Relationship between twist rate and optimal powder charge

[Spikebuck]

About 6 weeks ago I bought a new-to-me .54 Cal Virginia made by Larry Williams.

Link to the Original Post

As time has permitted, I've been at the range doing load workup. I started at 80 grains and worked up in 10 grain increments. I have also played with patch thickness and lube.

At 100 & 110 grs of 2F KiK it was pretty good. At 115 the group blew apart to about 3.5". I came down to 105 gr, splitting the 100 and 110 and that seems to be the magic number. At 50 yards I got one ragged 5-shot hole 1.5" high by 1.0" wide (center to center of furthest apart holes.)

I have been using up a box of .530 Hornady's, but I think Santa is going to be bringing me a new .530 mold, so I'll do my final workup after I get a chance to cast some ball.

So, here's my question. I have had three .54's. Each of those has been a 1-65 twist and barrel lengths ranged from 34" to 39". Each had square grooves. All three of those settled in on 90 grains of 2F as the best load. This rifle has a 1-70 twist and the barrel is 44" with square grooves (a GM). Could the twist rate be the main reason this one likes what seems like a heavy load for a .54? Is there any rough relationship between twist and load for a given caliber? Just curious. :idunno:

 

[coloradoclyde]

I'd say it was the extra barrel length.

 

[BrownBear]

Is there any rough relationship between twist and load for a given caliber?

I'm not convinced. I thought so when playing with a couple of really fast twist 54 cal rifles with shallow grooves, where round ball accuracy went south when charges got much over 60 grains of 3f. Turned out to be a case of them needing really tight patch/ball combos to engage that shallow rifling. Once I tightened things up, I could go right up the scale without loss of accuracy.

In your case I'm more inclined to wonder about small differences in some of the internal dimensions in that new barrel, compared to your others. Grove depth, land width, bore diameter, whatever. The 5" difference between your twist rates doesn't seem like a likely explanation.

 

[Spikebuck]

Turned out to be a case of them needing really tight patch/ball combos to engage that shallow rifling. Once I tightened things up, I could go right up the scale without loss of accuracy.

This was another thing I found interesting. My .016 pillow tick patches (standard oxyoke that are labeled .018 but aren't in my crush test...at least they are consistent over time) did better than the .012 crushed cotton (ToTW's billed .015 patches). But when I went to .020 denim, which went down pretty well after several very hard whacks with the short starter, or the .025 denim which not only required multiple hard whacks, but nothing short of hard effort to get down, the accuracy did not improve one bit. Didn't degrade either. So, I stayed with .016 since that only takes a couple moderate whacks and then slides down snugly but nicely...much preferred for hunting.

 

[Rifleman1776]

This rifle has a 1-70 twist

Some non-standard twists there. Most are 1:66; 1:72. Interesting.
The twist is the factor. Slower twists (usually, nothing is fixed in this game) require higher charges to stabilize for optimum accuracy.
My .54 w/1:72" twist requires north of 100 gr. charges for best grouping. I don't like that at all.
No need for you to push things. A 100 gr. charge behind a .54 ball will kill anything on this continent.
Work up you most accurate charge and stick with it.
Lesser charges will affect accuracy only minimally and still will kill anything short of a big grizzly very effectively.

 

[M. De Land]

You need to read your patches as you work up in powder volume as they will tell you more about load progression than will the target alone.
A round ball needs very little spin to stabilize and will work well in a variety of twist rates if the patch and lube are correct for the ball diameter and bore condition.
Also I feel barrel harmonics play a part in any overall accuracy picture even in our rather often thick/heavy barrels and this changes as pressure and velocity go up.
Most muzzle loaders are shot off hand mostly but the loads are worked up very often over sand bags from a bench and may or may not act the same.
From a harmonics stand point my guess is they very often are not.

 

[hanshi]

:thumbsup: +1

 

[Spikebuck]

This rifle has a 1-70 twist

Some non-standard twists there. Most are 1:66; 1:72. Interesting.

Pedersoli uses 1-65 in .54 caliber. I don't know historically about Green Mountain and all the things they offered, but from what I see, their .54's are 1-70 like mine is.

 

[Spikebuck]

You need to read your patches as you work up in powder volume as they will tell you more about load progression than will the target alone.

I probably need a patch-reading "primer" as it comes to subtle things. I always gather up and look at the patches. Through 110 grains they all looked good with no holes or tears, no burning. Just darkened/browned some...I don't, but they could be reused. At 115 grains, I didn't find any of the four I shot. I don't think they disintegrated, but I didn't find any either.

Besides hole, tears, and burning, what else should I be looking for?

 

[coloradoclyde]

op:

 

[M. De Land]

I find when I'm getting right to the edge of patch endurance there will be tiny holes at the bottom edge of where they fold around the ball.
Often the patch will look good until you hold then up to the light.
I am not sure what is causing this as accuracy is still good and I don't remember it occurring with light loads.
You may have to hold the patch up to the light to see them.
Another indication is how much more they are frayed around the edges as more powder is used.
This probably is from muzzle blast as they clear the muzzle and unburned powder granules are doing the damage.
One of the best test for maximum load is to shoot over snow or a bed sheet and when you start finding lots of unburned powder you have reached the top of the expansion ratio.

