Non traditional Gas Checks

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  • Last Post 28 December 2014
frnkeore posted this 18 December 2014

I resently saw a article by Glen Fryxell, talking about Vulcan GC's and they are about twice as long as standard Lyman/Ideal and Hornaday GC's. Does CBA have any rules regarding the size of GC's? Are the Vulcan GC ok to shoot in CBA matches? Frank

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fa38 posted this 18 December 2014

Rule 4.1 Cast Bullet -A projectile made of lead or lead alloy which has received its basic form by being cast of molten metal in a mold rather than being formed in a die. Except in the Plain Base Bullet class, a gas check having a sidewall height of no more than 0.10” may be attached to the base. Enlarging or reducing a cast bullet by bumping or swaging is permitted.

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frnkeore posted this 18 December 2014

These are the specs for the 6.5mm GC:

Hornady (crimp-on copper GCs).010” thick .061” deep, .273” OD .250” ID  Vulcan Check .013” thick .105” deep .273” OD .249” ID Vulcan Check .0145” thick .118” deep .272” OD .249” ID 

You have to add .013 or .0145 to the depth to get the height of them so, it appears that you can't use Vulcan in matches.

Thank you, Frank

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Ken Campbell Iowa posted this 18 December 2014

speaking of odd gas checks ... i wonder if a ring around the base would do the job ...does the solid base of the hornady check do anything ? seems would be cheeper to make rings.

i got a lot of fall-off aluminum tubing ... 0.312 od, 0.030 wall, 3-5 inches long. i don't have a 30 cal. that gets under 4 inch groups, so if somebody sends me a buck, i will send some tubes to cut up into rings to try. aluminum gas checks work fine, so aluminum ring checks results should be valid. ( if used for a jacket the lead would have to capture it, it won't solder to alum. might make a swaged jacket, i suppose. maybe survival ammo ? ) .

pm me if.

ken

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delmarskid1 posted this 19 December 2014

Ken Campbell Iowa wrote: speaking of odd gas checks ... i wonder if a ring around the base would do the job ...does the solid base of the hornady check do anything ? seems would be cheeper to make rings.

i got a lot of fall-off aluminum tubing ... 0.312 od, 0.030 wall, 3-5 inches long. i don't have a 30 cal. that gets under 4 inch groups, so if somebody sends me a buck, i will send some tubes to cut up into rings to try. aluminum gas checks work fine, so aluminum ring checks results should be valid. ( if used for a jacket the lead would have to capture it, it won't solder to alum. might make a swaged jacket, i suppose. maybe survival ammo ? ) .

pm me if.

kenCut these rings to fit in the front driving band spaces of the mold and cast them in place. Heck, all of them, just like rings on a piston.

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.22-10-45 posted this 19 December 2014

Few years back when seeking the ultimate .22 cast-bullet accuracy..I was discusted with the wavy base of commercial gas-checks. Even annealing & using a punch & die to fit std. lube-sizer didn't entirely true up bases...So I had Corbin make up a punch & die to fit reloading press that punches out center of gas-check leaving a narrow band about .032” wide around base. Need more testing to make up mind if this makes a difference.

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joeb33050 posted this 20 December 2014

It seemed to me that the height of gas checks is limited by the height of the gas check gozonta on the bullet. What we in the engineering game called the “doughnut-thimble problem". So I emailed Vulcan, asking about gas check height and drawings; and got a response: Joe,Thanks for contacting us. The sidewall height of our 6.5mm Aluminum Gas Checks are 0.0855"+/- .002” . We are in the process of working and getting specification sheets up on our website. I have attached our 6.5mm specification sheet. If you have any questions please don't hesitate to contact me. Thanks.John Overacker VulcanChecks191 Whitney RoadPenfield, NY 14526 So, it appears that Frank and the rest of us can stop worrying about being defrocked by the CBA for excessive gas check height, at least for now. What's next? Merry Christmas!

