The start-6bra Load development

[R.Morehouse]

RL-15 may be your friend. 32.something is going to get you a very accurate 3k+ load with no pressure.......Well it works for me anyway..

Regards
Rick

ps: jam away...

 

[Clancy]

I don’t think you want to jam just a whole lot since you said this is a PRS build.... you have to be able to extract a loaded round.

 

[MDM]

Noted, although I've jammed .010 for many years and never had a problem extracting a live round. I once had a bullet get stuck and dumped powder into my action a couple years back. It was a 140 hybrid jumped .020, the cause was debris. Go figure.

I'm going to do a seating test at 30.3 h4895 and 31.4 Varget and see what happens. I'll post up the results when I get around to it next weekend. Thank you all for the help.

 

[KeithF]

30.6gr-31gr H4895 is the most common window. It’s hot and humid in north Mississippi. I’m at 30.7 and will fine tune from there. .008 jam with 105 HVLDs.

 

[Thumper]

It may not like Hybrids, try some Berger 108 BT's, very forgiving. From .020 off to a hard jam and I bet you will find a seating depth that shoots.

 

[pat fulghum]

By the way... both 28" and 30" tune somewhere in the 30.6 to 31.1 H4895/CCI450/Hybrid105 window.


108s need to drop it down at least .5 gr

 

[MDM]

Might be getting somewhere. Its repeatable at .013 jump and its also very good at 31.3. H4895 looks good at 30.2 and +.013 as well. Time to shoot them at some distance and see which one it like best.

 

[JohnMill]

View attachment 1057544 Might be getting somewhere. Its repeatable at .013 jump and its also very good at 31.3. H4895 looks good at 30.2 and +.013 as well. Time to shoot them at some distance and see which one it like best.

Unconfuse me please. Are you calling +.013 a jump?

 

[MDM]

Sorry. Yes. To update, I settled on 30.4 H4895 and this little round shoots incredibly well.

 

[gasph]

In the load testing I have done on a new 6bra Brux 8 twist my most accurate load has been 30.4 of h4895 and a 105 hvld set at 8/1000 jamb which was 1.767 CBTO. I am using cci 400 primers. Going higher on the powder charge did not improve groups. I am also going to try varget and r15 but have not shot them yet. I have a little over 100 rounds on it now and have tested at 100 and 300 yards.

 

[MDM]

I'm about to chamber up a 7 twist .236 bore Muller to put on another action. No real need for the 7 twist shooting 105 but it's what I have. Hopefully I don't run into more pressure running a little tighter bore and faster twist.

 

[JohnMill]

So I've got my first 6 bra going. 170 rounds on the barrel. Brass is fired in and ready for load development. 28" bartlien, .105fb. This is a bit of a different animal for me as I'm coming from years of shooting a 6.5x47 and know where to load it. Let's start of with establishing a "jam" number. My touch point is 2.810 with a 105 hvld, however, my jam number is 2.860. (.002 neck tension) This seems a bit excessive to me as it's actually .050 in the lands before the bullet is nudged back when chambering. Is that excessive?

I was thinking about trying Eric Cortina's method for this round of load development, so I'd be starting that with the bullets .030 in the lands to find an initial charge weight. I can say that I'm starting to see some pressure at 30.8 H4895 and 31.8 Varget. Those both seen to top out at 2930-2950ish for velocity.

If I wanted to try the method that Tim Singleton has posted a lot about - testing a high, middle, low load and seating depth all at once, where should my 3 charge weights be with this little guy?

I guess I'm looking for some tips on where to start if I want to do an initial charge weight with 4895 and what jam length. Fyi, this is a prs type build, no bench stuff. Open to suggestions on how to kick this load development off.

Best thing you could possibly do is kick that idea of "no bench stuff" out of your head (LOL) Seriously we are having a ball with the bench stuff can't imagine anyone wouldn't

 

[Nature Boy]

Pretty sure he meant I should have tried 30.8 and 31 in my initial H4895 test.

