Pressure Increase with Gas-checks???

[BruceB]

In Brian Pearce's Q&A column in the latest "Handloader", he states:

"A gas check will bump pressures from 5,000 to 11,000 psi (in the .44 Magnum) when compared to a plain-base design."

This statement most certainly doesn't agree with my observations with the .44 Magnum cartridge in revolvers.

For several decades, I used the Lyman 429244 SWC, a gas-checked design, mostly WITHOUT the gascheck. These were not puffball loads, running the bullet at close to 1500 fps from my 7.5" Super Blackhawks. On the occasions when I did choose to use the gaschecks, there was no perceptible difference in the performance over the chronograph. All rounds fell within the expected velocity range for the same load without checks.

Even if the rise was "only" 5,000 psi as Brian stated, I would surely expect to see SOME difference. At an 11,000 psi rise, which is probably about a 25% increase (or more!) , there most definitely would be some signs. I would not expect my guns to exhibit the same behavior at all. They might not even allow extraction at such levels.

Comments?

[Bret4207]

I don't know Uncle Bruce. I think Brian is about the best of the new breed writers, but perhaps he's quoting an industry source or standard based on safety? My experience mirrors yours, a GC has never made a difference in any thing but accuracy and leading.

[felix]

Bruce, I have noticed an increase of pressure using a 250 LBT with check versus the latest RCBS Keith, the one with the largest crimp groove. There is a whole grain difference using the WC820 I have, 18.5 versus 19.5 for the same velocity. Accuracy the same (within reason), velocity the same (by trajectory) at a hunnert or so. Using the Ruger lever gun, having 18.5 inch barrel. It's more of a boolit profile difference, in my opinion. Both of these boolits appear (not measured) to be same length within the powder space after being seated properly for the gun. The LBT does have more bearing without doubt. ... felix

[wiljen]

So if I fire the same bullet with and without check over the same charge and lot of powder out of the same barrel, I should get a statistically higher velocity out of the checked bullet. All other things being equal, more pressure should equate directly to more velocity. I know the checked bullet will weigh slightly more which negates part of the advantage, but I think (especially in larger calibers with heavier bullets) that the extra weight would not offset 11,000 PSI more pressure.

[felix]

Correct, Will. ... felix

[Larry Gibson]

Hmmmmmm.....another test for the Oehler M43. Have the M43, now if I only had the time.........

Larry Gibson

[Naphtali]

Why the pressure increase? The only explanation that occurs to me is that the gas check increases diameter of bullet's base. Superior obturation yields higher pressures. But were this the reason for higher CUP, a GS mold could be made to account for thickness of GS's. And doesn't the CUP increase assume bullets are not undersize?

[felix]

I am trying to understand your question, and can't enough to answer. ... felix

[Naphtali]

I am trying to understand your question, and can't enough to answer. ... felixWhy the pressure increase when using gas checks?

[felix]

Depends on the fit factors, and the pressure curve presented by the load. May not happen at all in your gun/ammo combo. Can also happen in reverse when the boolit is too soft for the load. ... felix

[Bass Ackward]

I have seen more pressure from a check.
I have seen less pressure from a check.
The most common is no difference from a check.

I imagine that's how they came up with the hardness chart.

[Bret4207]

Why the pressure increase? The only explanation that occurs to me is that the gas check increases diameter of bullet's base. Superior obturation yields higher pressures. But were this the reason for higher CUP, a GS mold could be made to account for thickness of GS's. And doesn't the CUP increase assume bullets are not undersize?

The base shouldn't be any bigger after sizing and obturation won't occur the same in every load in a cylinder, much less between guns. Obturation can be a good thing or a bad thing, so the "superior" idea is lost on me. "GS"? Lost me there too.

It's like Felix said, each gun is a law unto itself. Some may show and increase, some not. 5-11K PSI though? Maybe on test equipment, but I'd like to see the source material to understand it better.

[rhead]

If the shape of the pressure curve was also changing there could be a change in the pressure without a corrosponding change in velocity, which is all we can measure in an instrumental manner. Any pressure diffeence that we can see would have to be great enough to flatten primers or stick cases.

[Naphtali]

Sorry, guys. I didn't notice my typographical error. I meant "GC" for gas check but typed "GS."

[454PB]

Maybe it's measurable with pressure test equipment, but I've never seen any "field" indications that the increase is anywhere near that much.

