Gas Check Fillet Ring ==> Counterproductive to obturation?

[Land Owner]

Looking at a gas check up close and personal I note that the radiused edge appears to be counter productive to sealing the boolit to the lands and grooves. We're cutting spru's and checking for complete "fill out" at the bottom of our lead boolits. Incomplete fill out or round edges and its into the reject pile.

Then we swag on a gas check that rounds the edges. Counter productive?

Pictures help:

"Ideal Base"
98654

"Gas Check"
98655

[Wayne Smith]

Look at bevel base boolits that have been used in competition for years. What matters is how the base of the boolit leaves the muzzle, not how sharp is the edge.

[Eutectic]

Then we swag on a gas check that rounds the edges. Counter productive?


The rounded edges are probably fine IF they are swaged uniformly upon gascheck installation..... (or upon firing) and that's a big "IF"!

We, in general, seem to be going to harder and harder boolits with alloys and particularly water dropping that can aggravate a balanced boolit base to gascheck fit.
You bring up obturation..... Not talked about near enough.... Boolit fit is pretty much of paramount agreement importance... but it is two-fold. Both static as talked about a lot, and dynamic fit upon firing. (less pondered)

This is why I use alloys and techniques as soft as possible and almost always fully anneal gaschecks. A perfect gascheck to boolit base fit can be approached in more ways than one.

Good topic!

Eutectic

[Outpost75]

When manufacturing gaschecks the header needs a slight draft and to form an internal radius at the corner wall in order for them to come off the punch.

[geargnasher]

Recover some gas-checked boolits and look at them, the bases after firing may surprise some folks. One person I know did some experiments with aluminum checks comparing squared bases (swaged in a special die/punch) to round right out of the check maker. The radiussed-based checks shot better at high velocity/pressure.

The last boolit I recovered was a .30-caliber from a deer, the base was so sharp it would cut, there were tails from the land displacement, and the overall base was slightly concave.

Gear

[JeffG]

Recover some gas-checked boolits and look at them, the bases after firing may surprise some folks. One person I know did some experiments with aluminum checks comparing squared bases (swaged in a special die/punch) to round right out of the check maker. The radiussed-based checks shot better at high velocity/pressure.

The last boolit I recovered was a .30-caliber from a deer, the base was so sharp it would cut, there were tails from the land displacement, and the overall base was slightly concave.

Gear

Very interesting, thanks for that.

[dtknowles]

The bullets used by short range bench rest shooters (100 and 200 yards) are flat based with small radius similar to the radius I see on gas checks. I don't see how this radius can be a problem.

Tim

[Land Owner]

I surmise, the larger the caliber, the less "radius effect". As I look forward to pouring .223 Rem, I think the "radius effect", if any, would be more pronounced.

[Eutectic]

I think any of our true experimenters would just love to be able to recover our fired boolit right at the moment it leaves our barrel with no outside influence to change its then pristine condition....
So to say "recover some gaschecked boolits and look at them" is fine... IF and it's a big IF we are sure nothing has influenced what we see prior to impact... A concave base can happen while still in the bore for instance... A poor base casting and even shotgun granular buffer can do it when used as a filler! Then extreme impact can do it. See the first picture. This is a .30-30 boolit cast 1 in 30 at 2200fps into wet paper!
The worse thing to look at are berm boolits hitting hard dirt. They will trick you where and why what you see happened. Game bullets can be variable to read.... Wet paper is pretty good as long as you don't mushroom to the point of 'rolling' the base over as in the first photo. The very best I've found is light fluffy powdered snow.... a big drift of it. You have to wait to spring comes to see your results unfortunately! A boolit may go six feet in the perfect drift and be pristine when found; even hollow points...

The second photo is a .25 caliber HP expansion. The gascheck is not annealed and is actually convex!
The third photo is more .25 tests with fully annealed gaschecks.
The forth photo is a .30-30 HP that impacted blowing all the HP off. But the thick un-annealed Hornady gascheck is as shaped when installed.
The fifth photo is a .414 Super Mag boolit in a 40,000psi load that displays perfect gascheck performance from an ANNEALED .416 Hornady gascheck.

Studying recovered boolits is quite a 'science' in other words!

Eutectic

98971
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[geargnasher]

http://castboolits.gunloads.com/attachment.php?attachmentid=98972&d=1394294062

Since this thread is, unfortunately, fading into oblivion already, I'd like to talk about this picture for a minute. Look at the lube. The forward band is filled to the brim with lube, even has rifling marks clearly defined in it, and just a little barrel residue picked up in the front edge. The lube in the rear lube groove looks like it got partly washed out, either from the case/throat/barrel transition, or simply from pressurization causing some lube to be smeared behind on the bore per Fryxell's "pumping" theory. I think it's safe to say no lube got blown around the boolit before it obturated the bore in this instance (a good example of proper static fit enabling proper dynamic fit and immediate bore obturation), and a flinger-fan like me would say the lube is far too hard for the circumstances......but.......the proof is aways in the shooting.

It's very interesting to me to read the story that one boolit tells us about many things.

