Known Loads too hot now..why

[Pdvdh]

OMG... If it was posted on *****Sniper's Hide***** - it must be true! That's a Five Star rated Forum.

I'll take some soapy water out with me the next time I shoot. I'll place enough on the exterior of the catridge case to wet it, but not so much as to taint the bore from the case neck forward, or to squeeze the water out in front of the case mouth upon chambering, firing, and cartridge case expansion at the moment of firing.

In fact I can't wait. I'm reloading right now. Same load I shot and chronographed both Saturday and Sunday, last weekend. As soon as I finish I'll walk out in the back yard and touch one off over my dual setup chronographs. I'll obtain two muzzle velocities, one from each chronograph, in order to provide ANY idication of any higher than normal pressures, and will also check bolt lift and case heads for any signs of additional pressure.

I won't waste any more than one fired round on this excercise in knocking the legs out from a bogus explanation for elevated cartridge pressure. I'll wear leather gloves, safety glasses, and snow machine helmet before touching one off. Just in case I'm the one that receives the education in the process...

Like I said. This is too funny... I will report back before the sun sets on Alaska's Kenai Peninsula.

 

[bigngreen]

What Happens When You Fire A Gun?

By M.L. McPherson
©Copyright 2008, The Varmint Hunters Association, Inc.

THE CASE
"As the striker hits the primer, it drives the case forward in the chamber (to the extent that headspace will allow). On some cases with poor headspace control (e.g., 35 Whelen), the striker can drive the case into the chamber with enough force to move the shoulder back and thereby increase headspace.

As the primer pellet explodes, it generates considerable additional force that works to drive the case forward (and will do so, if headspace control is inadequate) and the primer backward (the primer moves until it is supported by the bolt). For cases using small primers, this force is about 750 pounds; for cases using large primers, this force is about 1,500 pounds (cases that have small-diameter flash holes generate greater force).

As the powder charge ignites and chamber pressure begins to build, the hollow portion of the case stretches, to fill the available space. When chamber pressure reaches approximately 3,000 psi, the case walls begin to push against the chamber. Thereafter, as pressure progressively increases, case-to-chamber bonding becomes progressively more solid.

When the force inside the case becomes sufficient, the case body yields and the case head begins to move rearward. The amount of pressure the case can withstand before the case head begins to move rearward depends upon case wall thickness and hardness (in the area near the body-to-web transition), difference between web diameter and primer pocket diameter, and how long pressure stays above the threshold pressure (where case begins to yield).

In most typical loads used in modern guns, chamber pressure will always be sufficient to drive the case head rearward and thereby stretch the case walls. Depending upon case wall thickness and degree of wall thickness taper near the body-to-web transition, the case can elastically stretch some amount — typically several thousandths inch. When this stretching exceeds the elastic limit for that case, the case walls will permanently thin and lengthen. This damage usually occurs about 0.1-inch forward of the floor of the case web.

After chamber pressure becomes sufficient to initiate case wall stretching, the case head soon hits the bolt. As pressure progressively increases, it pushes the case head progressively harder against the bolt. Hence, the bolt will progressively compress and the action will progressively stretch until chamber pressure peaks. (Actually, owing to inertia, the case head will continue to push against the bolt, as the bolt continues to retreat, for some time after chamber pressure has peaked."

Now put some water between the case wall and the chamber and what will happen?

Sounds like a good test, dunk the cartridge in water just a little smudge won't do for the sake of gloating why not rip off 3 shots. I suspect that if the chamber has a tight head space the effects may be smaller than a longer head spacing, again don't know just a thought.
Buffallobob brought it up first, hopefully he will weigh in with more experience with it.

Maybe we should start a Myth Busters thread instead of hijacking this one?

 

[clhman]

Like I said. This is too funny... I will report back before the sun sets on Alaska's Kenai Peninsula.[/QUOTE]

Okay. That leaves you to about 11p tonight. I'll cross my fingers and hope you don't blow up. I think they will be too hot...

 

[clhman]

Wow I didn't know I broached such a controversial subject. I like the mythbusters aspect. We should all try it a different way and report our results.gun)

 

[bigngreen]

Wow I didn't know I broached such a controversial subject. I like the mythbusters aspect. We should all try it a different way and report our results.gun)

You never know what your going to start

Where were the shiny spots, case head or wall in the chamber, I don't think I caught where they were?

I'll have to get out of bed and check this thread tonight

 

[clhman]

Shiny spots were typical ejector marks across the case headstamp. Nothing on the case walls, shoulder or neck...

