Powder speed....308 Win, 20' tube

chambered221

stovepipe wrote:

I was on the Sierra site looking at the BC for the 168 and 175 SMK. Big jump in BC for the 175.

You do understand you'll be no where near that advertised .505 don't you ???

stovepipe

Nowhere near it? I forget the exact speed but they are all affected by speed and the BC's go up and down with same.

Got my data and recipes now from Sierra (Thanks boys!) and I the 175 is really slow, 200'/sec slower than the 168! There's so many interesting bullets from 150 to 168 for this. Gonna do a quicky chamber sizing with some fired brass before I pick my first batch of pills and after I get some rounds through it...which is Monday. Joy!

SyberShooter · Member Joined: Jul 23, 2010 Posts: 93 Location: Arizona

OK I'll bite - tell me why a Mohawk (Rem 600) that came with an 18.5" bbl would prove me wrong. And also why a BLR with a 20" bbl would do likewise. Are we talking loads of 4064?
A lot of the proof would have to do with which powder was being used. I failed to mention the discussion was in the context of how short to cut a FAL bbl down. One could assume that Nato milsurp would be the normal ammo for that rifle thus W846 would be the probable powder or of similar burn rate which would equate to BLC2 or AA 2230/2460 or similar. So I still think 18"-19" would be the minimum length barrel to completely burn a modern medium burn rate powder for 308. Smile

PaulS

SyberShooter,
Many tests have been done with rifles and pistols proving that the best powder for a given case has nothing to do with barrel length. The correct powder is decided by the size of the case and the weight of the bullet.
The tests also showed that the powder was completely burned in the first couple of inches and the expansion from that heat kept pressures high until the bullet exits the barrel. The muzzle flash and glowing bits are super-heated carbon and ash from the already burned powder. The term "powder burns" is a misnomer which is actually caused by the glowing bits of ash and not unburned or still burning powder.
The shorter the barrel the more glowing bits of ash and superheated gases exit with the bullet but the powder has already burnt - even with a 308 cut down to 10 inches. Yes some of the pressure is wasted due to the shorter barrel length but the same powder that gives the highest velocity in that barrel at 24 inches will give the highest velocity in the barrel when cut to 10 inches.

Elvis

yip you got my drift Sybershooter there is some plurry great .308s out there with shortish tubes they are no slouch on velocity and VERY accurate. I have seen write ups on .308 going even shorter (down to 16") and still getting good velocity. try some 130 grn hp speers if you want a quick load that works well on deer.

slimjim

Elvis wrote:

try some 130 grn hp speers if you want a quick load that works well on deer.

I had good results with 130gr Barnes TTSX!

chambered221

Yup ....... Gotta agree with Paul !!!

stovepipe

Good stuff boys.

Lookin' real hard @ that 155 Palma MK! Higher BC's than the 168 and most of the powders overlap........inlcuding VARGET Shocked

....neee-toe! Very Happy

So many choices....hope it has a tight chamber so I can sneak 'em up on the lands w/ one of these two pills while I still got enough shank for the mouth to hold onto. Fun stuff! Razz

SyberShooter · Member Joined: Jul 23, 2010 Posts: 93 Location: Arizona

Paul, thanks for the info - makes sense when ya think about it.

I suppose the old wives tale concept of powder burning all the way down the barrel is a misconception of the glowing debris and available pressure to blow them out in a large muzzle flash. Which would sorta represent the amount of potential power being lost.

stovepipe

chambered221 wrote:

Yup ....... Gotta agree with Paul !!!

Me too! A lot! ....when he aint hackin tiddler-bore's down to 10" to make a house gun outta it.... Shocked

slimjim

SyberShooter wrote:

I suppose the old wives tale concept of powder burning all the way down the barrel is a misconception of the glowing debris.

Could this be a left over from the black powder days? Also, couldn't this happen with modern powders if one loaded too slow a powder. Varget in my .45-70 behind a 405gr lead slug left unburned powder all the way down the barrel. I agree with Paul's explaination for a proper load with modern propellants.

Ominivision1

Yup, I too noticed this with Varget, and the solution was to increase the powder load, gradually the problem with unburnt powder went away while staying under max loads.

Elvis

isnt that the reason they say to crimp some loads?

stovepipe

Yep- complete combustion depends on the propper pressure!

Crimp can help, but its priamry function's for holding the pill still during recoil. Propper powder charges help too.
So does moving the pill out onto or just off the lands- this allows good pressure with less powder!

shrpshtrjoe

Elvis wrote:

yip you got my drift Sybershooter there is some plurry great .308s out there with shortish tubes they are no slouch on velocity and VERY accurate. I have seen write ups on .308 going even shorter (down to 16") and still getting good velocity. try some 130 grn hp speers if you want a quick load that works well on deer.

+1 I have a Rem 788 in .308 wjth the short barrel and most of the time it shoots better than I do Laughing