Gas check, HUGE difference!!

[1shot]

Beautiful sunny day so I took my Marlin 30AS out to test the same load/bullet with and without gas check.
Win LRP, 18grains of H4198, RCBS 30-150fn at .310" from wheelweights queched in water.
I shot these targets side by side, one round gas checked, one round without and so on. Five rounds at each.
Factory open sights at 50 yards, six o'clock hold.

I had no idea the difference would be so dramatic!! :shock: I am now totally convinced that they work.
1Shot

[Blammer]

yea, it's quite a difference in some loads and guns. good shooting!

[saskgunowner101]

Something about that group on the left looks vaguely familiar to me.

[Crusty Deary Ol'Coot]

Afternoon 1shot,

Veral Smith of LBT says that at times a gas check makes a big difference.

Sure did on yours.

Would be interesting to see two identical molds, except for the gas check shank and then shoot the plain base mold against the GC mold.

Having not shot a GC boolet, with and without the GC I sure don't know what to expect.

Thanks for posting!

Keep em coming!

Crusty Deary Ol'Coot

[MtGun44]

I find GCs to be a moderate PITA and absolutely have no use for them in pistols. With
a good design, I have had excellent results in all my pistols with plain based boolits.

HOWEVER - they sure do help in rifles much of the time! I have had some good results
without GCs in some rifle calibers, but it is very clear that rifles really need them sometimes.

Your results are in agreement with many of mine.

[44man]

Beautiful sunny day so I took my Marlin 30AS out to test the same load/bullet with and without gas check.
Win LRP, 18grains of H4198, RCBS 30-150fn at .310" from wheelweights queched in water.
I shot these targets side by side, one round gas checked, one round without and so on. Five rounds at each.
Factory open sights at 50 yards, six o'clock hold.

I had no idea the difference would be so dramatic!! :shock: I am now totally convinced that they work.
1Shot
I have explained this many times. You have lost a drive band by leaving the check off and the length no longer matches the rifling twist. A PB would shoot as good but you have shortened your boolits drive length by leaving off the check.
My 30-30 would do this at 100 yards but leave the check off and every boolit would keyhole at 50.

[OLPDon]

If you worked at it you could get unchecked to work as well just takes alot of small changes Gas checks are the equilizer they make up for quite a few short comming, Casting is much like Golf or building a better mouse trap.
Don

[cast367]

I use Hornady gaschecks for my 180 grs rcbs cast bullits.The best there is.
When I use home made brass checks , it gives a poor result, not good enough for
benchrest shooting at 100 meters. Rifles 308W ,30-06 and .30 m1 carb.
I have no idee the reason. Has someone an idee??

Cast 367

[Bret4207]

I use Hornady gaschecks for my 180 grs rcbs cast bullits.The best there is.
When I use home made brass checks , it gives a poor result, not good enough for
benchrest shooting at 100 meters. Rifles 308W ,30-06 and .30 m1 carb.
I have no idee the reason. Has someone an idee??

Cast 367

In a word- fit. You have to remember a GC or any other part of the boolit really isn't working alone. The GC protects the base, provides a tougher element in that area, changed the CoG, does all sorts if things. If one brand GC gives you a base that's .002 bigger than your home made GC, of vice versa, things change. It's our job to record these changes and figure out how to make them work for us.

[Dollar Bill]

I have explained this many times. You have lost a drive band by leaving the check off and the length no longer matches the rifling twist. A PB would shoot as good but you have shortened your boolits drive length by leaving off the check.
My 30-30 would do this at 100 yards but leave the check off and every boolit would keyhole at 50.\
No disrespect, but I have to question this statement. First, rate of twist required for minimum stabilization is based on bullet OAL, not just bearing surface. Second, if your statement was true, leaving the GC off would effectively shorten the bullet, requiring less twist to stabilize, so the keyholing you experienced when leaving the GC off was because of other factors, such as gas-cutting. Just trying to reason through the statement.

