changes with different amounts of neck tension. So if you used a different bushing or size expander then you would need to "re-find jam"***

 

[Panzer22]

The difference between jam and jelly? You can't jelly a bullet into the lands....



I always saw it as jump, touch and jam.I would imagine, touch is more of a "feel" and jam means that if touch is "0" then you are loading the bullet "+" in length from that 0, and jump is "-" that length from that zero. I don't believe that jamming always means that the actual ogive is going into the rifling that amount but its loaded long that amount. Like was said earlier the tension, coatings ogive type etc. will determine exactly how far it actually does go in. But if its repeatable to you and your tools, it doesn't matter. .010 jam may actually get you that far with one bullet, .020 jam may only get you .015 actual, and some people soft seat by using a very long jam , called a "hard jam" to use neck tension to control the actual depth, and the chamber as the final seating die... All sorts of stuff works, nothing is a given except we all feel the 0 different and all do it a little bit different. It's all about how you do it. If someone says hey this bullet loves to jump .010 I try to replicate it with my tools and equipment, and sometimes we match up close enough that the differences in TPE don't show, sometimes I end up with more or less and get the same result, and I'd bet a box of bergers that if he used his TPE to measure my results and I used mine for his we would get the same results on each others rifles as we did our own, but still different from each other.

This almost sounds like a B-movie script...I actually had to change it for all the innuendos... Wow.

 

[Erik Cortina]

Here's how it works.

Jump - bullet not touching lands.

In the lands - the distance between touch and jam. Oftentimes INCORRECTLY referred to as jam.

Jam - the place where the bullet will jam into the rifling and if bullet seated longer tham jam, rifling will seat buet deeper into the case. Jam is relative to neck tension, the higher the neck tension, the deeper the bullet will jam into the lands. If you load a bullet longer than jam, you will more than likely stick the bullet in the rifling if you try to extract a loaded round... Because the bullet is jammed!

jam/
verb

2.
become or make unable to move or work due to a part seizing or becoming stuck.

 

[Panzer22]

3. What clips or rifles do on ar15.com with wolf ammo.

 

[JORTZ]

All this talk of jam I'm going to go make a peanutbutter and jam

 

[Shynloco]

All that really matters is what you call your own "jam" !.!.!... its unique to you, and that's all that matters...

Do bare in mind, with the dummy method, the amount of neck tension/grip will also effect the measurement. Look at the marks/hashes on the bullets to determine how far and how hard the dummy ends up into the lands.

Donovan

Jelrod1,
What Donovan says is (IMHO) the best advice. Keep in mind that each rifle is UNIQUE. And I like (and use) your method of pulling the firing pin in determining exactly where a bullet nose "touches" the lands. I also use a Sharpie to black out the nose of a bullet so I can actually see the markings on the bullet in determining where the "touch" starts and then add .001 more, measure the ojive and chamber the carftridge. I keep doing that and measuring each setup to find out at what point the bullet begins to be pushed back into the casing to find max "jam." Without the firing pin, I can also better "feel" resistance when closing the bolt meaning I'm "into" the lands. Perhaps kinda anal. But it works for me so I know exactly where each of my rifles shoots the best using a particular load setting. Just my $.02 worth.

Alex

 

[jelrod1]

Thanks guys. Now it's all clear as mud . I guess my thinking is along the same lines as Erik for a definition of jam. I understand what matters is that You know how you got there with your rifle and how to repeat it, but conveying findings to others always seems to take explanation and I didn't know if y'all had agreed on anything. Thanks again.

 

[BoydAllen]

The main reason for asking this question is that when we try to communicate what we are doing to someone else he may think that we are doing one thing, when we are doing something else.

I am old school. To me jam is the longest that you can seat a particular bullet in a specific barrel, at the neck tension that is going to be used for the actual loads, without the bullet being pushed into the case as the round or dummy round is chambered. (Also, I do not "jam" bullets. I seat them at or so many thousandths off, or shorter than jam, or at touch or so many thousandths longer than touch.) I also find it useful to find where a bullet touches, and have a couple of tools to do that with. One thing about one of those tools, the Hornady tool absolutely does not require a fire formed case, as long as you have some sort of tool to measure cases from shoulder to head. Measure the case that Hornady sells, measure a tight fired case from the barrel that you are working with. If fired case is longer, add the difference that you get using the Hornady seating depth gauge, and you are good to go, with an accurate touch number.

 

[Webster]

I don't know if there is a correct definition of jam. I think most BR shooters look for a particular rifling engraving mark, a nick or square mark. Neck tension will determine how far you push the bullet into the rifling on closing the bolt. The definition doesn't really matter. Your method has given you a good number that can be used as a starting point. If a different method gave you a different touch or jam number it still is a starting reference. No matter the method you would still shoot with longer or shorter COAL to find out what works. That is what you are already doing. My 6BR is used for GH hunting and non-competitive BR shooting so I want to be back from jam so I don't lodge a bullet in the bore and dump powder in the action if I need to extract a loaded round. Also I don't want to try to remove a bullet stuck in the bore. The COAL in reloading manuals should be based on functioning in a magazine of a certain length. I single load since it's a 6BR with a non-functioning magazine. Every rifle has a different amount of free bore.

 

[BoydAllen]

After I have found jam, and decided where I am going to start an seating depth test relative to that loaded length, I adjust my seating die to produce it, and if it is one of my bench rifles, and I am seating with an arbor press die, I record the total length of the stem and cap of the seater die. Note, this does not work with Sinclair micrometer head for Wilson dies. From that point on, it is the name of the die used, and the stem and cap (combined) measurement that I work from. For other types of dies, I record the "ogive length" (a misnomer) noting the tool that was used to take the measurement, as in Stoney Point tool with 6mm insert. Obviously this would be for a specific bullet.

 

[1shot]

Now this is some good reading for a novice or expert alike. If for no other reason that to confirm that you are doing something right.
I use a combination of what several other posters do. If it's a cartridge that I've worked with before and it's a new bbl. cut with my own reamer, I already have a good idea for a starting point. Regardless, I also remove the firing pin assembly, blacken the bolt surface with a sharpie and seat the bullet. I have a dental magnifier, which is a fancy term for a big magnifying glass with a round fluorescent light around it. I us this as an aid to my failing near vision to measure the length and width of the marks with my calipers. I've found that in my 6.5mm barrels the rifling marks are about .052-.055 wide. I will repeat the process until I have a "square mark". (Ex. .055x.055) I record that base to ogive measurement and that is my "jam" dimension. I will work off of that measurement for load development as well as to see how much the throat has changed in a given number of rounds. This measurement is also handy if you switch bullet types and one bullet has a different profile than another. Base to ogive length will stay the same regardless of the bullet used, so you have a good starting point. As an aside note. I double check the engraving marks against what I find with a Sinclair bullet comparator (the 6 sided nut with a caliber choice on each flat) and find that this is a good back-up way to confirm that you are indeed seating into the lands as opposed to the bullet sticking at a point short of the actual rifling, possibly overly tight throat.
I hope this helps,
Lloyd

 

[dickn52]

All this talk of jam I'm going to go make a peanutbutter and jam

There ya go again messing with my head. I thought it was Peanut Butter and Jelly.