Long barrels, MV, and pressure signs

[hemiford]

I have several rifle projects with quite long barrels that are inching toward completion.
I know I'll have to experiment with different bullets and powders.
I do not have a chrono yet but this new Garmin looks interesting. However, even with a chrono,
the long barrels will give higher velocities without pressure signs so I can't compare velocity data
with other shooters, as evidence of overpressure.
So, starting off, can I only go by bolt lift and primer appearance for detecting overpressure ?

 

[Phil Rizzo]

If you are starting out with new brass I'd stay well below any kind of pressure signs, best you can tell. Reduce your charge at least 5% from a safe published maximum if possible. Some recommend 10%.
It prolongs brass life and you will likely need 100+ shots for the barrel to settle down to its "normal" anyhow.
There is no substitute for a good chronograph though, only thing I do without one is hunt, otherwise it's taking readings.
On the 2nd brass firing move powder charge up a LITTLE at a time until the pressure signs appear. Like .3-.5 depending on case size seems to work for me. Go slow here.
My rifles start to buck noticeably harder when pressure is getting up near max. Your gun will be similar but not the exact same as any others in the same caliber that you may reference.
Good luck, be safe, keep us posted.

 

[Rosebud]

Only thing I would add is work with slower burning powder using the longer barrels. Otherwise Phil is spot on.

 

[Mikecr]

This is where QuickLoad and a chrono really helps.
With it you would work up across a chronograph, calibrate QL, and see what your pressures are.

That much aside, pressure 'signs' are different animals and dependent on the build & your reloading plan. Often, they are not actual pressure problems.
I do a test I call MyMax, where I work up in charge with new cases while measuring case diameter at the web-line (widest portion).
I'll see growth, then leveling off (plateau), then a step change upward. That step change point has always worked out to SAAMI max (for me).
It is a point where FL sizing would be required.
If I run into issues along the way,, primer issues,, brass flow at bolt face,, poor extraction,, I stop to deal with those before continuing to MyMax.

With later load development I usually end up choosing a load near or just below MyMax.

 

[QuietTexan]

What chamberings? A lot of us shoot long barrels and can do data to compare. I'm a sucker for javelin barrels, getting a 36" 284 WIN done currently.

Or use QL to estimate FPS per inch of barrel to get a rough idea. Velocity is also dependent on bore condition, rifling, and other factors so direct comparisons aren't really a great tool for pressure other than being in a roughly correct 200 FPS range IMO.

 

[Phil Rizzo]

I have several rifle projects with quite long barrels that are inching toward completion.
I know I'll have to experiment with different bullets and powders.
I do not have a chrono yet but this new Garmin looks interesting. However, even with a chrono,
the long barrels will give higher velocities without pressure signs so I can't compare velocity data
with other shooters, as evidence of overpressure.
So, starting off, can I only go by bolt lift and primer appearance for detecting overpressure ?

If you get a chronograph, many many critical questions can be answered without blind experimenting. Beside helping you know simple velocity, accuracy nodes can be recognized as well as extreme spread and standard deviation.
And that's not all.

 

[hemiford]

Here's what's brewing:

25-06, 32-in blank, heavy varmint, 9-T, I was figuring to shoot 100-gr or so here.

7 RM, 32-in blank, MTU, 9-T

7 RM, 32-in blank, Sendero, 8-T

7 STW, 36-in blank, MTU, 9-T (I'd like to try even longer for another barrel) 175-gr ??

8mm RM, 32-in blank, MTU, 10-T, I have a bunch of factory Rem ammo, 185-gr & 200-gr

I don't have QL either but it sounds like a good investment.

 

[Phil Rizzo]

you can certainly justify a good chronograph.
and QL

 

[hemiford]

This is where QuickLoad and a chrono really helps.
With it you would work up across a chronograph, calibrate QL, and see what your pressures are.

That much aside, pressure 'signs' are different animals and dependent on the build & your reloading plan. Often, they are not actual pressure problems.
I do a test I call MyMax, where I work up in charge with new cases while measuring case diameter at the web-line (widest portion).
I'll see growth, then leveling off (plateau), then a step change upward. That step change point has always worked out to SAAMI max (for me).
It is a point where FL sizing would be required.
If I run into issues along the way,, primer issues,, brass flow at bolt face,, poor extraction,, I stop to deal with those before continuing to MyMax.

With later load development I usually end up choosing a load near or just below MyMax.

Mike, Hmm, case web growth you say.

 

[victor3ranger]

Here's what's brewing:

25-06, 32-in blank, heavy varmint, 9-T, I was figuring to shoot 100-gr or so here.

7 RM, 32-in blank, MTU, 9-T

7 RM, 32-in blank, Sendero, 8-T

7 STW, 36-in blank, MTU, 9-T (I'd like to try even longer for another barrel) 175-gr ??

8mm RM, 32-in blank, MTU, 10-T, I have a bunch of factory Rem ammo, 185-gr & 200-gr

I don't have QL either but it sounds like a good investment.

Holy smokes I would like to know what you end up pushing out of the STW barrel. Would really like to know how it does with 140-150's
That 7RM 9T would be very interesting to

 

[Mikecr]

Mike, Hmm, case web growth you say.

Well like you said, a longer barrel than related to in manuals can make it harder to compare by muzzle velocities.
But you can find out more directly what your local max is.
Use culled new brass for it.

 

[QuietTexan]

Here's what's brewing:

25-06, 32-in blank, heavy varmint, 9-T, I was figuring to shoot 100-gr or so here.

7 RM, 32-in blank, MTU, 9-T

7 RM, 32-in blank, Sendero, 8-T

7 STW, 36-in blank, MTU, 9-T (I'd like to try even longer for another barrel) 175-gr ??

8mm RM, 32-in blank, MTU, 10-T, I have a bunch of factory Rem ammo, 185-gr & 200-gr

I don't have QL either but it sounds like a good investment.

Yesssssssssssssssssssssss