Anyone know a good reference to find out what the max pressure/muzzle velocity is for various AR's? I've got an M&P 15T with a 1/8" 5R twist. Just wondering how high of a load (for hunting) I can go.

you might want to dig around in the ammo forum, check out the FAQ's and go from there or repost your question..

Pressure is limited by the case.  Even though 5.56 is specified at 62,000 PSI, reloading at that pressure will trash cases in 2-3 loadings.  The primer pocket expands.



Velocity?  That is question of bullet weight, pressure rise and muzzle pressure.  Since the bullet is a constant diameter, the energy the bullet acquires is a function of the pressure curve and length of the barrel.  A product of force and distance.






 

Thanks for the response Keith.

So basically, as long as I'm sticking with the reload manuals, I'll be good? I'm wanting to use it for hunting and want to get as much knock-down power I can get out of a .223 load without causing any issues with my AR.

Here is a suggestion, which helps some guys who are starting out if they get lucky enough to use something which has a high quality factory load.

If for example, you can locate a factory cartridge which uses your particular choice of bullet, then you can guide your own load development by using that ammo as a reference point for velocity.

Say you might like some 62, 69, or 77 grain bullet and was wondering about reasonable pressure and velocity. You would obtain or borrow a chrono and fire a representative sample of the store bought ammo with those bullets as a reference point.
Then, when you start your own loads, you would try to stay within the limits of a loading manual, but also see what the factory ammo was able to hit in your exact rig.

It is probably more important to find the best highest node and not just try and max out pressure. Remember, you are trying to hit hard and accurate, but it is also good to have a load that works in most weather that you intend to hunt under, hot or cold.

BTW, strain gages can be applied in a way that you can hide and use to measure load performance, if you are inclined.

I am surprised this has not been brought up...spend the money...(about $100)..especially with the cost of ammo...and buy a chronograph...the only way you will know for sure...

Beat by RR...:-)  5 minutes...

It really would not do you much good. Your particular rifle is what you have to work with.

Like you said in one of your posts you just got to use the available loading data and work up your own load. I've been doing this for a long time and most of the time it is for a hunting rifle that I am working the load up for.

It's a little uncanny how often the most accurate load also delivers near (book) max velocity.

I usually start out by pressure testing. When I get "the look" of the primer I am looking for I will start accuracy testing. When I find the "sweet spot" I will chronograph the load.

There are other methods and chronographing while pressure testing is also a good idea. I have had at least one caliber not show pressure signs when in fact it was producing velocities that were over max. Too far over max.

It also depends on the type of hunting your are doing.  Long barrels (20" or over) give high velocities without exceeding the 62,000 psi. Keeping the speed up usually improves terminal ballistics which is a good thing for most hunting.  Your 1:8 twist suggests a bbl, 20" or over.  Motor1's avatar shows a good sized, well appointed rig  for deer, varmints, and such.

Short barrels (16" and under) do not allow the bullet to accelerate to higher speed of the 20" bbl because of limited internal ballistics.  If you are hunting feral hogs, ground hogs, heavy brush game, and the like, 16" is probably sufficient.

[ETA] Practically all of Hodgdon's tabulated muzzle velocities for rifles are based on 24" test barrels.

Bullet construction is more important than wringing out that last 100 ft/sec.  Using a varmint bullet on deer/hog can limit penetration which will result in less than adequate performance.



A Winchester 64 grain Power Point, Sierra 65 grain Game King etc are the bullets for hunting medium game.  Drive them to 2800 ft/sec and you are good for 200 yard shots.


 

Everything on mine is stock. 16" barrel, all original parts. I'll admit, I just hopped on the AR bandwagon last month. Trying to find parts right now, well, you all know....lol I'd certainly like to do some upgrading but right now it's mags, optic and all the ammo I can get.

Anyway, back to the topic, I'll be hunting Michigan Whitetail. The deer we usually harvest aren't the biggest so I don't need a load to take down a mule. But I want to be sure that I'm packin enough power with what I have right now.

Check your barrel but I believe the M&P 15T has a 5.56 chamber.  If so then you can shoot 5.56 velocity ammo.  Check out the Hornady TAP line - they make both 223 spec and 5.56 spec and the velocity on the latter is higher.

Ive taken whitetail with the rifle in my avatar. It is 1 in 9 22" .223 I highly recommend the Sierra 65gr Game King, It performed great every time. I would still avoid heavy bone like front shoulders. I did notice too that there is now a 55gr Sierra Game King and it is getting very good reviews from deer and hog hunters. Personally I will stay with the 65gr. I load mine with Reloder 15 but since you only have 16 inches of barrel you may want to experiment to see what you can get out of it velocity wise. RL-15 may not be the best choice for the shorter barrel.

Yep, she's definitely a 5.56. We really only shoot out to about 50-60 yds so I suppose I don't need max velocity on it. Just want to make sure I'm not pushing the limits and putting unnecessary strain on it. With Washington all up in everyone's business about these, no telling how difficult getting parts could be in the future.

On a more positive note, hoping to bag a white tail next year and send a picture to Cuomo and Feinstein and tell them "Look! Peopleeee doooo useeee these toooo killll a deeeeeeaaaaaaaa!!!" (With a Cuomo press-conference voice lol)  see the link below, :20 seconds in. What an asshole lol

http://www.ksdk.com/video/2083935902001/1/Gov-Cuomo-gets-fired-up-about-gun-control-in-New-York