Faster powders for shorter barrels - say 1680 for a 16 inch 308

[bigedp51]

From the H.P. White Test Labratory

"1.4 Failure of a gun assembly from internal pressure may be from either
of two (2) failure mechanisms.

1.4.1 The general perception is that those failures are the result
of a single exposure to a CATASTROPHIC PRESSURE level. This
may be an over simplification in that the strength of the
assembly may have been degraded by previous repeated exposures
to excessive, but lesser, levels of pressure whose cumulative
effect is to reduce the ultimate strength of the assembly.

1.4.2 Repeated exposure to pressures which exceed the elastic limit
of a material will continually reduce the ultimate strength of
the material until the ultimate strength is exceeded by a
relatively low pressure level causing fatigue failure."

 

[supernova]

Just gonna set my lawnchair up right here and get comfortable with a bag of chips and some beer. What time do the fireworks start?

 

[Ganderite]

You are kind'a missing the fact that lots of good folks out there have pulled apart el cheapo 7.62x39 surplus rounds and dumped the powder load into a 303 Brit case, re-seated the surplus boolit into that ol' timer case, fired the round and said "wow, no issues .. kind'a a nice practice round actually". No death star galactic-ending thing happening at all.

A few uber brave guys have actually taken TWO AK rounds apart and loaded one of the boolits and the powder from, let's say, one and a fifth AK rounds into a 303 case and discovered that still didn't lead to the destruction of the universe. They actually found that it was a nicer shooter than a classic 303 load - and didn't cost them 58 bucks a box.

... Is the World about to end?

No one said you can't or should not use the powder from 7.62x39 in a 303Brit.

What I am saying is, given the same max pressure, that fast power will produce less velocity. In a long barrel and in a short barrel.

If you want to claim that in a short barrel a faster powder will produce a higher velocity than the powder that produces the best velocity in a long barrel, that is fine. No harm in contradicting the accepted facts.

You can claim the earth is flat, too.

I would like to see such a test shot in a pressure gun, so we can see the equal max pressures - but I don't have access to one anymore.

I will volunteer to conduct such a test as best I can - but I think most of us would rather see you do it.

 

[kc34]

No one said you can't or should not use the powder from 7.62x39 in a 303Brit.

What I am saying is, given the same max pressure, that fast power will produce less velocity. In a long barrel and in a short barrel.

If you want to claim that in a short barrel a faster powder will produce a higher velocity than the powder that produces the best velocity in a long barrel, that is fine. No harm in contradicting the accepted facts.

You can claim the earth is flat, too.

I would like to see such a test shot in a pressure gun, so we can see the equal max pressures - but I don't have access to one anymore.

I will volunteer to conduct such a test as best I can - but I think most of us would rather see you do it.

Yes, PLEASE let steelgray do the test and put his money where his mouth is.....................

 

[todbartell]

The jungle carbine was reportedly taken out of service because the troops who were issued these didn't like recoil and intense muzzle blast. Looks like folks here are on-track to come-up with a load that could have made the no. 5 gun a decent gun for use in its intended operating theater; i.e. the AA1680 load.

Can you post your AA1680 loads here for all of CGN to benefit from?

 

[Evanguy]

Yes, PLEASE let steelgray do the test and put his money where his mouth is.....................

Id let him do it if he wants. I only offered to make it impartial because i dont care either way. Im not trying to convince you all anything.

Hell we all can do it and compare notes and velocitys. Abd put this argurment to rest

 

[supernova]

My only experience with AA1680 was in an 18.5" guide gun and was a disappointment. Barnes had a load for their 250gr TSX in .45-70 showing 2600fps from a 26" bbl with their max charge. Since I was getting close to book velocity with both 4198s and 350 Hornady FNs I decided to try the TSX/1680 load. Unfortunately the velocity clocked around 2000 fps but worst of all the muzzle flash and blast was horrendous. I've heard other stories of 1680 fireworks in other cals with shorter barrels. Powder burn rate is just one aspect. Performance can vary in different cals quite a bit with the same powder. I'm with team old guy and their olde timey lab and range experience.

 

[Suther]

You can claim the earth is flat, too.

Bwhahahaha you sir just made my day.

 

['Boo]

Id let him do it if he wants. I only offered to make it impartial because i dont care either way. Im not trying to convince you all anything.