[runfiverun]

how does a boolit with a lighter material [copper] in the oal.
produce a heavier boolit???
i really don't think that a 245 gr boolit will increase pressure that much over a 240 gr boolit.
i think maybe there was some apples and oranges here..

[jack19512]

I loaded up 24 rounds for my Ruger Blackhawk 44 mag. These were all 240 gr. SWC cast using straight wheel weights. Out of the 24 rounds 12 were loaded with Unique and 12 were loaded with 296. Out of the two 12 round loads each were using gas checks on 6 of the rounds and the other 6 rounds without the gas checks.

According to my chronograph the loads using the Unique showed an increase of 20 fps using the gas checks and the loads using the 296 showed identical velocity between the gas check bullets and without. This was by no means anything concrete or scientific.

[Lloyd Smale]

if it does its minute. A gas check will also tend to clean a leaded barrel and if your plain base bullets are leading thats going to increase your pressure. So i guess a gas checked bullet can also reduce pressure. Could be that brain was shooting plain based bullets first in his test and had a slightly leaded gun that bumped the pressure when he shot the first of his gaschecked bullets. Something like this is hard to judge as its impossible to find two bullets to compare. take a plain based bullet and make a gas checked version and its a totaly differnt bullet. It might take more pressure to get velocity and it might take less. Another thing. Did he state both bullets were made out of the same alloy and have the same bhn as that can effect pressure too. Hell if he did one in the morning and one in the afternoon the difference in tempurature could have done it. Lastly brian pearce isnt the man to look up to that some think he is. Illl leave that one at that.

[Bret4207]

I loaded up 24 rounds for my Ruger Blackhawk 44 mag. These were all 240 gr. SWC cast using straight wheel weights. Out of the 24 rounds 12 were loaded with Unique and 12 were loaded with 296. Out of the two 12 round loads each were using gas checks on 6 of the rounds and the other 6 rounds without the gas checks.

According to my chronograph the loads using the Unique showed an increase of 20 fps using the gas checks and the loads using the 296 showed identical velocity between the gas check bullets and without. This was by no means anything concrete or scientific.

Well, thats a start. Thanks Jack. I'm sure Ken Walters (KLW) could give us the methods used to really test something like this if anyone wanted to do a real test. His past articles in Handloader were heavy on statistical things like this. It would have to be the same gun, brass, powder, primers, etc in the test. Then you'd have to switch powders, etc. and start compiling the differences.

[HeavyMetal]

I have a theory!

If you get out a bunch of reloading manual's and start comparing cast boolit information, particularly the manuals that list pressure, I think you'll see variationswhen comparing different designs between plain base and gas check boolits.

We have all noticed the reloading manuals showing "lighter" loads over the years. They have also been a little behind the times on cast boolits as well, no doubt a liabilty concern.

In the referenced Brian Pearce Q&A question I think Mr. Pearce was comparing this published load data. I do not think he was saying a Lyman 429244 cast boolit with no gas check, using the same load, would produce an additional 5,000 to 11,000 psi with a gas check on the base.

I agree with each gun is a rule unto itself, it's why we "work up " loads.

I also think some one will write in to Handloader Magizine and we'll probablely see a second explanation printed in the future.

[dwtim]

I know that GC bullets produce a big flash--much like condom bullets--with certain propellants. I get nothing noticeable in daylight with a big charge of AA9 and a PB boolit in my 357 Mag, for example; with a 358156GC, I get a flash. Could that be an indication of a more efficient burn?

As far as size is concerned, I get a "spring-back" with gas checks. The day my last batch of 156s came out of the sizer, they were a measured .358". As of today, three months later, the base bands are about .359", and the gas checks measure .360". I checked the zero on my calipers twice, cleaned the jaws twice and remeasured twice: it's three-sixty. This is with a high tin content alloy that also contains arsenic.

[wiljen]

how does a boolit with a lighter material [copper] in the oal.
produce a heavier boolit???
i really don't think that a 245 gr boolit will increase pressure that much over a 240 gr boolit.
i think maybe there was some apples and oranges here..

I was alluding to use of the same bullet with and without check, not the same design with and without gascheck. If you weigh a boolit before and after installing the GC it does in fact weigh more after.

[felix]

Yes, more efficient burn. ... felix

[Bret4207]

I have a theory!

If you get out a bunch of reloading manual's and start comparing cast boolit information, particularly the manuals that list pressure, I think you'll see variationswhen comparing different designs between plain base and gas check boolits.

