increasing charge and losing velocity

[Rem700CDLSF3006]

previously I had shot and chrongraphed some loads Hornady case 57.0 grains off H4350.Fed 210 gm primer 165 grain ballistic tip velocity was 2756 2764 2777 today I shot some more same everything except 57.2 grains and velocity was 2688 2688 2693 in dumbfounded

 

[Reloadron]

Ambient air temperature, that is the actual case temperatures of the cartridges? There are afew other variables which will effect velocity, but temperature is among the more common.

Ron

 

[Rem700CDLSF3006]

ron there was less than a 10 degree difference and is;nt H4350 supposed to be temp sensitive? I think I may just have a slow gun

 

[Reloadron]

ron there was less than a 10 degree difference and is;nt H4350 supposed to be temp sensitive? I think I may just have a slow gun

Strange. While 0.2 grain of charge isn't much you seem to be seeing a good bit of velocity change. The temperature change wasn't that great. Just plain weird. I got nothing as far as a good explanation.

Ron

 

[Rem700CDLSF3006]

thank you Ron me either it has me stumped the only thing diff was never fired brass vs 2 firing on other.

 

[rayatphonix]

I had a similar experience with an old Tikka 695 in 30-06. Never figured it out. As my load went up, accuracy went down so I stuck with the most accurate load. I'm using the same powder but 150 gn Nosler BT.

 

[fguffey]

I think I may just have a slow gun

Ambient is surrounding temperature.

Strange. While 0.2 grain of charge isn't much you seem to be seeing a good bit of velocity change.

I would expect a difference.

the only thing diff was never fired brass vs 2 firing on other.

If you started with new/unfired brass then necked sized there would be more volume in the case. If you full length sized the case back to minimum length there could have been a small increase in velocity.

F. Guffey

 

[GBExpat]

increasing charge and losing velocity

The only propellant with which I have ever experienced this is Trail Boss.

 

[Laphroaig]

Here’s my .02

You never mentioned what type of chrono you were using. I think that we put a lot of faith in $100 to $150 dollar instruments to record accurate velocities at the high power rifle level. There are many variables, such as level of lighting, the angle of the sun, ambient temperature that might slightly affect the readings? I’m not a rocket scientist, so I don’t know for sure.

Another possibility is the precision of the setup with regard to being exactly level. Just doing a rough calculation, the type of variability you describe could be explained by a less than 2 degree difference between the two range sessions. If you eyeball your chrono for level, I don’t think it’s very hard to make that kind of mistake. I’ve put a torpedo level in my kit to minimize that variable.

It just seems to me that we take our chrono readings as gospel and start blaming everything else under the sun.

Laphroaig

 

[fguffey]

has me stumped the only thing diff was never fired brass vs 2 firing on other.

Next time load 10 rounds with Hornady never fired cases with 57.0 grains off H4350 then load 10 rounds with 57.2 grains in never fired brass. Or load 10 rounds using fired cases with the same bullet, powder and primer, then load 10 more rounds with an additional .2 grains of powder.

F. Guffey

 

[spitballer]

Funny I use a lot of Nosler BT's in my .223 bolt rifle and it might be my imagination but I think the heavy copper base produces a little more pressure than standard jacketed bullets. The 55 grainers I use are kind of finicky and they seem to have a narrower optimum range than other products I've tried. When I've reached the point of obturation they let me know about it in no uncertain terms.

 

[fguffey]

Funny

So there is no difference between a case that is full length sized to minimum length and a case that has been fired twice?

F. Guffey

 

[Rem700CDLSF3006]

Lapro you may have hit the nail on the head getting to thinking of it it did have a slight angle to it

 

[gamestalker]

I see someone has already addressed chrony angle, but that would have been my first guess. I try to test velocities of varying charges during the same session, thus helping to maintain the same angle. Additionally, I take great care in how I set up so I can get a more accurate and realistic velocity estimate.

If the bullet crosses at a different vertical or windage angle, it will alter the recorded velocity. Consider that if the bullet travels an additional 1/4" across the chrony, that 1/4" is going to record a lower velocity by a little more than 2%.

GS

 

[243winxb]

This is reason for different velocity. >

only thing diff was never fired brass vs 2 firing on other.

 

[Reloadron]

Lapro you may have hit the nail on the head getting to thinking of it it did have a slight angle to it

That would be a very good possible. To get repeatable results the chronograph needs to be setup identical to the previous time. Well as close to identical as possible. It's all about how the light catches the bullet and the sensors pick it up.

Ron

 

[Gtscotty]

I've heard of velocity dropping a little once you get to, or slightly exceed max load, but assuming you are using a 30-06, you're about 2 gr below max. I would bet that the difference in measured velocity is related to some inconsistency in your chrono setup. Like other posters have said, I've seen similar variance based on chrono angle.