Hell we all can do it and compare notes and velocitys. Abd put this argurment to rest

If he wants to put himself into a pirate costume complete with authentic eye patch and hook in place of a hand let him fly at it. I would suggest that it is starting to look like he is purposely trying to get someone else to do something that may end up hurting or killing them.

 

[Ganderite]

STEEKGRAY WROTE: Lots of talk here but the bottom line is that testing proves that if you shorten and 7.62x39 barrel from let's say 20 inches to 16 inches the ballistic performance is pretty well the same.

If you do the same with a 308 then the drop-off in ballistic performance is huge and, in fact, the 16 inch 308 gun performs about the same as the 16 inch 7.62X39 gun.

The video comes up short because they don't properly explain why.

The specific reason why is that the AK cartridge uses a fast enough powder that most of the pressure has been delivered to the bullet before it leaves even a 16 inch barrel. In the case of the 308 round, the slower powder which is traditionally used in this cartridge means that most of the pressure delivered to the bullet is only achieved in a longer barrel.

When you shorten the barrel in 308 gun the drop off in performance is huge because the slow burning powder is mostly wasted.


He is misreading the information.

Lots of talk here but the bottom line is that testing proves that if you shorten and 7.62x39 barrel from let's say 20 inches to 16 inches the ballistic performance is pretty well the same.

Yes. This is because the 7.62x39 does not have enough capacity to use a slow powder that would reach max pressure, so a fast powder is used. Because it is fast, the pressure curve drops very fast and there is not much pressure to accelerate the bullet in the last half of the barrel.


If you do the same with a 308 then the drop-off in ballistic performance is huge and, in fact, the 16 inch 308 gun performs about the same as the 16 inch 7.62X39 gun.

No. I expect a 16" 308 to shoot 175gr bullets at a higher velocity (around 2,500 fps) than a SKS (18") would shoot a 124 gr bullet. I say "expect" because (like the OP) I have not yet done any testing. But I think I will. I have a 18" FR8.


The specific reason why is that the AK cartridge uses a fast enough powder that most of the pressure has been delivered to the bullet before it leaves even a 16 inch barrel. In the case of the 308 round, the slower powder which is traditionally used in this cartridge means that most of the pressure delivered to the bullet is only achieved in a longer barrel.

Yes and no. The 308 loses velocity because the powder is still developing pressure, which is lost in the shorter barrel.

"The specific reason why is that the AK cartridge uses a fast enough powder that most of the pressure has been delivered to the bullet before it leaves even a 16 inch barrel." The AK uses a fast powder because the case is too small for a slower powder, which would give it a higher velocity.

If you are trying to get velocity, you use enough powder to get max allowed pressure. Then you select the slowest powder that fill fit the case and get max pressure. In a 308, that is something like Varget or RL15 with a 175 gr bullet. It will get 2750 ish in a long barrel and 2500ish in a short barrel. (My estimate. I will find out.)

You are assuming that a faster powder in 308 will do better than a slow powder in a short barrel. If you were suggesting a reasonable powder, like 3031, no one would care. It would not take long to find out it would not work better.

But to suggest a 7.62x39 powder (very fast) like 1680 would out perform RL15 or Varget in a short barrel is not only ludicrous, but potentially dangerous.

I have a 26" 308 and a 18" 308 and I will shoot virgin cases with both powders in both rifles and publish the results. I already think I know the outcome, but am curious to see the actual numbers.

 

[Ganderite]

People will tell you that Accurate 1680 is too fast for a .308 etc. BUT I say the faster stuff makes total sense for short barrel guns like a 16" 308.

I figure people should match the burn rate to the barrel length. You got a 7" AR? Go with a faster powder or you'll have a huge fireball going on at your muzzle every time you touch-off a round. Got a 9mm carbine? Think of using a slower powder than you would use for your handgun.

IMO, one of the reasons to reload is so you can make these kind of adjustments to suit your situation. Reloading manuals won't help. Use Quickl*ad.

What do you base this on? Have you tried it? Or just a hypothesis?

Have you given up on the idea that the faster powder will produce a higher velocity than a slow powder in a short barrel?

 

[steelgray]

<snip>
If you want to claim that in a short barrel a faster powder will produce a higher velocity than the powder that produces the best velocity in a long barrel, that is fine. No harm in contradicting the accepted facts.

