TJC

It has no discernible impact in shooting sports.

Me neither without RS60, perhaps someone else will chime in. Average for 6.5 CM should be 2500-3000 but if you’ve been pumping them out at 3000 FPS with N550 then that could be it, i bet you’ve got some throat erosion ? I’ve heard good things about the 147 but you have to put them down at 2700+ to get optimal stability from a 1:8 twist, 1:7 seems to be a popular option for this particular bullet.

Thanks. So it could be down to both round count and Lot variation in addition to 50 FPS or so of the difference coming from the change in temperature. 2000 is a little on the low side to see velocity drop off so much especially if you’ve only been pushing a 139gr at 2800 but it depends on the barrel and how you’ve shot those 2000 (ie rapid hot strings) rounds. Throw in a little variation in Lots and that could explain it. If you want to keep the barrel but push for more velocity then you could try N550. You shouldn’t need as much powder which will help avoid the crunch issue you described. I’ve moved to buying components in bulk to avoid the Lot variation issues. Something to consider for the next barrel but it’s expensive upfront.

I doubt this is just temperature driven. 1>30C is approx 34F > 86F, a 52F change. If you said your velocity was c50 FPS different I’d imagine it would be temp driven but a 140 FPS change or 3 FPS per 1F is possibly too great. Some of the most temp sensitive powders are about 1FPS per 1F. I do think RS62 is more sensitive than they claim but not perhaps this much ?? How many rounds do you have through the barrel ? Are you using the same Lot of powder ? There have been reports of considerable variation in Lot to Lot consistency with RS powders.

So you are consistently getting 0.3 MOA with an ES OF 99 and SD of 28 !!! You aren’t going to be anywhere near 0.3 MOA at distance.

I went to a course in the US. I was the only one shooting a SFP MOA. Learnt the hard way and now only run FFP MIL.

Large primer. Tried some new loads. Incredibly there was no pressure signs. 44.5 2955 44.6 2964 44.7 2951 44.8 2969 44.9 2976 45.0 2978 45.1 2994 45.2 2989 45.3 2992 45.4 3013 45.5 3004 I’m backing down to a 2800 FPS load but interesting to see.

When do you get it ?

Very nice rig. Tubb has been at the top of the game for a long time now.

Me too for .308 /.260 / 6.5CM thx

26” + mod.

Don’t think so. Def no crunch on bullet seating and I load them pretty long ie over 2.90” OAL. I was just testing a couple of loads and will be backing down. Thx

What is your RS62 load with the 139gr and what velocity does that produce ?

I tried RS62 today for the first time in my .260 with the 139gr Scenar and was surprised by the velocity. Temp 75F / DA 1385 Three shot average velocity FPS: 44.5gr 2948 SD 11 45.0gr 2978 SD 9 I wasn’t expecting it to be nearly this fast...should I have been at these loads / is this typical for RS62 ??

Thanks !

Very interesting although a 7 degree spread isn’t perhaps wide enough to measure esp at the extremes of temp change. I’ve been testing VV N550 at 20F to 95F and found quite a lot of sensitivity with the same load lot / same number of rounds through the barrel with ES/SD remaining very constant. Just trying to understand if RS62 behaves consistently / linear at the extremes or whether it exaggerates at either end ? It sounds pretty stable in the mid-range for sure. Good thread btw.

I was wondering if you’ve done any detailed testing re temp sensitivity and how groups/ES/SD evolve at material changes in temp ? Thx

These look to be pretty interesting. A 6.5 bullet that can stay ballistic out to 2,000 yards. Expensive but a tool in the locker for specific circumstances. If anyone is ordering some or hears of a European importer I'd love to pick up a couple hundred. Thx