Gas Checks

[metweezer]

What criteria determines the necessity of a gas check? Is it caliber, velocity, amount of charge, pressure, etc. Currently, I am only getting ready to cast for 9mm but if/when I get into larger handguns I would like to know when a GC would be required. Thanks,
Steve

[462]

I've loaded the .357 Magnum Blackhawk to 1400+ fps without a gas check. Others have gone faster.

[TXGunNut]

Checks/lubes/alloys/twist rates. Seems to be a balancing act. Some loads need them, some don't. So far I've pushed boolits moderately hard and haven't needed them but haven't ventured past about 1800 fps in a .45-70 so far.
Future projects are 30-30 and 35 Remington so have been reading the GC threads around here. Fascinating!

[shotman]

most would depend on the alloy. Lyman used 1000fps years ago but that was up to what they tested. Some here say they shoot no check the was made for checks. I didnt fined they worked for me

[MtGun44]

I have shot 8 BHN at 1400+ in .357 mag with no issues, without GC. Up to 1350 or so with
.44 mag, no GC. Hardness doesn't seem to be much of an issue, even though the conventional
wisdom (outside of this site) is that "hard cast" (VERY undefined) is required for those kind
of applications. This is not a requirement.

Try it in your gun is the only way to know. The good designs pretty much work for the
magnum pistols for me without checks all the way up. For .357 Lyman 358477, 358429
are excellent, RCBS 38-150-SWC (used to be called 38-150-K) is excellent as is Lee
358 158RF. For .44 Mag, Lym 429421, RCBS 44-250-K, H&G 503 are all excellent versions
of the Keith boolit. LBT makes some good ones, too.

Fit is THE MOST IMPORTANT ISSUE, far beyond alloy, hardness or many other things. Use
throat diameter or +.001 to start, stick with what works best in your gun(s). IMO, GCs are
never necessary in pistols, but some will disagree with me. I hate to fiddle with them and
have been able to develop many great loads without using GCs. Do GCs work? Of course,
but are they necessary? Not in my experience with many pistols. I use GCs in most rifle
loads.

Bill

[onondaga]

I use a simple guideline, but you have to do some studying and math.

Learn the Lee method of selecting an alloy based on PSI of the load for rifles. If Lyman #2 alloy in a plain based boolit will not measure up to to the load , I use a gas checked boolit from Lyman #2 up to about 45,000 PSI. Higher than 45,000 PSI then I use straight linotype gas checked boolits. Those hard boolits from Lino do not expand at all.

#2 alloy boolits expand very well on game, especially flat nose boolits will get to double diameter as far in yards as there is 1000 foot pounds of energy in the boolit. They will mushroom that well and retain 100% weight, gas check or not.

Plain based boolits take extra gentle care to not damage the bases before or during loading also. Any little nick on the base edge can cause a pretty wild flier. Some loaders use gas checks just for that reason alone!

Gary

[geargnasher]

Like has been said, it all depends on your unique gun, alloy, boolit fit, pressure curve, peak pressure, velocity, rifling twist and style, and a million other things. Only way to find out is to push it with a certain alloy and when accuracy goes to pot and leading starts, you've exceeded the limit without a check.

I used paper gas checks made from manilla file folders in my .30-30 once and found that, while I was able to extend the useful non-leading range of my plain-based boolit by at least 300 fps (might be more, I never found the leading limit), the paper checks did not up the accurate velocity limit one iota. Still about 1400-1500 fps with the .30-30 and 14 BHN boolits depending on the powder used. All they did was stop the leading that came about at anything over 1500 fps with either the plain-based or unchecked gas-check version of that boolit (mould was cut for both PB and GC boolits).

So, the question might be one of accuracy limit or lead fouling limit, one may come before the other, but sooner or later when you keep upping the ante you will need a gas check, compacting filler, paper jacket, copper bullet, or something. In a 9mm checks would sometimes be nice to prevent leading at higher loadings, but not necessary if you get things right with pressure curve and alloy.

Gear

[Reg]

Also, the lube you use is also a factor.

[JIMinPHX]

Learn the Lee method of selecting an alloy based on PSI of the load for rifles.

Gary, would you mind expanding on that a little? I'm not sure what the Lee method is.

I've been told that a rule of thumb for a plain base boolit is PSI/1440=BNH. Is that it? Or is it something else?

[HARRYMPOPE]

"I've been told that a rule of thumb for a plain base boolit is PSI/1440=BNH"

I shoot quite bit of plainbase in my 30-06 and 7.62 x 54 with alloys from 10-22 BHN and can find no clear correlation to accuracy and hardness.Sometimes certain designs shoot better soft other times its the other way round.many times i often think its an issue of the alloy changing in the bullets size a bit rather than the alloy its self.I dont try to go much over 1250-1350 fps because even with hard PB bullets that's when i get an accuracy loss.

back on the subject-

I agree with mtgun44's take on GC's and pistols.

