Barrel Length and Chamber Pressure

[fiftybmg]

Your first and only source for reliable load data is the loading manual. What other people say they do is not reliable load data.

If the bullet is not in the manual yet, you can start low with another bullet of the same weight, and work it up.

The barrel length has nothing to do with the pressure safety of the load. It does affect the muzzle velocity, so for the information to be specific for a 26" barrel just means you should not expect to get the same velocity from your 24" barrel, you will get less.

The secondary pressure spike people speak of was discovered in the post-mortem analysis of a small quanitity of slow burning powder in a large case that blows the rifle up into little bits. Loads that are reduced tend to show the beginnings of that secondary spike.

 

[J E Custom]

JE , thanks for the info. I was wondering if you could tell me that if I cannot get the COAL of 3.700" that Berger specified, as it will not fit into my magazine, and my COAL is like 3.620 will that change the pressure?

Yes. shorter COAL and farther from the lands will lower the pressure. The norm is that If you are .020 to .030 off the lands pressure will be less than If you are seated against the lands. Some bullets like different amounts of jump, so you have to find out what your barrel and bullet combination likes.

I have a good friend that likes and only shoots Berger's and was having trouble with accuracy in one rifle/barrel and finally started backing off the lands in .010 thousandths Each time he would add .010 more the rifles accuracy improved. He kept going to see where it would top out and he ended up with .110 off the lands with the Berger and got great accuracy even though everyone was telling him, you need to seat the Berger's against the lands. the length they gave you is their recommendation and is normally good information, But all barrels and chambers are not equal and the jump has to be found on each rifle/cartridge to get the most out of it.

I start all of my rifles at mag length Minus .020 and go from there. On all of my big wildcats (Everything with powder charges over 90 grains I design in more freebore to keep the pressure under control and velocity up. Accuracy in these cartridges rely on excellent quality ammo (Very concentric).

J E CUSTOM

 

[Mike AVM]

Seating depth is critical to accuracy. I find a good load then tune with seating depth. Where people think it ought to be versus what the rifle likes are often two different things.

 

[JayCee49]

Great info all, thank you!

JC

 

[david g ranes]

Gents,
I got some load data to day for a new rifle and when the gentleman gave me the info he made a point of making sure I understood it was for a 26" barrel. I am not new to the game but by no means no anywhere near as much as I would like to know about reloading so I am posing the question. Does barrel length have anything to do with chamber pressure. If I use the load data in a rifle with a 24" barrel would there be any issues?

Best bet if you can't find the info for a cartridge your looking for go to Hodgson load data input your caliber of gun bullet weight powder you would like to use they know about what their powder will do than anyone else does their loads are usually a little light but gives you a very good starting point. David

 

[Mram10us]

Correct me if I'm wrong here. Assuming distance from lands is constant:
Shorter coal with same powder charge = higher pressure??
Pretty sure that is the case but I thought I read different in some of the posts

 

[Mikecr]

Powder doesn't care about OAL.
Better to think of starting pressure in terms of powder burn rate, load density, engraving force, neck tension, and ignition efficiencies.
With this, an extra ~50thou deeper seating could mean pressure goes up, down, or doesn't change at all.

 

[Mram10us]

Powder doesn't care about OAL.
Better to think of starting pressure in terms of powder burn rate, load density, engraving force, neck tension, and ignition efficiencies.
With this, an extra ~50thou deeper seating could mean pressure goes up, down, or doesn't change at all.

So internal case volume getting smaller via coal, with the same amount of powder, does not affect the pressure? That doesn't make sense to me.

 

[Orange Dust]

So internal case volume getting smaller via coal, with the same amount of powder, does not affect the pressure? That doesn't make sense to me.

Gets canceled out by increased freebore whentalking about smallamounts one way or the other. Touching and jamming into lands can increase it quite a bit.

 

[Mram10us]

Gets canceled out by increased freebore whentalking about smallamounts one way or the other. Touching and jamming into lands can increase it quite a bit.

The question above was talking about distance to lands being the same. See post #20

 

[Orange Dust]

The question above was talking about distance to lands being the same. See post #20

Sorry, missed that. If you push it back and keep distance the same pressure will increase due to less case capacity

 

[Mram10us]

Sorry, missed that. If you push it back and keep distance the same pressure will increase due to less case capacity

No worries. I miss stuff all the time.

 

[Mikecr]

So internal case volume getting smaller via coal,

Well, does the case volume actually get smaller? Depends on one bullet -vs- another then. Can depend on how much change, even if a volume change, vs- your load tolerance. Can depend on the proximity and change from land contact. For instance, seating deeper from touching/near touching by only 10thou can lower pressure, and then pressure might not go up again until seating ~100thou deeper.
A broad rule of thumb would fail tests.

 

[Orange Dust]

Well, does the case volume actually get smaller? Depends on one bullet -vs- another then. Can depend on how much change, even if a volume change, vs- your load tolerance. Can depend on the proximity and change from land contact. For instance, seating deeper from touching/near touching by only 10thou can lower pressure, and then pressure might not go up again until seating ~100thou deeper.
A broad rule of thumb would fail tests.

You missed it just like i did. We are asumming all else being equal.