Pressure signs

Ucsdryder

Well-Known Member
Joined
Jan 23, 2016
Messages
323
I’m trying to identify pressure signs and I think I have too many variables in the mix.

The easiest sign to identify seems to be bolt lift. A heavy bolt is hard to not identify. The question is whether a heavy bolt lift is a pressure sign or something else? What causes heavy bolt lift? I assume it’s the case expanding at the shoulders and the shoulder rubbing as it’s rotated to free the bolt when the handle is lifted? If this is true, it has to be a relative amount because all cases expand, so some expansion is ok and the bolt doesn’t get heavy, but excessive Pressure causes excessive expansion which causes heavy bolt lift?

Last night i shot virgin h1000 and 1x reloaded rl26 out of my 7 Saum. I was trying to find pressure and got a stiff bolt immediately from the 1x fired rl26. I had bumped the shoulders back .002-.003 and the bolt closed easily on the loaded rounds. I find it hard to believe I was hitting pressure already but the bolts were noticeably stiff (starting load 59.1gr and 2576fps out of a 20” barrel.

On my last round of h1000 I got a stiff bolt but no other signs of pressure. I just measured the shoulder and it was longer than the other virgin h1000 shoulders that I fired last night by .002”. So I assume I hit pressure there? That was with 64.6gr h1000 in adg brass with a 180eldm out of a 7saum. No ejector smear, no flat primer. A little mark where the cutout on the bolt face where the extractor is.

I never saw any extractor smears or flat primers or cratering on any brass h1000 or rl26. Just variations in bolt lift.

Im not even sure what help I’m asking for…I’m just confused! I am FL sizing and shoulder bumping, but am I doing something wrong on the 1x fired brass to cause the bolt lift? Should I ignore bolt lift and keep an eye out for primer/ejector signs?
Here are a couple of pictures. Not sure if they’ll help.

the gun shoots great, just trying to get into the 2700-2750fps range. The ladder test was 625 yards. The wind shifted from north to south at the end of the h1000 which explains the last 3 hitting far left.

I got out of order on the h1000 at the end as you can see on my note pad. Smh
 

Attachments

  • 4D4BFC3E-0245-4F91-B873-72040978CDE9.jpeg
    4D4BFC3E-0245-4F91-B873-72040978CDE9.jpeg
    843.6 KB · Views: 189
  • 75807D3F-9C24-4260-A7C3-DD48A36723C7.jpeg
    75807D3F-9C24-4260-A7C3-DD48A36723C7.jpeg
    331.7 KB · Views: 189
  • FC09B80B-BCF6-430C-AD2B-D705F597061A.png
    FC09B80B-BCF6-430C-AD2B-D705F597061A.png
    764.1 KB · Views: 189

Ucsdryder

Well-Known Member
Joined
Jan 23, 2016
Messages
323
I am an ignorant old man who does not care about pressure. If the bolt works easily and the group is good and the velocity is what I want, I go play.
What if the bolt doesn’t work easily? And you’re below where you should hit pressure? :)
 

Ucsdryder

Well-Known Member
Joined
Jan 23, 2016
Messages
323
if I’m bumping shoulders .002-.003 vs virgin brass at .005-.006 would that be a potential cause of heavy lift on 1x fired? Maybe it’s as easy as bumping shoulder an additional .002?
 

MagnumManiac

Well-Known Member
Joined
Feb 25, 2008
Messages
3,941
No- additionally your once fired brass should have more volume than new brass and slightly lower pressure
No….it will have more pressure than virgin brass because some of the pressure is used in virgin brass to fire form it.

OP, it is a well known fact that ADG brass hits pressure early, it is substantially thicker (LESS VOLUME) than other brands.

Stiff bolt lift is a sure sign you have surpassed safe pressures for THAT BRASS.
It matters not that you haven’t reached the book max, or the velocity you’re expecting.
Brass expands in ALL directions, it has a plastic tendency, which is why brass is used, it expands then shrinks, BUT if you expand it so much that the action also springs, the brass has lost it’s spring and doesn’t shrink back, this is what causes stiff bolt lift. This is bad for your bolts lugs and the actions abutments, over time with continuous hard loads, the 2 can gall and even setback over time.
ANY hard bolt lift is a sign to back off, whether other signs are present or not.

Cheers.
 

Mikecr

Well-Known Member
Joined
Aug 10, 2003
Messages
5,813
Location
NC, oceanfront
There is a difference between a pressure 'sign'(a sign of high pressure), and a pressure 'problem'(something often manifesting with normal pressure). For instance, a mis-timed bolt/action can cause difficult extraction/bolt turn without pressure signs. Someone mentioned oil in the chamber, and that is an example problem that could challenge normal extraction with relatively low pressure loads. Primers can flatten at normal pressures if your headspace is too high. If you run a load near problem pressures normally, then it doesn't take much(other than higher pressure) to run into problems.

What I'm suggesting is that a single problem, may not be a sign of excess pressure.
In my experience, excess pressure shows up all over the place. It's actually a test I run with every new chamber, brass lot, and new load development. I creep into what I call MyMax load, and log it.
I may hit problems on the way up, which I'll troubleshoot & fix before continuing upward. Then I'll hit a pressure sign, then a confirmatory sign, and stop. It's purely pressure. I love my QuickLoad/chrono in that they truly help with confirmatory information, when a particular combination may be concealing a sign..

Fired brass does produce higher pressure over new brass from a given load. This is one of many reasons to do load development with brass that is fully fire formed to stable, and not until then.
 

Orange Dust

Well-Known Member
Joined
Oct 23, 2015
Messages
2,394
Location
Mingo Swamp
I'm just gonna throw this out there as I have had it happen to me and I like to never figured it out, Exact same scenario as the OP, it ended up that the necks were causing the problem, turned them down to .013 and the problem disappeared
Overcleaning brass can cause this too. Never was an issue before liquid media. Try the same load with trimmed and uncleaned brass. Check neck clearance. Turn if needed. Make sure the throat is clean on the rifle. Most likely one of these is the problem, especially if no other signs of pressure exist. Another thing you can do is measure the web of the case. You have to use a micrometer, NOT calipers. Measure before and after firing. A .001 swell is overpressure by a couple of grains.
 
Top