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frnkeore posted this 20 December 2014

I loked at that sheet. It's very odd that Fryxell didn't get those measurements, check it out:

http://castboolits.gunloads.com/showthread.php?262509-New-article-from-Glen-Fryxell

Frank

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goodsteel posted this 21 December 2014

I used to make custom GC makers that were fit to specific bullets cast of specific alloy. They were used to make very precise GCs out of specific thicknesses of aluminum. I found that running the GC all the way to the first driving band, yeilded less accuracy than making just enough cup to hold the shank securely (usually .050-.060 cup depth). Strange that Vulcan found the opposite to be true? Also, there have been many people stamping aluminum checks out of much better material than cans for many years. There is even a gentleman in England who sells free forming aluminum in pre-cut strips specifically for this purpose, and he sent me a sample to try nearly three years ago and has been doing good business from it since. This is not a new concept. 

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OU812 posted this 22 December 2014

I prefer a gas check that has a flat base such as the Hornaday and Lyman. This is so I can glue down flat and sand the skirts down evenly. You will see a lot of high and low spots while sanding. Sanding also sharpens edge for better grip...you may have to flair to prevent shaving.   Vulcan and others are too rounded at base.

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.22-10-45 posted this 23 December 2014

Interesting point by goodsteel..gas-checks fitting all way up to first band less accurate. I have read where the space between top of check & bottom of 1st. band is useful for collecting any lead particles check scrapes from bore. I specified a little longer shank when I had Fred Leeth make my .22 moulds.

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R. Dupraz posted this 24 December 2014

Who needs gas checks?

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delmarskid1 posted this 24 December 2014

R. Dupraz wrote: Who needs gas checks?Vas is das? 

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R. Dupraz posted this 24 December 2014

Back in the mid sixties when I was still footloose and fancy free, I became aquainted with an old crotchety gunsmith in my home town by the name of Hank Mar. At that time, I though he was old, maybe in his fifties. This resulted in a long and enjoyable relationship.       He was a cast bullet shooter long before I met him and got me started. Matter of fact got my first mold from old Hank which I still have. A Lyman GC four cavity 358156. He gave me this bullet one day as he told how he and his buddies used to shoot and experiment with cast bullets. Don't recall all the details any more but it was an attempt to shoot cast fast as I remember.      An old Lyman design? Don't know Maybe someone here will recognize the bullet. Hank related back then how they used to cut these small lengths of copper tubing and drop them into the cavities before the lead was poured. Have just kept it since then.

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jhalcott posted this 24 December 2014

A couple of my buds bought this style mold for the 375 caliber guns. They cut up a bunch of little rings from 3/8 copper tubing. They put the rings on a hot plate, when hot enough they'd insert the ring into the mold. Pour in the hot alloy and HOPE the boolit came out okay. LOTS of cussin around that pot!

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RicinYakima posted this 24 December 2014

I believe it is the “Wilkes” design, written up in the 1970's and early 1980's. The copper rings were inserted into a standard mold and the lead poured around it. This was back in the days when bore leading was thought to be caused by the rifling stripping the bullet down to bore diameter, not groove size. From and engineering stand point this is impossible due to the malleability of lead alloys.

Ken Mollohan, Molly, told me that they “captured” some of these and found lead on the outside of the copper rings. This lead to the beginning of the theory that lead molecules were vaporizing from escaping powder gases, called windage, around the sides of the bullets. This was being blown ahead of the bullet and causing erosion of the sides of the bullet. The “Wilkes” died a well deserved death.