We have all noticed the reloading manuals showing "lighter" loads over the years. They have also been a little behind the times on cast boolits as well, no doubt a liabilty concern.

In the referenced Brian Pearce Q&A question I think Mr. Pearce was comparing this published load data. I do not think he was saying a Lyman 429244 cast boolit with no gas check, using the same load, would produce an additional 5,000 to 11,000 psi with a gas check on the base.

I agree with each gun is a rule unto itself, it's why we "work up " loads.

I also think some one will write in to Handloader Magizine and we'll probablely see a second explanation printed in the future.

If you start comparing info in manuals you'll never get anywhere. Some use pressure test barrels, some use rifles, some use a universal recv'r and test barrel. If you want to compare apples to apples you need to start with a standard test platform.

[HeavyMetal]

Bret 4207:
+1 on getting a standard test system! It would make manuals a much more "level' playing field for both newbie's and old hands alike.

Reloading mauals are a reference material and, because everyone has thier own idea of the "right" way to do things, can not be taken as gospel!

To many proffesional writers have, in the past, used this provided information as a source and sworn by it.

I need to get a current copy of handloader and read this article for myself before posting any addtional comments, however I do believe Pearce's answer could have been taken out of context.

[HeavyMetal]

O.K.!

I found my current copy of Handloader and looked up Pearce's Q&A section.

The questioin is asked on page 88 and is actually a request for load information for 325 grain Beartooth boolits in a 44 magnum.

In his response Pearce points out he is unfamilar with the Beartooth boolit line and at that time quotes the 5,000 to 11,000 psi difference a gas check will make when compared to a plain base boolit. He states this as an absolute which it is not.

He also explains that boolit seating depth can increase pressures as well. At least he got that part right!

I'll stand by my original post / thought on this matter: He's been reading to many re loading manuals!

However before we take Mr. Pearce to task to severly for his "information" let us remember that this information is printed in a widely distributed magazine and once information is in print it can ( and will ) be interperated in a lot of different ways by a lot of reloaders!

In his position I would have offered the same precationary statement just to keep a newbie out if serious trouble!

As a reloader gains more tools, toys and experience he can determine for himself what does and does not happen with gas checks: but only with load he makes and shoots in his own guns!

Because as we all know each gun is a law unto itself.

[MakeMineA10mm]

Elmer Keith writes:


June, 1973 Gun Notes column from Guns & Ammo magazine:
"Gas checks will keep bores clean but also raise pressures about 3000 psi in heavy loads, and induce gas cutting of the topstrap and cylinder junction. Gas checks are usually too hard to upset to fill the cylinder throats and permit cas to blow the lubricant out of the bullet grease grooves. I can see no useful purpose for gas checks in revolvers, though they are excellent in auto pistols and rifles, to prevent fusion of the bullet base as well as scraping the bore clean with each shot."


July, 1975 Gun Notes column from Guns & Ammo magazine:
"For the enlightenment of the readers, I had White's Laboratory run extensive ten-shot tests for both pressures and velocities with various loads in the 44 Magnum. During those tests my load of 22grs of 2400 with Keith hard-cast 250-grain bullets averaged around 1400fps and just 34,000psi. Also, extreme variation was less than 3000psi. Compare this with any factory 44 Magnum load and you will find it is a much lower-pressure load. We had one lot of factory 240gr JSP ammunition that on White's lab tests varied 11,600psi in just ten shots with some of the rounds going up to nearly 49,000psi."

Now, considering the day and age that Elmer was writing in, and considering he was a relatively non-wealthy cow-poke and big-game guide, I'd bet that he discovered the pressure difference mentioned in 1973 with GC boolits in the H.P.White's Lab testing that he referred to in 1975. I'd also guess the testing took place in the 60's some time.

Brian Pearce, I'm confident, is not dumbing down his writing too much for newbies since Handloader isn't exactly a popular magazine for those folks... Also, his specific reference to pressure changes through the addition of Gas Checks would also indicate he isn't "guestimating." (Though I'm also not discounting some statements here about just the difference in boolit design between the PB and GC boolits in question. Of course, if we're talking the EXACT same design, but one with a GC base and the other plain, then there may be an interesting comparison test...)

