Seems to me if you shoot a boolit 1 or 2 thou oversize it has to swag the boolit and check to bore size against all the pressure at the base of the check/boolit. Thus already doing what you want done.
Seems to me if you shoot a boolit 1 or 2 thou oversize it has to swag the boolit and check to bore size against all the pressure at the base of the check/boolit. Thus already doing what you want done.
Maybe not as simple as that. The boolit is oversized, but the part where the GC goes is very undersized. That diameter must be augmented by the thickness of the GC X 2 and may be very critical, especially if the aluminum used for the GC is not as thick as the copper GC, the boolit was designed for. The lead heel of the boolit may not obturate enough to force the GC to expand and make a good seal. We size our boolits, but not the part where the GC is fitted. Something to think about.
diplomacy is being able to say, "nice doggie" until you find a big rock.....
No matter how big you make a bullet, you always get "blow by" the bullet base before it "bumps up" and fills the bore. Sometime photograph a muzzle in slow motion. The first thing you'll see is a puff of (normally) white smoke, followed by the bullet and then a puff of regular smoke. The white smoke is "green gas" caused by the initial powder combustion and sneaks past the bullet base before pressure is sufficient to bump the bullet base and seal the bore. This is super hot and the source of some of our leading but not the main source. That comes about as a result of other causes during firing./beagle
diplomacy is being able to say, "nice doggie" until you find a big rock.....
Slightly off subject, but I been pondering it. What if you had a slightly hollow based bullet, with a PB gas check to match. Then pressure would push the skirt out but since it was more of a dish than a true hollow base, it would withstand a higher pressure.
I'm thinking no hollow base.. Just more of a gas check with a skirt. Imagine 2 checks back to back. If you sectioned one it might look like a Capitol H. Top Bart grabs bullet base.. Bottom part acts as hollow base bullet to obturate into rifling?
I'm thinking the gas check will be the same shape as the base of the bullet, it will be supported in the center, So the pressure expands them both outward. And I'm thinking a very shallow base, so there isn't any danger of skirt separation like with a normal deep HB bullet.
Maybe the I part of an H&I die, if it was made with a rounded center, would swage both a thin gascheck and the bullet base when sizing? Then normal plain based bullets could be used. Course my thought, I don't know how deep this HB would need to be.
I'm thinking the gas that escapes around the boolit happens as soon as the neck starts to expand and before the front of boolit seals in the bore. If the boolit is bigger than the bore it doesn't have to bump up to fill a hole smaller than itself. I believe that most leading from a proper sized boolit happens while the boolit is leaving the neck and hot gas is screaming past the edge of the base before the boolit has moved forward far enough to seal the bore. This is why gas checks usually work. Another cause is pushing a boolit into the rifling faster than it can begin to spin. There are other causes such as rough bores, worn throats, gas checks that don't get sized with the boolit (bad fit) and such.
I one wanted to see if you could totally seal the gasses behind a boolit put a dab of grease on the base of a flat base boolit and put an upside down gas check on the base similar to a shotgun wad. I don't think it would work but it would test the theory of an expanding gas check.
That might be an idea. I've shot loads of HB bullets and unless the "skirt" is perfect with no voids, you'll get blowouts with loads above factory levels. Can't push them at all from my experience. The aluminum check may prevent that. I have all my HB moulds so I'll try a few and see what happens./beagle
diplomacy is being able to say, "nice doggie" until you find a big rock.....
I was thinking if you didn't glue them on but just used a bit of grease just to hold them in place while loading them it might make them all come off as soon as they leave the barrel. I guess it's time to quit thinking about it and start trying some of these ideas.
Don’t forget we count on that initial blow by, to carry some lube with it to begin lubing the bore with lubed boolits. If you stopped all the blow by, maybe it would decrease the effect of the lube.
The initial bump should impact the base and "deform" it and squeeze sufficient lube into the groove for this purpose. Realize that we don't know about this process and are only speculating from facts that we have evidence for. We know the base "bumps" up for sure as we can see the impact on recovered bases. The rest is speculation and this whole process happens in micro seconds and we are unable to actually see what happens. The more we discuss, the more we learn about the process./beagle
diplomacy is being able to say, "nice doggie" until you find a big rock.....
I've gone to some reasonable lengths to insure VERY square/flat bases. With both,tooling and process control. In pretty durn accurate varmint rigs,we see it on "paper". Obviously not the only reason for UFO's... but is a contributing factor.
So you have that to consider. This QC needs to be well attended,basically taken off the problem list before you can fully test or take advantage of your proposal. Ex: your idea may work peachy,but the QC and process let issues creep in.
