Creating dummy rounds for 90 gn SMK

[jmcgowe]

I'm getting ready to order a drop-in replacement barrel for my Savage 12 F/TR in .223 and I want to set it up to handle the 90 gn SMK's. To do so, I will need to have the throat reamed to accommodate the longer bullet. Shilen will do that at no charge, IF I provide 4 dummy rounds. I've calculated what I believe would be the proper seating as recommended by others on this site, as well as by Robert Pitcairn in his excellent article "A Mouse on Steroids". My calculation is as follows:

- Case length to case neck/shoulder junction (per SAAMI) 1.556"
- Plus .020", as recommended by Pitcairn .020"
- Equals optimum seating spot of drive band/boat tail junction 1.576"
- BTO length of SMK 90 bullet (as measured) .655"
- Less boat tail length (estimated with calipers) .140"
- Equals bearing surface of bullet .515"
- Optimum BTO length of dummy round 2.091"

Can I get a sanity check on this calculation from you good folks? Does this make sense? Many thanks for any input. I've gotten very good advice/information from the site and have just made a donation (although I don't think it's shown up yet).

John

 

[skiutah02]

That's in the ballpark. With an ISSF cut chamber (0.169 FB), and 90SMK JAMMED 0.007", my BTO measurement is 2.089". Drew

 

[jmcgowe]

That's in the ballpark. With an ISSF cut chamber (0.169 FB), and 90SMK JAMMED 0.007", my BTO measurement is 2.089". Drew

Thanks, Drew. I pulled up a diagram for the Pacific Tool .169 reamer and note that the length to the end of the throat is 2.080, so your 2.089 with a .007 jam is right on the money. Given that one of my measurements was an estimate (boat tail length), I think I may be better backing off slightly and going with a dummy round of 2.080". Thanks for your feedback.

John

 

[skiutah02]

GTK. I've just started playing around with the 90SMK after about 2 years using the Berger 90vld. With the shortage of the vld, I want to have a backup option. My initial testing is quite promising out to 1000 yds. Have fun with the 90SMK. Drew

 

[BP1]

Drew,what powder and primer are you using with the smk.

 

[skiutah02]

H4895 with br4 primer in Lapua brass. 2815 fps

 

[jmcgowe]

BTW, for anyone interested in calculating an SMK dummy round length, I just heard back from Sierra that the designed boat tail length is .175". My old, tired eyes had estimated it at .140". OOP's.