vent hole size

[Dphariss]

The large exterior cone needs to be tested in a long string of shots without cleaning it in any way. I believe they need regular cleaning to prevent flashes.
The British tried about everything to get faster ignition but lhey apparently never tried the large exterior cone or discarded it since the late British guns usually have a liner much like the Chambers WL.
My next question would be does priming get into the cone and does this make something similar to the recessed breech by moving the prime closer to the bulk of the powder charge.


Dan

[bob in the woods]

A few years back, I built a flintlock bullet gun. 1 in 18 twist  .45 cal.  I shot this rifle at the 1000 yd matches in Ottawa.  80 gr FFg with a 535 gr bullet.  I had to change the liner often.  When the vent got too large , the give away was an increase in vertical stringing. Too much variance in elevation .
A round ball gun may not be affected as noticably, but , I found that the smaller vent size was more accurate in this rifle. Now, the other thing is that , this is the only rifle I've ever had to change a liner.
All my other guns are still with the original instalations, and that after a lot of use.

[Daryl]

A few years back, I built a flintlock bullet gun. .................  When the vent got too large , the give away was an increase in vertical stringing. Too much variance in elevation .
A round ball gun may not be affected as noticeably, but , I found that the smaller vent size was more accurate in this rifle. 

While the slug gun showed that the velocity variations gave him vertical stringing at long range, a round ball gun will show this within it's normal 'long' range as well, if 100 through 200 yards is 'normal'.  Anyone can test this with their rifle.  Merely fire a shot with 70gr., then one with 65, 60, 55, that sort of thing and see the where they fall at 50 yards.  25 yards is useful only for roughing in sites and testing to see if the gun will go off.

[northmn]

A few years back, I built a flintlock bullet gun. 1 in 18 twist  .45 cal.  I shot this rifle at the 1000 yd matches in Ottawa.  80 gr FFg with a 535 gr bullet.  I had to change the liner often.  When the vent got too large , the give away was an increase in vertical stringing. Too much variance in elevation .
A round ball gun may not be affected as noticably, but , I found that the smaller vent size was more accurate in this rifle. Now, the other thing is that , this is the only rifle I've ever had to change a liner.
All my other guns are still with the original instalations, and that after a lot of use.

From what I read slug guns in percussion eat nipples with some going to platinum and still going through them.  No reason for a flinter to be different.  Just as a thought.  Do vents wear out as much from shooting or from nipple picks in RB guns?  Some folks use some interesting picks, such as gas welding tip cleaners.  Vents last quite a while in more normal use.   One trick I copied for vents when I make one is to cone slightly on both ends, so that you have the funnel on the lock side and inside both.  While the English did not cone the exterior, they did design their pan to focus the flash on the vent.

DP

[Larry Pletcher]

My LM bullet gun went through a nipple in 10 full power loads.  At 50 gr it didn't matter but my reg load is 90 gr ffg.  The bullet is 540 gr.  It happed all at once (one shot).  It went from <2" groups to not staying on a basketball at 100 yds.

I replaced it with one with a platinum liner.  No problems since.  I have heard that shooters using Swiss go to larger grain sizes to make nipples last longer.  You evidently don't want to use fffg Swiss in a LR bullet gun.

Regards,
Pletch

[Dphariss]

While it is possible to shoot a RB gun for quite some time with a steel nipple if the lock is right a bullet gun will tend to eat nipples are a frightening rate.
One way to avoid this is to make sure the lock has a "heavy first lifting" of the hammer as Forsythe mentions. The greater pressure on the cap the less likely the hammer will rise as allow venting through the nipple. This is the hallmark of properly designed late flint or percussion lock. The mainspring, tumbler and link are designed to ease pressure on the tumbler at full cock and increase it as the tumbler rotates toward its rest position. Its all in the geometry and the lighter pressure reduces pressure on the sear at full cock allowing lighter trigger weights. The increase as it the cock falls helps overcome the increase in friction as the flint engages the frizzen. Speeding the ignition while allowing the low pressure at full cock. The good percussion guns used the same tumblers and such and the the "heavy first lifting" aided them by sealing teh nipple better and reducing the likelyhood of the hammer being blown back to 1/2 cock with high pressure loads.
When heavy charges and heavy bullets are used the pressure is so high that its not possible to keep the hammer on the nipple. Many slug guns went to a sealed ignition with a cap or modern primer to overcome this.
Pressures over 20000 are pretty easy to do and while breech design can reduce pressure to the base of the nipple somewhat  there is no "cure" other than platinum and its not really a cure just an increase in longevity.
Most bullet guns do not do well with FFFG powder no matter who makes it and FFG, 1.5F Swiss and FG are best since they reduce the pressure.
Bullets use the powder differently than RBs since the inertia is much higher and the pressure builds fairly high (relative to the RB) before the bullet moves. FFFG not only causes higher pressure, nipple erosion etc, but the higher pressure is also bad for the bullet and can cause the nose to upset too much with some designs.
A flintlock using slugs will eat vent liners too, unavoidable. Pressure is just too much for the technology.
Dan

