Long jump !

[Eligus]

I’m trying to get my head round this business of how far a bullet should be away from the start of the lands known as “jump” or “free space” ? ).

I’m using a .22 Hornet and according to some info I’ve read this should be fairly short – no more than 0.050” for preference. However, I have measured the distance to where the bullet contacts the lands, 1.592”. On a completed round the length to the start of the straight section of the bullet (where it will contact he lands) is 1.400”. This gives a distance of 0.19” “jump”, which seems very long. It will be even more with factory rounds as they are considerably shorter than my hand loaded ones.

Have I got this right and does it make much difference?

[strebblo]

No, it doesn't really make a lot of difference - if your homeloads are doing well a few hundred thou back from the lands, then stick with it. I was given that advice from Dicehorn who gets fantastic results with all manner of rifles and the results speak for themselves..

[dannywayoflife]

Seating depth I find is trail and error. If they are working at that depth why mess? If not then try some differing seating depths once you've found your optimum charge weight.

[Eligus]

Yeah, I wont mess with them , just wondered at the disparity.

[airgunnut]

when i got my marlin 357 the manual had 2 numbers - the max bullet length and the min bullet length, as long as the overall length of the bullet is between them there is no problems, i set up my seating die and made a bullet with no primer or powder to the max length as stated in the book then i got a very cheap set of verniers (you can get plastic ones for a few quid) measure the blank bullet then lock the vernier at that using glue or whatever, now when im loading i can just grab a random bullet and check to see if its too long or too short, (i wound the seating die in a nats so its between the min and max)

[amc577]

For cast bullets, a few thou distance is often recommended..for many spitzer type FMJ bullets (eg the 7.5 Swiss or the 6.5 Mauser), the actual bullet surface is some way from the lands even with factory rounds. With the Hornet, as already indicated, if you seated the FMJ up to the lands it would probably not fit the mag. I would not lose any sleep over it.

amc577

[Parabuteo]

it really is trial and error. it also changes from bullet to bullet.

A good load with my old Dolphin and a berger hybrid was about 35 thou off, but use 2156 or HBC and it was around 15 off.

you can often improve a group by deep seating as well with a long jump, it just depends if you can be arsed to try each and every possibility.....

[baconbuttie]

I've got loads of "jump" in the chamber of my 22-250 and when I started reloading I tried all the seating depths with 3 different bullets, right from touching (barely in the case) to minimum length. Made not a jot of difference to the groups so SAMMI spec (2.350" COAL) is where I seat to every time.

YMMV though

[Eligus]

I tried some more reloads today, rounds seated to an oal of 1.800" did much better than those of 1.850" (longer jump!).

[tacfoley]

I'll just throw in a few words here, since, as GaleforceEight often points out, I know everything there is to know I really should share some of it out, right? I've found that Remington-built rifles 'tend' to have a very long leade, and are therefore most sympathetic to retaining the orginal factory lengh of a cartridge to the point, on one such rifle of my acquaintance, that the bullet is not even in the neck of the case when it engages with the rifling, even with a standard ogive bullet, let alone a VLD type. On the other paw, rifles from Tikka and SAKO tend to have remarkably tight chambers, with very short leades, and are far more susceptible to being finicky where not only bullet design [with regard to the ogive] let alone case-length are concerned.

I reload for two .308Win, two 7.5x55, two 7x57 and a 6.5x55, as well as a good ol' .45-70. Each one has a 'sweet spot' with regard to 'jump', discovered after much shooting and trial and error. The Swiss rifles, a hundred years old and sixty years old respectively, both unsurprisingly shoot cartridges that use the same long ogive as the GP11 bullet, and any attempt to try another design - perhaps a little 'blunter' meets with instant intolerance in the form of wide-opened groups, and yet the K31 and K11 have much different internal dimensions with regard to the leade. The chambers, however, differ in such a minute amount that it is very difficult to detect any difference, even taking into account the numbers of cartridges that must have been fired through these guns in their long history.