You can claim the earth is flat, too. ... <snip>

I’m certainly not saying that an AA1680 loading, setup for normal operating pressures, would shoot faster out of a 16” barrel than out of a 24” barrel. That would be nutz.

But, based on what we know of the effect of burn relates in relation to barrel lengths, as Evanguy put it, a good possibility would exist that, for example, in a 303 British case

Powder X gives you 2400fps from a 24" barrel (slower powder)
Powder Y gives you 2200fps from a 24" barrel (faster powder)

If you cut the barrel to 16" there is a good chance that

Powder X may only be 2000fps whilst powder Y gives, say 2100fps

Both powders use the same load data in 24" and 16" barrels

I’ve gone beyond that to say that, even if both loads were to deliver say 2000 FPS in a 16", I’d go with the faster powder load because it would be the nicer shooter. Slow powders give up a lot of velocity as you move from a longer to shorter barrel and the loss is a result of much of the energy in the propellant being wasted as pressure which is still building AFTER the bullet leaves the bore.

As previously noted, (but for others, just tuning in) here’s a wordy but useful illustration of that.

This wasted pressure is worse than useless since it takes the form of a ridiculous fireball and an insane amount of concussion/ muzzle blast. Even if that powder has flash inhibitors, people will still not want to be anywhere near you when you are touching off rounds. If you are in a tree stand, make sure you are strapped in well and, if you are shooting at dusk or dawn, don’t count on seeing much until your eyes recover from the flash. Like I said, “where’d the deer go?”

I’m not obsessed with velocity. To me, a good load is one that delivers the ballistic performance necessary for the job, shoots well and is balanced for the gun involved.

Guys who will do anything to get the last FPS out of their 308 – even to the point of creating a load that yields ridiculous muzzle blasts should, IMO, just sell their 308, buy a 300 Win mag and just bring a step ladder with them when they hunt.

 

[Suther]

I’m certainly not saying that an AA1680 loading, setup for normal operating pressures, would shoot faster out of a 16” barrel than out of a 24” barrel. That would be nutz.

The funny part is where you think anything else you're saying isn't equally nutz...

The only way things would work in the way you describe is if your barrel is so short the slower powder cannot reach max pressure, which occurs in the first few inches. So if you're taking 3" barrels, MAYBE your idea is valid, otherwise you are wrong. Period.

Its all about case capacity. A bigger case can reach max pressure with a slower powder, whereas a smaller case will never reach max pressure even with a compressed load of slow powder. Alternatively, a big case full of fast powder will create far too much pressure. This is why different powders exist, not because of barrel length.

 

[Ganderite]

I asked: Have you given up on the idea that the faster powder will produce a higher velocity than a slow powder in a short barrel?


And you answered:

Powder X gives you 2400fps from a 24" barrel (slower powder)
Powder Y gives you 2200fps from a 24" barrel (faster powder)

If you cut the barrel to 16" there is a good chance that
Powder X may only be 2000fps whilst powder Y gives, say 2100fps

So your answer is "yes". You think a faster powder will give better performance in a short barrel than a slow powder.

To me, that makes no sense. The slow powder has more area under the curve, regardless of barrel length. Therefor the best powder is always the best powder. Period.

Using your example of 2400 and 2200 in a 24" barrel, a fast powder would get (I think) a bigger difference than 200 fps. More like 400fps slower. And I expect to find that in a 18" barrel, the fast powder continues to under perform.

 

[Evanguy]

That example used above was me just using random numbers to make sure i had figured out exactly what he was trying to say. The numbers were totally off the top if my head with no correlation to any real data

Then in a later post i simplifed it again too

"The claim that h4895 will have more velocity then the 1680 load in the 28" barrel but same load in the 18" the 1680 will have more FPS then the h4895 load"

 

[jethunter]

You are kind'a missing the fact that lots of good folks out there have pulled apart el cheapo 7.62x39 surplus rounds and dumped the powder load into a 303 Brit case, re-seated the surplus boolit into that ol' timer case, fired the round and said "wow, no issues .. kind'a a nice practice round actually". No death star galactic-ending thing happening at all.

A few uber brave guys have actually taken TWO AK rounds apart and loaded one of the boolits and the powder from, let's say, one and a fifth AK rounds into a 303 case and discovered that still didn't lead to the destruction of the universe. They actually found that it was a nicer shooter than a classic 303 load - and didn't cost them 58 bucks a box.

