Question length to lands

[jimparis]

I need to see what you think these measurments mean. I have 2 shilien savage prefit barrels chambered in 6BR 1in8 twist, one is a rifle barrel one is for a specialty pistol. I have been shooting BERGER 105 VLD's in both so I decided to try the hybrid in them. When checking length to lands the measurments came up as
Rifle barrel vld= 1.802 the hybrid=1.835
Pistol barrel vld=1.800 hybrid= 1.805
why would the hybrid in the rifle be a different length? the rifle round ct around 1000the pistol around 200 and the numbers are repeatable.
Thanks
Let me add to my original question readings where taken with hornady oal and comparator, used the same two bullets,if the vld measurments weren't so close to the same I can see the measurments being different. And I am guessing they used a reamer close to a sandard size.

 

[Dshooter]

What powder in rifle? Didn't know the 6br moved the throat that much or maybe that's normal erosion, but i know in my ultra mag, after 280 rounds my throat has moved .021....

 

[jimparis]

Varget 30.3 gr, but if erosion shouled the vld also be longer?

 

[Dshooter]

If the throats were cut identical to start, your saying the throat now is .030 longer in the rifle. Could be normal erosion for that caliber and 1000 rounds. I'm sure a 6br guy will chime in with their experience but that's what it sounds like to me....normal wear
.........Scratch that......I reread your post........

 

[Sheldon N]

Assuming you're using a bullet comparator tool, I would think the difference is due to the differing angles between the VLD and Hybrid nose shape. The bullet comparator does not contact the bullet in the exact same place as the rifling, so the differential between rifling contact point and bullet comparator contact point depends on the steepness of the angle and rate of curve/change of the nose of the bullet between those two points. This is why you see different measurements between bullets, and why you could see variability between the two rifles which have differing degree of throat wear.

 

[dkhunt14]

The VLD is a longer sleeker bullet but the contact point is farther back. The Hybrid is shorter on bearing and has a more blunt longer nose. When loaded it will be farther out the case to contact the rifling. Matt

 

[jimparis]

The VLD is a longer sleeker bullet but the contact point is farther back. The Hybrid is shorter on bearing and has a more blunt longer nose. When loaded it will be farther out the case to contact the rifling. Matt

The thing that got me thinking is if the rifle barrel and pistol barrel both were not close to the same with the vld bullet,I could see erosion making the difference

 

[jimparis]

^^^This. It's important to remember that you need to measure the distance to the lands with a Hornady OAL gauge (or similar) for the exact bullet you intend to load. By analogy, this is also why someone else's cartridge base-to-ogive measurements may have little relation to yours, even if using the exact same brand of comparator. Lot to lot variation in bullet length and small differences in the comparator hole diameter can dramatically affect CBTO measurements. For example, the Hornady aluminum comparator inserts have a decidedly smaller hole than the Sinclair steel inserts, which seat much closer to the ogive/bearing surface junction. CBTO measurements using the two comparators on the exact same round are quite different. However, these measurements are all relative, so as long as you consistently use the same comparator insert, you will generate useable readings.

I am useing the oal and comparator also same 2 bullets for readings between barrels

 

[DanSavage]

What it probably is, is the rifle has 1000 rounds down the tube,, the throat probably hasn't moved to far but the angle or lead of the rifling has changed enough to allow the bullet to reach out further than the pistol barrel.