My Swedish m1867: range report

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Metman2

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I've been testing a few smokeless loads for my mostly unmodified 12.7x44 r/b, using fireformed PRVI 8mm Lebel brass, trimmed to 44mm, with my home-cast Lee-mold 450gr bullets. The lead is scrounged from an indoor range that is mostly .22cal bullets and cast pistol rounds, so it is soft. Actual bullet weight averages 440 gr, and I don't bother sizing, but slather them in Lee Alox and let it dry out before seatling with a light crimp.

My load of choice so far (after nearly 200 fired rounds) is 24gr SR4759. I chronographed 5 rounds - and I realize that's a pretty small sample, but it just worked out that I couldn't do more. Mean MV was 931 fps, extreme spread 76 fps, std error 33 fps.

At 100 yards from a bench rest, I was pretty happy with the first couple of shots, then they started dropping and by the tenth shot they were several inches low:

http://s1093.photobucket.com/albums...ew&current=Lee515-450gr_SR4759_24gr_100yd.jpg

My first thought was "barrel leading". However, neither this time nor before has there ever been much lead to clean, so I discount that as a reason. I wasn't waiting more than 30 seconds or so between shots, and the barrel was getting warm - could this have caused the downward trend?

There was enough heat rising from the barrel that the target was shimmering, so it could have been me not holding true. I'm wondering whether a "mirage effect" due to heat rising off the barrel would cause me to aim low. Feel free to set me straight!:p
 
I would expect the first shot to be an inch or two high but the rest to be in a group. What I would suggest trying is firing one or two shots then letting the barrel cool for several minutes then repeat. If the barrel is warping when it heats up, firing all shots from a cool barrel should give you no increasing drop.

If heat mirage is the problem, then try putting a thin piece of dark cloth on top of the barrel ie something to reduce or eliminate the mirage

cheers mooncoon
 
mooncoon said:
I would expect the first shot to be an inch or two high but the rest to be in a group. What I would suggest trying is firing one or two shots then letting the barrel cool for several minutes then repeat. If the barrel is warping when it heats up, firing all shots from a cool barrel should give you no increasing drop.

If heat mirage is the problem, then try putting a thin piece of dark cloth on top of the barrel ie something to reduce or eliminate the mirage

cheers mooncoon
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Thanks, I will have to employ the shoot - cool off - shoot -,etc. method. I normally do that for testing, I was just having too much fun last time!

Ideally, I should chronograph each shot. That would confirm whether or not my hand loads are as consistent as I think they are. The bullets and powder are weighed, so I know they're pretty uniform, but my less-than-perfect cases could be the source of some error.
 
something I forgot to mention; if you are shooting smokeless through the gun, you need to put a pinch of dryer lint or similar against the powder to hold the powder against the primer. In longer cases, you get very variable pressures if the powder is loose. The alternative I guess would be to use Trail Boss powder which does not need to be held against the primer. At the moment however it sounds more like a warping or bedding problem

cheers mooncoon
 
The inconsistent ignition that would result from a too small powder volume would - in my opinion - show inconsistent and irregular bullet drop from one shot to the next, and not a regular downward trend. Indeed, I had seen this in my earliest experiments with H4198 powder, which is has a lower volume-per-grain ratio than SR4759.

I have tried loading with and without fluff. However, SR4759 occupies quite a good proportion of case volume, i.e. 2.5cc out of ~3.5cc usable volume in the Lebel brass. When omitting the fluff with SR4759, I didn't observe the kind of inconsistency that occurred with H4198 without fluff.

I've tried Trail Boss as well but haven't had time to explore it much. I'll have to run some simulations through my inner ballistics numerical model (the latter a subject for another post).


mooncoon said:
something I forgot to mention; if you are shooting smokeless through the gun, you need to put a pinch of dryer lint or similar against the powder to hold the powder against the primer. In longer cases, you get very variable pressures if the powder is loose. The alternative I guess would be to use Trail Boss powder which does not need to be held against the primer. At the moment however it sounds more like a warping or bedding problem

cheers mooncoon
Click to expand...
 
Here are a few loads from my own Swedish Rolling Block in 12.7X44. I use modified 50/70 brass:

450 gr Lee Cast

12.0 grs Trail Boss - 925 fps
13.0 grs Unique - 1040 fps (max)
28.0 grs SR4759 - 1500 fps (I now use 26.0 grs as a max, as this is higher than I prefer, even though it's a "published" load)
28.0 grs XMP-5744 - 1300 fps
32.0 grs H4198 - 1325 fps
50.0 grs pulled Swede powder - 1400 fps

The best of the bunch was the near full case of the surplus pulled Swedish powder (from the Marstar 8X63 ammo). The SR4759 was a close second. Someday I'll try H4350 - starting at 50.0 grs and going to a full case (likely 55.0 grs), but the pressure might be too low for an effective burn. Varget might be worth a try as well.

