Gas Checks and flatness

[redhawk0]

Hi guys,

I know we want to have gas checks solidly crimped on the base of our boolits. And...we want them perfectly flat. But...has anyone "intentionally" done any tests on GCs that weren't perfectly flat and how it effects accuracy in the nominal 100-150 yard range?

Just kinda curious...as I'm right now seating/crimping about 600 31141's with Gator Checks. And it got me to thinking....(dangerous...I know)

redhawk

[Thumbcocker]

I seem to remember reading something similar years ago but cant remember where. Handloader maybe? I do recall that a canted gas check made a noticible difference.

[fredj338]

The base drives the bullet, so any anomaly is going to affect accuracy. Dead flat is best, no base deformations is best.

[charlie b]

I haven't seen it with gas checks but several folks have done it with plain base by filing a cant to the base.

[Bazoo]

I use a gas check seat tool on my 450 and it seats them square. They are slightly rounded instead of perfectly flat, but they are consistent.

[redhawk0]

What really brought this up is when I was seating my GCs by hand I found a few that wouldn't sit flat on my tabletop (boolit had an obvious cant) I found just a few this way. What was really going on? I had a sprue cutoff that was raised just a skosh. A quick drag across some 120 grit and it flattens right out...then check again and run them through for the sizer/crimper step.

I figure the air currents coming in behind a fired boolit to push it along and would need something flat to push against...the flatter the better to keep it from veering off course. But I'm not sure how much effect it has since there is also a rotational aspect to it. I'm sure severe enough and the boolit would wobble and possibly tumble. Would a boolit traveling at 2000fps be that noticeable at 100 yards? I'm guessing it all depends on how severe the cant really is.

I just didn't know if anyone here did any physical tests.

redhawk

[PositiveCaster]

It isn’t aerodynamics. The real effect is when the bullet exits the muzzle. If one side of the base leaves the crown first, that causes the gas to vent at that location, pushing the bullet off axis similar to an uneven crown. Filing the base off-square replicates the effect and has been done a number of times. Will it cause you to miss a target? Depends on the amount of deformation, the range and size of the target. My advice? Don’t shoot them at something that matters.

https://castbulletassoc.org/forum/th...base-accuracy/


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[bmortell]

if one side isnt fully seated wont the ~30k psi or whatever push it the rest of the way on?

[gwpercle]

Another advantage of a lube/sizer is that it seats gas checks on straight and level .

I've been lube/sizing a big batch of 9mm boolits with gas checks and every one pops out flat and level ... haven't seen one yet that was catawampused .
Gary

[Alstep]

if one side isnt fully seated wont the ~30k psi or whatever push it the rest of the way on?

I was thinking the same thing.

[MT Chambers]

A crooked gas check is worse then a gas check that comes off in flight, in fact early Lyman checks were designed to come off in flight. It was never proved that it hurt accuracy, however a crooked gas check has proven to be a group wrecker, ask some of the famous shooters of CBA benchrest fame.

[waksupi]

if one side isnt fully seated wont the ~30k psi or whatever push it the rest of the way on?

That's pretty much what Felix and I determined years ago.

[edp2k]

That's pretty much what Felix and I determined years ago.

If the actual lead bullet base is square/true/no-defect and the GC is merely not pushed on 100%,
I can see the gas pressure seating it, yes.

However, if the reason the GC is canted is that there is a burr/bump/lead-flashing/non-square GC shank on the lead bullet base,
then pressure is not going to eliminate the lump-under-the-carpet, certainly not evenly.

[beagle]

In seating copper GCs with a Lee push through sizer, they will occasionally turn out with a dished center (slightly) and a slight ridge around the outer base rim. I fired them and noticed no affect on accuracy. The key is for them to be flat and not canted. That's asking for trouble.
I've been using Pat Marlin's PB pop can checks for about 3 years now and they always seem to give a smooth, flat base no doubt due to the softer material. Accuracy has been great and no leading./beagle

[mehavey]

if one side isnt fully seated wont the ~30k psi or whatever push it the rest of the way on?

Yes. And as long as the base underneath is flat, no harm/no foul.

[Dusty Bannister]

I suppose that if the flat base was the perfect idea, the lube size die makers would not have produced the "I" portion of the die with a concave surface. I even have some dies with the end of the "I" die drilled so that only the outer portion of the rod makes contact with the base of the bullet to ensure that if there is a sprue bump, it has no contact with the rod, so the edge of the bullet base is flat and square to the bore when fired.