Seating Gas Checks

  • 1.5K Views
  • Last Post 29 September 2021
cove posted this 05 September 2021

I have spent a lot of time fiddling around to make sure gas checks of my 30 cal bullets were seated squarely. Then, the other day it dawned on me that upon firing there is more than 20,000 C.U.P of pressure on the GC upon firing.  I would imagine this sort of pressure would firmly seat the check and squareness would be determined by the squreness of the base of the bullet. Any comments?

Attached Files

Order By: Standard | Newest | Votes
pisco posted this 29 September 2021

I made a punch to flare 30 cal g/c and it worked but have gone to using 8mm g/c on my 303 castbullets and they seem to crimp better

Attached Files

  • Liked by
  • JeffinNZ
sergeant69 posted this 28 September 2021

well............i disagree. at least heres what happened to me. i bought the NOE "finner tool" based on this thread. price is right. but on my 173 gr 30 cal cast, i get fins from nose to tail. it varies on severity. still working it out why. does same thing whether i used it handle held or sent to magma and converted  for a mastercaster. lyman mold. the NOE tool does put a nice rounded edge on the base, but the fins extend upward so the GCs still won't go on all the way, as in seat squarely before sizing. so i'm back to square one. the NOE tool does NOT remove finning, it simply rounds off the base. if i'm wrong, tell me. i'd love for it to work.

Attached Files

Brodie posted this 14 September 2021

My fairies are smaller than that, John, and they can ride quite happily even in the grease grooves.

 

B.E.Brickey

Attached Files

Ross Smith posted this 14 September 2021

Hope I'm not pirating the thread, but........ Does the NOE tool work both clockwise and counter-clockwise?

Attached Files

Premod70 posted this 13 September 2021

Great read, thanks to all for sharing knowledge.

Forrest Gump is my smarter brother.

Attached Files

John Alexander posted this 12 September 2021

Fins on the base are a minor pain but fins on the noses should be left on and shot as they swipe the air away so a crosswind can't push on the bullet and cause wind drift.  They also make it uncomfortable for the evil fairies that sometimes ride the bullet and steer it out of the group.  Just a helpful hint.

I have been shooting in our CBA national match all day in a switching wind with finless bullets and may be a little punchy.

John

Attached Files

RicinYakima posted this 11 September 2021

Some of my moulds from the 1890's were used as pliers and make fins. Even with my best attempts to correct them, they have little fins. 

Attached Files

OU812 posted this 11 September 2021

I've never cast with a mould (i have lots of moulds) that produced these so called fins on base of bullet. I have pressure cast and still no sign of fins on base. Are your sprue plates tight or flat enough to prevent fins? Must be a really worn out mould?

Attached Files

Shuz posted this 10 September 2021

Thanks for the info fellas. I have to get one of those tools!

Attached Files

JeffinNZ posted this 09 September 2021

Here you go.

Bullet Base Chamfer Tool – Manual | NOE Bullet Moulds (noebulletmolds.com)

Cheers from New Zealand

Attached Files

Tom Acheson posted this 09 September 2021

Shuz,

This tool is from NOE. Cannot access their website so I can’t recall what they promote it as. But it does a good job of trimming the ocassional fins at the base of a bullet.

Tom

Attached Files

cove posted this 09 September 2021

Well the above comments are certainly interesting and as per usual, there is not a definitive answer.  In answer to some of the comments, I anneal the Hornady GCs and the reason for that is so they do not spring back after passing through sizing die. The mold is a custom Accurate mold and there is not much resistance as the bullet passes through the sizing die, the resistance is felt when the GC is crimped into place. So, my concern is that there is very little resistance to keep the GC firmly pressed against the bullet base as it enters the push through Lee sizing die.  I have over 6,000 rounds through the barrel and have never encountered a case where the GC came off in flight (lots of shots using a chronograph). The alloy is on the soft side 20-1, so I was hoping the 20,000+ CUP pressure would force the GC firmly on the bullet base upon firing.  Accuracy is good, so I am getting the the GC on square, or the GC is squared up on firing.  As John Alexander pointed out, only a controlled series of tests with GCs seated unsquare and recovered without being deformed can answer this conundrum.

Attached Files

  • Liked by
  • JohnForrest
John Carlson posted this 09 September 2021

NOE makes a tool to trim the fins off the base of the bullets.  Similar to a case neck chamfering tool.

