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M70 "freebore"allowed in barrel?
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January 18, 2017 - 2:22 am
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Have a M70 in 7mmMag, to engage the leade with a bullet, the distance is greater than SAMMI specification?

Is there a known measurement that shouldn’t be exceeded?

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January 20, 2017 - 6:57 am
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To make sure I understand your question…  Is the leade longer than SAMMI spec, or is it the throat that is longer than SAMMI spec?  I think you must be referring to the throat.  In either case, it is really a discussion of what you are shooting (caliber and bullet weight).  With a heavier bullet and a longer barrel, a bit longer freebore can actually benefit accuracy.  If you are shooting light, fast rounds, a longer freebore is not ideal, but it’s definitely not a safety issue. 

By the way, how long is “greater than SAMMI spec”?  A few thousandths, or something much greater?  If it’s an issue for you, you always have the option of having the barrel rechambered one or two thread pitches deeper and eliminating the issue.

Good luck with it!

Justin

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January 23, 2017 - 2:46 am
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According to SAMMI Spec, [pg 44 for 7mmRemMag} the leade’ runs from a minimum length of 2.654″ (from bolt face) to a maximum of: 2.7256″.

 

My reloaded rounds measure (using a Sinclair Hex nut comparator) to the bullet diameter as “Soft=seated by closing the bolt is: 2.741”.

The difference is: 0.0604 [[which is greater.]

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January 23, 2017 - 6:46 am
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Thanks for the clarification.  

It would be good to know if the added length (measured from the end of the case neck portion of the chamber) is in the throat, or in the leade.  It seems unlikely the angle on your leade was cut wrong (usually around 1.5 degrees), which means most likely the extra length is in your throat.  That’s not a problem for your 7mm.  Heavy round shooters frequently ask for a bit longer throat in a custom barrel.  In your case, (assuming it is in the throat) I can’t imagine the extra 60 thousandths will make any noticeable difference in how the  rifle shoots.  

Take it out, develop a round for it, and see if you like how it shoots.  I wouldn’t waste much time worrying about that extra 0.0604″ unless the rifle won’t group.

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January 23, 2017 - 12:43 pm
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That’s what the problem is. Using commercial ammo, groups were size of paper plate @ 50 yds.

 

“Soft-seated” so that bullet would enter the barrel, noe holding 1-1.5″ @ 100ds.

 

This a first series post 64 [with out the bolt guide lug, that was added by the 1970-71 revision].

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January 23, 2017 - 8:57 pm
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Well, a push-feed post-64 is easy to re-seat the barrel deeper, so your best bet might be to do this and re-chamber.  One thread pitch deeper would eliminate the added freebore.  This would be a very straightforward job for any gunsmith who is a qualified machinist.  

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