 

[coloradoclyde]

Lots of good information and possible solutions, but can we truly say that the problem has been identified?

 

[Rifleman1776]

Lots of good information and possible solutions, but can we truly say that the problem has been identified?

We don't know that he has a "problem". Most barrels have a optimum load. Changeing things changes things. He just needs to shoot and test which work best in his rifle.

 

[coloradoclyde]

Exactly! :thumbsup:

 

[Spikebuck]

Lots of good information and possible solutions, but can we truly say that the problem has been identified?

I don't consider this a "problem." If I had to shoot 150 grains THAT would be a problem. :shocked2:

I've read quite a few posts over time here where people are shooting 95 or 100 gr of 3F Swiss in bores this size...which is probably equivalent or in excess of my 105 of KiK 2F. The way this gun is built, the felt recoil of this load is almost imperceptible. Probably the very best rifle I have shouldered in terms of felt recoil.

My post was more one of trying to understand barrel dynamics and why this one would require over 15% more load than the other three .54's I've worked up loads for.

MD: I hold up patches to the light each time I collect them. Thanks for the info on those tiny "pin holes" in a circle around where the base of the ball would be set on the charge. While I have not seen those with this rifle, I have noticed those and pretty much disregarded them in the past because accuracy, as you state, was not yet suffering. Good to now know that they may be an indication that it's "getting close." Your post has helped me understand a couple of additional things to look for. I have always looked, then discarded the patches, but now I think I'll save some at each load development session (I usually take 5 or 6 trips to the range to work on load development) so I can go back and review them in succession. THANKS!

 

[coloradoclyde]

Again! I think it is related to the longer barrel
longer barrel = different harmonics/whip.
longer barrel = lower pressure upon exit, it takes more powder to maintain the same pressure levels in a longer barrel.

Yes! this is only speculation and can only be verified by testing.....but that's where I would start.

 

[Elkeater]

Yet more speculation: Try less powder with Fg

 

[TMan51]

So, here's my question. I have had three .54's. Each of those has been a 1-65 twist and barrel lengths ranged from 34" to 39". Each had square grooves. All three of those settled in on 90 grains of 2F as the best load.

I was wondering about that recently, and the relationship of patch/ball combinations to actual pressures. ??

For years I've pondered the numbers in my Lyman Black Powder Handbook, and wondered if patch thickness had a correlation to where they will give up and come apart. What will a barrel sustain for pressure?

Of note, I stored a Track of the Wolf Hawken I built from a kit many years back, and it had picked up a film of rust when I hauled it back out this past summer. To be sure I removed it all, I used a very fine lapping compound on a tight patch, and carefully swabbed until it was gone and no rough spots could be felt. At the same time, I cleaned up the crown, and did a modest coning on the muzzle end. When I started testing my loads, I was able to get from a previous max of 90gr of Goex 3F, to 110gr with an 0.018 greased patch. I don't think I affected the bore dimensions, but it did smooth out the bore a lot, judging by the way balls were seating.

I'm thinking bore condition and patch durability are related. ???

 

[nkbj]

Spikebuck,
All I can say is that yeah, I think there is a generalized relationship in there somewhere on charge versus twist but nothing I could come up with holds up all the time.
Seems that the rifling pattern and other particulars make each barrel it's own rule book.

 

[Dphar]

About 6 weeks ago I bought a new-to-me .54 Cal Virginia made by Larry Williams.

Link to the Original Post

As time has permitted, I've been at the range doing load workup. I started at 80 grains and worked up in 10 grain increments. I have also played with patch thickness and lube.

At 100 & 110 grs of 2F KiK it was pretty good. At 115 the group blew apart to about 3.5". I came down to 105 gr, splitting the 100 and 110 and that seems to be the magic number. At 50 yards I got one ragged 5-shot hole 1.5" high by 1.0" wide (center to center of furthest apart holes.)

I have been using up a box of .530 Hornady's, but I think Santa is going to be bringing me a new .530 mold, so I'll do my final workup after I get a chance to cast some ball.

So, here's my question. I have had three .54's. Each of those has been a 1-65 twist and barrel lengths ranged from 34" to 39". Each had square grooves. All three of those settled in on 90 grains of 2F as the best load. This rifle has a 1-70 twist and the barrel is 44" with square grooves (a GM). Could the twist rate be the main reason this one likes what seems like a heavy load for a .54? Is there any rough relationship between twist and load for a given caliber? Just curious. :idunno:

Different rifles use different powder charges. The difference between 65 and 70 is slight. Its not as though we were dealing with a 48 compared to a 80 or 96. I have a 50 caliber 44" long gain twist, beginning and ending twist proprietary, that the maker tells me shoots best with 120 gr of FFF. I shoot 109 and have never gotten to 120.
The blown groups with 110 could easily be patch related. There is a lot of crappy foreign made fabric out there. I have had to abandon blue stripe ticking all together the stuff is now too weak for use.
My go to load for a 66 twist 54, and that of another long time shooter/builder, was 100 gr of FFF Dupont/Goex. I now use 90 gr of FFF Swiss. 38" barrel gives 1900+.

Dan