45 colt load..................Scratching my Head over this one.................

[markp]

  Last week I loaded 5.5 grains of trial boss behind a 250 gr cast  bullet With  winchester primers  and clocked it at 615 fps   five shot averge. This week I loaded the same load only with a 200 gr bullet same make same cast design.  Every thing else was the  same . I figure I am going to get an xtra 150-200 fps velocity.
 
 My five shot averge showed  479 fps velocity ??  A  drop  in velocity of 136 fps ?

The velocity variations were pretty close . The load seemed accurate .

What am I missing ??

[v-man]

May get lots of differing answers but same powder charge and less bullet weight means less chamber pressure, hence less energy pushing the bullet. Makes sense to me. The charge never reached peak of power curve cause bullet was easier to move. Am I missing something?

[KAYR1]

V-Man, those are my initial thoughts exactly, but I dont know for sure. Did the above poster check reloading data for pressure/velocity info?  I love the .45 LC, but its and old cartridge, built for black powder, and suitable in new, strong guns for high pressure. 

Trail Boss powder addresses many of these issues. If it were me, I would double check my loads, charge weights and data.

[Savage]

Try a really firm crimp. I don't think you're getting complete powder burn.
Savage

[Bart Solo]

According to the Hodgdon  Reloading Data Center 5.5 grains of Trail Boss behind a 200 grain cast bullet is supposed to result in a velocity of 706 fps, and a pressure of 8000 PSI.  By way of comparison 5.8 grains of Trail Boss pushing a 250 grain cast bullet is supposed to generate a velocity of 727 fps and a pressure of 12,700 PSI (close to the max for a colt or clone SAA.)  I suspect that what has been written above explains why the velocities are similar when comparing the two bullets, and no doubt higher pressures build behind the heavier bullet (the starting load for a 250 grain bullet is 4.5 grains with 606 fps and 8800 CUP, but 5.5 is the starting load for a 200 grain bullet.)  What I don't understand is the dramatic drop in velocity.  I suspect there is something amiss in the loading of the 200 grain bullets. Maybe the crimp isn't tight enough.  Maybe the wax isn't sealing the bullet properly.  It  is hard to say from here, but something is amiss.

How dirty are the 200 grain bullet cases after firing?

[markp]

   The cases were pretty filthy !!! Beyond normal I would say.

[Steve P]

Shorter bullet = more case capacity = less internal pressure.
Shorter bullet = less barrel engagement = easier to push down the bore = less external pressure.

Better crimp will help you build up the internal pressure.
Use a carbide sizer die and only size your case to bullet seating depth (if you only shoot these in one gun).
No need to full length size a straight wall case being shot in the same gun every time.  It leads to what has been called the "coke bottle" effect.  Your full length sized case will look like ) (.  This is a little exaggerated on the computer, but becomes very apparent when comparing sized and unsized cases side by side.  This will stop the blow by which causes the cases to be dirty.

Steve

[cwlongshot]

I agree with suggestions of a good crimp and incomplete/inconsistent burn.

Excessively dirty cases are par for the coarse with such lite loads. The pressure created upon firing is not sufficient to seal the brass case in the chamber to prevent the sooting.


CW

[markp]

  I will load a small batch with a firm crimp and see if the velocity changes.
  I am well below what velocity the books say.  I will post the results.


 Thanks for all the responce.
 
 

[Bart Solo]

Make sure your bell is large enough when you run your expander die. Shaving lead is a big problem with cast bullets. The bell has to be large enough for the bullet to start into the case fairly easily, but not too large as that will result in reduced case life. 