You can use 50/70 loads in the 12.7X44R, as it's essentially a slightly shortened 50/70. Published loads tend to be for a max of 18K psi, which is well within the Rolling Block's limit. Here are a few more loads for 450 gr bullets, taken from the 3rd and 4th editions of the Lyman Cast Bullet Handbooks:

IMR4227 - 26.0 grs
Re7 - 35.0 grs
IMR3031 - 39.0 grs
IMR4895 - 42.0 grs

All had a Dacron filler.
 
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Andy said:
.......... Here are a few more loads for 450 gr bullets, taken from the 3rd and 4th editions of the Lyman Cast Bullet Handbooks:

IMR4227 - 26.0 grs
Re7 - 35.0 grs
IMR3031 - 39.0 grs
IMR4895 - 42.0 grs

All had a Dacron filler.
Click to expand...

Have you shot with 42 gr of IMR4895? According to my information sources, that would result in peak pressure around 25 Kpsi. OK for modern repros, but I'm not so sure I'd care to try it in my 1870's vintage rifle.
 
Metman2 said:
Have you shot with 42 gr of IMR4895? According to my information sources, that would result in peak pressure around 25 Kpsi. OK for modern repros, but I'm not so sure I'd care to try it in my 1870's vintage rifle.
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According to my information source (Lyman), it would be about 20K psi. If you wouldn't care to use it, you shouldn't.
 
Metman2 said:
Have you shot with 42 gr of IMR4895? According to my information sources, that would result in peak pressure around 25 Kpsi. OK for modern repros, but I'm not so sure I'd care to try it in my 1870's vintage rifle.
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I realize now "my information sources" sounds pretty lame, I've been referring to some old declassified US Army documents which can be used to estimate peak pressure. If Lyman has pressure data, that's cool.
 
Metman2 said:
I realize now "my information sources" sounds pretty lame, I've been referring to some old declassified US Army documents which can be used to estimate peak pressure. If Lyman has pressure data, that's cool.
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Your information sources aren't so bad. "Approximately 25K" and "Approximately 20K" cross over at "Approximately 22.5K".

What so few people understand is that even if you use "published loads" that list all of the components and the resulting pressure, and you follow it religously, that pressure figure is only true:

- with the specific equipment used that day and within its error limits;
- with that powder and that brass and that primer and that bullet, in that gun with its unique chamber and barrel; and
- that day with its unique humidity, pressure and temperature.

It's absurd to state with certainty that "my load is 23.7K psi", based on "published loads". It's "approximately 23K psi" makes sense if one understands that it could well be 20K psi or 25K psi.
 
Andy said:
Your information sources aren't so bad. "Approximately 25K" and "Approximately 20K" cross over at "Approximately 22.5K".

What so few people understand is that even if you use "published loads" that list all of the components and the resulting pressure, and you follow it religously, that pressure figure is only true:

- with the specific equipment used that day and within its error limits;
- with that powder and that brass and that primer and that bullet, in that gun with its unique chamber and barrel; and
- that day with its unique humidity, pressure and temperature.

It's absurd to state with certainty that "my load is 23.7K psi", based on "published loads". It's "approximately 23K psi" makes sense if one understands that it could well be 20K psi or 25K psi.
Click to expand...

It was my stilted way of phrasing "my information sources" that sounds a bit lame. The declassified US Army models agree pretty well with published loads, for the most part. But to use them, there are parameters you have to know (or rather, estimate) that might discourage people from bothering. To start calculating with all the parameters you mention quicly gets so complicated (as they may either reinforce or cancel each other), that a practical, efficient model has to combine some of them, e.g. the so-called "shot start pressure". The diifferent outputs that one obtains by running an ensemble of simulations with varying inputs gives one an idea of the variability of the actual pressures, as well as how sensitive the results are to the inputs. For example, when I first set up and ran the Baer-Frankel model, I was astonished to see how sensitive the maximum breech pressure is to the case volume. The smaller the volume, the higher the pressure, of course, but it's not a linear relationship.

Obviously numerical modelling is not everyone's cup of tea. I happen to do it for a living in another field (which my CGN handle alludes to). It requires calibration and initialization from real data, with all its variability, so it's a combination of art and science. Not like the phony computer programs one sees in movies or TV.

All this to say that the safe approach I've chosen for my old gun is to consult as many info sources as I can. The level of precision obtained is low (~10% or worse), but one can still be pretty certain of being safe.
 
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