I play with this from time to time... and feel there is some room for improvements. Good luck with your project.
just like the instructions for these in photo #2, and these GCs are basically accomplishing the same thing you are pursuing?
https://castboolits.gunloads.com/sho...-Checks-before
“Some people spend an entire lifetime wondering if they made a difference in the world. But, the Marines don't have that problem.” Ronald Reagan
oley55
Yep, except you don't need the fancy gc, just use the normal gc. The instructions say to put the cup side toward the boolit and I am thinking an inverted normal gc might work even better. It might work like a shotgun wad and expand as soon as the neck of the case expands and then again as the boolit leaves the case sealing the throat. Not having a high speed camera, I can't test for gasses exiting the barrel prior to the boolit. I have never seen the type of gc shown in post 1 so I can't try them either. I suspect they didn't perform as advertised or they would still be available.
This discussion is a what if thing and I sure don't have all the answers, but another thing I wonder is if the gas we see exiting the barrel prior to the boolit is super compressed air or blow by. Does this gas show up on a bore seated bullet? If so, is it blow by or super heated compressed air that was in the barrel ahead of the bullet? These are just ideas that are bouncing around in my head and I value others opinions on such matters as it gives me other ideas to consider. I wish I had the test equipment to test some of my theories.
beagle,
did you pursue the domed gas check thing any further? Just idle curiosity because I stumbled across these domed base guards from Corbin for swaged lead bullets and it triggered a recollection of this discussion.
http://www.corbins.com/bgk-1.htm
http://www.corbins.com/gascheck.htm
“Some people spend an entire lifetime wondering if they made a difference in the world. But, the Marines don't have that problem.” Ronald Reagan
That looks like a "spin off" of the old Harvey zinc gas checks applied during casting except they swage them on which takes a lot of expensive equipment. I tried the Harvey's back when they were the rage and they worked pretty well but I was shooting in a .45 ACP and that didn't justify the expense and effort so I moved on.
The base guard looks like a pretty fair setup and I believe it should work really nice if you're into swaging.
Haven't followed up on my original concept because of the virus and some other health problems.
When we were tinkering with making nose first adapters for Lyman and RCBS dies, we made bottom "punches" out of 5/16" bolt stock. One of the punches I made was a .30 and it was slightly undersize for the die. This left a small raised portion around the edge of the bullet bottom on the check when the check was seated. They shot well in the .30/30 as we were messing with steel plates at 100 yards for amusement. I recovered a bunch of the fired checks. There was a noticeable lack of blackening at the base caused by "blow by" on these checks. That started me wondering if a slight dome or ridge around the outer perimeter of the check wouldn't enhance sealing and eliminate blow by./beagle
diplomacy is being able to say, "nice doggie" until you find a big rock.....
It does suck our age/health interfering with our tinkering efforts. I hope things are getting better for you.
I'd say yes a definate spin off. Here is a couple paragraphs cut from the first Corbin link:That looks like a "spin off" of the old Harvey zinc gas checks applied during casting except they swage them on which takes a lot of expensive equipment. I tried the Harvey's back when they were the rage and they worked pretty well but I was shooting in a .45 ACP and that didn't justify the expense and effort so I moved on.
The pity is I can "just" afford my current efforts and swaging for me is an unlikely endeavor, but I sure do like tinkering.The conical shape of the BG disk is what makes it work so well. The idea of using a zinc washer was tried and used with limited success in the 1950's (see the Harvey Prot-X-Bore for more info). It turned out that the washers could not be cut precisely enough to seal the bore, and that one edge was always rounded while the other was sharp. If the bullet maker put the rounded edge toward the bullet, there was no scraping or burnishing action to clear the bore. Also, if the washer was even a few ten thousandths smaller than the bullet, gas would leak around it and melt the lead into the bore.
But making the BG disk undersized and conical solved the problems. First, the disk gets its final diameter by being flattened when it is attached to the bullet. This makes the disk grow in diameter until it contacts the die walls. Then the surplus metal is forced to extrude forward and form a burnishing tool edge, because it is supported on the other side by a solid steel punch and cannot move that direction. The only way it can move it toward the relatively soft bullet material. This is exactly what we want: a base that is exactly the diameter of the bullet, with a scraper edge facing forward to clean the bore when fired.
“Some people spend an entire lifetime wondering if they made a difference in the world. But, the Marines don't have that problem.” Ronald Reagan
BP | Bronze Point | IMR | Improved Military Rifle | PTD | Pointed |
BR | Bench Rest | M | Magnum | RN | Round Nose |
BT | Boat Tail | PL | Power-Lokt | SP | Soft Point |
C | Compressed Charge | PR | Primer | SPCL | Soft Point "Core-Lokt" |
HP | Hollow Point | PSPCL | Pointed Soft Point "Core Lokt" | C.O.L. | Cartridge Overall Length |
PSP | Pointed Soft Point | Spz | Spitzer Point | SBT | Spitzer Boat Tail |
LRN | Lead Round Nose | LWC | Lead Wad Cutter | LSWC | Lead Semi Wad Cutter |
GC | Gas Check |