[44man]

\
No disrespect, but I have to question this statement. First, rate of twist required for minimum stabilization is based on bullet OAL, not just bearing surface. Second, if your statement was true, leaving the GC off would effectively shorten the bullet, requiring less twist to stabilize, so the keyholing you experienced when leaving the GC off was because of other factors, such as gas-cutting. Just trying to reason through the statement.
No gas cutting, I recovered most of the boolits in my trap and there was none. Rifling marks were clean with no skidding. Damage on one side from hitting the rubber.
But drive length IS important as are boolits with too long of a bore ride in the wrong rifling style.
I was shooting the 308-165 SIL boolit, take a look at the drive area compared to the length of the boolit---it is a LONG boolit, yes? Wouldn't you say I lost a high percentage of the drive area by leaving off the check? What overall length did I lose? The thickness of a gas check?
Now the boolit 1shot is shooting has better drive bands and is the reason he still shot round holes but he still made the drive area too short. He is not that bad off though and a load workup again to adjust for the change in the boolit might bring back groups.
You can prove that overall length is not as important as you think by taking two boolits, one with a long bore ride and another with Loverin grooves but AT THE SAME LENGTH. For that matter take two jacketed of the same length but one with a boat tail and another flat base. You will see the best load and velocity for each will not be the same.

[felix]

Besides that, DB, a boat tail eliminates weight at the projectile tail, and that is the WRONG place to do that without adding sufficient twist to compensate. On the other hand, hollow base projectiles will help the twist situation somewhat by increasing the dynamic inertia. A hollow point does that too, plus taking weight off the nose which even helps more. Whatever the change, the projectile must spin appropriately for any comparison to be fruitfully made. ... felix

[JesterGrin_1]

Very good information. To add to the length VS Bore I found this to be true in my 45-70 Marlin GS. I found the 300Gr to not shoot nearly as well as the 350Gr and larger Boolits. My thinking was the length or bore ride of the 300Gr was too short for the bore.

[HangFireW8]

I use Hornady gaschecks for my 180 grs rcbs cast bullits.The best there is.
When I use home made brass checks , it gives a poor result, not good enough for
benchrest shooting at 100 meters. Rifles 308W ,30-06 and .30 m1 carb.
I have no idee the reason. Has someone an idee??


Please measure your home made checks with a micrometer, before mounting and on a boolit.

Do the same with the Hornady, and tell us the results. You may find your answer before getting back to us.

-HF

[nvbirdman]

I have often wondered if the gas check not only protects the base against gas cutting, but also adds a good square base with no imperfections to the boolit.

[goofyoldfart]

may be a little off topic, but, I generally shoot PB in my revolvers. just use an over the power meat tray divot that is 20 or 30 thousands over size. It acts as a gas check with the plus of putting the powder up against the primer. been doing this since I read about it in the American Rifleman written up by a NASA scientist that worked in ablations dept. as he was a cast shooter and ran out of gas-checks. I believe it was in '75 or '76. works fine in straight wall cases and can be made to work in shouldered cases as well if glue is used. I always used Barge Contact cement (due to doing a lot of leather work at the time). the only problem with the shouldered cartridges was that it was a PITA aligning the divots to the base.
on a side note : went to the storage shed this afternoon and while rummaging around in the dark corners I found a loading box that has been hidden for years. found 4000 gas checks-- each for 30 cal and 8mm. plus 4000 primers. the gas checks had a price of 4.00 a K. Couldn't find a price on the primers, But they were Herter's --If that tells you their age. I'll have to test some of the primers to make sure that they are good, though they were in an USA ammo can all that time with the gas checks. Life is good :)

[MtGun44]

Unless your shed is in the Arizona desert somewhere and has been baking for 40 yrs at
135F, you are probably going to have perfect results with the primers, esp in an ammo
can. Wow, you made a time machine - you shipped cheap primers to your future self,
saving large amounts of money and beating the primer shortage. You sure are smart!
;-)

[44mag1]

I have explained this many times. You have lost a drive band by leaving the check off and the length no longer matches the rifling twist. A PB would shoot as good but you have shortened your boolits drive length by leaving off the check.
My 30-30 would do this at 100 yards but leave the check off and every boolit would keyhole at 50.

I knew there was a six cents about you

[Bret4207]

I have often wondered if the gas check not only protects the base against gas cutting, but also adds a good square base with no imperfections to the boolit.

Yes, provided it goes on straight and isn't malformed. A check also has to be large enough to fit the groove to an extent. A too small check is a waste of money.

[Dollar Bill]

Thanks, 44Man and Felix. Good stuff. I appreciate it, gentlemen.