Venting a Drum

[DBox]

I've read about venting a drum to improve ignition of a caplock but I can't find anything about how to do it. Can somebody explain it, please?

 

[paulvallandigham]

I know of two ways to vent a percussion drum, but the only reason to do so is to prevent hammer blow back due to a weak mainspring you can't replace.

One way is to drill a very small hole( 1/64") at an angle in front of the nipple, into the drum, so that gas is vented forward and upward. This is fine if you always hold the forestock several inches from the trigger guard. However, if you move your hand back during off-hand shooting- say, when shooting uphill-- you risk having your fingers not only burned, but flesh blown off, by that hot gas.

The other way to vent the drum, is to drill that very small hole through the middle of your Clean out Screw. I did that with a foreign made gun that was discontinued. I could not replace the spring( I looked hard). The hammer would lift up enough, even with modest powder charges, to let the cap come off the nipple. I change nipples, etc. and nothing else helped. Today, You can buy the " Hot Shot Nipple, that has a hole drilled through the top sides of the nipple, to vent gas to not only prevent blow back, but to free the percussion cap from its grip on the nipple, to make for easier removal.

The hole in the clean-out screw vents gas to the right side of the gun, like a vent hole in a flintlock. You have to warn people not to stand close on the side of your gun when you are shooting. I have seen debris spit as far as 6 feet on one occasion from that hole in my clean out screw. That is the downside.

I did this work on my gun about a year before all the after market nipples, Like the HotShot, from Uncle Mikes, and the " Spitfire", from ? , and the Ampco bronze alloy nipples came on the market. I didn't know about Deer Creek having parts for a lot of CVA and other European made guns, so I would check with them for a replacement spring. And, I have since learned some other tricks to strengthen springs. For that reason, I would not vent my drum again- certainly not to prevent blow back of the hammer.

Venting to improve accuracy sounds like an interesting idea, but I would want to see the before and after result on my chronograph, and on paper, before I considered venting my drum permanently. Replacement clean out screws are available, so it would not be a costly series of tests to do.

Oh, I chose the 1/64" bit to drill the hole through the center of my clean out screw largely because it just fit into the screw slot of the clean out screw- TOTALLY ARBITRARY! But it worked. I was doing a lot of trick shooting for my club at demonstrations with that gun in those days, and I got the peace of mind knowing that a percussion cap was not coming back at me, or sailing off into the crowd of on-lookers.
:thumbsup:

 

[J.D.]

The information I have seen on venting a drum goes back to the days of percussion conversions of flint guns. There seemed to be a number of converted guns blown up, due to a number of reasons.

The fix was to vent the drum to act as a pressure release, preventing blown barrels.

IMHO, there is absolutely no reason to vent a drum in modern guns.

One reason to NOT vent a drum, other than serving no purpose, is exposing the load to moisture. IMHO, keep that powder charge dry.

God bless,
J.D.

 

[Zonie]

In the 1970's several writers advocated drilling a vent in the drum to improve the reliability.

The idea was that with a vent located between the nipple and the breech, the flame from the cap would not be trying to enter a blocked area (the bores breech).
Because it wasn't working against the "dead ended hole" it would get much closer to the powder charge giving it a much better chance of igniting the powder.

The vent also added an additional air escape to the hole thru the nipple so the act of ramming the ball would blow more loose powder down into the drum and closer to the nipple.

I had a CVA Frontier rifle I built from a kit and it often misfired even though I was using real black powder and I had read about venting so I decided to try it on this gun.

The descriptions said to drill a 1/16 inch diameter hole into the drum between the nipple and the side of the barrel, angling it about 45 degrees from horizontal with it pointing towards the muzzle. That way, the blast of flame would be directed away from the shooter.
This small hole intersected the existing flame hole from the nipple to the breech.

I figured that this was an inexpensive gun so why not?

After drilling my vent the reliability of the guns ignition went up to over 95% even using the cheap Italian caps of the time.

Although the reliability went up the consistency of accuracy seemed to go down. Even increasing the powder charge to make up for the lost pressure thru this new vent didn't really seem to bring it back.
For this reason I decided to not do this to my other guns.

