Is Radius-Groove Rifling the culprit?

[40calFlintlock]

All flintlocks that I have, have traditional square groove rifling. Conducting an engineering experiment (called Design of Experiment [DOE]), I have been able to get excellent groupings on these rifles. Recently, I had a 32 flinter built and it has radius-groove rifling.

Today, I went shooting for the umpth time and, still using the DOE method, I cannot get the rifle to group. I shoot using a bench-rest so the rifle placement is consistent.

To date, I've put in excess of 200 balls down-range. The inputs I used previously, that gave me a .545 inch average group, today barely stayed on a 10X10 target. Other times, what gave me a 6inch spread would give me a 2 inch grouping. The only difference between all the flinters I have, beside caliber, is this one has radius-groove rifling. Is it me, or is the radius-groove rifling the culprit?

Has anyine else experienced similar results? :surrender:

 

[jamesthomas]

What is your patch thickness? You will need at a minimum a .020 patch if you are using a .315 rb. and even thicker if the ball is a .310 roundball, a .015 patch will not fill the grooves to get a good seal.

 

[Turtle Creek]

Could be that individual barrel has an issue but I do not think it is that cut of rifling.
I'm guessing you mean a round bottomed rifling cut= radius groove?
I've a Colerain round groove that shoots the X out from day one regardless of patch thickness.
I shot .010/.015/.018 and settled on the .018 as the patches could be used again but in all thicknesses it shot plumb.

 

[Zonie]

What do your shot patches look like?

Any signs of burn thru where the ball meets the bore?

If it isn't sealing the rifling and is being burned by the hot powder gasses, accuracy will be poor.

Any signs of the patch being torn during loading?

Although the round bottomed grooves seldom cut the patches, a sharp edge at the muzzle crown can.

 

[Captjoel]

Another question for you has to do with the small caliber 32 and it's short comings at long ranges and windy days. What distance are you practicing at with this rifle? I always shoot my small bore rifles at short 25 yards or less and then only attempt longer ranges on windless calm days.

 

[wattlebuster]

What Zonie said +1 :thumbsup:

 

[40calFlintlock]

To all: Thanks! :hatsoff:

Now to answer questions;

Yardage is kept to 25yards. My inputs are:
20grains, 30grains, 3fg, 4fg, .310 swaged Rb, .315 swaged Rb, oxyoke .010 dry-lube patch, .018 pillow ticking with Crisco.

I've shot every possible combination of grain size, powder granulation, ball size, and patch thickness. Unfortunately, I did not look for any patches for gas by-pass.

The last time I went shooting, the best combination was: 20grains of 4Fg powder, .315 Rb, and .010 patch. The result was an average distance between 3 shots of .545. Yesterday, using th same inputs, the spread was kept within a 3in X 6in area :idunno:

The backboard is 3/4in thick compressed sawdust & glue board. The balls were punchin through without problems, so I know once (if) I get this rifle to group, it will have great effect on squirrels.

When I've used 30 or 40 grains, I could keep three shots on an 8.5 X 11 sheet of paper, so I reduced the powder charge. Additionally, the .315 Rb and .018 patch gives me the most grief and widest spread - 3 shots with avg distance of almost 6inches...benched!

I clean the barrel with an alcohol wipe and dry cloth patches when shooting a specific combination of inputs. Then, when I am going to change the inputs, the barrel is scrubbed with soapy water and dried completely to replicate shooting from a clean bore.

 

[Rifleman1776]

the .315 Rb and .018 patch gives me the most grief and widest spread

Interesting, that combo, with right charge and lube would be what I would guesstimate to be where your sweet spot might be.
Your "dry lube" might not be a good mix and, personally, I have found Crisco to be good only for pie crusts.
Small ml calibers are very finicky.
Suggest you stick with 3Fg. The 4Fg isn't needed.
Do the fit test thing. e.g. using a big clump of your patch cloth, seat the ball about one inch down the bore then pull back out. The ball should show both rifling and cloth weave imprints. It will give you a good idea if the rifling is gripping the ball properly. If it isn't you need to go larger with the ball. Yep, that will mean starting all over with the patch/charge combo. But, it is shooting, the weather is still nice so it will be fun.
Keep us informed of your quest.

