I am shooting mostly 77gr SMK out of this rifle. I just measured (using hornady chamber gauge and Comparator) my length to contact the lands and was surprised to see that the Factory 77gr SMKs are theoretically in the lands by quite a bit.
Does this sound right?
Depends upon the age of the chamber.
Regardless of your chamber measurement, you would know when you closed the bolt whether the bullet was in the lands.
I have two 'out of the box' new Savages that had Federal GMM rounds touch the lands when brand new.
I actually set the GMMs back 0.005 in OAL to get them to chamber easily. After 100 rounds or so, I didn't have to do that any longer.
I have found that most Federal GMMs are seated about 0.005 short of SAMMI recommended OALs, but you may have gotten some OAL outliers or your chamber was bored a bit short.
My other 7 new Savages didn't have any problem - at least 0.005 from the lands, brand new.
My new Savages that were bought after 2010 all had chambers that were close to SAMMI OALs.
My oldest 2008 vintage had a chamber that was 0.080 deeper than SAMMI.
All my Savages now have thousands of rounds down their tubes, so throat erosion has long ago eliminated any concerns.
My 12 FV .223 still groups great with 77 SMKs with OALs around 2.360 after 5670 rounds.
Since I reload, after the throat begins to erode, I simply seat the bullet out to the match the jump that works best for the individual bullet in that particular barrel.
Thank you for the reply - I went ahead and did some additional work on this issue. I made up 3 dummy rounds (no powder or primers) and started with normal seating depths and chambered them looking for contact with the rifling. I noted the CBTO and then pulled the bullets and re-seated .035 longer and performed the same bolt close test...to my surprise I need to go out VERY far before I reached the "jam" point and the lands themselves seated the bullet back for me. Here is my data:
Bullet #1 - Started CBTO at 1.871 and after chambering and extraction measued 1.871
Bullet #2 - Started CBTO at 1.905 and after chambering and extraction measured 1.905
Bullet #3 - Started CBTO at 1.942 and after chambering and extraction measured 2.942
Pull bullets and reseat
Bullet #1 - 1.977 ....still 1.977
Bullet #2 - 2.012....still 2.012
Bullet #3 - 2.048 NOW measured 2.047 AND was sticky to extract
I lengthened to 2.066 CBTO and waxed the bullet and upon extraction (which was tough) CBTO measured 2.055.
So the "jamming" seated the bullet for me 11 thousands (.011)
Still processing what all this means..because the Hornady tool told me 1.857 CBTO was touching the lands. Via my testing I am assuming i was approaching the lands somewhere between 2.012 and 2.048 CBTO.
That is a spread between the two methods of .184 (seems like alot)
The COL at CBTO depth 2.055 is 2.44 inches...WELL above the magazine specification length of 2.26
Any thoughts of the ramblings i just spit out??
You can't go off of the measurement where it jammed in the lands- and then you extracted it-- because as you mentioned "it was tough".... That often pulls the bullet out of the case a little-- or sometimes a lot--
It should be a repeatable number (within a small degree of error).... so if you don't get the same result doing the test more than once then you have a problem in your procedure.
And .184 is a mile.... so something is wrong. But your number of 2.055 can not be correct because at 2.047 it was sticking..... and you don't know that the bullet didn't pull a little on that one. So you need to work between 2.012 and 2.047 (if that's the process you are going to use)
When I do tests like this I strip the bolt. No extractor, ejector or firing pin. Then I chamber and feel what it is doing. I use a rod down the bore to 'eject' the round. That way the bullet is not dislodged from it's position, no matter how tight it is in the lands. No I do not use loaded rounds for this.
I do use a marker on the bullets to see when they are 'marked' by the rifling. They will be marked a couple thousandths before the bullet actually touches the lands.
FWIW, all of my .223 loads with the 77SMK's were 2.280oal. That was a jump of around .020".
Thank you everyone...this is all great feedback...notnsure why I am sweating it as the rifle shoots lights out with the 77gr SMKs over 23.3gr Varget seated at 2.26. I just want to start start playing with seating depth. Most likely I will attempt what is suggested above and see what I get.
I was fire-forming some new Starline .223 brass this weekend using some powder (H335) and bullets (Hornady 60gr VMax & Sierra 55gr SBT that I don't favor and was suprised how well the flat based Hornadys shot at 100 out of the 1:7 twist. The 55gr Sierras did much worse
Posting Permissions
Reply With Quote
Bookmarks