Into the lands - definitons

T

tiny68

Member
Ok. Newbie question again. Working on tuning my 30BR. I understand "kissing the lands" as bullet is just making contact. Define "light jam" and "hard jam". +0.010"? +0.030"? I shot some 125 TNTs that where 0.060" into the lands and they shot great. The bolt still wasn't diffifult to close.

Thanks for an explanation, tiny
 
OK...... here's how I define them. FWIW

I let the gun "define" the jam.

Jam varies between barrels and calibers with ogive and leade angle being driving factors. Different rifling configurations have some effect.





I start like this:

-My "Base Reference" for a given combination is found by setting some bullets long using .002 interference fit. Now I let the gun seat the bullets to length. If the barrel is new and bullets try to stick I use a cleaning rod. My bullets generally don't stick because I try to match leade to ogive and I start a new barrel by shooting it about 20-30 times using long-seated bullets. I fire for effect and I DO NOT use the long-seated bullets to "hold the cases back against the boltface" even though I may be fireforming cases at the time. This initial firing seems to take any burrs off of the leade. ANYway..... I use a .002 as my "baseline jam set." I measure using the Sinclair "ogive nut" and write everything down. I also check several times for falsing.

-A "light jam" is established by using a lighter interference from slip-fit to .001 interference.

-"Deep jam" is found using .003, .004 or even .005 of interference. Mostly "Deep Jam" for me is relevant only to VLD style bullets which may be varied as much as .100 in seating depth.

-"Falsing" can occur anywhere from light to deep jam, care must be taken. Sometimes a "gizzie" made from a barrel stub helps.


If you achieved .060 jam with the 125's my guess is that you've got a fairly steep leade angle approaching 2 degrees per side. That's pretty deep to be not really feeling it.


hth


If nothing else. maybe it'll get the ball rolling :)


al
 
If you believe you are that far into the lands and bolt closes easily you are probably actually pushing bullet back into case. At .040" my bolt will really close noticeably hard.

Dick
 
Call me "old school" here...... but to me any time you are are using the term"Jam" it means bolt closer is seating the bullet by .XXX".

For seating of say 0.020" into the lands, it is just that: seating "into the lands" and is not jam seating.

- So if you tell me you are seating your bullets at ITL=.015" I understand you to mean they are engraving the lands by .015".
- If you say your at Jam=.015" I understand you to mean the bolt-closer is jam-seating the bullet the last .015".
- If you say your OTL=.015" I understand you to mean your "off the lands" by .015" with no engraving.


Happy Shooting
Donovan Moran
 
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I don't believe "jam" is a finite thing. Jam is a condition tied to neck tension and to the amount of work hardening in the case neck. Jam will vary as the physical properties of the neck change from use.

Mike Swartz
 
I use to call - - -

Jam where the bullet just touched the lands but it seemed to confuse the issue so I now call that "Kiss". Jam is a broad term. I have found that with .004 neck tension I can easily seat bullets .015 in. I have found generally that accuracy comes around .006 in most of the barrels I have owned to date. (all .30 cal barrels). I do have one now that likes them just touching with the load I am using. Lots of neck tension will assure a good measurable jam.
 
Into The Lands

I like what Donavan said. "Jam" is a relative term. Saying ".010 into the lands" seems to be a more accurate description as to what is happenning.

In 100-200 yard Benchrest, many of us have found that moving a bullet into the lands at, what first glance would seem like a ridiculous amount, is where many bullets, especially the "double radius" variety, like to shoot.

For instance, I tell shooters that, with the combination I shoot, I "make the marks appear twice as long as they are wide". I really do not know how far into the lands I actually move the bullet to achieve this, never measured. I can feel the bullet lightly "crunch" as the bolt closes.

It is one of the strange quirks that appears when using 133 with this particular style of bullet.........jackie
 
Jackie ...

What is a "double radius" bullet ??? I know what a radius is but what is a double radius ??? Where is it measured ??? Art
 
Thanks for discussion

Ok. Makes more sense. I'll go back and make some more measures. 0.060" into the lands seemed deep for me to, but that's what my notes said. Much more testing to do.

Tiny
 
Art

Perhaps one of the bullet makers will come on and insert some thoughts, but untill then, here is a good guess.

On a single radius ogive bullet, the ogive follows a constant circle as it arcs toward the shank. This arc is a radius that is 7 times the diameter of the bullet caliber. For instance, take a 30 caliber bullet with a 7 ogive. That ogive, if continued out in a full circle, would represent a radius of 2.156 inches. On a double radius, it may start out at about a 6 or 7, (more blunt), and as it progresses toward the shank, it changes into a higher number, say a 10 or 11. I do not know of any that start at an higher number at the point, and then goes to a lower number as it gets to the shank.

