Confusion...

[maseh2os]

Hey all,

Got a couple of questions for ya. Apologizing ahead of time as this will be a bit lengthy.

First a bit of background. My friend and I recently completed our first rifle builds. We built pretty much identical rifles, chambered in 6.5 Creedmoor, Savage action, Criterion 26" barrel. While our chambers certainly seem identical (as evidenced by measuring cases from both after several firings), we seem to have slightly different throating, his consistently measuring .026" shallower when measured with the Hornady OAL gauge.

We have been working on load development, and run into a few confusing bits of data. We are using 140gr Berger VLD's, H4350 powder, RCBS Charge Master, Wilson neck and seating dies, and Sinclair comparator for seating depth measurement.

First, his rifle seems to shoot slower than mine and I can't figure out why. On average, about 20fps less than mine with the same exact load. We are both seating .010" into the lands, his OAL obviously being .026" shorter than mine due to difference in distance to lands. Because of this, I would have thought that his would shoot a bit faster, due to the decreased case capacity from slightly more bullet intrusion, thus raising his pressure a tad above mine. Am I missing something here?

Second, we shot several groups today, 30 shots each total. All the same powder charge and at our normal seating depths. However, the first 15 shots for each of us was loaded in once fired brass, having only had a factory load in it before today. The second sets of 15 were from twice fired brass, once from factory, once reloaded. Not only did we have our usual 20fps average difference between his and mine, but we both had about a 25fps increase in velocity when going from the once fired to the twice fired! The consistency and ES got quite a bit better in the second set as well.

I am at a loss as to why this might be. I would think the once fired brass would be just as formed to our chambers, or really darn close, as the twice fired.

This really has me worried now, because now I'm figuring we are going to have velocity issues every time we get new brass, needing to fire it twice just to get better consistency and back to expected velocities. Not only that, if I'm guessing right we'll have similar problems whenever we go to FL size and bump the shoulder! Anybody else have this happen? Causes? Remedies?

Any help you guys can give would be much appreciated! Thanks in advance,

maseh2os

 

[rscott5028]

Here are some thoughts to consider...

Each barrel/chamber is different. If 2 barrels are chambered by the same smith with the same reamer to the same specs, the chambers may be very close and able to use each other's neck-sized brass.

You didn't mention how precisely you set your headspace on each rifle and if that was the same or even if the same reamer was used.

It sounds like there's a definite difference between the throats and/or headspace in your 2 rifles. ...perhaps even tooling marks. It might be interesting to have a look with a borescope. But, that's not going to change anything.

Nonetheless, the barrels will often have subtle differences that often amount to more than the 20fps differences that you're seeing. Both velocity and accuracy may differ.

Also, barrels will see changes in velocity during some arbitrary break-in period. And, they may not settle down at exactly the same rate.

As time goes on, the throats will errode at slightly different rates.

Velocity is a function of many factors, some of which you have already pointed out.

I don't have statistics to make a solid claim. But, I personally prefer my twice-fired brass because it's been through my whole process, and doesn't yet require full length resizing or annealing.

I don't think you can draw any final conclusions until you've shot 100-200 rounds.

In any case, I don't see any reason to be overly concerned by your experiences thus far.

-- richard

 

[maseh2os]

Ok, so it sounds like I have had my expectations set a bit too high regarding the side by side performance of these rifles.

And come to think of it, I'm pretty sure we only have ~150 rounds through them, so for all I know we haven't quite finished the break in period.

I have to say I am still a bit concerned about their long range accuracy from shot to shot, when using a mix of once or twice or three times fired brass. It concerns me because we are planning to hunt with these, and thus would like to be able to take any shot within the effective range of the bullet and KNOW where it is going to end up. Looking at a ballistics program though, it only shows a +/-1.5" difference in drop at 600yds when fired 25fps faster or slower than nominal. Should I consider this good enough? Should I worry more about making consistent ammo and becoming a more consistent shooter more than that amount of velocity variance?

 

[rscott5028]

I'd like to see others weigh in on both of your posts. But, here's my opinion again...

How the MV of the 2 rifles compares side by side is of little consequence. You may actually find that one prefers a different load than the other.

25fps variation from shot to shot is a bit much for longer range hunting. There are a lot of things you can't control when you hunt. But, you should be getting close to single digit spreads with good handloads.

Every detail counts in your handloads. Once fire, twice fired... trim to length, OAL, neck tension, powder lot, etc...

Chrony's are a great tool, but they are not always very precise. The statistical averages will help you develop a good drop charts. But, your long range groups will help you determine how far you are comfortable shooting.

In any case, +/- 1.5" at 600 yds due to 25fps is only one factor. Environmental conditions, wind, and shooting position will have a lot to do with shot placement not to mention ranging an animal accurately and then dialing in before they move.

It's all very doable. But, it takes practice. A good spotter is a huge help.

Happy hunting,
Richard

 

[cahunter805]

Some great advice has been already given. Some barrels are just slower than others. I will add this. Keep your brass sorted by times fired. I keep them in ziploc bags or coffee cans with the times fired and how it was resized written on the bag. I would neck size the brass until chambering becomes hard and then just bump the shoulder.

 

[maseh2os]

Thanks again for the replies everyone, this has been great!

Every detail counts in your handloads. Once fire, twice fired... trim to length, OAL, neck tension, powder lot, etc...

So far we have kept our brass sorted by firings, though haven't seen a difference between second and third firing so far. It was only the once fired cases that showed difference from the cases with more firings. We have been neck sizing using Wilson dies, and haven't seen a need bump shoulders yet.

A fellow on another forum suggested that one might obtain some consistency using a Redding body die to uniform all cases, new brass, once fired, twice, etc. He felt that this would give you as close to identical cases, regardless of number of firings, thus giving you more consistency upon firing.

Does this theory hold water? Or should we just keep doing what we're doing?

 

[rscott5028]

Cases continue expanding slightly to fill the chamber on subsequent firings. By around the 4th firing, you will need to bump the shoulder back.

Collet dies, Neck sizers, bushing dies, hand dies, full length, etc... are all viable methods that people use for hunting and competition.

The key is to develop a method of procedure that works for you and to maintain consistency.

I have have not seen it, but Shawn Carlock at Defensive Edge has come out with a DVD about handloading for long range hunting. They have an excellent reputation. So, I expect that it's very worthwhile. There are lots of articles on this site as well.

-- richard