... Is the World about to end?

You understand Biped was joking, right?

 

[Ganderite]

That example used above was me just using random numbers to make sure i had figured out exactly what he was trying to say. The numbers were totally off the top if my head with no correlation to any real data

Then in a later post i simplifed it again too

"The claim that h4895 will have more velocity then the 1680 load in the 28" barrel but same load in the 18" the 1680 will have more FPS then the h4895 load"

Yes, that is the assertion that makes no sense.

I suppose if the barrel was cut back to 3 ", it might get close.

 

[steelgray]

I asked: Have you given up on the idea that the faster powder will produce a higher velocity than a slow powder in a short barrel?


And you answered:

Powder X gives you 2400fps from a 24" barrel (slower powder)
Powder Y gives you 2200fps from a 24" barrel (faster powder)

If you cut the barrel to 16" there is a good chance that
Powder X may only be 2000fps whilst powder Y gives, say 2100fps

So your answer is "yes". You think a faster powder will give better performance in a short barrel than a slow powder.

To me, that makes no sense. The slow powder has more area under the curve, regardless of barrel length. Therefor the best powder is always the best powder. Period.

Using your example of 2400 and 2200 in a 24" barrel, a fast powder would get (I think) a bigger difference than 200 fps. More like 400fps slower. And I expect to find that in a 18" barrel, the fast powder continues to under perform.

I wouldn't get hung-up on the individual numbers - they were suggested as an illustration of the idea by Evanguy - not me. I support them as an illustration (only) - as intended

What I would consider is the suggested relationship among the no.s; so that the slow powder losses FPS more quick than the fast powder - as barrel lengths shorten (something that is a a fact). Further, what is suggested by the example (or illustration) is that, as the barrel length get short, any significant speed advantage that the slow burning load had is largely lost - as suggest by the video in field testing.

Whether a point is reached where faster powder actually gains a performance edge I don't know - nor does that matter much to me. As mentioned, I'll take a balance load over one that features excessive concussion any day - if the two deliver similar performance. The video finds that slow powder loaded 308 does in fact underperforms compared to the 8" 7.62x39 and the 8" 308 is a pig to the point that no one actually wants to shoot it - but that is a fairly extreme example. I think rather than throwing the gun away they could think of using contender loads from Lyman 49 or ... wait for it ... cook up an AA1680 load

As for my testing, I am not retired guy - as I suspect to be the case for some of you folks. I am behind on many deadlines and don't see myself having the opportunity to test these things fully for a while.

When I do get a chance, I will probably just load up some QL-based 125 gr. AA1680 loads and see how they shoot in my 16" Mossberg - comparing these to some 125Gr H414 rounds I already have on-hand - which I know produce an unpleasant muzzle blast in my gun. If the AA1680 load achieves equivalent accuracy and about the same point of impact - without all the drama of the other H414 load I will be happy. I don't even see myself having the time to do even this limited testing a for a few weeks.

I'm pleased to see that others who are better set-up for this testing may be prepared to do so, in a more rigorous fashion, in the mean time.

It is clear that we do not share priorities. I do not understand this obsession with getting the fastest load at any price - including ridiculous muzzle blast. Like I said, just buy a 300 Win mag and take a step ladder with you when you hunt. As I have already indicated, I'd rather have a balanced gun that does the job well and that I actually enjoy shooting

 

[todbartell]

Slow powders give up a lot of velocity as you move from a longer to shorter barrel and the loss is a result of much of the energy in the propellant being wasted as pressure which is still building AFTER the bullet leaves the bore.

A 303 British 174gr / H4895 load, peak pressure comes when the bullet has traveled 1.2" down the bore

 

[woodchopper]

I have a 300WM, I throw a 200grn bullet at 2960FPS and its not unpleasant.

what the hell is the step ladder for? perhaps where you hunt you have some weird limitations.

if your going to buy a short barrel carbine perhaps you need to look at something that is chambered with an appropriate case/chamber.

308 is not going to work as it was designed for rifles with 20" barrels.

I would not buy a 300WM with a 18" barrel either it would be a waste of case capacity, bigger cases, more powder but slower powder, more velocity, barrel length does not really change that but a shortened barrel will result in a loss of potential velocity.

perhaps what you need is a 30-30, that has a reasonable case capacity for a faster powder, and a shorter barrel will be sufficient to use what potential there is in that case.