Load Testing: IMR 7625 powder

[1SOW]

Quick question, Wobbly.  My HBRN-TPDS push tests to over 1.2, so loading them at 1.16 is plenty away from the lands.  I'm sure you're in the same boat, so I'm wondering why you chose 1.13 over something longer.

I tried to find his posts where he mentioned just that issue, but didn't find it.

There are differences between rifle oal/cols and pistol oals.   In rifles, a short jump to the rifling usually makes a noteable improvement in performance.  Not so much so in pistols.

One immediate "gain" with the shorter 1.125-`1.135"/1.140" ( a concession to Wobbly ) commonly used 124grRN oals, is retention.  The bullet tends to be held tighter, builds a tiny bit more pressure before release and also loads "straighter" in the case.  Hitting the ramp when feeding won't knock the bullet out alignment as easily as a 1.160 oal.

Mine also tend to "gain" accuracy in this same range of oals.  I found a post by "Clint" who has done a lot testing on this subject and found the same accuracy gain with the 124 HBRN at shorter oals.  I suspect the above "gains" have something to do with that.

Wobbly will add his thoughts with a clearer explaination than I can 'gen' up.

[1SOW]

Here's something interesting -- if I seat my HBRN to 1.3, the seating depth will be .001 shallower than where I've been seating my HBFP, and I think we can agree that .001 is a wash.   However, I need 4.5 grains to get the HBFP to 1050.   You're getting the HBRN there at the same seating depth with 4.3.   

And now I'm curious.  I'm going to have to load up the two at the same seating depth and see what happens.  I'll let you know tomorrow. ;-)

The "HB"RN is a deceiver, because that hollow base  ADDS to the empty case volume---maybe .005" or more.. 
Hope this makes sense.

[IDescribe]

That's interesting.  The only other variable I can think of is that with extra jump space, the bullet is actually traveling faster and has more momentum when it hits the lands. 

Tomorrow I will be shooting HBRN at 1.13 and HBFP at 1.065, which are effectively identical in terms of seating depth.  The HBRN will have a jump space of a little over 0.07 while the HBFP will have a jump space of .01.  We'll see what happens.  I'm curious about accuracy, of course, but I'm also curious about velocities for the same powder charge at the same seating depth.

[IDescribe]

Here's something interesting -- if I seat my HBRN to 1.3, the seating depth will be .001 shallower than where I've been seating my HBFP, and I think we can agree that .001 is a wash.   However, I need 4.5 grains to get the HBFP to 1050.   You're getting the HBRN there at the same seating depth with 4.3.   

And now I'm curious.  I'm going to have to load up the two at the same seating depth and see what happens.  I'll let you know tomorrow. ;-)

The "HB"RN is a deceiver, because that hollow base  ADDS to the empty case volume---maybe .005" or more.. 
Hope this makes sense.

I definitely get the hollowback cavity increasing case volume relative to a non-HB, but in this case, Wobbly is using Berry's HBRN, and I'm using Berry's HBRN-TPDS and HBFP, so all 3 bullets in question are Berry's 124 hollowbacks.   Or am I missing something else?

[1SOW]

Yes, it makes logical sense to load to the same "seating depth" for both the 124gr hollow base bullets.  Actually it's somewhat "logical"  to load ALL 124gr bullets to the same seating depth,  but that  usually isn't going to give the same performance with "very different" bullet bullet shapes.  When no oal data is available for a specific bullet, that's a place to start.

Interested in your results.

[Wobbly]

I definitely get the hollowback cavity increasing case volume relative to a non-HB, but in this case, Wobbly is using Berry's HBRN, and I'm using Berry's HBRN-TPDS and HBFP, so all 3 bullets in question are Berry's 124 hollowbacks.   Or am I missing something else?

There are only 2 bullets in question, the 124grn HBRN and the 124grn HBFP. All that extra description ("-TPDS") comes with the bullet. In other words, you can't get a HBRN without also getting the thick plating and double striking. That makes it too much for my little fingers to type.

Sorry for the confusion.   

[Wobbly]

I'm impressed how 7625 shows a very reliable progression with .1 grain changes

Wobbly,  did you notice any differences with the "Mag" primers?  Hotter?, burns cleaner?, snappier? Make you feel younger?

I'm looking for any slight increase in bullet speed. Just wondering if the 6K+ mag primers now in stock will force me to rework all my favorite comp formulas, or conversely, can I use a mag primer to boost me a reliable 10 fps so I have a choice (more powder being my sole choice at present) of how to make PF. Once I find an OAL that feeds well and leaves plenty of room for powder, I'm reluctant to seat .005" deeper to get me "over the top".

Quick question, Wobbly.  My HBRN-TPDS push tests to over 1.2, so loading them at 1.16 is plenty away from the lands.  I'm sure you're in the same boat, so I'm wondering why you chose 1.13 over something longer.  Educate me, please. 