 

[Pdvdh]

What Happens When You Fire A Gun?

Now put some water between the case wall and the chamber and what will happen?

Sounds like a good test, dunk the cartridge in water just a little smudge won't do for the sake of gloating why not rip off 3 shots. I suspect that if the chamber has a tight head space the effects may be smaller than a longer head spacing, again don't know just a thought.
Buffallobob brought it up first, hopefully he will weigh in with more experience with it.

Maybe we should start a Myth Busters thread instead of hijacking this one?

I don't want to add so much water that the water ends up being squeezed out forward of the case neck, thereby fouling the bore. I absolutely agree that a water-wetted bore downstream of the bullet and case neck will increase case pressures. I absolutely disagree that placing a thiin film of soapy water solution between the cartridge and the chamber walls will increase pressure. The reason I'm going to use a soapy solution is because the soapy water is slippier than non-detergent water, and the soap will break the surface tension of the water and allow for a well-wetted thin film of water over the entire case surface, rather than a bead of water here & there, as appears on a freshly waxed auto finish.

The reason I'll only fire one shot, is based on 4+ years of college engineering education, 30 years of engineering practice, 35 plus years of shooting and reloading experiences, and avid research and education related to reloading, hunting and shooting; I know that the pressure will not be increased, and that case head flow into plunger holes or ejector slots in the bolt face will not be increased by the lubricity of water between the cartridge case and the chamber walls. Call me cocky of you choose. I have no doubts.

Place water or any other liquid in the bore and pressures will increase.

BuffuloBob stated that he was grasping at straws trying to identify a plausible explanation for increased pressures because clhman stated that factory rounds were jamming up in the .22-250 - which would imply a possible common source of elevated pressure for both the reloads and the factory ammo. Like I said, I have no explanation for elevated pressures from the factory loaded ammo. Any bore fouling or blockage should have been removed with the first shot fired in that .22-250. If the following shots were also sticking, I'd pull the bullets and conclude the factory loaded ammo either wasn't factory loaded ammo, or that the factory loaded ammo was defective for some unidentifiable reason.

BuffaloBob never said he had high confidence, or any personal experiences to believe, in his hypothosis.

I'm seating bullets now...

 

[Loner]

Didn't see him claim pressures were high, He (Bob) merely stated it would act like
they were high. Bringing in ejector marks,( the description is one of bolt swipe) primer flow or case head flow is erroneous to the argument.

 

[300remum]

Was actually shooting last week end never had a problem
before with this load. (94 gr retumbo behind a 200 accubond)
even tried 95gr. Without any pressure sign.
But last week end fired 5 shots, 3 had ejector marks and hard bolt lift
didn't understand why. Guess what? it was the first time
i shot these in the rain and i didn't bother wiping the shells.

 

[bigngreen]

Some think that the chamber pressure will rise due to water taking up area I don't think that is what I have seen. What I have seen is the same chamber pressure but the case is reacting to that pressure differently and I wouldn't think that would show up in bullet velocity. Pressure I don't think increases in the chamber but the pressure is only taken by the surface area of the bolt face with no help from the case wall. Sorry if my point is confusing just not as good with the put together of the word!

I would agree with anything being in the bore will cause pressure, been there.

If loads were developed with a dry chamber and you change the state of the chamber surface there will be a change in the relationship between the case wall and the chamber, won't there, won't that allow the brass to move back at a more accellerated rate due to lack of resistance of the case wall?

One may need a strain gauge that would measure the force applied to the bolt face and chamber.

I make a living fixing what engineers screwwed up!

 

[Pdvdh]

Re: Great Horny Toads! Foot in Mouth!

Good thing I only shot once!

Just mess'in with ya. My next Post will include the real result. I must have a weather, water, and soap proof rifle...

 

[Buffalobob]

Thank you 300Remum!!

The first time I ever experienced excessive bolt thrust was 30 years ago with a really hot loaded 7mmWby. Ejection was really difficult so I pondered the situation and decided that putting case lube on the case before firing it would cause it to come out really smoothly. 100% exactly wrong!!! Had to put a cleaning rod down the muzzle and use a hammer to pound on it to help get the case out.

Last summer my daughter and I were shooting a F-class match and it began to rain and we were doing alright until the drying towel go so wet we could not longer dry the cases and they were damp and the bolt lift got bad but we continued and the towel got wetter then the cases were wet with drops on them and then the bolt stuck. We DNFed right there. Went home and took the rifle apart and dried everything. Everything was good to go for the next match.

