Lapua scenar 139g HPBT for 6.5 x 55 bullet flight

[maver]

Hi There,

OK I am by no means a bench rest shooter but I like to shoot from prone or the bench to see what my bullet load and gun can do at 100 Metres.  I was expecting that at least it would be dropping in on top of each other within half an inch group at least but at 100 Metres this is not the case.  Do you work of the same theory that I have been told which is:  The 139g (or other similar weight) HPBT bullet over 100 Metres has not yet settled into flight until it gets out to around 200 yards or so travelling at around 2600 fps. 

Your thoughts and experience on this topic is much appreciated.  Unfortunately I do not have easy access to shoot further than 100 Metres at present to test the theory for myself.

[GTKF]

I use Sierra 140 gr HPBT in a 260 Rem at 2775 fps. It shoots 3/8 MOA at 100 yds. Don't think ther's an issue with it settling. Is the twist rate fast enough (1 in Have you done much work to develope the load with the 139s

[maver]

Hi GTKF

This weekend I just got my hands on my new RCBS Chargemaster 1500 and I love it.  I put together about 20 rounds each of the following for the 6.5x55 steyr pro hunter II

139g lapua scenar HPBT
Lapua brass
45gn, 45.5gn, 46gn, 46.5gn and 47gn of Vhitavouri N560 powder
CCI large rifle primers.

The results at 100Metres from the bench resting on a harris bipod were from one extreme to the other.

I believe my shooting of the bipods hold and trigger control was very similar with all the rounds fired so I can only assume that it was the powder charge that made the difference as I used the same bullet seat depth for all the rounds...it was 80.02mm but this varies when measuring the OAL as bullet tips tend to vary the length.


With the 46gn and 46.5gn I seen the best results with 12 shot groups.  With 45gn 45.5gn and 47gn they were well open at 100 Metres.

see following posts with attached photos

[maver]

46 46.5 and 47 grain loads

[yankee]

You are on the right track.  I would try 5 round batches then work with what works best.  I forget what the twist rate for the prohunter has, that may or may not be a problem like many American rifles that are twisted to slow.  The lapua 139 is a long bullet almost identical in preformance and shape to the sierra 142.  It is a bit longer than the 140 sierra that gtkf mentions.  Look at your best groups and work with the seating depth, usually longer or closer to the lands is better. You may be limited to how long you can go by the magazine length.  You can try cartridges longer than the magazine by single loading them. If you find they are a lot better shooters you may have to go to a shorter bullet such as the sierra 140 mk which has a different shaped ogive. 
 My feeling is that if a bullet is not spinning correctly when it leaves the barrel it will not get better, in other words if it isn't shooting good at 100 it will not shoot good at 200.
There are many variables that make a rifle shoot or not. 

[maver]

shame on me ..i do not know the twist rate in the pro hunter.  well i cant recall it and where I had read it.  I must have a look in more detail.

I will do a little work in seeing how far out i can seat the scenar 139g in the case neck and ensure that it fits in the magazine also.  Do you think that if I get it seated out to its safest point that I should crimp it also.  I use a Lee press and have the Lee crimp.

i will have to get my hands on a few sandbags to rest the rifle on as a bipod is not the steadiest and with no rear support on the butt a sandbag might give me better results...

[yankee]

Don't bother crimping you can cause some other problems you don't need now.   .003 to .004 inch difference between sized and loaded neck diameter will be enough to hold the bullet securely.  I look for about 1/16 to 1/8 inch in front of the tip of the bullet to the inside of the magazine case with the case head of the bullet against the rear of the magazine.  Another rule of thumb for seating depth is to have the bullet seated into the case at least one bullet diameter.   My first sand bags were the legs cut off of an old pair of jeans. Sew one end then fill and secure the other end. Have fun.

[maver]

After a little bit more reloading and getting my hands on a friends front rest and sandbags I have come upon a great little 5 shot group at 100M.  Although I have left out the not so great groups so perhaps it might be down to trigger control and a little cant on my scope) for the same load and seating depth.

Have a look at attached pic(sorry its a bit blurry but was taken too close by a camera phone).

6.5 x 55 steyr prohunter mark II
46g Vitavuori N560 powder
fireformed lapua brass  - cleaned and prep'd
lapua scenar 139g HPBT
COAL 80.02 mm. (about 3.15 inches) measured from bullet tip to case head - I have ordered a sinclair hex bullet comparator so this might give me more precise measurements as most bullet tips give different results due to them being tossed around in the box.

I also got a great wee group (photo not included at this time) with all the above except for 46.5g powder and bullet seated out a little further at 81.5mm (3.20 inches).