Nothing promising in my 4895 loads then?

I also used the Cortina method. Found the node at 30.8 of H4895, 2,930 fps using 108g Berger BTs

Looks like you have a similar node with less powder between 30.2-30.4 and similar velocity.

Finding a node around 2,930fps has been repeated so many times by so many people that it can’t just be coincidence.

I’d take 30.3 and do a seating depth test.

 

[Nature Boy]

Sorry. Yes. To update, I settled on 30.4 H4895 and this little round shoots incredibly well.

Didn’t see your update but it matches what I suggested. Shoot some at distance and let us know.

 

[10at6]

By the way... both 28" and 30" tune somewhere in the 30.6 to 31.1 H4895/CCI450/Hybrid105 window.


108s need to drop it down at least .5 gr

In my rifle the 108 shoots same loads and basic velocity as 107 Sierras and 105 Hybrids..never saw a reason to back it off

 

[FrankG]

I'm about to chamber up a 7 twist .236 bore Muller to put on another action. No real need for the 7 twist shooting 105 but it's what I have. Hopefully I don't run into more pressure running a little tighter bore and faster twist.

Be careful with the tight bore. Anytime you change the total surface area of the bore size you effect pressures. Groove will effect more than the bore but either way when you change it you effect it. Seen some test barrel in a 6.5mm where the groove and bore where .0005” undersize on each from min. Spec. Drove up pressures 8k-10k psi.

Twist for the most part has no effect on pressures.

 

[FrankG]

I just finally shot my 6BRA yesterday with formed cases. Prior to shooting it yesterday the barrel only had 47 rounds on it.

H4895 and 30.5gr.
107 tipped SMK
-.010” off the lands
Fed205M primer
7BR Rem. Brass necked down.

Shot them thru the chronograph. Averaged 2868fps (26” barrel, 5R, .237” bore, 1-7 twist). Shot a 10 shot group on one string and had a ES of 19 and a SD of 7. 9 of the 10 rounds went into a .368”. Dropped one round a little out the bottom but it was me. Cross hairs dipped when I broke the trigger. It was round #9. I’ll post a pic tomorrow.

Also shot the new 110gr. Hornady ATIPS thru it as well. Only had 22 bullets so I didn’t have a lot to play with. Used the same load etc...just a different bullet and got 2822fps avg. but had these in Lapua 6br brass and got a ES of 18 and a SD of 6. They also shot excellent. I didn’t have a lot of them and right away went to my 430 yard target. Came up 7min to start with and ended up taking off .625”. So ended at 6.375” for come ups (1/8moa click scope).

All I used was a bipod and a bag.

Jamming the bullets does not guarantee best accuracy and being your using the gun as a repeater in PRS type matches etc...I wouldn’t jam the bullets. You need reliability first. The range gets shut down and you are told to clear the gun and the bullet stays stuck in the bore and now you got a mess.

Later, Frank
Bartlein Barrels

 

[FrankG]

Here is a picture of the group and the rifle. The rifle is a early/mid 70's Savage 112V single shot. Was originally a .243win but of course the barrel was toast when I got it. Tuned/adjusted the factory trigger. Breaks clean and right at 3#.

You could pretty much call this our drop in Savage prefit barrels. When the blank got contoured before rifling etc...Justin threaded it at the same time.

Scotty in the shop chambered it for me and cut and crowned the muzzle as well as pillar bedded the stock.

On the action I bought a .250" thick recoil lug and after truing up the receiver face I had Todd double pin the recoil lug to the receiver in the cnc mill. Pinned the lug at the 3 o'clock and 9 o'clock position.

I trued/cleaned up the bolt face and shortened the ejector spring so the rounds don't eject out of the bolt when you open it and lapped the bolt lugs.

 

[FrankG]

Here is a pic. of the 110 Hornady ATIPS loaded.

 

[HTSmith]

Here is a pic. of the 110 Hornady ATIPS loaded.

That must be one long bullet. How much is in the neck?