Case Over pressure Due to neck sizing only.

[Breeny02]

Hi there,

I'm new to the forum however not new to shooting.

I have been reloading for around 12 mounts now, and have came across some problems I'm hoping some Experienced loaders have answers to.

My load is for the .243 WIN and is as follows; Nosler Custom case; CCI BR2 primer; 41.3 grains of AR22009; Berger 95 grain VLD target. COAL 2.744" 0.060" off lands.

I have worked up and been using this load for for some time now, however on my last two shoots, showed signs of over pressure, Velocity and POI changes. I have fired these cases six or maybe seven times.

I have only ever neck sized the cases, and noticed that they all are starting to get harder to chamber and some to extract, I have double, if not triple checked all other measurements, being; COAL; Powder charge; case length ect.

My question is, can neck sizing only cause pressure problems and how if so?

My solution will be to just full length size all my cases after every four or five shots, am I on the right track??

Cheers Breeny.

 

[eric32]

After so many firing on a piece of brass the body will start to "swell" thus a FL sizing when the case start to get harder to chamber will put you back to SAAMI specs.

But here is some food for thought since you case are expanding with every firing. Why not just FL size ever time in order to keep the same consistency in all your brass thus creating a more consistent load all around. Since each case will expand at its given rate, each case will differ from the next in a given box.

 

[Breeny02]

Thanks Eric,

I thought that might be the problem.

The reason I have been neck sizing only, is that it's
Been my perception that the fire formed cases
have showed better accuracy than when new.

I also Belive you get better case life from neck sizing,
Due to Not working/ stretching all the brass??

 

[daniel brothers]

Breeny... I always thought the same as you.... now I'm confused.

 

[dkhunt14]

That's probably since formed they fit the chamber better. Bumping the shoulder 2 thousandths with a full length won't hurt. Most competitive shooters full length size. I need the cases to go in the gun and come out easy. if not it upsets the gun in the bags. I have never seen a full length sized case be less accurate. Matt

 

[eric32]

Thanks Eric,

I thought that might be the problem.

The reason I have been neck sizing only, is that it's
Been my perception that the fire formed cases
have showed better accuracy than when new.

I also Belive you get better case life from neck sizing,
Due to Not working/ stretching all the brass??

Case life will be affected by too much of a shoulder bump when FL sizing. To remedy this adjust your dies to bump shoulders .001 or .002. As far as over working the case neck a bushing/Die neck honing can reduced the amount of sizing of the neck to only what is needed.

I tried this experiment a long time ago took 10 cases FL sized and 10 case Neck sized none out preformed the other. The velocity was also within 5 FPS of the avg of the 10 FL cases and 10 Neck sized cases.

 

[artbosco]

F/L size all the time and a lot of the problems associated with neck sizing only [cases expanding until they won't chamber, interior volume expanding erratically so there is no consistency in interior pressure, bullet deformation as pressures changes exert different forces on the base of the bullet, etc., etc.] cease to exist.

Go to a minimum size neck chamber [.003" to .004" total clearance] or better yet an undersized neck chamber [where you have to turn necks] so that the barrel's center line/axis and the bullet's center line/axis line up and things get even better and accuracy greatly improves.

 

[bigedp51]

Qusstion, what happens when copper builds up in the bore?

Will it cause a pressure increase.

What happens when carbon builds up?

Will it increase chamber?

The only way I would think your cases would effect chamber pressure is if the neck is thicker for some reason.

You could have the dreaded cream filled donut with sprinkles on top.

I wouldn't blame the brass until all aspects were covered and eliminated.

 

[dmoran]

Unless one is using mild loads, F/L sizing every time will prevail over Neck-sizing only (but even on mild-loads it has its limitations). As the cases start making more contact, pressures can rise as well as inconsistent pressures (higher ES).
Some will argue the point, and say they get better accuracy by necking only, but in the competition realms that I have been involved in, I've yet to see that hold up.
The key to F/L-sizing is the amount we re-size and the die setup.

My 2-cents
Donovan

 

[jlow]

I doubt that your case will continue to expand and increase case volume such that you will get pressure problems with, especially if your load is relatively hot (I don’t know this and you will have to confirm).

Each time you fire the case will get more work harden but the reason they are getting harder to chamber is likely a combination of a number of things. One the case may get slightly bugger, and your shoulders will likely also get longer (too much headspace). The last one maybe your necks are getting longer to the point that they are bumping up against what is called the “second shoulder” in the chamber which is where the chamber narrows and only the bullet is suppose to be in the area past that. When the case neck gets long enough to bump against the second shoulder, it will force the neck into the bullet like crimp. This will hold the bullet when the round fire and cause increase chamber pressure. This can be yet a third reason for hard chambering.

Most people will tell you that you can just shoulder bump and neck size for bolt fired rounds but there is a limit to how many times you can do this. You should of course always measure the OAL of the case to make sure the above is not happening.

 

[Breeny02]

Jlow, I think your comment on the case neck jamming into the second shoulder is what im experiencing.
I have mesured it best I can, and have also coloured in the neck are of the hard to extract fired case and chamberd it, once its pulled out the texta is missing rubbed off the area arond just behind the neck...

