loading rounds to lands....

bsand

bsand

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So I have finally got time to learn how to use the damn OAL gauge to find distance to lands.

I get a OAL measure of 2.925" with a 175 SMK in 308 win.

Rifle is a remington 700 5r with about 2200 rounds down range.

If that is the distance where its contacting the lands, at what distance should I try? I know I should be using bullet comparators, I just forgot to put them on before coming back inside.

I was thinking at lands, and in 0.005" increments away from lands?

my current load is 43.5 gr varget 175smk gm210m in a lapua case.
 
I hand load .308 as well and normally start 20 thou off lands as I haven't found my rifle likes it being close to the lands and likes the 'jump'. I then tend to go further away, rather than closer for best accuracy but ymmv. If you haven't, I would also take a number of measurements rather than one to make sure you are gauging it correctly.
 
Make multiple measurements with multiple of the same type of bullet and average it out.
start at .020" i go aslow as .005" and as high as .040".
Don't start playing with lands until you find your powder charge. Just start at .020" and test your powders. THEN play with the lands.
 
With 2200 rounds down the tube you have likely pushed the leade out a bit more than when the rifle was new. It all changes with use.

Here is something else to consider. Most bench rest shooters load to engage the lands. Yes this increases pressures but then again, the chambers in their rifles are reamed to very tight tolerances etc, etc.

If you neck resize only, you can likely get away with being closer to the leade. If you full length resize and have a chamber on the large side then you should load off the leade. You need to bleed off the initial pressures and action shock to some extent.

Today's cartridges have relatively short necks in comparison to those such as the 30-06/303 Brit/ 30-40 Krag. Back in the day when cartridges were tapered to aid extraction and headspace on the rim long necks were essential for good accuracy. The necks would hold the bullet in line to the axis of the bore while pressures built up during firing and the expanding gasses pushed the bullet into contact with the leade.

Nothing has essentially changed since those days other than cartridges headspace on the shoulder. The problem with the latter is that nothing holds the case true to the bore axis in the chamber any longer and you can have a "tilt" condition if the chamber is large. This can and often does lead to poor or at best mediocre accuracy. Similar conditions existed with rimmed cartridges if headspace was excessive.

Some rifles will tolerate the bullet being seated way off the leade. I have a 6.5-06 on a mod 70 that I purchased over a decade past from eagleye. That rifle has a 1=10 twist rate and really doesn't like anything heavier than 140 FLAT BASE bullet. Stick a boat tail of the same weight in there and the pattern looks like a shotgun blast. The thing is the reamer used was made up for all available bullet weights up to 160 grain. There is no way to get closer than about .125in to the leade with any bullet weight. The relatively slow twist needs lighter shorter bullets to work well. I load 95 grain Amax flat base bullets to some screaming velocities in that rifle. The base of the bullet has cleared the neck of the case and is in the very thankfully tight throat completely before it touches the leade. The rifle is far more accurate than I would have expected.

I made this a bit long on purpose so that you would have some idea of why you may or may not be able to get away with your bullet being on or off the leade.

If you have a tight chamber and neck resize only then likely the closer you can get the bullets to the leade the better. If you have a normal sloppy chamber and like to load hot then you should stay back from the leade. How far back will be up to you to determine from some trial and error with different lengths at the range.

Just remember everyone of the girls you dated were different same goes for the rifles we shoot. Some will take anything you feed them and handle it well. Others are just so darn fussy that ?????
 
If you are mag feeding, that will determine your max OAL.

If single feeding, as long as there is enough shank in the neck to hold the bullet securely, 20 thou off and load tune.

Odds are the leade is getting long and you may get into a situation where the bullet leaves the neck BEFORE it can fully engrave and be supported by the rifling. At this point, accuracy falls off the planet.

Go to a bullet with a longer bearing surface to extend life (usually this means more bullet weight) OR just rebarrel with a chamber to suit.

Jerry
 
bsand said:
So I have finally got time to learn how to use the damn OAL gauge to find distance to lands.

I get a OAL measure of 2.925" with a 175 SMK in 308 win.

Rifle is a remington 700 5r with about 2200 rounds down range.

If that is the distance where its contacting the lands, at what distance should I try? I know I should be using bullet comparators, I just forgot to put them on before coming back inside.

I was thinking at lands, and in 0.005" increments away from lands?

my current load is 43.5 gr varget 175smk gm210m in a lapua case.
Click to expand...

I normally start .015" off the lands.

One thing to consider when measuring over all length is that hollow point target type bullets don't always measure the same AOL because any small variation of the jacket gets squeezed to the tip. If you examine a few from a given batch you can often see differences at the tip. That is why you need to us a Sinclair hex nut bullet comparator, so your measurement is from where the bullet contacts the ogive. I have tested batches of hollow point match bullets where the OAL varied by .020" yet thy were still good shooting bullets as long as your seated length was based on actual contact point with the lands.
 
Seating just on the lands means you'll have to measure every 50 rds or so and adjust accordingly. I usually jam 10 thou or I'm back 10-20 thou. I don't like being right at the lands if I don't have to.
 
As mentioned above, lots of guns work well quite a ways off the lands - the bullet really doesn't jump - it is still almost all still in the case even with the longest "jump" unless the throat is burnt out on an old barrel.

For hunting, it is best to load to work in all guns of that calibre. Cleaning up all the powder and finding a rod to get the bullet unstuck from the throat can be a real bother/embarrassment.

I'm not a real benchrest shooter, but I will theorize that if there is any variation - say 2 thou, it would be better to have that variation between 18 to 20 thou from the lands than from 0 to 2 thousandths.

If there were more variation in "jump", the pressure spike could vary a lot.
 
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