Lastly, I'd be careful drawing too many conclusions from non-lab type testing. There are lots of variables unaccounted for, and pressure signs and velocity are not exactly conclusive proof. For example, when I was much younger and dumber, my buddy and I had our "regular load" for the 44 Magnum with the Lyman 429244GC SWC. It was taken out of an OLD Lyman manual (when the 44 Magnum's performance was increased by upping it's pressure limit), and consisted of a charge of 2400 that was well over Elmer's old load. That load was fired a few thousand times out of both a 70's vintage nickel 29 and my 80s vintage 629. Both guns were pre-endurance package. If we braved very hot weather during the Summer (95F+) to go shooting, the cases would often stick in the chambers, but in cooler weather, they'd fall right out... Both guns are still shooting today with no ill effects other than a very mild case of cylinder end-shake. (Not bad enough to warrant fixing yet, and that's with a few thousand more rounds down-range, albeit with lighter loads...) YMMV...

[GLynn41]

In one article I have by ross Seyfried -states that gc did not raise the pressure -HPWhite did the testing for him-- regardless I still use them - at least partially because my cast are also used in a 41/445 TC -- and it is mighty fast if you want it to be--- took a whitetail last year with an .41 xtp at 2275-- it is my sons gun and he is not a purist--

[Whitespider]

I’m not so sure Pearce was stating a fact, but more of a theory. Thinking about it, there’s no possible way to prove (or disprove) a GC, in and of itself, will raise pressure. At least there’s no possible way for most of us, with limited equipment and resources, to accurately test this.

First of all, the pressure/velocity relationship is relative. In other words, an increase in pressure results in an increase in velocity only when everything else remains equal (exactly the same). If the velocity of a GC design boolit is measured with and without the GC in place, the “everything else” has not remained equal, because you’ve added the GC. By adding the GC the bearing surface and weight has changed. And if you use two boolits identical in design, except one is designed for a GC, the bearing surface remains equal in length but not in composition (friction). Possibly this last example is what Pearce was talking about, pressure could be measured with special equipment, but a velocity comparison would be meaningless.

[klw]

Well, thats a start. Thanks Jack. I'm sure Ken Walters (KLW) could give us the methods used to really test something like this if anyone wanted to do a real test. His past articles in Handloader were heavy on statistical things like this. It would have to be the same gun, brass, powder, primers, etc in the test. Then you'd have to switch powders, etc. and start compiling the differences.

Sorry. Never used gas checks.

It wouldn't, however, be to hard to see the effects. Just do a controlled study using everything exactly the same EXCEPT that half the bullets had gas checks and half didn't. You'd need to do the two studies at the same time and probably over several months. BUT if you plotted the results on an excel spreadsheet you could see if the gas check had any effect on accuracy. Kind of labor intensive but it would work. I'm sure about that as this is the way I look at changes in handgun loadings.

[Swagerman]

Say, how can you equate the pressure by merely using a chronograph, don't you need a fancy test barrel like the ammo company's have that measure CUP?

Get your hands on one of those and tell me what you get with plain base cast bullets and the gas checked ones.

Jim

[BABore]

If shooting the same gas check capable boolit, with and without the GC, it would stand to reason that when not using the GC that you are reducing the boolits bearing surface length by at least 0.050". The copper GC would also have a higher coefficient of friction over lead. If no obturation of the GC shank occurs, I could see a reduction in pressure based on this. Velocity may stay nearly the same too even though it should drop with the pressure. I would think this would be due to the slightly lower friction, bearing length, and weight. Only way to compare things apples to apples would be two boolits of identical weight and bearing length. One with a GC, and one without.

Bottom line, who gives a hoot. I always work up for the boolit at hand. Change something, do it over. Just can't see working up a max load for a bollit and intentionially leave the GC off for grins, then putting the GC's on for the next time out. Usually works the other way around.

[Boerrancher]

I have my own theory with this Q&A article of Mr Pearce's. I think it, like most of the articles in these gun and hunting magazines today, was written from a bar stool on a notebook PC. I could be wrong, but that is my opinion.


Best Wishes from the Boer Ranch,

Joe

[floodgate]

Swagerman:

One of the "chronographs" (was it the now-discontinued Oehler Model 35???) also has piezo-transducer pressure-measuring capability.

Fg

[Bret4207]

Swagerman:

One of the "chronographs" (was it the now-discontinued Oehler Model 35???) also has piezo-transducer pressure-measuring capability.

Fg

I think you got it Doug. Boy I wanted one of those!