Written by Ballistic Technician Philip Mahin
It was my understanding that Sierra’s 90gr HPBT GameKing #1615 was going to be the greatest thing since sliced bread in a 257 Roberts, and boy was that a correct statement!
I was finally able to purchase a limited run Ruger 77 Hawkeye chambered in the 257 Roberts cartridge. The factory walnut stock is shaped to fit me like a glove so it points easy and the trigger is clean. This makes it an easy shooter and is more than likely the reason it has shown me the accuracy it has. The 4-12×40 scope is mounted as low as it can be without touching the barrel and has a simple duplex reticle, just like I like a hunting gun to have.
It wasn’t going to be long before the 2017 deer season would be upon me so I had to work fast and find a combination it liked. We offer many bullets in the 0.257” diameter that can be used for hunting and since whitetail was on the menu, I decided to stay with our 100gr bullets or lighter. In my ladder testing, our #1615 90gr HPBT GameKing was an exceptional choice and it showed a preference to RE-15 powder. The charge it liked was only producing 2,900fps but the extreme spread was next to nothing and sometimes producing duplicated velocities for the first two shots from a cold barrel. By the way, those first two shots always touched at 100 yards and always right where the scope said they should be.
I’ll save the rest of the accuracy reports and scope set up for another post but for now, I’ll share how the bullet performed on impact. I didn’t have time to make any reduced loads (for expansion at distance information) so I set up jugs at 100 yards and shot what I had. My calculations show this bullet impacted at 2,550fps and it has 52 grains (around 58%) left. I found it in the third jug so it stopped within eighteen inches of penetration and of 
the three, it was the only one that wasn’t completely obliterated. If I would have made contact with a whitetail in that initial outing, it would have proven to be extremely effective on a broadside shot. This is also going to be my go to coyote gun when it comes time for that so I may have other reports to share in the future.
Till then, be safe and enjoy your shooting.
Sierra Bullets 
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Just looked at the website and saw your post. I have shot that same bullet for years from an old 722 257 Roberts that I had the barrel set back and rechambered to a 257 Ackley Improved. Chrono’d at 3450fps, that bullet has accounted for truckloads of critters (pronghorn, mule deer, whitetails, coyotes, etc). Having grown up in the badlands area of South Dakota, this has been my go to rifle for a long time, 25+ years. It would print those bullets into 5 shot groups that would measure less than 0.750 on the outside (right at 0.5″ after subtracting the bullet diameter).
Rifle wears a Leupold VXIII 4.5-14x with a fine duplex and zero’d at 2.75″ high at 100 yards.
Great bullet! I look forward to seeing more reports.
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That is fantastic! My next post will be on how some of our other bullets compare to our 90gr HPBT and hopefully, I’ll have at least one good photo of the rifle as well. Till then, be safe on your hunts.
Philip Mahin, Ballistic Technician
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I have been shooting the sierra 90 gr hollow point since 1976 in a ruger m77 257 roberts
Imr 4064 is the most accruate power i have found for me. Routinely hit prairie dogs at 300 yards
This is the bullet that made the roberts my favorite rifle.
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