 

[Bob J]

Has anyine else experienced similar results? :surrender:

40calflinter - Like you, my other two flintlocks that I shoot a lot have square-bottom rifling and both shoot great. Just received my custom-built .62 jeager and it has a Rice barrel with round-bottom grooves. My first day out with .600 balls it shot fine at 25 yards, but at 50 it looked like a buckshot pattern. The .020 ticking patches were shredded. Went back out and tried 'er with thicker denim, about .025. It started trying to group, but not good enough. The patches were still showing some burn-thru.

Went out Friday with some .610 balls and .018 pillow ticking. Shot 1.25" with 75 grains and under 3" with 90 grains...MUCH better! Still some room for improvement with the heavier charge, and I think I've found a possible culprit. These patches are pre-lubed pillow ticking, and upon close inspection, just noticed they appeared to older and somewhat dried out. Also, measured thickness turned out to be .015, not the .018 it states on the package.

Going back out in a few days with some new prelubed .018 pillow ticking, and work on tightening up the groups some more.

My point? It might take some work/experimentation with lubes and patch thicknesses, but I believe you will get it sorted out. As previously suggested, I would stick with 3f. Perhaps try 15 grains and 25 grains. Also suggest trying "wonder lube" (I now get mine in the form of "premium lube" from Eastern Maine Products) or Birddog6's paste lube.

 

[hanshi]

No, the problem is definitely not the fact that the bore has radius rifling. I have two with radius rifling and If I ever get another rifle it will have round bottom rifling as well. An op wad might help but strong patches thick enough to fill those deep grooves are needed.

 

[Albanyco]

Have you checked the muzzle crown to see if it was cut properly? Is the barrel firmly fitted to the stock? Have you tried a different lot of powder? Just a few things off the top of my head.

 

[Dane]

You've GOT to look at your used patches, they are going to tell the story. I would guess they will be little burnt rings.
Larger ball/patch combination. Definitely NOT radius groove rifling. I have 4 right now, and they shoot very well.
Get rid of the Crisco and prelubed patches. Use thicker material and liquid lube. If it's a modern, quality barrel, it will shoot.

 

[Dphar]

Have you slugged the bore to see if its uniform? Even a tight patch on a short bearing surface jag can be very informative too.

Dan

 

[irishtoo]

try a fiber wad between powder and prb

 

[MJMarkey]

This may be too obvious. but was the Testing on your 32 done on a windy day? Even light winds can have a huge influence on a small round ball.

 

[Rifleman1776]

This may be too obvious. but was the Testing on your 32 done on a windy day? Even light winds can have a huge influence on a small round ball.

Sometimes the obvious is the easiest overlooked.
Great question.

 

[40calFlintlock]

Thanks one and all for your time and input! :hatsoff:
I've tried 15grains and had more mis-fires & hang-fires than successful shots. :surrender: I calculated that there wasn't enough powder to keep the ball/patch from covering the vent hole. Multiple times, the charge would push the ball about 1/4 - 1/3 way down the barrel, and the gasses would vent out of the vent. Sounded & looked like a model rocket engine. So I stopped using 15grains :surrender:
Shooting was done on calm days with very little to almost no wind. I shoot at the Log Cabin in Lodi, Ohio. Their range has hundreds of patches, so trying to find mine would require another set of eyes to watch where it went.
I’ll perform the barrel inspection suggestion and look for patch cutting and rifling impression. I will get a thicker pillow-ticking or jean material, use a different lube than Crisco with the .315 Rb, and stick with 3fg powder.
Thanks for everyone’s help! :thumbsup: