School me on burn rates & loading for the AR-10?

[fusiachi]

I gather that the main issue is uncovering the gas port at the proper spot on the pressure curve, but I'd be grateful for any more detailed knowledge that you'd care to share. I've heard the 4895's mentioned in several "no slower than" conversations, so if there's a commonly accepted range of powders for this platform that would be good to know. The specific rifle I'm going to be loading for is a DPMS LR 308B. I'm assuming that the location of the gas port comes in to play in this discussion so here's an image of the rifle.

Thanks in advance.

 

[our gang]

Re: School me on burn rates & loading for the AR-10?

VARGET..... that's all you need to know with the 150-168 gr bullets. Oddly enough CCI 250 is the best primer.

 

[Rovieairto]

Re: School me on burn rates & loading for the AR-10?

The port pressure thing is a WAY over discussed detail of selecting a powder for a properly designed/built gas operated autoloader.
The LR308 should cycle fine with a pretty wide range of powder burn rates and quantities.
That said Varget and RL-15 are hard to beat in a 308.

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

It's good to hear that I might be over-analyzing this. Is there anything that I should be looking for other than normal pressure signs on my brass that might indicate a powder that's either too fast or too slow for this rifle? Am I correct in assuming that regardless of the burn rate, peak pressure will occur prior to gas entering the operating system & that a too-slow powder will manifest itself with extraction and ejection difficulties while one that's too fast simply won't cycle the action reliably?

 

[Rovieairto]

Re: School me on burn rates & loading for the AR-1

Generally the slower powders will increase cycle energy, especially in a carbine length gas system.
This still becomes a non issue as it should fall within the design margins of the gas system.
Extraction and ejection difficulties are symptoms of other problems (nonsurpressed).
It is true that you could select powders that would yield either too much or too little cycle energy but those powder choices (and weights) would be drastic.
Generally you want the fastest powder that will almost totally fill the case without signs of excessive pressure while giving top accuracy.
This ideal powder speed will change as you change bullet length, bullet weight, seating depth, bullet coatings, primer etc.
Too slow a powder and your velocities will suffer but peak pressure will be low, too fast of a powder and your velocities may be lower than what is achievable with excessive peak pressures.
Peak pressure will occur well before the gas port with all reasonable powder choices.
Look for a marked reduction in the primer cup radius (mild flattening) as a way to read top pressures.
Ejector flow on the brass should not be present.
You just want to make sure that your system is running fine and all the weakest links aren't being excessively loaded.
For my .308 AR I found that 45.0 Varget or RL-15 almost filled the case (no crunching) and yeilded pressures high enough to start flattening my CCI BR-2's with out appearing excessive. There has been no apparent brass deformation with this load and so I feel that pressures are acceptable (by me). Accuracy has been great.

I hope that this helps

 

[AK10mm]

Re: School me on burn rates & loading for the AR-1

VARGET,works great in the FAL variations also,not temperature sensitive either.

I've never used RL15,so can't comment on it.

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body">
Ejector flow on the brass should not be present.

</div></div>

That's one thing that's got me scratching my head a little bit. A moderate Benchmark load (41 gr.) that I worked through on my way to developing a 155 load for my bolt gun shows a bit of ejector smear in my DPMS while 42.4 gr. under the same bullet shows no pressure signs at all in the bolt gun.

 

[TCA4570]

Re: School me on burn rates & loading for the AR-1

If all you want is burn rate charts, then google is your friend.
Lots of info.

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TCA4570</div><div class="ubbcode-body">If all you want is burn rate charts, then google is your friend.
Lots of info. </div></div>

Thanks, but my question was what to do with the information on the BR charts, not how to find it.

 

[Falar]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fusiachi</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body">
Ejector flow on the brass should not be present.

</div></div>

That's one thing that's got me scratching my head a little bit. A moderate Benchmark load (41 gr.) that I worked through on my way to developing a 155 load for my bolt gun shows a bit of ejector smear in my DPMS while 42.4 gr. under the same bullet shows no pressure signs at all in the bolt gun. </div></div>

Armalite released a tech note on brass markings. Unlike bolt guns, where ejector flow is a sure sign of high pressures, apparently with ARs ejector marks are to be expected

Look at #5

www.armalite.com

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Falar</div><div class="ubbcode-body">

Armalite released a tech note on brass markings. Unlike bolt guns, where ejector flow is a sure sign of high pressures, apparently with ARs ejector marks are to be expected

Look at #5

</div></div>
<span style="font-style: italic"><span style="font-weight: bold">
5. Circular mark on edge of base, with shiny brass or shaved brass in evidence. Caused by case
being pressed into ejector hole, with some burnishing or cutting as the bolt rotates.</span></span>

Outstanding. Thanks for that.

 

[Rovieairto]

Re: School me on burn rates & loading for the AR-1

Well this gentleman sounds like a newer reloader and because brass hardness can vary wildly it is not a good idea to accept any brass flow on the case head.
The fact is this is a sign that the material cannot handle the pressure and is yielding.
This is not what you want and some cases may not begin to yield until in excess of 70 Ksi.
Some at under 50 Ksi.
Armalite (Eagle arms bought the name Armalite) has printed misinformation before.

I once read a study they put out that said that a rifle doesn't even begin to recoil until the bullet was 20 feet from the muzzle.
Some of their tech note are surprisingly good however.

 

[Falar]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body">Well this gentleman sounds like a newer reloader and because brass hardness can vary wildly it is not a good idea to accept any brass flow on the case head.
The fact is this is a sign that the material cannot handle the pressure and is yielding.
This is not what you want and some cases may not begin to yield until in excess of 70 Ksi.
Some at under 50 Ksi.
Armalite (Eagle arms bought the name Armalite) has printed misinformation before.

