Cold bore conundrum!

[jcerne]

Hi All,

I trying out a new bullet in my Savage target rifle and am getting the best groups from a cold bore, which I’ve never seen before in any rifle. Usually, the cold bore shot is off a little and then the rifle settles down, but with Bart Avenger 68gr boat-tail bullets, the opposite is happening. The rifle is a Savage Target action with a 26" Shilen stainless select match bull barrel (0 freebore, 14” twist, ratchet groove) in 6BR Norma. I’m using a load that worked well for Bart’s 68 gr Ultra FB and Berger 68gr FB Target. The load was: Lapua cases (annealed), VV N133 29.1gr, CCI BR-4 primers, with bullet seated at jam or 0.005” back from jam.

All the shooting was done at 300 yards with very light wind and a temperature of around 34 F. All the groups were five shots. On the first day (please see Target 1), the first group from a clean, cold bore was around 0.6” ctc, which made me happy. Then the groups started to open up.


I didn’t make much of this behavior until it happened again the next time I shot this rifle a few days later under similar conditions. The first group from a cold, fouled bore was about 1.0” ctc (please see Target 2), and then the groups started opening up. I didn’t the clean the bore before the second session since I only had 20 shots after the last cleaning and was curious to see how the rifle shot these bullets with the bore already fouled. On the second day, the bullets were at jam for the first two groups and 0.005” back from the jam for the last two groups.



I’m wondering if the barrel is expanding slightly when warm, making the bullet fit a bit looser and causing accuracy to drop? Or maybe, the powder/cases warm up a bit in the pre-heated chamber, causing a slightly higher MV, which brings the rifle out of tune? I doubt this is the case since I’ve never seen that much sensitivity to MV in this rifle, but I’m running out of ideas. The only thing I can think of is to try some other powder weights at 300 yards.

If you have seen this before and/or have any ideas what is going on and how to fix it, please let me know.

Thanks,
John

 

[NC/Br Shooter]

I'm curious too.

 

[cwebster]

I have a factory Sako 6ppc that does the same thing. 1st 5 shot group after cleaning the tightest of the day. It does it over and over. Go figure........

 

[boltfluter]

Before I changed anything powder wise, I would go .020 into the rifling. Just as a test, you may be pleasantly surprised. Good luck and keep us posted.
Paul

 

[RGRobinett]

Reading your, "<- slight wind", comment on the top right target, @ 300 yd., for a full value (9:00 O'Clock, or, 3:00 O'C;lock) wind, you should expect about 0.9" of wind-drift per 1MPH variation wind velocity: a quartering wind would about 1/2 of that, or, 0.45 inches . . . RG

 

[jcerne]

Reading your, "<- slight wind", comment on the top right target, @ 300 yd., for a full value (9:00 O'Clock, or, 3:00 O'C;lock) wind, you should expect about 0.9" of wind-drift per 1MPH variation wind velocity: a quartering wind would abot 1/2 of that, or, 0.45 inches . . . RG

Good catch on the wind note! Yes, I was suspecting a slight increase in wind as the cause on the first day, and this could have contributed. On the second day there was no wind (according to flags at 50 and 250 yards), so I think that this result is inherent in the rifle/load. Of course, group sizes vary randomly and conditions change, so there is a possibility this is just a coincidence, but I think there's a better chance that it's a problem with this particular load.

 

[mudduck]

Maybe from stress still in barrel from rifling process

 

[jcerne]

Maybe from stress still in barrel from rifling process

I've read about button-rifled barrels, like the one I'm using, having built-in mechanical stresses that cause POI changes as the barrel warms up, unlike cut-rifled barrels. I don't think that's what going on in this case. The last time I shot this rifle was with Berger 68gr FBs at a 300yd match in September, it shot a 99-2x (see below, 11 shots well within the 1.5" 10 ring), a 97-1x and a 99-1x, so I don't think it's any basic problems with the barrel. Nothing changed except for the bullet, which looks really promising for the first 5 shots!

 

[varget204]

Double Check Action screws, check torque, be sure to tighten front one last

 

[gpoldblue]

Hi All,

I trying out a new bullet in my Savage target rifle and am getting the best groups from a cold bore, which I’ve never seen before in any rifle. Usually, the cold bore shot is off a little and then the rifle settles down, but with Bart Avenger 68gr boat-tail bullets, the opposite is happening. The rifle is a Savage Target action with a 26" Shilen stainless select match bull barrel (0 freebore, 14” twist, ratchet groove) in 6BR Norma. I’m using a load that worked well for Bart’s 68 gr Ultra FB and Berger 68gr FB Target. The load was: Lapua cases (annealed), VV N133 29.1gr, CCI BR-4 primers, with bullet seated at jam or 0.005” back from jam.

All the shooting was done at 300 yards with very light wind and a temperature of around 34 F. All the groups were five shots. On the first day (please see Target 1), the first group from a clean, cold bore was around 0.6” ctc, which made me happy. Then the groups started to open up.
View attachment 1500730

I didn’t make much of this behavior until it happened again the next time I shot this rifle a few days later under similar conditions. The first group from a cold, fouled bore was about 1.0” ctc (please see Target 2), and then the groups started opening up. I didn’t the clean the bore before the second session since I only had 20 shots after the last cleaning and was curious to see how the rifle shot these bullets with the bore already fouled. On the second day, the bullets were at jam for the first two groups and 0.005” back from the jam for the last two groups.
View attachment 1500731


I’m wondering if the barrel is expanding slightly when warm, making the bullet fit a bit looser and causing accuracy to drop? Or maybe, the powder/cases warm up a bit in the pre-heated chamber, causing a slightly higher MV, which brings the rifle out of tune? I doubt this is the case since I’ve never seen that much sensitivity to MV in this rifle, but I’m running out of ideas. The only thing I can think of is to try some other powder weights at 300 yards.

