frustrated with 6BR velocity

[john1c]

I'm sure most of you have seen Hodgdon's load data for the 6BR loading Varget and 8208 XBR shooting the 107gr. bullets:

Bullet Weight (Gr.) Bullet Diam. Min. Grs. Vel. (ft/s) Max. Grs. Vel. (ft/s)
107 GR. SIE HPBT Varget 26.0 2367 29.0C 2620

107 GR. SIE HPBT 8208 XBR 24.0 2380 26.7 2555

According to data provided by Hodgdon, Sierra, Berger, etc. my loads seems pretty right on. So just how do you guys manage to get such high velocity in the 2850+fps range with those two powders?

I shoot a rem700 with an 8t, 3 groove, .094 freebore, .272 neck, 27” Pacnor super match barrel. And here are two loads that will create a bit of pressure, ejector mark and cratering:

Berger 108
Varget - 27.5gr
Wolf SRM
Lapua (shoulder bump .002)
0.010 from land
Velocity – 2618

and

Berger 108
IRM 8208 XBR – 26.9gr
Wolf SRM
Lapua (shoulder bump .002)
0.010 from land
Velocity – 2648

I know some of you will say not to worry about the velocity and just focus on accuracy but the velocity is important to me when shooting out to longer distances. And to make things difficult, I don’t want to try other powders as I already have a lot of varget, 8208xbr, and benchmark.

How many of you are maxed out shooting at such low velocities? Do I just live with it? Get another barrel? What?

 

[Bob3700]

John,

First thing I would do is shoot over another chronograph and get a second opinion on the velocity issue.

The first chrono I shot over gave me very low velocity and I was disappointed as well. Turned out the chrono screens were not the correct distance apart and that gave incorrect readings.

Second, WIth the BR, I would send my bolt to Ger-Tan and have the firing pin bushed to the smaller size. This will help greatly as far as pressure indications on the primer. Rem firing pins are large and the hole around them larger and show cratering with the least bit of pressure. The Wolf SRM is the ticket as that I what I use in my BRX.

Your freebore is a little short for 107 gr bullets. Most will be up in the .104-.115 inch range and yours is cutting into your powder capacity.

Give a different chrono a try and see what you get. I would expect mid 2700 fps from your load. Ger Tan also has fast turn around service on the bolt bushing.


HTH

Bob

 

[JLM]

John,

I shoot 107 smk's over 28.9 grains of Varget with CCI 450 primers. I have a Savage Target action and a Benchmark barrel. .100" freebore. Stockade Rifle did the work for me. I went with less freebore because I thought I'd have a need to shoot lighter bullets, and I wanted to be sure I could get a decent seat in the neck.

I don't have a chronograph. When I worked up loads we started at 27.4 grains and went up from there. Groups noticeable got tighter at 28.9 and opened up at 29.3 so I settled there and couldn't be happier. There may be another node for me with more powder, but it's been so much fun to shoot I really haven't had the desire to mess with it.

The best I could come up with velocity was getting zeros out to 500 yards and then messing with a dope spreadsheet and I come up with about 2850 fps.

I'm kinda with you. There's guys stuffing 30 grains of varget in a case with 107's. I think I'd be compressing powder if I tried that.

Jeff

 

[MarkS]

John,

Same as Bob said in cratering. Br are bad to crater with a unbushed factory bolt. I am running 30.5 gr Varget in a Hall action to get 2800 f/s ( I punched this barrel to 6BRX and was getting 3050 F/S, but shot best at 2975 f/s). I have not used 8208, I think it would be too fast for heavy bullets, this may be one problem.

If you want the most speed for your BR, try RL15

Mark Schronce

 

[Travelor]

Your velocities are low due to your powder charges being low.

The usual warnings of working up loads in your rifle applies here.

The "sweet spot" load for a lot of 6mmBR's is 30 grains of Varget with a 105-107 grain bullet. I get velocities of 2950 +/- woith this load in two of my 6mmBR's. I have one 6mmBR with a tight neck chamber that will not shoot this load without showing definite pressure problems. I switched to VV550 and use 30.5 grains for similar velocities with no excessive pressure signs.

I have started using IMR 8208 xbr with a Berger 105 BT bullet loaded with 29 grains .030" off the rifling and am getting 2954 fps +/- 7 fps and excellant accuracy out to our ranges max of 600 yards.

George

 

[john1c]

Thanks for the response guys!

I have tried 2 different Chronographs (CED M2), same low velocity.

I should get the firing pin bushed to get the cratering resolved but that won't help with the ejector marks. Ejector marks are my main concern. I think I clean my barrel pretty good (using JB) but could it be that I still have carbon buildup and that's what is causing the pressure?

Could there be a 2-300 fps difference when comparing .094 to a .104 freebore?

I would love to load 29gr. of 8208xbr but that will scare the bajesus out of me. Especially when considering I am already getting ejector marks when loading 26.9gr.

I guess my questions are, is there something wrong with my rifle? Or is there something wrong with the way I reload, clean, etc.? Should I get another barrel or is the rem700 action holding me back?

