Have been struggling trying to find an accurate load for a Rem 700 in 6mm Rem. Fighting thru the chicken or the egg thing. Problem with rifle? Ammo? Both? A lot of moving parts to consider.
So after reading up on COAL for the umpteenth time, finally took it upon myself to actually measure distance to lands and it was highly illuminating. It would appear that what the manuals say to do regarding COAL.....both in instructions and in load data.....is mostly hokum.
The epiphany? The one number that seems to matter as a reference point is distance from bolt face to lands and that is entirely unique to each rifle, and changes over time as throat erodes away.
So getting to the bottom of this, I measured distance to jamb for 7 of 8 bullets I have in 6mm. I used a couple methods that gave similar results, but for this discussion will use the one where I put a bullet in a slightly neck sized case such that it would slide, but stick. Then chambered the round, jambing bullet ogive into the lands. This gave me two measurements. One was COAL when seated to jamb. The other was distance from bolt face to bullet ogive when seated to jamb (jump = 0.000)
The differences were pretty wild. The only bullet that came close to being right following load data was a Sierra 85 gr hpbt game king. Load data had it at 2.825 and at that depth, the bullet jump to lands was 0.019. Relative to SAMMI specs, that tells me the lands are about where they are supposed to be.
At the other extreme was a Hornady 103 gr ELD-X, which Hornady load data says to seat to 2.810.....perhaps they suggest that because it is a depth that will allow the loaded case to fit in magazines and chamber. But at that depth, the bullet would have a jump of 0.188.......or nearly 3/16 inch. Hornady themselves also say ideal jump is only 1/32" or about 0.031.
So two bullets, both loaded to nearly identical COAL as per published load data, yet due to bullet dimensions and design, wildly different jump to lands. Even more worse, when explaining all this in their book, Hornady themselves say a long jump can be detrimental.......leading to lower velocity and higher pressure bordering on dangerous levels, yet put that into load data anyway.
However the one thing that ended up constant with all 7 bullets when forcing them into jamb.....was distance from base of case to the ogive, when measured with a bullet comparator. Max range was only 0.010 (+/- 0.005 from mid point). Essentially, they were all about the same.
If all this is correct, then loading just got a lot easier. Once the seating die is set to where it needs to be, it works for all bullets (at least as a starting point). COAL is what it is and as long as loaded round will fit in magazine and feed correctly, it's all good.........and irrelevant.
So after reading up on COAL for the umpteenth time, finally took it upon myself to actually measure distance to lands and it was highly illuminating. It would appear that what the manuals say to do regarding COAL.....both in instructions and in load data.....is mostly hokum.
The epiphany? The one number that seems to matter as a reference point is distance from bolt face to lands and that is entirely unique to each rifle, and changes over time as throat erodes away.
So getting to the bottom of this, I measured distance to jamb for 7 of 8 bullets I have in 6mm. I used a couple methods that gave similar results, but for this discussion will use the one where I put a bullet in a slightly neck sized case such that it would slide, but stick. Then chambered the round, jambing bullet ogive into the lands. This gave me two measurements. One was COAL when seated to jamb. The other was distance from bolt face to bullet ogive when seated to jamb (jump = 0.000)
The differences were pretty wild. The only bullet that came close to being right following load data was a Sierra 85 gr hpbt game king. Load data had it at 2.825 and at that depth, the bullet jump to lands was 0.019. Relative to SAMMI specs, that tells me the lands are about where they are supposed to be.
At the other extreme was a Hornady 103 gr ELD-X, which Hornady load data says to seat to 2.810.....perhaps they suggest that because it is a depth that will allow the loaded case to fit in magazines and chamber. But at that depth, the bullet would have a jump of 0.188.......or nearly 3/16 inch. Hornady themselves also say ideal jump is only 1/32" or about 0.031.
So two bullets, both loaded to nearly identical COAL as per published load data, yet due to bullet dimensions and design, wildly different jump to lands. Even more worse, when explaining all this in their book, Hornady themselves say a long jump can be detrimental.......leading to lower velocity and higher pressure bordering on dangerous levels, yet put that into load data anyway.
However the one thing that ended up constant with all 7 bullets when forcing them into jamb.....was distance from base of case to the ogive, when measured with a bullet comparator. Max range was only 0.010 (+/- 0.005 from mid point). Essentially, they were all about the same.
If all this is correct, then loading just got a lot easier. Once the seating die is set to where it needs to be, it works for all bullets (at least as a starting point). COAL is what it is and as long as loaded round will fit in magazine and feed correctly, it's all good.........and irrelevant.
