base to OJ measurment difference -new to me

[bheadboy]

this is the question, I have ALWAYS checked the brass base to bullet oj with the chamber/bbl clean, dry and usually find that .020 jump shoot fr me in the 222 family group

before the stoney point/hornady produce I would seat a bullet in sized empty case on the long side and jam, measure the scratch and seat accordingly with a little jump.\

for grins this weekend after shooting I took my 223 and used dry brush and dry patch then did the measurement.
the result is the length to oj measure .018 shorter than in the bbl clean. then I cleaned the bbl dried it carefully and remeasured the length grew back to the original measurement --

thus I am assuming the burned powder even brushed out, is enough to cause .018 SOONER contact with the bullet.

this is obviously what happens at the range, soooooo if you want jump do you measure "dirt"or clean and do you allow for residue if you dry brush?

Bob

 

[barefooter56]

bheadboy,
Clean and dry. both the chamber and the barrel is the way I do it.
Take care!

 

[jlow]

FWIW, I was taught to never use a dry brush or dry patch when the barrel was dirty.

What you say may be true but I don’t think the energy associated with the bullet encountering the fouling is quite the same as encountering the lands?

 

[CatShooter]

this is the question, I have ALWAYS checked the brass base to bullet oj with the chamber/bbl clean, dry and usually find that .020 jump shoot fr me in the 222 family group

before the stoney point/hornady produce I would seat a bullet in sized empty case on the long side and jam, measure the scratch and seat accordingly with a little jump.\

for grins this weekend after shooting I took my 223 and used dry brush and dry patch then did the measurement.
the result is the length to oj measure .018 shorter than in the bbl clean. then I cleaned the bbl dried it carefully and remeasured the length grew back to the original measurement --

thus I am assuming the burned powder even brushed out, is enough to cause .018 SOONER contact with the bullet.

this is obviously what happens at the range, soooooo if you want jump do you measure "dirt"or clean and do you allow for residue if you dry brush?

Bob

Because of the angles of both the ogive and the leade... the length of the "scratch" is not equal to the amount of jam.

You need a calibrated micrometer seater to make these measurements.

A vernier helps too.

 

[bheadboy]

Catshooter,
your answer poses an interesting question, I do have the vernier, the micrometer seater.

thought, if I use the hornady (stoney point) gage and get the bullet to the point of feel operating the gage as designed, I also get a scratch back from the case mount. from what you indicate this scratch if from the leade?
not the lands?

age is showing here

Bob

 

[C Valentine]

this is the question, I have ALWAYS checked the brass base to bullet oj with the chamber/bbl clean, dry and usually find that .020 jump shoot fr me in the 222 family group

before the stoney point/hornady produce I would seat a bullet in sized empty case on the long side and jam, measure the scratch and seat accordingly with a little jump.\

for grins this weekend after shooting I took my 223 and used dry brush and dry patch then did the measurement.
the result is the length to oj measure .018 shorter than in the bbl clean. then I cleaned the bbl dried it carefully and remeasured the length grew back to the original measurement --

thus I am assuming the burned powder even brushed out, is enough to cause .018 SOONER contact with the bullet.

this is obviously what happens at the range, soooooo if you want jump do you measure "dirt"or clean and do you allow for residue if you dry brush?

Bob

Because of the angles of both the ogive and the leade... the length of the "scratch" is not equal to the amount of jam.

You need a calibrated micrometer seater to make these measurements.

A vernier helps too.

Well you just threw a fly in my soup! do you mean to tell me that those 4 perfect little marks on the bullet are not an indication of how much the bullet is jammed? (I can measure them down to about .015 but beyond that my eyes are not good enough.) Can you elaborate a bit?

 

[CatShooter]

this is the question, I have ALWAYS checked the brass base to bullet oj with the chamber/bbl clean, dry and usually find that .020 jump shoot fr me in the 222 family group

before the stoney point/hornady produce I would seat a bullet in sized empty case on the long side and jam, measure the scratch and seat accordingly with a little jump.\

for grins this weekend after shooting I took my 223 and used dry brush and dry patch then did the measurement.
the result is the length to oj measure .018 shorter than in the bbl clean. then I cleaned the bbl dried it carefully and remeasured the length grew back to the original measurement --

thus I am assuming the burned powder even brushed out, is enough to cause .018 SOONER contact with the bullet.

this is obviously what happens at the range, soooooo if you want jump do you measure "dirt"or clean and do you allow for residue if you dry brush?

Bob

Because of the angles of both the ogive and the leade... the length of the "scratch" is not equal to the amount of jam.

You need a calibrated micrometer seater to make these measurements.

A vernier helps too.

Well you just threw a fly in my soup! do you mean to tell me that those 4 perfect little marks on the bullet are not an indication of how much the bullet is jammed? (I can measure them down to about .015 but beyond that my eyes are not good enough.) Can you elaborate a bit?

Sure...

Let's say you have a ramp that is 5 feet long and raised 1 foot at one end.

And you have a truck with an overhang in the front that is 5 feet long and has a 1 foot, 1 inch rise.