John Carlson. CBA Director of Military Competition.

Attached Files

Shuz posted this 08 September 2021

Who makes a tool to remove fins on the base of cast boolits?

Attached Files

John Carlson posted this 08 September 2021

NOE also makes a gas check expander tool.  Works quite well but rather a slow process and does add another step.

John Carlson. CBA Director of Military Competition.

Attached Files

Shopdog posted this 08 September 2021

Can't edit,above nose as cast with this batch is .3003-5

Attached Files

Shopdog posted this 08 September 2021

Interesting you brought.up bumping Tom;

Dig out a 1990 R700VS,bone stock 308 from a safe yesterday. Was shooting 175's and doing well. Wanted to try some Lee 150's.

This particular batch of 150's cast a cpl "tenths" large on the bore ride,@ .3083-5 so was up early this am. turning up a tapered nose die to be used in the little C frame press. All went smoothly on the die. One of the first tests on its use was to go well past what the original design/depth measure was aimed at.

Now to the good part;

At that level of pressure exerted on the naked base.... it got bumped up in diameter. Didn't need to measure it because,#1 wasn't planning on going that deep,and don't with the nose size. #2,pretty durn obvious it "grew" because of how I pre seat checks(see my post above). On the as cast base,how snuggly the GC goes on is,like weighing,a quality check on the bullet.... IOW's,if the check isn't going on with the same discernable effort,that bullet has issues.

The point of the post is for folks that for whatever reason,their GC's are "loose".... you can in fact bump the bases before install. And like Tom said... after as well. Which I also tried,at the design limit. Simply put the check on before hamfisting the poor nose way to aggressively. The difference is slight,but noticeable. You just need to try it both ways and decide which is better,before or after on that particular setup. I'm NOT bumping the base on this one,for reasons stated(l like the as cast fit)..... just thought it interesting.

Shot this afternoon and would be called a liar if I posted the group size on the first 10 out of the gate. Pretty big grin is an understatement.

Attached Files

  • Liked by
  • RicinYakima
Tom Acheson posted this 07 September 2021

Bumping bullets hasn't been duscussed here. But the force applied to the bullet as it is bumped will complete the check seating effort AND the bullet base will be very flat and have a sharp corner on the perimeter of the check.

Bumping also uniforms the exterior profile of the bullet which influences the fit in the chamber. I found the seating depth of a bumped bullet vs. an unaltered bullet (in my Savage .308) varied between the two bullets. And the accuracy was much better with the bumped bullets.

Another step but....

Tom

 

Attached Files

  • Liked by
  • Maven
  • RicinYakima
Wm Cook posted this 07 September 2021

I have two molds I use for .312-.313. Gas checks spin on both at times. On one the bullet shank is small and the crimp can’t grip the base well enough to hold it tight. On the other the base is too large and the check deforms in my sizer. Some of these spin. Some are crooked. On the latter I got by with a pan head screw to flare the checks before crimping. Not ideal but I got by.

So I guess bases can come out too small or too large and gas check will effect accuracy to the point they could fall off in flight. I have a check maker coming from Pat Marlin and I hope with different thicknesses of material I can get a good firm grip on both.

I’v often seen some of the seasoned contributors to CBA talk about recovery of projectiles. Sorting out fliers verses non fliers is next to impossible after a group is shot (as in Tom’s reference to his .223). However shooting a couple of five 5 shot groups with accredited bench practices in a firearm that has a proven accuracy history with correct and incorrect check seating is doable.

The big caveat as MP suggested, is that gas checks play a part in accuracy but making 25 bullets that can shoot 5 individual groups that aggregate <1” with="" cast="" bullets="" creates="" a="" long="" list="" of="" things="" and="" each="" of="" those="" variables="" has="" to="" be="" done="" the="" same="" way="" every="" time.="" bill.="" with="" cast="" bullets="" creates="" a="" long="" list="" of="" things="" and="" each="" of="" those="" variables="" has="" to="" be="" done="" the="" same="" way="" every="" time.="">

A “Measured Response” is as effective as tongue lashing a stuck door.

Attached Files

John Carlson posted this 07 September 2021

NOE makes a tool similar to a case neck chamfering tool which does a nice job of removing any fins.  I've also gone to seating checks in a push through sizing die.

John Carlson. CBA Director of Military Competition.

Attached Files

Show More Posts
Close