Pressure Signs, general discussion (I'm shooting .260 Rem., RL17)

[stoutheart]

Hi all, I'm relatively new to precision long range shooting and reloading but have been hunting a long time. I'm pretty OCD and I think I'm doing a thorough job with my prep and loading but I still have lots to learn.

This fall I picked up a new Tikka Sporter in .260 Rem. with a 20" barrel.
Ammo components are as follows: New Lapua brass, Lapua 139 Scenar bullets, RL17 powder, CCI standard large rifle primers.

I'm loading at .020 jump with puts my loaded rounds at about 2.98 O.A.L, 3.348 as measured with a Sinclair hex comparator.

The only similar load on the Alliant web site was for 41 grains of RL17 with a Speer bullet, loaded to spec. length. I loaded 10 break-in rounds, starting about 10% below that and worked up to 42 grains in my first string, seeing and feeling no pressure signs. Temps were 45-50 degrees.

I then loaded 10 more, up to 45 grains in .5 grain increments. I shot those at lunch today - 45 degrees, ammo kept in my jacket pocket to stay out of the chilly breeze. Still no real pressure signs.

These are the slight changes in case dimensions I'm getting.

Case head measurement, taken at base just ahead of the rebate:
new, unfired Lapua: .469
40 Grains and up: .470
42 Grains - 44 grains: .471
44.5 - 45 grains: .472 with a more visible line of expansion just above the rebate

Case length:
No noticeable change, varies by about .002 in this lot of brass but 90% are within .001

Primers:
The 44. 5 and 45 grain loads look like the primers are very slightly flattening, just a small decrease in the side to base radius on the cup.


So..... 45 grains sounds like a hot RL17 load but I also have more case capacity than spec. loads so I knew pressures would be lower.

I'm looking for advice on reading pressure signs. The great articles on the Rifleman's Journal blog and others I have found seem to say that as soon as you see any slight pressure marks from the ejector or extractor, you are over pressure and should back down. I'm not seeing anything at all.
My thought is that I'll load up another batch up to 48 grains and look for pressure signs just because I'd like to know, but is this foolish?
Any advice with Lapua brass specifically? Does is show those signs at normal high pressures or do yo have to get way too high to see them?
Anything I'm missing?

I don't have a chronograph yet so no velocity data, sorry. And I know I'll have to re-test when I'm shooting at 80 plus this summer......

Thanks for the help,

Matt

 

[jpretle]

You might take 3 of those cases and fire them w/ that 45g load, and measure each after each firing. If you get a .002-.003 increase in measurement after say, 5 firings, I would say you have reached a max load. It all depends on how much use you want to get out of your brass.
Bob Hagel, in his book, 'Guns, Loads, and Hunting Tips', has a great dissertation on measuring case-head expansion.
Well worth not only a read, but a study.

 

[stoutheart]

Thanks, I'll get a copy of that book.

 

[jonbearman]

Where would you find the book?

 

[stoutheart]

I found it here, or try your local book shop - http://www.amazon.com/Guns-Loads-Hunting-Tips-Hagel/dp/0935632387

 

[spclark]

New brass will tend to suffer stretched case heads with moderate- to high-end loads. My recent practice has been to 'condition' new match brass with a couple firings at a relatively conservative load level before moving up to loads I'd expect to shoot in an important match.

Primet pockets seem to last longer as a result, which to me is a plus.

Do you know what your TIKKA'S chamber specs are? If it's a generous chamber you'll see case head expansion pretty quick even with moderate loads unless you take care to resize to minimum dimensions between firings.

I suggest you'll be better off over time evaluating your loads' performance (accuracy + reliability) down-range rather than loading to 'near max' based on your interpretation of what might (or might not) be indicative of high chamber pressure loads.

 

[dooley]

Stouheart, I tapped your figures into Quickload and at 45gr of Rel 17 you are approx 8,000PSI over max pressure, I to use Rel 17 in a 260, but my max load has never been more than 42.5grs + 139gr scenars and this is with a much stronger action than yours, (Accuracy International) With a short barrel you will be better off with the 123gr scenars, but you will have to bring your coal down as the 123gr bullet is shorter than the 139, I have never found the scenar bullets mind a 100 thou jump to the lands, also Quickload is a valuable tool, so is a Chrono, Modern Tikka rifles tend to be a bit generous in their chambering so cases will stretch a little, I hope this helps, Regards, dooley

 

[savagedasher]

43.5 is near max that is 57,000 psi . Larry

 

[stoutheart]

Thanks for all of the replies, very helpful info. I think I'll do some group testing along the lines of the ongoing thread from Erik Cortina on long range load dev. at 100 yards. My thought is to test 40.5 to 43.5 grains. I will watch case dims. over time and a chrono is on the list.

Does this load range seem like the right one to focus development on at this point?

Also, to the title of the thread and to keep it on topic more or less, are there any other pressure signs I should be looking for?
I forgot to mention in the first post that I could not detect any sticky bolt lift with any of the loads.

So far, on my old .308 I've been using Brian Litz's BCs then truing MV in my ballistics solver based on impacts at about 700 yards. (That's max range at my house.) This seems to be getting me pretty consistent algorithms from 100 - 700 and I'll do this with the .260 as well as soon as I settle on a load. I'm looking forward to pushing out to 1000.


Again, thanks for all the help.

Matt

 

[stoutheart]

.....there was a post by Erik here, as well as a reply by me, but they seem to have disappeared. I tried loading the thread in another browser and it was the same so I'll repost.

Erik cautioned against going up to 48 grains, which is the conclusion I reached as well based on the other replies in the thread. What do you think about the accuracy testing window I mentioned in my last post of 40.5 - 43.5 grains? Does that sound like the right load range and way to approach it?

My barrel is 1:8" twist as so far has been shooting most of my test loads into 1/2" and smaller if I do my part. I shoot off a bipod with a sand sock, generally prone only.

Thanks, Matt