Drilling Out Touch Hole

[rancher]

I drilled the touch hole out on my Lyman GPR to get better ignition. How much if any does this negativley affect performance? I was wondering if the loss in pressure could create significantly lower velocitites.

 

[Tom Compton]

YES. How much depends on how much you opened the vent and what powder charge you were using.

Slightly slower and impact slightly lower.

 

[LRB]

Depends on how much larger you drilled it. I have found that anything over 1/16" causes an accuracy loss to some degree. I would not even consider anything larger than 5/64", and I would question that. Just my opinion, but if 1/16" is not reliable, I would look for other causes. One thing I have found that greatly increases reliability, and speed, is to cone or cup the entrance of the vent. Not so much that the frizzen won't seal it though, and it is good to have a vent tunnel at least .030 deep before it opens to the internal cone. This directs more fire into the vent tunnel without enlarging the hole. Buy yourself another liner, and try it. I think you will be pleased with the results.

 

[fyrfyter43]

The best thing I ever did to my GPR was to get an RMC vent liner.

 

[ebiggs1]

I tried several different touchhole variations on my TC Hawken. TC’s have a .070 touchhole stock from the factory. The first drill I had that would not fit was a 5/64th. I also tried other sizes. It is my opinion that it doesn’t help, at least very much. But I don’t like .0625 either so I leave them at .070. I do like the TC, RMC type touchhole liners better than the ones with the screwdriver slot in them.

 

[hanshi]

Vent hole liners usually come with tiny openings that cause reliability problems. On any gun I acquire the liner comes out before it is even fired. I take a Dremel tool and make sure the liner is well coned. After installing it back in the gun I run a 1/16" drill bit through the undersized hole. Some claim to have problems with 1/16" holes and go to 5/64" or even larger. I have experienced excellent reliability with 1/16" openings and don't want anything larger.

 

[ohio ramrod]

If my memory serves me right (which it seldom does anymore) Muzzle blasts had an article a few years back where they tested several different hole sizes in vent liners and had the best results with a 1/16 hole. For consistant iqnition and accuracy.

 

[tg]

I can't speak of the Lymans, but I opened the vent on my flintlocks (4 of them at the time) to 5/64 and found faster and more reliable ignition, one gun does not have a liner only a hole coned from the inside and it is fast enough that I can shoot well offhand and hunt with it and it did ok on a couple of trail walks,the main thing I was looking for was to recreate the experience that those who shot the originals might have had and still have an accurate gun,and that is how it has worked out

 

[rabjr]

Surprising how easy it is to add a tad more powder to the charge. Any lose of pressure problems, solved! :wink:

 

[Larry Pletcher]

If my memory serves me right (which it seldom does anymore) Muzzle blasts had an article a few years back where they tested several different hole sizes in vent liners and had the best results with a 1/16 hole. For consistant iqnition and accuracy.

It's been a while, but I wrote the article in MuzzleBlasts that you refer to. I addressed speed and consistency but did not deal with accuracy. Going larger than 1/16" doesn't necessarily make the ignition faster. It may help ignition if the hole hasn't been kept clean.

I should point out that there are 5 drill sizes between 1/16" and 5/64".

1/16"-.0625"
#52---.064"
#51---.067"
#50---.070"
#49---.073"
#48---.076"
5/64--.078"

Compared with 1/16", a 5/64" hole is HUGE. Based on area 5/64" is 55% bigger than 1/16". I would respectfully suggest that one should work up from 1/16" in smaller increments than that. Bits like that are available in any good hardware.

I have been satisfied with a 1/16" hole in my latest gun, but drilled to .067 (#51) to allow a pipe cleaner to fit. Clean is the key.

Regards,
Pletch

 

[Birddog6]

I have drilled over a hundred of them & coned them for guys with GPR & GPH rifles. (Quit counting) and never had a single problem & it makes a Incredible difference. I drill them to 5/64" & cone them on the inside & slightly , put a lil Antisieze on the threads, BARELY SNUG it in & go have fun.

