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

@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 csmiffy

@mimms2 I thought I read years ago that they did prove it?
Took a certain set of parameters
A certain powder type, in a certain size case as in maybe 308 or bigger, and massive underloading like less than 50% of volume. Something like that
Then it was relatively repeatable.
Not generally a few grains under minimum but quite a lot like a cock up with the powder thrower or misinterpretation of load data. @grandpamac do you remember the details or is it indeed a myth

Greetings Csmiffy,
The article that I mentioned in an earlier post was in Handloader about 40 years ago. The rifle was a .240 Gibbs and the writer found he was able to produce pressure spikes with reduced loads and holding the rifle muzzle down before firing. This was in one rifle with his components. The .240 Gibbs is based on the .30-06 case with the shoulder moved well forward and increased to around 40 degrees. If there ever was a barrel burner this would qualify so the rifle would likely have had a rough leade. The writer had purchased the rifle second hand so there is another unknown. I have seen the statement that laboratories have failed to demonstrate pressure spikes from reduced loads of slow powder in large capacity small calibre cases but have never seen any detail to back it up.
Regardless the caution applies to a specific small group of cartridges and may have been reduced or eliminated by modern manufactured powders. 40 years back there was a lot of military surplus slow powder about which was never originally intended to find its way onto a handloaders bench.
So to ease Kiwi Sapper's mind none of this applies to the .308 or .303. The main danger here is a too light load failing to ignite the powder at all, or the powder being omitted completely. This can leave the projectile just far enough in the barrel so that a second round can be chambered behind it and very bad things happening if the trigger is pressed. I have heard first hand of both of these happening recently, fortunately both were detected and no harm was done.
Regards Grandpamac.

Originally Posted by Kiwi Sapper

What Ho Chaps,

My thanks for your helpful and reassuring posts. I now understand that:

Case neck to projectile contact should be the diameter of the projectile.......Although this precludes my efforts to substantially reduce bullet jump in my 308. So be it. I asked, you answered, I follow.

As I seek "hot loads like a gay guy seeks a couger," and as an x civil servant, "I can follow the handbook instructions", <80% low loads are of no interest" SO filling "air space" with modern powders will not be an issue.


The "Boat tail" comments are particularly helpful and reassuring. I only have a left over 80 pack of them which I will save for the rainy day I runut of FMJ for the Spanish FR 8 which is #2 308.

Just a couple of "things'..........

Thing 1......I learned a new word today....concentricity I Googled and apart from understanding a central point of a circle....I am still Duh and fail to understand the link to projectiles...apart from being round and "balanced'


Thing 2......I still lack guidance on my query "does the OAL measurement as given in the appropriate dies have any relevance to the above? i.e not to be exceeded under any circumstances"

I understand @mimms2 post ( Thank You) "..OAL depends on projectile and a more useful measurement is "Base to Ogive" as homing in on "bullet jump" i encountered another new word Ogive and I have acquired the goodies required to measure that and it is the measure for improvment ......even if I can't achieve it because of chamber length.

SO, is OAL a safety Law or guidance?


Again, many thanks.



P.S. @grandpamac....

I followed your guidance re projectiles for the Parker Hale Mauser 308 and now have a goodly collection of Hornady Interlock 150 flat base . The 80 BT 's are leftover from seeing which she liked :>)

Greetings Kiwi Sapper,
In answer to your specific Question no 2. The maximum OAL listed in some manuals is there as a suggestion only. Provided you have the projectile seated far enough into the case to keep it there and the cartridge will fit in the magazine there will be no problem. Some testing that I have read showed that a longer jump to the rifling does reduce velocity somewhat. Seating the projectile further out to be close to the rifling in the same chamber reduces velocity a little more. I seat the projectiles further out in my 6.5 with no problems.
Regards Grandpamac.

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 Happy Jack

As I understand it going longer than the OAL means it won't feed or probably wont feed from the magazine. There must be other reasons but being new to all this I don't know them.

My thoughts entirely.

Originally Posted by mimms2

OAL is determined by SAAMI spec which is what manufacturers cut chambers to, make magazine length to etc.
It's usually "good enough" but the golden dimension for me has been 0.02 ogive to lands.

Ah, now that is of use as I am aware that several views exist on "touching" to 'away from". So if the chamber length and magazine allow it, that 0.02 will also b my goal.

Thank You.

Originally Posted by Marty Henry

Cast lead is a bit of a different matter. For me 10 grains of blue dot certainly is nowhere near a full case but under a 180 grains cast lead projectile my martini enfield loves it. No filler. Actually a full case of blue dot would be very bad i suspect.

Bother..............I was progressing nicely with 303 and 308 and modern powder then you bring this up...Now I'm going to have to look at my Martini Enfield as casting lead is on the to do list for my MLE.......Now extended to the M.E, but as I don't.want to buy, (even if I could) another powder so will have to workout a lower powder charge for 2208.

Thank You.......I fink. :>)

Originally Posted by grandpamac

..................
So to ease Kiwi Sapper's mind none of this applies to the .308 or .303. The main danger here is a too light load failing to ignite the powder at all, or the powder being omitted completely. This can leave the projectile just far enough in the barrel so that a second round can be chambered behind it and very bad things happening if the trigger is pressed. I have heard first hand of both of these happening recently, fortunately both were detected and no harm was done.
Regards Grandpamac.

having fired a lot of WW 2 303, I am now VERY conscious of a click.....bang

Or even worse, a click.......

Consequently the latter causes me to freeze for 15 seconds then eject and "peer myopically down the long hollow thing." :>)

Originally Posted by mimms2

I have 2208 recipies for both 303 (to match the sellier belot 150gn loading) and 308. I'll post them when I get to a PC as reference.

All assistance gratefully received. Thank You

Originally Posted by Kiwi Sapper

having fired a lot of WW 2 303, I am now VERY conscious of a click.....bang

Or even worse, a click.......

Consequently the latter causes me to freeze for 15 seconds then eject and "peer myopically down the long hollow thing." :>)

I'd suggest waiting a tad longer. NRANZ requirement on their ranges is 30 seconds and that's for modern ammo not cantenkerous old milsurp.

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 zimmer

I'd suggest waiting a tad longer. NRANZ requirement on their ranges is 30 seconds and that's for modern ammo not cantenkerous old milsurp.

Good point..........I can count to ten, add in the fingers and then do the toes.:>) Sweet as. :>)

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?

Originally Posted by Kiwi Sapper

Good point..........I can count to ten, add in the fingers and then do the toes.:>) Sweet as. :>)

Yep, if you open that bolt and a hangfire does go bang you may end up less 5 or more of those counting aids.

At least with a smle you can manually recock without opening the bolt and try again.
Although I've generally found if they don't go off with the first strike they won't go off at all.

Originally Posted by mimms2

I've heard this story before. Maybe even from you. How do you know you got "double detonation".... and what exactly is that, anyway...

(some keyword searches are SEE, secondary explosive effect; and detonation, which is the super-sonic propagation of "an explosion" which afaik is impossible in this scenario as powder is rather carefully engineered to deflagrate (burn at subsonic speed)...rather than detonate. And the transition has been carefully studied by folks clevererer than me. And if they reckon it ain't too likely, I'll reckon it aint too likely.

BA....Boom definate pause between them....really made a fella flinch something aweful.