Thread: "Air space" in 303 British and 308 Winchester caseloads...Dangerous?

Originally Posted by Kiwi Sapper

With reloading 303 and 308 I am now looking at reducing the projectile seating depth to reduce the "bullet jump" I currently have with commercial loads. Sadly, there are 3 gray areas of my knowledge.

1...Having entered reloading via black powder, I am very conscious of the danger from air space in BP rounds and with the reduced seating depth of 303 and 308 projectiles, is the increased airspace in the case a danger, as it is for B.P. I am using when using ADI AR2208.

If not, great, if so, would the usual space fillers for B.P. be suitable?

2...Reducing the projectile seating depth, results in less length of the projectile in the case. For safety and pressure, is there a minimum length of projectile required in the case.....or is it that it must just be solidly fixed?

3...Does the answer to 2 also apply to boat tail projectiles as they have a tapering end which, dependent upon the taper, reduces the ability of the case to securely hold the projectile?


Finally does the OAL measurement as given in the appropriate dies have any relevance to the above? i.e not to be exceeded under any circummstances.
Thank You.

I suguest you buy a reloading manual preferably put out by the manufacture of the projectiles you are using, load your ammo with the overall length as given
and the start load and work up in 0.5 grain steps until you find the most accurate powder charge this will give you a known load to check other loads performance
against, choose a powder that gives the best velocity with 90% case capcity compressing modern smokeless powders is not recommended when starting out,
With the .308 and .303 Brit 2206H and 2208 are the easiest to work with both lead and jacketed bullets for reduced loads use Trail Boss, Stay within recommended
powder charge weights and you can't go wrong, And forget about S.E.E it does not happen.

@Kiwi Sapper

Concentricity of bullet seating refers to the bullet axis being concentric with the bore axis. Not a problem in round balls, but in long and pointy bullets it is. A oblong bullet engaging the rifling at an angle will, if you trace the progression of its very tip, progress in a corkscrew manner through the barrel, and on exiting fly in a corkscrew trajectory until the spin stabilises it ... at a random point in the corkscrew trajectory. And it flies straight from that point on. This theory predicts that if you zero your rifle at a particular point, bullets will tend to hit AROUND this point, and with less initial corkscrewing the smaller the ring diameter. That is, if you shoot 20 round groups, the groups should be less dense around their middles.

Back to @winaa's comment that he believes concentric rounds are more important than jump.

Originally Posted by Cordite

@Kiwi Sapper

Concentricity of bullet seating refers to the bullet axis being concentric with the bore axis..............Back to @winaa's comment that he believes concentric rounds are more important than jump.

Ah, thank you.
My ponderings were something along this line but as it is not an issue over which I have any control, ( apart from buying suitable projectiles) I disagree with winaa's view. I believe I have more ability to affect accuracy with projectile seating depth.

Originally Posted by Kiwi Sapper

Ah, thank you.
My ponderings were something along this line but as it is not an issue over which I have any control, ( apart from buying suitable projectiles) I disagree with winaa's view. I believe I have more ability to affect accuracy with projectile seating depth.

Seating depth and concentricity are related.

Consider why people seat just off the lands. ON lands may of course cause a pressure spike, so just off lands is desirable. But why try and get as close as possible to the lands? It is for out of a desire to have the projectile engage concentrically. A long throat risks the bullet having too much time and space to misbehave (deviate from concentric) before it locks into the rifling.

Originally Posted by Cordite

Seating depth and concentricity are related........

Yup, so that is why I will try to follow mimms2 golden rule, ".....the golden dimension for me has been 0.02 ogive to lands.


Am I wrong?

Cannot remember without reading back but wasn't it a reasonable load of ball powder?