I am not real sure who conceived this, rumor has it that Speedy was trying to re-polish a point up die once, it came out like that, shot great, and every body said "hmmmm".

Some examples of single ogive bullets are Fowlers, Watsons, the vast majority of 7 3/4 ogive bullets that come out of Niemi dies, Knights, etc. Some examples of double Radius bullets are The Barts Ultra and Headhunter, and the Bruno 00 Boat Tail........jackie
 
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Tiny

You mentioned that the 125 TNT's were shooting great. Can you give me an idea about 5 shot group size at 100 yards? I have also shot TNT's. I can even say that I have won a lot of club matches with them. The only thing I have found in my gun, is that they rarely shoot less than 1/4" at 100 yards. They will shoot .25" - .35" at 200 yards regularly. If all we shot was a 200 yard game, I could do as well with TNT's as any custom bullet. In my gun custom bullets agg about .1" smaller than the TNT's at 100 yards. I should mention that this was the case 8 years ago. The TNT's may have changed since then. Have you shot groups at both distances in near dead calm conditions? If so, how did it compare to the results I found years ago?

Michael
 
My groups (no laughing please)

Michael,

Being a rookie, "well" for me is not well for you pros. I have just started tuning. On my shaky shooting bench with dowl rods and orange construction tape for wind flags, I shot a mid 0.3s agg at 100 yds. This is with a Savage action and a Douglas barrel. I had a lot more horizontal than vertical so I think the bench and learning to read some real flags is going to go a long ways. I, by all definitions, am a rookie at this sport. If I can get it to shoot in the low 2s I would be thrilled. I have only shot at 100 yds. Dead calm conditions haven't existed in Oklahoma in over 5 years (since I started shooting and reloading again).....:D:D

tiny
 
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Dead Calm

What are you talking about. Its dead calm here yesterday. Definition of dead calm in Oklahoma is anything below 20MPH.:D:D:D
 
Seating depth or actually ogive to lands is extremely relative to so
many particulars. When you hear in the lands or jam, I always ask
for more information. We do have a terminology issue here. I was
shown an extremely super group for 10 shots recently, in the .140
league. Just off jam , well, in questioning further, it was farther in the case.
We need to know where jam is and where the marks just go away. With
a 1 deg 30 min throat common to most BR chambers, this becomes a fine
point. It is all relative to the bullet and barrel.
Thinking about it another way, If you tried to press a .243 pin thru a
.242 hole, you would have a pressure issue. On the other hand
a.242 pin thru a .243 hole would have no resistance, and no
pressure. This situation does exist in barrels, but to a lesser degree.
Lands of narrow configuration , all things otherwise equal, give
lower pressure. Many barrels are a little over and many bullets are
a little undersized.So many things, when added to peculularity's
of powder. Switching to another bullet because it looks the same
can get us in (out of tune fast).
In a fresh chamber, the ends of the lands are concave. This changes
very rapidly. Having looked at them after each of the first 10
rounds( one shot, clean and inspect with bore scope)before the next shot.
The lands will become convex and become smoother quickly . Throat
advancement does slow down after that.
For me,the biggest culprit in establishing a true jam length is
neck tension. I have rarely seen consistancy less than .005" seating
with the bolt. There is also a question of, does the bullet pull out
a few thou when extracted.
I find it much easier to start at the marriage of lands, via a stub
go back from that or go in 5-10- 20 0r 60 if you like. What ever makes
your barrel happiest. Terminology is easy then, and we are all talking about the same thing
 
Fyi

tiny68 said:
I shot some 125 TNTs that where 0.060" into the lands and they shot great. The bolt still wasn't diffifult to close.
Click to expand...

FYI - I did a couple of more measurements. I seated a bullet in an empty case at 0.060" into the land. I closed the bolt as gently as I could and then removed the cartridge and remeasured. It was pushed back into the neck to where it was only 0.004" into the lands from my measured kiss. I then took a black sharpie and marked the bullet black. Upon closing the bolt, with the same 0.004" into lands seating depth, I only got light markings on the bullet. In fact it didn't even engrave down to the copper like I have seen in the past with smoked bullets.

I haven't tried anything jumped yet.

More general question: once you find a optimum charge, how much can the optimum change with seating depth (jump versus jam)? Can the two parameters be adjusted (tuned) independently?

tiny
 
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