F class shooting. Jumping or in the lands
- Thread starter No i deer
- Start date
Erik Cortina has a good video on this. You are actually in the lands a long way before you reach the jamb point. This is because the ogive radius and angle of the chamber where the rifling starts are two different angles, and they can make contact for some distance before it becomes noticeably tight and then jammed.
Ned Ludd
Silver $$ Contributor
I believe most would use the term "hard jam" as the point at which a bullet is pushed into the lands far enough such that attempting to close the bolt will cause the bullet to be pushed deeper into the case neck, rather than moving further into the lands. In other words, "hard jam" would represent the point at which force required to push the bullet farther into the lands is greater than the force holding it in the case neck.
The problem with such a term is that is it so poorly defined that it can differ widely due to variables such as bore/groove configuration, bullet diameter, neck wall thickness, interference fit (neck tension), etc. In my opinion, "hard jam" is a poor choice of terms for the simple reason that it can vary widely from setup to setup. Using a term that is so poorly defined and can vary widely between different setups is asking for trouble, because measurements relating to "hard jam" in one person's hands may have little relation to the same measurement taken by someone else.
The problem with such a term is that is it so poorly defined that it can differ widely due to variables such as bore/groove configuration, bullet diameter, neck wall thickness, interference fit (neck tension), etc. In my opinion, "hard jam" is a poor choice of terms for the simple reason that it can vary widely from setup to setup. Using a term that is so poorly defined and can vary widely between different setups is asking for trouble, because measurements relating to "hard jam" in one person's hands may have little relation to the same measurement taken by someone else.
Gargoyle
Finder Outer
Would you consider "hard jam" the ogive touching the lands or the point where the bullet won't engrave any further into the lands?
Ned Ludd
Silver $$ Contributor
I would consider "hard jam" the point where the bullet cannot be pushed further into the lands upon bolt closure; i.e. the point past which the bullet starts moving deeper into the neck. That would be consistent with a point past which the bullet would not engrave further; i.e. move deeper into the lands, but rather would start seating deeper into the neck upon bolt closure. My understanding is that such a point might be 20-25 thousandths into the lands in some people's hands. However, it might be much different than that value due to a number of factors such as I listed above. In other words, "hard jam" is much like CBTO or "touching" measurements, which depend heavily on factors such as the specific Lot# of bullets used and the diameter of the caliper insert hole, among other things. As such, these kind of measurements can differ substantially between users and therefore only serve as a very crude estimate that may be useful as a starting or reference point, but cannot be considered as a "solid" or "well-defined" measurement other than for a specific setup in the hands of a single user.
Gargoyle
Finder Outer
My thinking was, If I can be at lands when chambering and then only into the lands .002-.003" upon firing via the shoulder bump moving forwards, I can unchamber/extract/eject an unfired round without any undue fussing with the seating depth of the bullet.
So, I load "to touch".
So, I load "to touch".
Hoot
Silver $$ Contributor
Am the only person reading this thread, who's bullets more often than not would prefer to seat back further in the case rather than engrave, more than say 1mm? I enjoy experimenting with a lot of different bullets and powder combinations and occasionally, I'll pair up a bullet with one of my caliber chambers that goes in and I feel the reluctance to continue. Again, occasionally, if I continue to use light but consistent force, they wind up going in further. Not like they're engraving their way deeper. More like the last inch of working your fingers into a glove. The few times that's happened, I write it off to pairing up a bullet with my throat, that is a "glove fit". There's not much engraving when I remove the bullet. it seems like just a good ogive fit to my throat. That's all. I usually write a note to pursue that combination first since my gut feeling is that its a good thing. I enjoy tinkering, I admit it. An example was the Hornady 123 Amax and my particular (AA) 6.5 Grendel barrel. Shoots like a house afire across many powders. Hence the gut feeling with others that exhibit that phenomenon. The Lion's share of my pairings go in and just plain stop after meeting the lands. Admittredly, I HBN all my bullets and go the step further of plunging the necks in the graphite powdered beads that Imperial sells. Perhaps I'm over-lubed. I know my imagination sure is. 
Hoot
BTW, I do try reducing the mandrel size to get more resistance and I do carefully anneal after every use.
Sorry for "going off the reservation" With three+ months before comfortable shooting weather returns up here and I'm all about comfortable, it'll just get worse.
Hoot
BTW, I do try reducing the mandrel size to get more resistance and I do carefully anneal after every use.
Sorry for "going off the reservation" With three+ months before comfortable shooting weather returns up here and I'm all about comfortable, it'll just get worse.
Last edited:
I had 32 loads left over from a match that were all loaded to TOUCH. Last week I did some informal testing. I seated the bullets in pairs, .003” deeper into the case, from touch out to .030” OFF. 22 loads, 11 pairs. The last 10 I jumped from .060” to .080” in .005” increments. Touch was one ragged hole and -3 wasn’t bad. Then the groups opened up until -18, which was literally one hole, then they opened up again. -30 was one ragged hole.
-60 was a tight ragged hole, and continued good out to -80, showing no vertical. A broad node like that is very tempting. But that far OFF?? These were 6mm, 105VLD’s.
I feel My choice is to go with TOUCH, or .065” OFF. I won’t get to test before the next match. I DON’T KNOW WHAT TO DO ???
-60 was a tight ragged hole, and continued good out to -80, showing no vertical. A broad node like that is very tempting. But that far OFF?? These were 6mm, 105VLD’s.
I feel My choice is to go with TOUCH, or .065” OFF. I won’t get to test before the next match. I DON’T KNOW WHAT TO DO ???
It's all well and good until you stick a bullet during an important match. Murphy's law is rule number one.
Hi Norm.
I was hoping you'd jump in..
Getting older I've found myself more indecisive..
I've not needed ITL's ammo before too win medals..!!
I won a several medals this year including some at the European championships and I was in the BigMacs team that won gold..
There ya go. I think you have answered your own question. Keep winning those medals and don't worry about creating possible headaches.
Aim lower
Take both loadsI had 32 loads left over from a match that were all loaded to TOUCH. Last week I did some informal testing. I seated the bullets in pairs, .003” deeper into the case, from touch out to .030” OFF. 22 loads, 11 pairs. The last 10 I jumped from .060” to .080” in .005” increments. Touch was one ragged hole and -3 wasn’t bad. Then the groups opened up until -18, which was literally one hole, then they opened up again. -30 was one ragged hole.
-60 was a tight ragged hole, and continued good out to -80, showing no vertical. A broad node like that is very tempting. But that far OFF?? These were 6mm, 105VLD’s.
I feel My choice is to go with TOUCH, or .065” OFF. I won’t get to test before the next match. I DON’T KNOW WHAT TO DO ???
Find “touch” and work from there
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.