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Mr_Logic

Increase in load pressure

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Right then...

 

Hopefully a quick one but something tells me it'll be a pain! I have a load for the .243 which is 80gr SBT over 44 gr H414, PPU brass, CCI200 primer.

 

It was fine in my Winchester, and the last few of that batch were OK in my new Howa.

 

I made a new batch, same load, and now I get flat primers and I even had to hammer out a case from the breech.

 

Everything was the same, but I have changed case tumbling media from corn to walnut as that's what was in stock. I have verified that the cases didn't have any crud in them - cleaned out primer pockets and give a good blow through the flash hole to verify it's empty of stuff.

 

The only other oddity is a bunch of Norma cases which did size fine first time round have been nigh-on impossible to size the second time round - they weren't used for this load and I guess the issue is unrelated.

 

Any ideas why my load suddenly gives more pressure?

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1) change in brass, internal volumes will differ,

 

2) change in the seating depth of the bullet.

 

3) Were all brass full length sized before using in the new gun.... this could lead to your stuck case incident......

 

4) change in any one component means you rework a new load.

 

5) check scales to see that its measuring a constant powder weight....

 

6) tumbling media will have no effect on the case pressure as its only a cleaning routine...

 

 

ATB.

 

 

Snap.

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1) change in brass, internal volumes will differ,

 

2) change in the seating depth of the bullet.

 

3) Were all brass full length sized before using in the new gun.... this could lead to your stuck case incident......

 

4) change in any one component means you rework a new load.

 

5) check scales to see that its measuring a constant powder weight....

 

6) tumbling media will have no effect on the case pressure as its only a cleaning routine...

 

 

ATB.

 

 

Snap.

Thanks Snap, replies below...

 

1. Brass is the same - the original and new batches were both in PPU.

 

2. Originally they were seated to the same OAL, 2.700. Both batches were originally made with the same OAL and tested. The Winchester had a long throat, so I have reduced to 2.645 to try, but same issue.

 

3. Full length sizing only, I only have a full length sizing die.

 

4. Not changed any.

 

5. They're a pain, as they are light and my work surface rubbish, but I have checked as much as possible, any variance only +/- 0.1 gr

 

6. That's what I thought. My only worry was that this stuff did turn to a very fine dust for quite a bit - my cupboard was covered in it!

 

Could there be some issue with my die set maybe? Very odd one.

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1) change in brass, internal volumes will differ,

 

2) change in the seating depth of the bullet.

 

3) Were all brass full length sized before using in the new gun.... this could lead to your stuck case incident......

 

4) change in any one component means you rework a new load.

 

5) check scales to see that its measuring a constant powder weight....

 

6) tumbling media will have no effect on the case pressure as its only a cleaning routine...

 

 

ATB.

 

 

get yourself a nexk sizer die mr logic things will be more consistant.

 

Snap.

Thanks Snap, replies below...

 

1. Brass is the same - the original and new batches were both in PPU.

 

2. Originally they were seated to the same OAL, 2.700. Both batches were originally made with the same OAL and tested. The Winchester had a long throat, so I have reduced to 2.645 to try, but same issue.

 

3. Full length sizing only, I only have a full length sizing die.

 

4. Not changed any.

 

5. They're a pain, as they are light and my work surface rubbish, but I have checked as much as possible, any variance only +/- 0.1 gr

 

6. That's what I thought. My only worry was that this stuff did turn to a very fine dust for quite a bit - my cupboard was covered in it!

 

Could there be some issue with my die set maybe? Very odd one.

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Most likely causes :-

 

Operator error

 

Scale error [ cheap scale are ok but you can't rely on them to be accurate if they don't stand on a good surface, even then are not ideal for consistent hot loads]

 

Hard extraction [ usually operator error,incorrectly sized case or over loaded. What was the case like on the way in ?]

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The only other two things i can think off is that, operator error is one,

 

And if the case was hard to load (chamber) then the howa could have a tighter throat, hence the case doesn't need to expand as much leading to a build up in pressure within the case....

