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Posted: 6/16/2014 2:27:27 PM EDT
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Ok sorry if this has been covered but I couldn't find any
doing a mega maten question any downside to do a 12.5" Also how bad will the accuracy change say out to 400 |
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Be prepared, a 12.5" .308 SBR is LOUD AS HELL. Depending on the shooter that could be an upside or downside.
As far as accuracy you should not have any problems as long as you use quality parts. However, you will have to compensate more for bullet drop with the loss in velocity due to having a short barrel. This data is from another thread so take it for what it's worth: 150 gr HPBT Win 748 loaded to a chamber pressure of 56.4K PSI WARM load 45 gr NOT a starting load. I chose 748 as the powder as it is most like NATO powder.
26" = 2918 FPS MP= 6.6K PSI ––99.6 % powder burnt -2836 ft/lbs 24" = 2873 FPS MP= 7.4K PSI ––––––––––––––––––––––––––––2750 ft/lbs 22" = 2823 FPS MP= 8.2K PSI ––––––––––––––––––––––––––––2655 ft/lbs 20" = 2766 FPS MP= 9.2K PSI ––98.7 % powder burnt -2548 ft/lbs 18" = 2700 FPS MP= 10.5K PSI ––––––––––––––––––––––––––––2428 ft/lbs 16" = 2623 FPS MP= 12.0K PSI -97% powder burnt ––––2291 ft/lbs 14" = 2531 FPS MP= 14.0K PSI ––––––––––––––––––––––––––2133 ft/lbs 12" = 2417 FPS MP= 16.7K PSI -94% powder burnt ––1946 ft/lbs 10" = 2273 FPS MP= 20.5K PSI ––––––––––––––––––––––––––1721 ft/lbs 8.0"= 2080 FPS MP= 26.0K PSI -87% powder burnt. -1441 ft/lbs 6.0"= 1800 FPS MP= 34.1K PSI -79.4% powder burnt -1080 ft lbs Also, I would suggest investing in an adjustable gas block to assist in getting the rifle functioning reliably. ETA: fixed jacked up formatting |
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Yea figure it would be loud as hell as my 10.5" 300blk
and 11.5" 5.56 are 14.5 isnt worth the stamp 16 maybe a better route to go or just do 2 uppers and build the 12 later.... I am still getting parts together so have some time to figure it out would like to hear if anyone has one build and how they like it |
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Yea figure it would be loud as hell as my 10.5" 300blk and 11.5" 5.56 are 14.5 isnt worth the stamp 16 maybe a better route to go or just do 2 uppers and build the 12 later.... I am still getting parts together so have some time to figure it out would like to hear if anyone has one build and how they like it I have one with a DPMS AP4 barrel cut down to 12.5. I haven't shot it very much but I like it so far, it is very LOUD!! I did have to get an adjustable gas block to get it to run reliably but now it runs with no issues with a variety of ammo. I haven't stretched it's legs yet as I'm still figuring out if I want to put a 1-4x scope on it or a Eotech with a 3x magnifier. I built it more for fun than to reach out an touch someone past 300 meters or so. |
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it's going to be a whole different ballpark of loud than the .300 BO, which is loaded to use up the powder in a short barrel, or the 556, which is a small case capacity round.
I have a LWRC in 6.8mm, the PSD, and it's a great gun for fighting, but not fun to shoot at all, unless supressed. Without a supressor, it's not enjoyable to shoot with overhead cover even with plugs and muffs. 308 is not a good round for short barrels. |
as the shooter you really won't notice any difference if you already shoot 300blk and 5.56 from sbr's , at least not to me. the only real difference to me is the weight of the gun , especially with a suppressor. 308 even out of a 12.5" barrel will shoot through stuff that 5.56 and 300blk can't touch , while not optimum it's no slouch out of a shorter barrel if you don't mind the weight trade off 
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When I get around to 7.62 ARs, I'll have a 12.5" .308 upper and a 20" .260 upper .260 inches are bigger than other guns. I don't know what this means A .260 gives up a lot of muzzle velocity for barrel length. 22-24" is short for one of them. Although, they're muskets with cans on them. |
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as the shooter you really won't notice any difference if you already shoot 300blk and 5.56 from sbr's , at least not to me. the only real difference to me is the weight of the gun , especially with a suppressor. 308 even out of a 12.5" barrel will shoot through stuff that 5.56 and 300blk can't touch , while not optimum it's no slouch out of a shorter barrel if you don't mind the weight trade off I'll second this....reason I have a 308 SBR is because it packs a hell of a lot more punch than 556 and I imagine a 300 blk. I built a 300 blk for the subsonic sound suppression but at 200 meters the ballistics suck. I've seen haji's (we still called them muj before the powers that be said that wasn't allowed anymore) take 20-30 green tip in order to kill them but I've also seen my buddy stateside fire 3 fatal shots with 9mm ball ammo (self defense and all three rounds were deemed to be individually fatal) so even weaker rounds can be immediately fatal if in the right place. If ever faced with a situation where I'm going house to house and room to room I'll take my 308 SBR over 556 or 300 blk any day of the week....but obviously it's for fun or kind of a novelty item for now. If you can afford it I would recommend the 12.5 308 and just build another upper with a longer barrel for accuracy like the dude that recommended the 12.5 SBR and the .260. Best SBR por sub gun IMO for clearing houses would be something in .45 cal, like a tommy gun (too heavy) or an HK UMP (a little off topic). |
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