Perhaps if I had worked at it I could have found a good load for that gun but I had other rifles to shoot so the Frontier received a brass tack "Indian" decoration and I ended up selling it for $125.

 

[buckhorn]

Same thing happened to me as with Zonie.
I bought a 38" .40 cal. bbl (drop in) for my Renegade. After
about 6 or 7 shots, it would hang fire.
Someone drilled a little hole in the clean-out screw which helped
completely with the hang fires but the accuracy worsened.

Now, I just tap the rifle on the left side a few times to get powder into the channel.

 

[CZMark]

Before I tried venting a drum, I would install a Hot Shot nipple as Paul advised. I have used these with great success on my caplocks.

 

[J.D.]

A friend who is a stickler for accuracy says, that in his testing, the hot shot nipples reduce accuracy because they allow a reduction of pressure, much the same way a shot out touch hole on a flint gun does.

He consistently shoots 1 1/2 inch groups at 100 yards, but the groups fired with the hot shot opened up considerably...in his estimation.

For most folks, that loss of accuracy isn't an issue. Few of us can shoot well enough to notice, but for someone who can....

 

[paulvallandigham]

All he has to do is add enough powder to make up the difference represented by the velocity loss he claims to experience. That is what we do with Flintlocks, too. Put the gun over a chronograph, with a solid nipple, and then the HOt shot nipple, to determine the before and after velocities.

 

[J.D.]

He did that Paul, didn't work to preserve accuracy.

All guns are different, so everyone has to perform their own experiments to see what works and what doesn't. However, several others who are capable of 1 1/2 inch groups at 100 yards have reported the same loss of accuracy wit hotshot nipples, no matter how they refine the powder charge.

Again, these boys are capable of much better groups than 90% + of us normal ML shooters, so the average shot won't notice the difference.

God Bless,
J.D.

 

[paulvallandigham]

There is actual accuracy, Which can be verified by using a chronograph to find the right velocity for a particular gun, so that the barrel vibrations( Harmonics) work with the shooter. That " Sweet spot " can be found with different powders, different primers, different nipples, different wads, etc.

And then there is " Shooter accuracy". The latter can be and is affected by what the shooter has going on in his head about his equipment.

If a great shooter thinks he's using something that is going to rob him of accuracy, it does!

It doesn't matter that in someone else's capable hands, the gun so equipped shoot rings around the owner's groups, and shoots tinier groups all day long. If he thinks it won't shoot, it won't. Over 50 years of watching other shooters and shooting with them, I have seen this time after time.

I am always amazed at how silly some shooters are about guns. A man I knew who had more money than sense bought an extremely expensive shotgun one day. He fired a total of 2 rounds of Skeet with the gun, ( 50 shots) and decided that the gun was NO GOOD, and traded it at a substantial loss of money the next week for another gun. He claimed the gun had been made to his measurements, but it just wasn't going to work for him! He never considered that perhaps he might be having an off- day, with any gun he shot, or that it might take more rounds shot through that gun to get used to the balance, feel, trigger pull, etc.

If you believe that Swiss Powder is giving your better performance, than Goex, it probably will.

If you believe that FFFg powder gives you better performance than FFg, it probably will.

But, I am willing to bet that if you submit yourself to a blind test, where you don't know what is in the gun, you won't see any real difference.

Its difficult to believe when you are new to this sport, but accuracy is 95% mental, and only about 5% physical. We have lots of shooters who own excellent equipment, and are pretty good shooters. But we have lots of shooters who have no clue how to get their heads into the game, and they beat themselves, all the time.

Performers call it " stage fright"; Golfers- the "Yips". What it is called doesn't really matter. What does matter is for every shooter to learn how to focus his thinking on the next shot, and block out everything else. I call it " getting in the zone". This has to begin with what you think about your gun and equipment before you even load the first round down the barrel.

 

[DBox]

I appreciate the input. My little rifle does fine if I do my part. I think I won't worry about venting it if it'll do anything against my accuracy. Thaks to all.