Benchmark 40gr Vmax & 50gr Vmax 1/9 16inch

[JGC]

Anyone have experience ? Trying to figure some velocity's and accuracy loads. Loaded up some Benchmark with 40gr vmax and 50gr vmax to test in my Free Floated 1/9 DPMS 16 inch/223/5.56 Barrel

Test Loads:
40gr start load 25.5, 26, 26.5*Near Max Benchmark Powder
50gr Start Load 25,25.5,26*Near Max Benchmark Powder
COAL 2.260/FedCase:1.750
*Maybe I can load them up more but I rather keep it safe. Goal is a consistent accurate high velocity load.

Shoots 55gr federal 1/4 inch, best group was from 53 gr vmax but they were sold out and figured I would play and load with some higher velocity stuff for varmints out to 350 or so

Any advice appreciated ahead ,
JGC

[Unclenick]

The 2.260" COL is SAAMI maximum (2.126" is SAAMI minimum). It may be long for a very light bullet because it may fail to get an adequate grip on it. I would use the bullet manufacturer's recommended COL for the bullet to start, then play with seating depth for fine tuning the load later. The Hornady recommendations from their 10th manual (current edition) are:

Vmax bullet COL's in 223 Rem:

40 gr = 2.200"
50 gr = 2.240"
53 gr = 2.240"
55 gr = 2.250"
60 gr = 2.250"

Figure your 16" barrel will produce about 91% of the velocity a 24" SAAMI test barrel does if your chamber is as tight. Less if it isn't. Only a chrongraph will tell you. With the 53 grain V-max if I assume about 2900 fps, the JBM stability estimator gives you a gyroscopic stability factor of 2.3. A lot of match bullets are run at around that number in service rifles. Benchrest shooters like something closer to 1.5, so I suspect you'll find a 60 grain V-max may be your best choice. The 50 and 40, especially the 40, will like a 12" twist better. Note that JBM has a bullet length and plastic tip length list, both pieces of information being needed for the stability estimate.

[JGC]

thanks a lot for the data uncle, i will be ordering some 60gr next for sure, just trying to get some velocity out of this barrel while maintaining accuracy, I know its not a 20 or 26 but I know I can get a little more reloading and consistency, iam used to stretching them out since I load .308 off the lands granted its not a bolt gun but my friend handed me some 55gr vmax he loads with xbr and they were at mag length max, so I should seat them a little deeper.. if anyones tried these loads please post target pics.
62 always shot great just dosent seem to have anywhere near the velocity of the 53gr, sorry got hooked when I shot those 53gr's lol they sure zoom zoom

[Stats Shooter]

If you want a rule of thumb for seating depth, you need at least 1 caliber's worth of bearing surface below the case mouth.

For example, a .224 diameter bullet needs 0.224" of bullet bearing surface below the case mouth, where the bearing surface is the largest diameter portion of the bullet and actually contacts the lands and grooves.

This of course assumes you are not already too long for the chamber.

With short and light bullets, you do not have much room for adjustment since there isn't a lot of bearing surface to begin with.

[JGC]

can 40 & 50 gr at ar mag length cause damage? my thinking was I could minimize pressure a bit by seating them at 2.260 and work up the loads. they seem to be seated enough in there, other than the bullet or powder falling out is there a risk? confused

[Stats Shooter]

It's about holding the bullet straight for one thing. If there isn't much bearing surface below the case mouth, it wouldn't take much to induce run-out in a loaded round as you chamber it from the magazine. If you have a .224 bullet for instance, and only .10" of bearing surface below the case mouth, you are asking a lot out of 1/10 of an inch of brass.

[Unclenick]

JGC,

Pressure is complicated in rifles. If you get the bullet too close to the throat it goes up. If you get it too far into the case, it goes up. The plot below shows it for a round nose bullet, but that's shape that has to move a lot to get the same difference due to proximity of the the throat that a Spitzer nose bullet gets with much less difference in depth.

That said, even if you are touch the throat you will be OK with a charge that is reduced 10%.

As to hold on the bullet, if it takes too little force to dislodge the bullet, you can fail to get consistent or adequate ignition. Touching the lands is one way to eliminate that and seating deeper is another. It's not uncommon to tune accuracy be adjusting seating depth. See this Berger article.