Bullberry Loading
Data Notes
The loading
data was developed using an OEHLER 43 Personal Ballistics Laboratory
using Bullberry barrels. All loads were weighed or measured using
a combination of a RCBS 5-10 powder scale and a LYMAN Autoscale. Dies
by REDDING in a RCBS ROCKCHUCKER press. Case forming was performed
in an RCBS AMMOMASTER and trimmed on a RCBS TRIM PRO power case trimmer.
No loads exceeded 48,000 psi at any time.
The maximum loads were determined by firing multiple strings under
different conditions on different days. Minimums were established
using the same basic
criteria but the total number of strings and rounds per string were
reduced.
Minimums are not the usual reduced by 10% as most manuals recommend.
Because of the low fill ratio (powder to available space) the pressures
became extremely erratic when reduced below the points shown.
Powder selection
Fourteen (14) powders were tried with various bullet weights and cases.
These are as follows:
| AA 2015BR
|
Pressures
erratic due to high pressure and low case fill |
| AA 2460
|
Pressures
erratic due to high pressure and low case fill |
| AA 2495BR
|
Acceptable
pressure and case fill, but extreme muzzle flash with most loads
|
| AA 2520
|
Pressures
erratic due to high pressure and low case fill |
| AA 2700
|
Extremely
high pressure |
| ALLIANT
RL-12 |
High pressure
with low case fill |
| ALLIANT
RL-15 |
Acceptable
pressure and case fill |
| HODGDON
BLC-2 |
High pressure
with low case fill |
| HODGDON
H-322 |
High pressure
with low case fill |
| HODGDON
H-4895 |
Acceptable
pressure and case fill |
| IMR 3031
|
High erratic
pressures acceptable case fill |
| IMR 4064
|
Acceptable
pressure and case fill except ran out of room with lightest bullets |
| IMR 4320
|
High erratic
pressures acceptable case fill |
| IMR 4895
|
Acceptable
pressure and case fill |
| WINCHESTER
748 |
High pressure
with low case fill |
Rotating cases
lengthwise end-over-end several times helps to uniformly distribute
the powder and contributes to much more uniform pressures and velocities.
Ball type powders
appear to be contra-indicated due to the low case fill ratio. Powder
position is critical to pressure but appears to be less so for velocity.
Powders located predominantly in the primer end gives higher pressure
versus lower pressures if at the bullet end, however, in the limited
testing that was done to test this phenomena (approximately 500 rounds)
the velocity did not vary significantly unless the powder charge was
reduced below about 80% of the case fill ratio.
Bullet seating depth:
Bullet seating depth was determined by seating the bullet .025 from
contact with the lands. Bullets seated deeper or further out can and
will in some cases radically affect pressure with out significant
increase/decrease of velocity.
Fire forming:
Brass was first full length resized in a standard 30-30 Winchester
die. The 6mm cases were then necked down using a tapered shouldered
25 caliber die to a point slightly below the position of the base
of the neck on the finished case. Cases other then the 6mm's were
reduced in one step and by sizing in a tapered shoulder sizing die
for the appropriate caliber to the correct neck base position. Improved
cases were then sized in the appropriate full length sizing die. All
cases were trimmed to the correct length, those not requiring trimming
were all trimmed for uniformity.
The powders used for fire forming varied by whatever was on hand,
but the lowest reduced load of any loads shown will fireform without
excessive pressure.
Sticky opening as a sign of pressure: HOG WASH!
At the point that sticky opening of the action occurs, maximum pressures
have been exceeded! This phenomenon can occur at 50,000psi to 60,000psi.
Some frames appear to have a greater ability to not display this sticking
even with loads that typically register above 54,000psi. While the
sticky opening is a good indicator of over-pressure it is not adequate
to reduce a load by a couple of tenths of a grain and think that all
is well.
Life of brass varied from as few as 15 loadings to as many as 30 as
long as pressures were kept below 48,000psi. The first sign of brass
failure was neck cracks and low neck tension on seated bullets, followed
by stiff extraction. Stiff extraction (not to be confused with sticky
opening) is seen as difficulty in the extractor moving the brass reward
in the chamber (extraction).
One or the other or both of these conditions can occur together. Stiff
extraction is due to the brass losing it resiliency. Brass can continue
to be used but extraction gets stiffer.
Neck tension (bullet pull weight) does not seem to significantly affect
pressures or velocity, variations are noted but unless the neck tension
is so low that the bullet can be seated by hand, it doesn't seem to
make that much difference.
