Reloading for shorter barrels?

tinker

tinker

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Minuteman
Aug 28, 2017
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north of philly
#1
Never really messed with shorter barrels before but starting to. (16" 6.5cm)

Initially not impressed with accuracy using ammo I loaded for my 26" 6.5CM.

I know it will be was down on Velocity (getting about 2550 instead of the 2800+ I was getting).

I got wondering about how much velocity you really need to stabilize 123gr and 140 gr.
I know I won't be able to get the velocities I achieved before without being way over pressure.

Curious how diff people's loads are for shorter barrels vs longer and effect on accuracy?
 
#3
tinker said:
Never really messed with shorter barrels before but starting to. (16" 6.5cm)

Initially not impressed with accuracy using ammo I loaded for my 26" 6.5CM.

I know it will be was down on Velocity (getting about 2550 instead of the 2800+ I was getting).

I got wondering about how much velocity you really need to stabilize 123gr and 140 gr.
I know I won't be able to get the velocities I achieved before without being way over pressure.

Curious how diff people's loads are for shorter barrels vs longer and effect on accuracy?
Click to expand...
Your 16" 2550 velocities is about what I was getting with my 18". I could get 2700 but I was trashing peterson brass in just a handful of firings. Shot fine as an 8 twist with 140s, no tumbling etc that I could tell.
Yeah its known more wind to account for and hold but thats just the nature of whacking off 40% of the bullets runway when compared to a 26" barrel.

Most all combustion is done in the first few inches of the barrel so unless you are super duper sbr short the best velocity load for a 16" will be the same as a 26". Where exactly that best spot is load wise depends more on the barrel and component combinations that just barrel length. Start low and work up.
 
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#5
Velocity is only a minor factor in stability until the SG starts to drop below 1.3. Then the impacts of ambient conditions and BC reduction become more significant. One thing to consider on accuracy is that slower powders take longer and more barrel length to burn out completely. Unburnt powder can affect the dispersion of the bullet from impact on the base of the bullet on muzzle exit. The result is that faster burning powders in shorter barrels may improve the accuracy/precision over slower burning powders even though they will typically cause some loss in velocity.
 
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#6
Doom said:
Velocity is only a minor factor in stability until the SG starts to drop below 1.3. Then the impacts of ambient conditions and BC reduction become more significant. One thing to consider on accuracy is that slower powders take longer and more barrel length to burn out completely. Unburnt powder can affect the dispersion of the bullet from impact on the base of the bullet on muzzle exit. The result is that faster burning powders in shorter barrels may improve the accuracy/precision over slower burning powders even though they will typically cause some loss in velocity.
Click to expand...
Because of this I was thinking of trying some varget instead of h4350.

Guess I just have to do a complete load workup. I was able to get some intial 3/4 moa 5 shot groups but that was just my plain 140gr 26" load.

I did a little bit of 123gr and started low but wasn't super impressed. In all honesty though I did not cover a very wide array of powder charges and may have started a little too low.
 
#7
tinker said:
Because of this I was thinking of trying some varget instead of h4350.

Guess I just have to do a complete load workup. I was able to get some intial 3/4 moa 5 shot groups but that was just my plain 140gr 26" load.

I did a little bit of 123gr and started low but wasn't super impressed. In all honesty though I did not cover a very wide array of powder charges and may have started a little too low.
Click to expand...
2550 with H4350 in a 16" isnt too low. You wont ever get a 140 going that fast in a short barrel with out spiking pressures.

Varget with a 123, sure.
Varget with a heavier 140 is not going to suddenly make more speed just because the bullets ability to accelerate is stopped sooner in a short barrel... without a corresponding spike in pressure.

Your powder choice should be based on matching the bullet mass and chamber/bore volume so that the optimal powder makes the right amount of gas to fill the sapce behind the bullet as it moves down the bore increasing the available volume behind it which is to be pressurized.
 
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#8
spife7980 said:
2550 with H4350 in a 16" isnt too low. You wont ever get a 140 going that fast in a short barrel with out spiking pressures.

Varget with a 123, sure.
Varget with a heavier 140 is not going to suddenly make more speed just because the bullets ability to accelerate is stopped sooner in a short barrel... without a corresponding spike in pressure.

Your powder choice should be based on matching the bullet mass and chamber/bore volume so that the optimal powder makes the right amount of gas to fill the sapce behind the bullet as it moves down the bore increasing the available volume behind it which is to be pressurized.
Click to expand...
I had not loaded the 140s for the 16", loaded for the 26". I was just trying them out.

The 123s I am loading for the 16. I am no where near expecting any velocity close to the realm of a longer barrel. My loads aren't near max for my 26". I just trying to see if a little more will help. Only time will tell. If I see pressure signs of course I am going to stop.

I tried googling to see what kind of velocity people were getting with shorter barrels but honestly didn't see much referencing accuracy with shorter barrels.
 
#9
tinker said:
I had not loaded the 140s for the 16", loaded for the 26". I was just trying them out.

The 123s I am loading for the 16. I am no where near expecting any velocity close to the realm of a longer barrel. My loads aren't near max for my 26". I just trying to see if a little more will help. Only time will tell. If I see pressure signs of course I am going to stop.

