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Barrel Lengths, Rifle Design

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RifleDude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:16
Originally posted by Edsel Edsel wrote:

Hm.

Won't be getting any answers for barrel length, the way things are looking...


18-20" and 178 - 200 gr with reasonably high BC (above .450 or so) is GTG, but I thought we already answered the barrel part.  You're not going to get a consensus answer, though; opinions vary.
Ted


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 338LAPUASLAP Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:17
Wow and you wonder why people leave before they can get a good answer.          
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:18
... bullet weights given your Sig Sauer 716 PM reference, which tells me you're interested in 7.62 rather than 5.56.
Ted


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Post Options Post Options   Thanks (0) Thanks(0)   Quote cheaptrick Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:19
Originally posted by Edsel Edsel wrote:

...and I am outta here.

 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:21
Originally posted by Edsel Edsel wrote:

...and I am outta here.


Why?  You got answers to all your questions, and during the time we got off-topic, we were posting simultaneously before we had a chance to read your follow-up comments.

For my part, I apologize for helping steer the thread off-topic, however you did ask about barrel length considerations AND rifle design, and gas system length and type is directly related to both.
Ted


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 338LAPUASLAP Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:28
That is the shortest tower I have ever seen.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rancid Coolaid Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:39
And I recall the slats being MUCH further apart.


On the barrel length, sorry, I missed that it was a 716, so we are talking 308 and not 223.  In which case, I would say 600 yards is OK, 800 is pushing it, depending on exactly what is expected.  It is not a precision rifle and should not be counted on to function as one.

With a 16" tube, expect most ammo (LR118, Balck Hills 168 SMK, and the like) to exit the barrel in the ballpark of 2500, give or take (LOTS of variables.)

Does that help.


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Post Options Post Options   Thanks (1) Thanks(1)   Quote 338LAPUASLAP Quote  Post ReplyReply Direct Link To This Post Posted: October/31/2012 at 16:59
5ft I remember 50ft basic 80ft selection maybe 75ft.

I pm'd the OP and I believe he has enough info.

Keep HJ'ing this thread. It will keep up my entertainment value.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gulf1263 Quote  Post ReplyReply Direct Link To This Post Posted: November/01/2012 at 00:16
IMHO, 5.56 mm barrel length has to do with mission.
Shorter barrels are handy, especially in the semi-auto formats if they are to be used for combative type missions..i.e door kicking, room clearing, etc..
For varmitting use, a 20 inch barrel gives more velocity, allowing the bullets to open up at longer ranges.
Piston guns are not necessary until you get into the really shorter barrels, say 11.5 inches and shorter, especially in full auto.
I run an 18 inch full auto, FNC piston gun but in truth would have been happy with a GI M-4 with a 14.5 inch, even though I don't kick doors for a living anymore.
For a bolt gun, a 22 inch barrel gives a little extra zing but in a heavy barrel a 20 inch shoots fine.
I think a lot of folks buy something other than an M-4 for the Chicks Dig It factor, rather than a real need.
You can get away with a cheaper gun that you won't run hard versus one that your life will depend on and that you train weekly with.
A hobby gun is fine to bring out to the range and play with.
I saw a S&W MP-15 for $775.00 recently, shoot it until you wear out the barrel, upper receiver and several bolts, then stick a BCM upper on it and shoot it some more.
The lower will last quite a long time.
A friend puts about 300 rounds a year on his Eagle carbine built in the early eighties and it is fine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BeltFed Quote  Post ReplyReply Direct Link To This Post Posted: November/01/2012 at 11:00
Gosh, I was going to weigh in on the OP's original question, concerning sight radius, and open sights vs CQB rifles with optics, etc, etc.
I like bullpups, you can get a 20" barrel for the same package as a CAR 15 with a 16" barrel and a collapsed stock. However, many countries that use the AUG choose 16" barrels for general issue.
Speaking of pistons, the Styer AUG uses a short stroke piston which is attached to the barrel, so if you change barrels from one length to another, you have the correct size gas port.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PPD7800 Quote  Post ReplyReply Direct Link To This Post Posted: November/02/2012 at 08:54
ok ref. BBL length here is some results that a smith found out.
 

BBL Length vs. Velocity

 

 

This is from well known maker Charlie Sisk:

 

For a long time I have wondered about how barrel length affected velocity. I had always been told you need a certain length barrel for certain calibers. I have read when folks compared one gun to another with different lengths but I always thought that was not an apple to apples comparison. So I did a few tests myself.
All these were Shilen barrels. I used the same brass through out the whole test. All weighed to with 1 grain. Bullets were tested on the Juenke machine. Powder charges were weighed to .1 grain. The same rest, chronograph,
Redding
press, primers all from the same lot, bullets for the same box, same lathe, same crowning tool, same cutoff tool, and each rifle done from start to finish on the same day. Ambient temperature was the same because I shoot from inside the shop. I held the rifle the same way on the rest every time. I shot ten rounds first to break in the barrel. Then cleaned with Sweets and fired one fouling shot. Then shot five rounds and took the average. I used a midrange load form the Nosler book, not too hot, but certainly not a reduced load. Here is what I got.

22-250 Hodgdon 380 34 grains Federal GM210M Remington brass 55 grain Ballistic Tip
27” 3469 fps
26” 3451
25” 3425
24” 3407
56 fps spread from highest to lowest

270 Winchester Hodgdon 4350 54 grains Federal GM210M Winchester brass 130 grain Sierra
27” 3115 fps
26” 3093
25” 3071
24” 3054
23” 3035
22” 3027
21” 3001
114 fps spread from highest to lowest

300 Winchester mag Federal GM215M Winchester brass 74 grains of Reloder 22 180 grain Partition
27” 3055 fps
26” 3031
25” 3024
24” 3003
23” 2984
22” 2960
95 fps spread from highest to lowest

340 Weatherby Federal GM215M 250 grain Sierra 81 grains Reloder 22 Wby brass
27” 2837 fps
26” 2817
25” 2809
24” 2791
23” 2777
22” 2755
21” 2731
106 fps spread from highest to lowest
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 338LAPUASLAP Quote  Post ReplyReply Direct Link To This Post Posted: November/02/2012 at 08:58
rule o thumb 20-30fps per inch...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rancid Coolaid Quote  Post ReplyReply Direct Link To This Post Posted: November/02/2012 at 11:21
Originally posted by 338LAPUASLAP 338LAPUASLAP wrote:

rule o thumb 20-30fps per inch...

Less with a custom barrel or polygonal barrel, more for a factory barrel.
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