[bob in the woods]

Just to add more info re the bullet rifle...I was using barylium vent liners. I bought a half doz of them and thought that would do. Interestingly, I shot the 300 and 400 yd match with the same liner.
2 sighters and then 10 for score. At 600, 1/2 through, I noticed the velocity variation. It is not great mid string, to score a 9 or 8 and have the next shot drop to the bottom of the board, then the next just barely scoring etc. Too late to change . At 800, 900, and 1000 I changed liners each target.  I came to believe that 12 shots was about it for accuracy with those liners. You really need a sturdy shield to protect the poor guy to the right of you when shooting this gun from prone at these matches!
Overall, I was surprised at the accuracy that I got. With so many variables, it was very tiring shooting a day long course. With my Sharps, I can settle into a nice solid position, and sometimes get off my entire string as fast as the markers can raise the target, if the coditions are good. Getting up to load, then getting back into shooting postion is tiring in itself. Adding the flint/ pan maintenace, and the priming and ...you get the idea. A 1/2 hour is not a lot of time for 12 shots.
Now, my round ball flinters have not had problems with opening group sizes, etc due to vent deteriation
and that is after in excess of a thousand rounds. If it is there, it must be slight, cause I can't see it
in my targets. Come to think of it, this might have something to do with my .36 losing its liking
for FFFg and  and striking up an affection for FFg. Maybe I should try changing the vent liner!

[Larry Pletcher]

Thank you for your posts.  I gave thought to a flint LRML but always seem to have too many projects going.   It's interesting that your vents gave out about the same rate as a nipple  does in a percussion gun.   Just for my own curiousity:
What was the vent diameter you started with?
What was the vent diameter when accuracy went south?

You might be the only fellow I know who has experience with a flint LR bullet gun.  Thank you for sharing your thoughts.
Regards,
Pletch
PS - I wonder if anybody makes a platinum vent liner for flint LRMLs.   

[Larry Pletcher]

The large exterior cone needs to be tested in a long string of shots without cleaning it in any way. I believe they need regular cleaning to prevent flashes.
. . . . . snipped. . . ..
My next question would be does priming get into the cone and does this make something similar to the recessed breech by moving the prime closer to the bulk of the powder charge.

Dan

In our next session we plan to run a series with the large ext coned vent to see what happens when shot with no cleaning.  With that test over we'll probably move to the dished breech.

In large ext cones I believe that prime does indeed enter the cone, placing prime close to the barrel charge instead of moving barrel charge close to the vent.  On my gun the ext. cone is quite small and probably doesn't narrow the distance between charges much.  I do like prime as close as I can get it - against the barrel.

Regards,
Pletch

[SR James]

I don't pay attention to in-lines but most of them use bullets and I don't recall having heard anything about nipple burn out with them.  Wouldn't the same factors be at work with them as with LRMLs?  I would think the use of hot bp subs with them would make it even more of a problem.  Not trying to discuss the "I" word guns, just curious.

[Larry Pletcher]

I don't pay attention to in-lines but most of them use bullets and I don't recall having heard anything about nipple burn out with them.  Wouldn't the same factors be at work with them as with LRMLs?  I would think the use of hot bp subs with them would make it even more of a problem.  Not trying to discuss the "I" word guns, just curious.

The system on the inlines are likely to be more like the sealed ignitions in slug and heavy bench  guns.   Hope some can answer this metter than I .
Regards,
Pletch

[Daryl]

Those infernal bolt actioned muzzleloading guns using shotshell primers are as Pletch said, a sealed ignition type and would not suffer the same burnout as a real muzzleloader does, when shooting slugs.  Rest assured, when using 100 to 150gr. of powder, those closed ignition guns are pushing pressures from 20,000 towards 30,000 psi.  I-for one, would not do that in a 15/16" barrel in .50 cal.