Varying powder charge summer/winter?

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ben_g
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Varying powder charge summer/winter?

#1 Postby ben_g » Fri Jun 29, 2018 1:00 pm

Bit of a newbie question.

We all know that ambient temperature/ammo temp has some effect on velocity. I haven’t seen It severely affect groups in my previous open chambering using 2209 or 2208

I have just recently worked up a load in my Dasher with RL-15 that is showing much promise in our current temps of around 12-15 degrees Celsius.

My question is what sort of change in charge weight do people find they need to maintain the same velocity between winter (low teens) and summer (up to mid 30’s)?

I will of course test myself but looking for a ballpark figure with double based powder. Currently running 33.4gr which is running 3050fps, is the variation needed usually say a whole grain or even more or usually just a few tenths?

Hoping someone has some data and experience with this powder. I want to persist with it as I am comfortably in the higher node without any pressure signs.

Cheers

Ben.

RDavies
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Location: Singleton NSW

Re: Varying powder charge summer/winter?

#2 Postby RDavies » Fri Jun 29, 2018 7:14 pm

With a Dasher sized cartridge and 2208, and those temperature differences, I would be changing the load by about 0.25gn.
RE15 is a lot more temperature sensitive and I haven't done any temperature tests with this powder, but I would guess it could require up to 0.5gn change????
Can you get AR-comp which is supposed to be very similar speed but much less temperature sensitive?

ben_g
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Re: Varying powder charge summer/winter?

#3 Postby ben_g » Sat Jun 30, 2018 8:22 am

Thanks rod.

Did a little digging online and in extreme tests (below freezing to high 40’s) RL 15 looks to be about 3 times more sensitive than 2208. About 1.6fps per degree vs 0.5

However that’s a basic interpolation of minimum and maximum and assuming the change is linear.
It would appear between 10 and 32 degrees RL-15 does not suffer too badly as the rate of increase flattens out at these temps.

I will just have to keep some data over the coming months and learn for myself.
So far Rl-15 is giving good results on paper and is significantly faster than 2206H, I lost faith in my current lot of 2208 in my 6.5x47L and haven’t yet tried it in the Dasher. I’m keeping it for fireforming loads.

Pommy Chris
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Re: Varying powder charge summer/winter?

#4 Postby Pommy Chris » Sun Jul 01, 2018 9:33 am

ben_g wrote:Thanks rod.

Did a little digging online and in extreme tests (below freezing to high 40’s) RL 15 looks to be about 3 times more sensitive than 2208. About 1.6fps per degree vs 0.5

However that’s a basic interpolation of minimum and maximum and assuming the change is linear.
It would appear between 10 and 32 degrees RL-15 does not suffer too badly as the rate of increase flattens out at these temps.

I will just have to keep some data over the coming months and learn for myself.
So far Rl-15 is giving good results on paper and is significantly faster than 2206H, I lost faith in my current lot of 2208 in my 6.5x47L and haven’t yet tried it in the Dasher. I’m keeping it for fireforming loads.

I did some tests with ball powders in a 308 and messed with temperature. Shooting at 600 yards with a round left in the sun on a car dash for 30 mins it made sod all difference to cool rounds. I repeated the test again putting a round in a freezer bag next to a frozen block and another in the sun first thing in the morning and the rest in the shade. The one in the bag went low and the hot one went high but similar tests with 2208 showed similar results. 2208 is supposed to be more temperature stable but IMO unless you do something silly and leave bullets in a hot car it wont make any difference form my results anyway..
Chris

RDavies
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Re: Varying powder charge summer/winter?

#5 Postby RDavies » Sun Jul 01, 2018 12:29 pm

Pommy Chris wrote:
ben_g wrote:Thanks rod.

Did a little digging online and in extreme tests (below freezing to high 40’s) RL 15 looks to be about 3 times more sensitive than 2208. About 1.6fps per degree vs 0.5

However that’s a basic interpolation of minimum and maximum and assuming the change is linear.
It would appear between 10 and 32 degrees RL-15 does not suffer too badly as the rate of increase flattens out at these temps.

I will just have to keep some data over the coming months and learn for myself.
So far Rl-15 is giving good results on paper and is significantly faster than 2206H, I lost faith in my current lot of 2208 in my 6.5x47L and haven’t yet tried it in the Dasher. I’m keeping it for fireforming loads.

