Same charge loaded a month apart yielding different Velocities.

[Boxcar77]

Hello all and Happy New Year. First post here after reading here for many months. I used to spend most of my time over at SH, but really enjoy reading the concise thought posts and answers here.

Now to the crux of my problem;
About 2 months ago I loaded 20 rounds for my 6.5x47L, but was unable to shoot them until yesterday. I also loaded another 20 rounds the night before I went shooting. I went out yesterday to get some velocities and DOPE with a new Supressor. I was kind of confused with the results.

Load data;
Virgin Lapua Brass, all sized in the same Redding Bushing die with a .287 bushing giving me .002 of neck tension with no shoulder bump.

Berger 130VLD all the same lot seated CBTO @ 2.199"

41.6gr of H4350 all dispensed from the same Chargemaster warmed up 30 minutes before each bench session. (Powder was from the same container) So lot # variances can be culled out.

CCI450 Primers from the same package/lot number.

All velocities were obtained with a Magnetospeed V3

The results were.
2 month old rounds;
Avg Vel-2861
ES-19
SD-8.6
Rounds loaded the day before yielded;
Avg Vel-2847
ES-19
SD-6.5

Now my question, as I have been reloading for less than a year and am always looking to learn.
Why the difference in Velcities, it's not extreme but it equates into .01 mil throughout my dope sheet. The SD good throughout the rounds. Am I experiencing cold welding of the bullets to the brass on the 2month old rounds raising the pressure and velocity? I know the typical answer of load all my competition rounds at the same time. I'm just trying to understand why this happened.

 

[Dusty Stevens]

Different humidity on your powder hence the reason benchrest shooters dont preload.

 

[Proclaim]

My guess would be that the Chargemaster dispensed a different amount of powder from one loading to the next. It wouldn't have to be much to see the difference that you are experiencing. That's why I started weighing all my competition loads on a Sartorius Basic scale that weighs to the hundredths of a grain. I even know some competition shooters that use even better scales than mine that measure to ten thousandths of a grain.

 

[Boxcar77]

My guess would be that the Chargemaster dispensed a different amount of powder from one loading to the next. It wouldn't have to be much to see the difference that you are experiencing. That's why I started weighing all my competition loads on a Sartorius Basic scale that weighs to the hundredths of a grain. I even know some competition shooters that use even better scales than mine that measure to ten thousandths of a grain.

Different humidity on your powder hence the reason benchrest shooters dont preload.

Completely reasonable and understandable thanks.
@Proclaim I've been considering getting a better scale and throwing short with the CM and trickling up. This helps reaffirm my want for a more precise scale.

 

[Patch700]

Tighter bullet grip .... conduct your test again only this time seat the rounds you plan on leaving sit for a period of time long , then bump them to where they should be the day of use.

 

[savagedasher]

Neck bonding Bullets tend to stick when they have ben loaded for some time.
Which did you shoot first?
Larry

 

[Boxcar77]

I shot the fresh reloads first with about 20 minutes in between to shoot some pistol rounds

 

[savagedasher]

Dirty barrel also Larry

 

[ARIZONA_F_CLASS]

temperature change.

 

[lpreddick]

I had this happen so often and learned about " cold bonding" on this site. Seating long then seating to the desired depth the day you shoot works but there were always a few not shot and later...the same problem was there. I suspect an increased pressure is needed to break the " cold bond" and this increase pressure results in increased velocity, thus decreased barrel time. Jumping bullets with this situation is asking for this to happen. I read about " jamming" bullets into the lands and gave it a try. WOW! Cases loaded today shoot to the same poi as ones loaded months and occ years ago!!! Seat a bullet .005 deeper in a round loaded months ago and they often " pop" or give a slight resistance, then move...this is " cold bonding". Shoot these with ones loaded today and poi is almost identical. I suspect the pressure required to move the bullet " jammed" is WAY higher than pressure to move a " cold bonded" one.

 

[chkunz]

This is interesting and it reminds me of a practice I saw the military shooters use many years ago to try to improve the accuracy of their M118 ammo. They would use a Lyman "nutcracker" tool to break the seal between the bullet and case. You would see them on the line doing this just before the match. They would set the bullet seating die to seat the bullet a little deeper than the standard length thereby breaking the seal. Obviously they were not concerned about bullet jump on the M14.

 

[artbosco]

Hello all and Happy New Year. First post here after reading here for many months. I used to spend most of my time over at SH, but really enjoy reading the concise thought posts and answers here.

Now to the crux of my problem;
About 2 months ago I loaded 20 rounds for my 6.5x47L, but was unable to shoot them until yesterday. I also loaded another 20 rounds the night before I went shooting. I went out yesterday to get some velocities and DOPE with a new Supressor. I was kind of confused with the results.