If you pull the truck up to the ramp, the low end of the ramp, and the low part of the truck overhang are together, and the other end of the overhang is 1 inches over the ramp.

This is the place you are when you "find the throat" with the bullet.

Now, drive the truck forward a a few inches... in short order, the high end of the overhand would have dragged all the way up the ramp, and the high ends of both would against each other.

Now,if you were to judge how far the truck moved, you would say 5 feet, because the damage was 5 feet long... but the truck only went 4 or 5 inches.

To your bullet situation...the angle of the two parts are very close - when you move one a little, it touches the other for a long mark, because that you are thinking that the carbom has built up 5 feet, instead of 4 or 5 inches.

Make any sense??

 

[bheadboy]

Catshooter,
yes, I am thinking now that my "old" method of using a long seated bullet in a sized empty case and chambering it - then measure the lands marks for all the lands -averaging them and then seating to clear is worth comparing to the Hornady method

for one thing the bullet is very loose in the throat of the dummy case and thus as it is pushed forward towards the rifling it can easily tilt down until the bottom of the bullet hits the throat, get scratched, and then finally seat in the lands. so the scratch is meaningless as far as the base to oj measurement.

Bob

 

[C Valentine]

this is the question, I have ALWAYS checked the brass base to bullet oj with the chamber/bbl clean, dry and usually find that .020 jump shoot fr me in the 222 family group

before the stoney point/hornady produce I would seat a bullet in sized empty case on the long side and jam, measure the scratch and seat accordingly with a little jump.\

for grins this weekend after shooting I took my 223 and used dry brush and dry patch then did the measurement.
the result is the length to oj measure .018 shorter than in the bbl clean. then I cleaned the bbl dried it carefully and remeasured the length grew back to the original measurement --

thus I am assuming the burned powder even brushed out, is enough to cause .018 SOONER contact with the bullet.

this is obviously what happens at the range, soooooo if you want jump do you measure "dirt"or clean and do you allow for residue if you dry brush?

Bob

Because of the angles of both the ogive and the leade... the length of the "scratch" is not equal to the amount of jam.

You need a calibrated micrometer seater to make these measurements.

A vernier helps too.

Well you just threw a fly in my soup! do you mean to tell me that those 4 perfect little marks on the bullet are not an indication of how much the bullet is jammed? (I can measure them down to about .015 but beyond that my eyes are not good enough.) Can you elaborate a bit?

Sure...

Let's say you have a ramp that is 5 feet long and raised 1 foot at one end.

And you have a truck with an overhang in the front that is 5 feet long and has a 1 foot, 1 inch rise.

If you pull the truck up to the ramp, the low end of the ramp, and the low part of the truck overhang are together, and the other end of the overhang is 1 inches over the ramp.

This is the place you are when you "find the throat" with the bullet.

Now, drive the truck forward a a few inches... in short order, the high end of the overhand would have dragged all the way up the ramp, and the high ends of both would against each other.

Now,if you were to judge how far the truck moved, you would say 5 feet, because the damage was 5 feet long... but the truck only went 4 or 5 inches.

To your bullet situation...the angle of the two parts are very close - when you move one a little, it touches the other for a long mark, because that you are thinking that the carbom has built up 5 feet, instead of 4 or 5 inches.

Make any sense??

Nope... don't know about the carbon build up stuff and maybe I shouldn't hijack the OPs question dealing with that, but in a clean barrel if I set a bullet to a jam and chamber it, I have four very equal marks around the circumference of the bullet made by the lands. I can increase my seating depth by a couple of thou and see the difference in the new smaller marks as the bullet is backed off the lands. Maybe we are not talking about the same thing. Having said that, if my bullet is not concentric in the case, I will sometimes get what I call a scuff as it enters the chamber and the land marks are not quite as consistent with each other. As far as the OPs comment about fouling buildup, if his rifle likes a jump and the copper and carbon fouling built up enough on the lands, couldn't he be effectively shooting with a jam, or in the case of a heavy carbon ring, more of a jump? Even though that fouling material is a bit softer than barrel steel? Maybe why rifles get to the point where they lose accuracy sometimes after many firings without cleaning?

Good heavens, if I don't get to get out of this house and go shooting soon I am going to drive myself crazy reading these forums! LOL

 

[CatShooter]

I do it differently. I use a tool that goes in the muzzle and measures the distance from a closed bolt - then it measures the distance to the nose of a bullet that is against the leade (rifling)... the difference is my OAL to "kiss" the rifling, and I use the seating micrometers to adjust from there.

 

[C Valentine]

I've done it that way too but I basically stopped dealing with COL because there seems to be too much variation due to inconsistencies in the bullet nose. I just deal with CBTO now. I use the RCBS Precision Mic...it gives me very consistent results which seem to be confirmed by marks on the bullet when I move my Micro Seater die to a jam. That little bullet tool they provide can be a pain though....my Savage extractor doesn't seem to want to grab it unless I have the set screw in it tightened juuuuust right.