Slow BR? Pressure Signs?

[mattri]

6mm BR in a 26" Shilen .272"

To avoid pressure signs am using a 27.8gr H4895 load under a 105gr A-Max. 28gr shot well but saw spikes in warmer weather.

Tried some "go to" loads with Varget and again was too hot.

27.8gr of H4895 yields 2725fps with an ES of 11 and an SD of 6.

Load is very accurate and stable, just slow.

Cannot seem to push for higher velocities without running into pressure issues- seems like maybe a slow barrel or??

Just shoot it as is?

 

[noload]

I do not know why you are getting pressure with those loads, check your neck clearance. Check for Carbon in neck area of the chamber. Whats the twist rate. Something is keeping the bullet
from going down the barrel the way it should, Powder scale accurate?

 

[mattri]

1:8 twist, borescope shows a clear barrel, no neck interference and scale checks out- gun shoots great, just slow.

 

[dmoran]

Chronograph?
And how does it compare to actual target drops.

 

[memilanuk]

What kind of pressure signs? Cratered primers, or ejector wipe / sticky bolt?

If its the latter, yep, you got problems.

If its the former, without the other signs... contact Gre-Tan Rifles and send your bolt to get the firing pin hole bushed. That will effectively eliminate the cratered primers.

 

[mattri]

D) all of the above

Chonographed strings confirmed over and over.

Drops from 200-600 are dead on.

 

[Changeling]

This doesn't make sense! Have the cases been trimmed back enough the correct amount for the cartridge length relative to the length in the chamber ?
Are you using a 6mm barrel or a .22, I would spec the internal barrel size? Is this a brand new setup?
What kind of pressure signs are you getting, you never answered that question?

 

[BradY]

How many rounds down the barrel?

 

[gotcha]

What brand of Brass ??? ........... .236 or .237 bore ??

 

[mattri]

6mm .237 Lapua brass 600 rounds down the barrel, its always been slow.

Sticky bolt, cratered primers, swipe marks on case heads.

The 2725 load is accurate, stable and no signs of pressure.

Not super worried about it but thought it was interesting enough to post.

 

[BradY]

Might just be a slow one then. My last couldnt get above 2850fps and 28.4gr of varget without marks on the brass. And it was a 30 inch barrel. This latest one is only 30 rounds old but doing 2830 with 29.2gr varget and Im expecting a speed increase around 100-200 rounds.

 

[stansrifles]

I have never owned a 6mmbr what is the maximum velocity obtained with the 105 grained bullet accurately.Stan

 

[comagutsa]

Might just be a slow one then. My last couldnt get above 2850fps and 28.4gr of varget without marks on the brass. And it was a 30 inch barrel. This latest one is only 30 rounds old but doing 2830 with 29.2gr varget and Im expecting a speed increase around 100-200 rounds.

Brad my 6BR is getting 2907fps with 30.3gr of 2208/varget with the 108gr bergers with magnetospeed 30" barrel (just checked yesterday haha)
and 2950fps with 30.6gr of 2208 105gr berger hybrids ,, i start getting slight pressure at 30.8gr

cant wait to face off with ya haha

 

[BradY]

Your BR is a freak. Im bringing the 284 next time!

 

[fm1947]

Shilen 6br a little tighter run a bit slower

 

[mattri]

Interesting- I didn't know that.

Very happy with rifle and the round, people are thrilled when they get a fast barrel, mine as well embrace the slow ones too. It seems to really like the A-maxs but may try some SMKs just for kicks.

Built the gun primarily to eliminate variables so as to focus on wind reading and shooting form/technique. Semi successful- as it turns out the rifle/load is pretty accurate and stable- but unfortunately I really suck at the rest

 

[boltfluter]

I have a slow one as well. Drives tacks at 2700 fps with a 105 Berger VLD. Drops confirmed to 750 yds. Using Varget. Will go faster but opens up. Any suggestions?

Thanks, Paul

www.boltfluting.com

 

[fm1947]

I guess the question would be do you prefer accuracy or speed if it drives tacks , then thats pretty good

 

[carlsbad]

You need speed in wind. 200 fps makes a big difference when you're cutting through wind. My 6br barrel is relatively slow too. It is a 30" 1-8tw Brux. I'm using 28.5 grains of N150 and shoots a lot of 1/4" groups at 100 yards. Very accurate at 600 yards too. but when the wind starts gusting, those with less windage adjustment hit more targets than I do.

I'm going to try some slower powders to get more velocity without pressure signs. I have bushed my bolt and don't really have firing pin issues but don't like flat primers and hard bolt lift. --Jerry