Home Forums Hunting & Shooting Ask The Gunwriters Tight chamber,fast barrel?

I have a 7wsm that was built with a Brux barrel and custom reamer. When I was loading R-22 and 162 amax’s,I would get 3000 FPS 2 grains shy of max book load. I tried R-26 to max load of 3170 and am almost 4grains shy of max. This is using magneto speed that is consistent with other calibers. So what does the consensus say?

Tight chamber, max pressure with less powder....

Yeah... you have speed, pressure is the issue... tough to measure that scientifically...

Snug bore....chamber won't make it faster......

Tight barrel, not chamber.

Listen to aalf...

There are no free rides, regardless of cause. Outlandish velocity equals outlandish pressure. A couple years back I started a ladder run with a 6.5 x 55 Swede. It's a nail driver, but 4 or 5 grains short of book max loads with IMR 4350 I was getting heavy bolt lift. Still need to Chrony it to see what's going on.

If your bullets are getting crimped in the neck by a tight chamber would that do it.

Max velocity is usually approaching max pressures. A pair of 270's with 22" bbls and 150gr NPt's are coming close to max velocity and I'm .8 grains below Alliant's max charge of RL-26 with a 24" bbl pressure barrel.

With easy extraction and good accuracy, I stopped right there.

I have a 25" Douglas bbl 270 that seems to be very fast. In the 90's I had that rifle hooked up to a Oehler Ballistics Lab and compared my loads to factory loads, and it was under max pressure even though I was making quite a bit more velocity for a given charge in the manuals. I don't know how much the longish barrel may account for that.

For sure if brass is creeping up into the neck area. Still have a buddy that reloads but historically paid no attention to cartridge dimensions. He shot great patterns with his 22-250. I was gathering his brass as he was firing a string, and could see rifling marks on the very end of their necks. An obvious pinching of case necks as he cammed his bolt over. We did some length trimming and annealing and got him back into some reasonable accuracy.

Most commercial arms are not made with tight necks, but some picky shooters will special order such to minimize cartridge fatigue. They will typically turn/ream necks to very specific dimensions. Weatherby gets around potentially high pressures by having a stretch of freebore immediately ahead of the cartridge ( i.e a small length of smooth bore that lets ones slug get a running start before it hits any rifling).

Took delivery on a Borden 300 WSM full custom. First test loads with Norma brass were giving pressure problems with the low end book loads, enough to lock the bolt down. Had to beat it open with a 2x4.

When I went home distraught, I called Mr. Borden and explained. He said it is the Norma brass which is notorious for that. Suggested I change brass. I switched to Remington brass & the problem went away immediately. The same load in Remington brass clocked 3310 fps with no pressure signs.

I think most of us know that loading up some thick walled military brass will put pressures through the ceiling if the loads aren't adjusted due to the smaller internal capacity. Even different commercial cases vary in capacity and pressure/velocity with the same load.

A tight chamber will affect the internal capacity of a fired case too, in some cases more than that thick brass. Tighter chamber, more pressure.

The only pressure signs I got was when I went over 3200fps. That was a little primer flow. No hard bolt lift and primers still had rounded edge. This load is on alliant’s website. I think it is safe,just have never got to max load that much short of book load before.

Thanks Hutch

Too thick of necks for the chamber will also increase pressure.

Hutch,

Primer appearance is notoriously unreliable as a pressure indicator--unless of course one leaks or blows. But other indicators, like cratering and flattening, are often caused by other factors.

In 1947 General Hatcher, in his book HATCHER'S NOTEBOOK, mentions the uselessness of primer appearance in judging pressure, but doesn't go into details. If he had, we might not have so many loading manuals and handloaders touting it.

Load data is put together with a certain lot of brass, primer, powder, and bullets, AND SHOT IN A SAAMI SPEC CHAMBER. If any variance exists in these, the result will vary from the data. You said yourself that you used a custom reamer. Without knowing the specs of that reamer, by your results, I'd guess it was a minimum spec reamer.

There are no problems here. You are getting top speed with a few grains less powder. If the accuracy matches your needs, you have a winner. If you want to keep loading hotter, imagining you have a "fast" gun, you are free to do so, but understand that in general, when you are at the velocity for the data, you are usually at the pressure for that data.

You're ignoring the most reliable "pressure sign" the home reloader can have, short of using a strain gauge......your chronograph. If your velocity is higher than normal, then most likely so is your chamber pressure. Why folks refuse to accept that, and instead think they have some miraculously "fast" barrel, is beyond me.

Jeff

Thanks Jeff, but I’m not ignoring my chrono.I worked up 1 grain at a time and 68 gr gave me a little over 3200.I backed down a half grain to 3170 which alliant says is safe. Very accurate and no traditional pressure signs. Other than specialized equipment that’s all I have to go by right?

Thanks Hutch

Gotcha, reading comprehension problem on my part! . My apologies. Yep I'd just stop at what the Alliant data says is a safe max velocity. I just don't buy into the whole fast or slow barrel thing. If a barrel is considered "fast", it's likely due to some dimensional difference that causes pressure(and thus velocity) to develop with less powder than average. Again sorry for the misunderstanding.

Jeff

No problem. Just getting feedback from people with more experience than I have.

Thanks Hutch