Looking for data for Retumbo with a 153gn SST for the 7mm wby mag. I have 1/2 lb of retumbo and am determined to find a use for it. I found published Nosler data for 150 gn and 160 gn partitions but these are compressed loads and the partition is is a lot shorter than the SST. Any info would be much appreciated. I'm looking at starting with 75.5gn and working up but I would sure feel better about it if I could find closer data. Thanks for looking.
The only thing I found to work on my Mark V 7 Weatherby Mag was Norma MRP powder with a 140 gr Barnes TSX. With the large freebore I just couldn’t get anything to shoot well. Not to say I wouldn’t try another bullet or powder but I found one that works and don’t feel like dealing with the recoil while testing another. I would have thought Retumbo to be for bullets heavier that the 150 range.
I admit that I was surprised that Nosler found the best accuracy with it under a 150gn Partition. Whole reason I have Retumbo was for my 300-Wby under 220gn rn, but I sold that rifle and was left with the Retumbo.
Please do post up what your results are, I've found a working combo for mine but extra data is never a bad thing. Do you know what twist your rifle is? I think Weatherby told me mine was a 10 twist, I've got it all wrote down but honestly I haven't put the rifle in a case since the October of 2014 and have maybe put 10 or 12 shots down the bore since then. Can't deer hunt with it in Illinois, haven't been out west hunting since 2014 and its a tad overkill on coyotes around here.. especially when I have a 243 that's more accurate, lighter and less recoil.
The info I found shows a 1:10 twist. My results so far has seamed to back it up. Longer 160gn bullets won't stabilize well in mine. I have some shorter 160gn Partitions that according to Berger's barrel twist calculator, should stabilize fine but I haven't had a chance to work through them.
I had tried the 168 Berger VLDs and the 154 Hornady Interbond with no success. A Weatherby guy, who also rolls his own, told me I won't have any luck with the 168 VLD. Weatherby factory loads the 154 Interbond and another concoction with a 140 gr TSX. When they had my rifle and test fired it they did it with their 140 grain factory loads, in talking with that tech afterwards he said Norma loads their ammunition so I may look in their manual but he could not tell me what Norma loaded in the ammunition. Following the Norma manual I found the load that works for me. Seeing what they did with the rifle I have thought about going back and trying the Interbond bullet again and seeing if I have more successful results.
Well I finally received some decent weather with a calm winds. I did drop the start weight down a little. Starting at 74.5gn, my best accuracy came at 78.5 gn, grouping at just at 1". That has been about the best this rifle has grouped with anything. With this bullet at an OAL of 3.37" load started to compress around 77 gn. That OAL is the longest I can get in the rifles magazine reliably. I would have liked to try up to 79.5 gn but it would have compressed so much I was concerned with pushing out the primer. Never saw any sign of over pressure. I did have one primer fail at 76.5gn with a pin hole. I contribute this to the primer in use, Remington LRM brass cup primers. I had this occur another known load also fired same day. I appeared to be a problem with the primer cup not sealing to the pocket under pressure. LOAD AT YOUR OWN RISK! Final Load Bullet: Hornady .284" 154gn SST Brass: Norma Never fired, Full length sized, trimmed 2.395" Primer: Remington LRM Powder: Retumbo Charge weight: 78.5gn compressed OAL: 3.37"