 

[MEHavey]

previously I had shot and chrongraphed some loads Hornady case 57.0 grains off H4350.Fed 210 gm primer...

Same Temperature?
Same lot of powder?
Same lot of primers?

[..and/or if same all above...]

How long since last use of that same powder ?

 

[jgh4445]

Also, were the loaded rounds lying around in the sun the first time getting warm and not so for the second firing? Heated up rounds build up a bit more pressure thereby possibly increasing velocity. I use one of those small playmate coolers or a small soft sided one to store ammo in when its in the car on the way to the range and while at the range. I want to keep the temps down as much as I can and insure consistency. Just a 15 minute stop for gas or snacks on the way to the range can cause a drastic temp change inside of a car or truck.

 

[fguffey]

Rem700CDLSF3006 previously I had shot and choreographed some loads Hornady case 57.0 grains off H4350.Fed 210 gm primer 165 grain ballistic tip velocity was 2756 2764 2777 today I shot some more same everything except 57.2 grains and velocity was 2688 2688 2693 in dumbfounded

Load 10 rounds with 57 grains of H4350, same case, bullet and primer, then load 10 rounds with 57.2 grains of H4350 using the same cases, bullets and primers. Use new, factory cases or use all once fired cases.

Then there is that part about sizing, neck size, partial? size or return the case to minimum length. Then? go to comparing necked sized cases to factory minimum length/full length sized cases.

F. Guffey

 

[taliv]

The chrono is the culprit but my advice is to read a bit on testing methodology in science. some relatively simple additions like a control group can eliminate a lot of guesswork

Save a couple of your old loads to shoot before trying the new stuff. I often do this when I change barrels to see changes in velocity

 

[Grumulkin]

previously I had shot and chrongraphed some loads Hornady case 57.0 grains off H4350.Fed 210 gm primer 165 grain ballistic tip velocity was 2756 2764 2777 today I shot some more same everything except 57.2 grains and velocity was 2688 2688 2693 in dumbfounded

1. Velocities will frequently be different on different days. Both temperature and relative humidity play a role (they both affect air density) for velocities measured at longer ranges and not much of one when measured close to the muzzle. If in one shooting session you had set your cartridges in the sun while on another you had kept them cooler, velocities could be different depending on the powder.

2. If you have heated up the barrel with multiple shots, velocity can start decreaseing.

3. Powders all have a certain pressure at which you'll get optimal burning. Too much or too little and you'll no longer have optimal pressure.

4. Another thing to think about. If the pressure is too high, the gun will blow up and the bullet won't go far, i.e., velocity will be very low. There is a continum below that at which velocities will be lower without blowing the gun up.

 

[spitballer]

So there...

...beats the heck out of me! All I know is there are times when a (slightly) higher charge actually causes a slower velocity. No, I don't think it has anything to do with the case volume... I think it's the dreaded "O" word...

 

[fguffey]

...beats the heck out of me!

I posted this to a draft.



.2 grain? What makes a difference?

I built a rifle, it was a wildcat with the 30/06 case as the parent. I had 4 receivers I needed to test. I was informed when I purchased the 4 rifles the receivers were suspect. I needed to form cases and test the receivers. I used one barrel, one bolt and 4 receivers to form 40 cases.

I used H4895, I used 46 grains, 46 grains was the maximum for a 150 grain bullet. Again, I needed to form cases and I needed to test the receivers so instead of 150 grain bullet I used a 200 grain bullet. It was about this time it was suggested I was into some 'risky stuff'.

I did not agree. The one barrel, one bolt in 4 receivers resulted in .001" difference in the length of the 4 chamber.

The cases formed and the receivers did not fail. Risky stuff? The 46 grains of H4895 with the 200 grain bullet was at the very jagged edge of being the maximum after the cases were formed. I am not talking about .2 tenths of a grain of powder, I am talking about 50 grains difference in bullet weight. The maximum charge of powder for a 200 grain bullet is 40 grains when using H4895.

F. Guffey

 

[spitballer]

fguffey I don't have the tools or expertise to achieve the things you are able to achieve but I understand occasional skepticism. On publicly posted threads where the only qualification to profess knowledge is a functional keyboard we sometimes have to separate the wheat from the chaff. and personally I think it's a good thing that my fellow reloaders have been adamant about erring on the side of caution. Using this forum has also has given me newfound respect for the responsibilities of our moderator who has rightfully locked me out a time or two: refusing to discuss a subject to prevent others from succeeding obviously can't be confused with refusing to discuss a subject to prevent others from hurting themselves.