IMHO, Drilling them out & coning them makes them ignite faster, less delay in the ignition, and more consistantly.

As far as the velocity loss, bump the charge up 5 grains & you are usually right back where ya were, except now it goes off every time........ :grin:

On a regular rifles. (W/O patent breech) I usually drill the vents to .070 and sometimes the over .54 cal bores .078. (5/64") just depends on the rifle, how the lock works, amount of sparks I get, & how it performs, etc.

:wink:

 

[Fishhog]

Been using a #50 drill myself in my 3 TC hawkens and they are as fast as I could ask for.My question is that I hear of accuracy loss when the hole gets bigger,I know velocity goes down..But like Birddog says bumping a few grains more SHOULD get the velocity back,how would the accuracy really suffer?All things being equal I can't figure how group size can suffer,elevation maybe..Might be wrong but would like to be enlightened and learn something new,never can know too much..Ray

 

[Larry Pletcher]

Birddog,
Just dawned on me that the article research was done straight cylinder vent holes rather than vents releaved inside of out. I don't want to mis-represent what I worked on. I do drill drill bigger than 1/16", but the reason is to make cleaning easier rather than to increase speed. I think "clean" makes flintlocks work best.

Regards,
Pletch

Birddog - private message coming with question about one of your builds.

 

[John Wasmuth]

TG I did that with my pedersoli as you suggested some few years ago and it worked out super slick.

 

[hanshi]

If my memory serves me right (which it seldom does anymore) Muzzle blasts had an article a few years back where they tested several different hole sizes in vent liners and had the best results with a 1/16 hole. For consistant iqnition and accuracy.

Cool! I finally did something right for a change. :applause:

 

[Birddog6]

Birddog,
Just dawned on me that the article research was done straight cylinder vent holes rather than vents releaved inside of out. I don't want to mis-represent what I worked on. I do drill drill bigger than 1/16", but the reason is to make cleaning easier rather than to increase speed. I think "clean" makes flintlocks work best.

Regards,
Pletch

Larry,

If the vent hole is .070 to .078" you can get a white pipe cleaner in there easily & clean the vent hole out. I do this when I take one out to shoot it, swab the bore & get all the rust inhibitor out, then take a white pipe cleaner & bend the very tip a bit, insert it in the vent liner & wipe all the rust inhibitor residue out, etc. Have been doing this since I started shooting flintlocks & it has always worked for me. I cut the pipe cleaners in to 3 so I have 6 clean ends to use from one cleaner, rather than 2 ends. :wink:

 

[BenCoogle]

Sorry, but Ya'll are going to have to explain to me just how touch hole size is going to affect accuracy. If a load is worked up with one size or another, whats the difference?

I built one gun in .54, 1 1/8" AF that I drilled to #50 size. I got maybe 50% flashes in the pan. I opened it up to 3/32", :shocked2: which is what I normally use :shocked2: , problem solved!

 

[Birddog6]

If you have a load that is accurate, you are shooting a specific velocity. When you open the vent hole larger, you let more gasses out & thus have less velocity on the ball. Now...... that doesn't mean it is enough velocity change to make a difference, however, it could make enough dif. to change your grouping. Thus it is suggested if you change the vent hole to a very much larger dia., you then test your loads again & see if the groups changed & if they did, bump the charge up 3-5 grains to compensate for the escaping gasses out the vent, = same velocity as you originally had = group is back where it was....

:wink:

 

[cowpoke1955]

My .54 GPR had a lot of flash in the pan with the factory vent liner. I drilled the liner to 1/16" and coned it. This seemed to help, but still had some issues. I then drilled it to 5/64" and now is almost 100% reliable. As for accuracy, I was able to squeeze out one 3/4" group at 100 yards from a bench. If opening my touch hole hurts accuracy, I can live with that :thumbsup:

 

[larry wv]

3/32 is a BIG hole. Shootin 3f I suppose you could just whack the stock a couple times and not bother to prime. 5/64 is about as brave as I get. Not running you down Happy New Year. Larry Wv