Compression

[jednorris]

When I load Swiss 1-1/2 B.P. I try to keep the compression uniform from one round the next. I drop the powder into the case from the scale pan then put a wad just inside the case mouth. I then tap all sides of my reloading block for about 60 seconds to settle powder before I finish seating the wad. The powder column in each case seems different and I figure that that changes the amount of compression I get from round to round. Using a compression die could equalize my powder column , but it would also have different amounts of crushed powder in each case. Everyone talks about correct amount compression in thousands, what am I missing.

[country gent]

With my loads I do a slow pour thru the funnel ( it takes about 20 -30 seconds for the 45 90s charge.) This gives a reasonable powder height in the cases. I then insert the .060 napa rubber fiber wad in the mouth and seat lightly onto the powder charge with a dowel. Then compress in powder die to depth so that the bullet just sits on the wad when hand seated. then insert 2 .002 tracing paper wads and hand seat bullet down.

I normally use Olde Ensforde in q 1 1/2FF in cartridges. My compression for the desired velocities seems to run around .125 I measure the compression from mouth down. case mouth down to poured charge and wad, Then subtract this from compressed depth.

I load my rounds in this way.
deprime by hand an clean
remove any media from flash holes and prime
drop charges I weigh each charge and pour in case as above or use a drop tube depending on day.
hand seat wad onto powder
compress in die
seat the 2 TP wads
wipe base of bullet and hand seat bullet down on to wads
Run into a bushing die to set neck tension Mine is a meacham die, but regular die can be used by setting high in the press ( usually about .400 high works for me).I want the tension so that the bullet stays but can still be turned by hand.

Loading as above gives me very good SD and ES numbers, and very good accuracy out to 500 yds. I believe the lighter neck tension allows the bullet to center easier when chambered. The setting neck tension as I do also seems to give more concentric loaded rounds.

[martinibelgian]

Don't worry about it, compression is a result, not a goal. And yes, use that compression die, is serves to give you uniform cartridge OAL.

[Chill Wills]

Don't worry about it, compression is a result, not a goal. And yes, use that compression die, is serves to give you uniform cartridge OAL.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Correct and stated in few words.
This is maybe the most misunderstood part of loading for BPCR.

Another way of saying it is, Compression is Incidental. The reason the old black powder cases are large is they need to be to get the desired velocity with the correct range of bullet weights. BP is not very efficient by smokeless standards, so that is why we use large volume cases. Basically, from a compression standpoint, you fill the part of the case under the bullet with powder and adjust one way or another to find the best accuracy. Assuming all else is up to the task, high quality powder results in accuracy. Poor quality powder results in lesser or even poor accuracy. Not much surprise there.

Find the accuracy sweet spot, which is the place in the barrel vibration where the bullet leaves the muzzle at the same time in the swing. Again, do this by adjusting the amount of powder in the case. The compression this produces to get the bullet in the case in the same place "is what it is".

Interestingly, there appears to be an entire cult grown up with volumes written around the meaning and importance of compression, and one kind or brand of powder liking a certain amount of compression and what it does. It is a goose chase. Just adjust up or down until accuracy is the best and the compression is what it is.

Michael Rix

[Knarley]

Mr. Martini, Mr. Wills,
Thank you for clearing that up.......:D

[prs]

When I load with desire for best accuracy I do use Swiss ffg. I do not charge according to volume, but rather weigh the charges. Then I settle and lightly compress. Getting the first weighed charge to be the correct volume to stay comressed by the bullet, but NOT crushed, is tedious; but once you get the correct charge for that lot of powder it is easy enough. I think Swiss does better with only modest compression, that is my experience. YMMV

prs

[Don McDowell]

Don't worry about it, compression is a result, not a goal. And yes, use that compression die, is serves to give you uniform cartridge OAL.

This nails it.
I know one shooter that is very hard to best in target rifle matches that mashes the snot out of Swiss. I know another that doesn't hardly compress OE at all. As in most things reloading it's what the target says that matters.

[Chill Wills]

This nails it.
I know one shooter that is very hard to best in target rifle matches that mashes the snot out of Swiss. I know another that doesn't hardly compress OE at all. As in most things reloading it's what the target says that matters.

I agree with you Don. There are some good guidelines in BPCR accuracy and a lot of exceptions.
Basically, there are a lot of right ways to do it.