I did some tests with ball powders in a 308 and messed with temperature. Shooting at 600 yards with a round left in the sun on a car dash for 30 mins it made sod all difference to cool rounds. I repeated the test again putting a round in a freezer bag next to a frozen block and another in the sun first thing in the morning and the rest in the shade. The one in the bag went low and the hot one went high but similar tests with 2208 showed similar results. 2208 is supposed to be more temperature stable but IMO unless you do something silly and leave bullets in a hot car it wont make any difference form my results anyway..
Chris

My results with W748 showed very definite differences between hot and cold weather. Once I got the bolt back from Matt, with a new extractor, I stuck with ADI powders after that. I suspect that RE15 would be one where small temp differences do matter.

ben_g
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Re: Varying powder charge summer/winter?

#6 Postby ben_g » Mon Oct 22, 2018 6:40 am

So the weather is warming up a little here so I took the chronograph out and tested on Saturday as the forecast was initially for mid to high 20’s.
It only made it to 24C in the end so not a big swing in temp.

The load I had settled on in winter ended up being 33.1gr of RL-15 and in ambient temps of 10C was giving me velocities of 3015fps on Saturday that same load averaged 3035fps in ambient temps of 24C so an increase of 20fps for 14C increase in temp.

We shot 800yards that day and even though it has sped up some the group was still a respectable 3.5” high for a 15shot match.
So it looks like in moderate temps in spring this load will shoot early morning and during the day. But for temps over 30C I am going to drop .3r at a guess. (.2gr increments giving approx 15fps increases in speed when tested yesterday)

So yes it’s somewhat temp sensitive, I plan on giving it a run at Canberra, will probably bring a cooler bag and keep ammo in it, And will load a batch of cases in case of 30+ temps)

RL-15 definitely gives performance though, I ran it all the way to 34.0gr yesterday achieving 3105fps, there were small pressure signs at this point with a slightly heavier bolt lift.

Tim N
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Re: Varying powder charge summer/winter?

#7 Postby Tim N » Mon Oct 22, 2018 2:44 pm

Would velocity variation due to temp also be related to to the expansion of the barrel steel?
I'm guessing the barrel would get smaller as the barrel steel would expand internally and externally?
Which may contribute more to velocity than the actual temp of the bullets????
Just a thought
We don't rise to the level of our expectations, we fall to the level of our training. Archilochos 680-645 BC

mike H
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Re: Varying powder charge summer/winter?

#8 Postby mike H » Mon Oct 22, 2018 4:08 pm

Tim N wrote:Would velocity variation due to temp also be related to to the expansion of the barrel steel?
I'm guessing the barrel would get smaller as the barrel steel would expand internally and externally?
Which may contribute more to velocity than the actual temp of the bullets????
Just a thought

I always thought that steel expanded when heated and shrunk when cooled,in that way some joints were given a shrink fit by heating the outer collar piece to fit over the inner piece,then cooled for a tight fit.For this to happen the outer piece would hardly expand internally,I suggest that if you took a piece of steel the same thickness as a barrel and as long as the circumference of the barrel and heated it,it would expand and lengthen the most on the longest side,if we turn that piece of metal back into a barrel the expansion of diameter would be greater than the normal temperature barrel.My opinion only,no engineering degrees to support it.

ben_g
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Re: Varying powder charge summer/winter?

#9 Postby ben_g » Mon Oct 22, 2018 4:23 pm

I don’t know about your theory Tim, but I do have data from a chronograph session back in winter.

I fired 17shots (15+2shot stage)with the magnetospeed attached, starting with fouled but cold barrel, first shot was 3015fps, last shot 3020fps. Barrel was pretty hot by the end, if temps were affecting bore dimensions enough to increase pressure surely you would see it during an ordinary string??

pjifl
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Re: Varying powder charge summer/winter?

#10 Postby pjifl » Mon Oct 22, 2018 7:41 pm

Steel heated uniformly will expand such that every dimension is increased in the same proportion. Both the exterior and interior diameter expand. From an engineering point of view this is definite.

If the bore is being heated such that heat transfer to the outer surface is much slower than the input of heat to the bore, the barrel will not have a uniform temperature. While it is this state, the lack of thermal equilibrium will expand the bore inwards a little bit more than the outer will expand outwards. Thus there will be a short time when the bore may contract a tiny amount.