George

[geargnasher]

Jim, the Lee method is to use boolit strength as a guideline for determining how much PRESSURE a given alloy can handle and maintain accuracy. Richard Lee explains that, according to his experiences, accuracy increases with pressure up to about 90% of the compressive strength of the alloy, then it can go the other way or leading can start. So if you have a 15 bhn boolit you can expect it to be most accurate around 19,000 PSI give or take.

While Lee's guidelines are very one-dimensional, I've found it to be quite useful and accurate using conventional loading methods and lubes, although a few "advanced" loading techniques and tweaks can often make his theory totally irrelevant.

Gear

[JeffinNZ]

Also, the lube you use is also a factor.

Lube is important when you have a less than perfect fitting bullet. If the alloy is right and the fit is perfect then I reckon you could just about us butter as lube.

[DukeInFlorida]

Get yourself a copy of this free book:
http://castboolits.gunloads.com/showthread.php?t=36854

Glenn covers this question perfectly.

The fast answer is that when a bullet is cast with the exact correct alloy for the gun and speed, and sized exactly correct for it, and the exact proper lube is used, you virtually never need a gas check.

However, if any of those three factors is a bit off............ the gas checks makes up for it. It's kind of a fudge-factor adjuster. Gas checks allow you to cast and load without having to be scientific and exact about every detail.

That, in a nutshell, is what Glenn says in the book, and I agree with his assessment.

He goes on to explain, in great details, how it all works. The whys and hows.

The free book is a must have for every casting library. To print it out uses a LOT of paper. Like 187 pages or so. But it's worth every tree!

[PacMan]

So there you have it.No real answer but all the replys were right on.
You did ask about use of GC when you went to larger handguns and my limited experience is that for the most part as the caliber increses the less need there are for gas checks if everything else is right.
Now i have been shot down here on the following but it is still just my thoughts. Buy a good GC mold and start with it.Once you get a load that you like then get a none checked mold and start working with it.
You may very well gave a gun that will shoot a none checked bullet very well at max velocity(without modifications) but the chances are better with a checked bullet.
I'm ready for the flamming as usuall.
Dwight

[Bret4207]

What criteria determines the necessity of a gas check? Is it caliber, velocity, amount of charge, pressure, etc. Currently, I am only getting ready to cast for 9mm but if/when I get into larger handguns I would like to know when a GC would be required. Thanks,
Steve

Your gun and load are the sole criteria involved in whether or not you'll need a GC. Each gun is a rule unto itself. Each load ( boolit design, size, lube, alloy, charge, crimp, seating depth, etc) is different in each gun. Some guns with some loads may need a GC at 1000 fps. Others may not need a GC at near 2K. Powder can make a big difference.

There's also the question of if you mean shooting a GC design w/o a GC as so many try to do. That's a different question with the same answer.

IMO most people choose a design based on what they see in a picture. If it appeals to them they go with it, if it has a GC it may or may not be part of the appeal.

[onondaga]

Your formula is pretty darn close to Lee. Bear in mind that the Lee theory is based on plain based rifle boolits. Gas Checked boolits will greatly extend the Lee predictions. I wholeheartedly suggest reading the Lee 2nd edition. MidwayUSA has it cheap. There is also a formula in the book for predicting pressure drop with each one grain drop in charge that is very useful with the theory application.

The Lee theory is based on the ultimate compressive strength of any particular boolit alloy.Lee postulates the the compressive strength in PSI is directly related to the BHN of boolit alloys. Lee translates a relation to load PSI in his charts, and that the accuracy sweet spot is slightly below the permanent deformation point in the strength of boolit alloys. It is all very logical and works for me. I have repeatedly proven his theory laddering up loads and watching group size change as he predicts.

I will warn you that you have to be a really good shot to see this happen on paper and that people who don't shoot excellently to begin with will be dismayed or think the theory is baloney. If you can't work up one hole groups at 50 yards with a good rifle and load laddering anyway the theory will be pretty much useless to you for selecting boolit alloys and predicting accuracy sweetspot.

It is a hoot for a marksman to see this happen as predicted by Lee....but you gotta walk the walk!

Another warning! After doing this a couple hundred times you likely will get arrogant or even unable to constructively comment on some of the loads, alloys and group sizes that you see published.. and commented about. You will unconsciously have developed a "Liar" gauge or meter and either keep your mouth shut or go off ranting and such, in an unhealthy and unfriendly manner..

There are people that jitter around on the bench wildly and shoot so much that sooner or later they get a good group no matter what load they are shooting.



Gary

[geargnasher]

Amen on the "must be able to shoot in the first place", Gary. Excellent synopsis, too. Did you ever do technical writing of some sort?

