velocity increasing same load

[bgblue1978]

Ive been shooting 155gr tipped match king over 46.1 gr varget at oal of 2.810, which is .005 off the lands based on hornday seating depth tool. Ive been keeping a log of velocities with weather data. when i started with this load last august it was 95 deg and avg velocity was 2937, rifle had 508 rounds through it. the velocities seemed not to fluctuate much and made sense with temp for the remainder of the year (78deg- 2922, 75deg- 2915, 86 deg-2926 etc). recently though ive gotten higher velocities and pressure signs (flat primers). last shooting was 50 deg and velocity was 2930 i changed lots of powder and bullets within that time period and unfortunately didnt document it (lesson learned).

My question is, should i just load down until i get the velocity back where it was (based on projections on my graph of the 1st few months of that load), or do i need to redo my ocw testing? i know redoing the testing is safe way but trying to avoid wasting resources.

Thanks in advance for reading this and any advice you guys have.

 

[Twoboxer]

. . . recently though ive gotten higher velocities and pressure signs (flat primers). last shooting was 50 deg and velocity was 2930 i changed lots of powder and bullets within that time period and unfortunately didnt document it (lesson learned).. . .

You changed powder and bullet lots, and now see pressure signs at a cool 50 degrees.

I'd back off the charge to find something closer to what I think the velocity would be using the old batches . . . compare that target to the original charge weight's target . . . and make a decision.

 

[dkhunt14]

If you are showing pressure at 50 degrees, it will probably be too hot at 90 degrees. I would also check and clean my throat real good. Could be a carbon buildup. Matt

 

[Texas10]

+1 on the carbon ring check. You can also perform your BTOG again and look for any changes. Carbon build up will show a shorter apparent distance to lands. If you don't have an endoscope camera or bore scope, I recommend you get one to use to check chamber, throat, lands, muzzle etc. Even a cheap endoscope camera (<$100 for used Snap-on BK5500) will tell you a lot.

 

[Ledd Slinger]

Definitely could be due to different lot of powder and bullets, but I would agree on starting with checking how clean the bore is first. Couple days ago I posted that Sinclair has the Lyman bore cam on sale for $175. Should still be available. Will tell you everything you need to know.

The Lyman is much better than any 'straight view' endoscope or bore cam you'll find on ebay or amazon for $100. Can't see anything with those anyhow. I tried that route a couple times and they are all basically worthless. Gotta have the 90 degree view provided by the Lyman or Hawkeye to really see whats going on

 

[carlsbad]

Your target will tell you but one of the key parameters in load development is matching muzzle velocity, coal, jump etc to barrel frequency to get the nodes to match the bullet exit. So if you aren't getting the performance you expect, adjusting your velocity back to where you had it would be a good thing to try. --Jerry

 

[jlow]

It could be the powder or bullet, or carbon ring as per Matt's suggestion. The other thing it could be is your neck could be getting longer (if you have not been trimming your case neck) which could cause the neck to crimp on to your bullet. That can really increase pressure and MV....

 

[bgblue1978]

Thanks guys. im not comfortable leaving it as is even if targets look good because i live in central texas...flat primers in January can be big trouble in august.

I trim before every loading so no issues there.

My plan right now is a good cleaning, reevaluate oal to lands, and then load up with charges from 45 to 46 grains to see #1 where pressure signs start and #2 where i get back to the velocity i expect. thanks for the help.

 

[Bart B.]

I don't think adjusting powder lots' charge weights to produce a given velocity is worth the time and materials unless your biggest 10-shot group averages are smaller than 1/4th MOA.

For decades, Sierra Bullets used the same load details across all lots of components in unprepped full length cases for quality tests. Their 10-shot test groups of their best match bullets averaged 1/4th MOA.

 

[Rsadams]

It's not uncommon to see changes from one pound of powder to the next... I also live in Central Texas and I can promise you if your seeing pressure signs at 50 degrees you will definitely have a problem when it's 112 in a few months... I have a summer and winter load for here... Back it down a bit since your useing a new lot of powder and work back up you should be able to tell in just a few rounds were you need to be again... This is why alot of people buy 8 pounders so they are not changing lot numbers so fast... Safety is worth testing at any price..

 

[bgblue1978]

Bart, i agree and like i said i wouldn't bother changing anything because the guns shoots better than i do, but the pressure signs is what worries me enough to change the load. if cleaning the throat fixes the issue then i would will happily leavr it and just know that i need to clean more often.

 

[chop house]

I trim before every loading so no issues there.

there was an active thread a few weeks back about the carbon ring, effects on increasing pressure (velocity) and getting rid of it. more than one member suggested leaving your brass neck longer to give it less room to form. so, maybe?

 

[bgblue1978]

Interesting, i always thought that necks of different lengths would have different amounts of friction on the bullet and produce higher ES numbers.

 

[nonnieselman]

I don't think adjusting powder lots' charge weights to produce a given velocity is worth the time and materials unless your biggest 10-shot group averages are smaller than 1/4th MOA.

For decades, Sierra Bullets used the same load details across all lots of components in unprepped full length cases for quality tests. Their 10-shot test groups of their best match bullets averaged 1/4th MOA.

Sierra also shoots indoors in a controlled environment. That helps a bunch.
Seen their .338L group with 300gr SMK at 300 that was just silly small.

Ive seen more difference between lots recently with Varget compared to the past.