Shooting one round over a chronograph proves nothing about water in the chamber. In F-class your chamber is going to be hot because of your rate of fire and it will evaporate a certain amount before trouble starts showing up. If your chamber is cold then it will take lesser amounts. Some of it will depend on how rough or smooth your chamber is to begin with.

Both times I have had issue was in custom chambers. I have never noticed it in factory chambers but then I don't hunt much with factory chambers. I

Water in the chamber is different than water in the barrel. I have stuck a 22 rifle barrel 3-4 inches deep in the water and shot fish many times. I don't recommend it but I have done it.

 

[clhman]

HAHA phorwath, you had me. I look forward to your real results. I'm going to try and shoot tomorrow. I'll post mine then.

 

[Pdvdh]

Explanation of the prior photos: Identical load as fired today except 0.5 grain heavier powder charge of H1000. The incipient case head separation was visible on the casing before I fired it in the back yard over the chronographs last weekend. To make matters worse, I had run the casing into my body sizing die with the wrong shellholder in the RCBS press, which headspaced the casing around 0.008" shorter than normal. Meaning I had excessive headspace on a casing that was already showing the separation ring of an impending case head separation. I debated whether or not to pull the bullet and toss the casing, but decided to take a chance and the photo is what I got for a result. Enough mess'in around.

I did fire one soapy water lathered up cartridge across the chronographs, as set up in back yard. Chronographs were used to catch higher or lower velocity - an indication of higher or lower cartridge pressure. Here's a photo of the chronograph arrangement with the soapy water in the spray bottle balanced on the skyscreen rail.

This casing was slicker than snot on the outside. Almost dropped it on the ground. Velocity across the Oehler 33 was 2936 fps. Velocity across the PACT Pro was 2958 fps. This 2936 fps velocity is in comparison to the 4-shot string average velocity chronographed across the Oehler 33 last weekend of 2941 fps. Last weekend my PACT Pro was hit or miss and didn't give enough data to provide a 4-shot average comparison to today's velocity. But today's velocity data were good to go. The difference in velocities between the two chronographs run right about 20 fps when they're both hitting on all 8 cylinders - the Oehler ~20 fps slower than the PACT. So there was no evidence of any additional pressure based on the muzzle velocity obtained with this soapy-water lathered cartridge.

In all honesty, there was a slight plunger hole indentation, and slightly increased resistance to bolt lift. So I'll eat some crow... I understand bigngreen's last post completely, about less friction between exterior of casing and chamber wall. And yes, anything that decreases the coefficient of friction between the case walls and chamber would be expected to result in a some increase in bolt thrust. If one had a tool/device both sensitive and accurate enough to measure subtle changes in bolt thrust (lbs force), that would be easy to demonstrate. I remain doubtful that the presence of water, restricted solely to the chamber/cartridge interface, will result in significantly increased case head setbacks into the bolt face with equally pressured cartridges. Otherwise cartridge manufacturers would place a warning on their factory ammo, "Shoot only DRY cartridges in rifles". Or, "Do not hunt and shoot in the rain." No?? If the placement of a film of water on the brass exterior jams a bolt closed, in all likelihood the loads are over book maximums - that would be my best guesstimate. And I'm guilty on that count. I'd say 75% or more of my hunting loads are over-charged with powder, relative to the maximum loads listed within reloading manuals.

Sorry about the mess'in with ya photos. Couldn't resist. BTW, that's the first time I've experienced partial case head separation. I knew I was pushing it. I decided to take a chance during maximum load workup with the Hornady 162 Amax bullets in the back yard last weekend. As I stated, the bright ring of incipient case head separation was visible about 1/3 of the way around that case before I touched (torched) it off. I did wear shooting glasses prior to letting fly with this casing. The big problem was that I had set the shoulder back too far on this .280 RCBS Imp, through use of the wrong shellholder. Also, in a stroke of bad luck, that powder charge was the greatest one I fired, and the first one to show plunger hole indentation on the case head of these Lapua brass cases. Other than less than stellar judgement and a little bad luck - in that this casing happened to be the one that pushed pressures over Max - the casing would have made it through one more firing. I don't think the partial case head separation would have happened, overload and all, other than the casing headspace was set back too far. The case was ready to let go and the extra 0.008" stretch was all that was necessary.

I didn't include a photo of the case head from the soap lathered casing because the plunger hole indentation wasn't very impressive.