Never played with seating depth, but had a load that shot lights out one day, then the next time you loaded the same load it did not?

[bgcatty]

Consistency of your hand loads is the key to accuracy. It takes time to tune a load to a firearm; but once you get it right you confirm every parameter and “write it down” and stick to it over and over. You will then know when you hit the sweet spot for your reloads.

 

[NyleRN]

Never played with seating depth, but had a load that shot lights out one day, then the next time you loaded the same load it did not?

ITS BECAUSE an inconsistent bump of the case shoulder from your loading procedures adjusts your bullet seating depth, despite your base to o-give measurement being the same. Ur screwin up, bud.

There are a myriad of nuances in precision reloading. Primer crush, powder charge, brass prep, neck tension, concentricity, seating depth, neck clearance, etc…. The two most impactful are powder charge (finding a resonating point in the barrel harmonics where the tuning fork of a barrel is at it’s most absolute standstill, and additional powder evens off in velocity before increasing again), and bullet seating depth.

When adjusting bullet seating depth, most find “the lands”, which I could talk about for a day… and back off 20 thousandths. They measure base to o-give to get a start point. They then test 3 thou deeper for more jump per string, until they find two depths (6 thou) that are consistent. This is your seating depth node. You'll want to load on the longer end of your node to account for future throat erosion, so you won't have to adjust seating depth until it pulls out of the node.

BUT WAIT…. Bullet seating to the lands relationship is not just a base to o-give calculation. When the firing pin is struck, the case drives forward until the shoulder makes contact with your chamber, thereby pushing the bullet forward that same distance. SO, if your shoulder bump from fired chamber is not consistent, you will be adjusting your seating depth differently every time you reset your die. Even though you are seeing the same base to o-give measurement, the differing shoulder setback will change how deeply the bullet sits away from the lands before ignition, despite a consistent base to o-give measurement. Follow?

Do you neck size? Stop it, that’s stupid. Your shoulder continues to grow and change each firing, and changes your seating depth.

Do you full length size, but set your die by touching the shell holder and calling it good? Each time you do this, you are adjusting your bullet seating depth by the difference in how far it pushed the case shoulder back during resizing from it fire formed.

The only way to gain any meaningful data from bullet seating depth adjustment, is to consistently bump your shoulders the same amount. Typically, 2 thou is a good place to start. The only way to ignore bullet seating depth, but to maintain a consistent load, is to consistently bump your should the same amount each firing.

How many rounds down this barrel? Are you running loads on the upper end? Have you re-measured to see if the rifling has eroded forward some?

 

[Paul 7.62]

How many rounds down this barrel? Are you running loads on the upper end? Have you re-measured to see if the rifling has eroded forward some?

Most of us are running warm loads, P-dogs or F-Class, F-Class open is running 180 grain 7mm bullets at 2750 to 2850, P-dog shooters are running 22 cal bullets, 3200 to 3800 fps, and 6mm bullets 3400 to 3600 fps so barrels wear out after so many rounds depending on caliber and chambering, plus how many rounds you put though them in a days shooting. Some p-dog shoots are 300 to 500 rounds a day and the guns get hot. .223 barrels last the longest say 3000 rounds but have them only last 1500 rounds on some of them. Hot 6mm like 6XC, 6 Remington and .243 are good for 1500 rounds or so but have had some only go 1000 and others close to 2000. F-Class rifles are 1500 to 2000 round count barrels and between practice and matches they don't last long. A F-Class shooter has 20 minutes to fire off 20 rounds for score and unlimited sighter before calling for record during the first match, and then has 3 more matches that day with 2 sighters and 20 rounds each match. Besides that's why they make gunsmiths and barrel makers.