In the 'All New 2nd Edition 1988' reloading manual edited by Edward Matunas I read on page 98: 'Benchrestshooters long ago discovered that a rifle invariably shoots best with a specific bullet jump. And the top performance continues when bullets of different types are used as long as this actual bullet jump is maintained'... Page 99: 'When the best jump has been proven by range testing for a specific bullet, it can save a lot of hassle if other bullet types could be loaded to the same one best jump length...' In Lyman�s �48th Edition Reloading Handbook� Bryce Towsley states on page 94: 'All bullets are not the same and you must determine the correct seating depth for each make, style and weight of bullet individually. The ogive shape and design will determine where the bullet will contact the rifling and this will vary from bullet to bullet'. I agree on that and this statement is in line with what Matunas said. Towsley: 'Some bullets will shoot best with a longer or shorter gap and again the only way to tell us for sure is by shooting for groups. ...' This latter remark means a great difference with the statements of Matunas. Does this mean that for a different type of bullet you have to find out again its best jump or �gap� for that rifle? I know you have to find out for every individual bullet its own bullet jump (depending on ogive, weight etc.). If you take a Sierra .277 and measure the OAL with a Stoney Point Chamber Gauge, you could find 2.832 inch. Than you back off, say .020�, to 2.812, which you found to be the sweet spot and most accurate jump for this bullet in this rifle. Then you take an AccuBond of Nosler and the OAL is 2.960 inch. The best gap for the Sierra was .020�, so you make your rounds with the AccuBond to 2.940�. Correct? Or do you have to find out the best free run for this bullet again? What is your opinion?
Jan.

Interesting... Here is how I load with different bullets.

I find C.O.L. at the Ogive of each type bullet and seat about .010 , .020 etc back for each type bullet, generaly.

I play around with the distance from the lands on all bullets . But I usually find that my rifles that shoot real tight , shoot tight groups generaly at any land distance though I usually try and keep it about .010.
Generaly my rifles shoot seirra and nosler bullets the best , but speer and hornaday shoot just as tight out of certain rifles.

This is really interesting. I can't say I have found any hard, fast rules, but it seems that bullets of "like size and weight" tend to like the same seating depth. In other words, if I find that my 270 likes 130 grain Sierra's at .020 off the lands, then it will usually shoot 130 Hornadys, Nosler's and Speer's the same distance. Even 140's seem to like the same distance. However, if I go down to a 90 or 100 grain bullet, the seating depth "sometimes" changes. Perhaps the ogive shape has some effect as well. I can't confirm either way.

In load development with a new bullet, I typically start at the depth that I have found other bullets to shoot well at. Once the optimum charge is found, I then play with seating depth to see if it has any effect.

It would be interesting hear other's experience.
John

Jan, just a couple of comments. First, it is important that you realize (as you probably do), that to keep the "jump" the same with two different bullet types, you need to relate this to the OACL as measured with a bullet comparator. Otherwise you would not be able to take into account the different ogive forms of the different bullets. That was the easy part.

Secondly, I happen to think that it is an over-simplification to suggest, that there is an "overall best" distance to seat all bullets off the rifling in a particular rifle. Why? Maybe this is a special case, and certainly these bullets are not the easiest to get to shoot, but take Barnes X as an example. I have found numerous references where people report that lo-and-behold, seating the X deeper than expected produced an improvement in accuracy. That goes against the theory of a "best bullet-land" distance. Consequence: you can probably use observed values of promising bullet-land distances as a starting point, but there is no guarantee that this will be where you eventually want to end up. More fiddling to do, I'm afraid

Naturally, this all assumes you are not using 0 bullet-land distance. A lot of competive shooters swear by this, as seating the bullet into the lands eliminates problems of getting the bullet started straight down the bore. Apart from causing concerns with pressure (can't load to max loads), this is impractical for other applications where you might want to remove your cartridge from the chamber, without running the risk of dumping powder all over the rifle.
- mike

Thank you folks. Yes, Mike, I sure do use a comparator (Stoney Point). I think you noticed I diminished the COAL's with one inch in my post, you are right!
I reloaded thousands of rounds for my Sendero .270 and was curious on comments of other reloaders on the statements of Matunas and Towsley. My sweet spot with most bullets from 130 tot 150 grain is .029" off the lands, and this was real tricky with the new AccuBonds 140 grainers. With these, I grouped .68 MOA and better (three 5-shot groups), a longer or shorter gap of .005" opened up to about 1 MOA. Could (by the way) not get good results with Barnes X(LC) and Scirocco, tightest groups about 2 - 3 MOA, even with gaps to .060" and other reloadingtricks.

I believe finding the exact, correct bullet jump distance for each bullet type is a lot more important to a benchrest shooter than to a hunter!!