I once read a study they put out that said that a rifle doesn't even begin to recoil until the bullet was 20 feet from the muzzle.
Some of their tech note are surprisingly good however. </div></div>

From my experiences reloading for ARs it seems accurate. I get what some would call ejector swipes with some XM193 and M855, and some factory Winchester .308 loads. When handloading swipes start appearing WELL before published max loads while the primers still look pristine.

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body"> ...and because brass hardness can vary wildly...
</div></div>

Yep, it's Federal brass, definitely on the softer end of the spectrum.

 

[amk]

Re: School me on burn rates & loading for the AR-1

I have shot many hundreds of reloads with 175smk and federal brass with mild to warm loads from my AR10 in the last 2 months, ejector wipes are absolutely going to happen before you flatten any primer, from the first round of FGMM case to the last, problem is that it can and will eventually lead to a FTE, a small sliver of brass will jam into the ejector hole and stop the ejector from forcing the case out of the port. Big delema, Federal brass shoots very accurately and is everywhere as once fired, but LC brass is too and is very close to the same case capacity, (most years)but doesn't shoot
as well accuracy wise, but you will mash primers way before you get ejector swipes.

 

[Rovieairto]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: amk</div><div class="ubbcode-body"> problem is that it can and will eventually lead to a FTE, a small sliver of brass will jam into the ejector hole and stop the ejector from forcing the case out of the port. </div></div>

This was a problem I've had with a LR308 and a LR260.
I noticed that the ejector was shaving brass (looking kind of similar to ejector flow). I filed and smoothed the ejector face so that it doesn't create any more shavings.
I also, very lightly, filed the two locking lug corners that scratch the brass necks during extraction and rat tail file and stone the feed ramps.
Adhesive backed velco over the brass deflector prevents dents in the brass as well.
These little details seem to make a difference.

I don't get ejector flow but to be fair the brass I've been using has been through several reloadings and has likely work hardened.

My .308 load is:
45.0 RL-15
155 A-max, lapua scenar, SMK (moly)
CCI BR-2, BHA brass

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body">...I filed and smoothed the ejector face so that it doesn't create any more shavings...
</div></div>

Did you just touch it up with some lapping compound or did it take something more aggressive?

 

[amk]

Re: School me on burn rates & loading for the AR-1

I looked at a m110sass bolt face and the ejector looks more like a m1a ejector, cut at three different angles, this may or may not have something to do with a concern of brass slivers in the ejector hole.

 

[Rovieairto]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fusiachi</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body">...I filed and smoothed the ejector face so that it doesn't create any more shavings...
</div></div>

Did you just touch it up with some lapping compound or did it take something more aggressive? </div></div>

I used a file to round the corners and then a stone to finish smooth it.

This is something that I've done with small frame AR bolts in the past but I feel that it is most important with the larger bolt.
The ejector is pretty huge and should've been smaller IMO.

 

[fusiachi]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rovieairto</div><div class="ubbcode-body">

I used a file to round the corners and then a stone to finish smooth it.

This is something that I've done with small frame AR bolts in the past but I feel that it is most important with the larger bolt.
The ejector is pretty huge and should've been smaller IMO. </div></div>

Thanks for that. I think that your comment on work-hardened cases was right on as well. I put a couple of rounds of the 4064 load I prefer in my bolt gun (same brass, 4th loading) through the DPMS and the ejector marking was barely visible.

 

[Grump]

Re: School me on burn rates & loading for the AR-1

All of this comes down to poorly educated GUESSING until and unless someone can come up with a reliable statement of what the REAL SPECS are for port pressure.

I know them for the M14 type (and it's a +/- 2000 PSI window), but have never seen it published for the AR types shooting .308/7.62 NATO cartridges.

And don't bore me with those endless discussions of the .0015 differences in some chamber dimensions between the two rifles, and the vagarities of whether 52KPSI in CUP really equals 59KPSI PIEZO. Ammo dimensions of each are much more identical than the chamber specs anyway.

I just want to know the port pressure specs, and whether they are measured in CUP or PIEZO. I'll figure it out from there.

 

[Greg Langelius *]

Re: School me on burn rates & loading for the AR-1

If port pressure concerns you, the AR is less susceptible to it than the M1A/M14 and M1 Garand.

Those rifles have well accepted admonitions not to go heavier than 180gr and slower than IMR4064. Taking this in mind, I think you'd be safe with the same admonitions in the AR-10.

For the M1A, my 1Kyd supersonic load is 42.2gr of IMR4064, Rem brass, Fed 210M, and 175SMK loaded to a mag friendly 2.825-2.830" OAL.

As loads go it's relatively generic, and I suspect something quite like it would work well in your AR-10.

Greg

 

[Rovieairto]

Re: School me on burn rates & loading for the AR-1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grump</div><div class="ubbcode-body">All of this comes down to poorly educated GUESSING until and unless someone can come up with a reliable statement of what the REAL SPECS are for port pressure.

I know them for the M14 type (and it's a +/- 2000 PSI window), but have never seen it published for the AR types shooting .308/7.62 NATO cartridges.

And don't bore me with those endless discussions of the .0015 differences in some chamber dimensions between the two rifles, and the vagarities of whether 52KPSI in CUP really equals 59KPSI PIEZO. Ammo dimensions of each are much more identical than the chamber specs anyway.

I just want to know the port pressure specs, and whether they are measured in CUP or PIEZO. I'll figure it out from there. </div></div>

Where did this guy come from and why is he ranting?

Grump: I won't bother you with anything