Armory Sponsor
Posted: 8/8/2016 10:47:43 PM EDT
|
Need some advice on a situation I’ve not encountered before. Did some early load development during the first 100 rounds fired out of a new Savage 110 with a 26” barrel in 338 LM, a new caliber for me, using 100 new Lapua cases.
Tested N570 and IMR7977 under 300gr Berger Hybrid OTM bullets using 0.7gr increments from 87.3gr to 92.9gr. IMR7977 gave slightly stiff bolt on extraction at 91.5 and 92.2 so the higher charges were pulled. IMR7977 didn’t look all that accurate at the lower weights either. N570 ran all weights very happily showing no pressure signs whatsoever. 87.3gr (2650fps) and 90.1gr (2733fps) both looked very good. Neck-sized the 100 cases and made some test rounds using N570 at 87.3gr and 90.0-90.2gr. On the second use of these cases, all of these rounds/charge weights chambered easily. But all resulted in very stiff bolt lift on ejection. And there’s a faint but visible ejector mark on most of the cases. Maybe 338 Lapua cases do not spring back as much as I’m accustomed to in other calibers. And I can understand the cases eventually not wanting to chamber without FL sizing. If it’s “just” a spring-back issue fine . . . maybe in this caliber/chamber they need FL resizing every firing. But I’m concerned there may be something else going on here that I don’t understand. Any thoughts? |
|
You are over pressure before you get to the stage of a sticky bolt. With a sticky bolt, you are really pushing it. Drop your load down as your rifle is telling you that your loads are too hot. Don't continue to shoot loads that are over pressure. I don't load this caliber and could not find any data for 300 gr bullets with those powders. How far off the lands are your loads? When loading 90 grs of powder .7 gr steps are a waste of components. I would use 1.5 gr to 2 gr steps. |
| Wow, not sure if typos on this pagehttp://www.vihtavuori.com/en/reloading-data/rifle-reloading/-338-lapua-magnum.html but it lists 80.9 as max with the Berger? |
|
Quoted:
You are over pressure before you get to the stage of a sticky bolt. With a sticky bolt, you are really pushing it. Drop your load down as your rifle is telling you that your loads are too hot. Don't continue to shoot loads that are over pressure. I don't load this caliber and could not find any data for 300 gr bullets with those powders. How far off the lands are your loads? When loading 90 grs of powder .7 gr steps are a waste of components. I would use 1.5 gr to 2 gr steps. I know pressure is an issue before sticky bolt occurs. That's why i stopped shooting the IMR7977 before hitting book max. But of ~75 rounds fired from new cases using N570, NONE showed bolt lift issues - or any other pressure signs. In the second firing of neck-sized only, ALL of those charges exhibited sticky bolts. What changed? COL = 3.792", BTO = 2.950" which is 0.015" off the lands. I like using 0.75% load increments for OCW, and that runs closest to 0.7gr increments. Quoted:
Wow, not sure if typos on this pagehttp://www.vihtavuori.com/en/reloading-data/rifle-reloading/-338-lapua-magnum.html but it lists 80.9 as max with the Berger? Yup, pretty scary lol. Here's the thing: The max for 300gr Scenar (92.4gr @ COL 3.681", 2653 fps) and 300gr Sierra (91.3gr @ COL 3.602", 2746fps) are much higher. The Berger is .084" longer than the Sierra, and my COL with the Berger is 0.190" longer than the Sierra COL, and 0.111" longer than VV's COL for the Berger. So I checked Quickload using my COL (3.792") and 93gr N570 produced 55.5k pressure vs a max of 60k. I also checked all the internet references to N570 and 300gr Bergers that I could find and no loads or load ranges were below 89gr. So I started at 87.3gr . . . and everything worked just fine through 92.6gr, the highest load . . . for the first firing of the Lapua cases. Not so much for the second firing :) The reason I'm asking here is pretty clear. Yes, the second-firing loads concern me. But why didn't it happen the first time through? ~75 rounds is not a small test. |
