6.5CM/RS62 Updates

[VarmLR]

I thought it might be of interest to those dipping their toes into 6.5CM to share ongoing data.

I have now put around 400 rounds through the TAC A1 and the barrel seems to have gained velocity quite considerably over new, with velocities checked every 100 rounds.

I have also logged chrony'd velocities with temperature all with the same load.

Results as follows:

139 Scenar, 44gr RS62/SR Lapua brass/Murom KVB223 Magnum:  10shot strings.

New barrel/fresh brass/5 degrees C                      2633fps           31ES/SD10 (not good on any level)   

200 Rounds/1F brass/10 degrees                          2650fps           16ES/SD9

350 Rounds/1F brass/22 degrees                           2701fps          15ES/SD6

400 Rounds/1F brass/24 degrees                           2707fps         15ES/SD5.8 

I haven't batched bullets or brass and haven't loaded to any greater tolerance than 0.1gr so the stats are respectable enough but can be improved to get everything into single figures with a little more care.

Temp sensitivity appears to be 4 to 5fps/degree which is a surprise as I had reckoned this powder to be less temp sensitive than viht,;  however, how much of the velocity increase is due to the barrel speeding up with bedding in and how much is temperature related is a moot point so probably not worth drawing too many conclusions.  Incidental comparisons with a shooting colleague using LR primers in 6.5 gave 100 fps more (24 degrees C) for almost 1 full grain less powder (same barrel length).  The trade off using SR brass is longer brass life but less velocity potential.  I was shooting 100% fill ratio loads so 2700fps seems to be the limit with SR brass in my rifle with RS62.  I could seat out another 20 thou and compress loads slightly and probably make 2750 to 2800fps max. but it isn't worth going to extremes for the pressure rise.

I will update this post further when I have another hundred or so rounds through the barrel just to double check that the increases have been more related to barrel bedding than temperature issues but my own conclusions are that for the ES/SD I'm achieving, it is not worth going to SR brass for CM when many people now seem to get 10 or more reloads from good quality LR brass for less powder used and similar SD results.

[frogfoot]

Very interesting post, I would be very interested to see velocities when the temperature starts to drop, so we can get a handle on whether the velocity increase is due to temp or barrel break in.

[No i deer]

Sounds like a job for RS60.

By the time you settle on a load the barrel life is diminishing quite fast.i guaranttee you RS60 will give you great velocities and accuracy you want.it was superb in my 6.5x47 when I tried it out of curiosity and I ran a hunting load with 140gr amaxs. I had a boat load of H4350 then for target work.ive enough left for about 35 loads now ?

[VarmLR]

I don't quite see the logic there as RS 62 is single base (unless comparative load results are for way less charge using RS60), lower energy and the conclusion is that reverting to LR brass and RS62 will give more than adequate velocity for what is a very slippery bullet.  43gr of RS62 in LR brass is not that stiff a load.  Most of my shooting is sub 700 yds with perhaps once monthly incursions to 1000 and at that range I have no problems with accuracy using that powder...it's one of the most accurate load combinations that I've shot in fact.  I guess the point is that I can't really see much benefit in using SR brass but am quite happy using RS62.

[No i deer]

Looks more like velocity gained from temperatures you recorded.i am not really sure what your trying too acheive if you think barrel is speeding up.if you entered correct weather conditions in your your bal cal poi will be very close.after the 600yds shoot at bisley 2 Sunday's ago I fancied trying my 284 with my 162gr amax load out at 600yds to see how accurate it was and how the balcal would do.cold bore shot was 3 inches low bang on line.i adjusted up and fired 3 more shots that were very good indeed.

[VarmLR]

First shot POI was very close.  The barrel has gained some velocity with bedding in which is no big surprise.   Temperature likely counts for most of the observed velocity gains the other day.  Bullets were kept in the shade where ambient temp was about 22 degrees.  I am not really trying to achieve anything....just noting and sharing outputs from SR brass loads for comparison with LR brass.  Velocities are on the nail for the purposes but not being reached as efficiently as for LR brass loads which I will be returning to and sticking with when this brass batch is done.  For the moment, accuracy is very good, the app has been calibrated with observed shot data over a wide temperature and distance range so the app data for the bullet is now on the nail.

[Tomo999]

I've just tried some Morom small rifle primers (KVB-223) for the first time in my RS62 / Lapua Scenar 139gr load development tests, and I was suprised at the drop in FPS (I also tweaked neck tension so this may well have had an affect too) 

24" barrel / 1:8 twist / 1200 round count.

I weight sort bullets and primers.

Using Lapua SR cases that are on their 5th reload.

best results were from 43.60grs RS62 seated 15 thou off the lands.

1st string of 5 shots - SD:3 ES:8

FPS          TEMP  

2668          63F   

2668          65F     

2670          66F

2676          66F

2675          64F

 

2nd String of 5 shots (shot later on in the day) - SD:1 ES:4!!

FPS          TEMP

2686        79F

2687        82F

2684        83F

2683        84F

2687        82F

 

Worst string of 5 shots was with 43.70grs RS62 seated 3 thou off the lands & with slightly different neck tension - SD:10  ES:29

FPS      TEMP

2726     81F

2732     85F

2716    84F

2745    84F

2732    82F

Interesting results; I was expecting 2720-2750fps with the 43.60gr load so I was a bit suprised at the low scores. 2680-90fps will still take me out to 1100 yds though before going transonic, so I'm going to replicate more of these 43.60grs bullets and try them out on a club day @ 900 yards on 02.06.18. I too am beginning to suspect slightly more temp sensitivity with RS powders.

 

 

 

 

[VarmLR]

All mine are loaded 30 thou off and there is a fairly large sweet spot between 43.7 and 44.2gr where ES is lowest, so your results pretty much mirror my own findngs.