finding lands?

[jelenko]

Are you attempting to find distance to lands, or are you measuring chamber length, aka headspace? You need to know your chamber length prior to establishing your distance to lands.

Except in belted cartridge cases, bottle neck cartridges index off the shoulder. So it is the distance from the shoulder to the lands that you are establishing, although we tend to measure by referencing off the case base. Now imagine using a cartridge case that is one inch shorter than the chamber, and how that would effect your measurements.

Regardless of the cartridge case you choose, you'll need to account for any difference between the base to datum length as compared to the actual chamber dimensions.

For instance, say you use a Hornaday LNL modified case that is .008 shorter than a case you've shot that is fully fire formed and chambers with a slightly stiff bolt drop. IOW, it fits the chamber precisely. Using the Hornady case to find and measure CBTO will yield a .008 error in the distance to the lands as compared to using a fully fire formed case.

Continuing on, whether you prefer to hand load using cases that are fully fire formed and fit the chamber snugly, or bump shoulder back for ease of chambering, you'll need to account for the difference when seating bullets IF your chosen bullet is sensitive regarding seating relative to the lands. In a worst case scenario, seating to touch during load development would yield very inconsistent results in SD/ES and target groups due to these variances in how the case was sized, how CBTO was measured, and consistency in bullet seating.

If the Hornady modified case headspaces to, say, 0 and the brass you are loading with is headspaced to 0, then the distance to the lands from the ogive would be the same - yes?
Thanks

 

[dgeesaman]

If the Hornady modified case headspaces to, say, 0 and the brass you are loading with is headspaced to 0, then the distance to the lands from the ogive would be the same - yes?
Thanks

Basically, yes. I think most of us keep our brass headspaced within .002. So you’ll be that close.

The bigger variable with the Hornady tool is how hard you push into the lands. So a zero reading with the Hornady tool tends to create little bit of jam in a loaded round.

David

 

[jelenko]

The bigger variable with the Hornady tool is how hard you push into the lands.

Yeah! Almost need incantations while doing it.

 

[INTJ]

Yeah! Almost need incantations while doing it.

Any old machinist or gunsmith will say how developing a consist method and feel is critical when measuring. I just figured the Hornady tools were a place to develop that. I find non VLD bullets pretty easy to measure. VLD bullets are harder, especially the really long tapered ones.

 

[Killick]

Any old machinist or gunsmith will say how developing a consist method and feel is critical when measuring. I just figured the Hornady tools were a place to develop that. I find non VLD bullets pretty easy to measure. VLD bullets are harder, especially the really long tapered ones.

When I was running VLDs exclusively I would always soft seat them and allow the lands to seat the bullet. It worked out pretty nicely...won a state championship and a state regional with both .308 and 6mm VLDs.

 

[jackieschmidt]

Every Gunsmith should furnish the shooter with one of these when he does a barrel for them.

There is always a drop off of the barrel. I can make one in 20 minutes. It’s worth is worth much more than any initial cost.

 

[INTJ]

Every Gunsmith should furnish the shooter with one of these when he does a barrel for them.View attachment 1182236

There is always a drop off of the barrel. I can make one in 20 minutes. It’s worth is worth much more than any initial cost.

That is a great tool until the throat erodes. That is the only reason I haven't made any for the barrels I chamber. It would be as easy and putting it in the three jaw and running in the reamer a little

 

[jackieschmidt]

That is a great tool until the throat erodes. That is the only reason I haven't made any for the barrels I chamber. It would be as easy and putting it in the three jaw and running in the reamer a little

it’s a reference tool to at least know where you started.

Since I believe that a fresh throat is essential to extreme accuracy, I set my barrels back on what many would consider a regular basis.

 

[bozo699]

it’s a reference tool to at least know where you started.

Since I believe that a fresh throat is essential to extreme accuracy, I set my barrels back on what many would consider a regular basis.

Jackie,
On your 6 br improved cases or I believe you shoot a lot of 30 br do you have a specific round count?.... accuracy degrade or what the borescope says?
Wayne

 

[jackieschmidt]

Jackie,
On your 6 br improved cases or I believe you shoot a lot of 30 br do you have a specific round count?.... accuracy degrade or what the borescope says?
Wayne

 

[jackieschmidt]

The 30BR is a whole different animal. I have gone as many as 1000 rounds before I set it back.

I have seen 6PPC barrels loose competitive agging capability after 450 rounds. That is barely 12 Aggs.

since a BR has even more powder capacity, the quilt edge accuracy should be gone at at least that number.

I have never been much for “chasing lands”. Once that throat starts to show any appreciable erosion, accuracy will fall off. I would rather freshen up the throat befor it gets out of hand.

Of course, there are those exceptional barrels that never seem to die. In my close to 30 years doing this, I might have had one.

 

[bozo699]

The 30BR is a whole different animal. I have gone as many as 1000 rounds before I set it back.

I have seen 6PPC barrels loose competitive agging capability after 450 rounds. That is barely 12 Aggs.

since a BR has even more powder capacity, the quilt edge accuracy should be gone at at least that number.

I have never been much for “chasing lands”. Once that throat starts to show any appreciable erosion, accuracy will fall off. I would rather freshen up the throat befor it gets out of hand.

Of course, there are those exceptional barrels that never seem to die. In my close to 30 years doing this, I might have had one.

Jackie,
Shooting long range I never know if it’s the gun, me or the conditions but I’ve often thought using a borescope that around the 500 count maybe I should set the barrel back but being reliant on a smith I have done it but not that often. I have my own reamers and my own lathes and mills just never set them up and my smith keeps my reams by what your saying is making me want to set those machines up more than ever before!... what can you get maybe 3 set backs before it’s a groundhog barrel ?
Wayne