Stability factor and bullet selection question

[CH Luke]

Using the Twist Rate Stability Calculator my 1:11 twist tells me to expect better performance with the 185 Juggs than the 200 Hybrid that I am about to start testing loads on tomorrow morning. The reason I am testing the 200 is an anticipated increase in 1000 yard competition this year and better performance over the Juggs at that range.

Right now I have what I consider an excellent 185 load with 2832 FPS and single digit SD and ES using standard Lapua brass. Right now I estimate that I have enough chamber size to have up to a 2.301 CBTO with the 200 and will start .0015 off that tomorrow.

Should I be using my new Lapua Palma brass to refine my 185 load (with the different primers) because the apparent mismatch in optimal barrel twist? I could save the initial 200's until the new barrel which should be due at the end of this season.

Will be time to buy a large supply of brass and bullets for this year in another six weeks so feedback from the experts here would be appreciated.

 

[Berger.Fan222]

Your conclusion is sound if you are shooting at lower elevations or sea level. But above 3000 ft, you should be good to go with the 1 in 11" twist and the 200 grain hybrid.

 

[CH Luke]

Excellent advice that makes sense. Thanks.
Here's what I think I'm going to do for the remainder of this barrel which I think runs along with this advice.
1) Test Juggs in Palma brass which I suspect will be able to duplicate the standard Lapua brass performance with a bit more primer pocket life.
2) Keep 100 Palma brass just for testing 200 Hybrids.
My local club allows me to test just about any day up to 200 and 2-4 times per month out to 600. Once I'm happy that both are as good as I can get them it's off to the 1000 yd range to prove to myself which one is my match round.

FYI. Had a bad test today. Turns out I had mixed up some of my older and newer standard Lapua brass while cleaning it and it got mixed into my last batch for sizing and priming. Turns out about 75% of the older brass had over 10 firings on it and was due to be retired according to my Ballistic Tools Swage Gage.
Needless to say the first one blew the primer (running 2708 with a 200 Hybrid) which I could not find until I got it home and disassembled and brought some bright light to bear.
Knowing you have some experience with this round here's a question on loads. I see Berger recommends a lower max with Varget on the 200 (39.9) than the Juggs (41.6). My favorite powder is H4895 that Berger calls for 40.5 max (less than Varget). I don't have Berger's recommended max on H4895 for the 200 Hybrid yet but gave a call in to them.
My efforts on Juggs with H4895 took me to 2.5 - 3.0 grains past their max of 40.5 for my best node. Logic being Berger has to cover themselves for SAMMI chambers which I do not have. Here's the question part.
What do you think about starting my 200 Hybrid testing with the new Palma brass at whatever the H4895 max is and working up in half grain increments? Thinking that 2675-2700 sounds like desirable velocity and based on the velocity of the one round today (2708) I suspect I will need to eventually test as far up as about 42.5 grains of H4898.

 

[CH Luke]

IMO, H4895 may be a bit fast for 200s, but I've never tried that combo. With Palma brass it might work fine. Most of the people I know that regularly shoot the 200s are using Varget. H4895 will usually net you about 20-30 fps higher velocity at the OBT node than Varget, but that slight increase in velocity may also come with increased pressure if your freebore isn't optimal for the 200s. Not a problem in standard brass if you're not running them right up close to MAX, but that can kill the primer pockets if you are. So Palma brass may well be the ticket.

I have a load for 185s with H4895 that is running ~2760-2770 fps out of a 30" barrel. It is very close to an OBT node and shoots very well. However, that particular rifle has suboptimal freebore for the 185s (.085" fb). With 185s seated at .015" off, the boattail/bearing surface junction is above the neck/shoulder, but just barely. According to Quickload, that load is somewhere close to 61 K psi. With a more appropriate freebore for that bullet (~.150"-.170"), the pressure would be significantly lower. As you might imagine, running that close to MAX pressure means that even little things like a new lot of 185s that was ~.025" longer has a much bigger effect on pressure/velocity/brass life than it might otherwise. Typically, that load has been in the 42.5-43.0 gr range for H4895, depending on lot-specific factors. Although the 200 Hybrid is certainly "more bullet" than the 185, I'd guess that with the proper freebore and seating depth, you might not be too hot running those up to 42.5 gr of H4895, but you'll really need to be careful and work up gradually. My guess would be that velocities much in excess of 2700-2725 indicate pretty stout loads with the 200s, with 2650-2700 fps being more along the lines of what I know others have been getting with 30" barrels using Varget. If you're not using Quickload, just watch your velocity and keep an eye out for pressure signs. With the Palma brass, they may be harder to spot, so velocity might be the best indicator.

Thanks very much - again. This will be on the bench with me Friday night when I start this weekend's test builds.