velocity loss using 257 roberts in an Ackley Improved

[joshua 35 whelen]

I have a .257 Roberts Ackley Improved with a 25" barrel.  All of the work was done by ackley himself so factory ammo gets a crush fit when in the chamber.  The paper work which came with the rifle from P.O. Ackley states the guy who initially wanted the rifle built had the barrel set up with a 1/4 inch of freebore and designed to shoot 117gr sierra bullets.  I used the Hornady light Mags the other day to just fireform and got the whole box in a quarter at 100yds.  This is no joke!!  Is there such a velocity loss that I shouldn't use it on deer this year if I zero it at 200yds?  Hornady says the light mag 117gr sst is doing 2910fps at the muzzle.  I did load some 120gr sierra hollow points up with the improved brass in the sierra manual it says the accuracy load was doing about 2800fps.  These loads got an 1" to 11/2 group at 100yds.  The Hornady factory load group just impressed me so much more but I can't find any info on the velocity loss when fire forming.  Will it make a difference on the deer?  I do not have a chrony and don't have the time to get one to find out right now.  I hear anything from 100fps to 300fps loss.  Thanks for your time.

[saltydog]

The light mags would not be my first choice for fire-forming brass - however it seems to be working for you. I would recommend you buy some Remington +P 257 Roberts brass for your use and load 10-15% below max load - The Hornady's lt. mags are a hot round and your brass is going to be subjected to quite a bit of pressure and your brass life will probably be lessened. FPS loss is in area you have been told but on the low side due to your 25" bbl.. From what I have observed original PO' barrels are quite tight chambered which will help keep brass stretch down and velocities up.  Nice rifle. 

[Catfish]

The only way to be sure what your velocity is is to crono your ammo. According to my Sierra manual there is 300 fps. difference in max. loads between the 2 rounds. hen I fire form for mine I load up varmint loads and go hunting. Like you I have always got good accuracy from my fire form ammo. I built mine as a varmint rifle though.

[joshua 35 whelen]

Will it be good for shooting deer to 300yds with the velocity loss?  I don't have time for a chrony as mentioned above and was wondering either with a guesstimate or knowledge on how much velocity you really lose when fire forming.  The barrel is an ackley premium with a quarter inch of free bore and approximately 25 inches long.  Shooting Hornady Light Mags at 2910 on the box.  I know Hornady loads hot but without the pressure like they advertise on the box.  I get zero pressure signs from it so I should be in the good.  It shoots this ammo great.  20 shots into a 1/2 inch with a cleaning between 5 shots at 100yds.  A cleaning consist of running a wet patch through (copper and powder remover) followed by a few dry patches.  It also shoots  Hornady custom ammo the same.  I have two extra boxes of light mag, that's the reason I am thinking of using it.  What does the information on the velocity being on the low side mean?  More than 300fps loss or less than 300fps.  If it is less than 300fps than I would think that it is good to go meaning I am getting like 2610 minimum.  If it is more like 2500 or less than I might reconsider since it is a 117grn SST plastic tip bullet.  Thanks for the information.

[Graybeard]

As stated there is no way to be certain the velocity loss but it won't be all that much to worry about. I'd hazard a guess that in a normal AI chamber firing standard rounds you'd lose 100-200 fps MAX and likely toward the lower end of that. BUT with a light mag load you pick up 100-150 fps over a standard non light mag load. So that's gonna put your velocity real close to what a normal .257 Roberts would deliver in a standard Roberts chamber and you might even get a bit more.

Now toss in that long 25" barrel and you likely are getting more than standard Roberts velocity with those rounds. Yes it's fully adequate at 300 yards.