Main difference between hollow base and flat base.

[jwrowland77]

Other than the obvious, what's the main difference in a hollow base and flat base when trying to reload. Advantages of each and disadvantages of each.

Let's use a 9mm 115 grain for the example.

Just a newbie trying to learn.

 

[rcmodel]

In theory, a HB will obturate and fit the bore at lower pressure then a flat base of the same hardness.

But in the case of 9mm bullets like Berry for instance, they are probably too hard to obturate anyway.

The other thing is, they often don't take up as much powder space when seated deeper for proper feeding.

rc

 

[Walkalong]

Berrys does it to get more bearing surface, and in theory, better accuracy.

 

[GLOOB]

Don't longer bullets need more rotation to stabilize? Theoretically, hollow base bullets in standard weights might not be good for long range accuracy out of standard twist rate barrels. Course depending on the barrel and load, you might get better stabilization.

Some cases get thicker below the point where a standard shaped bullet would seat. These cases will squish a hollow base bullet. I think this would make the HB bullet noticeably less accurate.

Pros: better neck tension. Can load extra long OAL's out of customized guns. Possibly better accuracy out of some guns for w/e reason: obturation bit that RCmodel mentioned leading to more consistent velocity; length vs rotational stability that I mentioned; more bearing surface might allow higher velocities esp in polygonal barrels, before the rifling starts to mess up the bullet. And you might also find the longer bullets seat more consistently straight/concentric.

Personally, I use the FPHB in 9mm, cuz they're easier to pick up, and they give better neck tension in crappy thin walled brass. If there's a difference in accuracy, I haven't noticed.

 

[1SOW]

Let's use a 9mm 115 grain for the example.

Let's arbitrarily say your flat-base 115gr bullet is is .530" long.

Take the exact same bullet and remove 8 grs of lead from the base and add it back into the bullet "length". The same weight bullet may now be .535" "long" with the exact same nose shape. (All amounts of lead and lengths are just made-up examples.) This added length is added back into the straight sidewall of the bullet and adds to rifling contact.

The amount removed and added to the length doesn't need a longer oal because the hollow base exactly adds back the same amount of airspace (8 grs of lead worth) below the bullet.

It used to be believed "hollowpoints" were the more accurate pistol ammo, but hollowpoints also make up the removed nose weight with a longer bullet sidewall.

I basically agree with 'rcmodel' above --mostly.
The Berry's thick plated 124gr HBRN is made to load up the 38 super speeds (1450 fps). I suspect this would increase the obturation of the hollow base when loaded that hot. With mild loads I agree that it wouldn't be as significant.

Just my thoughts.

P.S. Berry's now have a thick plated 115gr HBRN.

 

[JLDickmon]

In theory, a HB will obturate and fit the bore

them's pretty fancy words there, slim...