[tmanbuckhunter]

I'm still fairly new to BPCR. I tried it years ago, and had dismal results and put it up. 10 years older and wiser, with an extra 10 years of experience on top of the two I had at the time I tried it, looking back I realized my mistakes. With that being said, I am still learning but here are some of the things I have found so far at least in my case, with my rifle, with my choice of components.

As already stated, compression is not a goal rather, but an incident. With that being said, I do find, at least in my case, less compression is optimal. As I play with loads, I find with my choice of powder (Schuetzen 2FG in 45/70) the less I have to compress the charge, the higher my accuracy. This could be related to the fact that using a standard large rifle primer with a shorter burn time (is this outdated knowledge or still relevant today vs 1993? I'm talking to you Spence (RIP) and Paul), or that Schuetzen maybe doesn't like compression. I achieve minimal amounts of compression by slow pouring my charges, and then taking all my cases on a load block and pressing the load block against my tumbler for 8 full seconds per side. I have yet to try a drop tube.

I don't really think there is a right or wrong way. I'm finding that even in my trapdoor, if I size my boolits to the throat and groove, I can run an antimonial alloy with no issues, and good accuracy. There is so much to learn and the more I try new things, I'm finding quickly there is not enough time on earth to learn everything I need to learn about this, especially BPCR. I need to find a way to take these things to the after life with me. So much I don't know.

[Don McDowell]

I agree with you Don. There are some good guidelines in BPCR accuracy and a lot of exceptions.
Basically, there are a lot of right ways to do it.

You said a mouth full there. It's interesting how something works in one gun, but another chambered the same way will puke it's guts out... Load testing, and fouling control.
See you Sunday.

[greenjoytj]

No amount of compression applied to a column of granulated powder will never be evenly homogeneous throughout the powder column. Anyone that has dug a compressed charge out of a cartridge case knows as you dig deeper the powder is looser and the last bit just falls out.
For this reason I believe looking to improve accuracy at the bullseye by trying to vary powder compression is looking in the wrong place to solve the problem.
I look to vary the weight powder charge.

[Don McDowell]

That's an interesting theory, it begs the question if you need more powder and the bullet is already seated in the lands then you do you get by without more compression?

[greenjoytj]

Three schools of thought:
1) Made my point DM, need more powder I say why do you think you need more powder?
Are you looking to change barrel flexing harmonics so the bullet exits at top node instead of the bottom node?
Maybe less powder with fillers will do the trick or a lighter bullet, or more powder plus a lighter bullet.

2) In the smokeless powder world when a poster requests powder load recommendations to turn his 308Win into a 300Win Mag (read more power) the often repeated advice is.....”if you want more power buy a bigger gun” (read larger bore or bigger cartridge case or both), we have all read that phrase before many times.

3) Duplex the the powder charge with small amount of smokeless.


I don’t believe it’s correct thinking to fixate on trying to achieve a scientifically engineered method of determining powder compression by any length or volume measuring tools.
Only a powder weigh scale is required.

The degree of compression is a response to the weight of powder placed in the case and it will range from none with powder to the bullet base, to powder compressed in a steel die with so much pressure as to turn the of powder into a near solid plug to be slipped into a fired case and have the case resized around the plug of powder and a bullet set on top and crimped in place.
Powder compressed to that high degree will no longer be burning a the fg granulation rate that poured out of the canister.

[Don McDowell]

Why more powder? Size of groups,ie stringing either vertical or horizontal.Bullet stabilization. Fouling, and sometimes velocity requirements per range rules.
Lots of reasons experienced bp shooters add more powder.
Yes sometimes the powder is a mostly solid plug in the case, but if you fired those loaded rounds you wouldn't know whether it was a "plug" or not...

[yulzari]

I am so glad that my BPCR is a Martini Henry so I can just throw 85 grains into it followed by a greased cannalured bullet leaving air to fill the gap and back home for tea and biscuits.

However; the subject of compression reminds me of the reading I have been doing on solid black powder pellets done in the 1860s and 70s which involved pressing dry corned powder under hydraulic pressure into solid pellets and done on moulds which left a hole down the centre to burn outwards. This evolved into the solid black powder pellet charges used when nitro powders came in but not all nations were ready to make it so used the solid pellets to tide over their new small bore magazine rifles until they could make smokeless.