touch hole size and velocity

[ebiggs1]

Curiosity got the best of me again today. After reading the touch hole size debate I got the chronograph out for some testing. I have done this before and concluded there was some trade off by going larger but I documented it this time. So it can be published here with some validity to it. I always like to back up my statements with evidence or photos.

This is a typical 5 shot string but the others were similar.
Oh, particulars first. It is 62 degrees and 98% humidity. The rifle used is my 54 cal Lyman GPR kit gun with the L&R lock (can't say enough good about this lock especially over what Lyman uses) and a Davis trigger (ditto on this over Lyman). 70 grs GOEX 3f, GOEX 4f prime, 530 Hornady balls, cut at the muzzle patches (approx .017) with olive oil lube. Here goes;
1344 fps Hi
1332 fps Lo
1339 Av
This was a typical string was with the large .078 (5/64th) drilled out Lyman touch hole liner.

This next string was with the standard Lyman liner and I am going to guess it is 1.5 mm. I don't have my metric drill set right here but a 1/16th drill will not fit.
1423 fps Hi
1412 fps Lo
1419 fps Av

So you can plainly see the larger touch hole does cost you velocity. I had targets but I got them mixed up and they are so similar I couldn't tell which was which but that is an indication of my shooting ability not any accuracy problems. Certainly no hunting accuracy issues. And again this is a pretty big change in hole size, as I like 070 best.

But with that thought, just what do you have to do to regain the lost velocity? Well............an 80 gr load of GOEX 3f yielded 1457 fps Av. A little much so a 75 gr load was tried and it gave 1419 fps Av. It appears that going from a tiny hole to a large one coats you 5 grs of powder. But 5 grs of powder is a small price to pay with the absolutely horrible FTFs I had with the smaller hole. I bet it took two or three strikes per shot, simply unacceptable, but the larger touch hole never misfired. Bigger is better. :thumbsup:

 

[Macon Due]

Nice work Sir. So....it seems as if it's well worth the 5 grns. to get reliabilty like that.
Thanks for the test and report.........Macon

 

[Horserod]

EBiggs, Thanx for your report and figures. I have tested (myself) and came to the basic same conclusions as you have stated. I do not get reliable ignition with 1/16" touchholes. As you also stated, I believe a .070 to .072 hole would be perfect, but, I need to test further to document the results. Let us know if you succeed with this experiment to that effect.....Horserod

 

[carolina cowboy]

Thanks for that post Ebiggs, I just bought a used left handed flint lock, and in testing before buying, we had at least 3 or 4 to 1 flash and no bang, he said he thought it was his powder(like 6 years old and stored in his powder horn)...but I liked the rifle so got it anyway....took it home, cleaned it up, ordered powder, new flints, took it back to the range, new powder and flints it was more like 2 to 1 flash no bang, checked the touch hole after reading posts on here and it was under 1/16th(removable type)...drilled it out to 1/16th and now it is 1 out of 6 or 7 times it goes flash no bang, the rest of the time it is perfect( Loading it the same way each time,3FFF powder and 4FFFF prime, it is a 45 caliber)....so was wondering the down side of going to 5/64th’s .......

 

[gordy]

Good to see that a fairly controled test confirms what I suspected by trial and error . I much rather give up a few FPS velocity for reliability . I"m sure that there will be some that will question your test method , but , to me the proff is there . Thanks for the information . :thumbsup:

 

[ebiggs1]

This test is no scientific test and was not designed to be. This is an average guy walking outside loading his gun, not particularly exactly and shooting. Anyone will see these same results because there is no absolute controls used. I suspect this is more like our forefathers did it anyway. The gun which is also unremarkable was 100% reliable with the large touch hole. Next to useless with the tiny one and not even a consideration if your life depended on it working. It is little consolation if you have multiple FTF's but can proudly say, “But I have a tiny touch hole!”

 

[hanshi]

Interesting results with your test, ebiggs. I've always been well served by 1/16" touch holes but would not hesitate opening one up to get reliability.

 

[paulvallandigham]

Ernie: Ya Dun GOOD! We all know the multitude of variables that go into producing a given velocity from a given gun loaded by a given shooter. It doesn't matter. What you did is what the rest of us can do.

Discovering how little EXTRA powder it might take to reproduce the higher velocity of the smaller TH guns is the most important information you produced. And, shooters can verify that easily if they use a chronograph, as you have done.

WELL DONE! :bow: :thumbsup: :thumbsup: :hatsoff: :hatsoff: :hatsoff:

 

[Stophel]

This test is no scientific test and was not designed to be.

Actually, it IS a pretty scientific test. :wink:
You had the same gun, same range, same powder charges, etc. Only thing that changed was the touch hole diameter. Excellent.

 

[skywarp]

Cool! Thanks for doing the work.

I'll trade a few FPS for reliability any day.

Now to measure how much further the jet from the touch hole shoots toward your hunting buddy... :hmm:

 

[BrownBear]

That backs up what I saw a year or so ago, but "reverse engineered." A buddy had an older 36 that was drilled with no liner. Over time the vent was so hogged out it was scary. You didn't want to be within 15 or 20 feet of the right side when he shot. Talk about a flame thrower! :shocked2:

He was going to send it off to be drilled, tapped and a liner installed, so out of curiosity I chronoed it first. Then he brought it over and we chronoed it again after the liner was installed.

Holy cow. First off, it was safe to stand on his right and shoot. I don't remember the load combo he was using or actual velocities, but it was somewhere in the neighborhood of 1650 vs 1950 if I recall. He gained almost 300 fps with the liner.

He's on here now and then, so if he wants to provide better numbers or dispute my recollection, I'd welcome it.

 

[Larry Pletcher]

Hi Ebiggs,
Let me add my congrats. I appreciate your efforts. So often we draw conclusions without doing the work of controlling variables. Your efforts with variables is commendable. My complements.

Regards,
Pletch