 

i'd work up the load from scratch again....

 

ATB.

 

 

Snap.

 

 

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I have a load for the .243 which is 80gr SBT over 44 gr H414, PPU brass, CCI200 primer.

 

 

 

Ran the load through "Quickload" the results stated that the load was near max chamber pressure and that tolerances would produce dangerous pressures. It's likely that the two rifle chambers were / are different, the load might be safe in one rifle but in the other not so, and in my experience Howa rifles have tight chambers! Temperature can and will effect chamber pressures.

Data for the above is 3909 bar with a MV of 3273. A reduction to 43 grains would produce a MV of 3204 and a chamber pressure of 3648 bar, my advice would be to reduce to 43 grains, the load would still be deer legal.

 

John

Edited by HUnter_zero

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I have a load for the .243 which is 80gr SBT over 44 gr H414, PPU brass, CCI200 primer.

 

 

 

Ran the load through "Quickload" the results stated that the load was near max chamber pressure and that tolerances would produce dangerous pressures. It's likely that the two rifle chambers were / are different, the load might be safe in one rifle but in the other not so, and in my experience Howa rifles have tight chambers! Temperature can and will effect chamber pressures.

Data for the above is 3909 bar with a MV of 3273. A reduction to 43 grains would produce a MV of 3204 and a chamber pressure of 3648 bar, my advice would be to reduce to 43 grains, the load would still be deer legal.

 

John

 

 

1 grain difference equals 260 bar difference..... icon_eek.gif don't have quickload,

 

 

but i was thinking it would have to be a tighter tolerence in the howa....

 

nice one mate...

 

 

Snap.

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i use h 414 behind 87gn h/ps 43 00 45 gns of powder never had a sticky bolt but , i do back off the lands with 45 gns ,

 

 

best results with 43gns 2.70 aol cci mag primer only neck sized ;)

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43 gr was my next attempt anyway, but thanks for the info HZ - most useful. I was expecting to have to change the load, but the original batch worked OK which is what's had me puzzled.

 

No issues chambering the rounds, powder charges checked each time with the scale - chances are it was that, then. Did zero before use and used very gently, but my setup isn't ideal in terms of space and level surfaces - my bin cupboard with modified shelving. Best I can do in the tiny little house I've got sadly.

 

Does anyone make a bloody heavy scale that absolutely won't ever move unless purposely moved?!

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1 grain difference equals 260 bar difference..... icon_eek.gif don't have quickload,

Snap.

 

Quickload is a great tool for reloading, especially if like me you only have access to an out door range for testing loads. In the summer load development is fun, in the winter it's a drag. Quickload will enable me to compare different loads to known pressures and velocities, which on the whole results in similar barrel harmonics and thus accuracy from the comfort of my computer chair. I've been working up a 'theoretical' 75 grain dual purpose load for my 1in12 .243", 75 grain SP driven by H380. With luck the load should be suited to spring time roe & fox shooting. I've settled on a load now but have yet to test it. Obviously I don't recommend this form of load development unless versed in both normal and Quickload development techniques but it saves me time on the reloading bench and on the cold range. It never fails to amaze me how little changes effect pressures and velocities, it's possible to reduce the load, in doing so reduce the chamber pressure by 20%, yet only reduce the MV by 5%. Different powders produce different chamber pressures, different case volumes produce different results and so on. Quickload gives the reloader a chance to perform lab tests, albeit theoretical.

 

 

John

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What scales are you using at the moment ?

 

What about weighing your powder into small containers like muzzle loaders do in a less cramped part of the house.

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What scales are you using at the moment ?

 

What about weighing your powder into small containers like muzzle loaders do in a less cramped part of the house.

 

There are some very cheap digital scales that are very accurate and don't take up much room. In saying that I have a mate in the US on holiday who is picking me up an RCBS 5-0-5 scale with luck, so my Hornady scales might be up for sale at a very reasonable price.

 

John

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I have a set of Lyman beam scales, very lightweight and functional I guess, but not ideal in the slightest.

 

HZ if you are selling yours, let me know :)

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