Originally Posted by
Bret4207
I'll give you my understanding, it'll be in simple terms and is only my opinion.
Yes, there is a need for gas checks once you pass a certain point. That point varies from load to load and gun to gun, even ambient temp can affect it so your summer load might need it and your winter load not.
Obturation is an iffy thing, sometimes it happens and good results follow, other times it happens and bad things follow. Same for when there is no obturation. In a perfect world the would be no obturation- the boolit wild precisely fit the throat area and the powder would gently start the boolit down the barrel without distortion. That's why Harry Pope and Zischang and Schoyen and all the other old time lead boolit shooters used a false muzzle and muzzle loaded their guns. Most of us won't do that. We prefer fixed ammunition, so we try and hit a happy medium.
Different powders, primers, case shapes, throat shapes, seating depth, alloy, boolit design and size , rifling type and condition, even ambient air pressure can cause variations in the burn rate and pressure curve of a given load. SOME plain based boolits in SOME guns will be extremely forgiving of all those variables and will tend to shoot good up to somewhere around 2000 fps. At least those are the claims that have been made. You will occasionally hear of someone who gets 22-2300 fps for 5 shots or so. If this is true, these guys shouldn't even bother picking up a lottery ticket, they've used all their luck up!
In an average rifle those variables will stack up in a seemingly random order and usually limit your plain base shooting to under 1600 in general no matter how good a fit you have. That 1600 fps can be 1200 in some guns, 1700-1800 in others, larger calibers tend to be more forgiving. If, IF you go to a slower powder, a harder alloy, maybe a little larger boolit and a super lube and a filler you can up the speed. Maybe. It might work one day and not the next.
In handguns the PB generally works up to 11-1300 fps given good fit, etc as with rifles. Cartridges like the 45ACP can be used at factory velocity with PB with little problem, same for the 32 ACP and 380 ACP. Low pressure! Take a 9mm and you're good to a certain point and then it's lead city. Same for the 38, 357, 40S+W, 44 Special and Mag and of course the any of the other hotter rounds. Pressure seems to be the bad guy here and to me at least, it seems to work a little differently in handguns than in rifles.
A gas check just makes achieving higher velocity at a higher pressure easier. IMO boolit bases do not, and have never "melted". There isn't time enough , even under the pressures involved, for the heat transfer to take place. IMO what happens at the base is that the pressure pushes the lead around and like a rock thrown in mud there is some splashing. The rougher and weaker the base and alloy the more splash. Lead alloy is ductile and if you've ever hit an ingot with a hammer you can see that you don't get a smooth surface when you've hit it. I believe this takes place and the "splashed" particles are minute, maybe microscopic in size even.
The same general theory goes for the sides of the boolit once it's moving- only now you have hot gases trying to rush past the boolit through any gap between boolit and barrel. The alloy doesn't "melt", the gases abrade the boolit surface (and of course a rough barrel can help this happen too) and the particles of alloy are blown onto the barrel surface and pressed on by pressure. At least that's my understanding. There can also be the instance of lube failure where the alloy is actually rubbed into the barrel surface. I call it lube failure, but it may actually be something else.
So what does the GC do?
1- Provides a scraping action to the barrel. The edge of the check theoretically scrapes lead from the boolit ahead of it away from the barrel.
2- Provides a seal of sorts in a properly sized gas check/barrel interface. An undersized gas check is a waste of money. What the tolerance is depends on the gun and load, but as a general rule I want my checks at least bore size and preferably closer to groove size. If the check is under bore size it's effect is drastically reduced, may not work at all and is wasted money.
3- Provides a much stronger base to the boolit and one that remains square throughout the boolits journey up the barrel. This I've seen- seat a check crooked and shoot several groups with crooked checks and square checks. It don't take a genius to see the difference.
4- Makes achieving higher velocities at higher pressures EASIER. That doesn't mean the sky is the limit. There comes a point where the alloy can't take the pressure/velocity/rifling anymore and you get leading and wild shooting. But the GC makes it easier to go faster using pressure to boost speed.
That's my understanding at this point. 10 years ago I had a different opinion, 20 years ago it was different than that! I used to think hard, hard, hard!!! I thought that would solve all the problems. Not so. A GC won't solve it all either, but it does reduce the variables in most cases.