[Blackhawker]

Could be all of the above....pressure changes from more case volume, too little or too much crimp on one load vs. the other.  Someone mentioned load data from the books.  The velocities given in books are pretty much guidelines since every firearm, bullet, and powder lot is different and it is likely that one will get varied data from what the book states.  Lastly, and I don't think anyone mentioned this one yet, did you measure the diameter of each bullet?  Perhaps the 250 grainers had .001" more diameter than the 200's which also can create more pressure as well.  Cast bullet diameters (when purchased and not made from scratch) can vary from lot to lot and especially from mould to mould...at least that's what I've found.  Lastly, the calibration of your powder measure/balance may have changed from one week to another.  Perhaps you might verify the calibration of your balance and adjust your powder measure to it.  (just a thought) 

[markp]

  I  Loaded 8 rds of each side by side. 200 grain and 250 grain  5.5 grains of trail boss. So the likely hood of me doing somthing differnt would lesson.

The results were the same.   470 averge fps for the 200 grain and 636  averge fps for the 250 grain.

Both bullets are the same brand. Both say .452 diameter.  But as noted by blackhawker  this could possibly varry.

I was surprised at the diff in bearing surface between the two bullets. I think that is what its called
the actual part of the bullet that contacts the rifling.
if the bullet isnt sealing the barrel then some of the pressure could be escaping ahead of the bullet I believe ?
both  cases are filthy but the 200 grain case seems a little worse.

[SHOOTALL]

in the sierra manu. 8.9 grains of unique will get you 850 fps. with a 300 gr. bullet . to get the same fps with a 240 gr bullet you need 8.7 gr.
16.4 gr. of 2400 and a 300 gr. bullet 1000 fps the 240 gr bullet only needs 18.7 gr. of 2400 to reach 1000 fps .

[SHOOTALL]

It would seem that charge weight may only be part of the reason .

[Blackhawker]

With the OUTSIDE of the cases being sooty (as CW has suggested) is a good indication that the brass is not expanding enough to seal the chamber.  If some of the soot (burnt powder) is making it back on the outside of the cartridge, then some of the pressure is going that way too.  Hence, the 200 grainers have more soot...less pressure.....less velocity  
Also, I'd get yourself a caliper and measure those bullet diameters as well.

However, in order to spare yourself such agony, why don't you just jack up the load a little for the 200 grainers?  The cases should seal with a little more pressure and you'll get your velocity back.  Is there some reason why you want such low velocity?  Cowboy shooting regs??

[markp]

 I am learning a lot from this experiance (200 grain with less velocity then  250 grain ) and all the responces are helping me put this into some perspective. 
 
 I need pretty light loads when shooting  revolvers because of wrist problems.

 I may stick  with the 250 grain or I may bump up the powder charge for the 200.

 But I ll play with  it a bit and learn what I can. I wouldn't be learning much except for all the replies.

 Which I appretiate. Keep  em  coming.

   

 

[Savage]

I'd bump up the powder charge on the 200gr bullets for sure. At that low velocity, you're not too far away from lodging a bullet in the barrel. Looks like for the velocites you want with the 200gr bullets, it may be time to look at another powder. For light loads, it's hard to beat Bullseye. I've never used Trail Boss, but it sounds like the burn rate is too slow for what you want to do. If you are shooting these rounds in an old Colt or a reproduction, the groove dia might be as large as .454. I'd guess that the 200gr bullet is sized to .451-.452, and the 250gr is most likely .454. That could be part of the problem also. I'd also check the dia of both bullet weights to check that out as well. Good luck, I'm sure you'll solve the problem.
Savage

[zoner]

i was given a couple thousand .452 200 gr SWC cast bullets than normally would be used in 45 ACP target loads that i load in clean cases(clean your brass,buddy) with 7.5 grs of 231 and i crimp em with a Lee 45ACP taper crimp die...no keyholing,a super clean burn,accurate to 50 yds(haven't shot further) and i don't have a chronograph but i sure don't wanna try catchin one of em...try cleaning your cases and maybe something like 231 or bullseye

[kitchawan kid]

I have shot many loads the same and found trail boss to be cleaner then most other powders,with my own cast bullets un-sized from a lee mold and I  do use the lee crimp die.