If you have seen this before and/or have any ideas what is going on and how to fix it, please let me know.

Thanks,
John

Your load of 29.1gn/VV-133 in 6BR w/ a 68gn bullet is a little on the light side. A lot of shooters load that and MORE in the smaller 6PPC case...I don't but a lot of shooters do. I'd inch up on that charge or switch to maybe VV-135 especially looking at your verticle. Also it's not really unusual for groups to progressively open up...my experience. I generally shoot a couple of fouling shots,sighters as necessary,and 3 five shot groups before a cleaning session. I hope you're using enough wind flags for your 300yds.....if not, you may be missing conditions.
Good luck and stay safe.

 

[K22]

At 300 yards, wind, mirage, and shooter error is magnified. Thus, in my experience, it is difficult to diagnose problems at extended ranges.

I would move to 100 yards, repeat the test. I would also allow a couple of minutes between shots.

One the conditions I have experienced with factory barrel is that the more you clean them with aggressive copper solvents, the more unstable the groups become. I know this goes against all the expert opinions but if everything else fails to correct your problem then you may want to try the following, after all what do you have loose. Then retest.

After you have fired at least 20 to 30 rounds (to re-plate the bore with copper), try cleaning with just a general solvent like Hoppe's 9 or Shooter's Choice and a bronze brush to remove the carbon. This will also remove some copper but not all of it.

 

[JEFFPPC]

Jam to me is non repeatable so never used but beyond that switch to VV135. Start .015 in and back out .001 at a time. For starting poqder amoint Imwould start .5 gr under Bergers max. After finfing seating depth that start going up .q at a time in powder. When this is done now go .001 2 times both in snd out to see if you can sweeten it any. No testing eithout flags. Shotba shot whrn you missed s reserve and your effoet was wasted....but you probably did not realize it. Forget jam, think touxch is my advice. You can not see or verify jam.

 

[mikecr]

Pick which you want and develop for it.

 

[Infrequent Shooter]

At 300 yards, wind, mirage, and shooter error is magnified. Thus, in my experience, it is difficult to diagnose problems at extended ranges.

I would move to 100 yards, repeat the test. I would also allow a couple of minutes between shots.

One the conditions I have experienced with factory barrel is that the more you clean them with aggressive copper solvents, the more unstable the groups become. I know this goes against all the expert opinions but if everything else fails to correct your problem then you may want to try the following, after all what do you have loose. Then retest.

After you have fired at least 20 to 30 rounds (to re-plate the bore with copper), try cleaning with just a general solvent like Hoppe's 9 or Shooter's Choice and a bronze brush to remove the carbon. This will also remove some copper but not all of it.

i second this idea. and how hot is the barrel getting?

 

[Infrequent Shooter]

May try to let barrel completely cool and see what happens. should take out one variable.

 

[Rat Rifle]

Double Check Action screws, check torque, be sure to tighten front one last

This is interesting. For the last 15 years I have heard, “tighten the front screw first, then “tune” by bringing up the rear screw 5 in.#’s at a time” ???. I suppose there is more than one way to arrive at an acceptable solution. ???

 

[K22]

i second this idea. and how hot is the barrel getting?

As a hunter, the cold barrel shot is the "money shot" for me because you most often don't get a second chance. Small groups are nice, but POI consistency is a must along with reliability.

So, I grade my practice performance on the cold barrel shot. I let the barrel cool between shots during a range session. It's not so cumbersome in the colder months but can become tedious at the range in mid-summer. Still, I discipline myself to let the barrel cool. Some warming of the barrel is inescapable due to ambient temperatures and exposure to direct sunlight if you hunt varmints in the summer.

I see a lot of load testing at the range wherein shooters shoot sustained round sequences in sporter weight barrels hoping to find the optimum load. I truly believe this is an exercise in futility.

 

[BartsBullets]

I think your barrel wants to be shot clean and cool (not hot and Dirty). Try cleaning it after every group. Im guessing your barrel is carbon and copper fouling quickly. I rarely shoot my full blown bench guns more than 15 rounds before cleaning.

Bart

 

[Ned Ludd]

Good catch on the wind note! Yes, I was suspecting a slight increase in wind as the cause on the first day, and this could have contributed. On the second day there was no wind (according to flags at 50 and 250 yards), so I think that this result is inherent in the rifle/load. Of course, group sizes vary randomly and conditions change, so there is a possibility this is just a coincidence, but I think there's a better chance that it's a problem with this particular load.

If the cause is wind on one day, how reliable is it to blame the rifle/load on another day? That is a sample size of "1" for the two different occurences. There may be something going on here, but I would say you still have a long way to go to establish this as a trend specific to the rifle and load. As also noted by others, I would suggest reducing the distance and thereby the wind effects in future testing, and making sure the barrel doesn't heat up markedly during the testing process.

 

[jackieschmidt]

Just my opinion, if you are shooting at 300 yards with no flags, you are simply guessing.

That, and I don’t think your load is any where in Tune. You have both vertical and windage.

Unless there is something mechanically wrong with the Rifle/Scope combination, it all comes down to tune and condition reading.

Do you have the capability to load at the range? if yes, that opens up many opportunities not available from just guessing at home.