Half the fun is trying out a different set of measurements, although the fun is reduced somewhat by the sheer cost of quality bullets here in UK.

tac

[Eligus]

It's not only the cost, it's the availability as well, I seem to get through lots !

[harricook]

when i got my marlin 357 the manual had 2 numbers - the max bullet length and the min bullet length, as long as the overall length of the bullet is between them there is no problems, i set up my seating die and made a bullet with no primer or powder to the max length as stated in the book then i got a very cheap set of verniers (you can get plastic ones for a few quid) measure the blank bullet then lock the vernier at that using glue or whatever, now when im loading i can just grab a random bullet and check to see if its too long or too short, (i wound the seating die in a nats so its between the min and max)

and you can shoot 38 sp out of it too - which are about 3mm shorter ...... !!

Hows that for jump !

Cheers

Roy

[Parabuteo]

Half the fun is trying out a different set of measurements, although the fun is reduced somewhat by the sheer cost of quality bullets here in UK.

tac

On that not Tac it is surprising how small a change in load/jump can make a real repeatable difference.

I have been messing about lately with a load of once fired Fed 308 brass and the change of brass has made quite a difference to the required load.

load dev also means that huge gains in consistency can be had from small changes.

Load dev also allows you to try the less well known (and often cheaper) bullets, often with pleasant results.

Until I sold it Optimus HBC bullets were the best by far from my FTR Rifle, that's above the berger offerings and the 2156. And they were staggeringly consistent in weight and bearing surface/quality for a bullet costing £30 per 100 (when I last bought some). They were dismissed as Aussi shrapnel by many.....but I never saw any of the odd weights, chewed up meplats or debris in them as I saw regularly with Bergers.

Don't be fooled into thinking that because X uses bullet Y, its the only one to use. it probably means X has done loads of load dev before arriving at that conclusion and has bought several thousand, but if something demonstrably better comes along, would probably switch in a blink. Its what your rifle likes, no load dev, no specific data.

Course if you cannot hit a cows arse with a banjo.....

[james19306]

I'll just throw in a few words here, since, as GaleforceEight often points out, I know everything there is to know I really should share some of it out, right? I've found that Remington-built rifles 'tend' to have a very long leade, and are therefore most sympathetic to retaining the orginal factory lengh of a cartridge to the point, on one such rifle of my acquaintance, that the bullet is not even in the neck of the case when it engages with the rifling, even with a standard ogive bullet, let alone a VLD type. On the other paw, rifles from Tikka and SAKO tend to have remarkably tight chambers, with very short leades, and are far more susceptible to being finicky where not only bullet design [with regard to the ogive] let alone case-length are concerned.

I reload for two .308Win, two 7.5x55, two 7x57 and a 6.5x55, as well as a good ol' .45-70. Each one has a 'sweet spot' with regard to 'jump', discovered after much shooting and trial and error. The Swiss rifles, a hundred years old and sixty years old respectively, both unsurprisingly shoot cartridges that use the same long ogive as the GP11 bullet, and any attempt to try another design - perhaps a little 'blunter' meets with instant intolerance in the form of wide-opened groups, and yet the K31 and K11 have much different internal dimensions with regard to the leade. The chambers, however, differ in such a minute amount that it is very difficult to detect any difference, even taking into account the numbers of cartridges that must have been fired through these guns in their long history.

Half the fun is trying out a different set of measurements, although the fun is reduced somewhat by the sheer cost of quality bullets here in UK.

tac

I have to say my experiences with Tikka and Sako differ from this opinion with regard to short leades, I have had a tikka t3 .222 a sako 75.222 an now have a sako 85 .222 all of which seemed to have a loose chamber, all three have required a bullet oal of 60-70 thou greater than the saami spec to get close to the lands with hornady v-max and with something like the nosler ballistic tip which has a much deeper ogive I found impossible to get closer than 30thou away from the lands. Im currently running 40gr v-max with an oal of 2.205 which puts the ogive 10thou off the lands in my 85 varmint