standard .257 Roberts loads +p

[Argonaut]

I was Chronographing my .257 Roberts today.  I loaded some Hornady 100 Gr. interlock bullets with H4831.  Now the book ( Hogdon #27)  says that 49.0 Grains as max at 44,100 CUP produces 3010 FPS.  I loaded 50 grains of powder and using my Ruger #1 with it's 26 inch barrel I got 3250 average for 20 shots. extraction isn't a problem, and the primers don't look bad though they look flatter than with a load of 46.5 grains that I normally use. I have .01 bullet jump to the rifling.  Accuracy is pretty good. about 1.0 for 3 shots.  before the barrrel fouls at around 18 to 20 shots. ( normal for this rifle).

Does this seem too hot a load considering the rifle type? I use Winchester +P cases.

[Graybeard]

It's over book and as such definitely over SAAMI but on this round SAAMI is kinda low due to older rifles that might not take the same pressures as more modern rounds. It's likely not higher than other modern rounds the rifle is chambered for take easily.

Hornady Light Mag ammo in 6MM Remington (same case-different bullet diameter) make 3250 fps from a 24" barrel so considering the .257 Roberts using same case and larger diameter bullet has a better expansion ratio and thus can get about 100 fps more at equal pressure with same bullet weight I'd not be too concerned personally regarding the load.

BUT it is above SAAMI for sure.

[Argonaut]

I was using the 6 mm Remington as a sort of standard.  I use that same idea (expansion ratio) when loading for my .32 win spl, and using 30 WCF data with the same bullet weights of course.  I certainly would not use these loads or the date in a small ring mauser or any thing other than my #1, though I am sure a modern bolt gun would have no trouble with them. 

I have 25-06 performance in a smaller case. according to the speer ballistic tables, If I zero my .257 for 200 yards I will only have a bullet drop of 6.3 inchs at 300 yards. Of course shooting deer at 300 ACTUAL yards is very rare, it does tell me DON'T EVER HOLD OVER. If  I gotta miss, miss under. though i didn't hunt this year,  because of the pain in my feet, next year I hope to try this rifle on some eastern washington mule deer. If I can find a place to hunt. the folks on the east side don't like the folks on the west side much.  This side is were the work is.  we have plenty of blacktails to hunt, but for that you need a rain suit and a 12 gauge with 00 Buck and some slugs.

[Catfish]

My Sierra manual list 48.3 gn. of H-4831 as max. with their 100 gn. bullets, but that manual dose not give presures. As GB said, the Sammi presure for the .257 is 54,000 max. but with a good action and plus P brass you should have no trouble upping that to 60,000 psi. Just work up slowly and watch for presure signs.

[Graybeard]

You SHOULD NOT be getting .25-06 performance from a .257 and if you are you are WAY over safe pressure limits. The .25-06 has a good deal more case capacity and operates at higer pressure levels.

So if you are equally .25-06 velocity in a smaller case it can ONLY be due to excessive pressures.

I don't worry about increasing pressure in one to levels equal to the .25-06 if the rifle is safe at those pressures but to equal the velocity of one you are going WELL ABOVE equal pressure levels. One grain above a reasonable reloading manual max for a round like the .257 normally held to lower pressure levels doesn't particularly scare me but saying you are getting equal velocity to a much larger capacity case which runs higher pressures does scare me. I think in your rifle you may be exceeding safe pressure limits.

[Argonaut]

well I was comparing the data in my manual, .257 and 25-06, with 100 grain bullets using 100 grain bullets and h4831. Now the bullets aren't the same manufacture so maybe that is like comparing red delicious apples to granny smith.  they use a 24 inche barrel and I use a 26.  A nosler 100 gr partion bullets loaded to a Max charge of 54.3  grs of H4831 shows a velocity of 3172 fps with a pressure of 51,400 CUP for the 25-06. now the .257 roberts,  shows a load of 49.0 grains as max for a velocity of 3010 fps,  at a pressure of 44,100 CUP.  I Used two scales to check each other and I weighed every load.  Now I also load my cartridges so that bullet jump is about .01. This give me slightly more case capacity (very slight).  I don't have any extraction issues, cases pop right out, primers don't look any worse than say with my .243 with a near max loads.  I normally don't load to max in any of my rifles but because the .257 roberts is so under loaded.  I decided to work this one up. I didn't figure one grain over max wouldnt make such a differance.   I may have a chronograph issue,  I measured 20 shots in a row and shots 12 through 15 measured  3359, 3343, 3335, 3341 in that order. All other shots ran in the mid 3250's.

so now I am confused, i really shouldn't be getting these sorts of velocities, and my rifle doesn't seem to have any difficulty with case extraction.