As stated previously, seating the bullet deep into the case is important for accuracy increases. I usually seat these at 1.140", but my die was already set for 1.130" so I went with it.

 

[IDescribe]

Gotcha.  Is there a minimum seating depth you consider "deep enough" for that accuracy factor?  Also, is there a max seating depth with 9mm beyond which you consider pressures too unpredictable to mess with?


OKAY, the results are in:

Primer:   CCI SPP
Powder:  IMR 7625
Brass:     Starline
10-shot strings


Berry 124gr HBRN
OAL-1.3
Seating Depth-0.236
4.5 gr
1055 feet/sec
ES-27
SD-7


Berry 124gr HBFP
OAL-1.065
Seating Depth-0.237
4.5gr -- 1073
ES-24
SD-7

So with nearly identical seating depths, the HBFP with considerably less free-bore got 18 feet/sec more an average. 

[Wobbly]

Gotcha.  Is there a minimum seating depth you consider "deep enough" for that accuracy factor?  Also, is there a max seating depth with 9mm beyond which you consider pressures too unpredictable to mess with?

The longest OAL for 124grn RN is around 1.140".

The shortest OAL for 124grn RN is a mechanical limit. First you want the crimp to meet the ogive of the bullet. Then there is a point where the inside of the case gets thicker. Forcing a bullet into that area will simply swage the bullet to a smaller diameter, and that's not helpful.

 

[1SOW]

I have exactly the same experience with the HBFN being a little faster than the HBRN.   Mine are @ 1.135" and 1.065" respectively.   I use .1+ grs  less powder (n320) with the HBFN to make them close to the same speeds.   Approx. 129-130PF which works fine for my uses.

[IDescribe]

Then there is a point where the inside of the case gets thicker. Forcing a bullet into that area will simply swage the bullet

Out of curiosity, I took a cutting wheel and cut one of my Starline brass down the middle.  The wall starts thickening 0.300 in from the mouth.  That's actually quite relevant for the 147gr BBI's I've been playing with.  They push test to 1.129.  If I load them at 1.12, that's just .004 from where the wall starts thickening.  That' s not much of a window. 

[jameslovesjammie]

Out of curiosity, I took a cutting wheel and cut one of my Starline brass down the middle.  The wall starts thickening 0.300 in from the mouth.  That's actually quite relevant for the 147gr BBI's I've been playing with.  They push test to 1.129.  If I load them at 1.12, that's just .004 from where the wall starts thickening.  That' s not much of a window. 

This is also the reason why almost every 147 grain bullet is bevel based.

[jabbermurph]

That's a shallow push test result, ID.  I have been loading the BBI 147gr at 1.135ish.  I'll have to check my push test data, but I believe it was in the 1.150s.  The load I was running was at 1.145 w/ 3.3 grains of n320.  I dropped the OAL to 1.135 w/ 3.45 grains of n320 and these are like lasers.  I love 'em.  Great price and great customer service (I doesn't hurt that I shoot with the owner every other week either.)  Been wanting to try the 135 gr BBIs.  Chandler is starting a new coating this month, very excited about trying them.

[IDescribe]

Okay, I've got some BBI 147 data.  I need to say in advance that the data I'm going to show is NOT the complete data I've accumulated.  When I started testing this load, I started with 2.8, 3.0, 3.2, 3.3, 3.4.       3.4 was not where I needed it to be in terms of power factor for the shooting sports, but it was the highest I loaded for that first batch.  I am leaving that first batch out because on the second batch, I loaded at a longer OAL, so the earlier data doesn't line up.  I started the second batch where the first one left off -- at 3.4.  So here it is:

Powder:      IMR 7625
Primers:      CCI 500
Brass:         Starline -- Once-fired
OAL:           1.121   

The results from the ProChrono:

3.4gr     848 fps avg        ES-17    PF-124   
3.5gr     871 fps avg        ES-21    PF-127
3.6gr     889 fps avg        ES-16    PF-130   

A power factor of 130-135 is what I was shooting for with the top load, so I just barely made it.  I will probably load and test it at 3.7gr in the future. 

Also, I was confident that 3.6gr would make the power factor of 130-135 I was looking for, so I loaded up an extra 20 bullets at 3.6, which I shot against 50 rounds of MG 124gr JHP.   In terms of the differences in recoil between the 147gr and 124 grain bullets with the same powder at roughly the same power factor, I'm leaning away from the heavier bullet in terms of preference.  The slightly sharper recoil of the 124 grain bullets feels better to me.  I prefer the feel of the BBI 125gr bullets in the same PF range, as well.  The 147's definitely feel softer, but they don't feel better. I'm going to have to break out the 115's next. 

[1SOW]

IDescribe, I experienced the same using the Berry's 124 vs their 147s.  The 147s were softer but felt S L O W--and not as 'right' as the 124's.  In my case the 147s  also shot some higher.