Also to the OP: If the gas check isn't sized smaller than groove diameter, it won't be counterproductive to obturation. It's a press/swage fit in to the barrel, and the natural spring of the metal maintains a spring-loaded gas seal throughout the bumpy ride through the rifle. I know the intuitive thing is that a rounded edge will funnel and concentrate gas pressure on the weak, dynamic point (opposite of a cup-type seal, as in an automotive drum brake cylinder seal, modern shotshell wad, or a hollow-base bullet skirt?), but remember that as the surface area upon which the pressure acts is reduced, so is the force of the pressure. The check probably obturates the bore more due to the press-fit than from gas/fluid pressure maintaining obturation as in the parenthetic examples above). A flexible, cup-type seal requires pressure behind it to maintain seal, a gas-checked, interference-fit boolit does not.

Gear

[Eutectic]

Since this thread is, unfortunately, fading into oblivion already, I'd like to talk about this picture for a minute. Look at the lube.
Gear

[smilie=w:[smilie=w:[smilie=w:[smilie=w:

Gear... While I put that up there as my only convex gascheck photo I just knew you'd get me on the unpurged lube !!!!!

60% Beeswax, 40% Alox 350 and Carnauba (Maybe 5%) This was life before the "Extreme" thread before I checked things like lube purge! That Magma mold holds enough lube for black powder with two very generous grooves. Wet paper at 10ft seems to catch what lube didn't purge. Notice the later photos 'cleaned up their act'!

I'm sorry this thread didn't take off as well. Lot's to know about that little base cup!

Eutectic

[btroj]

Alox? Don't mention that around Gear, he breaks out in hives!

I hadn't noticed the lube in the photos, I was focused on the checks. I need to look at those things better. Bad Brad.

[geargnasher]

Well, the lube may not have all gone but it sure doesn't look like it would have affected the balance with its even distribution.....provided of course that air friction didn't melt it enough to fling off in big chunks willy-nilly on the way to a much more distant target. Who was it that said lube "either needs to all stay or go"? Well it's true, and I have a far more difficult time getting it to stay reliably than I do getting it to disappear quickly and have not chance to upset things downrange.

Mmmm, oven-roasted crow with an Alox 606 glaze, yup, I'll eat it and smile if any of you can figure out how to make a top-shelf Extreme Lube with it :bigsmyl2:

Gear

[Eutectic]

Mmmm, oven-roasted crow with an Alox 606 glaze, yup, I'll eat it and smile if any of you can figure out how to make a top-shelf Extreme Lube with it :bigsmyl2:

Gear

If Alox 606 type additions (aka LLA, Xlox, and other names that will be censored!) end up in "Extreme" I'll drive down and eat that meal right along with Gear!

I see several lube groove formulations listed with Alox 606 on board.... I really wonder if these mixes are tested thoroughly by the chefs including it?????:oops: I have yet to have a formula last over 20 rounds... It may start off flinging them in one hole; but groups open up slowly and keep going to double what the gun/load is capable of. It makes a tenacious goo for sure.... I've even thinned it out for heavy duty sizing lube!!! As we know from tumble lubing; too much ain't good! So we add 15% or so in a conventional lube??[smilie=b:

Alox 350 is the one to watch! Please don't be fooled by the first name "ALOX".... Many, many, posters here are named "JIM" for example...... But that doesn't mean they are just alike!!!
Alox 606 and Alox 350 aren't even close to the same! Their middle name is "Calcium" is about as far as it goes.

Some (15%?) Alox 350 along with Ester oils has merit. It will leave the bore steel 'pores' cleaner than anything I've tried... Older somewhat rougher bores don't seem to like it.... Newer slicker bores usually do. It may be the best lube going for 'hot rod' .22 Hornet loads! It lasts too! I've ran it 50 rounds without degradation and that's saying a lot for 2700-2900fps 35,000 psi loads in that small bore!! So it may/could be in a specialty lube... Maybe for my Hornet's at least. As I know it so far it may NOT be tolerant enough for "Extreme" across the board..

But it could be in our 'champion' finalist formulation.... We are still missing something... That something and Alox 350 may be just the ticket.... Who knows?:shock: It may just be a 'tweak' to settle things down like "Mikey's Ivory" has accomplished.

Don't count 15% Alox 350 in the mix out just yet....:mrgreen:

Eutectic

[44man]

That was me Gear.
Then again, guys forget what the GC is for! It is not to obturate in and of itself by pressure, that is done by the boolit and size to the bore and of course the size of the check also. The check must be the size of the boolit body, never larger as it will expand the brass when seated over what case tension the boolit needs. Smaller is no good either, gas will leak. So if you don't size your boolits, just use a die the size as cast.
The check was made at the start to halt the skid of softer boolits and harder rifle boolits. It's primary function is to grab the rifling without gas passages around it.
It is not a scraper, I have recovered many boolits with fully leaded checks because the boolit itself could not stop skidding and the check could not handle it. It is perfectly OK to have a boolit skid half its length but it must start turning before the base is reached.
I have recovered many factory boolits friends shot with half the lube broken out of grooves and even had boolits sent to me to test with half the lube in the bottom of the box. It is a pain to remove the junk and put a better lube on them.
The picture shown has an even amount of lube but the question is--will ALL do the same?
Obturate means "to seal or plug up", not to expand before it can obturate which comes after expansion. There is no need to expand when you have fit. Anytime someone says "bump up" he has no fit to start. Even a Minie' ball will not shoot right unless it fits first. That boolit was made to load over fouling in the hope it will go down the bore but it will not hit what you shoot at except with luck. Same with hollow base boolits that are undersize to start. Just makes more leading from skid.