The 1:8 barrel twist

[lysander]

Interesting... and possibly the explanation of how a mil pull down 5.56 has SO MUCH powder inside. If I'm tracking the powder has a certain retardant to allow for more propellant without an early pressure spike that could burst the case or worse.

Basically, yes.

[vicious_cb]

Well it looks like at least 1 military is going be using double based powder, barrel life be damned. Wouldnt be surprised if M855A1 is atleast a single based since they were chasing velocity since its inception probably some kind of special St. Marks blend.

[Molon]

Well it looks like at least 1 military is going be using double based powder, barrel life be damned. Wouldnt be surprised if M855A1 is atleast a single based since they were chasing velocity since its inception probably some kind of special St. Marks blend.

The powder used in M855A1 is a double base propellent.





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[lysander]

Well it looks like at least 1 military is going be using double based powder, barrel life be damned. Wouldnt be surprised if M855A1 is atleast a single based since they were chasing velocity since its inception probably some kind of special St. Marks blend.

As stated above, even though ball propellants are double based, they have some of the lowest flame temperatures and are the easiest om throats.

The propellant used in the M855A1 is SMP-842, a variation of CFE223.

[constructor]

1/8 is really what almost everyone should be running. 1/7 is military spec to stabilize the long ass M856 tracer, but it's overkill for almost every mag length round the average guy would ever use.

Agree and the 7 twist buttons are just plain old mil spec Enfield rifling with a 50:50 L-G ratio. You know what they say about opinions, I would much rather use a 8 twist 5R with a 30-70 L-G ratio that puts out 60-90 more FPS.

[lowprone]

Great thread !

[vicious_cb]

Agree and the 7 twist buttons are just plain old mil spec Enfield rifling with a 50:50 L-G ratio. You know what they say about opinions, I would much rather use a 8 twist 5R with a 30-70 L-G ratio that puts out 60-90 more FPS.

Im not following here, are you saying 1/8 gets more FPS because of less rotations or is it some kind of special rifling combined with a slower twist that does it. Is this like a Triarc track barrel that has some kind of special rifling that boosts FPS or something? I believe the track series barrels are also 1/7 so Im guessing the mfg'er doesnt 1/8 would benefit the barrel.

[vicious_cb]

Agree and the 7 twist buttons are just plain old mil spec Enfield rifling with a 50:50 L-G ratio. You know what they say about opinions, I would much rather use a 8 twist 5R with a 30-70 L-G ratio that puts out 60-90 more FPS.

Im not following here, are you saying 1/8 gets more FPS because of less rotations or is it some kind of special rifling combined with a slower twist that does it. Is this like a Triarc track barrel that has some kind of special rifling that boosts FPS or something? I believe the track series barrels are also 1/7 so Im guessing the mfg'er doesnt 1/8 would benefit the barrel.

[jwfuhrman]

Really wish they’d sell them separately, the KD4 barrels that is

[lysander]

Im not following here, are you saying 1/8 gets more FPS because of less rotations or is it some kind of special rifling combined with a slower twist that does it. Is this like a Triarc track barrel that has some kind of special rifling that boosts FPS or something? I believe the track series barrels are also 1/7 so Im guessing the mfg'er doesnt 1/8 would benefit the barrel.

Slower twist theoretically would give higher velocities for the same pressure profile as less energy is used to rotate the projectile. It was easily measured in old tank guns.