I've tested the Lee theory over and over myself, and I find the accuracy sweet spot sometimes ignores gas checks, being right where Lee says to look for it based on alloy alone. It ain't the whole story, but if you want a reliable, repeatable, quick-and-dirty load workup that works while doing nothing special to the brass or boolits when loading (other than basic FIT of course), then this method works very well and is a good foundation upon which to build advanced loading techniques.

Gear

[onondaga]

Yes, I am retired tech writer.

That gas check thing you mention... I ran into that with 30 caliber gas checks in a 31 caliber rifle..That is why I can only get .550X.645" groups from that Spartan 7.62X39 rifle. If the gas checks are smaller than the boolit it gets the targets confused.

Gary

[williamwaco]

I have shot 8 BHN at 1400+ in .357 mag with no issues, without GC. Up to 1350 or so with .44 mag, no GC. Hardness doesn't seem to be much of an issue, even though the conventional wisdom (outside of this site) is that "hard cast" (VERY undefined) is required for those kind of applications. This is not a requirement.
Bill



I use BNH 12-15 for plinking loads because it is easy to mix. For hunting loads, I use BNH 8-9 because it is soft and performs well.

Elmer Keith developed the .44 Magnum with an alloy that measures about BNH 10. He recommended 16/1 lead tin. ( He also liked 20/1)

When do I use a gas check? Never.

My personal experience covers handguns from .30 to .45 at velocities from 600 to 1600 fps.

Your question relates to handguns. The answer in my opinion to your question is NEVER. You never need a gas check with ( normal ) handgun loads. EXCEPT. If you have a gas check mold, failure to use a gas check will slightly degrade your accuracy with practice loads and more so with hot loads ( > 1200fps )

Leading: If you are getting leading with loads in this range, It is not caused by lack of a gas check. Most leading is caused by fit.

PS: I am not disagreeing with the guys discussing the Lee formula. In fact, I believe they are correct. I just don't think it is appropriate or needed for your 9mm.

[Bret4207]

Gary and Gear, my beef with Lee's formula isn't the formula itself, it's that either Lee or someone else said it was a LIMIT. I think you guys know well that every time someone says there's a limit of some sort in this game, a dozen really knowledgeable, honest guys will drop out of the sky with proof it just ain't so! I don't know who started the limit idea, but like the "harder is better" rumor it's done some damage.

[JIMinPHX]

"I've been told that a rule of thumb for a plain base boolit is PSI/1440=BNH"

I shoot quite bit of plainbase in my 30-06 and 7.62 x 54 with alloys from 10-22 BHN and can find no clear correlation to accuracy and hardness.Sometimes certain designs shoot better soft other times its the other way round.

That formula thing that I spouted out is just a rule of thumb. I too have noticed that the shape of the boolit makes a big difference too. The ratio of bearing surface to diameter seems to be the biggest factor. Boolits with lots of bearing surface can usually be run a fair amount softer & still give good results. The old style Bator, from molds that were made with the worn out cherry, is a good example of this.

Gary,
Thanks for clearing things up for me. That about covers what I was asking about.

[JeffinNZ]

I used to think the PSI/1440=BHN forumla was gospel until the day I did the numbers on rimfire ammo. You try it. Doesn't stack.

[44man]

I don't believe the limit stuff either having shot all kinds of alloys and all molds I make now are PB because of the cost of GC's mostly.
I base the need for a gas check on boolit hardness and accuracy results. As boolits get softer for my revolvers I start to see fliers at 50 yards and once too soft groups just get larger yet are still fine for hunting. Using a GC as I soften brings back a lot of accuracy and reduces fliers.
Leading has not been a problem except when I tried to shoot pure lead or soft boolits with a poor lube. Get too soft and a GC does not even help.
Your limit is where the boolit no longer holds the rifling in your gun or the boolit slumps beyond reason.
The next limit will be brass sizing the boolit or a crimp that can't fully open and also sizes the boolit as it scrapes through it.
I quit tweaking alloys for each gun and just use water dropped WW's. Mostly because I am lazy and they shoot better then I can shoot. :bigsmyl2:

[geargnasher]

I used to think the PSI/1440=BHN forumla was gospel until the day I did the numbers on rimfire ammo. You try it. Doesn't stack.

....and that brings up a point I was going to make earlier about the Lee formula not being "gospel": Expansion ratio makes a HUGE difference to the formula, as does barrel caliber. Straightwalled cases like the .22 Rimfire (I didn't think of that one, but good point!) and the big-bores like .45-70 have very low launch pressures because there is no bottleneck, and they also prefer faster powders than bottleneck cartridges. The pressure on the boolit base is much less if the pressure is dropping fast behind the boolit in a straight cylindrical system, but in a bottleneck the peak pressure often occurs when the boolit is an inch or two into the barrel and going half it's muzzle velocity. Pressures are much greater, and if alloy strength is exceeded by the pressure in these loadings it takes more work to keep the boolit from deforming in a negative way.

Gear