6BR Load Dev, Velocity and Heavy Bolt Lift

[RangeDust]

I did some load dev yesterday with the same powder charge just different seating depth. On the rounds seated deepest I got a very heavy bolt lift. Brass vas virgin, never fired, never sized. I am prepping this rifle for PRS and I want the lightest bolt lift with a accurate load. So far the most accurate groups were at 30-40 thousand off the lands. Should I back off the powder charge a bit? From what I read most PRS guys back off the velocity a bit in order to have a less recoiling load.

My BTOG is 1.835
Powder charge: 30gn Varget
Lapua SP virgin brass
Berger 105 Hybrid
Barrel: Bartlein 1/7.5 twist 26in. Brand new barrel (zero rounds)

BTOG | Velocity (10thou increments)
1.835 - 2791 fps
1.825 - 2787 fps
1.815 - 2783 fps
1.805 - 2786 fps (most accurate group 30thou of the lands) 0.14in
1.795 - 2796 fps
1.785 - 2764 fps
1.775 - 2841 fps (heavy bolt lift)
1.765 - 2848 fps (heavy bolt lift)

BTOG | Velocity (5thou increments)
1.800 - 2770 (second most accurate group 35thou of the lands) 0.20in
1.795 - 2777 (third most accurate group 40 thou of the lands) 0.23in
1.790 - 2772
1.785 - 2781
1.780 - 2781
1.775 - 2789
1.770 - 2788 heavy bolt lift
1.765 - 2774 heavy bolt lift

 

[HTSmith]

You probably should have started lower but now that you are at 30.0 Gr, I really don't see a need to reduce. As you seat deeper, you are reducing the size of the combustion chamber--thus raising pressure. Also new brass can be quirky--I've had pressure on the first firing and none after the first resizing. Your velocities are not at all out of line. I'd say roll with your 1.805" load. Be prepared for different results with fire formed brass. Just my $.02

 

[RangeDust]

You probably should have started lower but now that you are at 30.0 Gr, I really don't see a need to reduce. As you seat deeper, you are reducing the size of the combustion chamber--thus raising pressure. Also new brass can be quirky--I've had pressure on the first firing and none after the first resizing. Your velocities are not at all out of line. I'd say roll with your 1.805" load. Be prepared for different results with fire formed brass. Just my $.02

I went with 30gn as its been a proved load here on the forums. And I know its not over the limit. I will re-test with the sized cases and see what happens.

 

[cbrown1050]

In all of my 6br rifles just under 30 has shot the best. 29.8 grains of Varget with a 105 barts hammer or a 105 hybrid shoots the best. The hybrid is at a 15 thou jump

 

[RangeDust]

In all of my 6br rifles just under 30 has shot the best. 29.8 grains of Varget with a 105 barts hammer or a 105 hybrid shoots the best. The hybrid is at a 15 thou jump

I will test this load. Thanks very much.

 

[Kracken McGraw]

I will test this load. Thanks very much.

Since you already have gotten a good seat depth, you might learn some from just powder charges pretty quick from say 28.5 on up to your original charge.

 

[RangeDust]

Since you already have gotten a good seat depth, you might learn some from just powder charges pretty quick from say 28.5 on up to your original charge.

Got it. So do a 0.2 or 0.5 grain increments from 28.5 to 30 ?

 

[Kracken McGraw]

Got it. So do a 0.2 or 0.5 grain increments from 28.5 to 30 ?

.3 would split it up some over .2.

 

[LCazador]

After shooting the 6BR for more than 50 years I can say that it's best to fireform cases first with a moderate load and then work up your loads. Also uniform primer pockets to a consistent depth. I use .012" depth which gives me .006"-.007" seated primer depth. Additionally trim all the fireformed brass to a consistent length. I've always used magnum or Remington 7 1/2 primers with that primer pocket depth. Keep a constant eye on head diameter and don't exceed .0008". Brass volume has become very inconsistent of late.

 

[Kracken McGraw]

Keep a constant eye on head diameter and don't exceed .0008".

When you say this, if it gets over that number your load is to warm?

 

[LCazador]

When you say this, if it gets over that number your load is to warm?

Yes. If you continue with that load you will ruin your brass! It's the only way to monitor pressure properly. Waiting until you blank a primer or till you have heavy bolt lift is too late. With all that said the one thing that kills the 6BR is improper die set up and improper brass uniformity for each chamber. One of the successes of the 6PPC is that the brass had to be fireformed to that chamber from 220 Russian brass. So every piece of brass matched the chamber to start with. Nowadays guys buy a box of brass and immediately start load work before brass is even fireformed. There is no guarantee new brass is even close to your chamber size. A sizing die doesn't touch this part of the brass so you're stuck after you overexpand.

 

[Kracken McGraw]

Yes. If you continue with that load you will ruin your brass! It's the only way to monitor pressure properly. Waiting until you blank a primer or till you have heavy bolt lift is too late. With all that said the one thing that kills the 6BR is improper die set up and improper brass uniformity for each chamber. One of the successes of the 6PPC is that the brass had to be fireformed to that chamber from 220 Russian brass. So every piece of brass matched the chamber to start with. Nowadays guys buy a box of brass and immediately start load work before brass is even fireformed. There is no guarantee new brass is even close to your chamber size. A sizing die doesn't touch this part of the brass so you're stuck after you overexpand.

Thanks, that’s great knowledge from experience that you have shared.

 

[RangeDust]

Yes. If you continue with that load you will ruin your brass! It's the only way to monitor pressure properly. Waiting until you blank a primer or till you have heavy bolt lift is too late. With all that said the one thing that kills the 6BR is improper die set up and improper brass uniformity for each chamber. One of the successes of the 6PPC is that the brass had to be fireformed to that chamber from 220 Russian brass. So every piece of brass matched the chamber to start with. Nowadays guys buy a box of brass and immediately start load work before brass is even fireformed. There is no guarantee new brass is even close to your chamber size. A sizing die doesn't touch this part of the brass so you're stuck after you overexpand.

If the brass is over expanded doesn't the Redding small base made to fixed this problem?
On the case head diameter, is fire formed brass your point of reference or new brass ? Thanks.

 

[Bill Norris]

If the brass is over expanded doesn't the Redding small base made to fixed this problem?
On the case head diameter, is fire formed brass your point of reference or new brass ? Thanks.

Small base dies will fix the tight 200 line but it will do nothing for the expanded case head.

 

[RangeDust]

Small base dies will fix the tight 200 line but it will do nothing for the expanded case head.

If I understand well, if I have a case that continues to have a heavy bolt lift, that case is basically done?

 

[JFrank]

I wouldn’t worry too much, the case head would take a lot of pressure. I’ve hammered some cases without expanding to permanency.

 

[Bill Norris]

If I understand well, if I have a case that continues to have a heavy bolt lift, that case is basically done?

Probably will continue to have the click at the top of the bolt lift with that piece of brass.

 

[RangeDust]

Thanks all for all the tips. I will do another session with now fireformed brass and report the results. Do you recommend cleaning the barrel, leave it, or just clean the carbon with C4? The barrel has about 100rds so far.

 

[BW64]

29.8 with 105 Berger hybrids .005 off & .001 neck tension gives me 2867 fps. & about 1/4" group but 2nd & 3rd firing on brass. 26" barrel 1:8 no turn necks

 

[SKWERLZ]

I went with 30gn as its been a proved load here on the forums. And I know its not over the limit. I will re-test with the sized cases and see what happens.

Be careful with resized cases as you might find pressure even sooner than virgin cases.

26” barrel getting to 2750-2800 is pretty decent.