We got a note today:
Q: Dear Charlie, I am having trouble with my 10.5" SBR. I am getting 3 and 4 inch patterns at 100 yrds. What should I do to improve performance?
Aha. We have a reply !!
A: Let me start with the obvious. You are shooting an extremely short barreled rifle. The 10.5" is a "close quarter battle" rifle. It is not known for accuracy.
Well, some might correct me and say that the only thing that an SBR does not have that a rifle barrel has is velocity, and that is not accuracy, and that is technically correct. But, many other things go into the profile of a typical short barrel, that, taken as a whole, a short barrel tends to be much less accurate. I will not get into the variables, but have to mention this, lest others tell Charlie that he does not know what he is talking about.
The purpose of this rifle is to kick down doors and shoot targets that are 25 to 75 yards. At 50 yards, 4 MOA can hit just about anything. If you were to improve on your accuracy, this is what I would look for:
- Either shoot suppressed or not, but don't mix.
- Make sure you have a Carbine length gas system, not Pistol.
- Use a Colt or LMT chrome-lined barrel. Heavy SOCOM is even better.
- If you cannot find or cannot afford a Colt or LMT, then Daniel Defense.
- Make sure your gas port is at 0.070"
- Use 77gr Black Hills OTM ammo.
If you are running carbine gas, then it is the barrel or the ammo, or both, but on a good day, a 10.5" SBR is a 2.0 MOA gun. Some might be able to tune to a little better, but anyone who tells you they have a 1.0 MOA 10.5" gun at 100 yards is either very lucky, or telling you a fish tale.
Start with the ammo, since that is the cheapest option. Common wisdom has been that you can use lighter grain ammo with lower twist barrels (10 to 12) and shorter distances, and that longer distances (300 yrds +) need higher grain ammo and higher twist barrels (7-9). Think of a football. You want to really put the spin on a long throw, but can lob a shorter throw. This would lead to picking 55 grain for short distances, and a 1:12 twist in an SBR. The truth is two things: 1) faster twist seems to not do any harm to shorter distances, so you start seeing 1:7 and 1:8 barrels at all lengths, and 2) the 77 grain ammo just works great at the extremes: shorter barrels and longer barrels.
I would save the 55 grain for a 16" gun. The Army moved away from M193 55 gr. some years back in favor of an equally shitting round, the M855 62 gr. The snipers went for the 77 gr, and were amazed at the accuracy, so the door-kickers tried it, as it had a less pointed tip on their fast cycling Mk18s, and found it helped with both throat erosion and accuracy. The Obama administration, in its quest to rid the battlefield of lead, stumbled into a new round that is showing amazing results: The lead-free 62 gr steel-tipped M855A1. This round is a great flyer. It turns out that the added length (since armourers had to add more metal, as copper and steel are less dense than lead) helps stabilize this round for very long distances. The steel tip, however, would not be kind to an SBR. If you can find M855A1, use it in your 16" to 18" rifles, then ratchet up to 77 grain for 20" rilfes.
I can tell you that my SWAT clients swear by Colt barrels at under 16." I mean, they are throwing name brands under the bus all day long that I thought would be better. Chrome lining itself adds to barrel inaccuracy, but what it does at such high pressures of an SBR gas system is protects the throat from metal jacketed bullets slamming into it with increased velocity. Some barrel makers are better than others at chrome-lining and maintaining some accuracy. In the short barrels, there is a reason Colt, LMT and Daniel Defense barrels cost so much.