Could concave GC base cause accuracy problems?

[zomby woof]

I've been looking at the bases of my rifle boolits and wondering if the concave GC base can cause problems. It seems that the flatter and square the base of the boolit is, the straighter it will fly.
Is it worth the trouble of flattening the bottom of the GC?

[williamwaco]

My guess is that if they are concave, you are not getting them seated properly. Be sure they are completely seated and the gas check recess is the same width all the way around.

If you are using the Lyman 4500, do use the gas check seating tool that came with it.

If you are using Lee sizing dies, seat the check as firmly as possible. Set the bullet on the bench base down. Tap it on the nose with a very small hammer. TAP, don't WHACK. ( flat point bullets only of course ) Then size it nose up. If that helps, skip the tap and try sizing them base up.

[gnoahhh]

I got a batch of Hornady .30 checks that were very concave, and which resisted all attempts to flatten in the sizer on a couple of bullets (but not all) and took extraordinary effort to overcome in the check seater. My solution was to make a steel punch for in my small arbor press with a tip turned to match the base of the offending bullets. I then used it to flatten the bottoms of a bunch of GC's and voilá, perfection when seated.

[Larry Gibson]

As long as they are seated squarely and completely on the shank, no.

Larry Gibson

[grouch]

Another possible solution is to flare the sides of the gas check by using the head of a #8 round head screw, setting the check on a hard flat surface, setting the scew head in the check and tapping the screw with a hammer.
Grouch

[dragonrider]

How are you seating the GC's, ????

[Bret4207]

I've seen that type of base. Annealing the GC helped for me. I also found that some of my GC shanks tended to be rough and have some flashing. I took a tip from Skeeter Skelton and ran my thumb nail around the GC shank edge and it seemed to help.

If you're seating in an RCBS/Lyman type sizer bear down a bit more on the handle. That will bring things closer together. The GC should mate up to the GC shank base and unless the base is concave it should flatten out.

[zomby woof]

How are you seating the GC's, ????

I'm using a LEE push through. The Hornady checks from all lots I've had have the concave bottom. The concave is still there after I size. Short of using a GC seater to flatten them out. I was just wondering if this could effect groupings verses flat bases. The boolit exits the muzzle and how does the check's base effect how the boolit flies.

[Bret4207]

If the concavity is uniform around the base and the check is square to the boolits axis then in theory it's shouldn't make a diff. Thing is that if the concave is still there after seating then you aren't getting the GC in good contact with the base. I suggest you check the shank edge for something holding the GC off the base.

[zomby woof]

If the concavity is uniform around the base and the check is square to the boolits axis then in theory it's shouldn't make a diff. Thing is that if the concave is still there after seating then you aren't getting the GC in good contact with the base. I suggest you check the shank edge for something holding the GC off the base.

I don't think the sizer is holding the boolit back enough for the GC to flatten out as it's being pushed up.

[Wayne Smith]

I've always been of the opinion that when the big bulb goes off behind them they will flatten effectively! As long as they are concentric it's not a big issue.

[dragonrider]

Zomby woof, what diameter is the punch that you a pushing the boolits with???

Wayne I would think that you are right, how would we know for sure???

[zomby woof]

Zomby woof, what diameter is the punch that you a pushing the boolits with???


I tried using a .285" pin to flatten the check base, for a 30 cal. that turned out to be too much of a pain. I have the NOE GC seater die. That works also, just an extra step.

[Lizard333]

I had the same problem with some old hornady gas checks I picked up at a gargae sale. I had to anneal the GC's. Solved the problem. BTW, I had no accuracy issues. It was only used in a 357, shooting at no more than 25 yards. If they shoot good I wouldn't worry about it.

[Bret4207]

I don't think the sizer is holding the boolit back enough for the GC to flatten out as it's being pushed up.

Then I'd try annealing first. That will soften the check substantially from it's present work hardened state. Just dump as many as you like in your lead melt or heat them on a hot plate or with a torch till they get nice and blackish and are hot. Then let them cool. That's it.

You could also try blocking the boolit from entering the sizer die with a piece of wood or soft metal whicle you press the handle. That should seat the check and you can probably get it so the nose isn't mangled. Another way I've done it is to put the check on and give it a tap with a light hammer or even just push the boolit down hard onto a firm surface. It helps push the check into contact with the base.