So Morale of the story, I need too just full length size all the time, or every so often, or adjust my die to only size the neck and push the shoulder back????

 

[Goatsnguns]

I know what happens when you assume something…..however, I assume that Breeny is gauging pressure by flattened primers. I don't know how many times the cases have been fired/reloaded, but if it is many times, is it possible that the primer pockets have loosened up allowing the primer to be flattened with the same pressure?

Update: I reread the OP and see that 6 or 7 firings were mentioned….I may be headed for ass-dom!!!

 

[eric32]

Jlow, I think your comment on the case neck jamming into the second shoulder is what im experiencing.
I have mesured it best I can, and have also coloured in the neck are of the hard to extract fired case and chamberd it, once its pulled out the texta is missing rubbed off the area arond just behind the neck...

So Morale of the story, I need too just full length size all the time, or every so often, or adjust my die to only size the neck and push the shoulder back????

Yes and keep your barrel copper free, watch out for a carbon ring, keep your case OAL short, and shoot when life doesn't get in the way.

 

[mikecr]

What you're describing is not a 'pressure problem'. It's lack of proper sizing for the cartridge.
A 243win should & eventually has to be FL sized. Not because competitors FL size, but out of case design.
You can only get away with NS only, indefinitely that is, with greatly improved cartridges, and very close chamber clearances w/resp to new cases, and enough barrel steel around the chamber for load pressure. In other words, it takes a plan to do this.

 

[searcher]

Eric 32 brought up the "carbon ring" and when a load that shot well before starts to show signs of pressure, it is definitely something to look at. Unless you have a borescope to verify (or disprove) the existance of a carbon build-up that is pinching your necks, I'd soak your chamber a good while and really give it a scrubbing. Sometimes, the biggest mysteris can also come from simple oversights - so please don't be offended when I ask are you measuring your case lengths AFTER sizing? Was the outside temperature much warmer than when you had used the load with no problems? No switch in primers or in a new batch of powder?

 

[dkhunt14]

You could have a carbon buildup and the cases getting tighter in the chamber also raises pressure. To those who don't believe it I can give you a good example. If you take a 340 Weatherby and neck it down, neckturn it and fireform with a 15 in the rifling load. It now takes 1/2 grain less powder after forming to equal the velocity when fireforming. Whenever you move brass on firing it takes energy. The more you move it the more energy it takes. So the tighter the brass is the more energy goes into velocity and pressure. It works the same way on my 338 Lapua Improved. My chronograph and drops at 1000 yards prove this. Also I believe if it is full length sized it moves a little more to the chamber when fired and more bounce back to let the case come out the chamber. Matt

 

[mikecr]

I've seen just the opposite, with fully formed cases producing lower velocities per load, due to increased H20 capacities in the cases. This is completely predicted with QL and I've yet to see it wrong.

I can improve a cartridge with software and see how much H20 capacity will change with fireforming before ordering a reamer. Once the gun is built and I test for MyMax velocities/pressures to calibrate QL before/after improvement, there are no surprises.
The load always follows H20 capacities.

Load velocity also follows load density, and lower case capacity presented to a given charge increases load density, and velocities. It is initial confinement that matters most here.
A fully formed case has higher capacity than a new or FL sized case. Either by a little, or a lot, but it IS higher, and higher capacity for a given charge contributes to lower load density and velocities.
This is why it's a waste of resources to develop loads with new brass, instead of formed and sized as you will brass.

But OP's already described lack of sizing for a 243win, which most logically contributes to difficult chambering & extraction. There is no indication of a 'pressure problem'. It's simply a sizing issue.

 

[dkhunt14]

Along with the higher capacity you put in more powder to get more velocity. Look at a dasher. When you keep the powder the same the velocity increases slightly and therefore has more pressure. When you wanted the velocity to stay the same you had to back the 308 Baer off 1/2 grain to stay in your node. The Baer shot great groups fireforming and ran about 2750 with 73.5 grains of 4831SC with a 240 Sierra 15 to 20 in. To stay the same velocity you had to back down to 73. This is in a heavygun at 1000. I won many matches fireforming. So did a lot of other people. My chronograph and the minutes to get on at 1000 told me this. I have done it over a 100 times. That case always shot good while fireforming. This is facts. Matt

 

[Ggmac]

I just skimmed the posts but did anyone mention case trimming . After that many reloads I would think the neck is a little long and may be crimping the bullet .
Maybe he is using diff box/ lot of bullets , primers or powder . Has to be over the 100 per box of bullets and as we all know even if the same manuf and style, weight , the length is diff

 

[mikecr]

Along with the higher capacity you put in more powder to get more velocity. Look at a dasher.

This is the only thing you've said that makes sense.
Yes, when you increase capacity, you have to increase powder or starting pressure to regain velocity.
OK, look at the Dasher; It is fireformed to higher capacity. Subsequent loads at the same fireforming load would be lower in velocity. You have to increase powder beyond that of parent 6br to get more velocity(in fact, to get the same velocity).
Everybody knows this..

OP does not have a pressure problem, or any other problem because his brass is NEW. He's been shooting his brass.