UMC 55 vs others in my AR-15

[Grizzlypeg]

I've been having quite varied results with Remington's UMC 55 ammo in my AR-15 with 24" heavy barrel and 1 in 8 twist. I've had results vary from 3 shots into 3/4" with it, to downright scattergun.

I took her out to the range and compared 3 different loads in 4 firing sessions of 6-10 shot groups.

First, UMC55 on a cleaned and recently fouled barrel:

Then, Remington 69 grain match grade ammo:

Not sure if this should count as a 0.75" group or 1.5". The one shot out of the group could well have been my fault. If it was simply my fault, then I'd say this is a good load for my rifle and something to aim for in reloading.

Next, 10 rounds of my first attempt at handloads for the 223. These are IMR4895 23 grains into Winchester brass with Hornady 75 gr match bullets, COL 2.26".

Finally, another try at the UMC, just in case it was the recently cleaned barrel or my technique simply changing or improving.

No better than the first group.

Not sure what to try next. Maybe some lighter loads with the 75gr bullets? I'd like to try 69 grain bullets, but they seem scarce now and I haven't been able to find any. I'm looking for a load that will shoot MOA or less for long strings.

 

[Grizzlypeg]

Anyone have a recipe for success in their 1 in 8 with 75 gr bullets and IMR4895? Is the AR sensitive to the number of grains of powder?

 

[tiriaq]

You don't mention sights or shooting style.
It would seem that your rifle doesn't like the UMC 55s, no point wasting more time with them.
My rifle has a 19-odd inch long 1:8 barrel with .223 chamber. It shoots Hornady 68s very well, but I am using WC735, not IMR4895. Winchester cases, CCI400 primers. Its statistically meaningless, but while zeroing, I shot a 2 1/2" 3 shot group at 500m, with a sandbag under the forend, 5x scope. The rifle and ammuntion are capable of shooting clean on Service Conditions targets at all ranges - IF I do my part.

 

[Grizzlypeg]

This was under the best possible conditions, scope, rest at 100 m. The only downside is the quite heavy single stage trigger. I'm just not familiar with AR-15's and their accuracy potential. I bought this gun used and it looks in great shape. I'm hoping the results with the Remington factory 69gr match ammo confirms that it has accuracy potential. The dismal results with the umc 55 scare me.

 

[jennis]

Mine seems to like south african 556 or winnie 62 grain 223

 

[beltfed]

Your 75 grain load with the IMR 4895 powder is very promising. 10 rounds under 2" is a very honest group. Depending on how that load felt to you, I would maybe speed them up in .5 grain increments. What did they chrony at?
How was the run out?

I would try that very same load on another day, and do some distance shooting with it to see how it reacts.

It could very well be that the rifle is capable of much tighter shooting with that load and your heavy trigger is the limiting factor.

 

[Grizzlypeg]

I'm getting some better results with these reloads now. Same cases, same 75gr Hornady match bullet, same 23.0gr of IMR4895, but I pressed the bullets in to 2.250 col, and put much more crimp on the necks with the Lee "Factory" crimp die. I shot two groups of 5 shots, both were just a hair under 1" groups. I'm fighting this trigger problem (malfunction causing the bolt to move half way forward after each shot)) and having to load each shot separately. I need to chronograph these loads, something I haven't done yet. This might be good enough to test at a greater distance and see how the accuracy holds up.