I would like to ask for help please.

mtwarych · Jul 9, 2019

I recently purchased a 6.5 Grendle upper for myself.

In the process of working up loads for the Grendle, I came across an Alliant powder called AR-Comp and was fully impressed with the incredible accuracy using the powder.

I would like to use AR-Comp in my beloved 257 Roberts but I can't find any data up to and including the manufactures website.

The case volumes of the different rounds AR-Comp is commonly used in are right in the ballpark of the 257 Roberts.

Regrettably, I believe little data is available due to the 257 Roberts being old and overlooked.

Am I just dreaming or is there some source of data I am overlooking?

Would a program like Quickload help me?

Thank all for any information.

JW

PJGunner · Jul 9, 2019

"Regrettably, I believe little data is available due to the 257 Roberts being old and overlooked."

Yes, and a lot of the data available is kept deliberately low due to some rifles it came in were weak. First off, while i know of the Grendel's existence, I know nothing about the cartridge and to make matters even worse, I never heard of that powder.

I could probably WAG up a load if i knew the powder capacity of each cartridge case and the max and min load for the Grendel depending on what bullets are planned? or example let's say the Grendel holds less powder than the .257 Bob and you want to use say a 100 grain bullet. The start load for the Grendel should be a safe place to start and use as a basis to work up a load. At last that's what I'd consider trying. If the case capacities are reversed though.

There is also the consideration that the powder may not be suitable for use in the .257. I needed a starting point for Re17 for use in my 7x57 with the 160 gr. Speer Hot Core and there is no data, at least in my manuals I have on hand. So, I sent Alliant an E-mail and they came up with what I needed. I don't know what manuals you have but Alliant had my data and said it was in their new manual which I just haven't gotten around to picking up yet. Hornady has a new one as well that I have to get.

If I were in your shoes, I'd E-mail Speer asking for data using that powder and tell them which bullets you plan on using. They got back to me within 24 hours with what I needed.
Paul B.

1Shot · Jul 9, 2019

You could contact Alliant Powders. I load for the 6.5 Grendel, got 2 ARs. I use IMR 8208 and depending on the bullet make 120 gr bullet max load is 28 to 28.5 grs. I went to Hodgdon website and looked up data for the 257 Roberts with a 115 gr bullet and it listed IMR 8208 with a start of 34.8 and a max of 37.0 grs. Since MIR 8208 and ARcomp are pretty close in burn rate if you have a chronograph and want to do a little wild catting you could start at 35 grs AR-comp with 115/17 gr bullets and SLOWLY work up with a ladder test (load one round each with progressive .2 or .3 grs increase in the next round) comparing the velocity to known safe loads and watching for pressure signs and come up with a load. I have worked with a few wild cats in my time and this is how I come up with my loads. Once you get a feel for what the powder does with the ladder test you can drop down in bullet weight to 100 gr if you want and kind of know a ballpark of what it takes. .257 rifles are real deer killers. I have used 250 Savage, 25-06 and 257 Weatherby.

For those that do not know what the 6.5 Grendel is. It is basically the 220 Russian case necked up to 6.5. It uses a small rifle primer. For those that do not know what the 220 Russian is it is basically the 7.62x39 but the 7.62x39 uses large rifle primers. The 6.5 Grendel will push a 120/23 gr bullet around 2500 fps give or take from a 20" barrel. It is a fine little cartridge and in my opinion the best all round cartridge for the AR15 platform.

DrMike · Jul 9, 2019

I'm not entirely clear on your question. However, QL can be a valuable tool in making initial estimates of what is and what isn't possible.

E.g.

Code:

Cartridge          : .257 Roberts +P+ (not SAAMI)
Bullet             : .257, 120, Nosler PART SP 35643
Useable Case Capaci: 47.765 grain H2O = 3.101 cm³
Cartridge O.A.L. L6: 2.775 inch = 70.49 mm
Barrel Length      : 24.0 inch = 609.6 mm
Powder             : Alliant AR-Comp

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step    Fill. Charge   Vel.  Energy   Pmax   Pmuz  Prop.Burnt B_Time
 %       %    Grains   fps   ft.lbs    psi    psi      %        ms

-20.0   66    28.08   2349    1471   31580   6900    100.0    1.556
-18.0   68    28.78   2393    1526   33475   7013    100.0    1.523
-16.0   69    29.48   2436    1581   35464   7125    100.0    1.491
-14.0   71    30.19   2479    1637   37550   7235    100.0    1.456
-12.0   73    30.89   2521    1693   39736   7344    100.0    1.420
-10.0   74    31.59   2562    1749   42027   7451    100.0    1.384
-08.0   76    32.29   2603    1806   44428   7556    100.0    1.350
-06.0   77    32.99   2644    1862   46943   7660    100.0    1.317
-04.0   79    33.70   2684    1920   49577   7763    100.0    1.286  ! Near Maximum !
-02.0   81    34.40   2724    1977   52336   7864    100.0    1.255  ! Near Maximum !
+00.0   82    35.10   2763    2035   55226   7963    100.0    1.227  ! Near Maximum !
+02.0   84    35.80   2803    2093   58252   8060    100.0    1.199  !DANGEROUS LOAD-DO NOT USE!
+04.0   86    36.50   2841    2151   61422   8156    100.0    1.172  !DANGEROUS LOAD-DO NOT USE!
+06.0   87    37.21   2880    2210   64744   8250    100.0    1.146  !DANGEROUS LOAD-DO NOT USE!
+08.0   89    37.91   2919    2270   68224   8342    100.0    1.121  !DANGEROUS LOAD-DO NOT USE!
+10.0   91    38.61   2957    2329   71872   8433    100.0    1.097  !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba     82    35.10   2821    2120   64794   7765    100.0    1.155  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba     82    35.10   2678    1912   45349   8248    100.0    1.325

mtwarych · Jul 10, 2019

Gentlemen,
I really appreciate the help. To be honest, I am a scaredy cat when it comes to working outside the published reloading data.

After reading the replies, I have a grasp on how to work up the AR-Comp safely for my 257.

Like I said, I am a scaredy cat and will work on this project slowly and safely. I will update this post on my progress.

Thank you again for everyone's time and help.

JW

DrMike · Jul 11, 2019

mtwarych":2p59zqdc said:
Gentlemen,
I really appreciate the help. To be honest, I am a scaredy cat when it comes to working outside the published reloading data.

After reading the replies, I have a grasp on how to work up the AR-Comp safely for my 257.

Like I said, I am a scaredy cat and will work on this project slowly and safely. I will update this post on my progress.

Thank you again for everyone's time and help.

JW

In handloading, the bold die young (or at least sacrifice a fine firearm or two). It is still excellent advice to work up slow and watch for signs of pressure.

Elkman · Jul 14, 2019

Here is some info that I found on line. From the Allant web site "When it comes to reloading AR-style rifles as well as other rifles, there's a new powder choice on the market-AR-Comp™ from Alliant Powder. Alliant's new AR-Comp is the ideal powder for fast action, high volume AR shooters as well as those who enjoy shooting traditional rifles. Developed specifically for AR-style rifles and ideally suited for heavy 223 and 308 match bullets, AR-Comp delivers high performance ignition each and every time.

Suitable for all semi-automatic and bolt-action rifles
Ideal for heavy 223 and 308 match bullets
Very consistent across temperature extremes"
Loading data for similar cartridges is available, on line and you should be able to cross check with other reloading data for a start. www.alliantpowder.com