This does not really answer whether the bore tightness is enough to influence velocity. I have doubts. Some calculations may be worthwhile.

BTW, I suspect that a MagnetoSpeed does not have sufficient resolution to investigate some of the velocity changes mentioned and a Lab Radar will be needed.

Peter Smith.

ben_g
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Re: Varying powder charge summer/winter?

#11 Postby ben_g » Mon Oct 22, 2018 8:14 pm

I think the magneto is accurate enough to prove that barrel temp has minimal to no effect on MV (at a level where it will not push you out of a node) compared to an increase in ambient temp (therefore powder temp) which has seen an easily measurable increase in MV of 20fps for a 14C increase.

Perhaps you thought I was trying to support Tim's hypothesis with my above post, I was simply suggesting the the limited chrono sessions I have done do NOT seem to support the theory.

bsouthernau
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Re: Varying powder charge summer/winter?

#12 Postby bsouthernau » Mon Oct 22, 2018 8:58 pm

Tim N wrote:I'm guessing the barrel would get smaller as the barrel steel would expand internally and externally?


By and large the hole behaves the same as the stuff that used to be there would have.
Last edited by bsouthernau on Tue Oct 23, 2018 6:55 am, edited 1 time in total.

pjifl
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Re: Varying powder charge summer/winter?

#13 Postby pjifl » Mon Oct 22, 2018 9:25 pm

ben_g stated Perhaps you thought I was trying to support Tim's hypothesis with my above post, I was simply suggesting the the limited chrono sessions I have done do NOT seem to support the theory.

That is a fair comment. I was thinking more in terms of investigating V changes with bore dilation and contraction.

But anyone doing much experimentation should take into account that the LabRadar is an order of magnitude more precise than a Magnetospeed.
I have compared 3 LabRadars on the same projectile and the agreement is awesome. Similarly I have attached 2 MagnetoSpeeds to a barrel and a resolution of even 10 f/s seems well beyond their capabilities and the compared precision changes widely shot by shot.

Each has its place and is useful.

Peter Smith.

RDavies
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Re: Varying powder charge summer/winter?

#14 Postby RDavies » Tue Oct 23, 2018 6:37 am

Going from what I have seen at work heating large bits of steel on earthmoving gear with pin and bearing bores, I would agree that Tims theory has some merit when it comes to barrel heat from firing (but not ambient temps). The last time I heated a fairly large casting with a bearing bore in it was about 2Hrs ago but have seen the same thing quite a few times over the last 30 years. (Possibly Tim has found the same in his metal fab business?)
If a casting with a fairly thin section around the bore is heated gently from outside the casting, the bore usually expanded so we could fit pins or bearings. If the casting around the bore was quite big and we heated the bore area, the bore area shrunk down. I showed this to quite a few people at work over the years as they tried to get lots of heat into the bore and the pin didn't fit in the bore as it expanded inwards. I have sometimes suspected that when we get heat into our 6mm or 7mm bore rapidly while the outside of the 1.25" diameter barrel didn't get time to heat up, did the bore expand inwards around the throat area? Further on this, since the muzzle is often smaller diameter and heats up more slowly, does the muzzle end open up before the chamber end, causing the bore to loosen towards the muzzle?
I tried to experiment with bore pins a while ago t see if I could see this, but it tightened up at both ends very slightly, though this would realistically be at least partly due to fouling.
If the barrel is warmer due to ambient temperature, it would likely heat up gradually and from the outside inwards, so I suspect the bore would open up on a hot day. This would be easy to check with a barrel out of the action, then allowing it to heat up in the summer sun while you check the bore at each end with bore pins.
Now that we have IMR 8208, RE16 and RE23 which are supposed to be even more temperature stable than ADO powders, we could try these to see what happens with velocity as temperature rises.

Julian D
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Re: Varying powder charge summer/winter?

#15 Postby Julian D » Tue Oct 23, 2018 4:16 pm

It has been known to happen as a machinist, if you removed too much material from a bore, there is a trick with an oxy that will close up the dimensions of said bore, basically making it smaller, so the machinist can have another go at his size. Have personally seen it done on numerous occasions. Saving pineapples being fitted up said persons rear .....


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