FWIW, Ric

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Ken Campbell Iowa posted this 24 December 2014

before leaving this ” piston ring ” concept, if the rings are groove size + ... how does the gas blow by ?

if the gas blows by at ignition, when the bullet is hanging in mid air in an oversized free bore .... then shouldn't we be using base gas checks ... or piston rings ... of free bore diameter ... about 0.313...++ ... in a factory chamber ?

or if it is a ring in a front groove, and seated with interference against the ogive line in the chamber ... shouldn't it seal ?


wonder how the xcb approach does breech seated without base gas checks ... rhetorically speaking , those guys are running other tests ..so far ..

ken

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RicinYakima posted this 24 December 2014

Ken,

Most windage is on the lee side of the lands, where the bullet is forced to rotate. It is common for that gap to be three or four thousandths wide,  the length of the bullet. The harder the bullet the more pressure must be applied to move the metal back into the gap. The basis of the load with pressure to hardness of the alloy theory.

A 0.001” gap will allow 50,000 molecules, side by side, of carbon dioxide, at 4500 degrees, to blow past the bullet. The theory is that this is ripping lead molecules from the side of the bullet, and if the bullet fit is not good, or “lube” is not working, deposit it in front of the bullet on the bore.

Yes, I seat all of my 30 caliber match bullet gas checks in a .314” lube die, then taper the nose in an Egan .309” taper die to fit the throat.

Ric

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John Alexander posted this 24 December 2014

RicinYakima wrote: Ken,

Most windage is on the lee side of the lands, where the bullet is forced to rotate. It is common for that gap to be three or four thousandths wide,  the length of the bullet. The harder the bullet the more pressure must be applied to move the metal back into the gap. The basis of the load with pressure to hardness of the alloy theory. Ric Ric, Not to disagree with anything you have written but only to speculate.  It seems like the leading part of the driving bands should have a larger gap than the trailing part as the leading part gets to do more of the work.  I haven't been able to catch any undamaged bullets so don't know but I'm working on it. One narrow driving band should have a wider gap than the back edge of a bullet with more length of driving band or so it seems to me. Also a copper driving band should have a smaller gap because it is stronger.

Is it the “lube” clogging up the gap and stopping those 50K nasty lead molecules from getting through the gap that allows us to get away with a gap or the “lube” and other contaminants  coating the bore ahead of the bullet that prevents the vaporized lead from sticking and causing trouble.

I agree that it would take more pressure to move metal back into the gap.  But then the width of the gap to be filled be wider with more pressure-- thus more gap to fill.

If this is a problem that isn't being solved by lube or whatever, then extreme gain rifling with no twist ahead of throat and a bullet of mostly groove diameter would probably do it.

Gosh, trying to think about this stuff makes my head hurt and it's so hard to actually measure the things that need to be measured.  I wish Molly was in on this conversation.

John

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RicinYakima posted this 24 December 2014

John, I miss Molly very very much. We burned the emails up ten years ago about the subject, “What does bullet lube really do?” This is where the Wilkes driving bands subject came up. He was one of the few people I ever met who could think in multi-dynamics and then explain it so I could under stand what he thought was happening.   Yes, the copper driving rings are hard and stronger than the base bullet metal. But how does lead get on the outside of the rings after firing? Can the ring be bonded to the base metal or does gas leak under the ring? Why doesn't the ringed bullet with a gas check act like a jacketed bullet? Is it the weak open lube grooves? I don't know.   The marvel of modern “lubes", micro-waxes, and bees wax is the molecular structure. Molly would calculate the length of the decomposing molecules at 4500 degrees and 24,000 psi pressures. These were hundreds of time longer than the molecules of smokeless powder. These have to be small to make the powder “smokeless". Thus the name “vaporous gas check” was given to the theory that lube helps to seal the gases and pressure behind the bullet by plugging the windage loss.   Actually gain twist has the opposite effect. The rate increase makes the lee side gap ever increasing, as the driving side of the land forces the metal to move as it applies force to make the bullet rotate faster.   We need some Arty guys here, as I know they use copper driving bands on the cast iron projectiles.

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Maven posted this 24 December 2014

Re Wilk gas checks:  "Handloader” magazine reported on them extensively in the 1980's. Here's a link to Dave Scovill's comments on Wilk's innovation:  https://www.riflemagazine.com/magazine/PDF/hl134partial.pdf

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