Interesting range trip.
I am working up a load for my 6.5CM shooting the 140berger hybrids, Norma brass, FGMM 210M primers, H4350. 2.125 CBTO and jumping about 0.080.
My rifle is a Terminus Zeus action, Bartlien Med Palma cut to 19.4inches. I am shooting the ladder test with my TBAC Ultra 9 on it.
I got up to 44gr, 2,668fps, and no pressure signs. Bolt opened easy too. This is the first I’ve done for a 6.5CM. I’m very surprised. I feel like I saw a lot of folks saying they stopped lower. Heck, my 6.5x47L stopped at 40.3grs.
I am going to keep going up. I am trying to get 2,740fps to make the NRL Hunter Power factor.
Does anyone else have a load at like 45gr of H4350 for 140gr Berger hybrids?
That is high for a SAAMI chamber. And very fast for a sub-20” barrel.
Unlikely - but possible explanations:
1) Could be that your chamber or freebore dimensions might be rather roomy. Could be the chamber is oversize, or the freebore is longer than normal, or a bit of both. Maybe check your twice fired brass (diameters and case head to shoulder datum) against fired brass from another factory rifle in the same caliber. Could also measure water volume with a scale as long as overall case length is identical. Range pickup might be a place to start if you don’t have a buddy running the same caliber.
2) Could be that your brass is thin skinned. Very unlikely as Norma is usually rather thick and strong brass, and tend to pressure out sooner.
3) You could be the lucky recipient of a “fast barrel”. Bartlein tends to produce a few of those every week. [It seems they don’t know how to reliably replicate this happy accident, so don’t call them and ask for a fast barrel...]
4) Your powder batch might be off on burn rate. Back off two or three grains and do another pressure test: Ask a buddy to load say a 5 round ladder for you using his (different) batch of H4350. Load a 5 round ladder test for his rifle using your powder. Should tell you somethig!
5) Your primer batch might be on the weak side. Very unlikely. Of you want to be sure, switch primers and repeat your pressure test. I would not bother with this.
6) Bullet diameters are generally very accurate because the dies that are used to make them are precision ground. [Major safety issue if these dimensions vary too much, so the QA folks watch these carefully]. Have seen some manufacturers that make sequential batches that vary 0.1 or 0.2 thousands of an inch. Could not detect a speed change as a result. Easy to check if you have a micrometer, but incredibly unlikely for Berger bullets.
7) Not to be insulting or anything like that, but you might have subtle pressure signs and you might be missing them. Many rifles need to be seriously over max pressure before bolt lift becomes tight. Extract say 10 primers, put them under a magnifying glass with good lighting, and see if you have “muffin tops”. You want to see good radius on the primer edges. Or take a sharp photo with a macro lens and zoom in, alternatively use your bore scope, that works well as a cheap macro lens. Primers often provide the first pressure sign. Some rifles will show primer cratering due to the firing pin hole not being a tight fit, some will not.
A cautionary tale: Have used Lapua brass for years now. Superb quality and very strong. Found a 41.5 gn load of H4350 that shot the 140 gn Hybrid very well. Never seen any pressure signs with that load and used it for months. Then on a whim decided to square the case heads as an experiment to see if that made a difference to my results, as i already had the equipment (LE Wilson mini lathe, and all the cutters). Case heads lost some of their lettering as the case heads were (apparently) not perfectly square. [Or the Wilson case holders are not perfectly concentric, a real possibility.] Post tumbling, i suddenly realized that half the cases had clear full circle ejector marks on them. Not bright shiny marks, but still a full round circle, but it was a very shallow indentation. These marks were too feint to be visible on the lettering before. Now they were very visible. The load was probably slightly over pressure, i just did not know it. Backed off 1.0 grains and the ejector marks went away (and sadly group size opened up to 0.7”), eventually found the next lower node around 50 fps lower down.
And nope - squaring off the case heads made zero difference to my group size…. I don’t think the Wilson setup is accurate/concentric enough to do this properly. [Messing with powder charge did make a (very negative) difference!]
Btw: Have three rifles in 6.5 CM, and when new, all of them hit max pressure below 42.0 gn of H4350. The older barrels with 2,500 rounds (or more) on them need 0.5 gn (or a bit less) to hit max pressure, and speed is mostly similar to what these barrels delivered after 200 rounds. More freebore lowers pressure due to the erosion of the lands, allowing for more powder.
Do you know your freebore, was the barrel throated for 140 Bergers Hybrids - or something else?