 

[Moderator]

Some barrels are just slow. And, unfortunately. you can't necessarily predict by brand. I have a 27" PacNor three-groove barrel and it shoots about 2910 fps with 30.3 grains Varget, with Lapua 105gr bullets seated .015 into the lands.

One suggestion -- try the Lapua Scenars. They are skinnier than Bergers and Sierras and may work a little better in your PacNor barrel which typically have a very tight bore.

We've seen differences up to 150 fps in different 6BR barrels of similar length shooting the exact same load. Here's a test done with factory ammo:

http://bulletin.accurateshooter.com/2009/10/tech-tip-same-load-varies-in-velocity-with-different-barrels/

I DO recommend bushing the firing pin.

 

[Moderator]

There's guys stuffing 30 grains of varget in a case with 107's. I think I'd be compressing powder if I tried that.

NOPE. With a freebore of .100+ you'll have plenty of excess capacity at 30.0 grains. You'll probably hit pressure limits with Varget BEFORE you run out of capacity.

 

[TonyR]

I have a dummy round for my 6mmBR that measures 2.345 inches from the cartridge base to the bullet tip with a 107 SMK seated to touch the lands. The barrel is a 1:8 31 inch Krieger with about 1000 rounds through it. I start to get a sticky bolt lift as I approach 30 grains of Varget but I get about 2900 fps with excellent vertical from VV N540 and CCI450 primers without the pressure signs. The gun likes 29.5 gr Varget but I get better velocity and equal vertical with the N540. I am not sure how much speed you would loose with a 27 inch barrel. The 6mm Cartridge Guide on the home page of this site has some load data for N540 and I used that as my starting point. http://www.6mmbr.com/6mmbr.html

 

[Bob3700]

John,

I have chrono'ed three different custom 6mm BRs all with 28-30 inch bbls. They average 2800 fps with a 107 SMK and 30 gr of Varget.

Just my opinion, you really can't expect more than 2850 fps without running very high pressures.

I shoot a BRX and with 33.5 gr of Varget, 107 SMKs, Lapua, and Wolf SRM primers I average 3050 FPS. THe gun really shoots at that speed so there is no reason for me to go hotter. Could probably push 3100 fps but no need.

If you are shooting small groups, then I would be content with that. If you are looking for 1K ability, then you do have a problem. Give the bbl a good cleaning with JB, especially the throat and see if that makes any difference.

Bob

 

[LWolken]

The reality of the matter is that the 6br is a 2800fps engine with a 105gr VLD. Those who are getting higher velocities either have a long 28+ barrel, a fast barrel, or running alot of pressure or a combination of the above. My smith was able to push his gun into the 2900fps zone with N150? I believe. This is however a custom action with tight tolerances. 30 grains of varget in the same gun resulted in pierced primers in summer dog town conditions. The BR is a great chambering but if it was a 3000fps animal we would have no use for the BRX, dasher, xc, 6-6.5x47, 6mm Super, 6CM and all the others. Find a load that shoots accurately and safely and don't worry about the velocity.

Lance

 

[65BR]

The last BR I had, was a 26" Pac-Nor 3 grv 8t, shot 28.5gr Varget, mv 2850 w/Lapua brass.

Never tried another load, shot one group sub half inch at 330 yds, this was a Ruger No. 1 action..........

 

[Steve Blair]

FWIW:

Rifle: Savage 12F, factory 30" barrel, shot in 95° weather
Lapua case, 39.0 H2O
Sierra 107 MK, seated 2.385, just touching
32.5 Reloder 17, 4" drop tube into case
Wolf KVB-5.56M

2908.7 avg, 7.9/4.1 ES/SD
.389 @100 in windy conditions

No pressure signs and I have gone up to 34.10 with these components, but in cooler weather, around 50-60°.

 

[NorCalMikie]

John: Try loading your rounds (same load) with the bullets "jammed" into the lands maybe .005 or .010 and see if that makes any difference as far as pressure signs. In my rigs, jump will show pressure and it will go away with the bullets at a jam. YMMV.

 

[john1c]

Thanks again for all the responses.

I had a chance to take my rifle to Gary Eliseo and he was kind enough to boresight the barrel for me. Thanks Gary! He noticed that there is just a bit of carbon at the throat. To my eye, it's a tiny ring but Gary says that is most likely the reason for the excessive pressure.

So I went home and scrubbed the throat with some JB. This time instead of pushing my rod guide until it hit bottom, I backed out the guide a bit so I can really get at the throat.

Hopefully that will resolve the issue. I guess I'll find out when I get out to the range in the next couple of weeks. I'd sure be happy with a modest 2800 fps.

 

[strut64]

don't want to hijack thread but I thought Wolf primers were bolocked from being imported. Are they back on the market????

 

[dkhunt14]

don't want to hijack thread but I thought Wolf primers were bolocked from being imported. Are they back on the market????

This thread is 8 years old. Matt

 

[Bkluke]

I got rid of 2 CED M2’s because they were reading slow.