Load data;
Virgin Lapua Brass, all sized in the same Redding Bushing die with a .287 bushing giving me .002 of neck tension with no shoulder bump.

Berger 130VLD all the same lot seated CBTO @ 2.199"

41.6gr of H4350 all dispensed from the same Chargemaster warmed up 30 minutes before each bench session. (Powder was from the same container) So lot # variances can be culled out.

CCI450 Primers from the same package/lot number.

All velocities were obtained with a Magnetospeed V3

The results were.
2 month old rounds;
Avg Vel-2861
ES-19
SD-8.6
Rounds loaded the day before yielded;
Avg Vel-2847
ES-19
SD-6.5

Now my question, as I have been reloading for less than a year and am always looking to learn.
Why the difference in Velcities, it's not extreme but it equates into .01 mil throughout my dope sheet. The SD good throughout the rounds. Am I experiencing cold welding of the bullets to the brass on the 2month old rounds raising the pressure and velocity? I know the typical answer of load all my competition rounds at the same time. I'm just trying to understand why this happened.

Forget about SDs and all that other nonsense. What happened downrange on the target? That's all that matters. Tune with the proper: barrel, powder, primer, brass, bullet combination. Then fine tune with seating depth and neck tension. When you turn tight cloverleaf groups into one hole groups you've arrive at your goal. You don't tune with a chronograph.

 

[Drop Port]

This happened to me years ago. I had a tight shooting rifle turn into a one hole grouper with loaded ammo that had sat for a while (cold bonded). I was able to duplicate the load performance by bumping neck tension on fresh loaded ammo. Learned a valuable lesson on neck tension that day.

 

[LCazador]

if you don't tune with a chronograph, how else are you going to learn about cold bonding effects, neck tension effects, seating depth, and powder gaining weight or drying out effects? IMHO it's all guess work without a chronograph and and a good bench set up for load testing. Every rifle and every barrel is different! The amount of work and effort you put into your load development will represent itself on the target!

 

[chkunz]

I am an M14 shooter so what could I know about tuning loads and using the chronograph? But it seems to me that this is another tool that has some benefit if it is used properly. My limited use of the chronograph tells me that there is a lot to be learned in how to set one up and get good data. And then it is important to know how to analyze the data. I do not yet have the confidence in what I am doing to be able to have confidence in the data I am getting but I have not given up. The most encouraging thing I have seen is the reports on the MagnetoSpeed(sp?). This sounds like it will solve many of the set up issues with the standard chronographs and encourage more folks to use velocity as one of their load development tools. Now if the price will just come down.

 

[LHSmith]

if you don't tune with a chronograph, how else are you going to learn about cold bonding effects, neck tension effects, seating depth, and powder gaining weight or drying out effects? IMHO it's all guess work without a chronograph and and a good bench set up for load testing. Every rifle and every barrel is different! The amount of work and effort you put into your load development will represent itself on the target!

I guess, this is what separates short range from long range. I tune by target. Only time I use the chrono is when switching to a new powder or new jug or lot of powder.

 

[rogn]

"Cold bonding" can cause some real problems also,. For instance have a MTM box full of loads used in Africa a couple of years back, hadn't shot any for about 3 years, now they get a sticky bolt lift, Haven't had a chance to reseat.

 

[Boxcar77]

I had wondered/thought about the cold bonding, but seated the bullets anyway. Not thinking it we be so long in between range sessions, but work comes first. I'll chalk it up to an experience and learn from it.

@ Outdoorsman, This is a bughole load with the brake, but it opened up quite a bit with the supressor about .750 at 100 I also lost some velocity with the supressor but it was 60° during my initial load work up and 28° the day I mounted the supressor. I have some OCW's loaded up with Varget and R15 but I'll run that test in the spring when the temp comes back up. I think I'll do another load work up with H4350 with the supressor mounted.

It all seems like a bit much, But I enjoy the entire process of reloading from priming to shooting. I know a lot of shooters look at reloading as a necessary evil they dread doing, but to me I love the challenge of it, and the learning that comes along with it. My wife says I'm a bit obsessed.

 

[stubbicatt]

If I read OP's posting correctly, he added a new muzzle device, a suppressor, before testing the second batch? Could the muzzle device have affected his velocity in this manner?

 

[Boxcar77]

If I read OP's posting correctly, he added a new muzzle device, a suppressor, before testing the second batch? Could the muzzle device have affected his velocity in this manner?

Both batches were fired concurrently during the same range session with the supressor attached with about 15-20 minutes in between.