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Posted: 12/20/2007 4:59:37 PM EDT
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Help! The BRD has got me. I am currently looking into a sbr upper for ar number two. My initial thought was if I was going to go through the hassle of the sbr process, I was going for the gusto and get a 7.5" bbl length. I have read many threads and found almost everybody stays between 10.5 in. and 14.5 in. for bbl length. Why is this? Is this a velocity or functioning/reliability issue? If so, most AR pistols use a 7.5" upper. Why don't I see more people using the 7.5" uppers for SBR builds? The upper I am looking at is the model 1 sales 7.5" with 1/9 twist. With this twist and bbl length I should be fine with 75 gr. right? Alright Gurus, lets hear it......And thank you in advance for the school'n. |
I would think not. You might be told other observations, but I found that my 7.5" 1-9 barrel likes 40 gr projectiles the best. I found that 68 gr Hornady BTHP did not do so well out to 150 yards. This might be past the "usable" distance of the 7.5" bbl, which is why after a couple trips to the range with different types of handloads I'm in the market for a CMMG 10" 1-7 bbl. |
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Remember, Uncle Gene designed the AR with a 20" barrel. Any time you deviate from the original design of something you will have issues. Having said that, most of these issues have been addressed successfully over the years, but the tricky one is gas pressure. Also, not only do you need a certain twist rate to stabilize a bullet, but you also need a minimum barrel length as well. If you don't have a certain barrel length for a particular bullet, it will be unstable and will tumble after not too far, it won't be accurate, and then what's the point? This is also why most suppressor manufacturers won't warranty their cans on barrels less than 10 or 11". Also because the pressure levels are still way too high at these lengths. The extra gas beats up the carrier and the gun and shortens the lifespan of parts. Also, you will be hated by those all around you at the range, especially an indoor range!  You lose alot of velocity and therefore stopping performance at distances any farther than across the room. Going up to at least a 10.5" will be much better, IMO. If you absolutely must have an ungodly loud fire breathing blast dragon, then get it built by someone who knows what they are doing. For example, Noveske's 7.5" Diplomat upper is one example of a super short upper that is well made. Not cheap, but you know the gas is right. |
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