Home Forums Hunting & Shooting Gunsmithing What causes certain barrels to hit pressure before others

I don't own and have never shot these cartridges. I saw a video on YouTube where the person was complaining that his shorter barreled 6.5 PRC was essentially the same speed as his longer barreled 6.5 Creedmoor. Maybe the 6.5-284 needs a longer barrel?

Had a 6.5 X 284 2 barrels and lots of frustration never consistent accuracy and showed pressure signs. My chamber, dies and brass
were not the same.

Sold it and 6, 6.5 Creedmoors later no issues and not much slower.

Check the fit of your chamber with a sharpie or candle smoke it will reveal a lot.

PO Ackley ran some tests with a 30-30 Imp cartridge. This test indicated otherwise. I refer those interested to a Section titled "Pressure" in Vol I of his "Handbook for Shooters and Reloaders".

I just grabbed my copy if P.O.'s Vol#1 and disagree with you MM. Mr.Ackley's writing style is goofy at best and I have to reread paragraphs frequently. It ain't my fault my
experiences stick in my brain better than just reading about it. I would put my money on Mr.Sisk on this. Lotsa stuff happens very fast when the primer is punched.
I will say that PO was way ahead of his time. He described the new design of precision rifle cartridges a long time ago. I just wonder why it took so long
to get where we are now.

I have found the 6.5-284 to be the easiest .264 caliber cartridge to get to shoot well. It has won more 1000 yard BR matches than all the other 6.5s combined. I get 150 fps more than any of my Creedmoor chambered rifles.
My go to rifle is still chambered in 6.5-284. It is on a Phoenix action and wears the 3rd barrel. Best barrel i every had for it was a Chanlynn. The Shilen on it now is no slouch. I cut my barrels at 25" for my 284 builds.
I wore 2 barrels out shooting 142 grain Sierra match kings back before Bergers were widely available. My 1000 yd BR load used V V N160

I actually measured the pressure. John Barsness has the details in his books.

How does one measure the pressure on the locking lugs?

Fuji pressure film.

Hunting guns are terrible for barrel consistency, rough cut, undersized, oversized, etc. QC is virtually non existent. Forget the exterior shinny crap, an inaccurate rifle is worthless regardless of how pretty it is.

I found the article in GGII Charlie - thanks. I recognize that Ackley was trying to "sell" that minimum body taper (via an improved cartridge) reduces bolt thrust - and it doesn't when you're operating at higher (> 50 kpsi) pressures. Your Fuji film test show this. Brass actually does grip the chamber walls, which was my point. JB's article acknowledges that there can be zero bolt thrust when pressures are ~ 42 kpsi, or below, as the brass does not reach its elastic limit and stretch to conform to the full chamber length. At these lower pressures, primers out because the case does indeed grip the chamber wall. As JB writes, at about 50 kpsi, the brass stretches as pushes against the bolt face and transfers to the locking lugs. No attempt to discredit you - I think we are both right in regards to what we were trying to say.

Is it a tight neck? I had some issues with a 7mm arm gunwerks chambered for me years back. I bought a new lot of brass they had just had Hornady make for them and the necks were too thick for their reamer.

I picked up on the problem right away noting necks didn't expand at all when fired and rounds were a but tough to chamber even with new brass.

I even sent the rifle back to them and Mike said it was fine and that I didn't know what I was talking about. Aaron was cool about it and said he'd personally look into it. Several months later they announced there was an issue with their brass necks being too thick. It was fine if I turned necks but I didn't want to do that for a hunting rifle so I sold it to someone who did at a big loss.

Bb

Thanks for the replies. I believe it was a neck clearance issue. The problem went away with turning necks. Also I believe it was magnified by lack of primary extraction. It was a savage 111 with very little primary extraction. I wasn't the one shooting it but kept hearing that the fired cases would stick

Barrel length
Bore diameter
Rifling. Depth, style.
Bore smoothness
Throat length
Chamber dimensions

There are surely more that aren't here.


Bullets. How they interact with that bore.
How they are seated to interact with the throat.


All of those are factors, to varying degrees.

Length is the one folks jump on.
It's easy to measure, the rifle is often shorter that the one used in testing.

Every one of the listed factor come into play. Let them stack in your favor and you
might beat listed velocities with no issue. If they stack the other direction, you
have a slug.




Oh yeah.
Soft brass.
If you have a batch of too soft brass it will show pressure when your pressures
are below max.

So pressures are too high. For that brass.
Brass being the weakest link, if soft brass is showing pressure you are heading
toward a case failure. And, pressure numbers be damned, you don't want
case failure.