Does preferred seating depth change with bullet weight/type?

[jalan01]

apologies if this has been asked previously.. I understand the principles of having the ideal seating depth for loads in my rifle, and have worked out, by testing various seating depths, that the best for my rifle using a particular bullet (75gr A-Max) is 0.012" off the lands.

My question is - If my rifle likes 0.012" jump with these particular bullets, would the same jump from the lands apply to, for example, an 80gr A-Max.. or a 77gr SMK?, or do I have to go through the same testing of various seating depths for each and every bullet I want to shoot. I realise that c.o.a.l. varies with different brands/sizes as the ogive varies.. but just wondered if the jump also varied bullet to bullet, or if that would be a constant?.

[20series]

Some bullets like a jump some are less tolerant.

so you'll generally need to play about with different jumps to see what gives you the best results, but starting at 12'. Hth
Alan

[Half MOA]

I am thinking that if the ogive varies from bullet to bullet weight, so will the distance from the lands, so you may still need to experiment for desired accuracy.

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[jalan01]

[QUOTE=Half MOA;6850668]I am thinking that if the ogive varies from bullet to bullet weight, so will the distance from the lands.[QUOTE]

correct.. but I can still set to same distance to the lands of .012" with any size bullet if that is what the rifle likes.. I'm just being lazy really.. and hoping that all bullets will work at that distance as well as my 75 Amax so's I don't have to faff about ladder testing every type of bullet for optimum seating depth and I can just get on with load testing!

[Elwellaxe]

Ever man I know likes a jump as often as they can manage, are shooters any different?

[Si-snipe]

apologies if this has been asked previously.. I understand the principles of having the ideal seating depth for loads in my rifle, and have worked out, by testing various seating depths, that the best for my rifle using a particular bullet (75gr A-Max) is 0.012" off the lands.

My question is - If my rifle likes 0.012" jump with these particular bullets, would the same jump from the lands apply to, for example, an 80gr A-Max.. or a 77gr SMK?, or do I have to go through the same testing of various seating depths for each and every bullet I want to shoot. I realise that c.o.a.l. varies with different brands/sizes as the ogive varies.. but just wondered if the jump also varied bullet to bullet, or if that would be a constant?.

As mentioned by others the seating depth preference changes with different bullets. You also need to be careful when changing batches of bullets. Rarely are different batches exactly the same. Some variations are shocking. Using the same seating die position and transitioning into a different batch can lead to a large difference in the base to ogive measurement. I've seen noted Amax have shown 10-15 thou in this measurement. This can be the difference between an accurate load and one that is not (depending on your requirements/expectations).

[compactflash]

Always try a range of jumps with a new bullet if you want optimum accuracy and always measure new batches of bullets if you want to be precise with these measurements. As already said, bullet dimensions from batch to batch can vary considerably, even with expensive brands such as Bergers. It's just a side effect of the manufacturing process.

Don't be afraid of jumping bullets a long way either. If your chamber has a long throat you may not have a choice and it's better to load a few experimental rounds and test them rather than always wonder if it would work or not.

[Randy Bohannon]

Unfortunate the answer is that there is no clear cut answer to this.

bullets of the same general design may indeed prefer to be in the same rough area with regard to proximity to the lands, on the other hand very small differences that are invisible to the naked eye may result in them preferring to be somewhere else entirely.

the only answer is to try and to post your results back here, the Internet is full of questions like this but the posters never come back and post what happened when they tried it!

[zx10mike]

my 6 br likes 5-10 tho jump max
my 7mm shot the amax well with a 120 tho jump lol good luck.

the only rules are ... there are no rules.

[harry mac]

I have to start by saying I am not a bench rest or F Class shooter, so accuracy to the nearest "nth" of an inch is not my primary goal.
For me, I just seat all bullets one calibre deep, or with the base of the bullet level with the bottom of the neck, and play with the charge weight to find the most accurate load. I just stick then with whatever charge weight gives the best group.
I do that for all calibres and bullet weights.
If I played either of the games I first mentioned, my approach would probably be different, but this technique gives more than enough accuracy for deer and fox.

[kmahow2]

The top US civilian (ex Army) sniper competition shooter who was their champion for many years, had the following to say re .308, which may hold true for other calibres.

He always full size resized all his cases, it was always loaded to maximum magazine length. He used to practice by shooting golf balls at 750yds from a bipod, how accurate do you want to be ? His advice was to play with powder/primer/bullet combo until you get the sweet shooting one for your gun. Velocity is not a concern when accuracy is required, provided you are within the working range of the cartridge. By that he meant a portable 20-22" barrel 308 is an 800yd round, 1000yds is beyond its best accuracy potential due to barrel length & velocity. Yes 26-30" barrels & VLD bullets can make it reach but would you carry one in the field ? He also said that most people waste to much time measuring & calculating & not enough shooting

I assume the 75grain Vmax is in a 243 !? Similar rules apply based on application, YMMV !

Have fun.