I tried googling to see what kind of velocity people were getting with shorter barrels but honestly didn't see much referencing accuracy with shorter barrels.
Click to expand...

The accuracy is the same if not better in short barrels. The only difference is speed and a flatter shooting bullet (faster) will be inherently more accurate at distance due to dispersion.

It’s roughly 25fps per inch of velocity loss.
 
#16
I generally use the same powder in short barrels as long barrels, like the 16" AR 10 and the 30" bolt gun get the same powder.

The one that gets the highest velocity in the long barrel also gets the highest velocity in the short barrel.

But you'll have to test accuracy and S/Ds as each barrel is different regardless of length.
But the same powder used in these two extreme examples of barrel length had excellent accuracy, high velocity, and single digit S/Ds.
 
#17
I've only had one 18" 6.5 Creedmoor barrel, but I've had pretty good luck so far with N150 and 123 Scenars.

Approx. ~2850 fps with 40.0 grains N150 and Norma/RUAG brass. No noticable pressure signs. ~3/4 MOA accuracy.

Would have to look at my reloading book for SD's, but it was probably around 10. Mind you that's with reused Prime brass that's once fired in a different chamber, and potentially from a few different lots. This is my hunting barrel, so I treat it a bit differently than say my 28" 6BRA.
 
#22
spife7980 said:
2550 with H4350 in a 16" isnt too low. You wont ever get a 140 going that fast in a short barrel with out spiking pressures.

Varget with a 123, sure.
Varget with a heavier 140 is not going to suddenly make more speed just because the bullets ability to accelerate is stopped sooner in a short barrel... without a corresponding spike in pressure.

Your powder choice should be based on matching the bullet mass and chamber/bore volume so that the optimal powder makes the right amount of gas to fill the sapce behind the bullet as it moves down the bore increasing the available volume behind it which is to be pressurized.
Click to expand...
Didn't mean to start a fire storm with my comment. Shorter barrel accuracy may/can benefit from faster powders for the reason I stated but @spife7980 is correct that the powder still has to match the bullet mass and chamber/bore volume expansion rate to be suitable. There are other factors at play also such as barrel harmonics and velocity also have an effect on accuracy. If velocity is the primary concern then slower powders that can fit in the case and obtain full pressure will usually give the highest velocity in reasonably length barrels. This is because the pressure is held higher by the slower burning powder. There is really only one way to know for sure and that is to test after you have determined what factors/objectives your reloads need to make.

One of the benefits of Quick Load and Gordon's Reloading Tool is the ability to see case fill and Unburnt Powder predictions without having to actually guess at what the powders are doing. Someone posted a link on this forum (I think) to Little Crow Gunworks a day or two ago. I wasn't familiar with the guy or his site but checking it out I found this:



He actually is using a similar approach to what I use although I don't always agree with how he does his simulations.

As for the effects of unburnt powder on shot dispersion this subject is covered in Jeff Siewert's book Ammunition Demystified.
 
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#24
Doom said:
Didn't mean to start a fire storm with my comment. Shorter barrel accuracy may/can benefit from faster powders for the reason I stated but @spife7980 is correct that the powder still has to match the bullet mass and chamber/bore volume expansion rate to be suitable. There are other factors at play also such as barrel harmonics and velocity also have an effect on accuracy. If velocity is the primary concern then slower powders that can fit in the case and obtain full pressure will usually give the highest velocity in reasonably length barrels. This is because the pressure is held higher by the slower burning powder. There is really only one way to know for sure and that is to test after you have determined what factors/objectives your reloads need to make.

One of the benefits of Quick Load and Gordon's Reloading Tool is the ability to see case fill and Unburnt Powder predictions without having to actually guess at what the powders are doing. Someone posted a link on this forum (I think) to Little Crow Gunworks a day or two ago. I wasn't familiar with the guy or his site but checking it out I found this:



He actually is using a similar approach to what I use although I don't always agree with how he does his simulations.

As for the effects of unburnt powder on shot dispersion this subject is covered in Jeff Siewert's book Ammunition Demystified.
Click to expand...

as a side note I am trying an experiment. I have an old take off barrel that it turns out was shot out. Chopped ten inches off the chamber end and turned it into a remage barrel. Now trying to see if it will shoot again.

So far it went from 27" being shot out and shooting 1 1/2" groups to 3/4 with ammo not tuned for it. and some potential "maybe" with 123s and a faster powder.

Just doing it all for fun to see what happens.
 
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#25
My go to load for any 6.5 is a 140 ELDM with 42.0 gr H4350 in a Hornady case and that load has shot 1/2 moa in 5 different barrels going from 18" to 26" (one of them a gasser). It's 2800+ in the 26" pipe and 2620 in the 18". I've since run out of H4350 but have lots of N160, N150 and N555. I couldn't get a load to shoot as tight/not over pressure at that same speed with N160 with my go to load (42.5) with that powder running 2555fps in the 18" barrel. I might try some N150 (although I prefer that for .223) and will definitely try some N555. I just kinda balk at buying more H4350 at what it costs now compared to what I get Viht powders for, haha.
 
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