|
FYI
From Berger web page VIHT N570 max 90.0 gr with the 300 gr bullet http://www.bergerbullets.com/Reloading_Data/338Lapua300gr.pdf Max pressure is 68 KPSI, Two neck-size-only reloads seems fine to me. Drop your charge down to 55 KPSI and see how many neck-only loads you get. |
|
Quoted:
FYI From Berger web page VIHT N570 max 90.0 gr with the 300 gr bullet http://www.bergerbullets.com/Reloading_Data/338Lapua300gr.pdf Max pressure is 68 KPSI, Two neck-size-only reloads seems fine to me. Drop your charge down to 55 KPSI and see how many neck-only loads you get. That data combined with my longer COL and the first 75 rounds fired using N570 tells me the 87.3 and 90.1 loads can be OK. (BTW, Quickload uses the SAAMI max pressure of 60.9 KPSI.) Back in the reloading room I found some of the second-fired cases will rechamber fine, but most would only go in smoothly to the point where you are trying to close the bolt. And the resistance did not feel “springy” like it would be if the shoulders needed to be bumped back. I measured the cases that would NOT rechamber (as best I could) and found: - all had OALs 0.001" over SAAMI max. - BTO lengths 0.002" longer than cases that chamber easily. (I have not yet gotten an accurate headspace measurement.) - necks right at SAAMI max diameter except at the base where it’s difficult to measure precisely. At that point they appear to be 0.001" over max. So I plan to test trimming back and/or neck sizing some of the cases that won’t chamber to find out where the problem occurred. The sticky bolt lift doesn’t appear to be caused by expansion of the body. If the problem was caused by length growth, I can fix it. If it was caused by shoulder growth, I can probably fix that too. We’ll see. Thanks again for that Berger data :) |
|
Quoted:
What does Quikload tell you about internal pressure for your loads. You might use that as a guide. Yes, did that before starting because of the VV load data "issue". Using my COL (3.792"), my average bullet length, and QL's standard 113gr case capacity (Lapua is reported as normally larger, have not weighed mine yet) . . . 93gr N570 produced 55.5k pressure vs a max of 60.9k. I'm using 87.3gr and 90.1gr on the second firing and, after ~70 rounds with no issues using new cases, I'm now seeing heavy bolt lift on all charges. Brand new cases are grossly undersized, not so after the first firing. Yes. Don't know if you saw my reply to Happy2shoot above. I'll be able to test-adjust the cases that don't rechamber later today.If that works I'll do some additional case prep and fire a couple more. Sticky bolt, ejector marks - sounds too hot to me. Yes lol. But I want to know what changed from the first firing. I'm not ready to accept the fact that these charges are suddenly OP nor that cases slightly larger on the second firing somehow exceeded the brass's ability to snap back . . . except for that length issue. |
|
It's probably not sticky bolt. It's probably a poorly reamed chamber. Buy a chamber reaming / pollish brush. Perform the service to 338. Live happily ever after. My Savage was the same way. Use a hand drill, and go slow its self centering. Fixt.
By the way use a bit extension- you don't even have to remove the brl. The thing is is that it's not a terrible chamber. Like mine it could just be a little chatter in there. So you're not doing a full ream. Just polishing and removing shoulder material. Try this first- http://www.midwayusa.com/product/487170/flex-hone-rifle-chamber-hone-338-lapua-magnum-14-400-grit If it turns into a bitch of a persistent problem, take a sharpie out and color the body if the case. Chamber it and see where the sharpie is binding and scratching off the case. Then target that area behind the marks with this: http://www.brownells.com/gunsmith-tools-supplies/shotgun-tools/barrel-hones-accessories/rifle-polishing-system-prod651.aspx On mine I had to linger at the back of the chamber, there was a bind there where it would grab cases. |
Armory Sponsor